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                          3-CUBIC METER BIOGAS PLANT
                             A CONSTRUCTION MANUAL
                                                a VITA publication
                              ISBN 0-86619-069-4
                 [C] 1980 Volunteers in Technical Assistance
                          3-CUBIC METER BIOGAS PLANT
                             A CONSTRUCTION MANUAL
                                 Published by
                       1600 Wilson Boulevard, Suite 500
                         Arlington, Virginia 22209 USA
                     Tel: 703/276-1800 . Fax:703/243-1865
             This book is one of a series of manuals on renewable
             energy technologies. It is primarily intended for use
             by people in international development projects. The
             construction techniques and ideas presented here are,
             however, useful to anyone seeking to become energy
             Volunteers in Technical Assistance, Inc., wishes to
             extend sincere appreciation to the following individuals
             for their contributions:
                William R. Breslin, VITA, Mt. Rainier, Maryland
                Ram Bux Singh, Gobar Gas Research Station, India
                Bertrand R. Saubolle, S.P., VITA, Nepal
                Paul Warpeha, VITA, Mt. Rainier, Maryland
                Paul Leach, VITA, Morgantown, West Virginia
                              TABLE OF CONTENTS
           Cost Estimate
           By-Products of Digestion
           Heating and Insulating Digesters
           Prepare Foundation and Walls
           Prepare the Gas Cap Drum
           Prepare Moisture Trap
           Prepare Mixing and Effluent Tanks
           Output and Pressure
           Improvised Stove
           Possible Troubles
           A Listing of Recommended Resource Materials
           Useful Information for Methane
             Digester Designs
                          3-CUBIC METER BIOGAS PLANT
                             A CONSTRUCTION MANUAL
Biofuels are renewable energy sources from living organisms.
All biofuels are ultimately derived from plants, which use the
sun's energy by converting it to chemical energy through photosynthesis.
When organic matter decays, burns, or is eaten, this
chemical energy is passed into the rest of the living world. In
this sense, therefore, all life forms and their by-products and
wastes are storehouses of solar energy ready to be converted
into other usable forms of energy.
The kinds and forms of the by-products of the decay of organic
matter depend on the conditions under which decay takes place.
Decay (or decomposition) can be aerobic (with oxygen) or anaerobic
(without oxygen). An example of anaerobic decomposition is
the decay of organic matter under water in certain conditions
in swamps.
Aerobic decomposition yields such gases as hydrogen and ammonia.
Anaerobic decomposition yields primarily methane gas and
hydrogen sulfide. Both processes produce a certain amount of
heat and both leave a solid residue that is useful for enriching
the soil. People can take advantage of the decay processes
to provide themselves with fertilizer and fuel. Composting is
one way to use the aerobic decay process to produce fertilizer.
And a methane digester or generator uses the anaerobic
decay process to produce both fertilizer and fuel.
One difference between the fertilizers produced by these two
methods is the availability of nitrogen. Nitrogen is an element
that is essential to plant growth. As valuable as compost is,
much of the nitrogen held in the original organic materials is
lost to the air in the form of ammonia gas or dissolved in
surface runoff in the form of nitrates. The nitrogen is thus
not available to the plants.
In anaerobic decomposition the nitrogen is converted to ammonium
ions. When the effluent (the solid residue of decomposition)
is used as fertilizer, these ions affix themselves
readily to soil particles. Thus more nitrogen is available to
The combination of gases produced by anaerobic decomposition is
often known as biogas. The principle component of biogas is
methane, a colorless and odorless gas that burns very easily.
When handled properly, biogas is an excellent fueld for cooking,
lighting, and heating.
A biogas digester is the apparatus used to control anaerobic
decomposition. In general, it consists of a sealed tank or pit
that holds the organic material, and some means to collect the
gases that are produced.
Many different shapes and styles of biogas plants have been
experimented with: horizontal, vertical, cylindrical, cubic,
and dome shaped. One design that has won much popularity, for
reliable performance in many different countries is presented
here. It is the Indian cylindrical pit design. In 1979 there
were 50,000 such plants in use in India alone, 25,000 in Korea,
and many more in Japan, the Philippines, Pakistan, Africa, and
Latin America. There are two basic parts to the design: a tank
that holds the slurry (a mixture of manure and water); and a
gas cap or drum on the tank to capture the gas released from
the slurry. To get these parts to do their jobs, of course,
requires provision for mixing the slurry, piping off the gas,
drying the effluent, etc.
In addition to the production of fuel and fertilizer, a
digester becomes the receptacle for animal, human, and organic
wastes. This removes from the environment possible breeding
grounds for rodents, insects, and toxic bacteria, thereby
producing a healthier environment in which to live.
Applications:  * Gas can be used for heating, lighting, and
                       * Gas can be used to run internal combustion
                         engines with modifications.
                       * Effluent can be used for fertilizer.
Advantages:    * Simple to build and operate.
                       * Virtually no maintenance--25-year digester
                       * Design can be enlarged for community
                       * Continuous feeding.
                       * Provides a sanitary means for the treatment
                         of organic wastes.
Disadvantages: * Produces only enough gas for a family of
                       * Depends upon steady source of manure to
                         fuel the digester on a daily basis.
                       * Methane can be dangerous. Safety precautions
                         should be observed.
Construction time and labor resources required to complete this
project will vary depending on several factors. The most
important consideration is the availability of people interested
in doing this project. The project may in many circumstances
be a secondary or after-work project. This will of
course increase the length of time needed to complete the
project. The construction times given here are at best an estimation
based on limited field experience.
Skill divisions are given because some aspects of the project
require someone with experience in metalworking and/or welding.
Make sure adequate facilities are available before
construction begins.
The amount of worker-hours needed is as follows:
*  Skilled labor - 8 hours
*  Unskilled labor - 80 hours
*  Welding - 12 hours
Several other considerations are:
*  The gas plant will produce 4.3 cubic meters of gas per day
   on the daily input from eight cattle and six humans.
*  The fermentation tank will have to hold approximately 7
   cubic meters in a 1.5 X 3.4 meters deep cylinder.
*  A gas cap to cover the tank should be 1.4 meters in diameter
   X 1.5 meters tall.
$145-800 (U.S., 1979) includes materials and labor.
(*)Cost estimates serve only as a guide and will vary from
country to country.
When determining whether a project is worth the time, effort,
and expense involved, consider social, cultural, and environmental
factors as well as economic ones. What is the purpose of
the effort? Who will benefit most? What will the consequences
be if the effort is successful? And if it fails?
Having made an informed technology choice, it is important to
keep good records. It is helpful from the beginning to keep
data on needs, site selection, resource availability, construction
progress, labor and materials costs, test findings, etc.
The information may prove an important reference if existing
plans and methods need to be altered. It can be helpful in pinpointing
"what went wrong?" And, of course, it is important to
share data with other people.
The technologies presented in this series have been tested
carefully, and are actually used in many parts of the world.
However, extensive and controlled field tests have not been
conducted for many of them, even some of the most common ones.
Even though we know that these technologies work well in some
situations, it is important to gather specific information on
why they perform better in one place than in another.
Well documented models of field activities provide important
information for the development worker. It is obviously
important for a development worker in Colombia to have the
technical design for a plant built and used in Senegal. But it
is even more important to have a full narrative about the plant
that provides details on materials, labor, design changes, and
so forth. This model can provide a useful frame of reference.
A reliable bank of such field information is now growing. It
exists to help spread the word about these and other technologies,
lessening the dependence of the developing world on
expensive and finite energy resources.
A practical record keeping format may be found in Appendix II.
The design presented here <see figure 1> is most useful for temperate or

