DSD Dissertation May 2013

Anaerobic Digestion: Increasing electrical energy generation SID: 0926018

Increasing electrical energy generation through anaerobic

digestion: To develop a framework on energy generation

from biomass

By

Samuel David

BEng (Hons) Mechanical Engineering

SID: 0926018

Department of Engineering and the Built Environment

Anglia Ruskin University

May 2013


BEng (Hons) Mechanical Engineering ii

Declaration by the Author

This work is composed of my original work, and contains no material previously published,

produced or written by another person or organisation except where due reference has been

made. I have clearly stated the contribution of others to the production of this work as a

whole. I have read, understood, and complied with the Anglia Ruskin University academic

regulations regarding assessment offences, including but not limited to plagiarism.

I have not used material contained in this work in any other submission for an academic

award or part thereof.

I acknowledge and agree that this work may be retained by Anglia Ruskin University and

made available to others for research and study in either an electronic format or a paper

format or both of these and also may be available for library and inter-library loan. This is on

the understanding that no quotation from this work may be made without proper

acknowledgement.

Candidates signature ………………………..……………………….…………

Candidates Student Number…………………………………………………

Date ……………………………………………..……………………………………


BEng (Hons) Mechanical Engineering iii

Acknowledgement

Firstly, I would like to thank the almighty God for keeping me alive and giving me the ability

not to quit but continue studies. Secondly, I would like to recognise the people who braced

and assisted me greatly in this study:

Prof. Hassan Shirvani, my supervisor, sincere appreciation for his constant drive and

assistance during my participation in the Engineering and the built environment department

especially during this project, for his constructive advices, criticisms and his encouragement.

Eng. Robert Manful, for his encouragement, guidance and especially his support even in short

notice.

Eng. Kiev, a good friend, for his valued advice, insights and most importantly his support

leading me to do this project.

Dr. Alan Redmond, my tutor in Major project, for his encouragement and advice.

The Rivers State Scholarship Board that provided the financial requirement that helped my

study at Anglia Ruskin University.

I would like to also thank my classmates for their help, especially Edwin Fynest, Williams

Ibinabo, and Ruby Wokocha.

Special thanks to my true friends who always believed in me even when I could not believe

in my ability.

Lastly, I would like to genuinely appreciate my Dad D.D. Alabere, my Mom Agnes and my

brothers and sisters for their total love and faith in me.

Samuel David, Chelmsford, may 2013


BEng (Hons) Mechanical Engineering iv

Abstract

This study focuses on increasing electrical energy generation in anaerobic digestion (AD)

which uses a combination of established facts from previous investigations on anaerobic

digestion process. AD systems have issues with biogas yield which is caused by diverse

means such as the type of feedstock and method used, as well as the capital cost. The

combination of published research facts were used in WITNESS 12 simulation software for

the design.

The assumption that one shipped biogas container is within the range of 315 to 611 norm litre

per kg of volatile solid (NI kgVS-1

) was used. For one shipped container of biogas produced

from a mini digester there is a minimum of 315 NI kg VS-1

and a maximum of 611NI kgVS-1

.

A simulation was carried out for a month and it resulted in 11 shipped containers of biogas.

For 11 shipped containers, there is a minimum of 3465 NI kg VS-1

per month and a maximum

of 6721 NI kg VS-1

per month. The result from the simulation was promising showing a total

of 11 containers shipped from all locations of digesters.

Although this method appears to have potential, it has not been tried in the real world. It

would be useful for a practical study to be undertaken.


BEng (Hons) Mechanical Engineering v

Table of Contents

Acknowledgement ................................................................................................................... iii

Abstract ..................................................................................................................................... iv

1. INTRODUCTION .......................................................................................................... 1

2. Overview of Anaerobic Digestion .................................................................................. 2

2.1 History of AD ......................................................................................................... 2

2.1.2 Anaerobic Digestion ................................................................................................ 3

2.2 ANAEROBIC DIGESTION METHOD ..................................................................... 4

2.2.1 Hydrolysis ............................................................................................................ 6

2.2.2 Acidogenesis ........................................................................................................ 6

2.2.3 Methanogenesis.................................................................................................... 6

2.3.1 Hydrolytic bacteria............................................................................................... 7

Acetogenic bacteria /obligatory hydrogen-producing acetogens (OHPA) ......................... 8

2.3.2 Methanogenic microorganisms ............................................................................ 9

2.3.3 Interactions between different microbial consortia in the AD reactors ................... 9

2.4 Factors disturbing anaerobic digestion of foodstuff waste........................................ 11

2.5 Arrangement of the AD schemes .............................................................................. 13

3. Effect of Anaerobic digestion to the environment ............................................................ 14

3.1 Environmental benefits ............................................................................................. 14

3.1.2 Energy balance ................................................................................................... 14

3.1.4 Reduction in water and land contamination....................................................... 15

3.2 Difficulties in AD .................................................................................................. 15

3.3 Electricity generation ............................................................................................. 16

4. RESULTS FROM DIFFERENT GROUPS IN INVESTIGATING ANAEROBIC

DIGESTION......................................................................................................................... 17

5. Research method ............................................................................................................... 22

6. Design analysis ................................................................................................................. 23


BEng (Hons) Mechanical Engineering vi

7. Results .............................................................................................................................. 31

9 Reference .......................................................................................................................... 36

10 Bibliography ................................................................................................................. 38

11 Appendix ....................................................................................................................... 40

11.1 Ethics statement......................................................................................................... 40

11.2 Appendix B CV............................................................................................................ 1

11.3 Exit plan ...................................................................................................................... 3

11.4 Proposal ....................................................................................................................... 5


BEng (Hons) Mechanical Engineering vii

List of Tables

Table 1 livestock populations and farm residues in the UK and their potential for methane generation

and electronic output (MREC, 2011). ................................................................................................... 14

Table 2 presumed residence time .......................................................................................................... 31

Table 3 sections of Digestion process ................................................................................................... 32

Table 4 results ....................................................................................................................................... 32

Table 5 statistics of operations .............................................................................................................. 33

List of Figures

Figure 1 overview of AD process (MREC, 2011) .................................................................................. 5

Figure 2 overall process of anaerobic decomposition (Madigan et al., 2003) ........................................ 8

Figure 3 SEM display of lignon and cellulose degradation .................................................................. 19

Figure 4 Design framework .................................................................................................................. 23

Figure 5 Corn Stover source: google.co.uk ........................................................................................... 24

Figure 6 lignocellulosic source: google.co.uk ...................................................................................... 25

Figure 7 production rate & total capacity of the most common used AD process. (Arsova, 2010) ..... 25

Figure 8 Valorga AD reactor ( Arsova, 2010) ..................................................................................... 26

Figure 9 AD reactors, gas tank and stack (Arsova, 2010) .................................................................... 26

Figure 10 Daily methane production within 30 days in L-AD (brown et. al 2012) .............................. 27

Figure 11 Total methane yield within 30 days in L-AD &SS-AD (Brown et. Al 2012) ...................... 27

Figure 12 algae source: google.co.uk/search ........................................................................................ 28

Figure 13 S.D design (2013) ................................................................................................................. 29

Figure 14 Design process in Witness .................................................................................................... 30

Figure 15 quantity of biogas yield (using simulation) .......................................................................... 33

Figure 16 statistics of blockd,busy,idle and no. of operation ................................................................ 34


BEng (Hons) Mechanical Engineering 1

1. INTRODUCTION

Traditional forms of electrical energy generation such as through hydropower, nuclear, fossil

and coal have had significant negative consequences on the environment. These traditional

sources are finite and continual generation of energy from them is not sustainable. In the last

two decades, attention has been focussed on generating energy from renewable sources given

the issues relating to the tradition energy sources above. More recently parts of the energy

industry have been exploring energy generation from plant, human and animal waste. A

typical example is energy generation from sludge from wastewater treatment plants in the

UK. This research will focus on generating energy from plant matter (biomass) through

anaerobic digestion. In south-eastern United States, biomass technology is already leading the

region’s renewable power potential.

