How to install a biogas system

By Clifford Akumu

The cost of running farm machines can be very high, depending on the kind of fuel used. Biogas an environmentally friendly renewable fuel, is cost efficient not only for low-income earners, who cannot access electricity, but also farmers looking for an alternative clean source of energy.

Biogas is a by-product of anaerobic (without oxygen) breakdown of organic matter such as animal manure, crop and kitchen waste, and garden weeds. Anaerobic digestion is a fermentation in which waste is digested by microbes to produce methane gas (or biogas).

Mr. Solomon Njuguna, the founder of Ngerwa Final Solution, a company that develops and constructs biogas units, says that very many people are now opting to install biogas systems to avoid high electricity costs.

Biogas consists of 60 per cent methane and 40 per cent carbodioxide, with low levels of hydrogen sulphide and other gases. It can generate electricity for cooking, lighting, heating water, refrigeration and can run engines such as chaff-cutters.

Materials needed for biogas production such as livestock manure and others, including feed, food processing, and slaughterhouse waste, corn silage, industrial waste and sewage sludge, are readily available on the farm.

Setting up a biogas system involves several requirements thus, you must engage a reputable biogas expert to avoid disappointments.

“Always engage a qualified digester designer, builder or equipment supplier, to install your biogas system,” cautions Mr Njuguna.

A complete biogas unit for four cows, costs from Ksh50,000 to Ksh150,000. The charges vary depending on the size and location of the biogas plant.

“The cost of biogas installation also varies depending on the components chosen such as the foundation, digester effluent storage, roof, gas pump, boiler, hydra-ram and manure pump,” he adds.

According to Mr Njuguna, the capacity of the smallest biogas unit is 6m3. One or two cows or five to eight pigs should provide enough manure to run a biogas unit for a household of four people.

A biogas plant comprises of three sections:

Inlet – Here the biogas unit is fed with water and cow dung. This mixture is stirred with a stick until it forms the slurry.

Digester – This is an airtight tank or container where biological requirements of anaerobic digestion are controlled to hasten digestion and optimise biogas production.

Here, acid-forming bacteria decompose organic materials and release methane and carbon dioxide.

Outlet – This is where the digested slurry leaves the digester into the storage to be used as fertiliser.

Working of the biogas unit:

Kitchen waste (food remains, vegetable stalks) and fodder (Napier grass, brachiaria, purple guinea grass) or zero-grazing unit waste flow to the biogas digester, where the farmer adds a bucketful of water before stirring. Compared with other feedstocks, grass has suitable and promising characteristics as an energy crop for biogas production.

The quantity of gas produced from a biodigester depends on the type of feeds given to the cow. If a cow is given quality feed, the digester will yield more gas. Dry feeds produce more bacteria inside the cow than wet feeds and manure from animals fed on such feeds will process the gas faster, inside the digester.

Farmers can opt to put in 2kg of food waste each day. This will produce enough gas to cook with twice a day. A biogas digester requires extra water for anaerobic digestion so when water supply is limited you can harvest rainwater, recycle domestic water or practise aquaculture.

Remove any fodder and other waste materials such as pampers and sanitary pads that can cause blockages. Use a shovel or special metal called a D8.

Insert a photo of D8.

The system requires seven days for the gas to build up. Thereafter, it will   continuously produce enough gas.

For optimum performance, the biogas unit should have the following qualities:

– Be arranged to minimise heat loss;

– Provide a simple flow path for material through the system;

– Be as automated as possible and be accessible for maintenance and repairs;

– All pipes and gas lines should be made large enough to provide access for cleaning devices.

Safety measures include the following:

  • Equipment should be designed not to let biogas in or out and should be resistant to corrosion;
  • Electrical installations must comply with standards and regulations. The constituent materials, in particular digesters or combustion units, must be non-combustible;
  • When handling waste material, use personal protective equipment to avoid contact;
  • Wash hands before eating, drinking and before touching the eyes or nose;
  • Safety valves; digesters and biogas storage tanks must be equipped with safety devices that prevent excessive vacuum and overpressure;
  • Provide two sluice gates in the digester just in case one of them breaks down;
  • The digester inlet should have a check valve to prevent the biogas from flowing back.

A good biogas unit lasts for at least 30 years.

Benefits of biogas and bio slurry:

  • It is affordable and also safe to use;
  • It conserves trees, and reduces greenhouse gas emissions;
  • Biogas is smoke and soot-free, reducing respiratory health problems. This also reduces indoor air pollution;
  • Biogas reduces fuel expenses for cooking and saves money and time. Sale of bio slurry can be a source of extra income;
  • Farm productivity increases from using bio slurry as a liquid manure and an animal feed supplement.

Disadvantages of Biogas:

  • Less suitable for dense metropolitan areas.

Biogas expenses:

Though the initial cost of biogas plant installation has been a deterrent to some farmers, in counties such as Kiambu, a Pay-As-You-Go model allows farmers to purchase the biogas units through affordable payments. In this model, biogas companies absorb the initial installation cost and recover it, plus their profit, by charging farmers for every unit of power used. Consumers can pre-purchase energy units via M-Pesa or Airtel Money using their meters.

Consultant : Solomon Njuguna, Telephone: 0725913128

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