tcm1x9.gif (600x600)

tropical climates. It is a 3-cubic meter plant that requires
the equivalent of the daily wastes of six-eight cattle. Other
sizes are given for smaller and larger digester designs for
This digester is a continuous-feed (displacement) digester.
Relatively small amounts of slurry (a mixture of manure and
water) are added daily so that gas and fertilizer are produced
continuously and predictably. The amount of manure fed daily
into this digester is determined by the volume of the digester
itself, divided over a period of 30-40 days. Thirty days is
chosen as the minimum amount of time for sufficient bacterial
action to take place to produce biogas and to destroy many of
the toxic pathogens found in human wastes.
Table 1 shows the various stages of decomposition and the forms

tcmxtab1.gif (600x600)

of the material at each stage. The inorganic solids at the bottom
of the tank are rocks, sand, gravel, or other items that
will not decompose. The effluent is the semisolid material left
after the gases have been separated. The supernatant is biologically
active liquid in which bacteria are at work breaking
down the organic materials. A scum of harder-to-digest fibrous
material floats on top of the supernatant. It consists
primarily of plant debris. Biogas, a mixture of combustible
(burnable) gases, rises to the top of the tank.
The content of biogas varies with the material being decomposed
and the environmental conditions involved. When using cattle
manure, biogas usually is a mixture of:
     [CH.sub.4] (Methane)                     54-70%
     [CO.sub.2] (Carbon Dioxide)              27-45%
     [N.sub.2] (Nitrogen)                     .5-3%
     [H.sub.2] (Hydrogen)                      1-10%
     CO (Carbon Monoxide)                      0-.1%
     [O.sub.2] (Oxygen)                        0-.1%
     [H.sub.2]S (Hydrogen Sulfide)
     Small amounts of trace elements, amines, and sulphur
The largest, and for fuel purposes the most important, part of
biogas is methane. Pure methane is colorless and odorless.
Spontaneous ignition of methane occurs when 4-15% of the gas
mixes with air having an explosive pressure of between 90 and
104 psi. The explosive pressure shows that biogas is very
combustible and must be treated with care like any other kind
of gas. Knowledge of this fact is important when planning the
design, building, or using of a digester.
There are several points to keep in mind before actual
construction of the digester begins. The most important
consideration is the location of the digester. Some of the
major points in deciding the location are:
*  DO NOT dig the digester pit within 13 meters of a well or
   spring used for drinking water. If the water table is reached
   when digging, it will be necessary to cement the inside of
   the digester pit. This increases the initial expense of
   building the digester, but prevents contamination of the
   drinking supply.
*  Try to locate the digester near the stable (see Figure 2) so

tcm2x12.gif (600x600)

