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Practivistas Chiapas biodigester

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Project Page in Progress
This page is a project page in progress. Please refrain from making edits unless you are a member of the project team, but feel free to make comments using the discussion tab. Check back for the finished version on August 12, 2010.

Team Biogas: Julia Balibrera, Gina LaBar, Garnet Empyrion, and Annie Bartholomew

Team Biogas

International Renewable Resources Institute-Mexico

Appropedia Page: International Renewable Resources Institute-Mexico

General Information:

Executive Director Alex Eaton:

Director of the Board Ilan Adler:

Telephone: 011 (52) 55 3547 0221 or 011 (52 1) 55 1886 8210

Instituto Internacional de Recursos Renovables, A.C. Tlacotalpan No. 6 Bis, Int 301, Col Roma Mexico D.F. 06760 (52) 55 3547 0221

"IRRI Mexico is dedicated to promoting sustainable use of natural resources. We provide education, develop new technologies, and install systems that help low income families meet their basic energy, water, and sanitation needs in a sustainable way. Our projects aim to empower families, communities, and businesses to produce their own clean energy, obtain their own water, and manage their own resources and wastes in ways that benefit them and the environment simultaneously."[18]

IRRI's Mission

To promote programs and businesses that produce sustainable goods and services and help reduce reliance on fossil fuels. IRRI supports rural and low-income communities with the objective of improving the quality of life through generating, developing, and conserving local resources. IRRI’s vision is sustainable and equitable prosperity in a world without contamination."[19]

Objective and Background

In the summer of 2010, a collaboration between students of Humboldt State University and the International Institute of Renewable Resources (IRRI) will seek the construction and dissemination of a biodigestion system, the Biobolsa, within the community of San Cristobal de las Casas, Chiapas. The objective of this project is to promote the realization of further Biobolsa projects in the San Cristobal de las Casas area by constructing a successful Biodigester demonstration system in the eco-home of local architect Juan Hidalgo.

In Chiapas, Mexico, wood is used as a primary cooking fuel in rural communities. [1] Wood as a fuel has several drawbacks: it is labor intensive to collect, it contributes to deforestation, and upon combustion poses significant respiratory risks to users.[2] For these reasons, biogas as an alternative to wood fuel can improve the indoor air quality and overall quality of life for consumers in select applications. The most common management practices for livestock manure in Mexico typically consist of large open manure lagoons. [3] These practices result in the uncontrolled release of methane gas into the atmosphere. Methane gas as a greenhouse gas is approximately 21 times more potent than carbon dioxide. [4] The controlled decomposition of animal waste in a biodigester is one alternative to the existing management practices. Use of the Biobolsa system results in the sequestration of greehouse gases and conversion of the animal waste into a safe and effective fertilizer. (REFERENCES)


Criteria Description Weight
Level of Energy Generation Amount of Methane Produced 7
Level of Fertilizer Generation Amount of Fertilizer Bi-product Produced 5
Durability Needs to withstand use with no more than of $5-10 yearly maintenance. 8
Cost Needs to have enough spending to support project but not enough to bankrupt the community 9
Adherence to the Mission of IRRI Meets IRRI's educational standards 8
Level of Cultural Appropriateness Project must be able to be incorporated in the cultural setting of client. 9
Potential for Community Involvement Must be a demonstration biodigestor designed for educating the community. 10


Materials Unit Price (Pesos) Quantity Cost
High Density Polypropylene Biobolsa (3000 liters) and Kit [5] $8000 1 $8000
4" PVC pipe $35/m 2 meters $70
4" PVC wye fitting $25 2 $50
3/8" flexible hose (gas) $7/meter 55 meters $385
Cement $115/bag 2 $230
Chicken Wire $22/meter 1 $22
nails $0 1 $0
4" PVC pipe (for drainage system) $46/meter 5meters $232
Printing of Interpretive Signs $2 6 $10
Laminating of interpretive signs $16 6 $96
Glue (for PVC) $12.5 1 $12.5
Glue (for plastic sheeting) $0 1 $0
Corrugated Plastic Roofing Sheets $360/sheet 9 $3240
Post for roof (wooden) $50/post 6 $300
Buckets $15/bucket 2 $30
Cross Beams $30/beam 3 $90
Beams $15/beam 7 $105
Plastic Sheeting $45/5 meters 2 $90
stove $0 1 $0
Total $0

The Site Before

Poop Chute

Rubble Trench Construction

Digging the Biodigester Trench

Biodigester diagramed copy.jpg


Hydraulic Retention Time(HRT) = total liquid volume of system (L)/ daily input of water/effluent mixture (L/day)

This equation illustrates the amount of time that material (effluent) will reside within a biodigestion system before exiting as Biol[7], however due to sedimentation not all material will have the same HRT.

