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Performance Analysis of Anaerobic Digestion to extract Biogas from Kitchen Waste

1. Abishek Joel J, 2. Murali G, 3. Ravishankar M. 4. Sibichakravarthy M, 5. Sundhirasekar A Dept. of Mechanical Engineering, SNS College of Engineering, Coimbatore

Abstract—In day to day life, large amount of food waste is unutilized and disposed as wastage in many places such as restaurants, hostels, food courts, cafeteria, marriage functions etc., which is used for generation of biogas. Biogas production requires anaerobic digestion for which biogas reactors are required. In this project food waste was collected from different places as feedstock for the reactor. The anaerobic digestion of food waste produces biogas, a valuable energy resource. Anaerobic digestion is a microbial process for production of biogas, which consists of Primarily methane (CH4) & carbon dioxide (CO2).

The main objective of this work is to utilize food wastage for generation of biogas. This work was carried out in a reactor comprising of a plastic water tank with a crusher, gas purifier and gas collector using different source of food waste available in SNS COLLEGE OF ENGINEERING hostel mess and canteen.

Biogas can be used as energy source and also for numerous purposes. But, any possible applications require knowledge & information about the composition and quantity of constituents in the biogas production. It was realized through the observation and experimental test that by using 5 liter of source material with 5 different compositions of food waste and cow dung such as 100:0, 75:25, 50:50, 25:75, 0:100 for 15 days. It was inferred from the experimental observation to produce 3100ml of biogas in the 75:25 ratios. It was found that 75:25 ratio of food waste and cow dung is the best composition, based on this a test ring was fabricated and experiment was conducted in 120 liter digester and the biogas produced was analyzed.

Index Terms— Anaerobic Digestion, Bacteria, Digester, Gasification, Gasifier, Metabolism, Biogas, Critical Pressure, Enzyme hydrolysis, Acid Formation, Methane Formation, Fuel Properties.

1 INTRODUCTION

——————————  ——————————
ue to scarcity of petroleum and coal it threatens supply of fuel throughout the world also problem of their com- bustion leads to research in different corners to get access
the new sources of energy, like renewable energy resources. Solar energy, wind energy, different thermal and hydro sources of energy, biogas are all renewable energy resources. But, biogas is distinct from other renewable energies because of its characteristics of using, controlling and collecting organ- ic wastes and at the same time producing fertilizer and water for use in agricultural irrigation. Biogas does not have any geographical limitations nor does it require advanced technol- ogy for producing energy, also it is very simple to use and apply. Deforestation is a very big problem in developing countries like India, most of the part depends on charcoal and fuel-wood for fuel supply which requires cutting of forest. Also, due to deforestation it leads to decrease the fertility of land by soil erosion. Use of dung, firewood as energy is also harmful for the health of the masses due to the smoke arising from them causing air pollution. We need an eco-friendly sub- stitute for energy.
In 2003, Dr. AnandKarve[2][4] (President ARTI) de-
veloped a compact biogas system that uses starchy or sugary
feedstock material and the analysis shows that this new sys-
tem is 800 times more efficient than conventional biogas
plants..
Anaerobic digestion is a controlled biological degra- dation process which allows efficient capturing & utilization of biogas (approx. 60% methane and 40% carbon dioxide) for
energy generation. Anaerobic digestion of food waste is achievable but different types, composition of food waste re- sults in varying degrees of methane yields, and thus the effects of mixing various types of food waste and their proportions should be determined on case by case basis. BIOGAS is pro- duced by bacteria through the bio-degradation of organic ma- terial under anaerobic conditions. Natural generation of bio- gas is an important part of bio-geochemical carbon cycle. It can be used both in rural and urban areas

General Features Of Biogas

Energy Content	6-6.5 kWh/m3
Fuel Equivalent	0.6-0.65 l oil/m3 biogas
Explosion Limits	6-12 % biogas in air
Ignition Temperature	650-750 *C
Critical Pressure	75-89 bar
Critical temperature	-82.5 *C
Normal Density	1.2 kg/m3
Smell	Bad eggs

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change in organic matter brought about by living organisms) through anaerobic digestion, gas is generated. This gas is known as Biogas. Biogas is generated through Fermentation or bio digestion of various waste is by a variety of anaerobic and facultative- organisms. Facultative bacteria are capable of growing both in presence and absence of air or oxygen.

