Treatment of wastewater: Solid phase, anaerobic digestion, biogas digester/settler (small scale) 1
Treatment of wastewater:Solid phase, anaerobic digestion, biogas
digester/settler (small scale)
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Treatment of wastewater – Solid phase, anaerobic digestion, biogas digester/settler (small scale)
Troutman HeatherAsiedu-Danquah Kwadwo
January 11, 2015
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Technologies for Sustainable Water Resource Management
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Anaerobic Digestion Table of Content REAPHafenCity University
❖ Technology Overview (schematic)
❖ Detailing technology (Inputs and Outputs)
❖ Variations of the technology
❖ Case study
❖ Methodologies for determining best technologies for projects
❖ Outlook towards our project in Accra
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Anaerobic Digestion Guides REAPHafenCity University
Suitable for land and agricultural application.
Minimal-to-moderate training required for construction and maintenance.
Efficiency/productivity of system highly variable to place-specific factors.
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Anaerobic Digestion At a glance REAPHafenCity University
“Anaerobic digestion (AD) is a microbiological process whereby organic matter is decomposed in the absence of oxygen. This process is common to many natural environments such as swamps or stomachs of ruminants. Using an engineered approach and controlled design, the AD process is applied to process organic biodegradable matter in airproof reactor tanks, commonly named digesters, to produce biogas. Various groups of microorganisms are involved in the anaerobic degradation process which generates two main products: energy-rich biogas and a nutritious digestate” (Vögeli et al, 2014).
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Anaerobic Digestion The Benefits of Biogas Technology REAPHafenCity University
● Social:○ Improved sanitation: reduction of pathogens, worm eggs and flies○ Reduction of workload: less firewood collection○ Improved Indoor air quality: less smoke
● Environmental:○ Production of non-fossil energy○ Displacement of greenhouse gas emissions○ Organic fertilizer and humus production ○ Reduced deforestation
● Economic:○ Better health = increased work capacity○ Fertilizer for better crop yields (better health)○ Fuel substitution○ Increased productivity hours/day
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Anaerobic Digestion Technology Overview (schematic) REAPHafenCity University
Source: Tilley, 2008
Sizes: 1,000 - 100,000 L
Hydraulic Retention Time (HTR)>15 days - hot climate>30 days - temperate>60 days - high pathogen load
<15°C ambient requires addition of heat
�50°C sustained temp. in reaction chamber
Above or below ground
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Anaerobic Digestion Technology Overview (schematic) REAPHafenCity University
Source: Vögeli et al, 2014
Pretreatment: sort out inorganics and shred MSW to max 5cm diameter for increased efficiency (surface area for microbe attachment)
Normally,organic loading rate/volumes (OLR) equals slurry outputs.
Recirculation of these materials with new organic inputs increases microbial population, accelerating digestion.
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Anaerobic Digestion Inputs: Organics REAPHafenCity University
Energy Content:Human excreta < organics
Lignin is non-degradable in anaerobic conditions.
Source: Vögeli, 2014 adapted from Müller, 2007
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Anaerobic Digestion Inputs: Organics REAPHafenCity University
TS - total solids as feedstock 5-10% - optimal
VS - volatile solids biodegradable fraction of TS 70%-95% common <60% rarely considered
BMP - biological methane potential used to measure efficiency
0.36-0.53 m3/kg VS: avg. MSW
Biogas yield factors:type, composition, temperature, mixing
Source: Vögeli et al, 2014 adapted from Khalid et al, 2011
TS & VS in biowaste and biogas yield from AD
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Anaerobic Digestion Inputs: Wastewater REAPHafenCity University
116 studies26 countries 6 continents 80% in N.A. & Europe
Main factors for variation: geography, age, ethnicity, disease, diet (fiber intake), and treatment/conveyance technology used.
