January 1, 1985: Headlines: Environment: Biogas: Biofertilizer: Tulane University: The Biogas/Biofertilizer Business Handbook (Peace Corps, 1985)

Peace Corps Online: Peace Corps News: Peace Corps Library: Environment: January 1, 1985: Headlines: Environment: Biogas: Biofertilizer: Tulane University: The Biogas/Biofertilizer Business Handbook (Peace Corps, 1985)

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The Biogas/Biofertilizer Business Handbook (Peace Corps, 1985)

The Biogas/Biofertilizer Business Handbook (Peace Corps, 1985)

The Biogas/Biofertilizer Business Handbook (Peace Corps, 1985)

The Biogas/Biofertilizer Business Handbook (Peace Corps, 1985)


Main Points of the Handbook


Chapter one: An introduction

Chapter two: Biogas systems are small factories

Chapter three: The raw materials of biogas digestion

Chapter four: The daily operation of a biogas factory

Chapter five: The once a year cleaning of the digester

Chapter six: Tanks and pipes: Storing and moving biogas

Chapter seven: The factory's products: Biogas

Chapter eight: The factory's products: Biofertilizer

Chapter nine: The ABCs of safety

Chapter ten: Conclusion: Profiting from an appropriate technology


Third Edition


Michael Arnott

Printed By:


Information Collection and Exchange

Reprint R-48

July 1985


Peace Corps' Information Collection & Exchange (ICE) was established so that the strategies and technologies developed by Peace Corps Volunteers, their co-workers, and their counterparts could be made available to the wide range of development organizations and individual workers who might find them useful. Training guides, curricula, lesson plans, project reports, manuals and other Peace Corps-generated materials developed in the field are collected and reviewed. Some are reprinted "as is"; others provide a source of field based information for the production of manuals or for research in particular program areas. Materials that you submit to the Information Collection & Exchange thus become part of the Peace Corps' larger contribution to development.

Main Points of the Handbook

I. Purpose and Scale

A. The subject of this book is one approach to building and operating biogas systems, not biogas digesters. Biogas systems include raw material preparation, digesters, separate gas storage tanks, use of the gas to run engines, and the use of the sludge as fertilizer.

B. The systems can be profitably operated as cooperatively or privately owned labor-intensive small businesses. They are designed to meet local fertilizer and fuel needs, using local resources and skills.

C. Like rice and corn mills, ice plants and general stores, biogas businesses have supply, production, distribution, and management responsibilities. Operated as businesses, biogas systems have the potential to make a rewarding return on investment and a contribution to the wealth of the community.

II. Raw Materials

A. Animal waste.

1. Manure is the most common raw material.

B. Plant waste.

1. It is useful when shredded, ground or pulped, and partially composted before being put in the digester.

C. Digester slurry.

1. Slurry is raw material mixed with water or the liquid portion of used slurry.

2. Slurry is mostly water; it should be only eight to ten percent solid.

3. Slurry should have a 30 to 1 carbon to nitrogen ratio and a neutral to slightly base (alkaline) pH.

4. No floating matter, dirt, or sand should be in the slurry.

5. A 40 day digester detention time is recommended, with slurry added once or twice a day.

III. The Digester

A. Horizontal, above ground digesters with a two to three percent tilt down from inlet to outlet are recommended in this book.

B. A digester length-to-diameter ratio of five to one is recommended.

C. Ferrocement, mild steel, and galvanized iron, are the recommended digester and gas storage tank construction materials.

D. Separate gas storage tank(s) are recommended in this book.

E. 10 to 30 cubic meter capacity systems may be practical, but 50 cubic meter capacity and larger systems are practical.

F. A continuously maintained digester temperature of 35 degrees centigrade (96 fahrenheit) is recommended.

G. An annual cleaning of the digester to remove scum and dirt is recommended.

IV. Biogas

A. Biogas can be produced by anaerobic digestion at rates of one to two cubic meters of gas per cubic meter of digester space per day in the digesters described in this book.

B. Biogas composition is 60 to 70 percent methane which burns, 30 to 40 percent carbon dioxide which does not burn, and a trace of hydrogen sulfide which smells like rotten eggs.