It is worth noting that the generation of energy through anaerobic digestion is capital

intensive and often with significant operational costs but there is the potential for these costs

to be reduced.

The aim of this study is to develop a framework on energy generation from biomass through

anaerobic digestion.

Objectives

To provide a general overview of anaerobic digestion.

To investigate the effect of anaerobic digestion to the environment.

To analyse the benefits of biomass for energy generation.

To explore opportunities to harness more energy from biomass through anaerobic

digestion.

The research gives a summary of the definition of anaerobic digestion. Anaerobic digestion

is a process that microbes break biological matter in the absence of air to produce biogas and

nitrogen fertiliser.

The research also provides some consequences of using anaerobic digestion to the

environment as well as the benefits.

It also covers the aspect of improving the throughput of generating energy through anaerobic

digestion. This was done using the WITNESS 12 simulation software. The model simulation

display the feasibility of the design but might not give the same result when done in the real

world, since all requirements were not put into consideration.



2. Overview of Anaerobic Digestion

2.1 History of AD

Past evidence shows that the anaerobic digestion (AD) method is one of the ancient

technologies (Monnet, 2003). Nevertheless, the development of anaerobic digestion (AD)

started in 1859 alongside the first digestion plant built in Bombay (presently known as

Mumbai) at leper colony in India. In 1895, biogas was transformed from a sewage treatment

facility to be used in giving power to street lamps in Exeter, England. Investigation led by

Buswell and his team in the 1930s gave recognition to anaerobic microorganisms and the

environments that support methane production.

As the understanding of the AD process and its advantages developed, better tools and

operational techniques arose. Until the 1970s, it was commonly used only in the wastewater

treatment plants waste management (Palmisano et al. 1996). The amount of generated solid

waste continuously increases and due to the large environmental impacts of its improper

treatment, its management has become an environmental and social concern (Arsova, 2010).

Irrespective of the improvements, AD was affected badly due to the growth of aerobic

process and low costs of coal or fuel. Although AD systems were used for the treatment of

wastewater sludge digestion only, rising nations (example is India and China) grabbed the

technology.

Food waste comprises 12.4% of the total municipal solid waste (MSW), according to U.S.

EPA estimates. According to the 2006 state of Garbage survey of BioCycle and Columbia

University, this corresponds to over 40 million tons, (Arsova et al. 2008).

Slight gauge AD structures were frequently used for sanitation purpose and energy and many

failures were reported. However, operational enhancements and rising energy costs have

headed to a change of the waste treated and bigger range AD plants.

In the modern era, European nations are now under pressure to discover AD market for two

main reasons; advanced energy costs and progressively severe ecological policies.

Certain AD services have been in process for over two decades. In Europe, over 600 farm

scale digesters function, where the factor is ease. In accumulation to farm scale digesters,

Europe leads in huge centralised AD schemes.



2.1.2 Anaerobic Digestion

Anaerobic digestion (AD) is a microbial decomposition of organic matter into methane,

carbon dioxide, inorganic nutrients and compost in oxygen depleted environment in the

presence of the hydrogen gas (Arsova, 2010). This process is also known as bio-

methanogenesis. Anaerobic digestion is an eye-catching waste treatment method in which

both contamination control and energy regaining can be attained (Chen et al. 2007).

Anaerobic digestion, which produces biogas, has gained recognition over the years

essentially because of its encouraging energy balance, the fact that it works as a waste

treatment method and creates a recycle of nutrients to agricultural land. AD is also known as

a biotechnological process that takes place naturally in nature in places where there is total or

partial absence of oxygen. Such places include inter alia marshes, paddy fields, rubbish

dumps, digestive tracks of ruminants and the guts of insects such as termites (Garcia et al.

2000).

Anaerobic digestion process

Natural and anthropogenic (i.e. environmental pollutants and pollution) sources account for

30% and 70 %, respectively, of the methane released in the atmosphere every year.

Main natural sources of methane are wetlands and animal guts (mainly insects and ruminants)

while the main anthropogenic sources has been recognised in the fossil fuel processing

industries, rice fields and landfills. Biological activity has been recognized to be the cause for

more than 80% of the flux of the atmospheric methane (Palmisano et al.1996).

Biogas has been defined as gaseous or liquid fuel produced from biomass with an energy

content originating from methane (Energigas Sverige, 2011). Biogas production through AD

or biomethanation is an advanced technology which is evident by the increasing number of

biogas plants in both the developed and developing countries. For example over 6000 biogas

plants are in operation in Germany (Kusch et al., 2012). In addition, a biogas plants exist both

in small domestic scale as in developing countries such as India and China or in larger

community scale as in Denmark, Sweden and Germany (Sims et al., 2008). 64TWh per year

of energy in the form of biogas was produced in the EU in 2007 (Sims et al., 2008).

The drive for biogas production as renewable fuel is also politically motivated (Achu Nges,

2012). The European Commission’s directive on renewable energy has placed a target to be

achieved by each member state b 2020, i.e. 20% of energy from renewable sources in energy



consumption and a minimum target of 10 % for renewable fuel in domestic transport

(European Commission, 2009).

Sweden has a national goal of achieving 50% of the energy consumption through renewable

sources by 2020 and actually reached 47% in 2009. Nevertheless, in the transportation sector

the share of renewable was only 5.7% (Swedish Energy Agency, 2011). The renewable

energy used in the transport sector in Sweden is dominated by bio-ethanol and biodiesel, but

also include electricity from renewable sources, and biogas (Swedish Energy Agency, 2011).

Despite the advantages of the AD process, the technology has suffered drawbacks in areas

such as low methane yields, incomplete bioconversion, and process instability (Achu Nges,

2012).The main problems of the AD plants are feedstock purity, compost quality and ordure

emissions (Arsova, 2010). However proven to be effective for treating organics, anaerobic

digestion plants have difficulties in obtaining fairly clean feedstock that results in technical

difficulties with the equipment and poor compost quality. Increasing cost of feedstock and

operation of digesters below maximum capacity is also occurring as a result of regional

shortages of feedstock (Asam et al., 2011). Furthermore, the economic feasibility of these

plants has been questioned due to the high investment and operation costs (Arsova, 2010).

Observations show that the capital cost per ton of AD capacity is in the range of the mass

burn waste to energy. Also there are more than 40 different AD technologies available on the

market and it is challenging to identify the best one (Kelleher 2007).

2.2 ANAEROBIC DIGESTION METHOD

The digestion method occurs in a warmed, closed airless tank known as the digester that

generates the best situations for the microorganisms to ferment the biological material in

oxygen free surroundings (MREC, 2011). It is important that the digestion tank is warm and

mixed properly to generate the surroundings for the microorganisms to transform organic

substance into biogas, which is a combination of carbon dioxide, methane and slight amount

of additional gases (see figure 1). Mesophilic and thermophilic biological decomposition are

forms of anaerobic digestion process.



Mesophilic digestion: This occurs when the digester is heated to a range between

300C to 35

oC while the feedstock stays in the digester for 15 to 30 days. Mesophilic

digestion is most likely tough and accepting compared to the thermophilic method,

but gas creation is smaller; bigger digestion containers are vital and cleansing.

Thermophilic digestion: This occurs when the digester is warmed to 55oC and the

dwelling period is 12 to 14 days. Thermophilic digestion structures produces greater

methane, better pathogen, quicker throughput and virus ‘kill’, nevertheless needs

additional costly technology, better energy effort and a greater point of setup and

examining.

Figure 1 overview of AD process (MREC, 2011)



Biological process

The fundamental science of AD can be difficult and the method is best understood if it is

divided into three key stages: hydrolysis, acidogenesis (acid-forming stage) and

methanogenesis (Monnet, 2003).

2.2.1 Hydrolysis

Hydrolysis is a reaction that the fermentative bacterium breaks down the insoluble complex

organic molecules such as cellulose, into soluble constituents. The end product s of this

reaction are soluble molecules such as, amino acids and sugars; glycerol and long-chain

carboxylic acids (Shefali & Themelis 2002). Chemicals can be added during this process to

provide a higher methane yield and decrease the digestion time.