   excessive time is not spent transporting the manure. Remember,
   the fresher the manure, the more methane is produced as
   the final product and the fewer problems with biogas generation
   will occur. To simplify collection of manure, animals
   should be confined.
*  Be sure there is enough space to construct the digester. A
   plant that produces 3 cubic meters of methane requires an
   area approximately 2 X 3 meters. If a larger plant is
   required, figure space needs accordingly.
* Arrange to have water readily available for mixing with the
* Plan for slurry storage. Although the gas plant itself takes
  up a very small area, the slurry should be stored either as
  is or dried. The slurry pits should be large and expandable.
* Plan for a site that is open and exposed to the sun. The
  digester operates best and gives better gas production at
  high temperatures (35[degrees]C or 85-100[degrees]F). The digester should
  receive little or no shade during the day.
* Locate the gas plant as close as possible to the point of gas
  consumption. This tends to reduce costs and pressure losses
  in piping the gas. Methane can be stored fairly close to the
  house as there are few flies or mosquitos or odor associated
  with gas production.
Thus, the site variables are: away from the drinking water
supply, in the sun, close to the source of the manure, close to
a source of water, and close to the point where the gas will be
used. If you have to choose among these factors, it is most
important to keep the plant from contaminating your water
supply. Next, as much sun as possible is important for the
proper operation of the digester. The other variables are
largely a matter of convenience and cost: transporting the
manure and the water, piping the gas to the point of use, and
so on.
The amount of gas produced depends on the number of cattle (or
other animals) and how it is going to be used. As an example, a
farmer with eight cattle and a six-member family wishes to
produce gas for cooking and lighting and, if possible, for
running a 3hp water pump engine for about an hour every day.
Some of the questions the farmer must ask and guidelines for
answering them are:
1.   How much gas can be expected per day from both eight head
     of cattle and six people?
     Since each cow produces, on the average, 10kg of manure
     per day and 1kg of fresh manure can give .05 cubic meter
     gas, the animals will give 8 X 10kg/animal X .05 cubic
     meter/kg = 4.0 cubic meters gas.
     Each person produces an average of 1 kg of waste per day;
     therefore, six people X 1kg/person X .05 cubic meter/kg
     .30 cubic meter gas.
     The size of the plant would be a 4.3 cubic meter gas
2.   How much gas does the farmer require for each day?
     Each person requires approximately 0.6 cubic meters gas
     for cooking and lighting. Therefore, 6 X 0.6 = 3.6 cubic
     meters gas.
     An engine requires 0.45 cubic meters gas per hp per hour.
     Therefore, a 3hp engine for one hour is: 3 X 0.45 = 1.35
     cubic meters gas.
     Total gas consumption would be almost 5 cubic meters per
     day--somewhat more than could be produced. Running the
     engine will thus require conserving on lighting and
     cooking (or vice versa), especially in the cool season
     when gas production is low.
3.   What will be the volume of the fermentation tank or pit
     needed to handle the mixture of manure and water?
The ratio of manure and water is 1 : 1.
  8 cattle = 80kg manure + 80kg water = 160kg
  6 people =   6kg waste  +  6kg water =   12kg
                 Total input per day  = 172kg
     Input for six weeks = 172kg X 42 days = 7224kg
     1000kg = 1 cubic meter
     7224kg = 7.2 cubic meters
     Therefore, the minimum capacity of the fermentation well
     is approximately 7.0 cubic meters--a figure that does not
     allow for future expansion of the farmer's herd. If the
     herd does expand and the farmer continues to put all
     available manure in the tank, the slurry will exit after a
     shorter digestion period and gas production will be
     reduced. (The farmer could curtail addition of raw manure
     and hold it steady at the eight cattle load. If money is
     available and there are no digging problems, it is better
     to put in an oversized than undersized tank.
4.   What size and shape of fermentation tank or pit is
     The shape of the tank is determined by the soil, subsoil,
     and water table. For this example, we will assume that the
     earth is not too hard to dig and that the water table is
     low--even in the rainy season. An appropriate size for a
     7.0 cubic meter tank would be a diameter of 1.5 meters.
     Therefore, the depth required is 4.0 meters.
5.   What should the size of the gas cap be?
     The metal drum serving as a gas cap covers the
     fermentation tank and is the most expensive single item in
     the whole plant. To minimize the size and to keep the
     price as low as possible, the drum is not built to
     accommodate a full day's gas production on the assumption
     that the gas will be used throughout the day and the drum
     will never be allowed to reach full capacity. The drum is
     made to hold between 60 and 70 percent of the volume of
     the total daily gas production.
     70% of 4.3 cubic meters = 3-cubic-meter gas cap required
     The actual dimensions of the drum may well be determined
     by the size of the material locally available. A 1.4-meter-diameter
     drum 1.5 meters tall would be sufficient
     for this example. See Table 2 for other digester sizes.

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To reach optimum operating temperatures (30-37[degrees]C or 85-100[degrees]F),
some measures must be taken to insulate the digester, especially
in high altitudes or cold climates. Straw or shredded
tree bark can be used around the outside of the digester to
provide insulation. Other forms of heating can also be used
such as solar water heaters or the burning of some of the
methane produced by the digester to heat water that is circulated
through copper coils on the inside of the digester. Solar
or gas heating will add to the cost of the digester, but in
cold climates it may be necessary. Consult "Further Information
Resources" for more information.
MATERIALS (For 3-Cubic-Meter Digester)
* Baked bricks, approximately 3200
* Cement, 25 bags (for foundation and wall covering)
* Sand, 12 cubic meters
* Clay or metal pipe, 20cm diameter, 10 meters
* Copper wire screening (25cm X 25cm)
* Rubber or plastic hose (see page 00)
* Gas outlet pipe, 3cm diameter (see page 00)
* Pipe, 7.5cm diameter, 1.25 meters (gas cap guide)
* Pipe, 7cm diameter, 2.5 meters (center guide)
* Mild steel sheeting, .32mm (30 gauge) to 1.63mm (16 gauge),
  1.25 meters X 9 meters long
* Mild steel rods, approximately 30 meters (for bracing)
* Waterproof coating (paint, tar, asphalt, etc.), 4 liters (for
  gas cap
* Welding equipment (gas cap construction, pipe fittings, etc.
* Shovels
* Metal saw and blades for cutting steel (welding equipment may
  be used)
* Trowel
* Dig a pit 1.5 meters in diameter to a depth of 3.4 meters.
* Line the floor and walls of the pit with baked bricks and
  bound it with lime mortar or clay. Any porousness in the
  construction is soon blocked with the manure/water mixture.
  (If a water table is encountered, cover the bricks with
* Make a ledge or cornice at two-thirds the height (226cm) of
  the pit from the bottom. The ledge should be about 15cm wide
  for the gas cap to rest on when it is empty (see Figure 3).