C. Condensation traps are needed to remove water vapor from Biogas pipes.

D. Biogas (methane plus carbon dioxide) or methane alone can be used for several purposes.

1. The gas can be used for cooking, gas lights, and gas refrigerators.

2. The position taken in this book is that the best use for the gas is as fuel for stationary spark-ignition and dual-fuel diesel engines for mechanical power and with generators for electrical power.

3. It may be possible to use the gas to heat boilers that power simple "rankine-style" engines for mechanical and electrical power.

E. The carbon dioxide in biogas may have some uses.

1. Carbon dioxide should not be removed from biogas unless there is a practical use for it. The process of separation must be simple and low cost.

2. Carbon dioxide can be used in greenhouse operations to increase crop yields, and it may be practical to freeze the carbon dioxide to make dry ice.

F. The waste heat from engines fueled by biogas or methane must be used to maintain digester temperature at 35 degrees centigrade.

G. Only when digester capacity is big enough to make the use of an engine practical is it likely that the system will be profitable.

V. Biofertilizer

A. Biofertilizer is used digester slurry and is often referred to in this book as sludge.

B. Only when the sludge is used as a fertilizer can a biogas system be profitable.

C. After the sludge has been exposed to the air for a couple of weeks, it makes an excellent soil conditioner and organic fertilizer for crops and fish ponds.

D. The liquid portion of the sludge (90 percent) can be recycled and used in place of water to dilute fresh raw materials.

VI. Secondary Biogas System Projects

A. Flat-plate solar collector water heaters can be used to heat digesters and in a dual-fuel system with biogas to power rankine-cycle engines.

B. Composting can be a useful and necessary part of biogas systems.

C. Bioinsecticides can be a safe, simple method of pest control. When bioinsecticides are used with organic fertilizers, there should be an increase in crop yields and a decrease in crop losses.



If you've heard of biogas, odds are you connect it with one of the following: a technology that could make the world or at least the Third World completely or partly independent of fossil fuels, such as oil and coal; or, a "small is beautiful" idea that flopped.

As a Peace Corps Volunteer (Philippines, 1979-81), I spent much of my time working with biogas systems. Most of my first year back in the United States was devoted to the study of biogas technology. The product of my experiences and studies is The Biogas/Biofertilizer Business Handbook.

The purpose of the book is to answer the question: How can appropriate technology biogas systems contribute to the process of rural community development?

The Larger Issues

Biogas technology has been studied and applied in small, medium, and large scale projects since the 1940's and World War II. However, only since becoming a category of appropriate technology (a community development concept of the 1970's) have biogas systems enjoyed widespread success and failure.

Witold Rybcznski repeatedly cautions: "What if biogas plants benefit the rich and not the poor? What if wind machines are often too expensive? What if the solar heater falls apart after six months? What is no one wants to buy homemade soap? What if [appropriate technology]...cannot deliver the goods?" (Paper Heroes: A Review of Appropriate Technology, 1980).

The Canadian Hunger Foundation expands on these considerations by drawing attention to a full range of development needs in both Third World and industrial nations. "Some [groups] strongly advocated smaller-scale, nonpolluting, locally made technology. Their critics initially viewed them as anti-technology or anti-progress. In the face of formidable resistance, these alternative technologies tended to overpromote their cause. Hand, wind, [biogas], and solar power became panaceas [universal remedies]. In retrospect, those advocates generally agree that their emphasis on small scale was only part of the solution.

"A network of development issues--land reform, education policies, decentralized decision making, suitable consultants, and agricultural and industrial strategies, among others--must also be addressed...[Appropriate technology should ask] what style of progress or industrialization is wanted, what balance between large- and small-scale production is needed, what choices of technology will promote development, and who will participate in the selection of options" (Experiences in Appropriate Technology, 1980).

The ABC's of Biogas

Biogas technology is based on a simple principle: anaerobic digestion. Anaerobic digestion is the biological breakdown of organic matter by living organisms in the absence of oxygen. A liquid organic fertilizer, carbon dioxide, and flammable methane gas are the primary products of the digestion of organic waste by anaerobic bacteria. A natural place for this bacterial activity would be a swamp.

Composting is also based on a simple principle: aerobic digestion. Aerobic digestion involves the breakdown of organic matter by organisms that live in the same oxygen rich environment as we do. Compost fertilizer and carbon dioxide are the main products of aerobic digestion. Diagram 1 charts these two processes for organic decomposition.

