investigation of operating conditions for optimum biogas …495485/fulltext01.pdf · anaerobic...

Master of Science Thesis KTH School of Industrial Engineering and Management

Energy Technology EGI-2009-2011 Division of xxx

SE-100 44 STOCKHOLM

Investigation of Operating Conditions for Optimum Biogas Production in

Plug Flow Type Reactor

K.U.C. Perera

Abstract Biogas is a sustainable alternative for fossil fuels. This also provides a solution to bio wastes. There are various designs for the efficient production of biogas. Majority of biogas generation units use animal wastes as feed material. Plug flow type biogas digester was identified as more suitable for using non conventional feed stocks like green vegetations, municipal waste for the biogas production. These digesters have been reported to be more efficient in converting feed stocks with higher total solids content. The aim of this study was to investigate the variables associated with plug flow biogas digesters and to determine the operational parameters that will give optimum biogas production. In the study three feed rates were used. The highest specific methane production of 0.341 m3/kgVS per day was observed at feeding rate of 1.4kg per day. Highest VS reduction of 91.37% was observed at feeding rate of 1.4 kg per day. VFA profile and pH profile along the digester length showed the distribution of biogas production stages along the length of the digester especially at lower feed rates.

Master of Science Thesis EGI 2009:2011

Title Investigation of Operating Conditions for Optimum Biogas Production in Plug Flow

Type Digester

Name K.U.C.Perera

Approved

Date Examiner

Name Supervisors

KTH: Joseph Olwa OUSL: Dr. Gamini Kulathunga

Prof. Torsten Fransson

Contact person

Table of Contents

Abstract ii

Index of Tables ........................................................................................................................................................ iii

Index of Figures ....................................................................................................................................................... iv

Nomenclature ............................................................................................................................................................ v

Chapter 1: Introduction 1

1.1 Brief History ........................................................................................................................................................ 1

1.2 Biogas generation Process ................................................................................................................................. 1

1.3 Parameters affecting anaerobic digestion ....................................................................................................... 2 1.3.1 Total solid content ...................................................................................................................................... 2 1.3.2 Temperature ................................................................................................................................................ 2 1.3.3 Particle size .................................................................................................................................................. 3 1.3.4 Retention time ............................................................................................................................................. 3 1.3.5 Inoculums .................................................................................................................................................... 3 1.3.6 pH ................................................................................................................................................................. 3 1.3.7 Alkalinity ...................................................................................................................................................... 4 1.3.8 Carbon to Nitrogen ratio ........................................................................................................................... 4 1.3.9 Organic loading rates ................................................................................................................................. 4 1.3.10 Additives and inhibitors .......................................................................................................................... 4

1.4 Benefits and uses of biogas ............................................................................................................................... 5

1.5 Types of processes ............................................................................................................................................. 5 1.5.1 Classification by the way material is fed .................................................................................................. 5 1.5.2 Classification by operating temperature .................................................................................................. 7 1.5.3 Classification by fluid flow pattern .......................................................................................................... 7 1.5.4 Classification by biochemical change of feed stock .............................................................................. 8 1.5.5 Other classifications ................................................................................................................................... 8

1.6 Problem identification ....................................................................................................................................... 9

1.7 Objectives ............................................................................................................................................................ 9

Chapter 2: Literature review 10

2.1 Problems and difficulties in the existing plug flow digesters ....................................................................11

Chapter 3: Methodology and Experimental Set up 12

3.1 Experimental setup ..........................................................................................................................................12

3.2 Initial preparation .............................................................................................................................................14

3.3 Analytical procedure ........................................................................................................................................15 3.3.1 Total solids content ..................................................................................................................................15 3.3.2 Volatile solids content ..............................................................................................................................16 3.3.3 Chemical oxygen demand........................................................................................................................16 3.3.4 Volatile fatty acids.....................................................................................................................................16

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3.3.5 PH ...............................................................................................................................................................16 3.3.6 Gas composition .......................................................................................................................................16 3.3.7 Specific methane production ..................................................................................................................17 3.38 Volatile solids reduction ...........................................................................................................................17

Chapter 4: Results and Analysis 18

4.1 Gas volume and composition.........................................................................................................................18

4.2 pH variation of effluent ...................................................................................................................................23

4.3 VFA variation along the digester length .......................................................................................................25

4.4 Effluent COD ...................................................................................................................................................28

4.5 Process performance........................................................................................................................................29

Chapter 5: Discussion 31

Chapter 6: Conclusion 33

Bibliography 34

Annexure I Gas collection data 33

Annexure II Gas composition data 39

Annexure III pH Data 40

Annexure IV VFA Data 41

Annexure V COD Data 44

Annexure VI Data for TS and VS Determination 45

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Index of Tables

Table3.1: Feedstock characteristics 15

Table3.2: Feeding plan 15

Table 4.1: Daily average biogas production 18

Table 4.2: Composition variation of biogas for feeding rates of 3kg per day and 1.4kg per day in Digester 1 22

Table 4.3: Composition variation of biogas for feeding rate of 6kg per day in Digester 2 22

Table 4.4: pH Variation of effluent for three feed rates 23

Table 4.5: VFA variation along the digester length for feeding rate of 1.4kg per day in digester 1 25

Table 4.6: VFA variation along the digester length for feeding rate of 3 kg per day in digester 1 25

Table 4.7: VFA variation along the digester length for feeding rate of 6kg per day in digester 2 27

Table 4.8: Effluent COD variation for three feed rates 28

Table 4.9: Process performance 29

Table 5.1: Comparison between similar studies done in plug flow digesters 31

Table 8.1: Gas volume data 38

Table 8.2: Gas composition data 31

Table 8.3: pH data 40

Table 8.4: Titration volume data for 3kg per day 31

Table 8.5: Titration volume data for 1.4kg per day 42

Table 8.6: Titration volume data for 6kg per day 43

Table 8.7: Effluent COD data 44

Table 8.8: Feed stock TS and VS data 45

Table 8.9: Effluent TS and VS data 46

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Index of Figures

Fig. 1.1: Batch type Digester 5

Fig. 1.2: Semicontinuous Digester 6

Fig. 1.3: Continuous Digester 7

Fig. 3.1: Diagram of the Digester 12

Fig.3.2: Digester 1 13

Fig. 3.3: Digester 2 13

Fig.3.4: Inlet of the digester 13

Fig. 3.5: Gas Holder 14

Fig. 4.1: Daily average biogas production in Digestor 1 19

Fig. 4.2. Composition Variation of biogas for feed at 3kg/day and 1.4kg/day feed rates in Digestor 1 21

Fig. 4.3: Composition variation of biogas at feed rate 6kg/day in Digester 2 22

Fig. 4.4: Variation of effluent pH for different feed rates 24

Fig.4.5: VFA variation along the digester length for feeding rate of 1.4kg per day in Digester 1 26

Fig. 4.6: VFA variation along the digester length for feed rate of 3kg/day in Digester 1 27

Fig. 4.7: VFA Variation along the digester length for feed rate of 6kg/day in Digester 2 25

Fig 4.8: COD variation of effluent for different feed rates 29

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Nomenclature

COD Chemical Oxygen Demand mg/l DBR Dry Batch Reactor GHG Green House Gas HRT Hydraulic Retention Time NERDC National Engineering research and Development Centre n.d. no date OLR Organic Loading Rate TS Total Solids (%) VFA Volatile Fatty Acids mg/l Vo Average daily methane production m3/d VS Volatile Solids (%TS) VSin Volatile Solids in feedstock (%TS) VSout Volatile Solids in effluent (%TS) VSR Volatile Solids Reduction (%) W Weight of daily feedstock added (kg)

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Chapter 1: Introduction

With the fast depletion of non-renewable energy sources and high prices, investigation of all possible alternative energy sources especially the renewable energies such as solar, biomass, and wind has been increased. In most developing countries biomass waste is abundant source of energy, which can be utilised to generate energy and to produce manure for agriculture as a by product.