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  This ledge also serves to direct into the gas cap any gas
  forming near the circumference of the pit and prevents it
  from escaping between the drum and the pit wall.
* Extend the brickwork 30-40cm above ground level to bring the
  total depth of the pit to approximately 4 meters.
* Make the input and output piping for the slurry from ordinary
  20cm clay drainpipe. Use straight input piping. If the pipe
  is curved, sticks and stones dropped in by playful children
  may jam at the bend and cannot be removed without emptying
  the whole pit. With straight piping, such objects can fall
  right through or can be pushed out with a piece of bamboo.
* Have one end of the input piping 90cm above ground level
  and the other end 70cm above the bottom of the pit (see
  Figure 3).
* Have one end of the output piping 40cm above the bottom of
  the pit opposite the input pipe and the other end at ground
* Put an iron or wire strainer (copper screening) with 0.5cm
  holes at the upper end of the input and the output pipes to
  keep out large particles of foreign matter from the pit.
* Construct a center wall that divides the pit into two equal
  compartments. Build the wall to a height two-thirds from the
  bottom of the digester (226cm). Build the gas cap guide in
  the center top of the wall by placing vertically a 7cm X 2.5
  meters long piece of metal piping.
* Provide additional support for the pipe by fabricating a
  cross brace made from mild steel.
* Form the gas cap drum from mild steel sheeting or galvanized
  iron sheeting of any thickness from .327mm (30 gauge) to
  1.63mm (16 gauge).
* Make the height of the drum approximately one-third the depth
  of the pit (1.25-1.5 meters).
* Make the diameter of the drum 10cm less than that of the pit
  (1.4 meters diameter) as shown in Figure 4.

tcm4x21.gif (486x486)

* Using a flange, attach a 7.5cm pipe to the inside top center.
* Fix the lower end of the pipe firmly in place with thin, iron
  tie rods or angle iron. The cap now looks like a hollow drum
  with a pipe, firmly fixed, running through the center.
* Cut a 3cm diameter hole, as shown in Figure 5, in the top of

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  the gas cap.
* Weld a 3cm diameter pipe over the hole.
* Fix a rubber or plastic hose--long enough to allow the drum
  to rise and fall--to the welded gas outlet pipe. A valve may
  be fixed at the joint as shown.
* Paint the outside and inside of the drum with a coat of paint
  or tar.
* Make sure the drum is airtight. One way to check this is to
  fill it with water and watch for leaks.
* Turn the gas cap drum so that the outlet pipe is on top and
  slip the 7.5cm pipe fixed in the gas cap over the 7cm pipe
  fixed in the center wall of the pit. When empty, the drum
  will rest on the 15cm ledges built on either side. As gas is
  produced and the drum empties and fills, it will move up and
  down the center pole.
* Attach handles to either side of the drum. These don't have
  to be fancy, but they will prove very helpful for lifting the
  drum off and for turning the drum.
* Weld a 10cm wide metal strip to each of the tie rod supports
  in a vertical position. These "teeth" will act as stirrers.
  By grasping the handles and rotating the drum it is possible
  to break up troublesome scum that forms on the slurry and
  tends to harden and prevent the passage of gas.
* Place a jar of water outside the pit and put into it the end
  of a downward projection of the gas pipe at least 20cm long.
  Any moisture condensing in the pipe flows into the jar
  instead of collecting in the pipe and obstructing the passage
  of gas. Water then overflows and is lost in the ground.
  Remember to keep the jar full or the gas will escape. An
  ordinary tap when opened lets the water escape. Whether using
  the water jar or tap, do not let the length be greater than
  30cm below ground level or it becomes too difficult to reach
  (see Figure 3 on page 20).

tcm3x20.gif (600x600)