The anaerobic digestion of biogas systems takes place in airless metal, concrete, plastic, or brick tanks which can be built under or aboveground. Any of a number of designs are possible, but not all are practical.

A biogas system may be a two to three cubic meter digester with built-in gas storage tank and simple gas stove burner. A biogas system may be one or more 50 to 80 cubic meter digesters with slurry mixing basin, settling, aging and fish ponds, stationary engine, heat exchanger, electric generator, two or more gas storage tanks, and several other auxiliary pieces of equipment. Diagram 2 depicts the basic determinants for the design and capacity of a system.

Basic Q's and A's for Sizing and Using Systems

Are biogas systems primarily for the production of energy? No. Like composting, the primary product is organic fertilizer. Biogas systems have the advantages of producing:

· a more complete fertilizer;

· a more sanitary fertilizer; and e a fuel gas.

At the same time, biogas systems have certain disadvantages:

· the fertilizer is in liquid form; and

· the systems are much more expensive, complex, and susceptible to biological "breakdown" than compost piles are.

Can biogas be run from the waste of a few animals (fecal waste being the traditional organic matter used to fuel digesters)? Yes and no. A biogas system can produce a little methane and fertilizer from daily manure produced by a few pigs or cattle. But small biogas systems will not produce any profits unless subsidized in some way.





What are the primary purposes for building biogas systems?

1) The humus in the organic fertilizer gives nutrients to and conserves the topsoil. Topsoil, the medium in which plants grow, should be seen as a natural resource which is "mined" by farmers. Chemical fertilizers do little in the way of conservation. In fact, chemical fertilizers contribute to the increasing worldwide problem of topsoil erosion. The nutrient value of digester sludge, while harder to quantify than chemical fertilizer, is a high quality fertilizer for crops and fish ponds.

2) Methane (which is 60 to 70 percent of biogas) is the primary ingredient in natural gas, which is a piped gas used to fuel stoves, water heaters, homes, etc. In rural agricultural areas where bottled gas, gasoline, and diesel fuel is expensive, biogas is ideally suited for use in automotive-size stationary engines for the production of mechanical and electrical power.

3) Improved sanitation is a biogas system byproduct. The organic wastes that are processed in the systems would otherwise be breeding grounds for disease-causing bacteria, parasites, and insects.

What is the proper scale and organizational structure of biogas systems? As noted earlier, the scale and structure that is most profitable depends on many factors. One set of technical, political, and economic conditions can easily generate several different expert opinions.

For the same site, one expert might recommend a high technology biogas business that requires US$ 30-50,000 in capital; another might suggest many small family systems costing less than US$ 500 each; and a third expert may prefer a few small businesses or cooperatives needing equipment in the neighborhood of US$ 3,000 to US$ 5,000. Naturally, the designers that back a particular scale also champion different viewpoints on technical designs, raw materials, and uses of the products. Defining biogas systems as business enterprises, rather than as modified septic tanks, implies profitably operated systems that require business as well as technical skills.

The viewpoint of The Biogas/Fertilizer Business Handbook is that the small business or cooperative strategy is best. The digester capacities at this scale are 20 to 60 cubic meters, although total system capacities can be several hundred cubic meters. I believe the economies of scale for biogas systems and the technology's potential contribution to community development is optimized at the small business/medium-scale level.

If built as small, backyard operations, biogas systems tend to be too costly. If they are profitable on this level, which is rare, they make an insignificant contribution to the family or community except as status symbols. On the other hand, as divisions of large private businesses, they tend to increase private profits--with few benefits reaching the public.

The scale of Third World small business that best promotes biogas as a tool of community development is the general store and the rice or corn mill. In the United States and other developed countries, the best community development niche for biogas technology is somewhat different. While the most profitable level is still the small business and cooperative, the operation could be spread over a large geographic area. The enterprises could build and operate biogas systems under contract at several sites such as farms, restaurants, and markets.