Biogas is generated by anaerobic digestion of organic matter. It is composed of methane and carbon dioxide (Goswami, n.d.). Organic matter refers to agricultural residues, manure, and garbage and sewage waste. They originate from wide variety of sources spread throughout the world. Since they can be derived from relatively recently living material than fossil fuel, they are sustainable.

1.1 Brief History

There are records that biogas was used by Assyrians and Persians for heating water (Lusk, 1998). Marco Polo in his records mentioned that he had seen covered sewage tanks in China although it is not clear whether they have utilized the gas (Ding, et al., 2010). Alexander Volta identified the presence of methane in marsh gas (Wellinger, n.d.). Sir Humphrey Davy identified methane exists in the gas generated by anaerobic digestion of manure [Lusk, 1998]. In Europe the biogas generation was promoted during First World War and Second World War times as a solution to the fuel deficits (Lusk, 1998). The biogas technology started to spread in India by 1950 in rural household applications (Wargert, 2009). The first monograph on biogas was published in China in1935, which was the first publication on biogas in the world (Xiaodong, 2009). Following that in 1958 campaigns to promote the multiple uses of biogas helped the popularization of the technology in China (Lee, 2008). Biogas technology was supported by the government of China as they have identified importance of the technology for rural development. According to Sri Lanka Standards Institution (1292:2006), Continuous type digesters are found in Sri Lanka by 1960.

1.2 Biogas generation Process

Anaerobic digestion is the decomposition of complex organic compounds to simple matter by the micro-organisms. This process occurs in three major steps: hydrolysis, acidogenesis, and methanogenisis.

In hydrolysis aerobic micro-organisms convert complex organic compounds to simple forms which are soluble and can be consumed by the micro-organisms. Polysaccharides are converted into monosaccharides, lipids to fatty acids, proteins to amino acids and neuclic acids to purines and pyrimidines.

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In Acidogenisis facultative and obligate anaerobic micro-organisms convert the low molecular weight products from the first stage to lower molecular weight intermediate compounds of volatile fatty acids, alcohols, carbon dioxide and hydrogen.

The final step is the methane formation step where the anaerobic methanogen converts the acetic acids in to methane or reduce carbon dioxide by hydrogen to form methane. The basic chemical equation for anaerobic digestion of organics can be presented as below (Goswami and Kreith, 2007:

Organic matter+H2O+Neutrients new cells +resistant organic matter+CO2+CH4+NH3+H2S+heat ) (Goswami and Kreith, 2007)

1.3 Parameters affecting anaerobic digestion

1.3.1 Total solid content

Total Solid content for anaerobic digestion can be divided into three ranges. Low solids content refers to systems with Total Solids content less than 10% [Monnet, 2003]. Medium solids content refers to Total Solids content between 15-20% and High solids content refers to Total Solid content in the range of 22-40% (Monnet, 2003). Higher Total Solid content requires smaller digester volume due to lower water content.

1.3.2 Temperature

Anaerobic digestion takes place at two different temperature ranges.

Mesophillic condition 20-45 o C(Monnet,2003)

Mesophillic bacteria have lower metabolic rates. Mesophillic digestion requires longer retention times. But they are more robust to the changes in temperature. They are able of producing good quality effluent (Ostrem, 2004)

Thermophillic condition 50-65 o C(Monnet,2003) The fermentation is more efficient at the higher temperature process (Chengdu biogas research

institute, 1992). Destruction of pathogens is more efficient at thermophillic temperatures (Goswami, n.d.). The micro-organisms are sensitive to changes of temperature as smaller as 5oC (Chengdu biogas research institute, 1992).

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1.3.3 Particle size

Particle size affects the rate of reaction. The smaller the particles size the more the reaction rates due to increase in surface area. This increases the gas generation rate and reduces the amount of residue, which in turn reduces the digestion time. The particle size reduction allows the suspension of the particles that lowers the settling time and subsequently the flow of particles with the fluid.

1.3.4 Retention time

Retention time is the time needed for complete degradation of the organic material. This depends on the composition of the feedstock, temperature, pH and number of other variables which affect the anaerobic digestion process. Higher TS content in feed increases the retention time while favourable temperature ranges decreases the retention time. The smaller the particles size the shorter the retention time due to high reaction rates.

1.3.5 Inoculums

Micro-organisms produce biogas by digesting the organic compounds. Sufficient quantities of micro-organisms are needed for successful biogas production. Amount of micro-organisms in fresh material is below the required quantity of microbes. Therefore sufficient inoculums must be added at the starting of the process. The sources of micro-organisms affect the biogas production. Different types of micro-organisms have different capabilities in digesting particular type of material. By applying suitable cultures efficient biogas production can be achieved. Bacterial cultures can be obtained from cattle manure, sewage waste, and other biogas producing facilities or artificial cultures.

1.3.6 pH

The optimum pH values for the anaerobic digestion are in the range of 6.4 – 7.2. The optimum pH for methanogens is 6.6 -7.0(Monnet, 2003).Growth rate of methanogenic bacteria is slower than the acidogenic bacteria. At lower pH values and higher feed rates the growth rate of acidogenic bacteria increases. Therefore acid formation during acidogenisis reduces the pH of the medium and inhibits the methanogenisis process.

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1.3.7 Alkalinity

Alkalinity is the ability of the digestion medium to absorb protons or capability in neutralizing the excess acidic or basic conditions. Calcium carbonate is used as a buffer substance in digestion process and also used to indicate the alkalinity of the medium.

1.3.8 Carbon to Nitrogen ratio

For effective anaerobic digestion carbon to nitrogen ratio should be maintained between the range 20 -30(Chengdu biogas research institute, 1992). Lower C: N ratio causes ammonia accumulation in the digester and inhibits micro-organism activities. Higher C: N ratio causes lower gas production. Different types of material are mixed together to maintain the optimum C: N ratio of the feedstock.

1.3.9 Organic loading rates

Organic Loading Rate (ORL) shows the ability of a system to convert the feed stocks to end products. Exceeding the allowable OLR causes formation of inhibitors in the digester and may cause failures in the digestion process.OLR is either expressed as Chemical Oxygen Demand or Volatile Solids per unit volume of reactor. For a given feed stock and a reactor volume COD and VS related with retention time.

1.3.10 Activators and inhibitors

Activators can enhance the biogas production while inhibitors can reduce the biogas production. Activators or inhibitors are added in small amounts in order to enhance or reduce biogas production in digesters, respectively. These substances can be enzymes from organic or inorganic compounds. Leaves of plants, legumes and microbial cultures are examples of additives which are used for enhancing biogas production. Leucacena leucocephala, Acacia auriculiformis, Dalbergia Sisoo were reported in literature as enhancing agents of biogas production (Kohil, et al., 2004). Microbial cultures like actinomycetes and mixed consortia were reported as enhancing biogas production with cattle dung. These cultures stimulate enzymatic activities which produces biogas. Inorganic compounds that enhance biogas production are iron salts like FeCl3 and FeSO4, and heavy metals (Goswami, n.d.; Kohil, et al., 2004). Adapted micro-organisms can endure the effects of inhibitors and can avoid the effects on biogas production.

Some of the inhibitors which affect the biogas production are light, disinfectants, hydrogen sulphide and ammonia. These compounds affect the biogas production negatively when presents in higher concentrations [SEAI, www.seai.ie/Renewables/Bioenergy/Anaerobi./].

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1.4 Benefits and uses of biogas

Biogas is used in the following applications

Heating Lighting Electricity Generation Motor Fuel

The following are the some of the benefits of the biogas

Sustainable energy source Waste Management Reduce green house gas emission and other gas emissions which cause climate change Carbon neutral energy source Valuable by-product generation Reduce fossil fuel usage Rural development

1.5 Types of processes

1.5.1 Classification by the way material is fed

Batch –Fed Digestion

Material fed into the digester at a time and sealed only allowing the gas to exit. When the digestion is completed the residue is taken out and the next batch can be fed. Biogas generation volume varies with time for this type of reactor, but it requires less control when the process is implemented correctly.

