Limiting microplastic pollution from municipal wastewater ...

DEGREE PROJECT IN ENVIRONMENTAL ENGINEERING, SECOND CYCLE, 30 CREDITS

STOCKHOLM, SWEDEN 2020

Limiting microplastic pollution from municipal wastewater treatment

A circular economic approach

JORDY VAN OSCH

- 1 -

Limiting microplastic pollution from municipal wastewater treatment

A circular economic approach

Jordy van Osch

Supervisor

Andreas Feldmann

Examiner

Monika Olsson

Degree Project in Sustainable Technology KTH Royal Institute of Technology

School of Architecture and Built Environment

Department of Sustainable Development, Environmental Science and Engineering

SE-100 44 Stockholm, Sweden

www.kth.se TRITA-ABE-MBT 20462

- 2 -

Sammanfattning på svenska Den ökande mängden mikroplast som finns i miljön har understrukit brådskan i att identifiera, utveckla och tillämpa strategier där kommunala avloppsreningsverk (MWWTP) begränsar utsläpp av urbana mikroplaster. Samtidigt har den globala trenden mot en cirkulär ekonomi definierat villkoren för dessa scenarier i förhållande till vatten-energi-näring-näxan. Denna studie har tagit fram ett nytt ramverk mellan studier om reningsteknologier för avlägsnande av mikroplast i avloppsvattenströmmar och cirkulära ekonomiska mål från beslutsfattare med avseende på water-energy-nutrient nexus. Resultaten av denna studie bygger på befintliga bevis på att kommunala avloppsreningsverk släpper ut betydande mängder mikroplast i både mark- och vattenmiljöer. Denna studie har visat hur Multi-Criteria Analysis (MCA) kan användas för att analysera avloppsreningsscenarier utifrån deras förmåga att begränsa mikroplastföroreningar från reningsverk, samtidigt som man tar hänsyn till vatten-energi-näring-näxan. MCA har identifierat MBR-inci-eco som det bäst presterande cirkulära ekonomiska scenariot för att begränsa mikroplastföroreningar från nya verk. Detta scenario inkluderar en Membrane Bioreactor (MBR) med anaerobisk nebrytning, energiåtervinning genom förbränning och fosforåtervinning genom Ecophos. Om redan befintliga verk ska uppgradera sin anläggning för att begränsa mikroplastföroreningar, ses CASPACUF med Pyreg som energi-näringsåtervinning som det bästa scenariot. Det pulveraktiverade kolet med ultrafiltreringssystemet (PAC-UF) skulle sedan installeras som ett ytterligare poleringssteg till ett befintligt konventionellt system för aktiverat slam (CAS), vilket avsevärt minskar investeringskostnaderna. Framtida forskning kan använda dessa resultat för att undersöka nya mikroplastfiltreringsspecifika tekniker, affärsmodellinnovation för avloppsrening och förebyggande av mikroplastförorening vid källan och i stormvatten. Nationella och internationella beslutsfattare bör förbjuda distribution och försäljning av biosolids för direkt markanvändning för att begränsa mikroplastföroreningar från biosolids. Vidare bör åtgärder vidtas för att begränsa mikroplastföroreningar vid källan genom att stimulera policyer för ett förbud mot användning av mikrokulor, begränsa däckslitage och förbättra designen för e.q. tvättmaskiner.

- 3 -

Abstract The increasing amount of microplastics found in the environment have underscored the urgency to identify, develop and deploy scenarios in which municipal wastewater treatment plants (MWWTPs) limit the release of urban microplastics into the environment. Simultaneously, the global trend towards a circular economy has defined the conditions for these scenarios in relation to the water-energy-nutrient nexus.

This study has created a novel framework between studies into treatment technologies for microplastics removal in wastewater streams and circular economic objectives from policymakers with regard to the water-energy-nutrient nexus. The results of this study build on the existing evidence that MWWTPs release significant amounts of microplastics to both terrestrial and aquatic environments. This study has demonstrated how Multi-criteria Analysis (MCA) can be applied to analyse wastewater treatment scenarios for their ability to limit microplastic pollution from MWWTPs, whilst taking the water-energy-nutrient nexus into account. The MCA has identified MBR inci-eco as the best performing circular economic scenario for limiting microplastic pollution from MWWTPs in to be constructed plants. This scenario includes a Membrane Bioreactor (MBR) with Anaerobic Digestion, energy recovery through incineration and Phosphorus recovery through Ecophos. If already existing MWWTPs aim to upgrade their facility to limit microplastic pollution, CASPACUF with Pyreg as an energy-nutrient recovery is seen as the best performing scenario. The powder activated carbon with ultra filtration (PAC-UF) system would then be installed as an additional polishing step to an existing conventional activated sludge (CAS) system, significantly reducing upfront investment costs. Academia can build upon these results to initiate additional research into novel microplastic filtration specific technologies, business model innovation for wastewater treatment and microplastic pollution prevention at the source and in stormwaters. National and international policymakers should ban the distribution and sale of biosolids for direct land application to limit the pollution of microplastics from bio-solids. Furthermore, efforts should be put in place to limit microplastic pollution at the source by stimulating policies for a ban on the use of microbeads, limit tyre wear and improving design for e.q. washing machines.

Keywords: Microplastics; circular economy; wastewater treatment plant; resource recovery; Multi-criteria analysis.

- 4 -

Acknowledgement Firstly, I would like to thank my supervisor, Andreas Feldmann, for the many supervising meetings in which the progress of this study was discussed. His knowledge and past experience were a helpful guidance to my research. Secondly, I would like to thank my examiner, Monika Olsson, for taking her consideration and time to assess this report and attend the final seminar. My gratitude also goes out to the survey and interview respondents, the results in this study would not have been achievable without their expert knowledge and experience; Waterschap Vechtstromen, Roslangsvatten AB, Hoogheemraadschap van Schieland en de Krimpenerwaard, Waterschap AA en Maas, Svenskt Vatten, the US EPA and STOWA. In particular I would like to thank the Development Engineer from Gryaab AB for taking the time to partake in a video-conference, for sharing important insights, comments and feedback. Furthermore, I would like to thank my friends, family and classmates for their support, feedback and bright ideas during the completion of this research. This master thesis research has underscored my passion for the circular economy and its many applications to make the anthropogenic world a less destructive and more regenerative force on this finite planet. I am thankful for the opportunity to delve further into this subject and to lay the groundwork for my future career.

- 5 -

Table of Content Sammanfattning på svenska ....................................................................................... - 2 - Abstract ...................................................................................................................... - 3 - Acknowledgement ...................................................................................................... - 4 - List of Figures ............................................................................................................. - 6 - List of Tables .............................................................................................................. - 6 - Abbreviation ............................................................................................................... - 7 - 1. Introduction ........................................................................................................ - 8 -

1.1 Goal and research questions ................................................................................................. - 9 - 2. Literature review ............................................................................................... - 10 -

2.1 Municipal wastewater treatment plants and microplastic pollution ............................... - 10 - 2.1.1 Microplastic removal ....................................................................................................... - 10 - 2.1.2 Microplastic leakage ......................................................................................................... - 12 -

2.2 Existing and emerging technologies to remove microplastics from wastewater ............. - 13 - 2.3 From wastewater treatment to resource recovery ............................................................. - 16 -

2.3.1 Water recovery .................................................................................................................. - 16 - 2.3.2 Energy recovery ................................................................................................................ - 16 - 2.3.3 Nutrient Recovery ............................................................................................................ - 18 - 2.3.4 Other resources ................................................................................................................ - 20 -

3. Methods ............................................................................................................. - 21 - 3.1 Scenario creation ................................................................................................................. - 21 - 3.2 Scenario analysis ................................................................................................................. - 21 -

3.2.1 Decision context and system boundaries ......................................................................... - 21 - 3.2.2 Criteria .............................................................................................................................. - 21 - 3.2.3 Weighting of criteria ........................................................................................................ - 23 - 3.2.4 Grouping .......................................................................................................................... - 23 - 3.2.5 Scoring ............................................................................................................................. - 23 - 3.2.6 Normalization and sensitivity analysis ........................................................................... - 23 -

3.3 Interviews ............................................................................................................................ - 24 - 3.4 Focus .................................................................................................................................... - 24 - 3.5 Ethical review ...................................................................................................................... - 24 -

4. Circular economic scenarios .............................................................................. - 25 - 5. Results ............................................................................................................... - 26 -

5.1 Analysis of scenarios to separate microplastics from wastewater .................................. - 26 - 5.2 Sensitivity analysis ............................................................................................................. - 28 - 5.3 Validation of MCA results ................................................................................................... - 29 -

6. Discussion .......................................................................................................... - 31 - 6.1 Interpretation of results ....................................................................................................... - 31 - 6.2 Implications ......................................................................................................................... - 32 - 6.3 Limitations ................................................................ Fout! Bladwijzer niet gedefinieerd.

7. Conclusion and recommendations ..................................................................... - 35 - References ................................................................................................................ - 37 - Appendices ............................................................................................................... - 44 -

Appendix A: Selected P-recovery technologies after incineration or pyrolysis ........................... - 44 - Appendix B: Criteria and grouping ranges ................................................................................... - 45 - Appendix C: Stakeholders to interview .......................................................................................... - 47 - Appendix D: Scenario data ............................................................................................................. - 48 - Appendix E: Sensitivity analysis overview .................................................................................... - 55 -

- 6 -

List of Figures Figure 1 Ratio of treated and untreated wastewaters around the world (Corcoran, et al, 2010) ....... - 10 - Figure 2 Typical MWWTP in Sweden, including primary, secondary, tertiary and sludge treatment (Persson,2011), adjusted to include estimated microplastic flow in MWWTP (Sun et al., 2019) ....... - 11 - Figure 3 Visualization of membrane bioreactor system (Pandey et al., 2014). ................................... - 14 - Figure 4 Visualization RO process (Pervov et al., 2013). ..................................................................... - 15 - Figure 5 Visualization of PAC-UF system (Voigt et al., 2020). ........................................................... - 15 - Figure 6 Circular economic cycles in regards to MWWTPs ................................................................. - 16 - Figure 7 Hotspots for P recovery from the wastewater stream (GWRC, 2019) .................................. - 18 - Figure 8 Process flow of methodology .................................................................................................. - 21 - Figure 9 Visualisation of the system boundaries of this study ........................................................... - 24 - Figure 10 Visualisation of CE wastewater pathways for limiting microplastic pollution ................... - 25 - Figure 11 MCA Results visualised ........................................................................................................ - 26 - Figure 12 Sensitivity analyses of the MCA results ............................................................................... - 28 - Figure 13 Schematic flow of the EcoPhos process (Kabbe, 2019). ...................................................... - 44 - Figure 14 Pyreg process illutrated (Pyreg GmbH, 2020). ................................................................... - 44 -

List of Tables Table 1 Overview of existing technologies for microplastic removal ................................................... - 14 - Table 2 P resource recovery technologies for sewage sludge ash ........................................................ - 19 - Table 3 P resource recovery technologies after or during pyrolysis .................................................. - 20 - Table 4 Selected criteria for multi-criteria analysis ............................................................................ - 22 - Table 5 CE scenarios for limiting microplastic pollution from MWWTPs ......................................... - 25 - Table 6 MCA Microplastic pathways in wastewater treatment .......................................................... - 27 - Table 7 Overview of criteria and grouping range ................................................................................ - 45 - Table 8 List of stakeholders and experts for survey and interviews ................................................... - 47 - Table 9 Data for seven different scenarios .......................................................................................... - 48 - Table 10 Results of three sensitivity analyses ..................................................................................... - 55 -

- 7 -

Abbreviation AD Anaerobic digestion BAF Biologically Active Filters

CE Circular Economy DAF Dissolved air floatation DF Discfilter

EU European Union GAC Granulated Activated Carbon GHG Greenhouse gas

IVL Swedish Environmental Research Institute MBR Membrane bioreactor MWW Municipal Wastewater

MWWTP Municipal Wastewater Treatment Plant PAAS Product-as-a-Service PAC Powdered Activated Carbon

RSF Rapid sand filtration SSA Sewage Sludge Ash UF Ultrafiltration

WHO World Health Organization

- 8 -

1. Introduction In August 2019, the World Health Organization (WHO) underscored the need for further research into the leakage of microplastics into the environment (WHO, 2019). Microplastics have been found almost everywhere on Earth, from Antarctic ice sheets to the stomachs of seabirds, to our own faeces (Waller et al., 2017; Carr et al., 2016; Schwabl et al., 2019). Microplastics are particles smaller than 5 mm, consisting of tiny plastic granulates or fibres (Sharma and Chatterjee, 2017). Due to the chemical composition of plastics, these particles are resistant to degradation. Their small size makes them easily accessible to a vast range of organisms and transferable along the food chain. This results in the accumulation of potentially hazardous effects on both organisms and humans alike, causing alternations in chromosomes leading to obesity, infertility and cancer (Sharma and Chatterjee, 2017).

Microplastics mainly originate from sources such as synthetic fibres, automobile tire wear, industrial processes, household dust, and the deterioration of plastic surfaces (Nizetto et al., 2016). In high-income countries, the runoff from these emissions is conveyed to municipal wastewater treatment plants (MWWTPs). MWWTPs are fairly good at retaining microplastics through conventional treatment, over 90 percent of microplastics are retained in sewage sludge, a by-product of the wastewater treatment process (Nizetto et al., 2016). Nonetheless, MWWTPs are found to be significant sources of microplastic leakage into the environment (Mason et al., 2016). Due to the sheer volume of continuous discharge into the aquatic environment, the final effluent acts as an exit route for microplastics (Talvitie et al., 2017). It is estimated that between 3 billion and 23 billion microplastics are being released from MWWTPs each day in the United States alone (Mason et al., 2016). Whilst this pollutant release is significant, it dwarfs in comparison to the terrestrial microplastic emissions stemming from MWWTPs. In developed regions, about 50 percent of all sewage sludge is converted into agricultural fertilizer. This indicates that at least 50 percent of the retained microplastics will be released on farmlands (Nizetto et al., 2016). Neither European nor North American regulations mention microplastics in their restrictions on using sewage sludge containing harmful substances. It is therefore suggested that MWWTPs are a significant source of microplastic pollution to not only marine, but also to terrestrial, and freshwater environments (Bayo et al., 2016). Concurrently, the EU commission, parliament and council reached an agreement to facilitate increased use of waste-based fertilizers in 2016 (European Commission, 2018). Following in line with policymakers around the world, who are pushing forward circular economic objectives in order to reduce socio-technical pressures on the environment (Geissdoerfer et al., 2017). In a circular economy (CE), products and materials should remain in the economy for as long as possible, retaining their value, whilst waste is treated as a secondary raw-material that can be re-used, re-purposed or re-cycled (Ghisellini et al., 2016). MWWTPs consume large amounts of materials and energy to comply with discharge regulations, while wastewater simultaneously contains large amounts of energy, nutrients and other resources (Mo and Zhang, 2013). For MWWTPs to comply with the global movement towards a circular economy, it is crucial that the water-energy-nutrient nexus is taken into account in decision making. By complying to the circular economic objectives of policy makers, MWWTPS can transition from waste handlers to resource recovery facilities (Rodriguez, 2018).

Several studies have investigated which wastewater treatment technologies generate the highest removal rates for microplastics in wastewater streams. Other studies have researched which sludge handling technologies have the highest potential for destroying microplastics. Still other studies have investigated the optimal technologies for water, energy and nutrient recovery in MWWTPs. The global circular economic trend, underscores the urgency to identify, develop and deploy scenarios in which MWWTPs limit the release of urban microplastics into the environment, whilst safeguarding circular economic objectives in relation to the water-energy-nutrient nexus. There is lack of studies carefully reviewing the sustainability of different full-scale wastewater treatment scenarios, in which microplastic pollution is limited and the water-energy-nutrient nexus is taken into account. This study will identify and evaluate several of these scenarios through a multi-criteria analysis (MCA).

- 9 -

1.1 Goal and research questions This study establishes and assesses several scenarios for limiting microplastic pollution from MWWTPs and making MWWTPs a sustainable actor in a global circular economic system. The following research questions are answered in this report:

1. To what extent do MWWTPs act as barriers and/or entry points for microplastic pollution into the environment?

2. Which full-scale wastewater treatment technologies are able to remove microplastics from wastewaters whilst taking the water-energy-nutrient nexus into account?

3. Which full-scale sludge handling technologies are able to destroy microplastics whilst taking the water-energy-nutrient nexus into account?

4. What are the relevant sustainability criteria for assessing wastewater handling scenarios that limit microplastic pollution from MWWTPs whilst taking the water-energy-nutrient nexus into account?

5. Which wastewater treatment scenario limits microplastic pollution from MWWTPs whilst taking the water-energy-nutrient nexus into account?

6. Which bottlenecks exist between the favoured scenario and the desired deployment in the municipal wastewater supply chain?

- 10 -

2. Literature review In this literature review, the challenge of urban microplastic pollution through MWWTPs is evaluated in response to research question 1. Many recent studies have assessed how microplastics flow through MWWTPs and to what extent they are emitted in effluent streams. Furthermore, the research frontline in terms of microplastic removal and destruction technologies for MWWTPs is defined in response to research question 2 and 3.

2.1 Municipal wastewater treatment plants and microplastic pollution A MWWTP is a facility in which several combined processes treat municipal wastewater (MWW) and remove a number of pollutants (Hreiz et al., 2015). MWW is comprised of blackwater, consisting of excreta, urine and faecal sludge – and greywater, from laundry, bathing, commercial and industrial effluent (Corcoran, et al., 2010). Wastewater treatment aims to create an effluent that can be discharged safely into natural water bodies, with minimal impacts on the environment. Globally, there are many differences in terms of treatment ratios. High-income countries treat around 70 percent of the generated municipal and industrial wastewaters, while middle-income countries only treat about 28 to 38 percent. In low-income nations, only 8 percent of wastewaters get treated. In total, over 80 percent of all global wastewaters are released into the environment untreated (WWAP, 2017). This is mainly due to technical and institutional capacities, lacking infrastructure and financing (WWAP, 2017).

Figure 1 shows the ratio of treated and untreated wastewater, flowing into natural water bodies, for ten global regions (Corcoran, et al., 2010). This thesis will focus on high-income regions in which the treatment of wastewater is dominant, namely the North Atlantic, Western Europe and the Baltic Sea. These treatment facilities have a similar mix of wastewater entering the plant, and therefore use similar treatment processes (Nizetto et al., 2016).