In order to calculate the HRT, we measured the amount of waste produced by Juan´s pigs within a 24 hour period. Our HRT, based on three seperate collections, is:

3,000 liter / 2 liters of effluent + 12 liters of water = 187.5 days, or 6.25 months

This value indicates that the system will require 6.25 months to complete biodigestion given a daily input of 2 liters of waste. As we have stated, the pigs in question are 3 mature pigs and 4 young piglets. As the four piglets grow, the daily input of waste is sure to follow. That said, the HRT can be expected to decrease with time.

Àmortization = (cost of system) / ( (Energy Produced/Year) + (Emissions Reduced/Year) + (Fertilizer/Year) + (Health Benefits) + (Quality of Life)

This equation illustrates the amount of time the system will take to pay back its initial investment as a result of energy produced (displacing the cost of other fuel sources), emissions reduction (which can be translated financially due to carbon market equivalencies), fertilizer produced (displacing the cost of fertilizer) along with the non quantifiable benefits of improved health and quality of life.

Literature Review

Biodigestion describes the biological process by which organic matter is digested by anaerobic bacteria over the course of time. In the natural world, biodigestion occurs in a variety of anaerobic, that is to say, oxygen-free, environments, such as within marshes, rice paddies, and upon the ocean floor. A biodigestion system, or biodigestor, is a system which uses the metabolism of anaerobic bacteria in order to digest animal manure, producing biogas, a clean, renewable fuel source, as well as effluent, an organic fertizilizer which in the case of our Biobolsa system we call Biol.

Animal Waste

Animal waste is a broad term which considers all digestive products of an animal: feces, urine, respiration and fermenation gases. This project will focus on solid waste products, that is to say, animal feces, or manure. Manure is composed of undigested dietary residues, endogenous secretions and a variety of naturally occuring anaerobic bacterias; these bacteria are critical players in animal digestion, and some are sloughed off during excretion. Once excreted, manure undergoes a series of microbial conversions conveyed by these same anaerobic bacteria. [8]


Left to decompose in an open environment, a body of animal manure is digested by anaerobic bacteria leached from the digestive tract of the animal during excretion. This form of digestion is called fermentation, in which anaerobic bacteria render large macromolecules of undigested dietary residues into vaporized end products, methane and carbon dioxide. [9] Approximiately 90% of the energy of the manure is converted to these fermentation gases, assuming appropriate temperature and anaerobic conditions. The fact remains that open air decomposition of animal manure does not assure these characteristic conditions, with the result that -- "When manure undergoing degradation has a surface exposed to the atmosphere, volatile products and intermediates are emitted into the environment." [10]


Mismanagement of animal waste is problematic with consideration to both the health of the planet as well as the health of its inhabitants, humans and other animals alike.[11] The odors themselves can be harmful to human health, causing irritation of the eye, nose, throat, headache, nausea, vomiting. [12] Furthermore, the decomposition of animal manure in an open environment potentates the spread of a suite of zoonotic pathogens which are extremely transmittable to humans. Raw, or partially digested, manure retains hazardous pathogens which can be spread to humans through premature composting, agricultural run off and contamination of the water table. [13] The unmanaged (uncontained) decomposition of animal manure releases a host of environmentally destructive gases into the atmosphere, byproducts of fermentation. Furthermore, surface run off of manure contributes to the degradation of local ecology. [14] :


  • Methane: CH4 accumulates in the atmosphere, which has a greenhouse gas potential 20% more destructive than CO2 (Schulte, 1997)
  • Carbon Dioxide: CO2 is also released ; "Geological records show that, on current trajectories of CO2-e increase, we are likely to see sea level rise by around 25 meters, with temperatures 2-3°C higher and permanent El Nino conditions."[15]
  • Ammonia: NH3 is volatized, which causes acid rain (Lowe, 1995; Likens et al., 1996).
  • Nitrous Oxide: N2O is released, which contributes to ozone depletion. (Schulte, 1997).