* Build or improvise a mixing tank to be placed near the outside
  opening of the inlet pipe. Likewise, provide a container
  at the outlet to catch the effluent. Some provision may also
  be made for drying the effluent as the plant goes into full
In order to start up the new digester, it is necessary to have
3 cubic meters (3000kg) of manure. In addition, approximately
15kg of "seeder" is required to get the bacteriological process
started. The "seeder" can come from several sources:
     * Spent slurry from another gas plant
     * Sludge or overflow water from a septic tank
     * Horse or pig manure, both rich in bacteria
     * A 1 : 1 mixture of cow manure and water that has been
       allowed to ferment for two weeks
Put the manure and "seeder" and an equal amount of water into
the mixing tank. Stir it into a thick liquid called a slurry. A
good slurry is one in which the manure is broken up thoroughly
to make a smooth, even mixture having the consistency of thin
cream. If the slurry is too thin, the solid matter separates
and falls to the bottom instead of remaining in suspension; if
it is too thick, the gas cannot rise freely to the surface. In
either case the output of gas is less.
When filling the pit for the first time, pour the slurry
equally into both halves to balance the pressure on the thin
inner wall, or it may collapse.
Mix 60kg fresh manure with 60kg water and add it to the tank
every day.
The advantage of this model is that since the daily flow of
slurry goes up the first side, where the insoluble matter
rises, and down the second, where this matter naturally tends
to fall, the outgoing slurry daily draws out with it any sludge
found at the bottom. Thus having to clean out the pit becomes a
comparatively rare necessity. Sand and gravel may build up on
the bottom of the digester and will have to be cleaned from
time to time depending on your location.
It can take four to six weeks from the time the digester is
fully loaded before enough gas is produced and the gas plant
becomes fully operational. The first drumful of gas will
probably contain so much carbon dioxide that it will not burn.
On the other hand, it may contain methane and air in the right
proportion to explode if ignited. DO NOT ATTEMPT TO LIGHT THE
FIRST DRUMFUL OF GAS. Empty the gas cap and let the drum fill
At this point the gas is safe to use.
The gas cap drum floating on the slurry creates a steady
pressure on the gas at all times.   This pressure is somewhat
lower than that usually associated with other gases that are
under pressure but is sufficient for cooking and lighting.
Table 3, on the following page, shows gas consumption by
        1                           2                  3(*)
   Gas cooking             2" diameter burner         280
                          4" diameter burner        395
                          6" diameter burner        545
   Gas lighting            1 mantle lamps              78
                          2 mantle lamps            155
                          3 mantle lamps            190
   Refrigerator            18" X 18" X 12"             78
   Incubator               18" X 18" X 18"
                          Flame operated
   Running engines        Converted diesel        350-550 hp/hr
Note: These figures will vary slightly depending on the design
      of the appliance used, the methane content of the gas,
      the gas delivery pressure, etc.
    Table 3. Application Specification for Gas Consumption
Internal Combustion
Any internal combustion engine(*) can be adapted to use methane.
For gasoline engines, drill a hole in the carbuerator just near
the choke and introduce a 5mm diameter tube connected to the
gas supply through a control valve. The engine may be started
on gasoline then switched over to methane while running, or
vice-versa. For smooth running of the engine, the gas flow
should be steady. For stationary engines this is done by
counterbalancing the gas cap. (Refer to Table 3 on page 17 for
gas consumption.)
Diesel engines are run by connecting the gas to the air intake
and closing the diesel oil feed. A spark plug will have to be
placed where the injector normally is and arrangement made for
electricity and spark timing. Modifications will vary with the
make of the engine. One suggestion is to adapt the full-pump
mechanism for timing the spark.
(*)Some authorities recommend that when running the internal
combustion engines, the gas be first purified. This is done by
bubbling it through lime water, to remove carbon dioxide, and
through iron filings, to remove hydrogen sulphide.
The sludge product of anaerobic decomposition produces a better
fertilizer and soil conditioner than either composted or fresh
manure. The liquid effluent contains many elements essential to
plant life: nitrogen, phosphorous, potassium, plus small
amounts of metallic salts indispensible for plant growth.
Methods of applying this fertilizer are numerous and conflicting.
The effluent can be applied to crops as either a diluted
liquid or in a dried form. Remember that although 90-93% of
toxic pathogens found in raw human manure are killed by anaerobic
decomposition, there is still a danger of soil contamination
with its use. The effluent should be composted before use
if the slurry contains a high proportion of human waste. However,
when all factors are considered, the effluent is much
safer than raw sewage, poses less of a health problem, and is a
better fertilizer.
The continued use of the effluent in one area tends to make
soils acidic unless it is duluted with water (3 parts water to
1 part effluent is considered a safe mixture). A little dolomite
or crushed limestone added to the effluent containers at
regular intervals will cut down on acidity. Unfortunately,
limestone tends to evaporate ammonia; so it is generally best
to keep close watch over the amount of effluent provided to
crops until the reaction of the soil and crops is certain.
Because gas pressure is low, it will be necessary to modify
existing equipment or build special burners for cooking and
heating. A pressure stove burner will work satisfactorily only
after certain modifications are made to the burner. The
needle-thin jet should be enlarged to 1.5mm. To make a burner
out of 1.5cm water pipe, choke the pipe with a metal disc having
a center hole with a diameter of 1.5 to 2mm. An efficient
burner is a tin can, filled with stones for balance, having six
1.5mm holes in the top. The gas enters through a pipe choked to
a 2mm orifice. Or fill a chula or Lorena stove with stones and
insert a pipe choked to a 2mm orifice.
If possible, it is best to use a burner with an adjustable air
inlet control. The addition or subtraction of air to the gas
creates a hotter flame with better use of available gas.
Methane gives a soft, white light when burned with an incandescent
mantle. It is not quite as bright and glaring as a
kerosene lantern. Lamps of various tyles and sizes are manufactured
in India specifically for use with methane. <see image> Each mantle

tcmx31.gif (600x600)