2.2.2 Acidogenesis

Acidogenesis is also known as the acid-forming stage. In this stage, acetogenic organic acids

recognized as acid formers transform the yields from hydrolysis into simple organic acids,

carbon dioxide and hydrogen. The foremost acids made are propionic acid, acetic acid,

butyric acid as well as ethanol. The acid forming stage involves two reactions, fermentation

and the acetogenesis reactions. During fermentation, the soluble organic products of the

hydrolysis are converted into simple organic compounds, commonly volatile fatty acids such

as propionic, formic, butyric, ketones and alcohols. The acetogenesis is completed through

carbohydrate fermentation and results in acetate, Co2 and H2, compounds that can be utilized

by the methanogens. The existence of hydrogen hunting microbes is fundamental to ensure

thermodynamic possibility of this reaction (Ostrem & Themelis 2004).

2.2.3 Methanogenesis

Methanogenesis is the bacteria known as methane formers produce the stage methane. Two

third of the total methane formed is derived converting the acetic acid such as methanol

(Arsova, 2010). The other one third of the formed methane is a result of the reduction of the

carbon dioxide by hydrogen.

The progression of AD can be additional separated into four phases: pre-treatment, digestion,

and gas advancement and digestate treatment.



The level of pre-treatment relies on the form of feedstock. Feedstock is the word used to call

the substance hosted into the digester (such as manure).

Digestion stage takes place in the digester.

2.3 BIOCHEMICAL REACTIONS IN ANAEROBIC DIGESTION

The transformation of composite organic matter into methane and carbon dioxide is made

possible by the common action of four different microorganisms (MO). The important

microbial complex contains the hydrolytic bacteria, fermenting bacteria, acetogenic bacteria

and methanogenic Archaea(see figure 2). These groups of MO have created syntrophic

relationships where later participants of the food chain rely on the previous substrates, but

also they may have major influence on the earlier participants in the chain by removing the

metabolic products (Garcia et al. 2000).

The first group of MO is the hydrolytic bacteria. These organisms catalyse the hydrolysis

reaction through the extracellular hydrolytic enzymes they excrete. The subsequent

monomers from this reaction under fermentation straight to acetate or through the pathway of

the volatile fatty acids and alcohols facilitated by the consequently named lesser fermenters

or force proton reducers (Ralph & Dong 2010). These bacteria transform their substrates to

acetate, carbon dioxide, hydrogen, and possibly formate, which are later used by the

methagens (Schink, 1997).

2.3.1 Hydrolytic bacteria

Specialized microbial population of hydrolytic bacteria is responsible for depolymerisation of

these organic polymers (lignocelluloses, proteins, lipids and starch) towards their building

compounds, monomers (Arsova, 2010).

This is typically found to be the slowest and the rate-limiting period in the whole anaerobic

digestion process. Additionally, the ultimate methane yield is directly dependant on the

effectiveness of this reaction (Palmisano & Barlaz 1996).

Depending on the type of reaction the extracellular microbial enzymes (hydrolyses) catalyse,

these hydrolyses can be esterase (enzymes that hydrolyse ester bonds), glycosidase (enzymes

that hydrolyse glycosides bonds), or peptidase (enzymes that hydrolyse peptide bonds).



Figure 2 overall process of anaerobic decomposition (Madigan et al., 2003)

Acetogenic bacteria /obligatory hydrogen-producing acetogens (OHPA)

Acetogenesis is the stage when the products of the hydrolysis are processed to hydrogen,

carbon dioxide, formate and acetate (Arsova, 2010). This occurs naturally in well stable

methanogenic systems. Nevertheless, in practise, there are situations of electron or hydrogen

accumulation (e.g when methanogenesis is inhibited) when many fermentation products may

be formed (e.g. propionate, butyrate, lactate, succinate, and alcohols) as a mechanism to

remove the additional electrons or hydrogen. Organism that transform these fermentation



products to acetate, commonly display obligate proton-reducing metabolism and are

obligatory dependent on the hydrogen removal. This is the reason the acetogenic bacteria are

also called obligatory hydrogen-producing acetogens (OHPAs).

2.3.2 Methanogenic microorganisms

The main method of methane creation is across a syntrophic connection between acetate

oxidizing microbes and hydrogen-utilizing methanogenic Archea (Arsova, 2010). The

acetoclastic and hydrogenotrophic methanogens adds 70% and 30% individually to methane

creation in industrial wastewater treatment ( Sawayama et al. 2004).

Many methanogens have been remote and described to this point, but findings centred on 16S

rDNA cloning analyses, propose that the most commonly found methanogens genera in

biogas reactors, are Methanothermobacter (previously Methanobacterium),

Methanobrevibacter, Methanosarcina, and Methanosaeta (formerly Methanotrix) as

referenced in Archives of Env protection. Methanosarcina and Methanosaeta species

presently recognised to be controlled in huge scale Mesophilic and thermophilic digesters

treating wastewater and sewage sludge. Its dominance is as a result of its wide tolerance for

environment factors such as nutrients and temperature (Palmisano & Barlaz 1996).

2.3.3 Interactions between different microbial consortia in the AD reactors

As stated previously each group of anaerobic microorganism contain diverse microorganisms

responsible for different metabolic task. A characteristic of this anaerobic consortium is that

diverse types of anaerobic bacteria lower one organic compound interactively, distribution

energy and carbon sources from compound (Sekiguchi et al.2001).

These organisms have developed specific interdependent relationship called syntrophy,

distinct symbiotic cooperation of common reliance of the partner bacteria with detail to

energy limitation in a case neither partner can exist without the other and together they

display a metabolic action that neither one could do on its own. In this unique collaboration

between two metabolically diverse forms of microorganisms, they rely on each other for

degradation of a definite substrate for active reasons (Schink, 1997).

The collaboration between the microorganisms in methanogenesis has evolved due to the

need to apply the energy obtained from the electron donor substrate more efficiently.

Anaerobic degradation reaction is a reaction with low energy yield compared to aerobic



degradation. The reason is because the electron acceptor which is the carbon dioxide and not

oxygen like the aerobic degradation. Carbon in the carbon dioxide is in the most oxidized

state with a COD: C ratio of zero.

Reactions that occur are as follows as referenced in the environmental Microbiology (Ralph

& Dong 2010).

Conversion of propionate to acetate:

CH3CH2C00-+3H2O CH3C00

-+H

++HCO

-3+ 3H2

Free energy value: +76.1kj

Conversion of butyrate to acetate:

CH3 (CH2)2C00-+2H2O 2CH3C00

-+H

++2H2

Free energy value: +48.3kj

The above reactions have critical thermodynamics, except in syntrophy with the hydrogen

overriding bacteria and methanogenesis, these organisms cannot exist. Specifically, hydrogen

is the best vital transition and the hydrogen hunting reaction makes the whole reaction

actively possible. The following reactions occur as referenced in the Environmental

Microbiology (Ralph & Dong 2010):

Acetogenic reactions

2HC03- + 4H2 +H

+ CH3C00

-+ 4H2O free energy value: -104.6 kj

Methanogenic reactions

CH3C00- + H2O CH4 + HCO

-3 free energy value: -31.0 kj

4H2 + HC0-3 + H

+ CH4 + 3H2O free energy value: -135.6 kj

Looking from this aspect, hydrogen overshadowing methanogens makes important impact

not simply to the creation of methane however likewise in pushing the early phase of

oxidation of the organic substance which is to be degraded by heterotrophic bacteria in the

reactors. The intermediates formed in anaerobic degradation in reactors, butyrate, propionate

and acetate are the most vital in adding to hydrogen (Arsova, 2010). These substrates

specifically propionate and butyrate are also oxidized by the syntrophic group of fatty acid

oxidizers and hydrogen overriding methanogens (Sekiguchi et al. 2001).