  • contamination of the water table
  • Ammonia toxicification of water
  • Eutrophication of water: algal blooms
  • Phosphorous toxification of topsoil
  • Salination of topsoil

Potential as Fertilizer

The use of animal manure as organic fertilizer to improve crop yields is practice long applied by agriculturists around the world. For its high macro nutrient content, animal manure confers considerable amounts of nitrogen, potassium and phosphorous to germinating crops and can critically improve soil health. [16]. However, research has proven that manure that has undergone biodigestion is a more effective fertilizer than raw, or fresh, manure. [17] Furthermore, the application of raw manure to soil can potentially contaminate agricultural products with hazardous pathogens. These pathogens are heat-sensitive, generally destroyed by temperatures of 36 degrees celsius or greater. [18] Biodigestion, of which mesophilic bacteria are primary players, occurs optimally at 15-40 celsius. This means that the effluent produced is pathogen free.

Anaerobic Digestion


Anaerobic digestion is a series of processes in which microorganisms break down biodegradable material without oxygen. In order to promote this anaerobic process biobolsas and similiar systems are sealed to keep out as much air as possible. Anaerobic processes have the benefits of producing less biological sludge, minimal amount of energy required and methane is produced which can be used as an energy source. [19]

The digestion process begins with bacterial hydrolysis of the input materials in order to break down insoluble 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, hydrogen, and carbon dioxide. Methanogens, finally are able to convert these products to methane and carbon dioxide.[20] The methanogenic bacteria in stage three of the anaerobic digestion is responsible for the formation of methane. There are two common ways of forming methane, by splitting acetate (Equation 1) and by the reduction of carbon dioxide (Equation 2). The methanogens which splits the acetate is about half as common as the methanogens that reduced carbon dioxide which explains why the resulting biogas is normally around 65% methane and 35% carbon dioxide. Biogas is also made up of small amounts of other gases such as hydrogen sulfide and some water vapor. [21]

Equation 1:

CO2 +8H‐>CH4 +2H2O

Equation 2:

CH3COOH ‐> CH4 + CO2 [22]

Gas Scrubbing

Typically, biogas is composed of 55 - 65% methane, 35-45% carbon dioxide, a small fraction of hydrogen sulfide gas, and other trace gases. Of these impurities, the presences of CO2 (carbon dioxide) and H2S (hydrogen sulfide) are the most problematic. As both displace methane in biogas, both will reduce the combustion and efficiency of biogas. Furthermore, although H2S constitutes less than 0.5% of the gas stream, it is extremely corrosive. Any netal equipment used within a biogas system to convert the gas to either direct heat applications (a boiler) or to more complex energy exchanges (a generator) will therefore degrade relatively quickly. [23] The larger the system, the larger the impact the presence of gaseous impurties will have on biogas production. As we are building a small, size 3 Biobolsa system [24], the intended application of the biogas is relatively small and therefore will not require an industrial approach to gas scrubbing. In order to reduce the H2S in the biogas, our system uses a packet of non stainless steel wool in the gas regulator in order to oxidize the H2S to sulfur before it has a chance to degrade metal equipment interior to the biogas´s end-use.

Social Incentive

"Biogas technology not only supports national economies and the environmental protection, but as its main outcome for the local population it provides for a wide range of improvements in overall living conditions. Sanitary and health conditions improve and the quality of nutrition is enhanced by an improved energy availability. Through the provision of lighting and the reduction of time-consuming fuel gathering cultural and educational activities are supported. Employment, professional qualification and overall food supply of the local population can be improved as well. But biogas technology can also contribute to an accentuation of existing differences in family income and property. Establishing community-level biogas systems is a way to ensure that the technology benefits a greater number of residents. If social policies of a developing country are clearly focusing on poverty alleviation, biogas technology may not be the first choice among other "village technologies". It’s place is shifting rather towards the rural agricultural middle class, communities (for waste water treatment) and industries." Habermehl Stefan, Kossmann Werner, Pönitz Uta, Biogas Digest:Volume III Biogas - Costs and Benefits and Biogas – Programme Implementation <> (July 11, 2010)