1.1 Anaerobic Digestion

Biogas technology is concerned to microorganism. These are living creatures which are microscopic in size and are in visible to unaided eyes. They are called bacteria, fungi, virus etc. Bacteria can be dividing into two major groups based on their oxygen requirement. Those which grow in the presence of oxygen are called aerobic while the other grow in the ab- sence of gaseous oxygen are called anaerobic. When organic matter undergoes fermentation (process of chemical change in organic matter brought about by living organisms) through anaerobic digestion, gas is generated. This gas is known as Biogas. Biogas is generated through Fermentation or bio diges- tion of various waste is by a variety of anaerobic and faculta- tive- organisms. Facultative bacteria are capable of growing both in presence and absence of air or oxygen.

Aerobic and anaerobic fermentation can be used to decompose organic matter. Normally the aerobic fermentation produces Co2 , NH3 and small amount of the other gases along with the decomposed mess and evolution of heat. Anaerobic fermentation produces CO2 , CH4 , H2 and trace of other gases along with the decomposed mass. Aerobic fermentation is used when the main aim is to render the material hygienic and to recover the plant nutrients for the reuse in the fields. The residue is rich in C2 , N2 , P, K and other nutrients. In biogas plants the main aim is to produce the Methane and hence the anaerobic digestion is used. Here the complex organic mole- cules broke down to sugar, alcohols, pesticides and amino acids producing bacteria. The overview of anaerobic Digester system is shown in Fig 1.

Fig 1.1 The Anaerobic Digester process

This Anaerobic digestion is broadly classified into three phas- es:
 Methane Formation: Where the organic acids as formed above are converted into Methane (CH4 ) and CO2 by the bacteria which are strictly anaerobes. These bacteria are called methane fermenters. For ef- ficient digestion these acid formers and methane fer- menters must remain in the state of dynamic equilib- rium. This equilibrium is very critical factor which decide the efficiency of generation. The methane for- mers are very sensitive to pH changes. A pH value from 6.5 - 8 is the best for the formation and normal gas production [10].

1.2 Bacteria Involved

There are numerous types of microorganisms that are found to produce methane during anaerobic condition. Strictly anaerobic bacteria are the most common class of bacteria that produced methane, mesophilically or thermophilically within pH 4–7. However, a few facultative bacteria have been identi- fied as methane producers when the hydrogenase enzyme was found in these bacteria. Even though the production rate of methane was lower than in strictly anaerobic bacteria, the is- sue of sensitivity to oxygen did not raised here. Recently, me- thane production was found to be possible by aerobic bacteria.
To date, most of the research on methane production in-
volved anaerobic bacteria due to its high production rate and
the ability to use a wide range of carbohydrates. Clostridium
sp. is a typical acid and methane producer which ferments
carbohydrate to acetate, butyrate, carbon dioxide and organic solvent. Clostridium butyricum [11], Clostridium acetobutyri- cum [12], Clostridium beijerinckii [12], C. thermolacticum [13], C. saccharoper butylacetonicum [14], Clostridium tyrobutyri- cum [15], C. thermocellum [16] and Clostridium paraputrifi- cum [17] are examples of anaerobic and spore forming me- thane producer.

1.3 Sources of Waste

The waste used in this study was the peelings and food refuse from SNS College of Engineering canteen and Hostel mess. In SNS College of Engineering there are around two hostel mess and two canteens from which plenty of food wastes (approxi- mately 1000kg/ week) are available. The waste foods available in SNS College of engineering are as shown in Fig 1.2. The sources of waste are from mess, canteen of SNS College of en-

 Enzymatic Hydrolysis: Where the fats, starches and proteins contained in the cellulosic bio mass are bro- ken down into simple compounds.
 Acid Formation: where the microorganisms of facul- tative and anaerobic group collectively called acid farmers, hydrolysis and ferments are broken to sim- ple compounds into simple acids and volatile solids.

gineering.