In urban industrialized communities anaerobic digestion has been used for many decades to produce methane as an energy supplement for waste treatment plants. These systems have their problems: such as dilute slurries (often only 1/5 to 1/10 the concentration of rural biogas systems) and slurries polluted with toxic heavy metals. Many organizations are researching methods that would detoxify and recycle larger quantities of city sewage than is currently practical. Urban sewage based anaerobic systems are relatively complex when compared with the non-sewage applications of anaerobic systems designed for rural agricultural areas.

Biogas and Community Development

Why should biogas systems contribute to the community development process in both the developed and developing worlds? Operated as small businesses or cooperatives, there are several ways biogas technology can benefit a community.

The decentralization of energy and fertilizer production can bring control, profits, and Jobs to the communities that need the energy and fertilizer. Local enterprises are usually locally controlled. Local enterprises tend to buy their supplies and spend their profits in the communities that buy their products. Biogas systems provide a more labor-intensive approach to the production of fuel and fertilizer than fossil fuel and chemical fertilizer technologies.

The raw materials that biogas digesters turn into fuel and fertilizer are organic wastes which, if not processed quickly, can become "hazardous wastes" that host a wide variety of diseases.

Organic fertilizer, the primary product of digesters, is a very important but sometimes unrealized need of agricultural communities. Throughout the world, family farmers are finding themselves increasingly unable to afford the high risks and costs of "modern" farming. This is true in part because the use of fertilizer is more important to modern farming than it is when traditional methods are used.

A recent U.S. Department of Agriculture study discovered that while organic crop and livestock farmers in the midwest and western cornbelt states often don't get the same high crop yields as their modern neighbors who are dependent on chemical fertilizers, pesticides, and herbicides, the organic farmers have lower costs. This means that net returns per cropland acre of organic farms can be equal to or greater than those of chemical dependent farms (USDA, Report and Recommendations on Organic Farming, Washington, D.C., July, 1980).

The organic farm, which is usually a family farm, is in a mutually supportive relationship with the environment. The success of biogas technology depends on its being understood and applied in that context. The agricultural and AT context of organic farming is part of the social context of community development.

As Michael Todaro notes: "In the absence of appropriate (i.e., more labor-intensive) technologies of small-scale food production, of low-cost housing, of health measures, of small-scale manufacturing [e.g., biogas systems], and of low-coat training and education--attempts to 'get prices right' and even to redistribute assets can be rendered ineffective. The development of an active policy of promoting indigenous local technologies, research and development on relevant problems affecting the levels of living of all people, but especially the poor, may be indispensable to any viable long-run programme of growth without poverty in developing [and developed] countries" (Economics for a Developing World, 1977).

When this story was prepared, here was the front page of PCOL magazine:

This Month's Issue: August 2004 This Month's Issue: August 2004
Teresa Heinz Kerry celebrates the Peace Corps Volunteer as one of the best faces America has ever projected in a speech to the Democratic Convention. The National Review disagreed and said that Heinz's celebration of the PCV was "truly offensive." What's your opinion and who can come up with the funniest caption for our Current Events Funny?

Exclusive: Director Vasquez speaks out in an op-ed published exclusively on the web by Peace Corps Online saying the Dayton Daily News' portrayal of Peace Corps "doesn't jibe with facts."

In other news, the NPCA makes the case for improving governance and explains the challenges facing the organization, RPCV Bob Shaconis says Peace Corps has been a "sacred cow", RPCV Shaun McNally picks up support for his Aug 10 primary and has a plan to win in Connecticut, and the movie "Open Water" based on the negligent deaths of two RPCVs in Australia opens August 6. Op-ed's by RPCVs: Cops of the World is not a good goal and Peace Corps must emphasize community development.

Read the stories and leave your comments.

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Story Source: Tulane University

This story has been posted in the following forums: : Headlines; Environment; Biogas; Biofertilizer



By ahmed sambare ( on Thursday, May 26, 2005 - 7:36 am: Edit Post

please can I have one of the biogas book thank you

By Nimal Perera ( on Tuesday, February 13, 2007 - 9:28 pm: Edit Post

I wish to get a soft copy of "The Biogas/Biofertilizer Business Handbook" by Michael Arnott
Please advise me how to receive this as this is not available at the particular Web site
Thank you

Nimal Perera
Consultant / Scientist
Energy & Environment
Federation of Chambers of Commerce and Industry of Sri Lanka

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