Rwanda biogas project  - KIST Bio-Gas Production: Large & Small-scale Sustainable Biogas Energy Projects

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Biogas & bio fuel productions systems:

This biogas article discusses designs, methods, and projects for biogas production to obtain useful renewable-energy methane gas for use as a fuel.

Our page top photo of the KIST biogas project in Rwanda, described by the Ashden Awards for sustainable energy program is from the Ashden awards program.

Watch out: Because sewer gas contains methane gas (CH4) there is a risk of an explosion hazard or even fatal asphyxiation. and the chance that there are possible health hazards from sewer gas exposure, such as a bacterial infection we include here some safety warnings for people undertaking amateur biogas production projects.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Biogas Plants: Using Septic Gas or Sewer Gas for Fuel

Various efforts have been made to use sewer gas or septic gas as a fuel for heating or lighting deriving methane from bacteria-powered manure or even human waste or food waste digesters in many countries.

What is Biogas and How Is It Used Around the World?

Bio-gas is a mixture of methane (CH4) and carbon dioxide (CO2) produced by the break-down or digestion of organic waste such as manure, vegetable matter, sewage, or even food waste. The gas produced is clean and burns clean, providing a more healthy fuel than some alternatives such as wood.

Because biogas is high in methane it can be used as a fuel for cooking, lighting, or even powering vehicles or other machines. And because bio gas can be produced from waste material its production is considered a potentially sustainable energy source.

Quoting below, we refer to Ashden's explanation of biogas:

Biogas systems use bacteria to break down wet organic matter like animal dung, human sewage or food waste. This produces biogas, which is a mixture of methane and carbon dioxide, and also a semi-solid residue. The biogas is used as a fuel for cooking, lighting or generating electricity. Using biogas can save the labour of gathering and using wood for cooking, minimise harmful smoke in homes, and cut deforestation and greenhouse gas emissions. Biogas plants can also improve sanitation, and the residue is useful as a fertiliser

How is Biogas Produced?

Key in biogas production is the construction of a proper container (an anaerobic biogas digester) that is air-tight (and safe). When organic materials such as dung, vegetable matter, or sewage break down in the absence of large amounts oxygen (where anaerobic bacteria cause the desired decomposition) the result is a production of useful quantities of methane (CH4) that can be used as a fuel, along with carbon dioxide, and lower amounts of hydrogen and other trace gases.

This biogas production process produces little heat and an end product higher in nitrogen than if the same process is attempted in the presence of oxygen and aerobic bacteria.

The decomposition of waste matter by anaerobic bacteria occurs in two phases: acidic anaerobic bacteria break down the organic waste into peptides, glycerol, alcohol, sugars that are then further converted by other anaerobic bacteria into methane and the other materials listed above.

In large or commercial biogas production systems such as using large amounts of manure, the waste is mixed with water to form a slurry that is fed continuously through the digester. In smaller home or farm biogas producing designs the waste is fed into the digester in batches, manually and water is also added manually as required. -- various sources.

Large Scale Biogas Production & Use Projects

KIST biogas project under constructin - (C) AshdenWhile using sewage waste to produce methane involves both the explosion hazard cited just below, and the difficulty of dealing with a high percentage of liquid volume, some efforts to obtain usable methane fuel gases from sewage have been reported.

The New York Times reported (May 13, 2010) a successful 2005 prison project in Cyangugu, Rwanda using "beehive-shaped converters to house bacteria to ferment the waste." [Photo, left, from the Ashden award for this KIST designed program ]

Methane was collected for cooking and the residue was used as fertilizer. The project design was used in six other prisons, reported the Times who credit the sewage methane gas production system design to the Kigali Institute for Science and Technology (KIST). KIST received an Ashden Award for sustainable energy projects for this effort.

Productive sources of bio-gas (gobar gas in Pakistan and India) currently (to 2010) include landfill produced biogas (50% methane) and bio-digesters or advanced wastewater treatment systems (up to 75% methane) designed for methane gas production and capture.