In high-income countries, the most common form of MWW treatment is through centralized collection, whereby a sewer system collects MWW from businesses, homes and industries and transports it to a treatment plant. Today, the most common form is a sanitary sewer system. This system inhibits storm waters from entering the sewage system and transports the municipal wastewaters directly to the plants. This reduces the need for larger pipes and limits the overflow of untreated wastewater into the environment. (WWAP, 2017). As populations and industries have grown, so has the quantity of pollutants in wastewater, meaning the total volume and treatment needs are increasing (EPA, 2004). Conventional MWWTPs use physical, biological and chemical processes to remove pollutants from the effluent and typically consist of preliminary, primary and secondary treatment stages (Persson, 2011). Figure 2, on the next page shows a visual overview of a typical MWWTP in Sweden (Persson, 2011, p. 147). There are many variations to MWW treatment processes, however the depicted stages are generally accepted as standard practice in high-income regions (Persson, 2011). It should be noted that additional treatments can be undertaken depending on the wastewater flow rates and contaminant loads.

2.1.1 Microplastic removal New risks concerning ‘emerging pollutants’ have been recognized from the early 2000s onwards (Bolong et al., 2009). Emerging pollutants are defined as synthetic or natural substances that are not commonly controlled or monitored but have the potential to harm ecosystems and human health (WWAP, 2017). One emerging pollutant that has been detected extensively in MWWTPs are microplastics (Hu et al., 2019). Microplastics consist of tiny plastic granulates or fibres, smaller than 5 mm (Sharma and Chatterjee, 2017). These particles are resistant to degradation, as they are primarily made of

Figure 1 Ratio of treated and untreated wastewaters around the world (Corcoran, et al, 2010)

- 11 -

polyethylene, polypropylene and other synthetic and long-lasting polymers. They are easily transferred along the food chain, as their small size makes them accessible to a vast range of organisms. This results in potentially hazardous effects on organisms and humans alike, with some evidence showing chromosomal alternations that lead to obesity, infertility and cancer (Sharma and Chatterjee, 2017). It is estimated that humans consume between 74.000 and 121.000 microplastics per person annually (Cox et al., 2019). It is therefore of increasing importance to biological and human health to limit the pervasion of microplastics in the natural world.

The main origins of microplastics include synthetic textiles, automobile tire wear, industrial processes, household dust, and the deterioration of plastic surfaces (Nizetto et al., 2016). Fibres are the most common type of microplastic in MWWTPs representing 52.7 percent of the total. As most of the runoff from urban emissions is conveyed to MWWTPs, treatment can act as either a barrier or an entry point of microplastics into the environment. Conventional MWWTPs with a primary and secondary treatment stage retain over 86 percent of microplastics in the sewage sludge, whilst MWWTPs with tertiary treatment retain over 98 percent (Sun et al., 2019). Sun et al., (2019) have estimated the flow of microplastics within a conventional MWWTP including preliminary, primary, secondary and tertiary treatment. These are visualized in figure 2 (Sun et al., 2019). The liquid phase microplastic flow has been estimated based on reported data (red), whilst the microplastic flow in sludge phase (orange) was estimated according to the particle balance.

Preliminary treatment

Preliminary treatment prepares the wastewater for the other treatment stages by separating out larger particles and sand-like solids to prevent damage to equipment or interference with the other stages. The preliminary treatment include screening through a coarse screen, and grit removal through sedimentation (Persson, 2011). Preliminary treatment restricts microplastic flow to 41 ~ 65 percent relative to the influent (Sun et al., 2019).

Primary treatment

Primary treatment typically consists of gravity sedimentation to remove settleable solids, about half of which are removed during this treatment stage. The residue from this treatment stage is called primary sludge, which is a concentration of suspended particles in water. Some pathogenic organisms, organic compounds and nutrients are also contained in the primary sludge. Primary treatment reduces flows of microplastics to 2 ~ 50 percent relative to the influent (Sun et al., 2019). Therefore, preliminarily and primary treatment remove the majority of microplastics from the wastewater stream (Sun et al., 2019). This is mainly due to the skimming of light floating microplastics and the settling of heavier microplastics in the sedimentation processes. Fibres, the most common type, are retained through settling as they become entrapped in flocculating particles (Magnusson and Norén, 2014).

Figure 2 Typical MWWTP in Sweden, including primary, secondary, tertiary and sludge treatment (Persson,2011), adjusted to include estimated microplastic flow in MWWTP (Sun et al., 2019)

- 12 -

Secondary treatment

The secondary treatment stage often consists of a biological treatment process to remove biodegradable organic material. For this, an activated sludge process is most common, in this study referred to as the conventional activated sludge process (CAS) (Persson, 2011). Biological treatments use microorganisms to oxidize organic materials, which flocculate to form settleable particles. These particles are separated in sedimentation tanks, creating a concentrated suspension called biological sludge. Biological treatment processes limit emissions of oxygen-demanding organic materials (Persson, 2011). During this treatment process, the retained microplastics accumulate with the sludge flocculate or bacterial extracellular polymers in the aeration tank. These flocculates then settle in the settling basin. Secondary treatment processes further decrease wastewater microplastic flows to between 0.2 ~ 14 percent relative to the influent (Sun et al., 2019).

The contact time of microplastics with wastewater in the treatment cycle is an important factor in microplastic removal, as longer contact time increases surface biofilm coatings on microplastics. These coatings modify the relative density of the microplastics, making them neutrally buoyant, and thus more likely to surpass both skimming and settling processes (Rummel et al., 2017). The secondary treatment mainly removes larger particles, one reason is that only the fibres with neutral buoyancy remain, thus being resistant to further removal (Sun et al., 2019). Studies have shown that microplastics larger than 500 µm were nearly absent from secondary effluent (Mintenig et al., 2017; Ziajahromi et al., 2017).

Tertiary or advanced treatment

Tertiary or advanced treatment steps have been introduced to further improve effluent quality. The sediments of tertiary treatments are added to the primary and secondary sludges. Tertiary treatments often include chemical treatment stages to reduce phosphorus and nitrogen leaching, minimizing the nutrient overload of surface waters (Persson, 2011). Phosphorus is typically removed by chemical precipitation, while nitrogen is removed by nitrification and denitrification. The process step in which precipitation chemicals are added can vary in different MWWTPs (Persson, 2011). Microplastics interact with flocculants such as aluminium salt and iron salt, reducing their effectiveness in the coagulation process. To achieve the same removal results, additional chemicals are needed, increasing the cost of chemical treatment, though it is unclear to what extent chemical processes contribute to microplastic removal (Sun et al., 2019; Zhang and Chen, 2019). Another common type of tertiary treatment is the removal of pathogenic microorganisms and viruses through filtration-based technologies. Filtration-based tertiary treatment can provide additional microplastic removal, restricting their concentration to about 0.2 ~ 2 percent relative to the influent (Sun et al., 2019).

2.1.2 Microplastic leakage Despite high retention ratios, MWWTPs leak significant amounts of microplastics into the environment, with most MMWTPs processing millions of litres of wastewater each day (Mason et al., 2016; Sun et al., 2019). The smallest sizes of microplastics, between 20–100 µm and 100–190 µm are most abundant in MWWTPs effluent (Ziajahromi et al., 2017). Relatively speaking, more fibres are found in the effluent, as they can pass membranes or filters longitudinally (Sun et al., 2019). Mason et al. (2016), found that from an analysis of 17 plants in the United States, MWWTPs release over 4 million microplastics per plant per day through effluent water. It is estimated that between 3 billion and 23 billion microplastics are released from MWWTPs each day in the United States alone (Mason et al., 2016), amounting to between 5 600 and 43 000 tons of microplastic annually. Similarly, Sun et al. (2019), estimate that MWWTPs release 2 billion microplastics per plant per day on average. In the European Union there are 18 000 MWWTPs in operation, of these 68.4 percent treat at tertiary level, whilst 28.5 percent and 3.1 percent treat at secondary level and primary level respectively (WaterWorld, 2017; EurEau, 2019; EurEau, 2017). MWWTPs with tertiary treatment processes have an estimated 0 ~ 51 microplastics / L in their effluent, whereas effluent from primary or secondary treatment contains between 0,0009 ~ 447 microplastics / L (Sun et al., 2019). This means that, conservatively, European MWWTPs could be releasing 36 billion microplastics per day, or 67 000 tons annually, through their effluent. These high discharge levels suggest that microplastic targeting treatment technologies are necessary to avoid further emissions into aquatic environments.

Whilst aquatic pollutant release is significant, it dwarfs in comparison to the terrestrial microplastic pollution related to MWWTPs. Retained microplastics end up in sewage sludge, the by-product of MWWTPs. After being separated from the wastewater, sewage sludge undergoes further treatment, generally including a thickening, stabilization and dewatering stage. Treated sewage sludge is also known as biosolids. The EU has banned the disposal of biosolids into the ocean, and landfill disposal is

- 13 -

phasing out in most countries (PURE, 2012). Alternatives for ocean dumping or landfilling are energy recovery through incineration, or nutrient recovery through agricultural use (Usman et al., 2012). In the United States, approximately 55 percent of all produced biosolids are applied to land (WEF, 2010). Within the 26 EU Member States, about 49.2 percent of the produced biosolids is applied to agricultural lands (EurEau, 2017). The percentage of nutrient recycling varies greatly between the member states, in Ireland up to 80 percent of produced biosolids are applied in agriculture, whereas Greece and the Netherlands have no application of biosolids on land at all due to safety concerns of possible hazardous content (Mahon et al., 2017; Milieu Ltd et al., 2010). Nonetheless, the total amount of nutrient recycling through biosolid application is increasing within the EU (Milieu Ltd et al., 2010). The high usage of biosolids for agricultural applications, indicates that a significant amount the retained microplastics will be released on farmlands (Nizetto et al., 2016). Concentrations of microplastics can reach 1500 - 17 000 microplastics/Kg in dried treated sludge (Sun et al., 2019).

Nizetto et al., (2016) estimate that “a total yearly input of 63 000 - 430 000 and 44 000 - 300 000 tons microplastics is emitted to European and North American farmlands respectively” through the application of biosolids. Neither European nor North American regulations mention microplastics in their restrictions on using sewage sludge containing harmful substances (Bayo et al., 2016). Underscoring the need to identify, develop and deploy wastewater treatment and sludge handling methods that safeguard policymakers’ circular economic objectives whilst limiting microplastic pollution. Whilst the above-mentioned estimations have underscored the significance of microplastic pollution from MWWTPs, it is important to note that only 10 – 15 percent of all microplastic pollution arrives in the influent of MWWTPs. The other 85 – 90 percent enters the environment through e.g. storm water and surface deterioration of larger plastic pieces in the environment (EUreau, 2019).

2.2 Existing and emerging technologies to remove microplastics from wastewater Several studies suggest that advanced final-stage treatment technologies can further improve the microplastic removal ratios (Carr et al., 2016; Mintenig et al., 2017; Ziajahromi et al., 2017). Due to the sheer volume of effluent flow, only a microplastic removal ratio of 100 percent is considered satisfactory purification (Baresel et al., 2017). Tertiary filtration-based technologies retain the highest quantity of microplastics. To achieve a 100 percent removal of microplastics, the Swedish Environmental Institute has proposed a combination of several different tertiary or advanced treatment technologies: Ultrafiltration (UF) is a complementary technology to Powdered Activated Carbon (PAC-UF) or Biologically Active Filters (UF-BAF). However, in a study by Talvitie et al., (2017), BAF does not have a positive effect on microplastic removal rates, and thus will not be considered in this report. The complementary UF is proposed to be operating with a membrane of a nominal pore size between 0.01-0.1µm and pressure differences between 0.5 - 10 bar. Besides UF methods, reverse osmosis (RO) also provides complete removal of microplastics, with the correct pore size (Baresel et al., 2017; Mason et al., 2016; Mintenig et al., 2017; Talvitie et al., 2016). The removal efficiency of microplastics between rapid sand filtration (RSF) and dissolved air flotation (DAF) in secondary effluent treatment, and membrane bioreactor (MBR) in primary effluent treatment was compared by Talvitie et al. (2017). The highest removal efficiency was achieved with MBR (99.9 percent), followed by RSF (97 percent) and DAF (95 percent). Further research shows that when a pore size of 0,04 µm is used during the MBR process, all microplastics between 1 µm and 5 mm are removed from the wastewater stream (Baresel et al., 2017). The feasibility of microplastic removal through a dynamic membrane (DM) was evaluated by Li et al., (2018), and suggests that DM’s are an energy efficient way to filter microplastics out from wastewater, though further research is needed. None of the aforementioned technologies are specially designed for the removal of microplastics from wastewater. Treatment technologies that specifically target microplastics are still undergoing preliminary research, and thus have not been included in this study (Sun et al., 2019)

In sum, Table 1 on the next page provides an overview of the aforementioned full-scale treatment technologies that can be implemented to remove microplastics from wastewater streams.

- 14 -

Table 1 Overview of existing technologies for microplastic removal

No. Removal technology

Description Targets Estimated microplastic removal ratio

Remarks Source

1 MBR (UF) Membrane based on ultra-filtration followed by anaerobic digestion

Microplastics and other contaminants

99.9 % - 100 % Can be implemented as additional treatment to existing MWWTP or replace CAS systems.

(Talvitie et al., 2017; Baresel et al., 2017)

2 RO Reverse osmosis Microplastics, Antibiotics and other contaminants

99 – 100 % Can be implemented as additional treatment to existing MWWTP.

(Baresel et al., 2017; Sun et al., 2019)

3 PAC-UF Powdered activated carbon and an ultrafiltration

Microplastics, Antibiotics and other contaminants

99 – 100 % Can be integrated or supplementary purification step in existing MWWTP.

(Baresel et al., 2017)

4 DM Dynamic membrane of non-woven fabric, woven filter and stainless-steel mesh.

Microplastics and other small particles

99.5 % Could be energy efficient, can be implemented as additional treatment to existing MWWTP.

(Li et al., 2018; Zhang and Chen, 2019)

5 RSF Sand filtration with flow through pump.

Microplastics and other contaminants

97 % Can be implemented as add on to MWWTP, often polishing stage.

(Talvitie et al., 2017)

6 DAF Physical separation of microparticles with dissolved air flotation

Microplastics and other small particles

95 % Already implemented at many MWWTP as primary treatment.

(Talvitie et al., 2017)

7 UF-BAF Granulated Activated Carbon, provide surface for microorganisms to attach and consume organic material.

Microplastics, Antibiotics and other contaminants

Inconclusive Can be implemented as additional treatment to existing MWWTP. Mixed results from several studies.

(Baresel et al., 2017; Talvitie et al., 2017)

Selected treatment technologies

This report only includes treatment technologies that can achieve 100 percent microplastic removal ratios in full scale operations, as a 100 percent removal ratio is the only satisfactory purification result. Therefore, MBR, PAC-UF and RO/NF have been selected to be further analysed in this report in response to research question 2.

• Membrane Bioreactor A Membrane Bioreactor or MBR, is an activated sludge system that uses microporous membranes for solid and liquid separation, as shown in figure 3. The basic principle of membrane filtration is a pressure difference that draws raw wastewater through a microfiltration membrane surface, removing suspended material in the process. The solid / liquid separation process is enabled through a vacuum state downstream of the membrane, and air is introduced into the system to drive the biological treatment. An MBR system requires relatively high amounts of power for the pressure pump to prevent the membrane from fouling and force the water through the membrane. The production of reusable water, ease of operation and compactness make MBR ideal for municipal wastewater treatment, of which there were over 1500 in operation around the world in 2014. (Pandey et al., 2014).

Figure 3 Visualization of membrane bioreactor system (Pandey et al., 2014).

- 15 -

• Reverse Osmosis Reverse Osmosis or RO has the finest membrane filters of all membrane filtration systems, with a pore size ranging down to 0.1 nm, as shown in figure 4. RO closely resembles other forms of membrane filtration, as it is driven by high operating pressures, however it can remove much smaller molecules, including chemicals and pesticides (Ochando-Pulido et al., 2019). Pre-treatment is necessary, as the membrane is highly susceptible to fouling. The utilization of RO systems has increased in the last decade as system costs have decreased and water quality regulations have increased (Ramaswami et al., 2018).

• Powdered Activated Carbon with Ultrafiltration Powder activated carbon ultrafiltration processes, or PAC-UF processes, add PAC to a recirculation loop of the membrane system. The contaminants in the wastewater are absorbed by the activated carbon particles, whilst the ultrafiltration membrane separates the particles from the water. Figure 5 shows a visual overview of the PAC-UF system (Voigt et al., 2020). PAC-UF systems are used to treat wastewater contaminated with organic matter and micro-pollutants (Wintgens et al., 2005). The combination of PAC and UF is particularly interesting as UF membranes are capable of retaining all PAC particles. As wastewater regulations are tightening and membrane costs are decreasing, PAC-UF has become increasingly interesting for wastewater treatment applications (Löwenberg and Wintgens, 2017).

Whilst the above-mentioned research and technologies help reduce the amount of microplastics in wastewater effluent, they do not solve the issue of microplastics in sludge. Indeed, a more efficient microplastic filtration technology only means that the microplastic content in sludge is increasing. The Swedish IVL institute has stated that there is currently no method to separate microplastics from sewage sludge in a cost-effective way, therefore they see thermal treatment, such as mono-incineration, co-incineration and pyrolysis, as the only methods to destroy microplastics. A thermal sludge treatment process thus makes MWWTPs a sink for urban microplastic emissions (Baresel et al., 2017). In addition to removing microplastics from MWWTPs, future efforts should be directed towards the prevention of microplastics entering MWWTPs as will be further elaborated on in the discussion section of this report.

Figure 5 Visualization of PAC-UF system (Voigt et al., 2020).

Figure 4 Visualization RO process (Pervov et al., 2013).

- 16 -

2.3 From wastewater treatment to resource recovery Society’s current linear economic system is material-, resource- and waste-intensive. Our planet’s resources are finite, and a linear system is therefore not feasible for long-term human development. The Circular Economy (CE) offers an alternative approach, in which materials and products are transformed into resources for other processes at the end of life through re-using, re-cycling, re-pairing and re-manufacturing. This minimizes waste by closing the loops in urban systems (Stahel, W, 2016). A shift towards a CE would reduce humanity’s pressure on the planet significantly by reducing greenhouse-gas (GHG) emissions by up to 70 percent (Stahel, W, 2016).