burns about as bright as a 40-watt electric bulb.
Some biogas appliances manufactured by an Indian firm are:
  *   Indoor hanging lamp              *   Stoves and burners
  *   Indoor suspension lamp           *  Bottle syphons and
  *   Outdoor hanging lamp                pressure gauges
  *   Indoor table lamp
A digester of this type is virtually maintenance free and has a
life of approximately 25 years. As long as cow or other animal
manure is used, there should be no problems. Vegetable matter
can also be used for methane production but the process is much
more complex. Introduction of vegetable matter in the digester
is not recommended.
A trouble-shooting guide is listed below for possible problems
that may be encountered.
Defect               May be caused by       Remedy
No gas. Drum         a) No bacteria         Add some bacteria
won't rise.                                  (seeder)
                      b) Lack of time         Patience! Without bacteria,
                                            it may take four
                                            or five weeks.
                     c) Slurry too cold     Use warm water. Cover
                                            plant with plastic tent
                                            or use heating coil.
                     d) Insufficient        Add right amount of
                        input               slurry daily.
                     e) Leak in drum  or     Check seams, joints,
                        pipe                and taps with soapy
                     f) Hard  scum on        Remove drum; clean
                        slurry blocking      slurry surface. With
                        gas.                sliding-drum plants,
                                            turn drum slightly to
                                            break crust.
No gas at stove;     a) Gas pipe blocked    Open escape cock.
plenty in drum.         by condensed
                     b) Insufficient        Increase weight on drum
                     c) Gas inlet           Remove drum and clean
                        blocked by scum     inlet. Close all gas-taps.
                                            Fill gas line
                                            with water; apply pressure
                                            through moisture
                                            escape. Drain water.
Gas won't burn.      a) Wrong kind is       Slurry too thick or too
                        being formed.       thin. Measure accurately.
                                            Have patience.
                     b) Air mixture         Check burner gas jet to
                                            make sure it is at
                                            least 1.5mm.
Flame soon dies.     a) Insufficient        Increase weight on
                     b) Water in line       Check moisture escape
                                            jar. Drain gas line.
Flame begins far     a) Pressure too        Remove weights from
                        high                drum. Counterbalance.
                     b) Air mixture         Choke gas inlet at
                                            stove to 2mm (thickness
                                            of 1" long nail).
Checking for gas leaks is done by closing all gas taps,
including the main gas tap beside the gas holder, except for
Then to the open tap, a clear plastic pipe about a meter long
is attached, and a "U" is formed. The lower half of the "U" is
filled with water.
Using a pipe attached to a second tap, pressure is applied
until the water in the two legs of the "U" is different by
15cm. The second tap is then closed. The "U" is now what is
called a "manometer."
If the water levels out when the second tap is closed, a leak
is indicated and can be sought out by putting soapy water over
possible leaks, such as joints, in the pipework. <see image>

tcmx35.gif (600x600)