"Considerable workload reduction in rural areas: This is particularly true for rural women engaged in day to day household work. Installing a biogas unit will relieve her of the tiring and tedious job of collecting and ferrying firewood. Since, biogas burns cleanly, the rural homes will not suffer from smoke and consequently rural denizens will suffer less from physical problems like bronchial complications. Cooking is also easier with a gas stove and takes less time."

Economy watch (2010) <> (July 11, 2010)

"Conversion of natural organic waste into fertilizer: The conversion is carried out in a machine called the polythene bio gas digester. Cow dung slurry is put into the machine. The product is organic fertilizer of high quality. The fertilizer obtained is rich in nitrogen. It has been analyzed, that, fertilizer made by the polythene bio gas digester contains nitrogen content 3 times more than the product made by conventional processes. It is completely natural and free from harmful synthetic chemicals."

Economy watch (2010) <> (July 11, 2010)

Environmental Incentive

Carbon Offset & Methane Reduction

"Each year some 590-880 million tons of methane are released worldwide into the atmosphere through microbial activity. About 90% of the emitted methane derives from biogenic sources, i.e. from the decomposition of biomass. The remainder is of fossil origin (e.g. petrochemical processes). In the northern hemisphere, the present tropospheric methane concentration amounts to about 1.65 ppm(parts per million)...Unlike fossil fuel combustion, biogas production from biomass is considered CO2 neutral and therefore does not emit additional Greenhouse Gases (GHG) into the atmosphere...However, if biogas is not recovered properly, it will contribute to a GHG effect 20 times worst than if methane is simply combusted. Therefore, there is a real incentive to transfer biogas combustion energy into heat and/or electricity."

Singh, Chandan (2006) <> (July 11, 2010)

"Biogas not only releases far less carbon dioxide than fossil fuels, but it also produces smaller quantities of other pollutants such as heavy metals, sulfur dioxide, nitrogen and particulates...One of the gases produced by the decomposition of manure is methane gas, which is estimated to trap 20 to 30 times as much atmospheric heat as carbon dioxide, and reducing methane releases into the air is a crucial element of the fight to limit global warming. The relatively simple digestion process that produces biogas converts a foul-smelling manure pile from a methane-emitting climate villain to high-quality... fuel. And digestion doesn’t reduce the value of manure as an agricultural fertilizer. The important substance for plant growth is nitrogen, which remains in place after extraction of biogas...This leads to further environmental advantages. By reducing the weight and volume of fertilizer, biogas extraction cuts down on transportation pollution. And increasing the amount of fertilizer available from composted waste reduces the need for artificial fertilizers, which release the extremely powerful greenhouse gas nitrous oxide."

Advantage Environment (2009) < > (July 11, 2010)

The size of the biodigester determines offsets in regards to wood and carbon as well as the methane reductions. For example, "1 biogas plant is computed to save 32 liters of kerosene and 4 tons of firewood every year."

Economy Watch (2010) <> (July 11, 2010)

Another type:"Each biogas plant saves about 2.5 tonnes/year of fuelwood, equivalent to about four tonnes/year of CO2. And incidence of respiratory diseases has reduced among users."

The Ashden Awards (2010) <> (July 11, 2010)

"Another major environmental target is the mitigation of deforestation and soil erosion through the substitution of firewood as an energy source." Habermehl Stefan, Kossmann Werner, Pönitz Uta, Biogas Digest:Volume III Biogas - Costs and Benefits and Biogas – Programme Implementation <> (July 11, 2010)

Dissemination of Different Models

Worldwide, the dissemination of different models of biodigestion systems has seen three general trends of biodigestor design which are identified by their different countries of origin. [25]