However, recovering resources in a closed loop system requires clean waste-streams, and is often energy intensive and expensive due to technological complexities (Graedel and Allenby, 2010, p. 36). There is thus need for additional research into finding new and better pathways for the recovery of materials in waste, including wastewater. In 2015, the European Commission launched the ‘Circular Economy Action Plan’ to contribute to “closing the loops” and improving recycling and re-using of resources (European Commission, 2018). MWWTPs can play an important part in a circular system, as energy production and resource recovery are both achievable during the production of clean water (Neczaj and Grosser, 2018). The main drivers for creating a wastewater recovery industry are global demand for nutrients, recovery of water and energy production, or the water-energy-nutrient nexus (Mo and Zhang, 2013). Figure 6 shows the proposed cycles of wastewater handling in a circular economic model. The paragraphs below describe the different ways of maximizing water, energy and nutrient recovery in wastewater treatment, whilst taking microplastic filtration and destruction into account.

2.3.1 Water recovery CE strategies can function as a first line of defence against water scarcity. In an anticipated CE system for MWW treatment, water is cascading in accordance to different water quality standards for each use purpose (IWA, 2016). Wastewater reuse can be direct (planned) or indirect (unplanned). Indirect use originates from discharged wastewater into groundwater or surface water resources and will eventually end up as drinking water supply. Direct use of correctly treated wastewater includes e.g. agriculture and land irrigation, industrial purposes and groundwater replenishing. MWWTP effluent has been used for agricultural irrigation for many years, and the nutrients in wastewater reduces the need for synthetic fertilizers. Challenges associated with wastewater reuse are human health risk and high costs for reclaimed water delivery systems. Improvement of MWWTP effluent is crucial for sustainable water recovery strategies, as it would simultaneously increase the quality of natural waterbodies. MBR, RO and PAC-UF are suitable treatment processes for water recovery purposes, as microplastics, antibiotics, pathogens and other contaminants can be removed effectively. (Neczaj and Grosser, 2018).

2.3.2 Energy recovery MWWTPs consume a significant amount of energy (Maktabifard et al., 2018). Currently, wastewater treatment consumes 21 terawatt-hours annually in the United States alone, about 4 percent of the total electrical power produced in the United States (Maktabifard et al., 2018; Xu et al., 2017). In the EU, wastewater treatment consumes about 1 percent of the total electricity supply (Haslinger et al., 2016). Electricity demand for wastewater in high-income nations is expected to increase by 20 percent over the next decade, underscoring the need for further development of energy recovery (Yan et al., 2017).

Figure 6 Circular economic cycles in regards to MWWTPs

- 17 -

MWWTPs have the potential to recover energy through sewage sludge treatment. Nonetheless, the potential energy extracted from sewage sludge is typically not sufficient to create an energy neutral plant; therefore, adding renewable energy sources will increase the sustainability performance of MWWTPs in terms of GHG emissions. In addition, energy recovery would help significantly reduce MWWTP operation costs, as energy is the second-biggest operational cost after labour (Maktabifard et al., 2018). This report will consider those sludge treatment energy recovery practices that reduce microplastic pollution, including anaerobic digestion with biogas utilization, and thermal treatments with heat or power generation (Stillwell et al., 2010; Cowger et al., 2019).

Anaerobic digestion with biogas utilization

Creating biosolids from sewage sludge is often done through digestion. A common form of digestion is anaerobic digestion (AD), which produces biogas and biosolids. Biogas contains 60 – 70 percent methane (CH4) and 30 – 40 percent carbon dioxide (CO2) and other trace gasses, making it a useful fuel for heat, power or combined heat and power (CHP) systems (Ma et al., 2015). A MWWTP with an AD consumes about 40 percent less net energy as opposed to one without an aerobic digestor, significantly reducing its energy footprint (Neczaj and Grosser, 2018). AD has been used for MWWTPs with a flow of less than 4.000 m3 per day to flows of up to 757.000 m3 per day (Ghazy et al. 2011). Nonetheless, a capacity of at least 19.000 m3 of wastewater per day is necessary in order to produce electricity in a cost-effective way (Stillwell et al., 2010). As AD reduces the organic matter in sewage sludge by up to 50 percent, it is seen an essential step prior to drying and incineration. The reduction in organic matter optimizes the post-treatment process, while reducing costs. Today, AD is the dominant sludge stabilization technology in North-America, with 48 percent of all created sludge being digested (Schafer et al., 2002; Hale, 2018). In Sweden, approximately 70 percent of sewage sludge is treated in digesters to produce biogas (Bhasin, 2017). For MWWTPs to become resource recovery facilities with an energy neutral or energy positive footprint, AD can be applied as an essential component in the plant’s treatment processes (Edwards et al., 2015). This study therefore considers anaerobic digestion as standard practice for sludge handling systems, and the process will thus be included in this study.

Few studies have researched the effects of AD on microplastic abundance, however Mohan et al., (2017) suggest that AD has the potential to destroy microplastics contained in the digestate, though not considerably. Therefore, the biogas digestate, which remains after the digestion process, should be thermally treated or destroyed to prevent microplastic leakage from the digestate. It is recorded that the presence of microplastics in sewage sludge can reduce the quantity of biogas produced during AD processes by up to 27.5 percent, underscoring the importance of preventing microplastics from entering MWWTPs (Zhang and Chen, 2019; Jin et al., 2019).

Thermal treatments with heat or power generation

As mentioned, biosolids still contain microplastics after digestion and must be disposed of. Although most legislators encourage the reuse of biosolids nutrients in agricultural application, thermal treatments are the only full-scale pathways for microplastic destruction (Baresel et al., 2017; Cowger et al., 2019). If combustion temperatures are high (400 – 550 °C) microplastics and other organic components can be destroyed (Cowger et al., 2019). Thermal treatments include mono-incineration, co-incineration, pyrolysis and gasification.

• Mono- and co-incineration Sludge incineration is done through one of two commercially available technologies: fluidized bed furnaces or multiple hearth furnaces. Multiple hearth furnaces burn the biosolids in steps using hot air recycling and can be operated continuously or intermittently. Fluidized bed furnaces are newer, more efficient, easier to operate and stable, however only continuous operation is possible. Both incineration processes create heat, powering a steam turbine to generate electricity, and are suitable for medium to large MWWTPs. Advantages of incineration is the significant potential through energy recovery, the thermal destruction of microplastics and other contaminants retained in biosolids, and the possibility to recover phosphorus from the incinerated ashes (Stillwell et al., 2010; Baresel et al., 2017). Disadvantages are high investment and operational costs. Nonetheless, biosolid incineration is a feasible energy management strategy for MWWTPs, as up to 40 percent of the treatment plants energy consumption can be generated through biosolid incineration (Stillwell et al., 2010). Mono-incineration is the incineration of biosolids only. As the waste feed is equable, the phosphorus recovery potential is increased. Mono-incineration will be considered in this study. Sludge incineration typically occurs in temperatures ranging from 700 – 925 °C, to ensure complete destruction of toxic

- 18 -

organic materials (EPA, 2017). An alternative to mono-incineration, to avoid high dewatering costs, is co-incineration, in which 5 – 15 percent of sludge is added to the incineration process of household waste (PURE, 2012). However, the potential for nutrient recovery is greatly reduced when sludge is co-incinerated and will therefore not be included in this study (Bhasin, 2017). In Europe, only about 15 percent of all created sewage sludge is incinerated; however tighter regulations, including limits to landfilling and agricultural use, are leading to an increase in sludge incineration. The destruction of harmful substances such as microplastics, combined with the potential of energy and nutrient recovery make incineration of sewage sludge a well-equipped circular economic solution (Bhasin, 2017).

• Pyrolysis Pyrolysis is the process of thermally decomposing organic substances in an anoxic environment in temperatures ranging from 300 – 900 °C. Pyrolysis techniques, including catalytic pyrolysis, thermal pyrolysis and microwave-assisted pyrolysis, have been used to treat plastic waste in the past (Sun et al., 2019). This method decomposes the long chain polymers into oligomers. Recent studies have shown how co-pyrolysis with biomass could be a treatment method to turn microplastic containing sewage sludge into valuable gas, liquid and solid products, without producing toxic emissions (Burra and Gupta, 2018; Jin et al., 2019; Fytili et al., 2008). The pyrolysis gas and char can be used as fuels, whilst pyrolysis oils can be used in the chemical industry as raw materials (Fytili et al., 2008). Karaca et al., (2018) indicate that high temperature pyrolysis is the most efficient process for energy recovery from sewage sludge. High temperature pyrolysis operates at 850 °C and is sufficient to destroy harmful substances such as microplastics. Furthermore, it is possible to recover nutrients from the by-product sewage sludge char, making pyrolysis a circular economic solution for sludge handling. A pyrolysis system which includes AD has a better energy balance and a higher reduction in total greenhouse gas emission, as opposed to a pyrolysis system without AD as pre-treatment (Cao and Pawlowski, 2013). Therefore, a combination of AD with pyrolysis will be included in this study.

• Gasification Another novel thermal sludge treatment technology is gasification; however, it lacks widespread application due to relatively high investment costs and a lack of a developed by-product market (Samolada and Zabaniotou, 2014). As such, gasification is not considered in this study.

2.3.3 Nutrient Recovery The application of synthetic fertilizer has greatly increased the demand for extractable nitrogen and phosphates. As these nutrients are not recycled or brought back to their source, phosphate mineral resources are expected to become scarce or exhausted within 50 to 100 years (Van Vuuren et al., 2010). Effectively, the European Commission listed phosphate rock as a critical raw material in May 2014 (Neczaj and Grosser, 2018). It is therefore of increasing importance that nutrients in MWW and run-off water are recovered and reused. The biosolids created in MWWTPs can fulfil an important role in the nutrient recovery cycle. Nutrient recycling reduces the demand for fossil-based synthetic fertilizers and reduces the consumption of energy, resources and water (Neczaj and Grosser, 2018). A circular system for nutrient recycling can contribute to sustainable agricultural practices (Usman et al., 2012).

As shown in figure 7, there are currently three main commercially-scaled pathways for the recycling of phosphorus from sewage sludge, being 1) direct land application of biosolids; 2) P recovery from aqueous phase, and 3) P recovery from sewage sludge ash or char (Egle et al., 2016; GWRC, 2019).

Figure 7 Hotspots for P recovery from the wastewater stream (GWRC, 2019)

- 19 -

1) Direct application of biosolids

The phosphorus recycling rate for direct biosolids application is 90 percent as compared to MWWTP influent (Egle et al., 2016), and it is by far the most common type of sludge disposal in high-income nations (WEF, 2010; EurEau, 2017). However, there are currently no viable solutions to separate microplastics from the biosolids (Baresel et al., 2017; Cowger et al., 2019), and biosolids can contain 1500-17 000 microplastics/Kg (Sun et al., 2019). Thus, in the context of making MWWTPs microplastic sinks instead of sources, direct land application of treated biosolids is not seen as a viable solution and will not be considered in this study.

2) P recovery from aqueous phase

Phosphorus recycling from wastewaters can also be achieved through technical recycling of wastewater and sewage sludge. Nonetheless, microplastic particles are not destroyed during aqueous phase P-recovery processes, and the potential for leakage exists. Thus, P recovery from the aqueous phase is not seen as a viable solution in the context of microplastic removal and will not be considered in this study (Stowa, 2019).

3) P recovery after thermal treatment of sludge

There are opportunities for combined nutrient and energy recovery, however widespread application is hindered by limited market opportunities and economies of scale. P containing products can be produced out of ashes from incinerated sludge, or the pyrolysis process. The retrieval rate of P in sewage sludge ash (SSA) varies from 80 – 100 percent with respect to the wastewater input (Egle et al., 2016). One of the main advantages of P recovery after thermal treatment is the fact that microplastics and other contaminants have been destroyed during the treatment. Table 2 describes the different available P recovery technologies applied after incineration, whilst table 3 on the next page describes P recovery technologies after or during pyrolysis. Selection criteria were based on a P recovery rate of more than 80 percent (Phosphorus Platform EU, 2020). The technologies described all have a minimum of "TRL 7”, meaning that there is a system prototype in the operational environment (De Rose et al., 2017). As the P recovery market is rather novel, some new technologies might be missing from the selection. Based upon the technologies described in table 2 and 3, this study will take EcoPhos for P recovery after incineration and Pyreg for P recovery after pyrolysis into consideration. Both these technologies show the most promising advantages in terms of P recovery rates, integration and costs. Appendix A gives a further description of both selected P recovery technologies.

Table 2 P resource recovery technologies for sewage sludge ash

P recovery technology

Resource recovered

Process Results TRL Advantages Disadvantages Source

1 EcoPhos (applied after incineration)

Fertiliser / technical / feed grade phosphoric acid or DCP

Phosphates present in ash are dissolved using phosphoric acid. Insoluble containing metals go to a waste stream.

93 - 98%

P recovered.

9 Low energy consumption; Low investment costs; High value co-products; easy integration in incineration facility.

Limit number of full-scale operations in use.

(Phosphorus Platform EU, 2020; EcoPhos, 2020)

2 ICL – Fertilizer industry (applied after incineration)

Standard mineral fertilizers

Recovered materials are mixed into the phosphate rock or phosphoric acid-based fertilizer production process

100 % P recovered

9 No new process needed;

Infrastructure of fertilizer industry can be used.

Contaminants in ash are diluted in final product;

(Phosphorus Platform EU, 2020)

4 Kubota (applied after incineration)

P-containing slag.

Thermal treatment with temperature 1300°C. Part of the heavy metals, copper and zinc are volatilized.

90 % of P recovered.

9 Over 30+ full-scale operations; Phosphorus in slag equivalent value to phosphate rock.

Sludge disposal costs 20% higher as opposed to mono-incineration.

(Phosphorus Platform EU, 2020)

- 20 -

3 Ash2Phos (applied after incineration)

Di-calcium phosphate (DCP), - mono-ammonium phosphate (MAP).

Sewage sludge ash is dissolved in hydrochloric acid + lime (ambient temperature, no pressure).

90% of phosphorus, 10-20% of ion and 60% of aluminum recovered

7 Low labor intensity; Low investment costs; Aluminum hydroxide as a raw material for coagulants created;

Residue can be used in cement or concrete industry; only two full-scale operations.

(Phosphorus Platform EU, 2020; Easymining, 2020)

Table 3 P resource recovery technologies after or during pyrolysis

P recovery technology

Resource recovered

Process Results TRL Advantages Disadvantages Source

1 Pyreg (applied after AD)

P from pyrolyzed dry sludge

Carbonization reactor operated at 500 – 800 °C. This temperature results in a biochar with labile organic carbon content < 1%.

90 % recovery rate.

9 Decentralized system, so integration at MWWTP possible; Operating in almost 30 full scale units in Europe today;

Biochar not included in EU fertilizing products regulation.

(Phosphorus Platform EU, 2020)

2 Enersludge

(applied after AD)

P from pyrolyzed dry sludge

Pyrolysis of dry sludge at 450°C and a pressure 1–5 kPa in the absence of oxygen

100 % P recovered and char created.

7 Several types of fuels created; volume of solid residue low; low gas emissions.

Only 1 full scale plant in operation.

(Szaja., 2013)

2.3.4 Other resources Other resources that can be recovered from wastewater streams include heavy metals, absorbents, protein and enzymes, other emerging technologies are generating bioelectricity from sewage sludge through microbial fuel cells, aerobic granular sludge technology, anaerobic ammonium oxidation (Anammox), and biomass manipulation. Even though these technologies are promising none of the recovery technologies for these materials have been developed for full scale application (Gherghel et al., 2019). Therefore, this study has only taken water, energy and nutrient recovery into account.

- 21 -

3. Methods Firstly, the literature study defined current MWWTP processes, their capabilities of retaining microplastics and novel technologies to enable MWWTPs to become microplastic sinks. Secondly, a multi-criteria analysis (MCA) method was conducted, by which several different scenarios for transforming MWWTPs from microplastic sources into sinks have been assessed. Thirdly, interviews were held to identify gaps between the selected scenarios and their implementation. Figure 8 shows a visual overview of the methods used in different phases of this research.

Figure 8 Process flow of methodology

3.1 Scenario creation Qualitative research was conducted through a literature review of peer-reviewed studies, to obtain a clear image of the knowledge state on the subjects of MWWTPs, microplastic pollution and CE objectives for wastewater treatment. The literature review allowed for the identification of relevant theories, and gaps in existing academic work. The review demonstrates the understanding of relevant theories and concepts and has formed the foundation for the assessment of existing and emerging microplastic filtration technologies for MWWTPs. The literature study has been conducted through the collection, evaluation and analysis of a variety of publications in scientific databases. The research material consists of peer-reviewed papers, published reports and official websites of the EU and US EPA. Only literature sources released in the last 20 years (2000-2020) have been reviewed to ensure the relevance of the data. Data was held to high-quality standards, nonetheless certain limitations exist, such as reduced accuracy of data due to the use of multiple data sources.

3.2 Scenario analysis The identified scenarios were compared with each other through a matrix. This matrix was based on the literature study. Multi-criteria analysis (MCA) is a decision-making tool, predominantly used to assess decisions with environmental implication. An MCA-matrix compares impacts by giving a weight and score, to assess the impact of each criteria (Dodgson et al., 2009).

3.2.1 Decision context and system boundaries This MCA’s decision context defines which wastewater treatment scenario will convert MWWTPs from microplastic sources into sinks, whilst taking the water-energy-nutrient nexus into account. The different scenarios were assessed and compared with one another using several different criteria. All scenarios were based on the same functional unit of one cubic metre (m3) of influent wastewater. This functional unit was based on a collection of LCA studies performed on wastewater treatment processes (Larsen, 2018). The temporal boundary of the study is set to be 30 years, being the average lifespan of MWWTPs (Risch et al., 2015). None of the upstream processes related to construction materials and end of life stages of the treatment facilities were considered.

3.2.2 Criteria The chosen evaluation criteria were based on the literature review, CE objectives in regard to the water-energy-nutrient nexus and the three pillars of sustainability in response to research question 4 (Hansmann et al., 2012). The criteria were chosen based on measurability, non-redundancy and relevance. As such, the criteria in table 4 on the next page were selected. A further description of each criteria is given in Appendix B.

Scenario creation

•Literature Review

•Structured Interviews

Scenario analysis

•MCA•Semi-structured

interviews

Discussion

•Literature review

Conclusion and recommendations

- 22 -

Table 4 Selected criteria for multi-criteria analysis

Pillar Objective Criteria Type Indicator

Environmental

Minimize microplastic leakage in waterbodies

Removal of microplastics from wastewater

Quantitative % of microplastics removed from Effluent.