AEROBIC--Decomposing with oxygen.
ANAEROBIC--Decomposing without oxygen.
BY-PRODUCT--Something produced from something else.
CARBON DIOXIDE--A colorless, odorless, incombustible gas ([CO.sub.2])
                formed during organic decomposition.
DECOMPOSE--To rot, to disintegrate, to breakdown into component
DIA (DIAMETER)--A straight line passing completely through the
                center of a circle.
DIGESTER--A cylindrical vessel in which substances are
EFFLUENT--The outflow from the biogas storage tank.
FERMENT--To cause to become agitated or turbulent.
HP (HORSEPOWER)--Unit of power equal to 747.7 watts.
INSOLUBLE--Incapable of being dissolved.
LEACHED--Dissolved and washed out by a percolating liquid.
MANTLE--A sheath of threads that brightly illuminates when
         heated by gas.
METHANE--An odorless, colorless, flammable gas ([CH.sub.4]) used as a
NITRATES--Fertilizers consisting of sodium and potassium
NITROGEN--A colorless and odorless gas ([N.sub.2]) in fertilizers.
ORGANIC WASTES--Waste from living organisms or vegetable
SCUM--A filmy layer of waste matter that forms on top of
SEEDER--Bacteria used to start the fermentation process.
SEPTIC TANK--A sewage disposal tank in which a continuous flow
          of waste material is decomposed by anaerobic
SLUDGE--A thick liquid composed of 1 : 1 : 1 mixture of manure,
         seeder, and water.
SUPERNATANT--Floating on the surface.
TOXIC PATHOGENS--Harmful or deadly agents that cause serious
          disease or death.
  1 Mile                 = 1760 Yards                = 5280 Feet
  1 Kilometer            = 1000 Meters               = 0.6214 Mile
  1 Mile                 = 1.607 Kilometers
  1 Foot                 = 0.3048 Meter
  1 Meter                = 3.2808 Feet               = 39.37 Inches
  1 Inch                 = 2.54 Centimeters
  1 Centimeter           = 0.3937 Inches
  1 Square Mile          = 640 Acres                 = 2.5899 Square Kilometers
  1 Square   Kilometer   = 1,000,000 Square Meters  = 0.3861 Square Mile
  1 Acre                 = 43,560 Square Feet
  1 Square   Foot        = 144 Square Inches        = 0.0929 Square Meter
  1 Square   Inch        = 6.452 Square Centimeters
  1 Square   Meter       = 10.764 Square Feet
  1 Square   Centimeter  = 0.155 Square Inch
  1.0 Cubic Foot         = 1728 Cubic Inches         = 7.48 US Gallons
  1.0 British Imperial
        Gallon           = 1.2 US Gallons
  1.0 Cubic Meter       = 35.314 Cubic Feet         = 264.2 US Gallons
  1.0 Liter              = 1000 Cubic Centimeters    = 0.2642 US Gallons
  1.0 Metric Ton         = 1000 Kilograms            = 2204.6 Pounds
  1.0 Kilogram           = 1000 Grams                = 2.2046 Pounds
  1.0 Short Ton          = 2000 Pounds
  1.0 Pound per square inch              = 144 Pound per square foot
  1.0 Pound per square inch              = 27.7 Inches of water(*)
  1.0 Pound per square inch              = 2.31 Feet of water(*)
  1.0 Pound per square inch              = 2.042 Inches of mercury(*)
  1.0 Atmosphere                          = 14.7 Pounds per square inch (PSI)
  1.0 Atmosphere                          = 33.95 Feet of water(*)
  1.0 Foot of water = 0.433 PSI          = 62.355 Pounds per square foot
  1.0 Kilogram per square centimeter     = 14.223 Pounds per square inch
  1.0 Pound per square inch              = 0.0703 Kilogram per square
 1.0 Horsepower (English)                = 746 Watt    = 0.746 Kilowatt (KW)
 1.0 Horsepower (English)                = 550 Foot pounds per second
 1.0 Horsepower (English)                = 33,000 Foot pounds per minute
 1.0 Kilowatt (KW)    = 1000 Watt         = 1.34 Horsepower (HP) English
 1.0 Horsepower (English)                = 1.0139 Metric horsepower
 1.0 Metric horsepower                   = 75 Meter X Kilogram/Second
 1.0 Metric horsepower                   = 0.736 Kilowatt    = 736 Watt
(*)At 62 degrees Fahrenheit (16.6 degrees Celsius).
Biogas Plant: Designs With Specifications. Ram Box Singh, Gobar
      Gas Research Statin Ajit Mal Etawah (V.P.) India. The
      main part of this book is taken up with very detailed
      technical drawings of 20 different models of methane
      digesters for various size operatins and different climates.
      Also has designs for gas burners, lamps, and a
      carburator. No real written instructions, but would be
      very useful if used in conjunction with a more general
Biogas Plant: Generating Methane from Organic Wastes. Ram Bux
      Singh, Gobar Gas Research Station, Ajitmal Etawah (V.P.)
      India, 1974. The most comprehensive work on biogas. Gives
      the background of the subject, an extensive treatment of
      just how a biogas plant works, factors to consider in
      designing a plant and several designs, and instructions
      for building a plant and using the products. Profusely
      illustrated, this is considered by some as the "bible" of
Fuel Gas From Cow Dung. Bertrand R. Saubolle, S. J., Sahayog;
      Prakashan Tripureshwas, Kathmandu, April 1976, 26 pp.
      Fairly detailed manual for obtaining and using methane
      from cow manure. Includes a trouble-shooting section and
      specification charts for different size digesters. Written
      in straight forward, nontechnical language. Potential
      quite useful. Available from VITA.
Small-Scale Biogas Plants. Nigel Florida; Bardoli, India.
      Highly detailed manual. Gives step-by-step instructions
      for building and operating a methane digester. Includes
      modifications needed to cope with a variety of conditions
      and a detailed analysis of digested slurry and of the
      produced biogas. Also has a chapter on current
      state-of-the-art in India. Available from VITA.
Andrews, Johh F. Start-Up and Recovery of Anaerobic Digestion,
      8 pp. Clemson University. Available from VITA.
"Biogas Plant: Generating Methane from Organic Wastes." Compost
      Science. January-February 1972, pp. 20-25. Available from
Biogas Stove and Lamp: Efficient Gas Appliances, Examples of
      Plant Designs, Examples of Biogas Plants, Construction
      Notes. 4 pp. including illustrations. Available from
"Building a Biogas Plant." Compost Science. March-April 1972.
      pp. 12-16. Available from VITA.
Finlay, John H. Operation and Maintenance of Gobar Gas Plants,
      April 1976, 22 pp. with 3 diagrams. Nepal. Available from
Gobar Gas Plant, 4 pp. Appropriate Technology Development
      Association, PO Box 311, Gandhi Bhawan, Lucknow 226001,
      UP, India.
Gobar Gas Plants, 8 pp. with 4 diagrams. Indian Agricultural
      Research Institute. Available from VITA.
Gotaas, Harold B. "Manure and Night-Soil Digesters for Methane
      Recovery on Farms and in Villages. Composting: Sanitary
      Disposal and Reclamation of Organic Wastes. 1956, chapter
      9, pp. 171-199. University of California/Berkeley, World
      Health Organization. Available from VITA.
Grout, A. Roger. Methane Gas Generation from Manure, 3 pp.
      Pennsylvania State University. Available from VITA.
Hansen, Kjell. A Generator for Producing Fuel Gas from Manure,
      4pp. Available from VITA.
Hill, Peter. Notes on a Methane Gas Generator & Water Tank
      Construction, June 1974, 9 pp. Belau Modekngei School.
      Available from VITA.
Information on Cow Dung Gas: A Manure Plant for Villages,
      5 pp. Indian Agricultural Research Institute, Division of
      Soil Science and Agricultural Chemistry, Pusa, New Delhi,
Klein, S.A. "Methane Gas--An Overlooked Energy Source." Organic
      Gardening and Farming, June 1972, pp. 98-101. Rodale
      Press, Inc., 33 East Mine Street, Emmaus, Pennsylvania
      18049 USA.
Oberst, George L. Cold-Region Experiments with Anaerobic
      Digestion for Small Farms and Homesteads. Biofuels, Box
      609, Noxon, Montana 59853 USA.
The Pennsylvania State University Digester-Methane Generator,
      2 pp. Available from VITA.
Shifflet, Douglas. Methane Gas Generator, 1966. Available from
Vani, Seva. "Mobile Gobar Gas Plant," Journal of CARITAS India,
      January-February 1976, 2 pp. Available from VITA.
                                  APPENDIX I
                           DECISION MAKING WORKSHEET
If you are using this as a guideline for using a biogas plant
in a development effort, collect as much information as possible
and if you need assistance with the project, write VITA.
A report on your experiences and the uses of this manual will
help VITA both improve the book and aid other similar efforts.
                       1600 Wilson Boulevard, Suite 500
                         Arlington, Virginia 22209 USA
                     Tel: 703/276-1800 . Fax: 703/243-1865
* Note current domestic and agricultural practices that might
  benefit from a biogas plant: improved fertilizer, increased
  fuel supply, sanitary treatment of human and animal wastes,
* Have biogas plant technologies been introduced previously? If
  so, with what results?
* Have biogas plant technologies been introduced in nearby
  areas? If so, with what results?
* What changes in traditional thinking or practices might lead
  to increased acceptance of biogas plants? Are such changes
  too great to attempt now?
* Under what conditions would it be useful to introduce biogas
  plant technology for demonstration purposes?
* If biogas plants are feasible for local manufacture, would
  they be used? Assuming no funding, could local people afford
  them? Are there ways to make the biogas plant technologies
  pay for themselves?
* Could this technology provide a basis for a small business
* What are the characteristics of the problem? How is the problem
  identified? Who sees it as a problem?
* Has any local person, particularly someone in a position of
  authority, expressed the need or showed interest in biogas
  plant technology? If so, can someone be found to help the
  technology introduction process? Are there local officials
  who could be involved and tapped as resources?
* Based on descriptions of current practices and upon this
  manual's information, identify needs that biogas plant technologies
  appear able to meet.
* Do you have enough animals to supply necessary amount of
  manure needed daily?
* Are materials and tools available locally for construction of
  biogas plants?
* What would be the main use of the methane produced by the
  biogas plant? For example, heating, lighting, cooking, etc.
* Would you be able to use all of the effluent fertilizer or
  would you have more than you need? Would you be able to sell
  the surplus?
* Do a cost estimate of the labor, parts, and materials needed.
* What kinds of skills are available locally to assist with
  construction and maintenance? How much skill is necessary for
  construction and maintenance? Do you need to train people in
  the construction techniques? Can you meet the following
  -- Some aspects of the project require someone with experience
     in metal-working and/or welding.
  -- Estimated labor time for full-time workers is:
     * Skilled labor - 8 hours
     * Unskilled labor - 80 hours
     * Welding - 12 hours
* How much time do you have? When will the project begin? How
  long will it take?
* How will you arrange to spread knowledge and use of the
* How was the final decision reached to go ahead--or not to go
  ahead--with this technology?
                                  APPENDIX II
                           RECORD KEEPING WORKSHEET
Photographs of the construction process, as well as the finished
result, are helpful. They add interest and detail that
might be overlooked in the narrative.
A report on the construction process should include very specific
information. This kind of detail can often be monitored
most easily in charts (such as the one below). <see report 1>