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 Fig 1.2 Sources of Waste

The plastic buckets are used to collect the waste from the SNSCE hostel mess and canteens.

1.3. A Carbohydrate Waste

Food wastes from the institutions and contain high levels of carbohydrate and protein. Currently, food wastes from the institutions are mostly treated anaerobic ally. However, lactic acid, bio compost and energy from food wastes would be a value added strategy for treatment of food wastes. The organic constituent especially carbohydrate in food wastes could be a potential substrate for anaerobic Biogas production. The spe- cific
Methane production potential of food wastes was found to
be higher than sewage sludge. However, Methane production
potential increased as sewage sludge composition was in-
creased up to 13–19% of volatile solids. The maximum specific
Methane production potential of 122.9ml H2/g carbohydrate-
COD was found at 87:13 (food waste: sewage sludge). A com- parative study was carried out by Pan et al. [18] on Biogas production at mesophilic and thermophilic conditions. The Biogas yield from the thermophilicacidogenic culture was higher than that from the mesophilic culture at all tested food to microorganism ratio.
Continuous Biogas fermentation in a leaching bed reactor was carried out by Han and Shin [19]. At an optimized dilu- tion factor (D), from the reduced COD of the food wastes was converted to Biogas, volatile fatty acids, ethanol and carbon dioxide. It was suggested that control of D gave environmen- tal conditions favourable for Biogas production. Further, the efficiency was improved by enhanced degradation of slowly degradable matters. It delayed the shift of the predominant metabolic flow from Methane and acid forming pathway to solvent forming pathway. Potential of Methane production from highly concentrated, carbohydrate-rich wastewaters was reviewed by Van Ginkel et al. [20]. The biogas produced using wastewater from apple processing and potato processing in- dustries contained 60% Biogas with no methane generation.
When additional nutrients were added to the wastewaters, it showed an increase of Methane production. The overall Me- thane production was 0.9 L-H2/L medium for apple pro- cessing waster and 2.1 L-H2/L medium for potato processing wastewater. Rice slurry is another potential starch-based
waste from industry as rice is the most common dietary food. Rice contains carbohydrate, protein, lipid and water.

2 STUDY ON BIOGAS PLANT

ARTI – Appropriate Rural Technology of India, Pune (2003) has developed a compact biogas plant which uses waste food rather than any cow dung as feedstock, to supply biogas for cooking. The plant is sufficiently compact to be used by urban households, and about 2000 are currently in use
– both in urban and rural households in Maharashtra. The
design and development of this simple, yet powerful technol-
ogy for the people, has won ARTI the Ashden Award for sus-
tainable Energy 2006 in the Food Security category. Dr. AnandKarve (ARTI) developed a compact biogas system that uses starchy or sugary feedstock (waste grain flour, spoilt grain, overripe or misshapen fruit, nonedible seeds, fruits and

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rhizomes, green leaves, kitchen waste, leftover food, etc.). Just
2 kg of such feedstock produces about 500 g of methane, and
the reaction is completed with 24 hours. The conventional bio-
gas systems, using cattle dung, sewerage, etc. use about 40 kg
of feedstock to produce the same quantity of methane, and it
require about 40 days completing the reaction. Thus, from the
point of view of conversion of feedstock into methane, the system developed by Dr. Anand Karve [2] [3] is 20 times as efficient as the conventional system, and from the point of view of reaction time, it is 40 times as efficient. Thus, overall, the new system is 800 times as efficient as the conventional biogas system.
HilkiahIgoni [5] (2008) studied the Effect of Total Solids