From A CHINESE BIOGAS HANDBOOK [26] "Since the 1950s China has experimented with the production of biogas from agricultural wastes, a practice based upon an age-old Chinese tradition of cornposting human, animal and piant wastes to produce an organic fertilizer of high quality. The breakthrough came in 1975 when a process was developed to ferment the materials in an airtight and watertight container in order to produce methane gas." This "breakthrough" describes the innovation of the Chinese Fixed Dome biodigestor, which has been reproduced in over 7 million systems around the world although the majority of these systems operate in China. The system is constructed of cement, thereby requiring skilled labor and an extensive installation time. In the field, the design has shown structural weakness in the low production of gas and the frequent occasion of gas leaks. [27]

India The floating cover, or Indian, biodigestor was designed to address the problem of gas leaks in the Chinese Fixed Dome. In this model, the gas storage mechanism consists of a floating cover, typically constructed of fiberglass, which rises in response to the generation of gas, therefore having a larger gas storage capacity. Although over 3 million have been constructed around the world, this system too is difficult to effectively demonstrate as the system consists of moving parts of high industrial cost (fiberglass). [28]

Taiwan The Taiwenese, or "tubular plastic", design is the most economical of the 3 models discussed. As a result of high installation costs and difficulty in replacing parts, a continuous flow digester contained withing a plastic bag was developed in order to achieve 1) greater weatherability 2) more efficient gas production 3) cheaper and more uniform manufacture and 4) a shorter installation time. [29]

Our project is based on this tubular plastic model for a biodigestor. Specifically, we will be building a Biobolsa system, engineered by Sistema Biobolsa [30]


  • Current:
    • Of the approximately 250 industrial biodigester projects that the Clean Development Mechanism (a mechanism of the Kyoto Protocol) has funded 200 of those are in Brazil and Mexcio. Additionally, nearly 30% of all the 'waste gas recovery projects' are in Mexico making up about 110 projects of which the great majority are anaerobic digesters. [31]
  • Future:
    • Anaerobic digester systems may not be possible in some areas of Mexico due to water shortages. [32]

Logistical Analysis of Site

  • Address + GPS

Client: Juan Hidalgo Calle Tapachula #55 San Cristóbal de las Casas, Chiapas Mexico 16° 44’ 27.46’’ N 92° 37’ 39.78’’ W Elev. 2154m Espacio: 7m x 2.7m

Climate of San Cristobal

• Monthly temperature averages for San Cristóbal de las Casas

"January Avg low: 17° Avg hi: 29° Avg precip: 0.03 cm February Avg low: 18° Avg hi: 30° Avg precip: 0.19 cm March Avg low: 19° Avg hi: 33° Avg precip: 0.02 cm April Avg low: 21° Avg hi: 35° Avg precip: 0.61 cm May Avg low: 22° Avg hi: 34° Avg precip: 3.45 cm June Avg low: 22° Avg hi: 32° Avg precip: 14.23 cm July Avg low: 21° Avg hi: 31° Avg precip: 9.64 cm August Avg low: 21° Avg hi: 31° Avg precip: 12.78 cm September Avg low: 21° Avg hi: 30° Avg precip: 12.15 cm October Avg low: 20° Avg hi: 30° Avg precip: 3.45 cm November Avg low: 19° Avg hi: 30° Avg precip: 0.77 cm December Avg low: 18° Avg hi: 29° Avg precip: 0.28 cm"

Foreca 2010 <> (July 11, 2010)

• Daytime temperatures average from 19° C. (66° F.) in winter and 23° C. (73° F.) in summer. Overnight lows average from 5° C. (41° F.) in winter and 13° C. (55° F.) in summer. < > (July 11, 2010)

Thermophilic Bacteria

Micro-organisms which live in temperatures of 40°C-80°C are "thermophiles" and those that live in 10°C-47°C "mesophiles."[33] A study was performed to assess the effect of temperature variations on the performance of a mesophilic (35 degreesC) and a thermophilic (55 degreesC) upflow anaerobic filter treating a simulated papermill wastewater. It was found that the thermophilic produced much less diversity in bacteria than the mesophilic. The study showed that both systems had a decrease in productivity (produced less biogas) when temperatures were dropped to 35 degrees C.[34]

Tentative Schedule

  • Week 1:
    • Literature Review
    • Criteria
    • Meeting with IRRI (7/8)
    • Set up Site Visit with Kiva
  • Week 2:
    • Continue Investigation
    • Site Evaluation (Wed 7/14)
    • Arrange Site with IRRI and report to Lonny