Fig.1.1: Batch type digester (SLSI, 2006)

Man hole

Slurry

Gas outlet

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Semi- Continuous Digestion In this process a quarter to half of the total solids of the material inside the digester, during whole digestion process, is fed at the start-up of the digestion process. During the digestion process fresh material is fed and some digested material is taken out, intermittently. Fermented material remaining in the digester, without being removed can be taken out after sometime of operation and feeding can be started from the beginning. The biogas production is steady in this type of digesters. Start up process and discharging is labour intensive for this type of digesters. The biogas units mainly used in China is considered to be semi continuous type. This is used to digest other residues than manure. The straw is fed when the batch is loaded and the manure can be fed daily. Digested material can be withdrawn once in six months and the next batch can be loaded (Nijaguna, n.d.).

Fig.1.2: Semi continuous digester (SLSI, 2006) Continuous Fermentation After starting the operation of the digester regular quantity of material is fed continuously and same quantity of digested material is discharged. Quantity and quality of the fluid remains stable and the biogas production is also stable. This technology is suitable for both medium and large scale waste treatment and large scale biogas production. The floating dome type biogas digesters in India is considered equivalent to this type due to continuous sludge removal.

Level

Outlet

Gas outlet Man hole

Slurry

Level

Inlet pipe

Inlet pipe Outlet

Gas outlet Man hole

Slurry

Level

Inlet pipe

Inlet pipe

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Fig.1.3: Continuous digester (Prabhu and Stalin; 2007)

1.5.2 Classification by operating temperature

Constant Temperature Fermentation In this type of process the temperature of the working medium is kept constant. Therefore the biogas yield is stable. Water circulation jackets with heaters, insulation and passive solar heating can be used for maintaining constant temperature (Ostrem, 2004)

Ordinary Temperature Fermentation In this process temperature of the working medium changes with the air temperature or earth temperature and this process does not require control of temperature.

1.5.3 Classification by fluid flow pattern

Unstirred and Stratified Fluid Flow When the material is fed and not stirred it settles in three layers irrespective of whether the material is homogeneous or heterogeneous. When the material stratifies micro-organisms can only utilise nutrients in the near vicinity. Micro-organisms face the difficulty of utilising the nutrients away from them. The residue at the bottom occupies more of the inside space of the digesters. This will reduce the gas yield. To replace the residue entire material has to be removed.

Mixing pit

Inlet pipe

Floating Gas holder

Mixing pit

Floating Gas holder

Partition wall

Slurry

Outlet

Level

Gas outlet

Mixing pit

Floating gas holder

Inlet pipe

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Mixed Flow In this process material is well mixed by a stirrer. Therefore material and micro-organisms are well mixed and get contact with the feed. The gas formation is rapid and biogas yield is high. These types of digesters are used for large scale application where animal wastes and urban sludge is treated.

Plug Flow Theoretically material does not mix in the vertical direction. Digested material is pushed forward by the fresh material fed into the digester. This process gives more uniform retention times for the materials fed to the digester. Actual operation is rather complex and different.

1.5.4 Classification by biochemical change of feed stock

One Phase Digestion All the phases of fermentation; hydrolysis, acidogenisis and methanogenisis happens inside a single digester. In this type of digestion biogas yield per reactor volume and per unit mass of the feed stock is lower than for two phase digestion since acid production can affect the methane production phase.

Two Phase Digestion

Hydrolysis and acidogenis phases are carried out in a separate digester which is well mixed or a plug flow type digester. Methanogenisis phase is carried out in another type of digester like sludge blanket digester or anaerobic filter which are highly effective for the methanogenisis process. This gives more biogas yield per reactor volume and per unit mass of the feed stock.

1.5.5 Other classifications

Some of the other classifications of the digestion process are based on mode of growth of micro- organisms, concentration of the material, and number of digesters connected in the process. Digesters used in practice have a number of above mentioned features integrated in their operation. Therefore they cannot be categorized into the basic classifications.

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1.6 Problem identification

Great potential exists in the Sri Lanka for biogas generation and it is one of the sustainable solutions for the waste disposal problem in the country, for rural development of the country and reduction fossil fuel imports. First biogas digesters introduced were continuous flow type digesters. Continuous flow biogas reactors require regular water supply and is preferred for animal and human wastes. Considering these facts a new biogas digester was developed by National Research and Development Centre of Sri Lanka which is called as Dry Batch Reactor (DBR). The preferred material for Dry Batch biogas digesters are straw and animal waste. The moisture content of the input material should be more than 85% while for the continuous type digester solid content should be 9 to 10% (SLSI, 2006). Disadvantages of the dry batch system are difficulty in loading and unloading and bio sludge in larger digesters, unstable gas generation rate and the long operating periods. Several parameters affect the optimum performance of plug flow type biogas plants. However, no well established information is available for optimum operation of these types of biogas plants; hence the use of plug flow type has been neglected in compared to other types. Chanakya, et al. (2004) mentioned the failures in converting other types of biomass into manure like slurries for biogas production. This reason has led them to introduce two designs for the successful use of other types of biomass for biogas production. They are plug flow digesters and solid state stratified bed digesters (Chanakya, et al., 2004). The plug flow type digester has been used to deal with wastes like green leaves and other floating type vegetations which are not generally fed to the other continuous type or batch type digesters. Plug flow reactor is capable of transforming more organic solid waste into biogas. They are capable of converting feed stocks with Total Solids content of 11-14 % (Natural resources conservation service, 2004). There is no longitudinal mixing in ideal plug flow digesters. When the new manure is added the previous feed stocks move in plugs towards the outlet. Operation of plug flow digesters has rather complex behaviour than described above. Some of feed stock will travel faster than the others, and some will settle in the digester (Graves, et al., n.d.). There are a number of installations of plug flow reactors in the country with some having two phase installation design and others using effluent recirculation method. Identification of issues related to performances of these digesters is important for optimum utilization of feed stock resources and of the biogas produced. This will guide the path to sustainable use of bio energy.

1.7 Objectives

Objective of this study is to establish the operating conditions for optimum biogas production for different feed rates for food waste in plug flow type biogas digester.

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Chapter 2: Literature review

Kalia (1988) compared the performance of a plug flow type digester with a Janata biogas digester. Janata type digester is a unit which operates on semi continuous digestion principle and where the gas is collected in the digester itself under a fixed dome. He observed that plug flow type produces 16% more biogas than the Janata type digester. He also studied that gas production rate per unit of effective digester volume in plug flow reactor was 30% higher than for Janata type reactor. He also identified that plug flow type digester was less subjective to climate variation and has slightly higher temperature in winter season to produce more biogas.

In 1998, Anand et al. from Indian Institute of Science Bangalore has studied the suitability of plug flow type digesters for biogas generation from leaf biomass. Their aim was to develop suitable biogas digesters for other types of biomass feed stocks like municipal solid waste and leaves, except animal dung. Simple pre treatment methods for floating biomass types were discussed. They used clay as binder to increase the bulk density and made into briquettes as a solution to the floatation.

Ghosh and Liu (1998) studied phase separation during anaerobic fermentation of solid substrates in an innovative plug flow reactor. They stated that they used unmixed plug flow reactor which had zigzagging parallel channels with floors sloping towards the outlet. Slurries with 3-10% solids content were used as feed stocks. They conducted steady state runs at hydraulic retention time of 13 to 32 days at organic loading rates of 6.84 - 0.84 kgVS/m3d. They observed phase separation first when the organic loading rate was2.05 kgVS/m3d. Under this condition longitudinal variation of pH and Volatile Fatty Acid profiles showed lowest pH of 6.1 and highest Volatile Fatty Acid content of 1500mg/l. At this loading rate they observed acidogenic phase within the first 50cm from the inlet while the rest of the reactor was dominated by methanogenic phase. At an organic loading rate of 6.84 kgVS/m3d acidogenic phase was observed extending to 83 cm from the inlet. At this condition pH dropped to 4.4 and the Volatile Fatty Acid content of 9600mg/l. Chanakya et al. (2004) studied the use of anaerobic digestion technology for other types of biomass feed stocks as a solution for the limited availability of animal dung. Their solutions were based on the understanding of the underlying process of biomass fermentation. They proposed two designs, plug flow digester and solid state stratified bed digesters which are suitable for other types of biomass feed stocks. They have also discussed the adaptation techniques in order to optimize the uses of biogas technology for socio economic benefits and the numerous uses of biogas production.