Concentration of Municipal Solid Waste on the Biogas Pro-

duced in an Anaerobic Continuous Digester. The total solids (TS) concentration of the waste influences the pH, temperature and effectiveness of the microorganisms in the decomposition process. They investigated various concentrations of the TS of MSW in an anaerobic continuously stirred tank reactor (CSTR) and the corresponding amounts of biogas produced, in order to determine conditions for optimum gas production. The re- sults show that when the percentage total solids (PTS) of mu- nicipal solid waste in an anaerobic continuous digestion pro- cess increases, there is a corresponding geometric increase for biogas produced. A statistical analysis of the relationship be- tween the volume of biogas produced and the percentage total solids concentration established that the former is a power function of the latter, indicating that at some point in the in- crease of the TS, no further rise in the volume of the biogas would be obtained.

Kumar et al., (2004) investigated the reactivity of methane.
They concluded that it has more than 20 times the global
warming potential of carbon dioxide and that the concentra-
tion of it in the atmosphere is increasing with one to two per
cent per year. The article continues by highlighting that about
3 to 19% of anthropogenic sources of methane originate from landfills.
Shalini Singh [4] et al. (2000) studied the increased biogas production using microbial stimulants. They studied the ef- fect of microbial stimulant aquasan and teresan on biogas
yield from cattle dung and combined residue of cattle dung and kitchen waste respectively. The result shows that dual addition of aquasan to cattle dung on day 1 and day 15 in- creased the gas production by 55% over unamended cattle dung and addition of teresan to cattle dung : kitchen waste (1:1) mixed residue 15% increased gas production.
Lissens et al. (2004) completed a study on a biogas opera-
tion to increase the total biogas yield from 50% available bio-
gas to 90% using several treatments including: a mesophilic
laboratory scale continuously stirred tank reactor, an up flow
biofilm reactor, a fiber liquefaction reactor releasing the bacte-
ria Fibrobactersuccinogenesand a system that adds water during the process. These methods were sufficient in bringing about large increases to the total yield; however, the study was un- der a very controlled method, which leaves room for error when used under varying conditions. However, Bouallagui et al. (2004) did determine that minor influxes in temperature do
not severely impact the anaerobic digestion for biogas produc- tion.
As Taleghani and Kia (2005) observed, the resource limita- tion of fossil fuels and the problems arising from their com- bustion has led to widespread research on the accessibility of new and renewable energy resources. Solar, wind, thermal and hydro sources, and biogas are all renewable energy re- sources. But what makes biogas distinct from other renewable energies is its importance in controlling and collecting organic waste material and at the same time producing fertilizer and water for use in agricultural irrigation. Biogas does not have any geographical limitations or requires advanced technology for producing energy, nor is it complex or monopolistic.
Murphy, McKeog, and Kiely (2004) completed a study in
Ireland analyzing the usages of biogas and biofuels. This
study provides a detailed summary of comparisons with other
fuel sources with regards to its effect on the environment, fini- cal dependence, and functioning of the plant. One of the con- clusions the study found was a greater economic advantage with utilizing biofuels for transport rather than power produc- tion; however, power generation was more permanent and has less maintenance demands.
Thomsen et al. (2004) found that increasing oxygen pres- sure during wet oxidation on the digested bio waste increased the total amount of methane yield. Specifically, the yield which is normally 50 to 60% increased by 35 to 40% demon- strating the increased ability to retrieve methane to produce economic benefits.
Carrasco et al. (2004) studied the feasibility for dairy cow
waste to be used in anaerobic digestive systems. Because the
animal’s wastes are more reactive than other cow wastes, the
study suggests dairy cow wastes should be chosen over other
animal wastes.
Jantsch and Mattiasson (2004) discuss how anaerobic di-
gestion is a suitable method for the treatment of wastewater
and organic wastes, yielding biogas as a useful by-product.
However, due to instabilities in start-up and operation it is
often not considered. A common way of preventing instability problems and avoiding acidification in anaerobic digesters is to keep the organic load of the digester far below its maximum capacity. There are a large number of factors which affect bio- gas production efficiency including: environmental conditions such as pH, temperature, type and quality of substrate; mix- ing; high organic loading; formation of high volatile fatty ac- ids; and inadequate alkalinity.
Jong Won Kang et al (2010) studied the On-site Removal of H2S from Biogas Produced by Food Waste using an Aero-

