Design and fabrication of 3.60 m3 household plastic bio digester loaded with kitchen waste and cow dung for biogas generation

Abstract

A 3.6 m3  pilot plastic digester for family generation of biogas was designed, constructed and evaluated through physico -chemical studies using 50% cow dung and 50% kitchen wastes. The ash content of waste increased after digestion while the fibre and fat contents of the waste was 5.10 and 1.05% but significantly (p<0.05) decreased to 2.49 and 0.70% after digestion. The carbohydrate content of the waste was 11.02% which significantly (p<0.05) decreased to 7.91%. The volatile solid content of 50% cow dung + 50% cassava peel + yam peels + vegetable was  11.10%. The biochemical oxygen demand was 44.58% while the chemical oxygen demand was 139.20% before digestion but decreased significantly (p<0.05) after digestion. The pH of 50% cow dung + 50% cassava + yam peels + vegetable waste during digestion increased from 6.71 at day of charging to 6.81 at the 8th day after which it began to fluctuate between 6.68 and 6.85 throughout the retention period. Afternoon temperatures of both ambient and slurry were within the mesophilic (30 and 40°C) temperature which was higher than the morning and evening temperatures. The production of biogas started at the 2nd day by producing 406 L and increased each day till day 8, by producing 738 L and after which its production began to fluctuate between 572 and 718 L/day. Early biogas flammability was observed on the 4th day for 50% cow dung + 50% cassava + yam peels + vegetable. At the point of flaming, the methane content of the biogas increased significantly (p<0.05) to 65.65%, while the carbon dioxide decreased significantly (p<0.05) to 25.15%, for 50% cow dung + 50% cassava + yam peels + vegetable. The average biogas (0.601 to 0.505 m3/day) produced from the waste using 3.6 m3 capacity plastic bio-digester  could be sufficient to cook three times a day for household of 3 to 4 persons.   Key words: Bio digester, ash content, cassava, cow dung, biogas.