The energy that the microorganisms gain from the electron donor substrate is used for both,

cell maintenance and synthesis. Increase biomass yield relies on the fraction of the energy



that is accessible for cell synthesis. In methanogens, the fraction of energy accessible for cell

synthesis is fs0= 0.05 for acetate methanogens and fs

0 = 0.08 for hydrogen operating

methanogens. This little amount of energy accessible results to microbial growth yield of Y=

0.035 gVSS/gBODI and Y= 0.45gVSS/gH2 correspondingly for the acetate and hydrogen

functioning methanogens, and classify these organisms into slow growing organisms

(Arsova, 2010). Hence the methanogenesis is the rate restraining step in the anaerobic

digestion reaction and needs retention time at least 15-20 days for a stable state system which

is referenced in the environmental biotechnology: Principles and Applications.

2.4 Factors disturbing anaerobic digestion of foodstuff waste

The factors that affect the anaerobic digestion of foodstuff waste include; pH value, loading

rate, foodstuff composition, retention time, and the working temperature.

pH value: The pH value of the material used is very significant in the anaerobic digestion of

foodstuff waste. This is because the methanogenic bacteria behaves in a complex way when it

is in an acidic environment, throughout the acetogenesis stage it can lower the pH value

below 5 and reduce methane creation. Alternatively, surplus propagation of methanogens

will possibly point towards greater concentration of ammonia, which will increase the pH

above 8 and becomes restraint to the acidogenesis (Lusk 1999).

Having a constant pH at the beginning stage is vital to the creation of methane. To the

balance in the pH value calcium carbonate can be added. Nevertheless there are proofs that

the best range of acquiring full biogas produce is within 6.5-7.5, the variety of plants is vast

and their maximum value of pH differs with digestion method and substrate (Liu et al. 2007).

The connection between pH and methane yield according to L. Arsova (2010) is:

(

) (

)

Vmax is the maximal yield rate of methane (at 1 atm pressure & 00C), where Xm is the

methanogenic biomass (g/L), Km is the saturation constant of methane yield, Kim inhibition

constant of acetate on methane yield, Ka the detachment constant for acetate which is 1.728

E-5

and Ac is ionized acetate concentration (Liu et al. 2007).



Loading rate: The loading rate controls the quantity of unstable solids that will be put in the

anaerobic digestion system and in the event of overloading lead to low biogas yield. It can

also cause the propagation of the acidogenic bacteria to more reduction in the pH value which

disrupts the growth of methane.

Loading rate formula (Arsova, 2010);

Loading rate (

)

(

) (

)

Foodstuff composition: It is very important to know the type of foodstuff content to be able

to determine the bio- methanization potential (Arsova, 2010). The bio-methanization depends

on the concentration of carbohydrates, fats, fibre and protein; this is because of their diverse

bio-chemical features (Neves et al. 2007).

Retention time: Retention time is also known as the residence time. This is basically the

time spent by the feedstock inside the digester.

Formula for retention time (Asorva et al. 2010);

Temperature: The temperature is the most significant aspect in terms of operation in the

anaerobic digestion reactor since the bacterial groups existence in the reactor depends on it.

Although the bacteria can last in wide range temperature but the maximum range is within

the Mesophilic and the thermophilic temperature which is 25- 400C and 50-65

0C respectively.



2.5 Arrangement of the AD schemes

The scheme of the digester also relies on the quantity of the feedstock obtainable which

controls the volume of the reactor.

AD systems can be described by the following principles:

Filling rate in high and low solid contents. Low solid content is less than 15%

(likewise known as wet digestion) and high solid content of 25 to 30% (likewise

known as dry digestion).

Temperature functions in the thermophilic and Mesophilic temperature. The

thermophilic works in temperature between 50 to 650C and the Mesophilic works in

370C.

There is the single stage digester and the multi stage digesters. In the single stage the

entire reaction occurs in one reactor and the ecological situation are balanced to help

the bacteria. The multi stage digester involves two reactions in two different reactors

containers; one for hydrolysis and the other for acidogenesis.

The feed can be put in the reactor by continuous flow and batch. The continuous flow

reactor distributes the feed in a continuous process. The batch reactor allows reaction

to take place for about two weeks.



3. Effect of Anaerobic digestion to the environment

3.1 Environmental benefits

3.1.2 Energy balance

Considering emissions from transport operation, a suitably designed and activated AD plant

can reach an improved energy balance than other methods of energy creation (MREC, 2011).

The energy stability refers to the size of energy used up in plea to yield energy.

3.1.3 Reduction in greenhouse gases

Anaerobic digestion contributes to reducing the greenhouse gases (Monnet, 2003).

Methane (CH4) is a prevalent greenhouse gas if it discharges to the air (EPA, 2010).

Present removal of food residues and slurry cause methane to be released through

normal processes (MREC, 2011). Anaerobic digestion uses this process in order to

use the gas as fuel. A properly managed AD structure tends to increase methane

production, however not discharge any gas to the atmosphere, thus decreasing total

emissions (Monnet, 2003).

Anaerobic digestion offers an energy source with no remaining rise in atmospheric

carbon. When fossil fuel is used for energy creation it causes climate changes, but the

use of AD can help decrease the general numbers of carbon dioxide in the air and

diminish risks of temperature variation.

Table 1 livestock populations and farm residues in the UK and their potential for

methane generation and electronic output (MREC, 2011).

Resource Population Potential methane

yield

(m3/day)

Potential annual

electricity output

(Twhe/year)

Cattle 12,200,000 5,700,000 6.2

Pigs 7,900,000 800,000 0.9

Poultry 124,000,000 1,000,000 1.1

TOTAL - 8,600,000 9.4



The use of finite fossil fuels can be reduced or replaced by AD as a means of

generating energy (see table 1). The usage of fibre and liquor as an input to fertiliser

systems can in later decrease fossil fuel feeding in the creation of synthetic fertilisers.

If AD yields are properly used it can decrease the necessity for synthetic fertilisers

within a total fertiliser programme.

3.1.4 Reduction in water and land contamination

Inappropriate removal of animal slurries can result to land and water contamination.

AD builds a strong managing structure that reduces the chances of soil and water

pollution to happen, compared to the removal of untreated animal slurries (Monnet,

2003). This process can also lead to a reduction of about 80% of the 0dour and it

terminates nearly all weed seeds, thereby decreasing the necessity for herbicide and

other weed control measures.

3.1.5 Reduction in demand for peat

Peat is a varied combination of additional or fewer decayed vegetable (humus)

substance that has gathered in a water drenched environment and in the absence of

oxygen (Clarke et. Al 2002). The fibre made by the AD method can be used as a soil

conditioner, in certain occasions as a substitute for peat. Peat removal is a big

ecological problem, destroying the fragile ecosystems of the peat lands (MREC,

2011).

One of the objectives of this project focuses on the effect AD process has on the

environment. However there are other benefits including financial related ones.

For example, AD converts residues into possibly saleable products: soil conditioner, liquid

fertilizer and biogas (Monnet, 2003). It can as well lead to the profitable feasibility of farms

by reserving costs and profits inside the farm if the yields are used on site (Monnet, 2003).

3.2 Difficulties in AD

Even though anaerobic digestion process has been in use for the treatment of organic material

for a while, there are difficulties linked with it (Arsova, 2010). AD projects with the

possibility of much advancement will generate some risks and might have some possible

negative environmental impact; but it needs to be removed wherever possible or minimised.



AD has major capital and operational cost. It is doubtful that AD will be feasible as an energy

source only and so must be seen as an integrated system (Arsova, 2010).

The management structures of waste create delay in transportation and this can become a

problem in CAD plants and other means of transport should be investigated since it

significantly affects cost and emissions. For the possibility of reducing the distance travelled

between the productions of the storage tanks, feedstock and the digester the location of the

plant should be selected sensibly.

There might be certain risks in terms of health and safety to human healthiness with the

pathogenic content of the feedstock but it can be avoided with a suitable design and feedstock

treatment procedures (Arsova, 2010).