bic Sludge Bio filter for Steam Reforming Processing. They show that a bio filter containing immobilized aerobic sludge was successfully adapted for the removal of H2S and CO2 from the biogas produced using food waste. The bio filter effi- ciently removed 99% of 1,058 ppmv H2S from biogas pro- duced by food waste treatment system at a retention time of

400 sec. The maximum observed removal rate was 359 g-
H2S/m3/h with an average mass loading rate of 14.7 g-
H2S/m3/h for the large-scale bio filter. The large-scale bio
filter using a mixed culture system showed better H2S remov-

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al capability than bio filters using specific bacteria strains. In the kinetic analysis, the maximum H2S removal rate (Vm) and half saturation constant (Ks) were calculated to be 842.6 g- H2S/m3/h and 2.2 mg/L, respectively. Syngas was generated by the catalytic steam reforming of purified biogas, which in- dicates the possibility of high efficiency electricity generation by SOFCs and methanol manufacturing.
Taleghani and Kia, (2005) outlined the economic, and so-
cial benefits of biogas production.

3 DESCRIPTION OF PARTS

3.1 Crusher

Crusher is a manual machine used to reduce the size, or change the form of waste food like semi solid, so they can be more easily disposed of or recycled, or to reduce the size of a solid mix of raw materials, so that pieces of different compo- sition can be differentiated. Crusher is made by stainless steel by the attachment of bevel gears and blade.

3.2 Digester

A digester is a huge vessel where chemical or biologi- cal reactions are carried out. Anaerobic digestion is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen . It is used for industrial or domestic purposes to manage waste and/or to release energy. The digestion process begins with bacterialhydrolysis of the input materials to break down in- soluble organic polymers , such as carbohydrates , and make them available for other bacteria. Acidogenic bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen , ammonia , and organic acids . Acetogenic bacteria then convert these resulting organic acids into acetic acid , along with additional ammonia, hydrogen, and carbon diox- ide. Finally, methanogens convert these products to methane and carbon dioxide. The digester is made up of fiber material.

3.3 Valves

A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by open- ing, closing, or partially obstructing various passageways. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The ball screw valve is made by plastic ma- terial.

3.4 Gas Purifier

The gas produced from digester consists of carbon diox- ide, hydrogen sulphide and methane. The removal of both H2S and CO2 can be done by passing it through water. This simple process is used to produce a pure methane gas.

3.5 Pressure Gauge

Many techniques have been developed for the measure- ment of pressure and vacuum. Instruments used to measure pressure are called pressure gauges or vacuum gauges. The pressure gauge is a device used to measure the pressure inside the digester.

3.6 Flow Pipes

The pipe lines are made up of PVC (polyvinyl chloride). It’s used to flow the waste crushed food into the digester and also to flow the gas from digester to gas purifier.

3.7 Bevel Gears

Bevel gears are gears where the axes of the two shafts in- tersect and the tooth-bearing faces of the gears themselves are conically shaped. Bevel gears are most often mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well. The pitch surface of bevel gears is a cone. The bevel gears made by cast iron.

