MICROBIAL PRODUCTION OF BIOGAS FROM COW DUNG, CASSAVA PEELS, ABATTOIR AND CASSAVA PROCESSING WASTE WATERS IN AKURE METROPOLIS

Abstract

This study was aimed at evaluating the best kind of waste (solid, liquid or combination) that can stimulate production of biogas. Five kilograms each of cow-dung and cassava waste peel (blended into fine powder) were mixed with 5 liters of water separately. Also, five hundred liters of each abattoir and cassava processing waste waters were mixed with equal volume of water and left to settle separately for 24 hours. The prepared solid and liquid wastes (mixed with water) above were then fed into different bio-digesters fabricated with metal. The four bio-digesters were then monitored daily for different parameters including gas production, environmental factors like temperature and pH were measured on different days. Microbial (bacterial and fungal) isolation was done from the four substrates inside the bio-digester when decline in production of gas is noticed i.e. for cassava waste water, isolation was done on the 5th day, abattoir waste water isolation was done on 7th day, cow dung isolation was done on the 25th day, cassava waste peel was done on the 14th day of biogas production respectively by standard microbiological techniques. The bio-digesters were examined daily for gas production through the pressure gauge. Biogas produced were collected using gasometrical chamber and then analyzed for the percentage composition. Mesophillic temperature range of 32 -36oC and a pH range of 6.9 to 7.5 favoured the isolated microorganisms from bio-digesters containing solid and liquid waste. Fungi isolated includeAspergillus niger, Candida albicans and Monilla sp. while bacteria isolated includeEscherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. It was discovered that cassava waste water was the first to produce biogas. For cow dung, the biogas production was initially slow and low within the first 3 days but increase gradually. NaOH (1%, 3%, and 5%) reduce the acidity of the medium which favored the proliferation of microorganisms, and directly increases level of biogas production. It was also observed that methane content of cow dung was highest (67%) followed by methane content of cassava waste (51%). Though cassava waste water may be used to generate biogas to some extent, cow dung was better in biogas production. It is hereby recommended that cassava waste water should replace ordinary water that is often being mixed with cow dung for biogas production. Result of the abbatoir waste water indicates gas production after anaerobic biodigestion but this gas were not flammable, i.e do not burn which indicates a very low concentration of methane gas along side carbon dioxide, also absence of solids in the waste waters does not favour methane gas production but gas such as hydrogen gas, ammonia gas, hydrogen sulphide were produced from the waste water. The chemical composition of biogas reveals a high concentration of methane as high as 67% from the cowdung , followed by cassava waste peel as high as 51% while abbatoir waste water and cassava processing waste water recorded the lowets methane gas production at 18% and 15% respectively.