20-25 kcal/ kg body weight/day
Actual variation wet fecal gen.: 15–1505 (g/cap/day)126 g/cap/day : Low-income250 g/cap/day: High-income
Water L H2O/flush 6-14 flushes/cap/day 7 L grey water/cap/day 60-90*
* City of Hamburg, Germany (Sievers, et al., 2014)
Source: adapted by author from C. Rose et al., 2015
Daily wet & dry mass of feces produced by human populations
(14.2%)
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Anaerobic Digestion Inputs: Wastewater REAPHafenCity University
Design GuidelinesRule of Thumb:
20-30 L BG/cap/dayproduction
300-900 L BG/cap/daycooking need
(Kossmann et al., 2008)
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Anaerobic Digestion Biochemical Process REAPHafenCity University
(1) HydrolysisBacteria transform complex organic materials into liquified polymers and monomers(2) Acidogenesis
Acidogenic bacteria convert monomers of sugars and amino acids into acids + C2H6O + CH3CO2
- + H2 + CO2 + NH3 (indirect)(3) Acetogenesis
BOD & COD reduced, pH decreased - long-chain and volatile fatty acids and alcohols transformed to H+ + CO2 + CH3COO-
(4) MethanogenesisCH3COO- + H+ -> CH4 + CO2
Anaerobic Digestion / biomethanation / biomethanisation
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Anaerobic Digestion Parameters and Process Optimization REAPHafenCity University
1. Substrate Temperature
2. Available nutrients
3. Retention time (flow-through time)
4. pH level : 7-8.5 =i deal, < 6.2 = toxic
5. Nitrogen inhibition and C/N ratio : 8-20 = optimal
6. Substrate solid content and agitation
7. Inhibitory factors : heavy metals, antibiotics, detergents
1. ± 0.5-1°C/h perturbations can disrupt cycle
2.
3. Too fast = incomplete pathogen destruction vs. too slow = washout of bacteria
4. 6. Removal of metabolites, inoculation, preclusion of scum formation, avoidance of temperature gradient, uniform bacteria population density.
5. 7.
Source: GTZ, 2015
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Anaerobic Digestion Outputs: Biogas REAPHafenCity University
CH4 + CO2 + trace gases
Inefficient (compared to aerobic digestion) which is why biogas remains as byproduct.
Source: Vögeli et al., 2014 adapted from Cecchi et al., 2003
Typical biogas composition from biowaste
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Anaerobic Digestion Outputs: Biogas REAPHafenCity University
Biogas Appliances:
● Gas cookers● biogas lamps● radiant heaters● incubators● refrigerators● engines
150-300 L biogas/person/meal60-80% efficiency in biogas cooker
30-40 L BG/1 L H2O boil120-140 L BG/0..5 kg rice160-190 L BG/0.5 kg legume
120-150 L BG/day - biogas lamp
2,000-3,000 L BG/day - 100 L volume refrigerator
1 m3 BG = 2 L BG = 6 kWh = 21.6 MJ = 10 kg (wet weight) biowaste
Source: Vögeli et al, 2014
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Anaerobic Digestion Outputs: Digestate REAPHafenCity University
Rich in nutrients and soil organisms
Reduction of soil erosion
Reduction of nitrogen wash-out (production of plant-available ammonia rather than unavailable nitrate and nitrite)
Favorable crop reaction: potatoes, radishes, carrots, cabbage, onions, garlic, oranges, apples, guavas, mangoes, sugarcane, rice and jute
Unfavorable crop reactions: wheat, oilseed, cotton, baccaraFertilizing effect dependent on: plant type, soil type, climate Almost odorless
Source: EPA, 1995 adopted from Sommers, 1977
Amount of stable humus formed from digested sludge is twice the amount that will form from with decayed dung.
10 tons/ha - irrigated 5 tons/ha - dry farms (FAO, 1996)
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Anaerobic Digestion Outputs: Digestate Applications REAPHafenCity University
A. Post-treatment
1. Compost / landfill
2. Constructed wetland
3. Fish / animal feed substitute at rate < 20% (FAO, 1996)
B. Direct Use
4. Drip irrigation
5. Spread application to agricultural lands
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Source: Vögeli et al, 2014
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Anaerobic Digestion Health Risks REAPHafenCity University
Key to safe production of slurry (pathogen destruction) is retention time, which is governed by temperature.