4 PROBLEMS WITH LANDFILLS

The waste generated by this increasing urbanization of humans and industries will have to be sorted and processed. The most common waste management solution is land filling. The main problem with this is that landfills around the world are running out of space. The last landfill in the greater New York City area closed in 2001 and now 12,500 tons of garbage is transported daily outside the state by truck, barge, and train [1]. London currently sends 20 million tons of annual waste to
18 different landfills that are running out of space [2]. Montre- al, Canada, has a contract to send 1.3 million tons of waste each year to a landfill located 40 km away with permits that extend only to 2012 [3]. In 2006, nearly a million tons of the waste generated in Toronto, Canada, was trucked to landfills across the U.S. border into Michigan. As a solution, the City of Toronto has purchased a landfill site that is over 200 km away from the downtown area that opened January, 2011 [4]. Mexi- co City produces 12,500 tons of trash per day and sends it to a sprawling, polluted landfill that is running out of space [5]. As of 2011, two thirds of China’s cities are overrun with garbage and millions of tonnes of waste are sent to non-sanitary land- fills with one quarter of cities having no place to dispose of trash [6]. There is no simple solution to this waste problem. This is a pressing global issue that requires design and con- sumption paradigm shifts as well as new waste management solutions.

5 FABRICATION PROCEDURE AND EXPERIMENTAL

SETUP

Step 1: Manually operated crusher is fabricated with the ar- rangements of bevel gears and blade.

Step 2: Two fiber tanks for digester (120 liters) and gas purifier

(50 liters) tanks are purchased.

Step 3: The inlet and outlet ports are drilled as per the re-

quirement.

Step 4: Then the crusher, digester and gas purifier are assem- bled by using PVC pipes and gate valves.

Step 5: The pressure gauge is fitted in the purifier tank to measure the presence of methane gas.

Step 6: Finally all the air leakages are arrested by using M.C. seals and plaster of Paris

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6 CONCLUSION

FIG 6.1 BIOGAS PLANT

[12] Lin PY, Whang LM, Wu YR, Ren WJ, Hsiao CJ, Li SL,et al. Biological hydrogen production of the genus Clostridium: metabolic study and mathe- matical model simulation. Int J Hydrogen Energy 2007; 32:1728–35.

[13] Collet C, Adler N, Schwitzgue ´bel JP, Pe ´ ringer P. Hydrogen production

by Clostridium thermolacticum during continuous fermentation of lactose. Int J Hydrogen Energy 2004; 29:1479–85.

[14] Ferchichi M, Crabbe E, Gil GH, Hintz W, Almadidy A. Influence of initial

pH on hydrogen production from cheese whey. J Biotech 2005; 120:402–9. [15] Jo HJ, Lee DS, Park D, Park JM. Biological hydrogen production by immo-

bilized cells of Clostridium tyrobutyricum JM1 isolated from food waste

treatment process. BioresTechnol 2008; 99:6666–72.

[16] Levin DB, Islam R, Cicek N, Sparling R. Hydrogen production by Clostrid- ium thermocellum 27405 from cellulosic biomass substrates. Int J Hydrogen Energy 2006; 31:1496–503.

[17] Evvyernie D, Yamazaki S, Morimoto K, Karita S, Kimura T,Sakka K, et al.

Identification and characterization of Clostridium paraputrificum M-21, a chitinolytic, mesophilic and hydrogen producing bacterium. J BiosciBioeng

2000; 89: 596–601.

[18] Han SK, Shin HS. Bio hydrogen production by anaerobic fermentation of food waste. Int J Hydrogen Energy 2004; 29: 569–77.

[19] Van Ginkel SW, Oh SE, Logan BE. Bio hydrogen gas production from food processing and domestic wastewaters. Int J Hydrogen Energy 2005;

30:1535-42.

[20] Tchobanoglous G, Burton FL. Waste-water Engineering: treatment disposal and reuse. 3rd ed. New York: McGraw-Hill; 1991, p.1334.

From SNS college hostel mess and canteen 1 ton of food waste per week is unutilized which is used in this project to create biogas, Fixed drum type model is used in this project.
From the lab scale experiment 75:25 Ratio of food waste and cow dung will provide more efficient gas. From this experiment it is able to produce around 3100ml of biogas daily in a 5 liter reactor (digester). The same composition is imple- mented in the 120 liter digester and the gas produced in measured. The gas produced in this plant can be measured, analyzed & utilized for Diesel Engine in upcoming days.