tcmxrp10.gif (437x437)

Some other things to record include:
* Specification of materials used in construction.
* Adaptations or changes made in design to fit local
* Equipment costs.
* Time spent in construction--include volunteer time as well as
  paid labor, full- and/or part-time.
* Problems--labor shortage, work stoppage, training difficulties,
  materials shortage, terrain, transport.
Keep log of operations for at least the first six weeks, then
periodically for several days every few months. This log will
vary with the technology, but should include full requirements,
outputs, duration of operation, training of operators, etc.
Include special problems that may come up--a damper that won't
close, gear that won't catch, procedures that don't seem to
make sense to workers, etc.
Maintenance records enable keeping track of where breakdowns
occur most frequently and may suggest areas for improvement or
strengthening weakness in the design. Furthermore, these
records will give a good idea of how well the project is
working out by accurately recording how much of the time it is
working and how often it breaks down. Routine maintenance
records should be kept for a minimum of six months to one year
after the project goes into operation. <see report 2>

tcmxrp2.gif (486x486)

This category includes damage caused by weather, natural
disasters, vandalism, etc. Pattern the records after the
routine maintenance records. Describe for each separate
* Cause and extent of damage.
* Labor costs of repair (like maintenance account).
* Material costs of repair (like maintenance account).
* Measures taken to prevent recurrence.
                        Small Michell (Banki) Turbine:
                             A Construction Manual
                             Helical Sail Windmill
                         Overshot Water-Wheel: Design
                            and Construction Manual
                       Wood Conserving Stoves: Two Stove
                      Designs and Construction Techniques
                      Hydraulic Ram for Tropical Climates
                              Solar Water Heater
                      Making Charcoal: The Retort Method
                               Solar Grain Dryer
                        The Dynapod: A Pedal-Power Unit
                           Animal-Driven Chain Pump
                                  Solar Still
For free catalogue listing these and other VITA publications,
write to:
                       1600 Wilson Boulevard, Suite 500
                         Arlington, Virginia 22209 USA
                     Tel: 703/276-1800 . Fax: 703/243-1865
                                  ABOUT VITA
Volunteers in Technical Assistance (VITA) is a private, nonprofit,
international development organization. It makes available
to individuals and groups in developing countries a
variety of information and technical resources aimed at fostering
self-sufficiency--needs assessment and program development
support; by-mail and on-site consulting services; information
systems training.
VITA promotes the use of appropriate small-scale technologies,
especially in the area of renewable energy. VITA's extensive
documentation center and worldwide roster of volunteer technical
experts enable it to respond to thousands of technical
inquiries each year. It also publishes a quarterly newsletter
and a variety of technical manuals and bulletins.
VITA's documentation center is the storehouse for over 40,000
documents related almost exclusively to small- and medium-scall
technologies in subjects from agriculture to wind power. This
wealth of information has been gathered for almost 20 years as
VITA has worked to answer inquiries for technical information
from people in the developing world. Many of the documents contained
in the Center were developed by VITA's network of technical
experts in response to specific inquiries; much of the
information is not available elsewhere. For this reason, VITA
wishes to make this information available to the public.
                                      IN TECHNICAL
                              ISBN 0-86619-069-4

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