Plug flow digesters have the ability to treat ruminant manure with 11-14% Total Solids and for other manure types with 8-14% Total Solids (Natural resources conservation service, 2004). The digester retention time is mentioned as between 15-20 day for manure (Lamb and Nelson, 2002). In Some literature it is recommended that retention time should be more than 20 days (Natural resources conservation service, 2004). Length to width ratio of the digester flow path should be in the range of 3.5:1 to 5:1for manure (Natural resources conservation service, 2004). The ratio of the flow path width to depth should be less than 2.5:1(Xiaodong, 2009). Plug flow digesters are fabricated from concrete, steel, fibre glass or Poly Vinyl Chloride (Bordas, et al., 1981).

The plug flow digesters have shown their suitability to treat feed stocks with higher solid content. Plug flow digester is a simple design. It can process material like food waste, municipal solid waste and agricultural residues. Plug flow digester was shown higher gas production rate per unit of effective digester

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volume than other types of digesters (Kalia, 1988).This design has the ability to take the maximum use of such resources while contributing to the fulfilment of energy needs of the country. Better understanding of the process and relation between process parameters in the plug flow digester is required for the effective operation of the digestion process.

2.1 Problems and difficulties in the existing plug flow digesters

Issues related to plug flow digesters are as follows Leakages Many of the plug flow digesters are prone to leakages of both material and gas. This can be prevented by careful construction practices. Blockages Blockages may be due to unsuitable, indigestible material. These materials can block the inlets and outlets of the digester. The water vapour in the gas condenses and blocks the gas flow. Blockages can be prevented by paying attention to good operation practices. Structural Stability The digester structure is subjected to pressure from the earth from the outside surface and gas pressure and hydrostatic pressure from the inside. Plug flow digesters are longer than other digester types. Therefore special attention should be paid in the construction for structural stability of the plug flow digester. Interruption at Higher Feed Rates When the amounts of feedstock fed to the digesters are increased the micro-organisms cannot tolerate the increment in load and cause failures. Unexpected substances The feedstock fed to the digesters may make the fluid acidic, basic or poisonous depending on the composition of the material. Appropriate measures should be taken to restore the system to normal condition. Value addition to effluent Effluent from the plug flow digesters has a higher nutrient value as organic fertilizer. In some installations this effluent is merely disposed to the environment. This has higher economic value and a market potential.

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Chapter 3: Methodology and Experimental Set up

In order to evaluate the effect of feed rate on biogas production qualitatively and qualitatively, three feed rates were used. The feed rates used in kg/day were 1.4, 3, and 6.

3.1 Experimental setup

Plastic barrels commonly available in the local market were used for the fabrication of the digester. Diameter of these barrels is 0.47m which facilitates mounting and space requirement to keep the unit. Three barrels were fixed together considering the structural stability and the feasibility in supporting. The length of the digester was 1.58m. The length to width ratio was closer to 3.5:1. This satisfies the length to width ratio defined for manure based on the plug flow digesters (Natural resources conservation service, 2004). Hence the dimensions and volume of the digester are: The diameter of the digester = 0.47 m Length of the digester =1.58 m The digester volume ≈ 0.27 m3 Working volume ≈ 0.188 m3 The inlet of the digester was fabricated with a PVC pipe of diameter 11cm. The digester had three windows to observe the inside flow of digestion medium. Three sampling ports were placed in order to facilitate sample the withdrawal.

Fig. 3.1: Diagram of the Digester The gas holder was fabricated with another two plastic barrels both of which have one end opened. One barrel was filled with water and other which has an inlet and an outlet is dipped in the water. Two plastic tubes of diameter 12.74 mm are used for inlet and outlet. The gas produced in the digester flows to the holder and lifts it up. The produced gas amount can be estimated by the diameter of the barrel and the height of the holder that lifts up. The schematic diagram of the digester is shorn in Fig. 3.1. Two digesters of the same dimensions were fabricated in order to carry out two parallel tests with two loading rates simultaneously.

Gas Collecting Holder

Gas Outlet

OutletInlet

01 02 03

Sampling Ports

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Fig.3.2: Digester 1

Fig. 3.3: Digester 2

Fig.3.4: Inlet of the digester

Inlet

1 2 3

Sample Ports

Gas Outlet

Gas Holder Manometer

Inlet

Gas Holder Manometer

Sample Ports

Inlet Gas Outlet

1 2 3

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Fig. 3.5: Gas Holder

3.2 Initial preparation

Anand et al. (1998) in his research used leaf biomass 50kg/day for 5m3 digester initially and then increased to 100kg/day. The digester 50m3 for market garbage treatment designed by Sustainable Energy Authority which was intended to feed 1000kg/day was able to treat 500kg/day at operating conditions. The plug flow digesters developed by the NERDC of Sri Lanka has the capacity to treat 10kg/day for one cubic meter total volume of the digester. Daily feed stock allowed for the total volume of digester is taken as 10 kg per day per 1m3 total digester volume. The digester volume = 0.27 m3 Therefore daily feed stock = 10 x 0.27

= 2.7 kg per day ≈ 3.0 kg per day Therefore, feed rate of 3kg was selected first feed rate. 1.4kg is selected as the lower value from 3kg and 6kg was selected as other higher value from 3 kg. Operating time = 20 days For the bacteria culture to grow initial preparation of the digester should be done. This was done by feeding cow dung for seven days. The feeding rate of food waste was increased in steps in order to achieve the expected feeding rate and to avoid the acidification. The feed stocks were ground into smaller sizes using a domestic grinder to reduce the particle size. Calcium carbonate was used for the pH adjustment. Temperature variation during day time was between 28oC-31oC Composition of feed stocks for 1.4 kg per day in digester no 01: Food waste 350g Vegetables residue 700g Fruit waste 50g Water 300g Composition of feed stocks for 3kg per day in digester no 01: Food waste 450g Vegetables residue 900g Fruit waste 50g Water 1600g

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Composition of feed stocks for 6kg per day in digester no 02: Food waste 900g Vegetables residue 1800g Fruit waste 100g Water 3200g

Table3.1: Feedstock characteristics

Digester 01-1.4 kg per day Digester 01- 3kg

per day Digester 02 – 6kg

per day

Average T S Content (%) 16.1 5.7 5.7

Average V S Content (% VS) 93.3 92.3 92.3

Table3.2: Feeding plan

Digester No. Loading Rate (kg/day) Organic Loading

Rate(kgVS/m3day) Operating Time

(days)

01 1.4 1.12 20

01 3.0 0.83 20

02 6.0 1.67 20

3.3 Analytical procedure

The experiments were conducted during steady period of operation. Feed stocks were analysed for, TS content and VS content. The material discharged from the outlet was in liquid form. Effluent was analysed for COD, pH, TS, VS content. Material obtained from three sample ports along the digester length was tested for VFA content. Daily produced gas quantity was measure from the height of the gas holder that lifts up. The gas composition was analysed daily.

3.3.1 Total solids content

Percentage of solids was determined by heating known weight of the sample in a pre weighted crucible in a convection oven at 105oC for about 12 hours until constant weight is reached. Samples were cooled in a desiccators and final weight of the sample was measured (Clesceri, et al., 1998). W0- Weight of dish W1 – Weight of wet sample +dish W2 – Weight of dried sample+ dish % Total Solids =

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3.3.2 Volatile solids content

Samples analysed for total solids content was used for total solids determination. Weighted sample was heated in a muffle furnace at 550oC for 30 minutes. Samples were cooled in a desiccators and final weight of the sample was measured (Clesceri, et al., 1998). W3 - Weight of sample +dish after drying % Volatile Solids =

3.3.3 Chemical oxygen demand

The effluent samples were digested in Potassium Dichromate in Acidic medium and placed in the digester at 150oC for 120 minutes. Then the samples cooled to room temperature were analysed in Spectrophotometer model HACH DR/2010.