3.3 Electricity generation

According to GOV.UK (2013), the heat created from dry biomass waste, municipal wastes,

industrial wastes, demolition wastes and construction wastes can be used straight to warm

homes or create electricity, including the methane produced from the process.

The biogas produced from anaerobic digestion process can be burned in a gas boiler to create

heat unit to produce heat and electricity using the combined heat and power (CHP) system.



4. RESULTS FROM DIFFERENT GROUPS IN INVESTIGATING ANAEROBIC

DIGESTION

When looking for possibilities to enhance bio-degradability and biogas production from corn

stover, Zheng et al. (2009) proved wet state NaOH pre-treatment to be efficient. The process

involved three days treatment time with 88% moisture content under an ambient temperature

of 200C and 2% of NaOH dose.

Relating to the unprocessed Stover, the entire biogas creation and methane produce were

maximised by 72.9% and 73.4% respectively, and the breakdown time was reduced by

34.6% for 2% wet state NaOH processed stover. Wet state pre-treatment process used 86%

smaller pre-treatment time and 66.7% less NaOH does than solid state one, which could

significantly lessen cost and enhance the productivity of NaOH pre-treatment process.

According to Meester et al. (2012), the research group ENVOC from Ghent University

studied the ecological sustainability of anaerobic digestion since different perceptions and

their results shows that biomass is transformed at a balanced energy productivity alternating

from 15.35 to 33.3%. From a life cycle view, anaerobic digestion executes well by making

major resource savings. The group concluded that it is essential to regulate emissions in the

biogas making chain in order to increase environmental sustainability/

Since anaerobic digestion is capable to create biogas from diverse bases of biomass while

also creating a rich dig-estate, it can become a pronounced approach in the making of

renewable energy.

The digestibility of a starch polyvinyl alcohol (PVOH) biopolymer insulated cardboard

coolbox was examined by Guo et al. (2011) in a distinct anaerobic digestion (AD) structure

with significant factors considered. Conclusions show that with extremely active inocula, 58

to 62% biodegradation of starch PVOH based biopolymers are reachable in AD surroundings.

Energy responses and atmospheric emissions in AD process are identified as major

environmental burdens although optimisation of the energy might bring important ecological

profits to the AD method. Automated and organic treatment (AD of the biopolymer and more

reprocessing of the cardboard) developed as a naturally high quality matched with

uncontaminated anaerobic digestion for the starch PVOH biopolymer isolated cool box.

Adu-Gyamfi et al. (2012) studied the functions of six factors; the sort of restraining supports,

filling rate, inoculum stages, C: N ratio, trace nutrients absorptions and mixing rate on



maximising methane creation while maintaining a considerable level of process stability.

From the multi-factor enhancement research conclusions were drawn;

The type of immobilizing support had extreme impact on methane production,

resulting to above 60% of the whole effect in addition confirms the efficiency of

synthetic zeolites.

Feed level and inoculum consumed a related impact at their separate points of 18%.

Filling rates and inoculum stages at start up perform vital parts in methane creation.

The C:N ratio, mixing and trace nutrients had the slightest effect separately but major

cooperative causes were recognized.

Optimise enhanced methane production by over 150%.

An experiment was carried out by Fantozzi et al. (2011) on three different models of Organic

Fraction of Municipal solid Waste (OFMSW) from waste separation (WS); OFMSW slurry

(liquid fraction) and OFMSW waste (residual solid fraction). Anaerobic bio-gasification

potential (ABP) and anaerobic digestion (AD) tests were passed out in examining the

properties of inoculum and pH. Test results show that OFMSW acknowledged did not yield

substantial amounts of biogas and the investigation did not disclose the existence of methane.

Conclusion show that in obligation to have substantial biogas creations the pH controller in

the start-up stage is vital and OFMSW slurry need be diluted and inoculated.

Recognising that earlier studies have revealed that alkali pre-treatment previous towards

anaerobic digestion (AD) can raise digestibility of lignocellulosic biomass and methane

production, Li et al. (2011) calculated instantaneous alkali behaviour and anaerobic digestion

for methane creation from dropped greeneries in demand to shorten the process and decrease

capital cost.

In general, Solid-state (SS) anaerobic digestion (AD) needs greater inoculum levels than

liquid anaerobic digestion. Decreasing the quantity of inoculum permits improved reactor

productivity, but the outcome may lead to a growth in the build-up of VFA and end up in

reactor upset (li et al., 2011). The highest improvement in methane production was attained at

S/I ratio of 6.2 with NaOH loading of 3.5% which was 24 fold greater than that of the

regulator deprived of the addition of NaOH.

Molinuevo-Salces et al. (2011) investigated the influence of accumulating vegetal waste as a

co-substrate in the anaerobic digestion of pig compost consuming semi-constant stirred

container reactors operating at 370C(see figure 3).



Conclusions show that;

a. The adding of vegetal wastes to semi-constant anaerobic digester treating pig

compost had an encouraging result on methane generation. The upper buffer

capability of pig compost together with the upper carbon/nitrogen ratio provided

by vegetal waste enhanced method performance.

b. Scanning Electron Microscopy (SEM) images displayed that lignin and cellulose

were not totally degraded at the end of the investigational time.

Figure 3 SEM display of lignon and cellulose degradation



Coagulation and digestion of tannery wastewater were investigated by Song et al. (2001).

Based on results and observation these conclusions were made;

a. At an optimum pH of 7.5, the following removal efficiencies were attained by

coagulation: 32%-35.6% (COD), 64.0%-69.3% (SS), 77-99% (chromium), 85%-86%

(colour) by respectively the addition of 800 mgl-1

of aluminium sulphate.

b. The digestion of tannery wastewater was completely inhibited by a concentration of

260mg l-1

sulphide.

c. The coagulation of tannery wastewater considerably removes the sulphide contained

in the raw wastewater and improves the effectiveness of the digestion.

In general coagulation significantly reduced the concentration of sulphide and

improved the anaerobic treatability.

Brown et al. (2012) evaluated lignocellulosic biomass feedstocks which are switch-grass,

corn Stover, wheat chaff, yard waste, vegetation, waste paper, maple, and pine, for methane

generation in liquid anaerobic digestion (LAD) and solid state anaerobic digestion (SSAD).

Results show that methane profits of agricultural filtrates and perennial crops were greater

than those gotten from wooded biomass and yard waste through Liquid AD and Solid State

AD. The methane produce from waste paper was great through Liquid anaerobic digestion,

but little during Solid state AD because of acidification. Pre-treatment of wooded biomass is

recommended to raise the biogas profit for both Liquid AD and Solid State AD.

Resh et al. (2010) studied an Austrian anaerobic digestion plant at a slaughter house site

which completely practices animal by-products as substrate to enhance the options for the

exploitation of nitrogen rich animal by-products. The experiment results show that the

improvement of an anaerobic digestion plant of animal by-products is likely when the

nitrogen content in the process is decreased. The lessening of ammonia boosts the

degradation and addition of carbon does not improve fermentation.

Sawayama et al. (2004) examined the effect of adding 500 mg N/ ammonium in a fluidized

bed anaerobic digestion. Results show that the yield from fluidized bed anaerobic digester

and the methane concentration in the biogas produced, reduced the ammonium concentration

greatly by more than 600 mg N/ .



J. von Sachs et al. (2003) developed a new control approach for the methanogenic reactor of a

two level anaerobic digestion structure. The key reason was to use online titration of the

active volatile fatty acids into methanogenic level which proved successful.

Shu-guang et al. (2007) conducted an experiment on two dry anaerobic digestions of organic

solid wastes to observe the beginning behaviour under thermophilic and Mesophilic

conditions. The dry anaerobic digestion under thermophilic condition maintained a balanced

system while the dry anaerobic digestion under Mesophilic condition exhibited lowly start up

performance.

Ras et al. (2011) investigated the possibility of adding algae called “chlorella vulgaris” to an

anaerobic digestion component. This was done under two hydraulic retention times and it

yielded the maximum degradability of chlorella vulgaris within 28 days and 240 mlg-1

vss of

methane and also reduced the corresponding organic load by 51%.