Small Scale Biogas Production & Use - Home & Do-it-yourself Bio-gas Projects

Some readers have asked if they could just capture methane gas from their septic tank to use as a household fuel for heating, cooking, or gas lighting. And there are septic-tank-like systems designed for that purpose, but as we warn below, don't just try hooking up your septic tank to a gas burner.

While rural farmers and families have made use of manure (animal dung) as fertilizer and when dried, as fuel for eons, use of manure to produce biogas for local use is more recent.

Insinkerator Grind2Energy food waste processor - adapted from by InSinkeratorIndeed biogas can be produced, captured, compressed (like natural gas) and used as a fuel, including powering vehicles, and on a smaller scale, it has been successfully produced in home-sized biogas projects, such as in India and Pakistan where Ashden describes a one cubic meter floating-dome (thus safer) home-scale biogas plant installed by BIOTECH in a home in South India.

Manure from two to four cows or five to ten pigs can produce sufficient biogas to supply the cooking (and possibly lighting) needs for a single family.

Biogas plants in small scale projects produce methane or bio-gases from livestock manure mixed into a slurry using a system to which local toilets (producing human waste) may be connected.

Small biogas production systems and equipment are increasingly employed to use food or other organic waste as an energy source, both as home-made and commercially available equipment. In May 2015 the New York Times reported on the conversion of food scraps into a slurry used to produce biogas and fertilizer.

Insinkerator, Grind2Energy, and Quasar combine food waste grinding and naturally occurring bacteria to process organic waste. - Cardwell, Diane, "Food Scraps for Energy", The New York Times, 2 May 2015 p. B1-2.

An under-sink food waste grinder using "dry grind" technology to minimize water usage, produces a slurry that is drained to a storage tank for later transfer to a tank truck for movement by a food waste hauler to a processing facility. Contact information is provided below.

Typical Costs of Biogas Kits & Generator Systems

In our OPINION the economy of home biogas production may be best supported by purchasing either kits that contain the necessary biogas generator components or plans for do-it-yourself projects.

Information on Biogas Generators & Kits

Sources of Home Biogas System Designs, Plans, Biogas Kits & Biogas Components

Biogas and Methane Gas Safety Warnings

Open sewer cleanout in basement (C) Daniel FriedmanWatch out: We reported at SEWER GAS ODORS that because sewer gas contains methane gas (CH4) there is a risk of an explosion hazard.

At SEPTIC & CESSPOOL SAFETY we explain that gases produced in a septic tank are dangerous, as a potential source of explosion and as a cause of death by asphyxiation if someone falls into or deliberately enters a septic tank.

Readers should also beware that because some waste contains other toxins including heavy metals, amateur attempts to collect and burn sewage-produced gases could produce dangerous levels of carcinogens or other contaminants.

Don't try just piping or pumping sewer gas out of a septic tank or sewer line (our photo at right) for fuel use. We do not recommend just "hooking up your septic tank" to obtain methane fuel gas.

Watch out: Biogas Safety Advice from Werkgrop Terlindenv

A biogas leak can be smelled if the hydrogen sulfide has not been removed from the biogas. It smells like rotten eggs. No one should go inside large digesters unless they have a companion on the outside who can get them out in case they need help. Although the methane and carbon dioxide of biogas are not poisonous, a person may stop breathing if there is too much biogas and not enough oxygen in the air they are trying to breath.

Never allow negative pressure in a biogas system. Negative pressure occurs when the force created by the weight of the gases outside the biogas system is greater than the force inside the system. In normal operations the pressure inside the system should always be greater.

How much greater should always be measured on a pressure gauge (see Diagram 14
[in the company's literature- ed.]).

Negative pressure will pull air into the biogas system and the mixture of biogas and air might explode. If that does not happen, the oxygen in the air will kill the biogas bacteria and the gas production rate will drop. The only time the danger of negative pressure usually becomes a real possibility is when a person wants more gas from a digester than it can produce or there is an unnoticed gas leak.

