ABSTRACT
The rise in human population and the increase human activities have increased the organic waste, which consist of household food waste, agricultural waste, human and animal waste. Waste is disposed in landfill or discarded in borrow pits which has adverse effect to the environment and public health resulting in diseases like malaria, cholera, typhoid. The amount of organic waste produced each year is increasing dramatically there is need for waste management strategies such as source-separation, compositing and anaerobic digestion. Therefore this study aims at the production of biogas by aerobic digestion of biologically degradable wastes.
In this work, poultry waste and cow dung were used as substrates for biogas production in a fifty (50) litres cylindrical anaerobic digester. The anaerobic digester which is 420mm in diameter and a height of 950mm has various openings that carried check valves. The digester has an opening which serves as inlet for the feed and another opening, made at the bottom of the digester, serves as outlet for the feed and another opening, made at the bottom of the digester, serves as outlet for the digested waste. Poultry waste and cow dung used in this study were not more than one day old. Slurry of approximately 25kg of the mixed waste (consisting of 50% each of cow dung and poultry waste) in water were fed into the digester. Two types of animal waste (cow dung and poultry waste) were used to prepare three mixtures which were fermented separately to obtain biogas. In the first experimentation, the cow dung was mixed with waste at a ratio 1:5, like 50kg cow dung and 50kg water was mixed and 25 litres of the mixture was feed into the anaerobic digester. In the second experimentation, the poultry manure was mixed with water at ratio 1:5 as 50kg poultry waste and 250kg water was mixed and 25 litres of the mixture was feed into the anaerobic digester. In the third experimentation, the cow dung, the poultry manure was mixed with water at ratio 1:1:5 as 25kg cow dung, 25kg poultry waste, 125kg water was mixed and 25 litres of the mixture was feed into the anaerobic digester. Experimentations were performed for 30 days each.
Results showed that biogas from cow dung has a maximum yield of 0.35N/mm2, biogas from poultry manure has a maximum yield of 0.37N/mm2, and biogas from both cow dung and poultry waste has a maximum yield of 0.30N/mm2. In addition, we observed that biogas production was low at the beginning and end of the retention period of the anaerobic digestion process, because biogas production rate is directly proportional to the specific growth rate of methanogens. From the results of the study, we conclude that cow dung and poultry waste are a potential substrate in biogas digesters.