  • Week 3:
    • Class Installation (Tue/Wed)
  • Week 4:
    • Assist IRRI with public course
    • Second Installation
    • Tests and Infrastructure
  • Week 5:
    • Complete page on biodigestion on IRRI's website

Thought you might want this

The videos below include:

  • Alex Eaton on how to install the biogas system
  • Super adobe;Julia y Gina
  • Films brought to you by Enrique Díaz


  1. "One in four households use fuel wood for either all or part of their energy for cooking" [Masera O. 2005. From Cookstoves to Cooking Systems: The Integrated Program on Sustainable Household Energy Use in Mexico. Energy for Sustainable Development 9, no. 1: 25‐36.]
  2. "Visible improvement in rural hygiene: Biogas contributes positively to rural health conditions. Biogas plants lower the incidence of respiratory diseases. Diseases like asthma, lung problems, and eye infections have considerably decreased in the same area when compared to the pre-biogas plant times. Biogas plants also kill pathogens like cholera, dysentery, typhoid, and paratyphoid." Economy Watch (2010) (July 11, 2010)
  3. "The common practice for manure management at these large pig farms in Mexico is storage in open manure lagoons. These lagoons are anaerobic below the water level, and produce large amounts of methane that bubbles out of the surfaceof the lagoon." [Eaton, A.B. (2009) "The Role of Small-Scale Biodigesters in the Engery, Health and Climate Change Baseline in Mexico" Masters Thesis, HSU Environmental Resource Engineering.]
  4. To convert a known mass of methane to the universal CO2 equivalent (tonnes CO2e) global warming potential, multiply the methane mass by 21 (UNFCCC, 2008). [Eaton, A.B. (2009) "The Role of Small-Scale Biodigesters in the Engery, Health and Climate Change Baseline in Mexico" Masters Thesis, HSU Environmental Resource Engineering.]
  5. the IRRI Biobolsa system includes: the gas regulator system with sulfur filter, hose to connect to Biobolsa system and valve, a biogas reservoir bag and plastic net to suspend bag from roofing, a recycled PET plastic blanket to protect the Biobolsa, a repair kit for the Biobolsa and a use and maintenance manuel for the whole system. <> Manual de Instalación.
  6. Biol, a nitrogen rich liquid fertilizer, is the end product of the input effluent into the Biobolsa system. IRRI "Presentación_FIRA_lite.pfd"
  7. Biol, a nitrogen rich liquid fertilizer, is the end product of the input effluent into the Biobolsa system. IRRI "Presentación_FIRA_lite.pfd"
  8. Mackie et al "Biological Identification and Biological Origin of Key Odor Components in Livestock Waste" J Anim Sci 1998. 76:1331-1342.
  9. Mackie et al "Biological Identification and Biological Origin of Key Odor Components in Livestock Waste" J Anim Sci 1998. 76:1331-1342.
  10. Bhattacharya A. N. and Taylor J. C. "Recycling Animal Waste as a Feedstuff: A Review" J Anim Sci 1975. 41:1438-1457.
  11. "38% of pigfarms dispose of their wastewaters without any treatment directly into the nation's waterbodies, which in turn has a severe impact on the environment" Victoria-Almeida, et al. "Sustainable Management of Effluent from Small Pigery Farms in Mexico" Instituo de Ingenieria, Universidad Nacional Autonoma de Mexico, Cd Universitaria 04510 D.F., Mexico.
  12. Mackie et al "Biological Identification and Biological Origin of Key Odor Components in Livestock Waste" J Anim Sci 1998. 76:1331-1342.
  13. Guan, Tat Yee and Holley, Richard A. "Pathogen Survival in Swine Manure Environments and Transmission of Human Enteric Illness" Dept. of Food Science, Faculty of Food and Agricultural Science, University of Manitoba, Winnepeg, Manitoba R3T 2NT Canada.
  14. Mackie et al "Biological Identification and Biological Origin of Key Odor Components in Livestock Waste" J Anim Sci 1998. 76:1331-1342.