3.3.4 Volatile fatty acids

Samples taken from the sample port 01, 02, 03 were centrifuged to separate the liquid. Supernatant was mixed with Sulphuric acid and distilled .Collected distillate was titrated with Sodium Hydroxide and the volatile fatty acids content was calculated (Clesceri, et al., 1998).

3.3.5 pH

PH of the effluent was analysed using MI 160 pH meter. pH is an indication of the process stability of biogas production .

3.3.6 Gas composition

Gas composition of the daily generated gas was analysed by the chromatographic method. CH4, CO2, H2, O2, N2 content in the biogas was analysed. SHIMADZU GC 2014 model was used for the tests.

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3.3.7 Specific methane production

Specific methane production was calculated as below. V0 - Average daily methane production (m3/d) W – Weight of daily feed stock added (kg/d) % TS – Percentage total solids in feedstock %VS – Percentage volatile solids in feedstock Specific methane production

3.3.8 Volatile solids reduction

Volatile solids reduction was calculated as below (Brobst, n.d.). %VS in = VS in the feedstock %VS out = VS in the digested effluent VSR =

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Chapter 4: Results and Analysis

4.1 Gas volume and composition

Table 4.1: Daily average biogas production

Day No.

Volume of gas generated per day (L/day) Digester 01 Digester 02

Feed rate : 1.4kg per day

Feed rate : 3kg per day

Feed rate: 6kg per day

01 99 17 94 02 139 37 97 03 139 0 73 04 146 48 101 05 101 30 101 06 115 48 101 07 102 49 101 08 106 30 130 09 132 33 147 10 128 46 149 11 153 30 161 12 149 30 175 13 141 60 170 14 135 32 198 15 141 51 158 16 146 0 182 17 75 56 175 18 132 56 167 19 153 48 154 20 133 56 132

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Fig. 4.1: Daily average biogas production in Digestor 1

For the 6kg per day and 1.4kg per day higher biogas volume was generated. During the steady state experiments done at 3kg per day leakages occurred in the gas holder, therefore the generated biogas volume is lower than that for the other two feeding rates.

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Table 4.2: Composition variation of biogas for feeding rates of 3kg per day and 1.4kg per day in Digester 1

Time(Day) Feed rate of 1.4 kg per day Feed rate of 3kg per day

CH4 (% Volume)

CO2 (% Volume)

CH4 (% Volume)

CO2 (% Volume)

01 53 44 43 52

02 58 40 38 57

03 61 34 46 48

04 64 33 38 58

05 65 31 45 51

06 65 32 46 51

07 61 35 43 53

08 57 37 41 56

09 57 40 45 49

10 54 43 47 48

11 52 45 50 48

12 52 45 50 47

13 52 45 50 47

14 52 45 51 46

15 52 46 51 45

16 52 43 51 46

17 53 42 53 42

18 51 42 55 42

19 53 44 55 39

20 55 42 56 40

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Fig. 4.2: Composition Variation of biogas for feed at 3kg/day and 1.4kg/day feed rates in

Digestor 1

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Table 4.3: Composition variation of biogas for feeding rate of 6kg per day in Digester 2

Time(Day) Feed rate of 6kg per day

CH4 (% Volume)

CO2 (% Volume)

01 41 56 02 44 52 03 46 48 04 46 51 05 48 45 06 51 43 07 53 41 08 55 40 09 54 39 10 51 43 11 46 49 12 47 50 13 49 47 14 50 47 15 52 43 16 51 43 17 51 44 18 51 45 19 50 47 20 53 42

Fig. 4.3: Composition variation of biogas at feed rate 6kg/day in Digester 2 The composition shows high methane content in biogas for feeding rate of 1.4 kg per day.

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4.2 pH variation of effluent

Table 4.4: pH Variation of effluent for three feed rates

Time(days ) pH out – 1.4 kg/day pH out – 3 kg/day pH out – 6 kg/day

01 7.08 6.49 5.96

02 7.08 6.34 6.66

03 6.77 6.43 6.93

04 7.68 6.73 6.77

05 7.66 7.01 6.93

06 7.80 6.82 7.03

07 7.04 6.14 6.85

08 7.44 6.96 6.84

09 7.85 6.62 6.73

10 7.56 6.69 6.52

11 7.32 6.82 6.60

12 7.21 6.82 6.56

13 7.42 6.80 6.76

14 7.51 6.85 6.60

15 7.35 7.09 6.59

16 7.79 7.31 7.01

17 7.18 6.96 6.89

18 7.18 6.78 6.74

19 7.12 6.88 7.07

20 6.76 7.16 6.85

.

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Fig. 4.4: Variation of effluent pH for different feed rates

pH variation of effluent for different feed rates is an indication of process stability. For the three feed rates effluent pH does not show much larger variation between them. For 3kg /d effluent pH is in the range of 6.14 to 7.31. At 6kg/d pH varies from 5.96 to 7.07. For the three feed rates pH of effluent was usually within the range optimum range for the methanogenisis reactions. At 1.4kg/d methane composition was always above 50% with the pH variation in the range of 6.76 to 7.85.

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4.3 VFA variation along the digester length

Table 4.5: VFA variation along the digester length for feeding rate of 1.4 kg per day in digester 1

Time(Day) VFA1(mg/l) VFA2(mg/l) VFA3(mg/l) 01 9521 6854 5782 02 13246 6794 4804 03 10513 5849 4918 04 10827 7203 6466 05 12523 5367 3531 06 10003 4281 3370 07 9159 3987 3089 08 20134 4978 3008 09 8402 4603 2781 10 9052 3169 2084 11 9414 3451 1910 12 15417 4509 2707 13 8878 4281 2781 14 8295 4791 3303 15 8007 4402 2164 16 10874 4576 3625 17 7819 5166 3136 18 9601 6754 3169 19 10673 5059 4523 20 10459 4389 3062

Fig. 4.5: VFA Variation along the digester length for feed rate of 1.4kg/day in Digester 1

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Table 4.6: VFA variation along the digester length for feeding rate of 3kg per day in digester 1


Fig.4.6: VFA variation along the digester length for feeding rate of 3kg per day in digester 1

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Table 4.7: VFA variation along the digester length for feeding rate of 6kg per day in digester 2


Fig. 4.7: VFA variation along the digester length for feed rate of 6kg/day in Digester 2

VFA profile along the digester for 1.4kg per day and 3kg per day shows clear variation between the samples taken from sample port1, 2 and 3. This shows the variation of biogas production stages along the length for feed rates of 1.4kg per day and 3kg per day. High VFA concentration near sample port 1 is due to the dominance of acid production stage near the inlet. VFA concentration near the inlet varied from 8000mg/l to 20000mg/l for the OLR of 1.12 kgVS/m3d. VFA concentration near the sample port 01 varied from 4000 mg/l to 22000 mg/l for the OLR of 0.83 kgVS/m3d. Although the VFA profile shows

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similar pattern for feeding rate of 6kg, it shows larger fluctuations in VFA content near sample port 01 and 02. The VFA variation pattern was not prominent as for feeding rates of 1.4kg per day and 3 kg per day. At the feed rate of 6kg/d high VFA concentrations than for other two feed rates were observed throughout the reactor. At OLR of 1.67 kgVS/m3d, VFA near the inlet varied from 4000 mg/l to 32000mg/l. This VFA concentration has exceeded the inhibitory limits for methanogenisis reported in the literature which is around 8000 mg/l (Poprasert, 1996). Ghosh and Liu (1998) observed VFA concentration of 9600 mg/l at OLR of 6.84 kgVS/m3d at a pH of 4.4.