Thermophilic50-60°C : few days
Mesophilic20-30°C : > 20 days
Psycrophilic10-20°C : > 100 days
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Anaerobic Digestion Maintenance: Minimal REAPHafenCity University
Weekly/monthly (prophylactic) maintenance work● clean gas appliances;● lubricate movable parts (slides, guiding frame of floating drum plants,
taps etc.);● servicing of biogas-driven engines within the prescribed time intervals;● maintenance of pressure relief valves and under pressure valves;● maintenance of slurry agitator / mixer;● control gas appliances and fittings on tightness and function
Annual maintenance work● Check the plant in respect of corrosion and, if necessary, renew
protective coating material;● Check the gas pipes for gas tightness (pressure check). If necessary,
search the leakage and repair the parts concerned.
Repair: Problem Identification
Source: GTZ, 2015
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Anaerobic Digestion Types of Small Scale Biogas Digesters REAPHafenCity University
Numerous types exist
Simple in design and for small scale and domestic use
3 most common types
Fixed-Dome digesters Floating Drum digesters Tubular digesters
Horizontal PlantsEarth pit
Ferrocement
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Anaerobic Digestion Fixed-Dome Digester: Overview REAPHafenCity University
1 - Digester
2- Gas collector, fixed dome
3- Inlet for waste
4- Outlet
5 -Overflow tank
6-Scheme of Gas collector
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1
3
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5
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Anaerobic Digestion Fixed-Dome Digester: Example REAPHafenCity University
Constructed underground with bricks in Lesotho
Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).
Chinese fixed-dome plant
Janata model
Deenbandhu
CAMARTEC model
AKUT fixed dome plant
AKUT Maendaleo
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Anaerobic Digestion Floating drum digester: Overview REAPHafenCity University
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21 - Digester
2- Gas collector, fixed dome
3- Inlet for waste
4- Outlet
5 -Overflow tank
3
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Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).
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Anaerobic Digestion Floating drum digester: Example REAPHafenCity University
Floating drum digester for market and household waste in India
Constructed underground with bricks and metals
Constructed above the ground with fibre glass reinforced plastics
Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).
KVIC model
Pragati model
Ganesh model Pre-fabricated reinforced concrete
Fibre-glass reinforced polyester
Plastic water containers or fiberglass drums
BORDA model
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Anaerobic Digestion Tubular digester: Overview REAPHafenCity University
1 - Digester & gas holder
2- Inlet for waste
3- Outlet
1
2 3
Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).
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Anaerobic Digestion Tubular digester: Example REAPHafenCity University
Applied in Most south American countries
Examples of Tubular digestersVögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).