REFERENCES

[1] Madu C, Sodeinde OA. Relevance of biomass in sustainable energy- development in Nigeria. Proceedings of the National Engineering Confer- ence and annual general meeting of the Nigerian Society of Engineers

2001:220–7.

[2] General Environmental Multilingual Thesaurus (GE- MET).BiomassResources.<http://glossary.eea.eu.int./eeaglossary/biogas/>;2

000.

[3] Hobson PN, Bousfield S, Summers R. Methane Production from Agricultur- al and Domestic Wastes. London: Applied Science Publishers Ltd.; 1981, p.

269.

[4] Li Yebo, Stephen Y, Park, Jiying Z. Solid-state anaerobic digestion for methane production from organic waste. Renewable and Sustainable Energy Reviews2011; 15:821e6.

[5] Animal By-products Regulations (England) 2003. Statutory Instrument 2003

No. 1482 ISBN 0110466748. HMSO, London.

[6] EU Regulation Laying Down Health Rules Concerning Animal By-Products

Not Intended for Human Consumption (EC 1774/2002)

[7] Rongpin, Li-Shulin, Chen, Xiujin L, Saifullah L, Yanfeng H, et al. Anaero- bic co digestion of kitchen waste with cattle manure for biogas production. Energy and Fuels 2009;23:2225e9

[8] Rizk M, Bergamasco R, Tavares C. Anaerobic co-digestion of fruit and vegetable waste and sewage sludge. International Journal of Chemical Reac- tor Engineering; 2007:5.

[9] Gómez X, Cuetos M, Cara J, Morán A, García A. Anaerobic co-digestion of primary sludge and the fruit and vegetable fraction of the municipal solid wastes conditions for mixing and evaluation of the organic loading rate.Renewable Energy 2006;31:2017e24

[10] Foster, J.W. and Spector, M.P., (1995). How Salmonella survive against the odds. Annual Review of Microbiology. Vol 49, pp 145-174.

[11] Chong ML, Raha AR, Shirai Y, Hassan MA. Bio hydrogen production by Clostridium butyricum EB6 from palm oil mill effluent. Int J Hydrogen En- ergy 2009; 34:764–71.

[21] Steadman P. Energy, environment and building: a report to the Academy of

Natural Sciences of Philadelphia. Cambridge, London: Cambridge Universi-

ty Press; 1975. p. 287.

[22] Kiely G. Environmental Engineering. International ed. Boston: Irwin, McGraw-Hill; 1998, p. 979.

[23] Tchobanoglous G, Burton FL, Stensel HD. Waste-water Engineering: treat- ment and reuse. Fourth ed. New Delhi: Tata McGraw-Hill Publishing Com- pany Limited; 2003, p. 1819.

[24] ViessmanJr W, Hammer MJ.Water Supply and Pollution Control. New

York: Harper Collins College Publishers; 1993, pp. 513–679.

[25] Eckenfelder Jr WW. Industrial Water-Pollution Control. Boston Burr Ridge:

McGraw-Hill Higher Education; 2000, pp. 394–411

[26] Mattocks R. Understanding biogas generation, Technical Paper No. 4. Vol- unteers in Technical Assistance. Virginia, USA; 1984. p. 13.

[27] Agro climate research centre, Tamil Nadu agricultural university, Coimba- tore, Tamil Nadu, India.

[28] Bohm R., Martens, W. and Philipp, W. (1999) Regulations in Germany and

results of investigations concerning hygienic safety of processing bio wastes in biogas plants. In: Proceedings of the IEA workshop: “Hygienic and envi- ronmental aspects of anaerobic digestion: legislation and experiences in Eu- rope”. pp 48-64 UnivesitatHohenheim, Stuttgart, Germany.

[29] Ojolo SJ, Bamgboye AI. Biogas production from municipal solid wastes. In:

Proceedings of international conference on engineering. Lagos; 2005. p.

303e10.

[30] Xuereb P. Biogas – a fuel produced from waste,

<http://www.synapse.net.mt/mirin/newsletter/3836.asp/>; 1997.