[Homestead] Biogas Digesters, mostly polyethylene bag

Tvoivozhd tvoivozd at infionline.net
Wed Nov 10 17:27:22 EST 2004

It is not likely anyone is going to rush right out to build a biogas 
digester unless gasoline goes to ten dollars a gallon, or they own a big 
hog or chicken operation---but ever since Fry ran his his vehicles on 
PigPower, it has been a fascinating technology, fine integrated farming 
technique, and something to file away (where it won't disappear) for 
possible future use, along with other biofuel manufacture such as 
woodgas.com, Journey to Forever ethanol and McDonald's throwaway deep 
fat fryer discards, Peter Singfield (Belize denizen) use of sugar cane 
squeezings turned to vinegar, to which he adds cow manure pudding to 
generate methane etc.

(very simple, cheap polyethylene bag in hole in ground)

(integrated biosystems, mostly rice and fish---many links, some dead)

(integrated farm biosystems in tropics for food and energy. Sugar palm 
at top, next oil palm as source of farm fuel)

(also in tropics, use two-roll mill to squeeze sugar cane, ferment cane 
juice to vinegar with aid of photovoltaic air pump emitting air through 
a porous stone. Resultant vinegar is one component of methane 
production---the other component is cow patty soup.)

(farther north and based on pig manure---methane produced by 
plastic-covered pond of pig manure. Just a side note---while methane is 
not as compressible as LPG, in South Africa a good handling system is a 
compressor-truck that comes around, extracts CO2 from methane, 
compresses methane in high pressure metal tanks, removes hydrogen 
sulfide, in which form the methane is easy to use for vehicle engines or 
household cooking)

(scrub carbon dioxide from methane with limewater, ash etc. , and 
hydrogen sulfide

The Indian Agricultural Research Institute has reported the following 
method for removing carbon dioxide from biogas (as reported in Nepal's 
Biogas Newsletter). Biogas is bubbled through a solution of ten percent 
monoethanolamine (MEA) in water. The carbon dioxide content of the 
biogas is reduced to 0.5 to 1.0 percent by volume from an initial 
content of about 40 percent by single bubbling through a plain column 
6.0 cm (2½ inches) in height. The scrubbing column is made of an 
inexpensive plastic bubbler (5.0 cm in diameter and 15 cm in height), 
having only one opening. Maximum removal of carbon dioxide is observed 
when the bubbling coming from the opening comes out slowly enough so 
that each bubble is separate from the others and the stream of bubbles 
is never in danger of merging into a continuous "tube."

The ideal rate of flow is 100 milliliters per minute at the regulator. 
This rate yields 60 milliliters of pure methane per minute. A decrease 
in this rate of flow does not result in any increase in scrubbing 
effect. Initial pressure of the biogas introduced into the bubbler is 
10.0 cm (4.0 inches) of water column, and the drop in pressure head is 
about 5.0 cm (2.0 inches) of water.

Both caustic potash and MEA are equally effective. But MEA solution can 
be completely stripped of the carbon dioxide by boiling it for five 
minutes, after which it can be used again. MEA is also less caustic 
(able to cause chemical burns) than other solutions that can be used. It 
will not cause any damage to the skin in case of accidental contact.

(hydrogen sulfide scrubber using two-sizes impregnated Raschig Rings. 
Not here, but note that the Columbia Boulevard system uses a potassium 
hydroxide impregnated activated carbon filter to remove hydrogen sulfide 
from methane.

Hydrogen sulfide in a 2.8 percent concentration is hell on internal 
compustion engine valves, rings, pistons and cylinders---so corrosive 
the engine will wear out in a couple hundred hours.)

(diagram of commercial Apollo H2S scrubber)

(scubbing H2S from methane, converting the H2S to elemental sulfur---AND 
taking out water content with regenerative glycol solution)

(methane content, CO2,H2S, water)

(two-bag polyethlene-tube biogas system, on as biogas generator, one at 
kitchen to improve methane gas-flow and pressure.)

Farmer to Farmer notes on using HDPE instead of ordinary polyethylene 
bag, zipper for cleanoug, or joining sections, insulating trench, and 
solar heat to maintain polytube at 35 degrees Centigrade for optimum 
biological activity)
Farmer to Farmer Volunteer Trip Report May 12-24, 2002, Michael Tierney

What was the purpose and primary objective of your trip?
To survey several large and small dairy farms and propose the 
feasibility of developing manure biogas systems (or troubleshoot under 
performing existing biogas systems) that would supplement the energy 
needs of that farm. These energy needs could range from cooking gas, 
lighting and refrigeration for the small farm, to full-scale commercial 
electrical generation.