  15. Glikson, Andrew, PhD. “THE THREAT TO LIFE POSED BY ATMOSPHERIC CO2-e OVER 450 ppm” Submission to the Senate Inquiry into the exposure drafts of the legislation to implement the Carbon Pollution Reduction Scheme Australian National University Canberra, Australia
  16. "Animal manure is a valuable fertilizer as well, conferring inputs to the soil over and above the simple chemical nutrients of N, P and K. As an input into the crop cultivation systems, manure continues to be the link between crop and animal production throughout the developing world." Rodríguez et al. "Integrated farming systems for efficient use of local resources" University of Tropical Agriculture-UTA, Finca Ecológica, College of Agriculture and Forestry,Thu Duc, Ho Chi Minh, Vietnam
  17. "The biomass yield, and content of moisture and crude protein, of Chinese cabbage was highest when fertilized with biodigester effluent and lowest when fresh residual solids from manure were used." Thy, San and Buntha, Pheng "Evaluation of fertilizer of fresh solid manure, composted manure or biodigester effluent for growing Chinese cabbage (Brassica pekinensis)" Center for Livestock and Agriculture Development (UTA-Cambodia), POB 2423, Phnom Penh 3, Cambodia
  18. Ingham, et al. "Escherichia coli Contamination of Vegetables Grown in Soils Fertilized with Noncomposted Bovine Manure: Garden-Scale Studies" Department of Food Science,1 Hancock Agricultural Research Station,2 Lancaster Agricultural Research Station, 3 West Madison Agricultural Research Station, University of Wisconsin—Madison, Madison, Wisconsin (Received 5 March 2004/ Accepted 1 July 2004)-
  19. Ibanez, J. G., Hernandez-Esparza, M., Doria-Seranno, C., Singh, M. M. (2007).Environmental Chemistry: Fundamentals, 1st Ed., Springer, New York.
  20. TerraForm (2009)."Anaerobic Digestion" &amp;lt;;gt;.
  21. Eaton, A.B. (2009) "The Role of Small-Scale Biodigesters in the Engery, Health and Climate Change Baseline in Mexico" Masters Thesis, HSU Environmental Resource Engineering.
  22. Gerardi, M. H. (2003) “Microbiology of Anaerobic Digesters” 1st Ed., Hoboken, New Jersey.
  23. Taylor, John Poe , Removal of Hydrogen Sulfide from Biogas, August 2003.
  25. Eaton, A.B. (2009) "The Role of Small-Scale Biodigesters in the Engery, Health and Climate Change Baseline in Mexico" Masters Thesis, HSU Environmental Resource Engineering.
  26. Translated by Michael Cook, edited by: Ariane van Buren "A Chinese Biogas Handbook" Published by: Intermediate Technology Publications, Ltd. London WC2E 8HN United Kingdom 1979
  27. Eaton, A.B. (2009) "The Role of Small-Scale Biodigesters in the Engery, Health and Climate Change Baseline in Mexico" Masters Thesis, HSU Environmental Resource Engineering.
  28. Eaton, A.B. (2009) "The Role of Small-Scale Biodigesters in the Engery, Health and Climate Change Baseline in Mexico" Masters Thesis, HSU Environmental Resource Engineering.
  29. Eaton, A.B. (2009) "The Role of Small-Scale Biodigesters in the Engery, Health and Climate Change Baseline in Mexico" Masters Thesis, HSU Environmental Resource Engineering.
  30. [[1]]
  31. Eaton, A.B. (2009) "The Role of Small-Scale Biodigesters in the Engery, Health and Climate Change Baseline in Mexico" Masters Thesis, HSU Environmental Resource Engineering.
  32. Secretaría de Medio Ambiente y Recursos Naturales (2008) "Animal Waste Management Methane Emissions" Presentation prepared for Methane to Market. &amp;lt;;gt;
  33. Rose, A. H., and Wilkinson, J. F. (1979) "Advances in Microbial Physiology" Vol. 19, 1st Ed., New York, New York.
  34. Ahn, JH and Forster, CF (2002) The effect of temperature variations on the performance of mesophilic and thermophilic anaerobic filters treating a simulated papermill wasterwater. Process Biochemistry, 37 . pp. 589-594. ISSN 0032-9592