4.4 Effluent COD

Table 4.8: Effluent COD variation for three feed rates

Day No. Effluent COD (mg/l)

Feed rate : 1.4 kg/ day (Digester 1)

Feed rate: 3kg/day (Digester 1)

Feed rate: 6kg/day Digester 2

01 6225 7340 14850 02 7425 4370 14100 03 4900 5010 15350 04 5550 4750 17100 05 5900 4930 11350 06 5750 7050 17425 07 6800 7760 10475 08 7000 7750 13775 09 5425 7750 8575 10 5175 8600 11500 11 3050 6220 8850 12 4975 6740 7350 13 4275 6930 11825 14 6925 6660 7250 15 8125 6480 8300 16 5425 6950 7550 17 7425 7210 7825 18 4325 6160 7050 19 6775 7850 7450 20 4050 6260 7350

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Fig 4.8: COD variation of effluent for different feed rates

For feeding rate of 1.4kg per day COD of effluent varies between 3000 mg/l to 8000 mg/l. Effluent COD level varies between 4000mg/l to 9000mg/l for 3kg feeding rate. For 6kg of feeding rate effluent COD level varies from 7000mg/l to 17000mg/l. Higher COD level in the effluent was a result of reduced HRT. Arun, et al. (2005) reported COD reduction from about 40,000-50,000 mg/l down to 1200-3000mg/l. Higher COD values in the effluent is an indication of undigested organic matter presents in the effluent.

4.5 Process performance

Table 4.9: Process performance

Feed rate(kg/day)

Average Volatile Solids Reduction (%)

Average Specific methane production (m3/kgVS per

day) 1.4 91.37 0.341

3.0 89.36 0.120

6.0 85.92 0.219 The highest average specific methane production was 0.341m3/kgVS per day at OLR of 1.12kgVS/m3 per day. The average specific methane production is 0.120 m3/kg VS per day for OLR of 0.83 kgVS/m3day. For OLR of 1.67kgVS/m3day average specific methane production is 0.219 m3/kgVS per day. Relatively low biogas yield for feed rate of 3kg per day is due to intermittent leakages occurred during the steady state operating period. Intermittent leakages restrict the successful growth of methanogenisis bacteria

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culture. Low average specific methane production at feed rate of 6kg per day is due to the insufficient HRT for the larger quantity of feedstock to be digested inside the digester and due to the high VFA concentration produced at higher feed rate. OLR of 1.12 kgVS/m3day showed the highest average volatile solids reduction of 91.37%. OLR of 1.67 kgVS/m3day showed the lowest average volatile solids reduction of 85.92%.

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Chapter 5: Discussion

Highest average gas production was observed for the highest OLR, which is also the highest feeding rate. Low average specific methane production and methane content in biogas was observed at the highest feeding rate. Insufficient retention time and high VFA concentration due to high organic load reduces methane production which results in low specific methane production and low methane content in biogas. Highest average specific methane production was observed for intermediate OLR which is the lowest feed rate with high TS content. When the OLR is increased total feed rate is reduced by increasing TS content. At this condition the process is more stable and the hydraulic retention time increases due to lower feeding rate. High COD concentration in the effluent is also an indication of the insufficient retention time.

Table5.1: Comparison between similar studies done in plug flow digesters

Waste type Specific Methane Yield (m3/kgVS) Conditions Reference

Food Waste

0.120 0.83 kgVS/m3day

Temperature :28-31oC

Present Study 0.219 1.67 kgVS/m3day

Temperature :28-31oC

0.341 1.12 kgVS/m3day

Temperature :28-31oC Used cooking grease with swine manure

0.310

Cooking grease 2.5%, Temperature: 22-26oC (Botero, et al., 2010)

Food waste, Anaerobic sludge,

Digestate, Cow dung

0.278 Organic loading rate2.5

kgVS/m3day Temperature: 55oC

(Chaudhry ,2008) 0.2259

3.3 kgVS/m3day Temperature: 55oC

0.146 3.9 kgVS/m3day

Temperature: 55oC

Cassava peel 0.377

3.6kgVS/m3day Temperature :35-39°C (Cuzin, et al.,1992)

Cuzin, et al. (1992) reported specific methane production of 0.377 m3/kgVS for Cassava peel fermentation in a plug flow digester. Chaudhry (2008) reported 0.278, 0.2259 and 0.146 m3/kg VS production for municipal solid waste for OLR of 2.5, 3.3 and 3.9 kgVS /m3d respectively. VFA concentration along the length of the digester shows a large reduction from inlet to the middle span. This was more prominent at lower feeding rates. Lengthwise VFA variation is an indicator of the biogas production stages along the length of the digester. VFA results show that acidogenisis phase near the inlet and mathanogenisis phase near the outlet. High VFA concentration is a reason for low methane content in the biogas.

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Cuzin, et al. (1992) and group of researchers reported acetate accumulation of 10g/l in the feeding box at pH of 5 as a result of acidification due to higher loading rates. At this condition they observed 20% less biogas production than normal biogas production. VFA concentration exceeded the inhibitory limits mentioned in the literature. This did not cause full process destruction but resulted in low methane content in the biogas. Distribution of biogas production stages along the length of the digester reduces negative effect of high VFA concentrations at higher loading rates. Highest average VS reduction was observed for intermediate OLR which is the lowest total feed rate with high TS content. Lowest average VS reduction was observed at highest OLR which is the highest total feed rate. High COD concentrations were observed in the effluent. This is due to insufficient HRT.

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Chapter 6: Conclusion

Highest specific methane production and high methane content in biogas was observed at the lowest feed rate and for feed stock with high TS contents which is 1.4 kg per day. Although the total feed rate was lowest, OLR was a middle value at the highest specific methane production. This is due to high TS content of the feed at this feed rate. Highest VS reduction was also observed at the lowest feed rate with high TS content which is 1.4 kg per day. Insufficient HRT and high VFA content are reasons for lower specific methane production at the highest feed rate. The VS reduction was also the lowest for the highest feed rate. Lowest feed rate with high total solids content showed more stable operation and high specific methane production although the OLR is high. Increment in HRT at lower feed rate increases specific methane production. Further studies should be conducted to study the effect of TS content in the feedstock. Although the VFA concentration near the inlet was much higher than the inhibitory levels it did not lead to full process destruction. The VFA variation along the digester shows the variation of acidogenisis to methanogenisis stages along the digester length which is more prominent at lower feed rates. At higher feed rates high VFA concentrations were observed along the digester length with large fluctuations in VFA content. Higher VFA content and VFA fluctuations lead to process instability. Co digestion of food waste with cattle dung, sewage waste or other suitable sources help to control the high VFA concentrations. High COD content in the effluent is an indicator of the presence of undigested organic material in the effluent. The COD levels observed in the effluent for three feed rates are much higher than recommended levels for discharging effluent. This COD content can be treated in a second digester or the length of the digester has to be increased to convert COD in the effluent to biogas. Other reason for lower gas quality is the high VFA production in the digester. Within the limited time period experiments were done for three different feed rates. Further studies should be conducted to study the effect of TS content in the feedstock for biogas production. Future studies should be focused on importance of flow induced by the effect of pressure inside the plug flow digester on biogas production and its composition. Effluent nutrient content should be tested to be used it as an organic fertilizer. This source supplies high quality fertilizer which increases resistance of the plants to diseases and increase the richness of soil. GHG potential of methane in the biogas is 20% (Wightman, 2005) higher than carbon dioxide. Therefore it should be carefully trapped and used to avoid leakages.

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Natural resources conservation service; 2004 “Anaerobic digester-controlled temperature”; 2004Code366 Natural resources conservation service, Conservation practice standard, Available at [Accessed 15 March 2011] The encyclopedia of alternative energy and sustainable living “Plug flow digester”, Available at < http://www.daviddarling.info/encyclopedia/P/AE_plug_flow_digester.html> [Accessed 15 March 2011] SEAI - The Process of Anaerobic Digestion (AD), www.seai.ie/Renewables/Bioenergy/Anaerobi../

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Annexure I Gas Collection Data Table 8.1: Gas volume data

Day No.