In the search to find the best anaerobic technology, L. Arsova (2010) carried out his

investigation in Canada and Spain precisely Toronto and Barcelona. He learnt the best AD

processes are high solids, thermophilic methods that can yield up to 125 standard cubic

metres of biogas per ton of feedstock between 50%to 60% methane concentrations.



5. Research method

The research method used for this project involves collecting significant information from

valid sources in order to give an overview of anaerobic digestion and give a possible solution

to a more efficient way of producing electricity through anaerobic digestion.

The intent of this research is to attempt to give answers to the following questions.

What is anaerobic digestion?

How would biomass effect the environment?

To what extent will biomass benefit for energy generation?

How is electricity generated with anaerobic digestion?

This project proposed to apply quantitative, qualitative and descriptive information gathering

tools, but some of the methodologies were not followed due to limited access or means.

The intent was to gather data from questionnaires given to relevant professionals and

organisations, visit energy generation sites (preferably in the UK).

It is centred mostly on descriptive method which involves gathering information from already

investigated diverse projects on anaerobic digestion that is current and not outdated.

The reason the research was carried out in this manner is because using the right sample is

very important. A questionnaire can be done with people that do not have knowledge on

anaerobic digestion which could lead to an invalid result. The project therefore required

recommendations and answers from professionals. The information used for the project is

obtained from professionals and investigators who actually did the experiments and know

what they are talking about.



6. Design analysis

Design framework

The target is to create a system that will enhance electrical energy generation through

anaerobic digestion. This is not focused on a particular feedstock but all type of feedstock

that can be used for anaerobic digestion.

The research shows that anaerobic digestions end up with producing digestate, biogas that

contains carbon dioxide and methane. This biogas produced can be burnt in combined power

and heat unit to produce electricity and heat (GOV.UK, 2013). More biogas means more

electrical energy generation. Looking at investigations carried on anaerobic digestion there

were issues to be resolved.

The design (see figure 4) will be a combination of the investigations made by Zheng et al.

(2009), Guo et al. (2011), Adu-gyamfi et al. (2012), Li et al. (2011), Molinuevo-salces et al.

(2011), brown et al. (2012), Ras et al (2011), and L. Arsova (2010).

Figure 4 Design framework



Preceding investigation and information from professionals show similarities in terms of

issues with anaerobic digestion. Common problems were the efficiency of the anaerobic

digestion technology quality of the final compost product, the control of air emission,

feedstock quality, process instability, biodegradability, and also low methane yield. There is

another issue with the economic viability, report from Levis et al. (2010) tells that the number

of the operational cost fall in the range of the reported numbers for the anaerobic plants. Once

these problems are resolved or reduced to a reasonably level it will definitely lead to increase

in electrical energy generation.

Zheng et al. (2009) created a method of wet state sodium hydroxide to pre-treat corn Stover

that proved successful.

Figure 5 Corn Stover source: google.co.uk

The design (see figure 4) accepts all feedstock but when it receives a corn Stover as shown in

figure 5;

It sends it to Zheng area to be processed. The appreciate procedure in order to yield the right

result for Zheng’s et al. (2009) is to apply the wet state sodium hydroxide (NaOH) for three

days under a temperature of 200C with 88% moisture content. The amount of sodium

hydroxide should be 2% and the loading rate is 65 . If this is applied correctly, there

should be 72.9% increase in biogas, 34.6% lesser digestion time, 73.4% increase in methane

production (this is compared to using wet state without NaOH pre-treatment).

http://www.google.co.uk/url?sa=i&source=images&cd=&cad=rja&docid=xmdE9epPlqT_eM&tbnid=53VL88zyyeGolM:&ved=0CAgQjRwwAA&url=http://www.sciencedaily.com/releases/2007/07/070709103138.htm&ei=YNleUZrKHqau4ATK_4HYCQ&psig=AFQjCNH9IdIBKGlkm-317E3AMqbAeho3XA&ust=1365256928550351



Li et al. (2011) uses alkali treatment for fallen leaves (shown in figure 6). This should yield

82 L/kg of methane under a NaOH loading of 3.5% within the range of substrate to inoculum

ratio of 4.1. The total solid content should be about up to 20%.

Figure 6 lignocellulosic source: google.co.uk

Most techniques Adu-Gyamfi et al. (2012) used will be applied to every anaerobic digestion

regarding the type of feedstock it uses. This process in involves restraining supports such as

Sand, Molecular sieve, Dowex marathon beads, and silica gel, if done properly if should yield

a huge amount in methane production. The feed rate and inoculum levels should be done with

precision because it influences the production of methane. Optimisation is essential as well.

As shown in figure 7 Arsova (2010) through his search realised that Valorga Anaerobic

digestion technology is the best (although limited to locations because it was done in Europe

and America) for worldwide AD technologies Valorga is part of the best. The valorga

technology offers both mesophilic and thermophilic operation. See AD reactor in figure 8.

Figure 7 production rate & total capacity of the most common used AD process.

(Arsova, 2010)

http://www.google.co.uk/url?sa=i&rct=j&q=lignocellulosic&source=images&cd=&cad=rja&docid=EoBWdomp-Tc1aM&tbnid=HvyFyYWTBAEbpM:&ved=0CAUQjRw&url=http://www.hooch.org.uk/&ei=KuheUZLVMInssgbIzoDIAw&bvm=bv.44770516,d.Yms&psig=AFQjCNGW-Bx3lXT8rJ9rqVe2ojTBuVKTiw&ust=1365260698805592



Figure 8 Valorga AD reactor ( Arsova, 2010)

This method will be combined to the design but will have its own area (Arsova Area) with

high solid content (see figure 8).

Figure 9 AD reactors, gas tank and stack (Arsova, 2010)

The investigation Brown et al. (2012) directed proved fairly successful. After evaluation from

liquid anaerobic digestion to solid state anaerobic digestion results show that green



agricultural crops and remains yielded more methane than wood biomass. This design will

have a section for a bit of Brown’s et al. (2012) method where was significant increase in

methane production from waste paper during liquid anaerobic digestion shown in figure 10

and figure 11.

Figure 10 Daily methane production within 30 days in L-AD (brown et. al 2012)

Figure 11 Total methane yield within 30 days in L-AD &SS-AD (Brown et. Al 2012)



Ras et al. (2011) added chlorella vulgaris to anaerobic digestion using hydraulic retention

times, it yielded methane. Therefore a section will be laid for Ras’s et al. (2011) method for

algae (see figure 12).

Figure 12 algae source: google.co.uk/search

Molinuevo-salces et al. (2012) methods will work in the same area as Ras et al. (2011).

Molinuevo-salces et al. (2012) added vegetal waste to anaerobic digestion of swine manure

with hydraulic retention times. This method helped in terms of methane production. It will

be incorporated into the design. The addition of vegetal waste is significant to the amount of

methane yield.

The method of Guo et al. (2011) will have a section of a digester that allows the starch

polyvinyl alcohol biopolymer insulated cardboard to be used which have environmental

benefits. The vital techniques that lead to the environmental benefits will be added to all

digesters in different areas.

http://www.google.co.uk/url?sa=i&rct=j&q=algae&source=images&cd=&cad=rja&docid=WnOiFaIF2YiC6M&tbnid=n8uywlIBk8ftzM:&ved=0CAUQjRw&url=http://www.algaeventurecapital.com/&ei=IgNfUcCiGY_RsgakwoDIAQ&bvm=bv.44770516,d.Yms&psig=AFQjCNH8Fl24AwUN-Vi3_DfgL5d6gWRbTw&ust=1365267602539848



Figure 13 S.D design (2013)

Figure 13 displays exactly how the design will work. The design requires 6 digesters in

different locations having the same end product which is biogas. The digesters include;

Zheng, Arsova, Li, Brown, Ras, and Guo.



Figure 14 Design process in Witness

The simulation diagram shown in figure 14 gives an indication of how the design will work.

