By Dr Jesse Kagai
Biogas is a product of a process where micro-organisms decompose organic matter in the absence of oxygen. This organic matter can come from diff erent sources, e.g. animal manure, agricultural residues and by-products and food waste from kitchens and markets. The end products of this process are methane gas used for cooking and bioslurry used as fertilizer.
There is a huge potential for biogas production in Kenya because only a small fraction of the smallholder farmers have embraced this technology. The country’s large livestock population produces enough animal manure to be used as feedstock for biogas production. While this is so, many Kenyan households continue to rely on firewood for cooking, which leads to deforestation. However, the technology is gaining recognition, especially among smallholder dairy farmers, who are keen to reduce their operational costs.
The technology used to produce biogas is quite cheap and simple. It is easy to set up and needs little investment, especially when used on a small scale. The system has a quick return on investment, as it off sets the cost of energy used for cooking and the materials used for biogas generation (manure) are free.
Biogas as a renewable energy source
The current energy supply is dependent on non-renewable resources, and reserves are being depleted faster than new ones are being formed. Examples of these energy sources are firewood and charcoal. Unlike these sources, biogas is renewable and contributes to the preservation of natural resources by reducing the cutting of trees for firewood and charcoal burning. Cooking on biogas is fast and smokeless, leading to time-saving and improved family health, especially among women and children. It saves women and children from the daunting task of collecting firewood, leaving more time for other important tasks. The reduced indoor air pollution helps improve global health by reducing respiratory diseases caused by smoke from firewood and charcoal use.
In addition to cooking, biogas can also be used for lighting and heating water for domestic use. It can also be used to run small farm machines like chaff cutters and power generators. This helps smallholder farmers save on the fuel used for these machines, especially the chaff cutter that is used daily for animal feed processing. This is of economic importance to the smallholder farmer as it provides an additional income. One cubic meter of biogas is reported to be equal to 1 liter of kerosene, 2kWh of electricity and 4 kg of firewood.
Bio-slurry as an excellent fertilizer
One of the end products of a biogas plant is called bio-slurry. It is a valuable soil fertilizer rich in nitrogen, phosphorous, potassium, and micronutrients important for soil health and plant growth. Compared to normal manure, bio-slurry is of superior quality due to its improved fertilizer efficiency, which is readily available to the crops. Most of the organically bound nutrients, particularly nitrogen, are mineralized making them easily utilized by plants.
Bio-slurry is also safer to use compared to untreated manure because the process of biogas production acts as sanitization against active pathogens that may be present in the animal dung. This prevents disease transmission. It also kills, inactivates or slows the growth rate of weed seeds that are normally present in manure. Weed seeds may end up in manure products through feeding as well as bedding materials. Some seeds, including those from weeds, survive the intestinal passage and may compete with crops when applied in raw manure.
Bio-slurry in fishponds
In recent years, small-scale fish farmers have incorporated bio-slurry in their fish ponds to increase their biological productivity. Studies have shown that 50 kgs of bio-slurry produces 1 kg of fish by increasing Phyto and zooplankton biomass used as fish feed. This reduces commercial pelleted fish feed by up to 50%.
Organic waste reduction
Biogas can be produced from animal dung and organic waste materials from household kitchens and markets. Organic wastes, such as food leftovers, rotten fruits, and vegetables, can be used to produce cooking gas while helping manage the waste by reducing its volumes and disposal costs. The end product, which is a digested substrate, can be used as organic fertilizer.
Environmental advantages of biogas
Gas generated through bio-digestion is non-polluting, with no combustion taking place during its production, meaning no greenhouse gases are emitted to the environment.
Biogas production can help mitigate climate change by capturing methane from animal waste and utilizing it as an energy source. Methane is a known potent greenhouse gas responsible for global warming.
Biogas also helps reduce carbon dioxide, produced by the use of firewood and burning charcoal. Using biogas for cooking helps to reduce tree cutting, thus reducing deforestation.
Important points to note.
- A biogas plant requires a constant inflow of manure where you add fresh dung every day.
- Do not add manure that is too old.
- Do not add too much water.
- Do not add water with soap or disinfectants.
- Antibiotics are very harmful to biogas, so do not add dung with medicine residues or dung contaminated with milk from a cow treated for mastitis.
- Do not let oxygen into your biogas plant; always close gas valves and repair leakages.