Height of the gas holder (cm) Digester 01 Digester 02

Feed rate : 3kg per day *

Feed rate : 1.4kg per day **

Feed rate: 6kg per day ***

01 11.0 57.0 94.0 02 23.0 80.0 97.0 03 0.0 80.0 73.0 04 30.0 84.0 101.0 05 19.0 58.0 101.0 06 30.0 66.0 101.0 07 31.0 59.0 101.0 08 19.0 61.0 130.0 09 21.0 76.0 147.0 10 29.0 74.0 149.0 11 19.0 88.0 161.0 12 19.0 86.0 175.0 13 38.0 81.0 170.0 14 20.0 78.0 198.0 15 32.0 81.0 158.0 16 0.0 84.0 182.0 17 35.0 43.0 175.0 18 35.0 76.0 167.0 19 30.0 88.0 154.0 20 35.0 76.5 132.0

* Gas holder diameter for 3kg per day is 45 cm ** Gas holder diameter for 1.4kg per day is 47 cm *** Gas holder diameter for 6kg per day is 47 cm

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Annexure II Gas Composition Data Table 8.2: Gas composition data Day No.

Feed rate - 3kg per day (% Volume)

Feed rate - 1.4kg per day (% Volume)

Feed rate - 6kg per day (% Volume)

CH4 CO2 CH4 CO2 CH4 CO2 CH4 CO2 CH4 CO2 CH4 CO2 01 43.260 52.481 43.071 52.325 52.432 44.134 53.421 44.236 41.236 56.394 41.309 56.417 02 38.172 56.923 38.815 57.012 58.327 40.013 58.412 40.115 44.425 52.738 44.361 52.256 03 46.235 47.601 46.498 47.536 60.712 34.428 60.423 34.383 45.933 47.724 46.052 47.640 04 37.992 58.001 38.121 58.135 64.349 32.915 64.106 33.076 46.143 51.241 46.212 51.389 05 45.023 51.231 45.047 50.749 64.621 31.241 64.821 31.342 47.831 45.530 48.079 45.423 06 46.047 51.245 45.239 51.324 64.823 31.876 64.513 32.108 51.132 43.465 51.117 43.398 07 42.621 53.124 42.684 53.325 61.326 34.921 60.974 34.857 53.215 41.051 52.947 40.936 08 40.633 56.147 41.023 55.627 57.328 37.267 57.381 37.194 54.983 40.132 54.824 40.328 09 45.243 49.416 45.289 49.423 56.239 40.118 57.013 39.931 54.406 39.011 54.343 39.272 10 46.992 48.231 47.125 48.246 54.742 43.407 54.219 43.398 50.861 42.704 50.695 42.850 11 49.852 48.387 50.164 48.316 52.273 45.351 52.246 45.369 46.523 49.470 46.278 49.381 12 50.216 46.995 50.244 47.012 52.432 45.245 52.503 45.317 47.172 50.221 46.957 50.103 13 50.375 47.024 50.306 47.098 52.475 45.179 52.436 45.204 49.112 47.075 49.215 47.283 14 51.278 46.351 51.204 46.388 52.306 45.317 52.273 45.395 50.462 47.149 50.334 47.268 15 51.421 45.483 51.473 45.467 52.096 45.921 52.264 46.138 51.784 43.194 51.907 43.276 16 51.416 46.123 51.448 46.174 52.214 43.327 51.965 43.291 51.445 43.175 51.319 42.977 17 52.587 42.371 52.576 42.353 53.257 42.454 53.392 41.831 51.217 44.022 51.261 44.008 18 55.046 42.275 55.084 42.194 51.485 42.001 51.479 42.095 51.287 45.213 50.865 45.310 19 55.417 39.180 55.348 38.991 53.568 44.071 53.382 44.136 50.542 47.149 50.188 47.274 20 55.953 40.003 56.342 40.128 54.764 42.310 54.853 42.672 53.008 42.505 53.117 42.42

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Annexure III pH Data Table 8.3: pH data Time(days ) pH out – 3 kg/day pH out – 6 kg/day pH out – 1.4 kg/day

Trial 1 Trial 2 Trial 1 Trial 2 Trial 1 Trial 2

1 6.47 6.51 5.94 5.97 7.04 7.11 2 6.37 6.30 6.68 6.63 7.07 7.08 3 6.41 6.44 6.93 6.93 6.76 6.78 4 6.76 6.70 6.75 6.79 7.66 7.70 5 7.02 6.99 6.92 6.94 7.65 7.66 6 6.88 6.76 7.01 7.05 7.81 7.78 7 6.25 6.02 6.84 6.86 7.06 7.01 8 6.95 6.97 6.85 6.83 7.45 7.42 9 6.56 6.68 6.70 6.76 7.84 7.86 10 6.70 6.68 6.51 6.53 7.56 7.55 11 6.83 6.80 6.59 6.61 7.32 7.31 12 6.85 6.79 6.52 6.59 7.21 7.20 13 6.81 6.78 6.79 6.73 7.41 7.43 14 6.89 6.80 6.62 6.57 7.54 7.48 15 7.15 7.03 6.57 6.61 7.34 7.36 16 7.34 7.27 7.04 6.98 7.74 7.84 17 6.93 6.98 6.88 6.90 7.16 7.19 18 6.73 6.82 6.71 6.77 7.12 7.24 19 6.84 6.91 7.03 7.11 7.17 7.06 20 7.18 7.14 6.82 6.88 6.78 6.73

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Annexure IV VFA Data Table 8.4: Titration volume data for 3kg per day Day No. NaOH(ml) –(VFA1) NaOH(ml) – (VFA2) NaOH (ml)- (VFA3)


1 92.4 89.9 35.6 28.9 27.1 34.2 2 105.2 124.1 31.1 11.5 35 39.5 3 157.4 175.6 40.2 20.7 13.4 20.3 4 76.5 73 23.9 31.8 21.6 16.3 5 148.7 180.2 23.5 30.8 11.3 20.2 6 59.7 70.4 33.3 24.8 24.5 21.7 7 68.6 101.7 45.4 29.9 18.4 25.1 8 89.3 96.7 19.2 36.9 20.8 14.3 9 113.4 107.9 25.7 39.6 100.2 95 10 73.4 93.7 35.5 27.8 2.4 2.9 11 89.8 82.7 25.9 35.2 22.3 17.6 12 172.2 129.3 49.3 21.6 22 24.3 13 72.5 42.2 35.6 32.9 27.8 32.5 14 80.1 89.4 33.7 27.2 25.9 26.4 15 116.2 75.5 32.4 26.3 19.7 24 16 71.6 85.1 22.7 47.3 24.6 21.5 17 42.1 55.8 38.1 30.6 25.1 21.4 18 75.5 68 42.3 36.6 15.6 27.9 19 33.9 29.4 22 30.7 34.4 38.1 20 32.6 27.4 27.1 29.8 33.5 28.8

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Table 8.5: Titration volume data for 1.4 kg per day Day No. NaOH(ml) –(VFA1) NaOH(ml) – (VFA2) NaOH (ml)- (VFA3)


1 69.3 72.8 51.8 50.5 55.8 30.5 2 100.2 97.5 53.1 48.3 38.4 33.3 3 74.3 82.6 39.1 48.2 31.1 42.3 4 77.9 83.7 55.9 51.6 49.5 47.0 5 102.8 84.1 43.4 36.7 30.6 22.1 6 78.2 71.1 34.7 29.2 26.8 23.5 7 71.4 65.3 23.1 36.4 18.6 27.5 8 129.1 171.4 36.2 38.1 20.2 24.7 9 65.8 59.6 32.5 36.2 17.3 24.2 10 61.9 73.2 24.8 22.5 24.0 7.1 11 74.5 66.0 28.7 22.8 12.8 15.7 12 97.9 132.2 31.0 36.3 20.8 19.6 13 63.4 69.1 35.7 28.2 21.4 20.1 14 70.1 53.7 38.5 33 20.8 28.5 15 58.2 61.3 37.6 28.1 14.1 18.2 16 86.8 75.5 28.1 40.2 32.5 21.6 17 52.6 64.1 37.8 39.3 25.0 21.8 18 73.4 69.9 49.6 51.2 20.9 26.4 19 81.5 77.8 45.7 29.8 40.6 26.9 20 71.9 84.2 33.1 32.4 28.0 17.7