Minimize microplastic leakage in environment

Destruction of microplastics during sludge treatment

Quantitative % of retained microplastics destroyed.

Minimize GHG emissions into atmosphere Global Warming Potential of scenario Quantitative kg CO2- eq./m3 effluent

Maximize effluent water quality Water recovery potential Qualitative Low / Moderate / High

Maximize utilization of phosphorus Nutrient recovery potential. Quantitative % of phosphorus extraction ratio

Economic

Minimization of costs Operational costs Quantitative USD / m3 effluent

Investment costs Quantitative USD / m3 effluent

Maximization MWWTP income Additional revenue streams Quantitative Low / Moderate / High

Social

Maximization of public acceptance Consensus Qualitative Low / Moderate / High

Minimization of the technological complexity

Complexity Qualitative High / Moderate / Low

- 23 -

3.2.3 Weighting of criteria The weight of each criteria is determined according to the weighted sum model. The weighted sum model has been used, as the use of weighted averages underscores the independence between the judged strength of one criterion in relation to the judged strength of the other criteria’s (Dodgson et al., 2009). The weighted sum model is the most frequently utilized method for single dimension decisions (Pohekar and Ramachandran, 2004). Weights are based on the relative importance to the decision and founded upon a structured survey send out to a panel of experts. The weights for each criterion are given in Appendix B. The full lists of experts that weighted the criteria is given in Appendix C. The relative weight of each criterion was created by averaging the survey results. In the survey, each criterion has been weighted on a scale from 1 – 5, taking their relative importance into account.

1: Very low importance 2: Low importance 3: Medium importance 4: High importance 5: Very high importance

3.2.4 Grouping Each criterion has been assigned an indicator and these have been evaluated on a grouping scale from 0 to 5. The grouping was created in order to aggregate the criteria into quantifiable values, that can be used in the evaluation (Tsoutsos et al., 2009). A 5 represents a criterion with the greatest favourable performance, whereas 0 stands for a criterion with the least favourable performance. Groupings are both quantitative scales, as well as qualitative scales, depending on the availability of reliable data and the nature of the criteria. The qualitative scores are determined on their favourability, and thus can vary between several different qualitative criteria. The qualitative data has been evaluated on the same binary scale to create compatible results for both qualitative and quantitative criteria The grouping generated a range of values against which the criteria score can be judged. As scales are dependent on the nature of the criterion, not all scales are linear, and some have shortened intervals on one end to emphasize the relative importance of incremental differences.

3.2.5 Scoring Scoring results have been analysed according to a linear additive model, with the assumption that uncertainty is not built into the model and criteria are independent from one another. The linear additive model is commonly used by decision makers, for its robustness and effectiveness (Dodgson et al., 2009). The model multiplies the value score of each criterion by its assigned weight, after which the weighted scores are added together. A higher weighted score represents a more favourable outcome. The weighted score (WSx) of each criterion was calculated, by multiplying the scores (Sx) and weights (Wx) of the criterion (x) (1). As both weighting and scores were judged on a scale from 0 to 5, a maximum score of 25 and a minimum score of 0 can be obtained.

!" ! = %! ×'! (1)

3.2.6 Normalization and sensitivity analysis After weighting and scoring results for each scenario, the total scores for each pillar of sustainability were normalized in order to attain a final score between 0 and 5. Normalization ensures a balance between the three pillars of sustainability, despite the pillars not having an equal number of indicators. The overall normalized total (Nt) was generated to rank the scenarios against one another. The normalized weighted score for each pillar (WSp) was determined, by dividing the sum of all weighted scores (Ux) from one scenario by the sum of the weight for that pillar (y) (2)

!"( = ∑!" #!∑!" $ (2)

The normalized total (Nt) was obtained by summing the weighted score for each pillar (WSp) and divide these normalized scores by three, the total number of pillars (3).

)* = ∑#" &'() (3)

- 24 -

Great effort was put in ensuring the use of high-quality data, however uncertainties and limitations in data quality are unavoidable. Hence, a sensitivity analysis was conducted to determine the results dependence on particular preferences or weights. The weighting for each sustainability pillar was modified to reflect potential changes in preference, as weights are subjective figures, and may be vulnerable to bias.

3.3 Interviews The structured interviews were formulated through an online survey. The semi-structured interviews were conducted through a video conference. Several major stakeholders have been interviewed. These stakeholders include, and are not limited to the management of MWWTPs, national and regional waterboards and academic experts. The interviews aimed to define the weighing’s for each criterion in the MCA and to identify the bottlenecks between suitable scenarios and their deployment in MWWTP processes. Finally, the compiled data was assessed to discuss how the identified bottlenecks can be overcome. The key stakeholders selected include the following:

1) Three professionals employed at MWWTPs operations, engineer and management. 2) Three professionals employed at national and regional waterboards, with a portfolio on

wastewater treatment. 3) Two academic experts employed at an environmental protection agency and a research institute.

Table 8 in appendix C shows a full list of the stakeholders and experts that have been interviewed.

3.4 Focus This research aimed to aid in the implementation of wastewater handling scenarios in the context of municipal wastewater treatment. This research focussed on wastewater treatment plants that are operating for municipalities within high-income nations. These facilities likely have a similar mix of wastewater entering the plant due to similar consumption patterns amongst nations (Nizetto et al., 2016). Furthermore, these MWWTPs generally have similar characteristics in terms of primary and secondary treatment processes. The system boundaries of this study are visualised in figure 9, included in the system were municipal wastewater influent, the municipal wastewater treatment plant and sludge treatment methods. The sources of the municipal wastewater influent, the stormwater runoff and the destination of municipal wastewater effluent, nutrient application and heat and power recovery were excluded from the system boundaries.

Figure 9 Visualisation of the system boundaries of this study

3.5 Ethical review This research has given insight into future CE scenarios for limiting microplastic pollution from MWWTPs. Data has been gathered through a literature review and structured interviews. Those experts that were spoken to, responded voluntarily to the interview requests. A written consent has been taken, before using the, by respondents provided, information. The confidentiality of the provided information has been treated with high priority, the sole objective of this research is to gain knowledge in the field of wastewater management and microplastic filtration, to contribute to a future without microplastic pollution. Research has been performed independently, with the absence of commercial objectives or conflict of interest.

- 25 -

4. Circular economic scenarios Considering the literature review findings, several circular economic scenarios appear for limiting MWWTPs related microplastic pollution. The selected technologies for each circular economic objective are visualized in figure 10.

Figure 10 Visualisation of CE wastewater pathways for limiting microplastic pollution

The only known full-scale treatment technologies with the potential to achieve 100 percent removal of microplastics are MBR, RO and PAC-UF, and will thus be considered in the scenarios. In addition, these treatment technologies create sufficiently filtered effluent water for water recovery. Furthermore, CAS has been selected as a baseline wastewater treatment process In order to safeguard circular economic objectives, anaerobic digestion for energy recovery is considered an essential part of each scenario. Furthermore, energy recovery through thermal treatment, being incineration or pyrolysis, is deemed essential, as thermal treatment is the only available method to completely destroy microplastics. Nutrient recovery, in the form of P recovery is deemed an essential aspect of the circular economic scenarios as P is a critical raw material (Neczaj and Grosser, 2018). Several applicable methods for nutrient recovery have been identified in response to the advantages and disadvantages of these technologies, among them EcoPhos and Pyreg are selected for this study. In addition, land application of biosolids has been selected as a baseline P recovery technology. The technology selection in figure 10, have let to the creation of the scenarios in table 5, these scenarios will be further analysed in this report. In terms of energy recovery, anaerobic digestion is a sludge pre-treatment process that is applicable to all scenarios. Conversely, incineration and pyrolysis are two different thermal sludge treatment pathways. These applications result in three separate nutrient recovery scenarios.

Table 5 CE scenarios for limiting microplastic pollution from MWWTPs

No. Scenario name Treatment for microplastic removal / water recovery

Energy recovery (2) / microplastic destruction

Nutrient recovery

1 CAS CAS - Land application of biosolids 2 MBR inci-eco MBR Incineration P recovery from sewage sludge ash with EcoPhos 3 CASRO inci-eco RO Incineration P recovery from sewage sludge ash with EcoPhos

4 CASPACUF inci-eco PAC-UF Incineration P recovery from sewage sludge ash with EcoPhos 5 MBR Pyreg MBR Pyrolysis with Pyreg and P recovery from sewage sludge char ash

6 CASRO Pyreg RO Pyrolysis with Pyreg and P recovery from sewage sludge char ash 7 CASPACUF Pyreg PAC-UF Pyrolysis with Pyreg and P recovery from sewage sludge char ash

- 26 -

5. Results This section outlines the results of the MCA comparison between the seven identified scenarios, in response to research question 5. The robustness of results is debated in a sensitivity analysis.

5.1 Analysis of scenarios to separate microplastics from wastewater The MCA results are visualised in figure 11 below. The sources and calculation of the data can be found in Appendix D. The highest scoring circular economic scenario for limiting microplastic pollution from MWWTPs, is MBR inci-eco with a normalized overall score of 3,11. This scenario includes MBR with Anaerobic Digestion, energy recovery through incineration and P recovery through Ecophos. The second-highest scoring scenario is MBR Pyreg, with a normalized overall score of 2,67. This scenario includes MBR with Anaerobic Digestion and energy-nutrient recovery through Pyreg. The high performing scenarios which include MBR are mainly useful in the decision process of yet to be constructed MWWTPs. Since the MBR process can make the CAS process obsolete.

For already existing MWWTPs aiming to upgrade their facility in order to limit microplastic pollution from their plant, CASPACUF with Pyreg as an energy-nutrient recovery is seen as the highest scoring scenario. The PAC-UF system can be installed as an additional polishing step to an existing CAS system, significantly reducing upfront investment costs. The PAC-UF system scores a 2,65 as a normalized overall score. The baseline CASLand has a normalized overall score of 2,63. Three of the six analysed circular economic scenarios performed below the baseline. These scenarios are CASPACUF inci-eco with a score of 2,62, and the two circular economic scenarios with the lowest normalized overall scores being; the CASRO inci-eco scenario with a score of 2,33 and CASRO Pyreg scenario with a score of 1,94. Table 6 on the next page shows the full results of the MCA.

Figure 11 MCA Results visualised

2,63

3,11

2,33

2,62 2,67

1,94

2,65

1,80

2,00

2,20

2,40

2,60

2,80

3,00

3,20

1. CASland

2. MBR inci-eco

3. CASRO inci-eco

4. CASPACUF inci-eco

5. MBR Pyreg

6. CASRO Pyreg

7. CASPACUF Pyreg

- 27 -

Table 6 MCA Microplastic pathways in wastewater treatment

- 28 -

5.2 Sensitivity analysis

The sensitivity analysis verifies the robustness of the results. The aim is to determine if replicable results appear while the MCA parameters are changed. A sensitivity analysis was executed by increasing the weights of all criteria within one pillar by 1, while decreasing the criteria in the remaining two pillars by 1. If the weight would exceed the maximum weight of 5, the weight was set to 5. The calculation of the results follows the same normalization procedure as described in the methods section of this report. As can be seen in figure 11 no discrepancies in the results were found. All four scenarios result in MBR inci-eco being the highest performing scenario with the highest overall normalized score. Detailed tables of the sensitivity analyses are shown in Appendix E. In the environmental sensitivity analysis, the weights of all criteria in the environmental pillar were increased by 1 whilst the weights for the criteria in the other pillars were lowered by 1. In this sensitivity analysis the CASland scenario performed significantly lower as opposed to the MCA results. This is mainly due to the underperformance of CASland in respect to microplastic filtration and destruction. Nonetheless, several scenarios scored lower than the CASland scenario in environmental sensitivity analysis, this is mainly due the global warming potential for all scenarios. The higher emissions are explained by the higher energy intensity linked to more complex wastewater treatment and sludge treatment technologies.

The economic sensitivity analysis shows that the CASland scenario scores lower as opposed to the MCA results, this is mainly due to the lack of additional revenue streams in that scenario. The three scenarios which include incineration score lower in the economic sensitivity analysis due to the investment costs for each m3 of effluent. The three scenarios with Pyreg as a sludge treatment method score equal or higher as the MCA results, as investment and operational costs are balanced with the additional revenue streams created by the Pyreg by-products.

In the social sensitivity analysis, the three scenarios with Pyreg as a sludge treatment method score lower. This can be explained by the relative complexity of the Pyreg process, resulting in a lower normalized overall score for the social pillar. In addition, the consensus with regards to high performing treatment technologies for wastewater reuse, such as Reverse Osmosis, lead to an overall lower performance for the related scenarios.

Figure 12 Sensitivity analyses of the MCA results

1,80

2,00

2,20

2,40

2,60

2,80

3,00

3,20

1. CASland

2. MBR inci-eco

3. CASRO inci-eco

4. CASPACUF inci-eco

5. MBR Pyreg

6. CASRO Pyreg

7. CASPACUF Pyreg

MCA Results Sensitivity Environment Sensitivity Economic Sensitivity Social

- 29 -

5.3 Validation of MCA results

The MCA results have been validated through a combination of semi-structured and structured interviews with a panel of experts. The semi-structured interviews were conducted with a video conference. The structured interviews were formulated through an online survey. The interviewed stakeholders include, and are not limited to operators, engineers and management of MWWTPs, regional and local waterboards and an environmental protection agency. The interviews aimed to validate the MCA results and identify the bottlenecks between suitable scenarios and their deployment in MWWTP processes, in response to research question 6. Table 8 in appendix C shows a full list of the stakeholders and experts that have been interviewed.

Water reuse and limiting microplastic pollution

The department manager for wastewater treatment at the Dutch Regional waterboard, Waterschap Aa en Maas stated that “Preventing microplastic pollution can be combined with further reduction of nutrient emissions by additional polishing stages”. This underscores the MCA results in which the additional polishing technology PAC-UF has been identified to prevent microplastic pollution. Nonetheless, a Gryaab AB development engineer further stated that the current high removal rates of microplastics at MWWTPs will prevent existing MWWTPs to invest in new polishing treatment steps for microplastics only. These investments will only be made if regulatory demands for cleaning increase, or if a new MWWTP is being constructed. Therefore, future use of the MCA framework is preferred in the design stage of novel MWWTPs. A striking similarity in the answers of most respondents was the statement that microplastic pollution will not disappear no matter how well MWWTP filter microplastics out of the wastewater influent. A physical scientist from the US EPA stated that “No matter how good of a job we do at the MWWTP scale the problem will not be solved until we figure out how to keep plastic litter from entering waterbodies and prevent ocean dumping of trash in developing countries”. Signalling that preventing microplastic pollution at the source is the preferred pathway for limiting microplastic pollution from MWWTP. Furthermore, a development engineer from Gryaab AB underscored this by stating that “WWTPs are already designed to be good at removing particles, so the small fraction that do enter the WWTPs are removed by more than 98 %. Hence, efforts should be further directed to control at the source.”. In addition to preventing microplastics at the source, it was stated that a significant amount of microplastics do not pass through modern MWWTPs, as these microplastics are transported through storm water. Only combined sewer-systems handle storm water. A development engineer from Gryaab AB underscored this by stating that “The amount of microplastics that make its way to the wastewater is only a fraction of what is emitted directly to the sea by storm water, littering, fishing industry etc.”.

The statement was echoed by the Environmental Expert of Svenskt Vatten, stating that “Storm water seem to be one of the major sources of microplastic and storm water is normally directed to the recipient and not to the WWTP.”

Energy recovery and sludge handling

The finding that direct land application of biosolids should be avoided was highlighted by the manager of research at STOWA stating that “Microplastics should never be brought back in the environment by sludge application.” In addition, the importance of destroying microplastics in the sludge was affirmed by the manager of research at STOWA stating that “If microplastics in sludge can be eliminated, a big part of the problem is solved.”. In addition, “incineration or converting sludge into liquid or gaseous fuels is considered a sufficient method for microplastic handling” says a physical scientist from the US EPA. The use of thermal treatment methods to handle sludge and recover energy have also been mentioned by the same US EPA physical scientist stating that “We need to transform MWWTPs from energy consuming to energy producing facilities”. A development engineer van Gryaab AB also stated that it is “very important to use the energy that is left in the water”. The scenarios which include energy recovery technologies through incineration and pyrolysis are thus in line with the opinions of industry experts.

Nutrient recovery and sludge handling

The importance of recovering phosphorus has been underscored by several different stakeholders, as a physical scientist for the US EPA stated that “We need to be conserving and recycling every bit of phosphorus we can to preserve life for future generations”. In addition, the manager of research at STOWA stated that “mainly phosphorus has also many practical advantages in WWTP. Whilst

- 30 -

nitrogen is challenging due to market demands”. This validates this studies choice to focus on nutrient recovery technologies that recover P. Nonetheless a development engineer at Gryaab AB emphasized the importance of recovering nitrogen, carbon and all other trace elements. The importance of nutrient recovery was highlighted by a physical scientist of the US EPA, stating that “Treatment plants are chronically underfunded and are continually being asked to do more and more types of treatment. This is one of the big reasons that a resource recover model is important”. This highlights the importance of additional revenue stream creation, and thus the MCA result of PAC-UF with Pyreg, which creates several by-products that can feed into distinct revenue streams. This was again emphasized by a development engineer from Gryaab AB stating that “Creating additional revenue streams is very important for MWWTPs. We are currently paying for sludge handling”.

In sum, the interview results confirm the importance of several MCA criteria and validate the MCA results. One of the most important bottlenecks for implementation is the high investment costs for existing MWWTPs. Experts in the field stated that MWWTPs will not invest in polishing steps to improve microplastic removal, as microplastics are already removed with a retention ratio of over 88 percent. It is thus important that scenarios not only improve microplastic removal and destruction, but also create other benefits.

- 31 -

6. Discussion The increasing amount of microplastics found in the environment have underscored the urge to identify, develop and deploy scenarios in which MWWTPs limit the release of urban microplastics into the environment. Simultaneously, the global trend towards a circular economy has defined the conditions for these scenarios in relation to the water-energy-nutrient nexus.

This study has demonstrated how MCA can be applied to analyse existing and emerging technologies in the wastewater treatment supply chain for their ability to limit microplastic pollution from MWWTPs, whilst taking the water-energy-nutrient nexus into account.

