Biogas production overview

Kilifi Plantations also has a subsidiary biogas company in the name of Biogas Power Holdings (EA) Ltd.

Biogas Power Holdings East Africa Limited aims at supplying its customers with clean and sustainable energy that will not only fuel economic growth but also protect nature and the environment.

We lead our customers away from fossil energy supplies and a very costly unreliable electricity grid towards a decentralized supply from a renewable climate friendly energy source which aims at providing a clean, reliable and efficient alternative energy source.

Components of our Bio-gas Plant

The major components of the bio-gas plant are the digester tank, an inlet for feeding cow dung,sisal waste, gas holder tank, an outlet for the digested slurry and the gas delivery system for taking out and utilizing the produced gas for local consumption.

Biogas is produced in a special airtight tank called an anaerobic digester. The design of the anaerobic digester determines the first three steps in biogas production.

  • Airtight Environment. The anaerobic digester has to be airtight. The difficulty arises from trying to add fresh material without allowing oxygen into the system. The most common method of creating a continuous flow digester is the “teapot” or “P-trap” shape. Most biogas digesters are some variation of this teapot shape.
  • Archaea love water. When loading a digester, the water content in the material put in it should be taken into consideration. A head of lettuce, for example, looks very solid to us, however, it is 98% water. Dried rice is only 14% water. Regardless of the size of your digester, the “40-50-10 Rule” is simple rule of thumb to follow to get the correct volume: Forty percent material, fill the rest of the digester with water except for 10% headspace.
  • Neutral pH is an important parameter in anaerobic digestion, just as it is for aerobic composting. If pH is measured at the inlet, it will be slightly lower than neutral — usually around 5.5 — as fresh material is converted into acids. The pH will neutralize as these acids are converted into methane gas. By the time the liquid biofertilizer comes out the digester, it should be 7. If the pH of the biofertilizer is lower than this, it is an indicator the digester has been over-fed and is at risk to “sour,” or stop working due to low pH. If the pH at the inlet goes below 5.5, it is necessary to add some wood ashes or lime to buffer the digester. A soured digester has no bubble activity and instead of producing gas, instead it draws air into it. The top will be sucked in tightly against the surface of the liquid and if a brewer’s airlock is being used, the water in the airlock will be sucked into the digester. Restarting a soured digester is time consuming, and in most cases it is simpler to dump it out and start over.