What future volunteer assignments do you think are needed, and what are 
the next steps in moving the project forward?
Julio Solorzano of MAGFOR did mention at the end of our meeting that the 
World Bank “Agricultural Technology” project might have an interest in 
funding a few demonstration biogas digesters at small sustainable farms. 
If he was serious, I think a low cost approach would involve a 
collaboration of a volunteer, Professor Raul Botero Botero of Earth 
University with Ronald Blandon and Ing. Maria Mercedes Oblong to build 
an upgraded Columbia “tube type” digester out of a tough, black, 
lightweight, woven hi density polyethylene (HDPE) material that is 
widely used for pond liners in the United States. At the agricultural 
collage in Managua I saw a Swiss funded biotube type demonstration 
project, fed by pig manure, which will soon be rebuilt. Upgrading from 
the lightweight plastic forage storage tubing that is now used to the 
tough, ultraviolet resistant, HDPE would be an economical demonstration. 
The membrane material needs no ultraviolet (UV) protective covers and I 
understand it could be fitted with a zip lock type seam that can be 
opened and closed to form a gas tight tube that can be built to any 
length desired. This “plug-flow” membrane type digester will also 
provide gas storage at a pressure that makes it useable for appliances. 
It can also be zipped open and repaired when necessary. I can assist in 
getting membrane prices and the knowledge and materials for 
manufacturing the zipper type seam. Off the shelf appliances such as, a 
biogas cooking stove, gaslights and a biogas refrigerator should be 
installed at this demonstration project so the gas flows and livestock 
manure needed to operate them can be measured an compared with published 
figures. A small, duel fuel, biogas and LP gas fueled electrical 
generator would be an economical and useful addition to the demonstration.

I would improve the performance of the biotube digester by installing 
closed-cell insulation (like blue board) at the base of the trench that 
the biotube would be installed in. The black membrane plus a separate 
solar panel heated, thermal circulating pipe grid at the base of the 
trench would allow heating or, if necessary, cooling of the biotube 
digester to the more optimal 35 degree C.

I had a recent discussion with an Engineering Professor at my Alma 
Mater, the University of Wisconsin Civil and Environmental Engineering 
School, Professor Daniel Norguera, about my concept of a domestically 
manufactured, insulated, 3 chambered, fiberglass, solar heated, 
anaerobic digester that operates at a steady state of a thermophilic 
45-50 degrees C followed by a mesophilic phase at 35 C with a hydraulic 
detention design of about 20 days. The unit’s modular design provides 
flexibility plus I envision a simple low pressure, high volume in line 
hand operated mechanical pump system could be installed to store 
low-pressure gas in bladders such as truck tires inner tubes for peak 
gas demand. The gas storage will even out the 24-hour gas demand cycle 
and should allow a 4-5 pigs or 2-cow farm to generate enough gas in 24 
hrs for cooking, lighting and refrigeration for a family of 4-6 people. 
Manure storage could be provided by off the shelf polypropylene water 
tanks. The retail cost of Rotoplas brand water tanks in Nicaragua is 
$180.00 for a 291 gallon or $335.00 for a 661 gallon

Professor Noguera has lived in Columbia, and has some familiarity with 
the biogas technologies of South and Central America. He noted his 
willingness to provide some oversight opinions on such a project but has 
other persons he considers more involved in anaerobic digesters that he 
would discuss any funded projects with.

If funding requests for biogas demonstration projects were successful, I 
would complete my design of the portable anaerobic digester unit and 
peer review it to finalize the design. It seems logical to build and 
operate a prototype in Wisconsin, correct any problems, and ship two 
prototypes Nicaragua. If agreed to, one prototype could be installed at 
the Managua Agricultural College and one demonstration on a small 
Nicaraguan farm site with cooking, lighting and refrigeration 
appliances. The project could perhaps involve a cooperative research 
effort between the UW Madison Civil and Agricultural Engineering 
Departments and The Agricultural College in Managua. Perhaps Ronald 
Blandon would see this as a project where he would be a central figure 
in this collaboration.

Would Farmer to Farmer consider serving as a sponsoring agency for this 
educational project over a two-year period to provide expert volunteers? 
Funding and technical support might be provided by other sources like 
USAID, Peace Corps, World Bank / Japan Social Development Fund (JSDF), 
PRODEA or private organizational funds?