6.1 Interpretation of results

Conventional MWWTPs with a primary and secondary treatment stage retain over 88 percent of microplastics in the sewage sludge, whilst MWWTPs with tertiary treatment retain over 97 percent (Sun et al., 2019). Despite high retention ratios, MWWTPs leak significant amounts of microplastics into the environment due to high total effluent volumes (Mason et al., 2016; Sun et al., 2019). In addition, the direct land application of bio-solids releases a significant number of the retained microplastics on terrestrial environments in high-income nations. It is key that policymakers modify regulations in regard to bio-solid application to limit the release of microplastics on farmlands. Regulating the amounts of microplastics contained in bio-solids could increase the competitiveness of more sustainable although expensive nutrient recovery technologies.

This study has identified full-scale technologies that have the potential to maximize microplastic removal ratios in MWWTPs. Only treatment technologies that can achieve 100 percent microplastic removal ratios in full scale operations have been included. Therefore, the filter-based technologies MBR, PAC-UF and RO/NF were selected. These treatment technologies are suitable treatment processes for water recovery purposes, as microplastics, antibiotics, pathogens and other contaminants can be removed effectively.

There is currently no method to separate microplastics from sewage sludge in a cost-effective way, therefore thermal treatment technologies are the only full-scale technologies to destroy microplastics. These technologies have the potential for recover energy to significantly reduce MWWTPs operational and environmental costs. This study has included anaerobic digestion with biogas utilization, mono-incineration and pyrolysis. These thermal treatment technologies have been combined with selected nutrient recovery technologies, this study took EcoPhos for P recovery after incineration and Pyreg for P recovery after pyrolysis into consideration. Both these technologies show the most promising advantages in terms of P recovery rates, integration and costs. Several circular economic scenarios for limiting microplastic pollution from MWWTP have been identified with the aid of an MCA framework. The MCA has identified MBR inci-eco as the best performing circular economic scenario for limiting microplastic pollution from MWWTPs. This scenario includes MBR with Anaerobic Digestion, energy recovery through incineration and P recovery through Ecophos. The second-best performing scenario is MBR Pyreg, which includes MBR with Anaerobic Digestion and energy-nutrient recovery through Pyreg. The overall higher score for MBR can be explained through the fact that MBR replaces the CAS process, whereas RO and PAC-UF are additional treatment steps added to an already existing CAS process. Therefore, the GWP and costs of scenarios including CAS is likely higher. If a new MWWTP is constructed, the high scoring MBR scenarios would be best suited for limiting microplastic, whilst taking circular economic objectives into account. Most respondents in the interview results have highlighted the importance of an increase in additional revenue by a selected scenario. This indicates that a scenario including Pyreg such as MBR Pyreg might be more suitable for MWWTPs, as these scenarios can generate additional revenue streams onsite of the MWWTP. Pyreg can be implemented onsite at small, medium and large wastewater treatment plants, thus additional revenue streams can be generated by the MWWTPs themselves - as opposed to incineration plants, which are often centralized making onsite additional revenue creation more difficult. The MCA results did not reflect this difference. If already existing MWWTPs aim to upgrade their facility to limit microplastic pollution, CASPACUF with Pyreg as an energy-nutrient recovery is seen as the best performing scenario. The PAC-UF system would then be installed as an additional polishing step to an existing CAS system, significantly reducing upfront investment costs. As the investment costs and GWP of the CAS system construction will not be considered in such a decision process, it can be assumed that the CAS PACUF system will outperform the MBR systems. Three out of six scenarios underperformed relative to the CASland baseline. This can be explained due to its wide application and low complexity, leading to relatively low operational and

- 32 -

capital costs. It should be noted that this scenario has only been analysed to provide a comparative measure, the CASland scenario does not filter out microplastics significantly. This scenario can thus not be utilized for limiting MWWTP related microplastic pollution. The interview results have highlighted the need for limiting microplastic pollution at the source, as a significant amount of microplastics do not pass through modern MWWTPs. These microplastics are transported through storm water. Furthermore, the results of this study underscore that the direct application of biosolids on land is not sustainable and leads to an increase in microplastic pollution on terrestrial lands. This underscores the need for a ban on the distribution and sale of biosolids for direct land application The introduction of additional polishing steps after conventional MWWTP processes should only be seen as a solution for specific cases. The cost-effectiveness of additional treatment processes will most likely be unfavourable for most treatment plants. This was underscored by several of the interview respondents. It is estimated that the additional costs for polishing treatment technologies range from 0.08 to 0.20 euro / m3, which would create a total extra annual cost of 1.84 – 7.6 billion euros for all MWWTPs in Europe (EUreau, 2019). This is a high investment considering that only 10 – 15 percent of all microplastic pollution arrives in the influent of MWWTPs, the other 85 – 90 percent enters the environment through e.g. storm water. Additional polishing steps would thus only impact the total microplastic release into the environment with 0.5 to 3 percent. As investment cycles are slow and lifespans of treatment assets are up to 40 years, it could take decades before additional polishing steps have been implemented in all existing wastewater treatment plants (EUreau, 2019).

6.2 Implications

This study has created a link between studies into treatment technologies for microplastics removal in wastewater streams and studies into circular economic objectives with regard to the water-energy-nutrient nexus. The results of this study build on the existing evidence that MWWTPs release significant amounts of microplastics to both terrestrial and aquatic environments. The MCA results provide a new insight on how to limit MWWTP related microplastic pollution, whilst taking circular economic objectives into account. The inclusion of water recovery, energy recovery and nutrient recovery aspects into the decision-making process has created a novel framework for the pathway design of wastewater treatment. While previous research into microplastic pollution from MWWTPs has focused on retaining microplastics into sewage sludge, research into transforming the system of wastewater treatment for the benefit of microplastic pollution prevention was missing. The results of this study demonstrate that a systems approach, which includes wastewater entering the treatment facility to the treatment and disposal of sludge, is essential in order to limit microplastic pollution. The inclusion of the sludge treatment stage guarantees that retained microplastics are destroyed. The interviews indicated the importance of economic considerations in wastewater treatment, therefore an alternative for limiting microplastic pollution is the adjustment of operational parameters in existing MWWTP processes to improve microplastic removal ratios. For example, the ideal pore size of existing filtration systems or the hydraulic retention time in skimming and sedimentation processes would be worth investigating to increase microplastic capture. Future research should be focused on assisting MWWTP operators in identifying the desired operational parameters. None of the analysed technologies in this report are designed for microplastic removal or destruction. Innovative technologies for removing microplastics from the sludge are seen as important, nonetheless the wastewater sector sees these technologies as unrealistic in the near future (EurEau, 2019). Treatment technologies that specifically target microplastics are still undergoing preliminary research and have not been applied in a full-scale MWWTP (Sun et al., 2019). Additional research and development are needed into technologies that are specially designed for microplastic removal. Examples of known research-stage microplastic removal technologies include e.g. gravity-powered filtration systems (Beljanski et al., 2016) and ferrofluid extraction (Nace, 2019). Further research is needed in order to scale these technologies to full-scale MWWTP facilities.

None of the interview respondents have indicated business model innovation as a potential solution for the previously mentioned high investment costs of additional polishing steps. Research into business model innovation is suggested, as the investment costs of additional polishing steps might hinder the implementation of these technologies for microplastic removal. A circular economic business model in which treatment technology is provided to MWWTPs through a product-as-a-service (PAAS) model could significantly reduce the potential upfront investment costs. In a product-as-as-service model the manufacturer maintains ownership of their product, in this case advanced treatment technologies, as they make the equipment including maintenance and service available as a lease. This stimulates the manufacturer to design and produce equipment of increasingly higher standards to limit maintenance

- 33 -

costs, at the same time it eliminates the responsibilities of owning equipment for the user, such as the risk of losing financial investments or the burden of maintenance. This could make additional polishing technologies accessible to a wider range of treatment facilities. In a 2018 study, Sousa-Zomer and Miguel, indicated that “innovative water technologies include not only new sustainable technologies for water treatment, but also complementary innovation in business models to support the adoption of these technologies”. Business model innovation could help overcome the barriers of wastewater treatment technology implementation. Future research can focus on the implications of business model innovation and in particular product-as-a-service models for wastewater and sludge treatment technologies. Until the investment cost hurdle is overcome, the MCA framework can be used for the sludge handling pathways of existing MWWTPs. As the sludge handling pathways would still limit microplastic pollution while creating additional revenue streams and realising circular economic objectives. Neither European nor North American regulations currently mention microplastics in their restrictions on using sewage sludge containing harmful substances. New legislation to limit the contamination of microplastics in biosolids, will reduce the high microplastic release through land application and most likely stimulate research into microplastic removal techniques. This could increase the competitiveness of more sustainable although expensive nutrient recovery technologies. In addition to removing microplastics from MWWTPs, future efforts should be directed towards the prevention of microplastics entering MWWTPs. This was underscored by the respondents of the interviews. It is essential that future research is not only focussed on the pathways of microplastics in MWWTPs but also on preventing microplastics from entering the plants all together. The reduction of fibre release by washing machines, would significantly reduce microplastic pollution, as an estimated 52.7 percent of all microplastics entering the treatment facilities are textile fibres (Magnusson and Norén, 2014). Correspondingly, source prevention of tire wear will have a large impact on microplastic pollution. Research has shown that the cost-effectiveness of prevention measures at the source could outperform the cost-effectiveness of centralised collection of microplastics in a MWWTP (Han et al., 2018). As mentioned several times by respondents during the interviews, additional research is needed into the prevention of microplastic pollution through storm water. Historically, sewage was collected through a combined sewer system. In which both sanitary wastewater and storm water runoff was collected. The disadvantage of this system is the release of excess flow during heavy rains, releasing all sewage pollutants directly into the environment. Nonetheless the transition away from combined sewer systems has led to the current situation in which storm water is never treated. As the flow rate and quantity of microplastics within storm water is high, future research into the treatment of storm water is essential for limiting microplastic pollution into the environment. Future research or co-operative research with operational MWWTP, for creating accurate and relative data will significantly increase the robustness of the MCA results. Especially data in regard to the global warming potential of each scenario should be extracted with care, as this data is highly dependent on the parameters used in the referenced environmental analysis. This study has included the recovery of water, energy and phosphorus only nonetheless it should be noted that wastewater contains many other resources that have the potential to be recovered. Future scientific and technological advances will make it possible to recover a greater variety of resources at full-scale in a cost-effective manner. If new resource extraction technologies emerge, the MCA criteria should be reassessed for inclusion of a wider resource range to increase its circular economic potential. Nonetheless, MCA has proven to be a useful analysis tool for assessing a wastewater treatment scenario for its ability to limit microplastic pollution from MWWTPs, whilst taking circular economic objectives into account.

It is worth noting that the small sampling units in the referenced studies researching microplastic filtration technologies, might give false results, and a larger sampling volume would give a more reliable assessment of microplastic removal efficiency during tertiary treatment (Sun et al., 2019). There currently is no standard method for measuring the capture rate of microplastics. This means that past studies on different types of treatment facilities are not directly comparable, and it is thus not possible to fully identify best practice in removal of microplastics from effluent. There is thus need for a standardized method to measure and identify microplastics in MWWTPs. A standardised method could increase the reliability of the MCA, as the measured microplastic removal rates of different technologies become more robust. It is of high importance that MWWTPs can compare their removal rates with one another, in order to optimize operations for increasing microplastic removal. Future studies should be directed towards defining a standardised method for measuring microplastic capture performances in MWWTPs.

- 34 -

AD was included in all scenarios of this study however, several studies have indicated that energy deficits and costs could be lower if incineration is combined with a system that incinerates without AD as a pre-treatment. Future research should focus on assessing pathways in which AD is not considered and comparing these with systems including AD. In order for MWWTPs to limit their microplastic pollution, it is necessary to identify and breach the gaps between the identified technologies and their market application. Even though, interviews with stakeholders were conducted, further research into the gaps is required. This research should aim to provide all stakeholders in the wastewater treatment supply chain the necessary tools for scenario application. The results of this study have firmly underscored that the land application of biosolids is not a sustainable sludge treatment method in regard to microplastic pollution as the microplastics contained in the sludge are not destroyed. Future research is needed to fully grasp the effects of biosolid application on land for both human and ecological health.

- 35 -

7. Conclusion and recommendations This study has established and assessed several circular economic scenarios for limiting microplastic pollution from MWWTPs, aiming to make MWWTPs a sustainable actor in a global circular economic system. This study demonstrated how MCA can be applied to analyse existing and emerging technologies in the wastewater treatment supply chain for their ability to limit microplastic pollution from MWWTPs, whilst taking the water-energy-nutrient nexus into account. Despite high retention ratios, MWWTPs leak significant amounts of microplastics into the environment due to high total effluent volumes. The direct land application of bio-solids releases a significant number of the retained microplastics on terrestrial environments in high-income nations. The results of this study have firmly underscored that the land application of biosolids is not a sustainable sludge treatment method in regard to microplastic pollution. The three-pillars of sustainability being environmental, economic and social sustainability have proven to be a useful demarcation in the selection of assessment criteria. The MCA has identified MBR inci-eco as the best performing circular economic scenario for limiting microplastic pollution from MWWTPs. This scenario includes MBR with Anaerobic Digestion, energy recovery through incineration and P recovery through Ecophos. The management and design engineers of MWWTPs and regional waterboard can use these results in the design stage of to be constructed MWWTPs. The highlighted importance of an increase in additional revenue indicates that a scenario including Pyreg such as the second-best performing scenario MBR Pyreg, might be more suitable for MWWTPs, as these scenarios can generate additional revenue streams onsite of the MWWTP.

If already existing MWWTPs aim to upgrade their facility to limit microplastic pollution, CASPACUF with Pyreg as an energy-nutrient recovery is seen as the best performing scenario. The PAC-UF system would then be installed as an additional polishing step to an existing CAS system, significantly reducing upfront investment costs. The management and design engineers of MWWTPs can use these results to upgrade existing MWWTPs in a sustainable manner. The introduction of additional polishing steps after conventional MWWTP processes should only be seen as a solution for specific cases. The cost-effectiveness of additional treatment processes will most likely be unfavourable for most treatment plants. Research into business model innovation is suggested, as the investment costs of additional polishing steps might hinder the implementation of additional polishing steps for microplastic removal. The simultaneous inclusion of microplastic pollution, water recovery, energy recovery and nutrient recovery aspects into the decision-making process has created a novel framework for the pathway design of wastewater treatment. The management and engineers of MWWTPs can use the MCA framework to assess the sustainability performance of their own case specific wastewater supply chain in regard to microplastic pollution and the water-energy-nutrient nexus. Furthermore, existing plants can be retrofitted to always include thermal treatment of sludge to increase microplastic destruction. Academia can build upon these results to initiate additional research into novel microplastic filtration specific technologies, business model innovation for wastewater treatment and microplastic pollution prevention at the source and in stormwaters. National and regional waterboards should aim to develop a standardised monitoring procedure for assessing microplastics in wastewater streams in cooperation with waterboards from different nations. Furthermore, they should build upon these results to retrofit existing wastewater treatment pathways to always include thermal treatment of sludge and increase microplastic retention.

National and international policymakers should ban the distribution and sale of biosolids for direct land application to limit the pollution of microplastics from bio-solids. It is key that policymakers modify regulations in regard to bio-solid application to limit the release of microplastics on farmlands. Regulating the amounts of microplastics contained in bio-solids could increase the competitiveness of more sustainable although expensive nutrient recovery technologies. Furthermore, efforts should be put in place to limit microplastic pollution at the source by stimulating policies for a ban on the use of microbeads, limit tyre wear and improving design for e.q. washing machines.

- 36 -

The following short-term recommendations follow out of the results of this study:

• Use the MCA framework to assess the sustainability performance of specific wastewater supply chains.

• Create a standardised monitoring procedure for assessing microplastics in wastewater streams.

• Ban the application of sludge on land.

Th following long-term recommendations are made:

• Explore business model innovations to limit investment costs. • Retrofit existing wastewater treatment pathways to always include thermal treatment of

sludge and increase microplastic retention. • Ban the use of microbeads, limit tyre wear and improve design. • Research into microplastic pollution at the source and in stormwaters. • Research into the application of novel microplastic specific technologies.

- 37 -

References Akhoundi, A., & Nazif, S. (2018). Sustainability assessment of wastewater reuse alternatives using the evidential reasoning approach. Journal of Cleaner Production, 195, 1350-1376. Amann, A., Zoboli, O., Krampe, J., Rechberger, H., Zessner, M., & Egle, L. (2018). Environmental impacts of phosphorus recovery from municipal wastewater. Resources, Conservation and Recycling, 130, 127-139. Arévalo, J., Ruiz, L. M., Parada-Albarracín, J. A., González-Pérez, D. M., Pérez, J., Moreno, B., & Gómez, M. A. (2012). Wastewater reuse after treatment by MBR. Microfiltration or ultrafiltration?. Desalination, 299, 22-27. Baresel, C., Ek, M., Ejhed, H., Allard, A. S., Magnér, J., Dahlgren, L., ... & VA-verksaktiebolag, S. S. (2017). Handbok för refining av mikroföroreningar vid avloppsreningsverk.

Baresel, C., Harding, M., & Fång, J. (2019). Ultrafiltration/granulated active carbon-biofilter: efficient removal of a broad range of micropollutants. Applied Sciences, 9(4), 710. Bayo, J., Olmos, S., López-Castellanos, J. and Alcolea, A. (2016). Microplastics and microfibres in the sludge of a municipal wastewater treatment plant. International Journal of Sustainable Development and Planning, 11(5), pp.812-821. Beljanski, A. (2016). Efficiency and effectiveness of a low-cost, self-cleaning microplastic filtering system for wastewater treatment plants. 2016 NCUR. Bertanza, G., Canato, M., Laera, G., Vaccari, M., Svanström, M., & Heimersson, S. (2017). A comparison between two full-scale MBR and CAS municipal wastewater treatment plants: techno-economic-environmental assessment. Environmental Science and Pollution Research, 24(21), 17383–17393. doi:10.1007/s11356-017-9409-3 Bhasin, A. (2017). Recovery of Phosphorus from Incineration of Sewage Sludge.

Bolong, N., Ismail, A. F., Salim, M. R., & Matsuura, T. (2009). A review of the effects of emerging contaminants in wastewater and options for their removal. Desalination, 239(1-3), 229-246.