Different feedstock placed in different pipes but in figure 13 as conveyors then it is moved to

various digesters to be processed and then made (see Table 3).



7. Results

A model simulation for the design was carried out using the WITNESS 12 manufacturing

software in order to give an interpretation of how the system will work. However the methods

and times used might be slightly different from the real world but gives a representation of

how the system operates. The quantity of biogas yield is difficult to specify with the

Simulation software used, but it is assumed that one biogas container produced is within the

range of 315-611 NI kg VS-1

(norm litre per kg of volatile solid) for mini digesters.

Confirmation from researchers and investigators recognize that the residence time relies on

the kind of feedstuff material, quantity of feed, the structure of the anaerobic digestion

system, and the type of stage used.

The type of digestion used in the design is the thermophilic and the mesophilic digestion.

P.Vindis et al. (2009) established that the thermophilic digestion is superior to the mesophilic

digestion; reporting 494 to 611 NI kg VS-1

biogas in thermophilic condition and 315-409 NI

kg VS-1

in mesophilic condition. Mesophilic is done under 350C and thermophilic is under

550C. The shortfall of thermophilic digestion is its relatively high energy consumption. See

figure 14 for the type of digestion and the time used for the design.

Table 2 presumed residence time

Duration Type of digestion

Days hours

14 336 Thermophilic

15-40 960 Mesophilic

27 648 Thermophilic & mesophilic



Table 3 sections of Digestion process

Area Feedstock Digestion type Cycle time (minutes)

Zheng Corn Stover Thermophilic 20160

Li Lignocellulosic Thermophilic 20160

Arsova Solid content Thermophilic & mesophilic 38880

Brown Waste paper Thermophilic & mesophilic 20160

Guo PVA Mesophilic 57600

Ras Algae Thermophilic 20160

A test run was carried out under 44640 minutes which is about a month’s time and cycle

times assigned to each digester (see table 3) and a reasonable warm up time of 30000. The

result can be seen in table 4 and a graph representation in figure 15

Table 4 results

Name No.

Entered

No.

Shipped

W.I.P. Avg

W.I.P.

Avg

Time

Sigma

Rating

corner_Stover 23 2 21 21.13 41008.7 6

Lignocellulosic 23 2 21 21.13 41008.7 6

Solid_content 22 1 21 21.06 42741.82 6

waste_paper 23 2 21 21.13 41008.7 6

PVA 22 1 21 21.06 42741.82 6

Algae 24 3 21 21.17 39370.83 6



Figure 15 quantity of biogas yield (using simulation)

Table 5 statistics of operations

Name % Idle % Busy % Blocked No. Of

Operations

Arsova_Area 0 100 0 1

Guo_Area 0 100 0 1

Brown_Section 0 96.77 3.23 2

Li_AREA 0 96.77 3.23 2

Ras_Area 0 96.77 3.23 2

Zheng_Area 0 96.77 3.23 2

Store 31.68 68.32 0 11

From table 5 it can be seen that the busiest digesters are the Arsova and the Guo digesters. It

also gives an indication of the number of operations done by each digester in a month (see

table5 & figure 16).

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

No.Entered

No.Shipped

W.I.P. AvgW.I.P.

Avg Time SigmaRating

corner_Stover

Lignocellulosic

Solid_content

waste_paper

PVA

Algae



Figure 16 statistics of blockd,busy,idle and no. of operation

Figure 16 shows the percentage of blocked and busy areas. Blocked does not mean the

process cannot continue but it has to wait for a part to be finished before it can push it to the

next stage.

0 0 0 0 0 0

31.68

100 100 96.77 96.77 96.77 96.77

68.32

0 0 3.23 3.23 3.23 3.23 0 1 1 2 2 2 2 11

Statistics

% Idle % Busy % Blocked No. Of Operations



8. Conclusion

Anaerobic digestion gives renewable energy generation. The end result of this research is

based on the findings from the objectives which are;

1. To provide an overview of anaerobic digestion.

2. To investigate the effect of anaerobic digestion to the environment.

3. To analyse the benefits of biomass for energy generation.

4. To explore opportunities to harness more energy from biomass through anaerobic

digestion.

The research has provided a general description of anaerobic digestion and the process

involved. The effect of anaerobic digestion to the environment as well as the benefits was

documented.

With the aim to enhance the capabilities of anaerobic digestion system to increase electrical

energy generation, a combination of ideas from eight previous researchers; Zheng et al.

(2009), Guo et al. (2011), Adu-gyamfi et al. (2012), Arsova (2010), Li et al. (2011),

Molinuevo-salces (2011), brown et al. (2012) and Ras et al. (2011) showed significant

results. The model was tested using the WITNESS 12 software with a run time of 44640

minutes for a month which produced a sum of 11 shipped (biogas produced) part with the

assumption that 1 shipped part is within the range of 315-611 norm litre per kg of volatile

solid (NI kg VS-1

). It produced a maximum of 6721 NI kg VS-1

per month and a minimum of

3465 NI kg VS-1

per month.

Though the result from the simulation gives an indication of the potentials the design has,

more study and practical work would be needed to understand how this would work in

practice.



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http://www.peatsociety.org/peatlands-and-peat/what-peat

http://epa.gov/climatechange/ghgemissions/gases/ch4.html

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11 Appendix

Appendix A

11.1 Ethics statement

Scholars in the Department of the Built Environment are not allowed to use, contact or

include people under the age of 18 years, vulnerable people, nor anything concerned with the

social services and the NHS, which includes but is not confined to buildings, staff, service

users, and administration.

I confirm that my investigation follows the declaration for Built Environment scholars. I

ratify that I have spoken with my supervisor regarding issues raised according to the

proclamation prior to commencement of gathering data.

This research did not involve human participants; and no human or animal parts were used so

no risk involved. All the information obtained during the research was properly referenced

and had approval. Information was acquired through books, journals, articles, online and

matters of privacy will be safeguarded wherever possible. There were no issues with

copyrights, and non-academic materials used were properly examined to an acceptable level

before it was used. The data protection Act 1998 was observed during this research; no

personal data was passed to a third party.

In terms of risk involved in gathering data; reducing the possibility of collating data that is

not up to date with the current state of anaerobic digestion system is necessary. The

information used during this research was recent findings of the process.

ETHICS REVIEW APPLICATION SHEET

You must tick to answer each of the following, sign and date this form at the end, and include

this form within your written submission.

Statement for Built Environment Students. Students in the Department of the Built

Environment are not permitted to use, contact or include people under the age of 18

years, vulnerable people, nor anything concerned with the social services and/or the

NHS, which includes but is not confined to buildings, staff, service users, and

administration.

YES NO

1. I confirm that my research conforms to the above statement for Built Environment students.

2. Does your research involve human participants including but not limited to any of the following –

interview, questionnaire, observation.



3. Does your research involve accessing personal, sensitive or confidential data, including information

about companies or technical information about products or services?

4. Does your research involve ‘relevant material’ as defined by the Human Tissue Act (2004)?

5. Does your research involve participants who lack capacity to consent and therefore fall under the

Mental Capacity Act (2005)?

If you have answered NO to question 1 above then you are not permitted to gather data until you have

formal ethics approval from the Faculty. Contact Barbara Vohmann for details. Please note you may

have to wait some time for this and cannot gather any data until you have received ethics approval.

If you have answered YES to either or both Questions 2 and/or 3, you must demonstrate that you have

designed into your work ways to deal with the issues raised, for example - keeping identities of people

and/or organisations confidential, data storage and security, sampling strategy and informed consent,

risk assessment.

If you answered YES to Q2 or Q3 or both of these then your supervisor must agree and approve prior

to your commencement of gathering data that your ethics statement addresses the issues raised.

If you have answered YES to either or both question 4 and question 5, you need to submit your

application to your FREP and an NHS Research Ethics Committee (REC), even if the study does not

involve the NHS. Please seek further advice if you are unsure about which committee it needs to be

submitted to.

I confirm that I have addressed with my supervisor any issues raised here prior to commencement of

gathering data.