Gas storage Reservoir
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Anaerobic Digestion Horizontal Plants: Overview REAPHafenCity University
Horizontal biogas plants are usually chosen when shallow installation is called for(groundwater, rock). They are made of masonry or concrete
Problem: Leakage
1 - Digester
2- Gas collector
3- Inlet for waste
4- Outlet
1
2 3 4
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Anaerobic Digestion Earth Pit: Overview REAPHafenCity University
1 - Digester
2- Plastic sheet gasholder
3- Inlet for waste
4- Outlet
5 -Overflow
1
2 3
4
5
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Anaerobic Digestion Ferrocement: Overview REAPHafenCity University
1 - Digester
2- Plastic sheet gasholder
3- Inlet for waste
4- Outlet
1
2 3 4
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Anaerobic Digestion Variations of the Technology: Comparison REAPHafenCity University
❖ Design principle
Fixed-Dome Digester Floating Drum Digester Tubular Digester
Continuousfeed (Daily input)
Mixed digester
Continuousfeed
Mixed digester
Continuousfeed
Mixed digester
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Anaerobic Digestion Variations of the Technology: Comparison REAPHafenCity University
❖ Input materials
animal excrements, Human excreta, Household waste
animal excrements Household waste(in some cases Human excreta)
Domestic wasteanimal excrements
Fixed-Dome Digester Floating Drum Digester Tubular Digester
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Anaerobic Digestion Variations of the Technology: Comparison REAPHafenCity University
❖ Gas storage
Internal Gas storage up to 20 m³ (large)
Internal Gas storage drum size (small)
External plastic bags
Fixed-Dome Digester Floating Drum Digester Tubular Digester
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Anaerobic Digestion Variations of the Technology: Comparison REAPHafenCity University
❖ Gas pressure
Between 60 and 120 mbar
Up to 20 mbar Low, around 2 mbar
Fixed-Dome Digester Floating Drum Digester Tubular Digester
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Anaerobic Digestion Variations of the Technology: Comparison REAPHafenCity University
❖ Technical aspect
(High); masonry, plumbing
(High); masonry, plumbing, welding
(Medium); plumbing
Fixed-Dome Digester Floating Drum Digester Tubular Digester
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Anaerobic Digestion Variations of the Technology: Comparison REAPHafenCity University
❖ Lifespan
> 15 years
Low maintenance
(3–5 years in humid areas, or 8 –12 years in a dry climate)
High maintenance - Steel drum
5 years
Depending on chosen liner)
Fixed-Dome Digester Floating Drum Digester Tubular Digester
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Anaerobic Digestion Variations of the Technology: Comparison REAPHafenCity University
❖ Agitation
Biogas pressure Manual steering Not possible
Fixed-Dome Digester Floating Drum Digester Tubular Digester
Destroy swimming layers
Activate the activities of bacteria
Even distribution of temperature
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Anaerobic Digestion Variations of the Technology: Comparison REAPHafenCity University
❖ Size
5 to 200 m³
Up to 100 m³(small to middle-sized farms (digester size: 5-15m3) or in institutions and larger agro-industrial estates (digester size: 20-100m3)
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Fixed-Dome Digester Floating Drum Digester Tubular Digester
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Anaerobic Digestion Variations of the Technology REAPHafenCity University
Decentralised Co-Digestion
of Faeces and OrganicSolid Waste in Lesotho
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Anaerobic Digestion Case Study (Rationale of the project) REAPHafenCity University
Problem: lackof water and yearly emptying of septictanks Bodies involved: TED (Technologies for Econ. Dev’t) & BORDA (Bremen Overseas Research and Development Association)
Design: Waste water treatment & other organic matter
Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).
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Anaerobic Digestion Case Study (Description of the Design) REAPHafenCity University
Mainly black- and grey water from the toilet, bathroom, kitchen and laundry
kitchen waste and livestockwaste (pig and chicken manure)
Digester volumes: 8m3 to 100 m3 and sometimes more
1. Digester2. Anaerobic Baffled Reactor3. Planted Gravel Filter
Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).
Scheme of DEWATS Biogas System of TED-BORDA
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Anaerobic Digestion Case Study (Gas Production) REAPHafenCity University
Higher Biogas from animal excreta
Avg. cooking time for households with 5 people - 2.5 hours
Long gas storage can lead to a decrease in the average daily gas production
-Leakages -Automatic Pressure release
Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).
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Anaerobic Digestion Case Study (Quality and use of Effluent) REAPHafenCity University
Differences of COD’s
Target Effluent COD concentration -0.12 g/L
Use: Irrigation
Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).
COD of Inflow compared to effluent from Digester, ABR and PGF
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Anaerobic Digestion Case Study (Results of the project) REAPHafenCity University
Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014).