Burra, K. G., & Gupta, A. K. (2018). Kinetics of synergistic effects in co-pyrolysis of biomass with plastic wastes. Applied Energy, 220, 408-418. Cao, Y., & Pawłowski, A. (2013). Life cycle assessment of two emerging sewage sludge-to-energy systems: evaluating energy and greenhouse gas emissions implications. Bioresource technology, 127, 81-91. Carr, S., Liu, J. and Tesoro, A. (2016). Transport and fate of microplastic particles in wastewater treatment plants. Water Research, 91, pp.174-182. Corcoran, E., C. Nellemann, E. Baker, R. Bos, D. Osborn, H. Savelli (eds). 2010. Sick Water? The central role of wastewater management in sustainable development. A Rapid Response Assessment. United Nations Environment Programme, UN-HABITAT, GRID-Arendal. www.grida.no Cowger, W., Gray, A. B., Eriksen, M., Moore, C. and Thiel, M. (2019). Microplastics in Water and Wastewater, Hrissi K. Karapanagioti, Ioannis K. Kalavrouziotis. IWA Publishing. Cox, K. D., Covernton, G. A., Davies, H. L., Dower, J. F., Juanes, F., & Dudas, S. E. (2019). Human consumption of microplastics. Environmental science & technology, 53(12), 7068-7074.

De Rose, A., Buna, M., Strazza, C., Olivieri, N., Stevens, T., Peeters, L., & Tawil-Jamault, D. (2017). Technology Readiness Level: Guidance Principles for Renewable Energy Technologies. European Commission: Petten, The Netherlands.

Dodgson, J. S., Spackman, M., Pearman, A., & Phillips, L. D. (2009). Multi-criteria analysis: a manual. Easymining (2020). Ash2Phos – EasyMining. [online] Easymining.se. Available at: http://easymining.se/ash2phos/ [Accessed 29 Feb. 2020].

Ecophos (2020). Ecophos P-recovery. [online] Ecophos. Available at: https://www.ecophos.com/ecophos-group/p-recovery/ [Accessed 29 Feb. 2020]. Edwards, J. A., Burn, S., & Othman, M. (2015). Anaerobic digestion at wastewater treatment plants. Water: Journal of the Australian Water Association, 42(3), 83.

- 38 -

EEA. (2016). CO2 Emission Intensity. [online] European Environment Agency. Available at: <https://bit.ly/2YPYnv4> [Accessed 5 April 2020]. Egle, L., Rechberger, H., Krampe, J., & Zessner, M. (2016). Phosphorus recovery from municipal wastewater: An integrated comparative technological, environmental and economic assessment of P recovery technologies. Science of the Total Environment, 571, 522-542. EPA. (2017). Chapter 2: Incinerators and Oxidizers. U.S. Environmental Protection Agency. Research Triangle Institute. Research Triangle Park, NC 27709

EPA. 2004. Primer for Municipal Wastewater Treatment Systems . Office of Water Office of Wastewater Management. https://www3.epa.gov/npdes/pubs/primer.pdf EuReau (2019). Microplastics and the water sector - Current knowledge, challenges and possible solutions EurEau. (2017). Europe’s water in figures: An overview of the European drinking water and waste water sectors. EurEau.The European Federation of National Associations of Water Services.

EurEau. (2019). Water matters! 2019 Manifesto. EurEau. The European Federation of National Associations of Water Services. European Commission (2016) Energy, Transport and GHG Emissions Trends to 2050. [online] Available from: https://ec.europa.eu/energy/sites/ener/files/documents/ref2016_report_final-web.pdf [Accessed 23 Feb. 2020] European Commission (2018). Press corner. [online] European Commission - European Commission. Available at: https://ec.europa.eu/commission/presscorner/detail/en/IP_18_6161 [Accessed 23 Feb. 2020]. Forte, B., Coleman, M., Metcalfe, P. & Weaver, M. (2012). The case for the PYREG slow pyrolysis processin improving the efficiency and profitability of Anaerobic Digestion plants in the UK. WRAP. Project code:OIN001-408. Fytili, D., & Zabaniotou, A. (2008). Utilization of sewage sludge in EU application of old and new methods—a review. Renewable and sustainable energy reviews, 12(1), 116-140. Gebrezgabher, S., Rao, K., Hanjra, M. A., & Hernández-Sancho, F. (2015). Business models and economic approaches for recovering energy from wastewater and fecal sludge. In Wastewater (pp. 217-245). Springer, Dordrecht. Geissdoerfer, M., Savaget, P., Bocken, N. M., & Hultink, E. J. (2017). The Circular Economy–A new sustainability paradigm?. Journal of cleaner production, 143, 757-768.

Ghazy, M. R., Dockhorn, T., & Dichtl, N. (2011). Economic and environmental assessment of sewage sludge treatment processes application in Egypt. International Water Technology Journal, 1(2), 1-17.

Gherghel, A., Teodosiu, C., & De Gisi, S. (2019). A review on wastewater sludge valorisation and its challenges in the context of circular economy. Journal of cleaner production. Ghisellini, P., Cialani, C., & Ulgiati, S. (2016). A review on circular economy: the expected transition to a balanced interplay of environmental and economic systems. Journal of Cleaner production, 114, 11-32. Goldblum, J. (1993). Life, Uh, finds a way. Jurrasic Park. By Spielberg, S. [online] Universal Pictures. Kennedy, K and Molen, G. Available at: <https://bit.ly/2WWx3dz > [Accessed 1 April 2020].

Graedel, T. and Allenby, B. (2010). Industrial ecology and sustainable engineering. 1st ed. Upper Saddle River: Pearson education Inc., p.32. GWRC. (2019). FACTSHEET GLOBAL SUMMARY ON PHOSPHORUS RECOVERY Available at: < http://cwn-rce.ca/wp-content/uploads/Phosphorus-Recovery-Factsheet-January-2019.pdf> [Accessed 30 March 2020]. Hale, M., 2018. Maximizing Opportunities Of Anaerobic Digestion From Wastewater. [online] Water Tech Online. Available at: <https://www.watertechonline.com/wastewater/article/15550717/maximizing-opportunities-of-anaerobic-digestion-from-wastewater> [Accessed 30 March 2020].

Hanjra, M. A., Drechsel, P., Wichelns, D., & Qadir, M. (2015). Transforming urban wastewater into an economic asset: opportunities and challenges. In Wastewater (pp. 271-278). Springer, Dordrecht.

- 39 -

Hann, S., Sherrington, C., Jamieson, O., Hickman, M., Kershaw, P., Bapasola, A., & Cole, G. (2018). Investigating options for reducing releases in the aquatic environment of microplastics emitted by (but not intentionally added in) products. Report for DG ENV EC. Hansmann, R., Mieg, H.A. and Frischknecht, P., (2012). Principal sustainability components: empirical analysis of synergies between the three pillars of sustainability. International Journal of Sustainable Development & World Ecology, 19(5), pp.451-459 Hao, X., Chen, Q., van Loosdrecht, M. C., Li, J., & Jiang, H. (2019). Sustainable disposal of excess sludge: Incineration without anaerobic digestion. Water research, 115298. Haslinger, J., Lindtner, S., & Krampe, J. (2016). Operating costs and energy demand of wastewater treatment plants in Austria: benchmarking results of the last 10 years. Water Science and Technology, 74(11), 2620-2626. Hernández-Sancho, F., Lamizana-Diallo, B., Mateo-Sagasta, J., Qadir, M. (2015). Economic Valuation of Wastewater - The cost of action and the cost of no action. United Nations Environment Programme.

Hreiz, R., Latifi, M. A., & Roche, N. (2015). Optimal design and operation of activated sludge processes: State-of-the-art. Chemical Engineering Journal, 281, 900-920. Hu, Y., Gong, M., Wang, J., & Bassi, A. (2019). Current research trends on microplastic pollution from wastewater systems: a critical review. Reviews in Environmental Science and Bio/Technology, 18(2), 207-230. IWA. (2016). Water Utility Pathways in a Circular Econom, International Water Association. Published by the International Water Association. [online] Available from: <https://iwa-network.org/wp-content/uploads/2016/07/IWA_Circular_Economy_screen-1.pdf> [Accessed 23 Feb. 2020] Jin, Q., Wang, X., Li, S., Mikulčić, H., Bešenić, T., Deng, S., ... & Kumfer, B. M. (2019). Synergistic effects during co-pyrolysis of biomass and plastic: Gas, tar, soot, char products and thermogravimetric study. Journal of the Energy Institute, 92(1), 108-117. Judd, S. (2010). The MBR book: principles and applications of membrane bioreactors for water and wastewater treatment. Elsevier. Kabbe, C. (2015). Sustainable sewage sludge management fostering phosphorus recovery and energy efficiency. Final report P-rex.

Kabbe, C. (2019). Global Compendium on Phosphorus Recovery from Sweage/Sludge/Ash. London: Global Water Research Coaliation. Karaca, C., Sözen, S., Orhon, D., & Okutan, H. (2018). High temperature pyrolysis of sewage sludge as a sustainable process for energy recovery. Waste management, 78, 217-226. Kehrein, P., van Loosdrecht, M., Osseweijer, P., Dewulf, J., Garfi, M., & Duque, J. A. P. (2020). A critical review of resource recovery from municipal wastewater treatment plants–market supply potentials, technologies and bottlenecks. Environmental Science: Water Research & Technology. Kleemann, R., Chenoweth, J., Clift, R., Morse, S., Pearce, P., & Saroj, D. (2017). Comparison of phosphorus recovery from incinerated sewage sludge ash (ISSA) and pyrolysed sewage sludge char (PSSC). Waste management, 60, 201-210. Larsen H.F. (2018) LCA of Wastewater Treatment. In: Hauschild M., Rosenbaum R., Olsen S. (eds) Life Cycle Assessment. Springer, Cham Lazarova, V., Martin Ruel, S., Barillon, B., & Dauthuille, P. (2012). The role of MBR technology for the improvement of environmental footprint of wastewater treatment. Water Science and Technology, 66(10), 2056-2064. Li, L., Xu, G., Yu, H., & Xing, J. (2018). Dynamic membrane for micro-particle removal in wastewater treatment: Performance and influencing factors. Science of the Total Environment, 627, 332-340.

Löwenberg, J., & Wintgens, T. (2017). PAC/UF processes: Current application, potentials, bottlenecks and fundamentals: A Review. Critical Reviews in Environmental Science and Technology, 47(19), 1783-1835.

Ma, X. C., Xue, X., González-Mejía, A., Garland, J., & Cashdollar, J. (2015). Sustainable water systems for the city of tomorrow—A conceptual framework. Sustainability, 7(9), 12071-12105.

- 40 -

Magnusson, K., & Norén, F. (2014). Screening of microplastic particles in and down-stream a wastewater treatment plant. Mahon, A. M., O’Connell, B., Healy, M. G., O’Connor, I., Officer, R., Nash, R., & Morrison, L. (2017). Microplastics in sewage sludge: effects of treatment. Environmental Science & Technology, 51(2), 810-818. Mahon, A.M., O’Connell, B., Healy, M.G. et al. (2017). Microplastics in Sewage Sludge: Effects of Maktabifard, M., Zaborowska, E., & Makinia, J. (2018). Achieving energy neutrality in wastewater treatment plants through energy savings and enhancing renewable energy production. Reviews in Environmental Science and Bio/Technology, 17(4), 655-689. Mason, S., Garneau, D., Sutton, R., Chu, Y., Ehmann, K., Barnes, J., Fink, P., Papazissimos, D. and Rogers, D. (2016). Microplastic pollution is widely detected in US municipal wastewater treatment plant effluent. Environmental Pollution, 218, pp.1045-1054. Mihelcic, J. R., Fry, L. M. and Shaw, R. 2011. Global potential of phosphorus recovery from human urine and feces. Chemosphere, Vol. 84, No. 6, pp. 832–839. doi.org/10.1016/j.chemosphere.2011.02.046 Milieu Ltd, WRc, Risk and Policy Analysts Ltd (RPA). Environmental, economic and social impacts of the use of sewage sludge on land. Final Report, Part III: Project Interim Reports; 2010. DG ENV.G.4./ETU/2008/0076r. http://ec.europa.eu/environment/archives/waste/sludge/pdf/part_iii_report.pdf. Accessed 2 May 2018.

Mintenig, S. M., Int-Veen, I., Löder, M. G., Primpke, S., & Gerdts, G. (2017). Identification of microplastic in effluents of waste water treatment plants using focal plane array-based micro-Fourier-transform infrared imaging. Water research, 108, 365-372.

Mo, W., & Zhang, Q. (2013). Energy–nutrients–water nexus: integrated resource recovery in municipal wastewater treatment plants. Journal of environmental management, 127, 255-267. Nace, T. (2019). Irish Teen Wins 2019 Google Science Fair For Removing Microplastics From Water. [online] Forbes.com. Available at: https://www.forbes.com/sites/trevornace/2019/07/30/irish-teen-wins-2019-google-science-fair-for-removing-microplastics-from-water/#4b07ee16373f [Accessed 19 Feb. 2020].

Nättorp, A. & Remmen, K. (2015) Report on LCC of European P recovery processes. P-Rex. Sustainable sewage sludge management fostering phosphorus recovery and energy efficiency. Nättorp, A., Remmen, K., & Remy, C. (2017). Cost assessment of different routes for phosphorus recovery from wastewater using data from pilot and production plants. Water Science and Technology, 76(2), 413–424. doi:10.2166/wst.2017.212

Neczaj, E., and Grosser, A. (2018). Circular economy in wastewater treatment plant–challenges and barriers. In Multidisciplinary Digital Publishing Institute Proceedings (Vol. 2, No. 11, p. 614). Nizzetto, L., Futter, M. and Langaas, S. (2016). Are Agricultural Soils Dumps for Microplastics of Urban Origin?. Environmental Science & Technology, 50(20), pp.10777-10779. Northwest Biosolids (2020). Benefits of biosolids. [online] Northwest Biosolids. Available at: https://nwbiosolids.org/what-are-biosolids/product-use/agriculture [Accessed 9 Feb. 2020].

Ochando-Pulido, J. M., Martínez-Férez, A., & Stoller, M. (2019). Analysis of the Flux Performance of Different RO/NF Membranes in the Treatment of Agroindustrial Wastewater by Means of the Boundary Flux Theory. Membranes, 9(1), 2.

Oladejo, J., Shi, K., Luo, X., Yang, G., & Wu, T. (2019). A review of sludge-to-energy recovery methods. Energies, 12(1), 60. Otoo, M., Drechsel, P., & Hanjra, M. A. (2015). Business models and economic approaches for nutrient recovery from wastewater and fecal sludge. In Wastewater (pp. 247-268). Springer, Dordrecht. Pandey, A., & Singh, R. K. (2014). Industrial waste water treatment by membrane bioreactor system. Elixir Chem. Eng, 70, 23772-23777.

Pandey, A., & Singh, R. K. (2014). Industrial waste water treatment by membrane bioreactor system. Elixir Chem. Eng, 70, 23772-23777.

- 41 -

Persson, P. O. (2011). Cleaner Production: Strategies & Technology for environmental Protection. Industrial Ecology, KTH. Pervov, A., Matveev, N., & Andrianov, A. (2013). Decentralization of Wastewater Treatment in Local Utilities and Industries Applications.

Peters, G. M., & Rowley, H. V. (2009). Environmental comparison of biosolids management systems using life cycle assessment. Phosphorus Platform EU (2020). European Sustainable Phosphorus Platform - P-recovery Technologies. [online] Phosphorusplatform.eu. Available at: https://phosphorusplatform.eu/activities/p-recovery-technology-inventory [Accessed 29 Feb. 2020]. Plakas, K. V., Georgiadis, A. A., & Karabelas, A. J. (2016). Sustainability assessment of tertiary wastewater treatment technologies: a multi-criteria analysis. Water Science and Technology, 73(7), 1532-1540. Pohekar, S.D. and Ramachandran, M., 2004. Application of multi-criteria decision making to sustainableenergy planning—A review. Renewable and sustainable energy reviews, 8(4), pp.365-381. PURE (Project on Urban Reduction of Eutrophication), 2012. Good practices in sludge management. Turku, Finland: Union of the Baltic Cities Environment Commission. Available at: http://www.purebalticsea.eu/index.php/gpsm:good_practices [Accessed 8 February 2020]. PURE. (2012). Good practices in Sludge Management. Project on Urban Reduction of Eutrophication Pyreg GmbH, 2020. HOME - PYREG Gmbh. [online] PYREG GmbH. Available at: <https://www.pyreg.de> [Accessed 30 March 2020]. Ramaswami, S., Behrendt, J., & Otterpohl, R. (2018). Comparison of NF-RO and RO-NF for the treatment of mature landfill leachates: a guide for landfill operators. Membranes, 8(2), 17.

Rao, K., Hanjra, M. A., Drechsel, P., & Danso, G. (2015). Business models and economic approaches supporting water reuse. In Wastewater (pp. 195-216). Springer, Dordrecht. Rashidi, H., GhaffarianHoseini, A., GhaffarianHoseini, A., Sulaiman, N. M. N., Tookey, J., & Hashim, N. A. (2015). Application of wastewater treatment in sustainable design of green built environments: A review. Renewable and Sustainable Energy Reviews, 49, 845-856. Remondis (2020). Phosphorus recovery // REMONDIS Sustainability. [online] Remondis-sustainability.com. Available at: https://www.remondis-sustainability.com/en/acting/phosphorus-recovery/ [Accessed 29 Feb. 2020]. Risch, E., Gutierrez, O., Roux, P., Boutin, C., & Corominas, L. (2015). Life cycle assessment of urban wastewater systems: Quantifying the relative contribution of sewer systems. Water research, 77, 35-48. Rockström, J. and Klum, M (2012). The Human quest - prospering within planetary boundaries. Bokförlaget Langenskiöld. Rodriguez-Garcia, G., Molinos-Senante, M., Hospido, A., Hernández-Sancho, F., Moreira, M. T., & Feijoo, G. (2011). Environmental and economic profile of six typologies of wastewater treatment plants. water research, 45(18), 5997-6010. Rodriguez-Garcia, G., Molinos-Senante, M., Hospido, A., Hernández-Sancho, F., Moreira, M. T., & Feijoo, G. (2011). Environmental and economic profile of six typologies of wastewater treatment plants. water research, 45(18), 5997-6010. Rodriguez, D. (2018). Wastewater treatment: A critical component of a circular economy. [online] World Bank Blogs. Available at: https://blogs.worldbank.org/water/wastewater-treatment-critical-component-circular-economy [Accessed 22 Feb. 2020]. Rummel, C. D., Jahnke, A., Gorokhova, E., Kühnel, D., & Schmitt-Jansen, M. (2017). Impacts of biofilm formation on the fate and potential effects of microplastic in the aquatic environment. Environmental Science & Technology Letters, 4(7), 258-267. Samolada, M. C., & Zabaniotou, A. A. (2014). Comparative assessment of municipal sewage sludge incineration, gasification and pyrolysis for a sustainable sludge-to-energy management in Greece. Waste management, 34(2), 411-420. Schafer, P. L., Farrell, J. B., Newman, G., & Vandenburgh, S. (2002). Advanced anaerobic digestion performance comparisons. Proceedings of the Water Environment Federation, 2002(13), 468-484.