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Table 8.6: Titration volume data for 6kg per day Day No. NaOH(ml) –(VFA1) NaOH(ml) – (VFA2) NaOH (ml)- (VFA3)


1 70.1 51.2 44.1 52.4 18.2 13.1 2 100.3 90.6 74.3 58.8 2 4.3 3 65.9 83.8 58.2 72.5 44.9 40.3 4 67.4 74.7 48.9 57 39.7 46.8 5 112 123.9 89.3 74.6 49.3 39.8 6 254.8 219.2 170.2 125.9 49.2 42.9 7 215.8 194.5 71.1 58.4 32.5 36.4 8 71.5 93.2 48.5 52.9 31.2 38.5 9 34.6 30.9 18.5 14.2 39.1 32 10 162.4 192.8 36.7 42 46.4 39.1 11 220.6 212.1 42.2 46.7 27.3 38.2 12 56.3 93.2 41.2 36.9 27.9 39.4 13 66.1 36.8 54.8 42.3 19.1 18.2 14 132.2 103.1 125.1 95.4 85.4 123.9 15 246.2 233.3 41.4 37.2 31.6 28.1 16 53.6 36.2 45.8 34.5 39.7 34 17 39.3 54.8 29.7 41.4 25.3 30.6 18 44.1 32.4 27.8 32.5 36.8 29.1 19 71.2 86.9 36 31.3 16 25.7 20 195.7 150.2 55.6 71.4 16.5 23.2

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Annexure V COD Data Table 8.7: Effluent COD data Day No. COD - 3kg / day*

(mg/l) COD - 1.4kg / day ** (mg/l)

COD - 6kg /day** (mg/l)


1 367 367 132 117 286 308 2 190 247 139 158 286 278 3 250 251 104 92 308 306 4 234 241 97 125 351 333 5 249 244 108 128 229 225 6 344 361 126 104 314 383 7 371 405 118 154 193 226 8 404 371 142 138 280 271 9 381 394 94 123 171 172 10 429 431 81 126 234 226 11 301 321 63 59 175 179 12 356 318 59 140 149 145 13 339 354 95 76 235 238 14 325 341 126 151 168 122 15 311 337 152 173 153 179 16 348 347 127 90 128 174 17 389 332 176 121 149 164 18 292 324 85 88 166 116 19 422 363 144 127 121 177 20 307 319 81 81 154 140

* Dilution factor for feeding rate of 3kg/day is 20 ** Dilution factor for feeding rate 6kg/day and 1.4kg/day is 50

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Annexure VI Data for TS and VS Determination Table 8.8: Feed stock TS and VS data Day No Feed rates: 3kg/day, 6kg/day Feed rate: 1.4kg/day

W0 W1 W2 W3 W0 W1 W2 W3

1 34.2448 84.1330 37.1947 34.4357 90.8382 180.3087 104.6108 92.0148 2 39.0271 86.5893 41.9091 39.1891 47.2047 92.5328 55.0427 47.6532 3 40.2132 88.5198 42.6934 40.3623 45.8054 88.6455 53.1769 46.1153 4 - - - - 45.1767 83.7521 51.1379 45.5209 5 43.2009 89.4815 46.3706 43.5328 44.3417 87.2135 52.0671 44.7876 6 32.6570 80.5304 35.3379 32.7923 42.4974 84.8800 49.5242 42.7574 7 38.3652 84.8354 41.3333 38.5625 43.5025 84.3457 51.0719 44.0412 8 44.3494 91.5714 46.7859 44.4229 - - - - 9 44.7718 103.3205 47.6063 45.0606 44.3098 79.4315 51.0090 44.6370 10 - - - - 45.6091 81.2413 49.3021 46.0585 11 36.8400 88.2136 38.8532 37.0018 44.3021 86.1047 51.3705 45.1216 12 39.9746 85.3427 42.0546 40.1462 47.2237 89.6891 52.2791 47.3445 13 34.1900 90.6220 37.2527 34.5636 - - - - 14 35.7414 83.8133 38.8154 35.8412 47.1747 86.9842 52.9952 47.5306 15 45.1755 91.3552 48.0272 45.3437 48.2378 91.0534 55.8218 48.5762 16 - - - - 43.1691 84.0043 49.7113 43.6631 17 - - - - - - - - 18 34.1954 101.7835 38.7793 34.7549 - - - - 19 32.5817 86.4629 35.6931 32.8426 45.2131 88.2619 52.2513 45.8379 20 40.2367 92.6792 43.2334 40.5890 48.2384 90.7834 54.8425 48.8361

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Table 8.9: Effluent TS and VS data

Day No

Feed rate: 3kg/day Feed rate: 6kg/day Feed rate: 1.4kg/day

W0 W1 W2 W3 W0 W1 W2 W3 W0 W1 W2 W3

1 73.1704 121.8926 73.4687 73.2933 34.3465 81.1129 34.9717 34.5535 45.7827 101.1336 46.7413 46.3183 2 74.7183 122.8116 74.9872 74.8290 42.5194 90.8632 43.9022 42.9833 38.3224 88.9374 38.7971 38.4825 3 47.2055 96.0465 47.5049 47.3317 36.4131 84.8783 37.5968 36.7851 35.4210 83.5555 35.8318 35.5462 4 - - - - - - - - 44.7712 90.9472 45.1634 44.9403 5 45.2125 93.9252 45.5086 45.3587 39.9753 87.0472 40.6843 40.2929 40.2135 87.8526 40.6784 40.4208 6 73.1688 121.2645 74.4489 73.5891 35.9614 81.7207 37.0793 36.1573 39.0276 84.2160 39.4631 39.1215 7 45.8065 94.257 46.0958 45.9489 40.2363 90.4330 40.7462 40.3952 43.1691 90.4328 43.4427 43.2974 8 36.2167 84.5248 36.4711 36.2849 45.8112 90.6410 46.7359 45.9678 - - - - 9 34.2007 82.1305 34.776 34.5278 47.2233 94.2612 48.2143 47.6141 73.1695 106.3125 73.4856 73.3281 10 - - - - - - - - 44.3423 88.0031 45.1795 44.7702 11 43.2025 90.4537 43.4789 43.3163 31.5945 80.7109 33.4297 32.9253 42.5205 81.5102 42.9473 42.7510 12 38.3651 94.6759 38.6835 38.4959 43.1643 86.1694 44.4581 43.6081 44.3502 86.1603 45.0423 44.7423 13 44.3427 100.6103 44.6578 44.4821 46.4939 91.9606 46.6905 46.5945 - - - - 14 42.5190 91.3163 42.7983 42.6148 33.7623 87.2311 34.8737 34.3437 45.7834 90.3782 46.1828 45.9547 15 34.0243 82.7902 34.3098 34.1490 38.9636 90.6188 39.9012 39.2482 36.8409 84.1064 37.2813 37.0024 16 - - - - - - - - 43.2006 85.2306 44.1328 43.7175 17 - - - - - - -- - - - - - 18 42.5197 88.0042 42.7814 42.6461 42.4970 89.9968 43.4309 42.9709 - - - - 19 36.1668 83.4012 36.4508 36.3054 41.1238 85.1036 42.2476 41.4944 46.4935 86.3108 46.9020 46.7327 20 45.8061 93.9164 46.0848 45.9430 43.1682 88.3625 44.2464 43.6865 47.2051 87.4792 47.7619 47.5004

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