Applicant’s signature:

Date:

All materials submitted to RESC/FREP will be treated confidentiall



11.2 Appendix B CV

Samuel David

193 Meadgate avenue

Chelmsford

Essex

CM2 7NJ

07831985241

[email protected]

Personal Profile

I am a mechanical engineering undergraduate with excellent IT skills and a good team

competitor. In pursuit of this, I seek working in an encouraging atmosphere to further

improve these skills and learn new skills to make impact in such roles.

Education and Qualifications

Current Education

2010 – 2013 BEng (Hons) Mechanical Engineering

Anglia Ruskin University, Bishop Hall Lane, Chelmsford, CM1 1SQ

Expected: 1st class

Modules Include:

Applied mechanics Materials and processes

Stress and dynamics Design method and technology

project

Computer aided Engineering Mathematics for technology 2

Project Management

Thermofluids

Statistics and project quality

assurance

Modelling and simulation for

operation management

Dissertation Topic: Increasing electrical energy generation from biomass through anaerobic

digestion

Previous Education

2010 Cambridge Ruskin International College

Foundation certificate in engineering

2007-2008 Rivers State College of Art and Science

Foundation in Electrical electronics engineering

2004- 2006 Immanuel international Secondary School



National examination Council degree

2004 Odegu community secondary school

West African examination council degree

IT Skills

Microsoft Office Packages. (Word, Excel, PowerPoint, Project)

Basic knowledge on CATIA Software.

Skilled at using ANSYS software.

NI Multisim software.

Skills and Achievements

Team Working and Leadership

Excellent organisation and communication skills obtained by working in group

projects throughout education, participating as both a team player.

Worked in a group to design a model in CATIA.

Participated in a buddy scheme.

Effective Communication

Confident in giving presentations, developed during university modules.

Got involved as a youth choir coordinator, which is basically working with the youth

choir and choosing songs then updating the youth president.

Work Experience

2012 Anglia Ruskin Employment Bureau - Various Temporary Assignments

Student Ambassador - attended a variety of University events helping visitors with

enquiries and giving course specific presentations.

Catering Assistant – Keeping the restaurant area clean and tidy, washing up and

taking payments.

Room audit-Taking records of the number of people in a room assigned.

2011 RCCG city of David Cambridge

Singing with the youth choir and being able to relate to members of the choir.

Working with the youth president concerning things involving worship.

2009-2010 Samevedor Nigeria Limited

Recording office expenditure and managing the budget.

Paying workers.

Interests

Music.



Football.

Referees

Available on request

11.3 Exit plan

Module Skills developed Skills gap /

reflection

Proposed self-

development with

completion date

MOD002656

Computer

Aided

Engineering

CAE industry

understanding on

analysis,

manufacture and

test of a simple

component.

Ability to use

Ansys software to

test materials by

putting a force on

it.

Module finished in 4

months in Anglia

Ruskin University

(2012/3 Sem1)

EJ215047S

Applied

mechanics

Mathematical

approach on shear

force and bending

moment diagrams

beams.

Free body diagram Gained knowledge of

relating results of

calculation to real

life. (2011/2)

EJ230017S

Materials and

Processes

skills of using

equilibrium

diagrams as an aid

in predicting the

structures of binary

Understanding the

behaviour of

polymers and

specific welding

defect

Relating the

knowledge gained to

apply to other

materials. (2011/2)

MOD002668

Stress and

Dynamics

Application of

engineering

mechanics.

Understanding of

damped vibration.

Practice the

knowledge obtained

in real life.

(SEM1-2012/3)

MOD002385

Major project

Developed research

and study skills in

analysing,

reviewing and

managing research

Ability to compile

different

information and

putting it together.

Practice knowledge.

8 months

(2012/3)



and literature data.

MOD0022684

Thermofluids

Optimistic about

developing

understanding in

fluids or gases with

temperature

changes and

chemical reactions.

Expectation on the

ability to work

with natural gas

engines.

Practise and research.

(SEM2-2012/3)

MOD002665

Modelling and

simulation for

operations

Management

Positive on

increasing my

knowledge in

making models

statistically to

develop a data for

making technical

decisions.

Ability to make

models and making

managerial

conclusions.

Applying knowledge.

(SEM2-2012/3).

MOD002666

Project

management

Developed

understanding of

the functions,

activities and

techniques of

project management

Program evaluation

technique.

Applying the

knowledge gained in

the real world. (SEM

1- 2012/3)



11.4 Proposal

WORKING TITLE

The effect of anaerobic digestion on how to extract electricity

Rationale

Considering outside developing the technologies that allows solar and wind energy, we can

also look at using advanced materials to generate electricity. The subject of this proposal

developed from the interest of using alternative means to generate energy. Biomass is plant

matter used to generate electricity. Anaerobic digestion is a type of biomass system. In south-

eastern United States, biomass technology is already leading the region’s renewable power

potential.

Anaerobic digestion is the breakdown of organic materials into methane, carbon dioxide gas,

and fertiliser in the absence of air. Anaerobic digestion contributes to the reduction of

greenhouse gases. This research focuses to study the effect of anaerobic digestion on how to

extract electricity.

Problems involved with anaerobic digestion have potential negative environmental impact,

capital and operational costs. The possibility of problems involved needs to be removed

wherever possible.

Aim

To develop a framework on how to extract electricity from anaerobic digestion

Objectives

To provide a general overview of anaerobic digestion.

To investigate the effect of anaerobic digestion to the environment.

To analyse the benefits of biomass for energy generation.

To develop a framework on how electricity is created.



Methodology

This research project will begin with the literature review giving an overview of what

biomass is and the effect it has on earth. The questionnaire comes next; taking into account

that keeping identities of people or organisations should be confidential, and data storage,

risk assessment also. The next stage will be to talk about a possible design that could improve

anaerobic process after analysing the questionnaire, then conclusion, introduction and

abstract.

Proposed content of dissertation

Chapter 1: Introduction

Chapter 2: Literature review

Chapter 3: Research design and methodology

Chapter 4: Chapter 5: Ethics Statement

Chapter 5: Analysis of results

Chapter 6: Conclusion

Chapter 7: References



REFERENCE

Adu-gyamfi, N., Ravella, S.R., Hobbs, P.J.,2012. Optimizing anaerobic digestion by selection

of the immobilizing surface for enhanced methane production, 120,Bioresource

Technology,pp.248-255.

“Anaerobic digestion.” Clean water Report 29 Nov.2004:239. Academic Onefile. Web.10

Oct.2012.

Fang, H. , 2010. Environmental Anaerobic Technology: applications and new developments.

London. Imperial College press.

Fantozzi, F., Buratti, C., 2011. Anaerobic digestion of mechanically treated OFMSW:

Experimental data on biogas/methane production, Bioresource Technology, 102(19),pp.8885-

8892.

Kelleher, M. , 2007. Anaerobic Digestion outlook for MSW Streams. BioCycle, 48(8), p.51.

Lo, F.C., Lo,S.w., Chiu, H.Y, Lo,H.M, 2012. Effects of different SRT on anaerobic digestion

of MSW dosed with various MSWI ashes,125, pp.233-238.

Laclos, F. de, Desbois, H.S. & Saint-Joly, C., 1997. “ Anaerobic digestion of Municipal Solid

Organic Waste: Valorga full-scale plant in Tilburg, NL”. Water, Science Technology, 36(6-7)

pp.457-462.

Lim, S.-J. et al . , 2008. “Anaerobic organic acid production of food waste in once –a-day

feeding and drawing –off bioreactor”. Bioresource Technology, 99, pp.7866-7874.

Lusk, P., 1999. "Latest Progress in Anaerobic Digestion". Biocycle, 40.

Novarino, D., Zenetti, M.C., 2012. Anaerobic digestion of extruded OFMSW, 104,pp.44-50



11.5 Assessment sheet

DSD Dissertation May 2013

Documents

anaerobic digestion

department of engineering

original work

built environment department

major project

candidates signature

electronic format

valued advice