- 42 -

Schwabl, P., Köppel, S., Königshofer, P., Bucsics, T., Trauner, M., Reiberger, T., & Liebmann, B. (2019). Detection of various microplastics in human stool: a prospective case series. Annals of internal medicine. Shahtalebi, A., Sarrafzadeh, M. H., & Montazer-Rahmati, M. M. (2009). RO-NF MEMBRANE PROCESS FOR PHARMACEUTICAL WASTEWATER TREATMENT AND SEPARATION OF ANTIBIOTICS. Conference: 8th World Congress of Chemical Engineering, Montreal, Canada Shaikh, M. (2018). PHOSPHORUS RECOVERY FROM SEWAGE SLUDGE AND WASTE WATER TREATMENT. International Conference On Sustainable Solutions in Industrial Pollution, Water and Wastewater TreatmentAt: AMU, ALIGARH , UP, INDIA Sharma, S. and Chatterjee, S. (2017). Microplastic pollution, a threat to marine ecosystem and human health: a short review. Environmental Science and Pollution Research, 24(27), pp.21530-21547.

Singhirunnusorn, W., & Stenstrom, M. K. (2009). Appropriate wastewater treatment systems for developing countries: criteria and indictor assessment in Thailand. Water science and technology, 59(9), 1873-1884.

Soda, S., Arai, T., Inoue, D., Ishigaki, T., Ike, M., & Yamada, M. (2013). Statistical analysis of global warming potential, eutrophication potential, and sludge production of wastewater treatment plants in Japan. Journal of Sustainable Energy & Environment, 4(1), 33-40.

Sousa-Zomer, T. T., & Miguel, P. A. C. (2018). Sustainable business models as an innovation strategy in the water sector: An empirical investigation of a sustainable product-service system. Journal of Cleaner Production, 171, S119-S129.

Stahel, W. R. (2016). The Circular Economy. Nature. [online] Available from: <https://www.nature.com/news/the-circular-economy-1.19594> [Accessed 23 Feb. 2020] Stillwell, A. S., Hoppock, D. C., & Webber, M. E. (2010). Energy recovery from wastewater treatment plants in the United States: a case study of the energy-water nexus. Sustainability, 2(4), 945-962. Sujathan, S., Kniggendorf, A. K., Kumar, A., Roth, B., Rosenwinkel, K. H., & Nogueira, R. (2017). Heat and bleach: a cost-efficient method for extracting microplastics from return activated sludge. Archives of environmental contamination and toxicology, 73(4), 641-648. Sun, J., Dai, X., Wang, Q., van Loosdrecht, M. C., & Ni, B. J. (2019). Microplastics in wastewater treatment plants: Detection, occurrence and removal

Szaja, A. (2013). Phosphorus recovery from sewage sludge via pyrolysis. Annual Set The Environment Protection, 15, 361-370. Talvitie, J., Mikola, A., Koistinen, A. and Setälä, O. (2017). Solutions to microplastic pollution – Removal of microplastics from wastewater effluent with advanced wastewater treatment technologies. Water Research, 123, pp.401-407.

Talvitie, J., Mikola, A., Setälä, O., Heinonen, M., & Koistinen, A. (2017). How well is microlitter purified from wastewater?–A detailed study on the stepwise removal of microlitter in a tertiary level wastewater treatment plant. Water research, 109, 164-172.

Tolkou, A. K., & Zouboulis, A. I. (2016). Effect of climate change in WWTPs with a focus on MBR infrastructure. Desalination and Water Treatment, 57(5), 2344-2354. Treatment. Environmental Science & Technology, 51 (2): 810–818. DOI: 10.1021/acs.est.6b04048

Tsoutsos, T., Drandaki, M., Frantzeskaki, N., Iosifidis, E. and Kiosses, I., 2009. Sustainable energ planning by using multi-criteria analysis application in the island of Crete. Energy policy, 37(5), pp.1587-1600.

Usman, K., Khan, S., Ghulam, S., Khan, M. U., Khan, N., Khan, M. A., & Khalil, S. K. (2012). Sewage sludge: an important biological resource for sustainable agriculture and its environmental implications. Van Vuuren, D. P., Bouwman, A. F., Beusen, A. H. W. 2010. Phosphorus demand for the 1970–2100 period: A scenario analysis of resource depletion. Global Environmental Change, Vol. 20, No. 3, pp. 428–439. doi.org/10.1016/j.gloenvcha.2010.04.004 Voigt, M., Wirtz, A., Hoffmann-Jacobsen, K., & Jaeger, M. (2020). Prior art for the development of a fourth purification stage in wastewater treatment plant for the elimination of anthropogenic micropollutants-a short-review. AIMS Environmental Science, 7(1), 69.

- 43 -

Waller, C. L., Griffiths, H. J., Waluda, C. M., Thorpe, S. E., Loaiza, I., Moreno, B., ... & Hughes, K. A. (2017). Microplastics in the Antarctic marine system: an emerging area of research. Science of the Total Environment, 598, 220-227. Water Environmental Federation (2010). [online] Wef.org. Available at: https://www.wef.org/globalassets/assets-wef/3---resources/topics/a-n/biosolids/technical-resources/wef-land-app-fact-sheet---rev0510.pdf [Accessed 10 Feb. 2020]. WaterWorld (2017). Analysis: Europe's Water/Wastewater in Numbers. [online] WaterWorld. Available at: https://www.waterworld.com/international/utilities/article/16201111/analysis-europes-waterwastewater-in-numbers [Accessed 17 Feb. 2020]. Wenzel, H., Larsen, H. F., Clauson-Kaas, J., Høibye, L., & Jacobsen, B. N. (2007). Weighing environmental advantages and disadvantages of advanced wastewater treatment of micro-pollutants using environmental life cycle assessment. In A. Köhl (Ed.), Micropol & Ecohazard 2007: 5th IWA Specialised Conference on Assessment and Control of Micropollutants/Hazardous Substances in Water (pp. 193-200). DECHEMA e.V., Society for Chemical Engineering and Biotechnology. WHO (2019). WHO calls for more research into microplastics and a crackdown on plastic pollution. [online] Who.int. Available at: https://www.who.int/news-room/detail/22-08-2019-who-calls-for-more-research-into-microplastics-and-a-crackdown-on-plastic-pollution [Accessed 9 Feb. 2020]. Wintgens, T., Melin, T., Schäfer, A., Khan, S., Muston, M., Bixio, D., & Thoeye, C. (2005). The role of membrane processes in municipal wastewater reclamation and reuse.

WTE, W., 2020. Cost Of Incineration Plant - Waste To Energy International. [online] Waste To Energy International. Available at: <https://wteinternational.com/cost-of-incineration-plant/> [Accessed 5 April 2020].

WWAP (United Nations World Water Assessment Programme). 2017. The United Nations World Water Development Report 2017. Wastewater: The Untapped Resource. Paris, UNESCO. Xu, J., Li, Y., Wang, H., Wu, J., Wang, X., & Li, F. (2017). Exploring the feasibility of energy self-sufficient wastewater treatment plants: a case study in eastern China. Energy Procedia, 142, 3055-3061. Yan, P., Qin, R. C., Guo, J. S., Yu, Q., Li, Z., Chen, Y. P., ... & Fang, F. (2017). Net-zero-energy model for sustainable wastewater treatment. Environmental science & technology, 51(2), 1017-1023.

Young, T., Muftugil, M., Smoot, S., & Peeters, J. (2012). MBR vs. CAS: capital and operating cost evaluation. Water Practice and Technology, 7(4). Zhang, Z., & Chen, Y. (2019). Effects of microplastics on wastewater and sewage sludge treatment and their removal: A review. Chemical Engineering Journal, 122955. Ziajahromi, S., Neale, P. A., Rintoul, L., & Leusch, F. D. (2017). Wastewater treatment plants as a pathway for microplastics: development of a new approach to sample wastewater-based microplastics. Water research, 112, 93-99.

- 44 -

Appendices Appendix A: Selected P-recovery technologies after incineration or pyrolysis

• EcoPhos EcoPhos is a wet chemical extraction and ion-exchange purification that can be utilized to extract P from sewage sludge ash or low-grade phosphate rock. Various full-scale plants are operating around the world (Kabbe, 2019). Figure 12 below shows a schematic flow of the EcoPhos process. EcoPhos has a P recovery rate of 93 – 98 percent.

• PyregThe Pyreg process uses the principle of dried carbonization to create biochar. It is a fast pyrolysis process. The input material is degassing at a temperature of 500 to 700 °C, after which it is carbonized by admission of an air stream. A conveyor belt passes the dewatered sludge through the system. The energy of the sludge is sufficient for the continuation of the thermal treatment, making Pyreg a self-sustaining carbonization process. Furthermore, it is possible to benefit from excess heat, ranging from 150 to 600 kWth that can be utilized for power generation or heating. The Pyreg process is visualized in figure 13 below. (Pyreg GmbH, 2020).

Figure 13 Schematic flow of the EcoPhos process (Kabbe, 2019).

Figure 14 Pyreg process illutrated (Pyreg GmbH, 2020).

- 45 -

Appendix B: Criteria and grouping ranges

The criteria and the selected grouping range are elaborated upon in table 7 below. Table 7 Overview of criteria and grouping range

Criteria Indicator Weight Description of criteria and grouping range

Environmental Criteria

Ability to remove microplastics

% of microplastics removed from Effluent.

4,00

The removal ratio expressed in the percentage of microplastic removed from wastewater treatment plant influent. The grouping ranges from < 98 percent up to 100 percent, as a removal efficiency of 100 percent is thus required to achieve this study’s aim (Baresel et al., 2017)

Ability to destroy microplastics

% of microplastics destroyed during sludge treatment.

3,75

The percentage of microplastic destroyed during the selected sludge treatment technology. The grouping ranges from < 98 percent up to 100 percent, as a destruction efficiency of 100 percent is required to achieve this study’s aim (Baresel et al., 2017)

Global Warming Potential of scenario

kg CO2- eq./m3 effluent

4,25

One of the major impacts of MWWTPs is their energy usage. The unit for this criterion is kg of CO2-eq emission per m3 effluent water. The grouping ranges from > 0.500 kg CO2- eq./ m3 to < 0.100 kg CO2- eq./ m3, this grouping is based on LCA research into different MWWTP typologies (Rodriguez-Garcia, et al., 2011). The global warming potential includes the emissions from the construction stages and operational stages of both the wastewater treatment processes and the sludge treatment processes. Transport of treated sludge is included as well. Furthermore, the avoided emissions due to energy and nutrient recovery are included.

Water recovery potential

Low / Moderate / High 3,75

The water recovery potential is scored on a qualitative scale ranging from low / moderate / high recovery potential. In which a high recovery potential is characterized by the production of potable effluent water, the most demanding reuse stage. A moderate recovery potential is characterized by a treatment technology that recovers water to the highest level of treatment however not potable reuse. These treatment technologies do provide the ideal pre-treatment option. The low recovery potential is characterized by a wastewater recovery potential that is in accordance to legal parameters for effluent water quality.

Nutrient recovery potential

% of phosphorus extraction ratio 4,25

Recovery ratio of phosphorus relative to the wastewater treatment plant influent. The grouping ranges from < 80 percent up to 100 percent, this grouping is based on research into P recovery from sewage sludge ash and pyrolyzed sewage sludge (Kleemann, et al., 2017). Economic Criteria

Operational costs (OPEX)

USD / m3 effluent 4,00

The operational cost of the treatment scenario is in important factor in the decision process. As MWWTPs are semi-or fully-publicly funded operations, minimized operational costs is of key importance to insure long-term operation. The grouping ranges from > 0.500 Euro / m3 down to < 0.050 Euro / m3, this grouping is based on peer reviewed LCA research into different MWWTP typologies (Hernández-Sancho, et al., 2015). This criterion considers the ability of local communities and governments to pay for the continuity of operations and maintenance.

Capital costs (CAPEX) USD / m3 effluent 3,88

The initial investment costs for the treatment scenario are expressed in USD, the baseline MWWTPs has a lifespan of 30 years. Grouping is based on the average investment costs in peer reviewed LCA studies and ranges from > 2250 Euro / m3 / d effluent down to > 1250 Euro / m3 / d effluent (Hernández-Sancho, et al., 2015). The capital costs consider the initial monetary costs for local

- 46 -

communities and governments or the construction and installation of the wastewater treatment scenario.

Additional revenue streams

Low / Moderate / High

3,75

Additional revenue is essential for MWWTPs in order to become a regenerative resource recovery which becomes a financial benefit instead of a burden for governments and communities. The additional revenue streams criterion is scored on a qualitative scale ranging from a low / moderate / high potential for additional revenue streams. In which a high potential is characterized by a scenario that creates a variety of potential marketable products such as water, energy and nutrients. A moderate potential is characterized by a treatment scenario that creates several options for additional revenue streams, however up to a limited extent. The low score is characterized by an additional revenue potential that is limited to low cascade water reuse and nutrient recovery.

Social Criteria

Consensus Low / Moderate / High 3,38

Each scenario is assessed on their acceptability by the public and legality by law. The social norms and traditions are important in the design stage of a treatment scenario, as it is of high importance that local needs are met. Social acceptance highly depends on people’s experiences, secular knowledge and social background. Treatment scenarios close to communities should have minimal odour, noise and visual impacts. (Singhirunnusorn, and Stenstrom, 2009). The consensus criterion is scored on a qualitative scale ranging from a low / moderate / high consensus. In which a high consensus is characterized by a scenario that outperforms treatment regulations, creates minimal odour, noise and has minimal visual impacts. A moderate consensus is characterized by compliance to treatment regulations and moderate noise, odour and visual impacts. A low consensus is characterized by minimal compliance to treatment regulations and relatively high noise, odour and visual impacts.

Complexity Low / Moderate / High 4,63

The complexity of a certain scenario is assessed and relative to the other scenarios. The simplicity of a treatment scenarios is a crucial factor for its implementation, as high complexity not only implies higher investment costs, it also implies more demanding labour skills. Lack of skilled works could thus present a major constraint when more complex treatments are selected. Simplicity could determine the operating success of the system in the long-term (Singhirunnusorn, and Stenstrom, 2009). The complexity criterion is scored on a qualitative scale ranging from a low / moderate / high consensus. In which a high complexity is characterized by a scenario that is relatively complex in construction and operations. A moderate complexity is characterized by average complexity in construction and operations. A low complexity is characterized by a treatment scenario that is commonly practiced and has a relatively simple operation.

- 47 -

Appendix C: Stakeholders to interview

Table 8 shows the stakeholders and experts that have answered the survey and those that have been interviewed to validate research results.

Table 8 List of stakeholders and experts for survey and interviews

MWWTPs operators, engineers and management:

Country Institution Description Contact Survey Interview

Netherlands Waterschap Vechtstromen

Regional Dutch water board, manages water barriers, waterways, water quality and sewage treatment in region.

Plantmanager at Waterschap Vechtstromen Yes No

Sweden Roslangsvatten AB

Regional Swedish water board, manages water barriers, waterways, water quality and sewage treatment in region.

Process manager at Roslangsvatten AB

Yes No

Sweden Gryaab AB

Regional Swedish water board, manages water barriers, waterways, water quality and sewage treatment in region.

Development Engineer at Gryaab AB

Yes Yes

National and Regional waterboards management:

Country Institution Description Contact Survey Interview

Netherlands Hoogheemraadschap van Schieland en de Krimpenerwaard

Regional Dutch water board, manages water barriers, waterways, water quality and sewage treatment in region.

Energy manager at wastewater treatment Yes No

Netherlands Waterschap AA en Maas

Regional Dutch water board, manages water barriers, waterways, water quality and sewage treatment in region.

Head of Wastewater department. Yes No

Sweden Svenskt Vatten Waterbody regulator of Sweden Environmental expert. Yes No

Academic experts:

Country Institution Description Contact Survey Interview

United States US EPA National environmental protection agency Physical scientist. Yes No

Netherlands STOWA

Research institute into the latest technologies and their applications for emerging contaminants removal

Manager of research STOWA. Yes No

- 48 -

Appendix D: Scenario data

The data from each scenario is shown in table 9 below. Table 9 Data for seven different scenarios

Crite

ria

Indi

cato

r

Scen

ario

Dat

a Environmental Criteria

Ability to remove

microplastics

% of microplastics

removed from

Effluent.

1 80 - 95% (EuReau, 2019).

2 99.9 - 100 % (Talvitie et al., 2017; Baresel et al, 2017)

3 99.0 - 100% (Baresel et al, 2017)

4 99.0 - 100% (Baresel et al, 2017; Sun et al., 2019)

5 99.9 - 100 % (Talvitie et al., 2017; Baresel et al, 2017)

6 99.0 - 100% (Baresel et al, 2017)

7 99.0 - 100% (Baresel et al, 2017; Sun et al., 2019)

Ability to destroy

microplastics

% in sewage sludge

retained microplastics

destroyed.

1 < 98%, AD could generate a possible reduction but not significant (Mohan et al., 2017)

2 100%, Complete destruction above 550°C. Incineration ranges between 700 – 925 °C (EPA, 2017)

3 100%, Complete destruction above 550°C. Incineration ranges between 700 – 925 °C (EPA, 2017)

4 100%, Complete destruction above 550°C. Incineration ranges between 700 – 925 °C (EPA, 2017)

5 100%, Complete destruction above 550°C. High temperature pyrolysis at 850 °C (Karaca et al., 2018)

6 100%, Complete destruction above 550°C. High temperature pyrolysis at 850 °C (Karaca et al., 2018)

7 100%, Complete destruction above 550°C. High temperature pyrolysis at 850 °C (Karaca et al., 2018)

Global Warming

Potential of scenario

kg CO2- eq./m3 effluent

1

0,219 CO2eq / m3 for the CAS process, the CAS process includes a primary settling tank (PST), an aeration tank (AT) for BOD removal, and a secondary settling tank (SST) for sludge thickening. The AD process includes digestion, dewatering and land application of sludge construction phases are not considered due to a lack of data, nonetheless previous studies have showed that the construction phase only has minor relevance in the total impact of wastewater treatment technologies (Bertanza et al., 2017; Soda et al., 2013; Peters and Rowley, 2009; Amann et al. 2018).