When opening a biogas digester for cleaning or repairing, do not use candles or smoke cigarettes. For light inside the digester, use a flashlight or have a person standing outside reflect sunlight off a mirror.

Make frequent smell checks for gas leaks in plastic pipes, Joints, clamps, and gate valves. Rats have been known to bite holes in plastic pipes.

Stoves and gas mantle lamps should be placed with fire safety in mind. Special care must be taken in buildings with grass roofs to make sure that gas lamps are a good distance from the roof.

If the rotten egg smell of biogas is noticed in a room, immediately open doors and windows in order to get rid of the trapped gas before looking for the leak. On no account should anyone smoke cigarettes in the room.

In case of fire in a house or engine room, shut the gas off at the gate valve just after the gas storage tank to keep biogas from feeding the fire.

When using any kind of gas, light the match first, then open the gas valve. If the valve is opened first and gas is allowed to flow without being lit for any length of time, large amounts of gas can escape and any flame might ignite a fireball.

Children must be taught not to play with fire close to biogas systems, in case there are any gas leaks which could cause a fire or explosion (A Chinese Biogas Manual, 1976).

Brass gate valves and pipes used in biogas systems must be of a lead-free type. The hydrogen sulfide in biogas will destroy lead, which will cause gas leaks. - Werkgrop Terlindenv (2015)

Also for general advice about methane gas safety in buildings, see DRAIN PIPING & SEWER ODORS for the full discussion of odors from building drains & drain piping.

Also see SEPTIC or SEWER PIPING LEAKS for odors from septic systems and sewer lines.

See PLUMBING VENT DEFECTS & NOISESfor an explanation of sewer gas leaks from building drain vent piping.

For a discussion of methane gas detection see Using the TIF 8800 Gas Detector.

Biogas Piping: Regulators, Check Valves, Safety Devices

Reader Question: is there danger if I use a simple bio gas system at home with out installing a non return valve on the gas outlet pipe

Biogas check valve model Varec Biogas 211 low pressure check valve, contact Varec Biogas3 September 2015 Roy Silva. said:
I am referring to a home made bio gas tank. Kindly let me know whether if there is any danger to use a simple bio gas system at home with out installing a non return valve on the gas outlet pipe to prevent the system from any back pressure. Thanks.


Interesting biogas design question, Roy. I'm not a biogas energy system designer nor a professional engineer, but I looked around for biogas piping design guidelines.

And you are quite correct, a check valve should be located on a biogas piping system in at least some circumstances, and possibly for safety, all.


Regulators will direct the gas to utilization equipment such as boilers and engine generators and may be located upstream or downstream depending on specifications.

Check valves should be located where a reversal of flow would damage rotating equipment or disrupt the system’s pressure balance.

Biogas can become explosive within flammable concentrations of gas and air. - Goth (2015)

Varec at is a producer of the type of low-pressure gas system controls you'd want to investigate.
Quoting the company's sales literature:

The Varec Biogas 211 Series Low Pressure Check Valve is ideal for low pressure gas control lines where reversal of flow must be prevented.

The check valve is normally installed downstream of (a) meters; (b) regulators; or (c) other gas control devices that could be damaged by an accidental reversal of gas flow, pressure or explosion shock waves. It is usually located in systems where gas flow between multiple digesters or gas holders must be prevented and when gas flow reversal between several pieces of equipment installed in parallel must be prevented. - Varec (2015)

Biogas System Safety, Piping Controls & Systems Research


Continue reading at METHANE GAS SOURCES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see SEPTIC METHANE GAS for more sewer gas test advice and reference material.

Or see BIODIESEL HEATING FUELS for information about using biodiesel in oil burners designed for heating appliances: boilers, furnaces, water heaters

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BIO-FUEL PRODUCTION & USE at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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