The lightweight, non-corrodible, portable, solar heated, modular 
designed, anaerobic digester should be a low cost and low risk project 
to fund. There is a large technical knowledge base on anaerobic 
digesters and the use of sour gas appliances. The proposed digester's 
advantage is that with its higher, optimal, temperature operation it 
should be much, smaller, faster and rapid at converting volatile organic 
substances to methane. Conceivably, since pathogen reduction is so 
significant, the higher initial thermophilic operating temperatures 
would make it suitable for combining human waste with animal waste. It 
could provide a low cost energy source that can be easily manufactured 
in Central America, Africa, Asia and any country with the desire to do so.

Any recommendations/suggestions for future volunteers, or comments?
This project for biogas energy integrates closely to the need to reduce 
the massive deforestation that is occurring in Nicaragua due to the 
demand for firewood. Providing cooking gas, lighting, refrigeration at 
small and midsize farms from biogas has large public health 
implications. However, the use of other biofuels, such as ethanol, could 
be explored to see if it could provide energy in a manner similar to 
what Brazil and other countries have done. You might consider sending 
volunteers with commercial ethanol production experience that could 
discuss and demonstrate how to use crop and other organic residues to 
provide a relatively clean, safe, storable and easily transported fuel. 
This might allow farmers to produce a product from residuals that would 
be salable to people in cities for homes or vehicles. Bio diesel is 
another subject to explore for running diesel generators and vehicles.

Large dairy facilities that want to consider biogas production have an 
obvious problem. The common or preferred method of maintaining dairy 
cattle is on pasture. I understand farmers pasture their cows because in 
a feedlot they do not get sufficient nutrition. Unless the nutritional 
issues are addressed, promoting the free stall type dairy cattle 
operations to obtain manure for biogas production may be counter 
productive. The primary issue at most of the large farms (except the 
Blandon farm) that I saw was the cows spent most of theirpasture versus 

It would be useful to have a visit and seminar by Professor Raul Botero 
Botero of Earth University in Costa Rica to discuss the performance of 
their biogas digester on their environmentally friendly farm model they 
developed at Earth University. The operator of the 1990 German designed 
biogas system at “EIAG” The Rivas Agricultural Collage was very 
knowledgeable regarding the day to day operation of the anaerobic 
digester that provides cooking gas and gas for classroom Bunsen burners.

It would be useful to expand our thinking from biogas production from 
animal manure to utilizing a mix of many residual organic substances for 
biogas production. For example, Los Angeles Airport has a demonstration 
biogas digester it feeds with ground cafeteria wastes. Agricultural 
markets might consider using market wastes to generate gas for 
adsorption refrigeration for meats and seafood preservation. Modular 
biogas generators would produce a clean fertilizer byproduct for city 

Rural human waste handling would be an excellent subject since outhouses 
are everywhere in rural areas and in some smaller cities. Composting 
toilet technology can be very effective in disease reduction and 
reducing water pollution. During this trip I saw composting toilets 
being built at a national park in Nicaragua. While they will work, there 
are better aeration designs that would make it less costly easier to build.

Please provide some comments on how the trip affected you personally, or 
how you feel generally about the Farmer to Farmer program.

Thanks to the extensive logistic support and advice from Arlen Albright 
I had an enjoyable, busy, and fulfilling experience. It was enhanced by 
being able to work with Aleen, my Peace Corps Volunteer daughter, as our 
pre-travel coordinator and interpreter during the second week of my 
assignment . My wife and I had been in Nicaragua last year to visit our 
daughter, so we had a sense of the country and some acquaintances who 
were helpful in introducing us to people in their communities. Ronald 
Blandon, Ing. Maria Mercedes Oblong and Estaban, our guardian and driver 
and Juillo, our interpreter for the first week, provided very 
professional yet personal host services. I think we introduced both 
basic concepts, such as the Columbia biotube type digester, to small, 
midsize and large farmer owners and more advanced operational 
discussions for those entrepreneurial people in Nicaragua who have 
independently built and effectively operate biodigesters on their farms.

I brought Spanish language brochures for the World Dairy Exposition in 
Madison and provided information to Ronald Blandon and Maria Mercedes 
regarding a UW Madison 3 day, pre-expo short course on International 
dairy operations. If I am in town I would be pleased to help them 
coordinate a visit to the Expo and arrange field trips to farms with 
bio-digesters and appropriate small cheese factory operations.

I find Farmer to Farmer emphasizes practical applications and promotes 
direct action. I would be interested in future assignments where I could 
work on integration of energy, agriculture and public health in rural 

(photo of two polytubes on ground under pule structure to provide 

http://www.ias.unu.edu/proceedings/icibs/rodriguez/picture6.gif (polybag 
under pole and thatch cover)

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