Cost of digester per m3 - 83 -667 USD
No regular emptying of storage tanks and problems associated with it
Biogas system replaces other energy systems
Effluent could be used for irrigation
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Anaerobic Digestion Methodologies for technology selection REAPHafenCity University
Main factors influencing selection of particular design:● Costs: construction and conveyance● Local materials● Durability (higher construction cost vs. long-term assurance)● Inputs (continuous vs. batch design), C/N ratio (20-30 optimal)
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Anaerobic Digestion Outlook: Biogas for Better Life REAPHafenCity University
The vision of the Initiative is to succeed in the implementation of biogas technology in African countries as a market-oriented partnership
between governments, private sector players, civil society agents and international development partners. The specific targets of the initiative
to be achieved by 2020 include:
● two million biogas plants installed (90% operation rate)
● 10 million Africans benefiting in daily life from the plants
● 800 private biogas companies and 200 biogas appliance manufacturing workshops involved or established
● 100,000 new jobs created
● comprehensive quality standards and quality control systems developed and in use
● one million toilets constructed and attached to the biogas plant
● 80% of the bio-slurry used as organic fertilizer
● agricultural production raised by up to 25%
● health and living conditions of women and children improved, and the deaths of women and children reduced by 5000 each year
● drudgery reduced by saving 2-3 hours per household each day in fetching wood, cooking and cleaning the pots
● health costs saved of up to US$80-125 per family, per year
● 3-4 million tonnes of wood saved per year
● greenhouse gas emissions annually reduced by 10 Mtonnes of CO2 equivalent.
The total financing required is $2 billion, out of which $800 million is to be expected from public funding (national and donors) and the sale of
carbon credits. For the latter, the Initiative developed a proposal for a new methodology specifically aiming at the trading of emission
reductions from household digesters.
Signed 2007 Nirobi
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Anaerobic Digestion Outlook towards further project (Accra, Ghana)REAPHafenCity University
3 MillionPopulation
15%% connected to wastewater treatment
80 million Amount wastewater generation/day in Liters
90% directly discharged into water bodies without treatment
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Anaerobic Digestion Outlook towards further project (Accra, Ghana)REAPHafenCity University
Thank you for your attention...
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Anaerobic Digestion References REAPHafenCity University
C. Rose, A. Parker, B. Jefferson, E. Cartmell (2015) “The Characterization of Feces and Urine: A Review of the Literature to Inform Advanced Treatment Technology” Critical Reviews in Environmental Science. Vol. 47, Is. 17, p.1827-1879
EPA - United States Environmental Protection Agency (1995) “Process Design Manual: Land Application of Sewage Sludge and Domestic Septage” National Risk Management Research Laboratory (EPA/625/R-95/001)
FAO - Food and Agriculture Organization of the United Nations (1996) “Biogas Technology: A training manual for extension” Support for Development of National Biogas Programme (FAO/TCP/NEP/4451-T)
GTZ - Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), GmbH. (2015) “AT Information: Biogas” Information and Advisory Service on Appropriate Technology (ISAT).
Kossmann, Werner; Pönitz, Uta; et al. (n.d.) “Biogas Digest: Biogas Basics” Information and Advisory Service on Appropriate Technology (ISAT). Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), GmbH. vol. 1.
Lüthi, Christoph et al, 2011. Community-Led Urban Environmental Sanitation Planning (CLUES). Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf, Switzerland.
Sievers, Jan Christian; Oldenburg, Martin; Albold, Andrea; Londong, Jörg (2014) “Characterisation of Greywater - Estimation of Design Values” KREIS Project. German Federal Ministry of Education and Research (BMBF)
Tilley, Elizabeth et al, (2008) “Compendium of Sanitation Systems and Technologies” Swiss Federal Institute of Aquatic Scienceand Technology (Eawag). Dubendorf, Switzerland.
Vögeli Y., Lohri C. R., Gallardo A., Diener S., Zurbrugg C. (2014). “Anaerobic Digestion of Biowaste in Developing Countries: Practical Information and Case Studies” Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dubendorf, Switzerland
Wim J. van Nes & Tinashe D. Nhete (2007) “Biogas for a better life: An African initiative” Renewable Energy World Magazine 10(4) <http://www.renewableenergyworld.com/articles/print/volume-10/issue-4/bioenergy/biogas-for-a-better-life-an-african-initiative-51480.html>