The CO2 emission intensity of electricity consumption used for this study was a typical value 0,295 CO2 eq per kwh (EEA, 2016)

2

0,133 CO2 eq / m3 for MBR, incineration and Ecophos. MBR replaces the CAS process, therefore the energy consumption of 0,75 kWh / m3 (Akhoundi et al., 2018) for the MBR process has been taken to calculate 0,221 CO2 eq / m3. The advantage of AD being 0,003 CO2 eq / m3, the advantage of incineration being 0,072 CO2 eq / m3 and the advantage of Ecophos being 0,013 CO2 eq / m3 were all deducted from the MBR process. Therefore the

- 49 -

process includes MBR, sludge treatment processes, such as thickening (5% DM), anaerobic digestion, dewatering with polymers (30% DM), a mono-incineration plant for sewage sludge, a waste management process for treatment and disposal of wastes, and Ecophos for P recovery. Construction phases are not considered due to a lack of data, nonetheless previous studies have showed that the construction phase only has minor relevance in the total impact of wastewater treatment technologies. Assumptions were made by downsizing the data from a 100.000 PE plant (24.000 m3) to a 10.000 m3 plant (Amann et al. 2018; Cao and Pawłowski, 2013)

The CO2 emission intensity of electricity consumption used for this study was a typical value 0,295 CO2 eq per kwh (EEA, 2016)

3

0,267 CO2 eq / m3 for RO, incineration and Ecophos. RO can be incorporated as an additional treatment step, therefore the energy consumption of 0,6 kWh / m3 (Plakas et al,.2016) for the RO process has been taken to calculate 0,177 CO2 eq / m3. CAS process has been 0,090 kg CO2eq / m3 for a MWWTP with P removal by iron dosing, and sludge treatment processes, such as thickening (5% DM), anaerobic digestion, dewatering with polymers (30% DM), a mono-incineration plant for sewage sludge, a waste management process for treatment and disposal of wastes, and Ecophos for P recovery. Construction phases are not considered due to a lack of data, nonetheless previous studies have showed that the construction phase only has minor relevance in the total impact of wastewater treatment technologies. Assumptions were made by downsizing the data from a 100.000 PE plant (24.000 m3) to a 10.000 m3 plant (Amann et al. 2018).

The CO2 emission intensity of electricity consumption used for this study was a typical value 0,295 CO2 eq per kwh (EEA, 2016)

4

0,149 CO2 eq / m3 for PAC-UF, incineration and Ecophos. PAC-UF can be incorporated as an additional treatment step, therefore the energy consumption of 0,2 kWh / m3 (Plakas et al,.2016) for the PAC-UF process has been taken to calculate 0,059 CO2 eq / m3. CAS process has been 0,090 kg CO2eq / m3 for a MWWTP with P removal by iron dosing, and sludge treatment processes, such as thickening (5% DM), anaerobic digestion, dewatering with polymers (30% DM), a mono-incineration plant for sewage sludge, a waste management process for treatment and disposal of wastes, and Ecophos for P recovery. Construction phases are not considered due to a lack of data, nonetheless previous studies have showed that the construction phase only has minor relevance in the total impact of wastewater treatment technologies. Assumptions were made by downsizing the data from a 100.000 PE plant (24.000 m3) to a 10.000 m3 plant (Amann et al. 2018).

The CO2 emission intensity of electricity consumption used for this study was a typical value 0,295 CO2 eq per kwh (EEA, 2016)

5

0,190 CO2 eq / m3 for MBR, Pyrolysis and Phosphorus recovery. MBR replaces the CAS process, therefore the energy consumption of 0,75 kWh / m3

(Akhoundi et al., 2018) for the MBR process has been taken to calculate 0,221 CO2 eq / m3. The Pyrolysis system has a GWP of -0,031 kg CO2 eq / m3 this includes energy use and GHG emissions of Plants construction, Sludge dewatering, Sludge drying, AD operation, Pyrolysis operation and Biochar transport. The output and GHG emissions avoided are Natural gas substitution, Crude oil substitution, Fertilizer substitution, Biochar soil N2O reduction, and Biochar carbon storage

The CO2 emission intensity of electricity consumption used for this study was a typical value 0,295 CO2 eq per kwh (EEA, 2016)

6 0,320 CO2 eq / m3 for RO, Pyrolysis and Phosphorus recovery. RO can be incorporated as an additional treatment step, therefore the energy consumption of 0,6 kWh / m3 (Akhoundi et al., 2018) for the RO process has been taken to calculate 0,177 CO2 eq / m3. The Pyrolysis system has a GWP of -0,031 kg

- 50 -

CO2 eq / m3 this includes energy use and GHG emissions of Plants construction, Sludge dewatering, Sludge drying, AD operation, Pyrolysis operation and Biochar transport. The output and GHG emissions avoided are Natural gas substitution, Crude oil substitution, Fertilizer substitution, Biochar soil N2O reduction, and Biochar carbon storage. In addition, the GWP of the CAS system has been used as a treatment base being 0.175 CO2 eq / m3. (Cao and Pawłowski, 2013; Bertanza et al., 2017).

The CO2 emission intensity of electricity consumption used for this study was a typical value 0,295 CO2 eq per kwh (EEA, 2016)

7

0,202 CO2 eq / m3 for PAC-UF, Pyrolysis and Phosphorus recovery. PAC-UF can be incorporated as an additional treatment step, therefore the energy consumption of 0,2 kWh / m3 (Plakas et al,.2016) for the PAC-UF process has been taken to calculate 0,059 CO2 eq / m3. The Pyrolysis system has a GWP of -0,031 kg CO2 eq / m3 this includes energy use and GHG emissions of Plants construction, Sludge dewatering, Sludge drying, AD operation, Pyrolysis operation and Biochar transport. The output and GHG emissions avoided are Natural gas substitution, Crude oil substitution, Fertilizer substitution, Biochar soil N2O reduction, and Biochar carbon storage. In addition, the GWP of the CAS system has been used as a treatment base being 0.175 CO2 eq / m3. (Cao and Pawłowski, 2013; Bertanza et al., 2017).

The CO2 emission intensity of electricity consumption used for this study was a typical value 0,295 CO2 eq per kwh (EEA, 2016)

Water recovery potential

Low / Moderate /

High

1 Low, conventional activated sludge processes do not produce effluent water of high quality, and thus applications of effluent water are limited (Kehrein et al., 2020).

2 Moderate, MBR produces water suitable for many demanding types of reuse, however not for potable water reuse (Kehrein et al., 2020; Arévalo et al., 2012)

3 High, RO as a polishing stages produces potable effluent water, the most demanding reuse stage (Kehrein et al., 2020).

4 Moderate, UF produces water suitable for many demanding types of reuse, however not for potable water reuse (Kehrein et al., 2020)

5 Moderate, MBR configuration produces water suitable for many demanding types of reuse, however not for potable water reuse (Kehrein et al., 2020; Arévalo et al., 2012)

6 High, RO as a polishing stages produces potable effluent water, the most demanding reuse stage (Kehrein et al., 2020).

7 Moderate, UF produces water suitable for many demanding types of reuse, however not for potable water reuse (Kehrein et al., 2020)

Nutrient recovery potential

% of phosphorus extraction

ratio

1 100 percent recovery with direct application (Phosphorus Platform EU, 2020)

2 93 – 98 percent recovery with EcoPhos (Phosphorus Platform EU, 2020)

3 93 – 98 percent recovery with EcfoPhos (Phosphorus Platform EU, 2020)

4 93 – 98 percent recovery with EcoPhos (Phosphorus Platform EU, 2020)

5 90 percent recovery with Pyreg (Phosphorus Platform EU, 2020)

6 90 percent recovery with Pyreg (Phosphorus Platform EU, 2020)

7 90 percent recovery with Pyreg (Phosphorus Platform EU, 2020)

- 51 -

Economic Criteria

Operational costs

Euro / m3 effluent

1 Total 0,321 € / m3

0,263 € / m3 averaged for a CAS plant, with an effluent of 18.500 m3 / day (Rodriguez-Garcia et al., 2011). Whilst land application of sludge has an average cost of 0,058 € / m3 (Kalderis et al., 2010)

2 Total 0,327 € / m3

MBR 0,293 € / m3 (Akhoundi et al., 2018) plus incineration 0,024 € / m3 (Waste to energy international, 2020) and EcoPhos 0,0104 € / m3 (Egle et al., 2016) (Using USD – EURO conversion rate of May 2018)

3 Total 0,501 € / m3

0,263 € / m3 averaged for a CAS plant, with an effluent of 18.500 m3 / day (Rodriguez-Garcia et al., 2011). RO operations are 0,204 € / m3 (Nattorp et al., 2017; Plakas et al., 2016) plus incineration 0,024 € / m3 (Waste to energy international, 2020) and EcoPhos 0,0104 € / m3 (Egle et al., 2016) (Using USD – EURO conversion rate of May 2018)

4 Total 0,327 € / m3

0,263 € / m3 averaged for a CAS plant, with an effluent of 18.500 m3 / day (Rodriguez-Garcia et al., 2011). PAC-UF operations are 0,054 € / m3 (Nattorp et al., 2017; Plakas et al., 2016) plus incineration 0,024 € / m3 (Waste to energy international, 2020) and EcoPhos 0,0104 € / m3 (Egle et al., 2016) (Using USD – EURO conversion rate of May 2018)

5 Total 0,323 € / m3

MBR 0,293 € / m3 (Akhoundi et al., 2018) plus Pyreg 0,0299 € / m3 (Forte et al, 2012)

6 Total 0,497 € / m3

0,263 € / m3 averaged for a CAS plant, with an effluent of 18.500 m3 / day (Rodriguez-Garcia et al., 2011). RO operations are 0,204 € / m3 (Nattorp et al., 2017; Plakas et al., 2016) plus Pyreg 0,0299 € / m3 (Forte et al, 2012)

7 Total 0,345 € / m3

0,263 € / m3 averaged for a CAS plant, with an effluent of 18.500 m3 / day (Rodriguez-Garcia et al., 2011). PAC-UF operations are 0,054 € / m3 (Nattorp et al., 2017; Plakas et al., 2016) plus Pyreg 0,0299 € / m3 (Forte et al., 2012)

Investment costs Euro / m3 /d

1 Total 1268 € / m3 / d

Investment costs for CAS are estimated at 1268,03 € / m3 / d (Young et al., 2012)

2 Total 1875 € / m3 / d

Investment costs for MBR are estimated at 1690,71 € / m3 / d (Young et al., 2012), whilst investment of incineration is 171,56 € / m3 / d (Waste to energy, 2020) and investment of EcoPhos plant is 12,26 € / m3 / d for a plant of 195.000 m3 / d (Nättorp and Remmen, 2015).

3 Total 2184 € / m3 / d

Investment costs for CAS are estimated at 1268,03 € / m3 / d (Young et al., 2012), whilst investment costs of RO are 732,50 € / m3 / d (Plakas et al., 2016). The investment of incineration is 171,56 € / m3 / d (Waste to energy, 2020) and investment of EcoPhos plant is 12,26 € / m3 / d for a plant of 195.000 m3 / d (Nättorp and Remmen, 2015).

- 52 -

4 Total 1752 € / m3 / d

Investment costs for CAS are estimated at 1268,03 € / m3 / d (Young et al., 2012), whilst investment costs of PAC-UF are 300 € / m3 / d (Plakas et al., 2016). The investment of incineration is 171,56 € / m3 / d (Waste to energy, 2020) and investment of EcoPhos plant is 12,26 € / m3 / d for a plant of 195.000 m3 / d (Nättorp and Remmen, 2015).

5 Total 1766 € / m3 / d

Investment costs for MBR are estimated at 1690,71 € / m3 / d (Young et al., 2012), whilst investment of Pyreg is 74,85 € / m3 / d (Forte et al., 2012) .

6 Total 2075 € / m3 / d

Investment costs for CAS are estimated at 1268,03 € / m3 / d (Young et al., 2012), whilst investment costs of RO are 732,50 € / m3 / d (Plakas et al., 2016). The investment of Pyreg is 74,85 € / m3 / d (Forte et al., 2012).

7 Total 1643 € / m3 / d

Investment costs for CAS are estimated at 1268,03 € / m3 / d (Young et al., 2012), whilst investment costs of of PAC-UF are 300 € / m3 / d (Plakas et al., 2016). The investment of Pyreg is 74,85 € / m3 / d (Forte et al., 2012).

Additional revenue streams

Low / Moderate/ High

1 Low, land application generates marketable Phosphorus products, nonetheless the quality is limited due to contaminants.

2 Moderate, Ecophos generates marketable Phosphorus containing products of high purity (Egle et al., 2016)

3 Moderate, Ecophos generates marketable Phosphorus containing products of high purity (Egle et al., 2016)

4 Moderate, Ecophos generates marketable Phosphorus containing products of high purity (Egle et al., 2016)

5 High, Pyrolysis creates a variety of potential marketable products (Samolada and Zabaniotou, 2014).

6 High, Pyrolysis creates a variety of potential marketable products (Samolada and Zabaniotou, 2014).

7 High, Pyrolysis creates a variety of potential marketable products (Samolada and Zabaniotou, 2014).

Social Criteria

Consensus Low /

Moderate / High

1 Moderate consensus, CAS is a standardized process, however regulations are tightening, in terms of circular economic objectives (Geissdoerfer et al., 2017)

2 Using the more conservative value, this scenario is rated with Moderate consensus. As MBR was seen as a high consensus treatment technology by Judd (2010) and incineration is viewed with low consensus.

Low, incineration has a well-developed legislative frame, nonetheless there is strong public opposition against incineration due to emitted fumes. Especially plant siting in the vicinity of residential areas (Oladejo et al., 2018; Samolada and Zabaniotou, 2014).

3 Using the more conservative value, this scenario is rated with Low consensus. As RO was seen as a low consensus treatment technology by Plakas et al (2016), as water reuse for potable water application is not accepted, and incineration is viewed with low consensus.

Low, incineration has a well-developed legislative frame, nonetheless there is strong public opposition against incineration due to emitted fumes. Especially plant siting in the vicinity of residential areas (Oladejo et al., 2018; Samolada and Zabaniotou, 2014).

- 53 -

4 Using the more conservative value, this scenario is rated with Low consensus. As PAC-UF was seen as a moderate consensus treatment technology by Plakas et al (2016) and incineration is viewed with low consensus.

Low, incineration has a well-developed legislative frame, nonetheless there is strong public opposition against incineration due to emitted fumes. Especially plant siting in the vicinity of residential areas (Oladejo et al., 2018; Samolada and Zabaniotou, 2014).

5 Using the more conservative value, this scenario is rated with Moderate consensus. As MBR was seen as a high consensus treatment technology by Judd (2010) and Pyrolysis is viewed with moderate consensus.

Moderate, Pyrolysis has lower emissions and heavy metal release, as opposed to incineration, this suggest a reduced public opposition. Nonetheless, pyrolysis permitting may be an issue due to unclear legislative frame (Samolada and Zabaniotou, 2014).

6 Using the more conservative value, this scenario is rated with Low consensus. As RO was seen as a low consensus treatment technology by Plakas et al (2016), as water reuse for potable water application is not accepted, and Pyrolysis is viewed with moderate consensus.

Moderate, Pyrolysis has lower emissions and heavy metal release, as opposed to incineration, this suggest a reduced public opposition. Nonetheless, pyrolysis permitting may be an issue due to unclear legislative frame (Samolada and Zabaniotou, 2014).

7 Using the more conservative value, this scenario is rated with Moderate consensus. As PAC-UF was seen as a moderate consensus treatment technology by Plakas et al (2016) and Pyrolysis is viewed with moderate consensus.

Moderate, Pyrolysis has lower emissions and heavy metal release, as opposed to incineration, this suggest a reduced public opposition. Nonetheless, pyrolysis permitting may be an issue due to unclear legislative frame (Samolada and Zabaniotou, 2014).

Complexity Low /

Moderate / High

1 Low complexity, as CAS is a standardized process (Bertanza et al., 2017)

2 Using the more conservative value, this scenario is rated with Moderate complexity. As MBR was seen as a high complexity treatment technology by Judd (2010) and Incineration is viewed as having low complexity. Incineration is an established technology (Samolada and Zabaniotou, 2014).

3 Using the more conservative value, this scenario is rated with Moderate complexity. As RO was seen as a moderate complexity treatment technology by Plakas et al (2016and Incineration is viewed as having low complexity. Incineration is an established technology (Samolada and Zabaniotou, 2014).

4 Using the more conservative value, this scenario is rated with Moderate complexity. As PAC-UF was seen as a high complexity treatment technology by Plakas et al (2016) and Incineration is viewed as having low complexity. Incineration is an established technology (Samolada and Zabaniotou, 2014).

5 Using the more conservative value, this scenario is rated with High complexity. As MBR was seen as a high complexity treatment technology by Judd (2010) and pyrolysis is viewed as having high complexity (Samolada and Zabaniotou, 2014).

6 Using the more conservative value, this scenario is rated with High complexity. As RO was seen as a moderate complexity treatment technology by Plakas et al (2016) and pyrolysis is viewed as having high complexity (Samolada and Zabaniotou, 2014).

- 54 -

7 Using the more conservative value, this scenario is rated with High complexity. As PAC-UF was seen as a high complexity treatment technology by Plakas et al (2016) and pyrolysis is viewed as having high complexity (Samolada and Zabaniotou, 2014).

- 55 -

Appendix E: Sensitivity analysis overview Table 10 below show the results of the three sensitivity analyses.

Table 10 Results of three sensitivity analyses

1. CASland 2. MBR inci-eco

3. CASRO inci-eco

4. CASPACUF inci-eco

5. MBR Pyreg

6. CASRO Pyreg

7. CASPACUF Pyreg

MCA Results 2,63 3,11 2,33 2,62 2,67 1,94 2,65 Sensitivity Environment 2,22 2,79 2,22 2,43 2,48 1,91 2,42 Sensitivity Economic 2,33 2,76 2,19 2,54 2,60 1,97 2,62 Sensitivity Social 2,52 2,95 2,30 2,48 2,62 1,85 2,58

- 56 -

- 57 -