ABSTRACT
There is a great deal of environmental pressure in many parts of the country to ascertain how organic waste can best be handled in the absence of appropriate disposal methods can cause adverse environmental and health problems. Anaerobic digestion has been considered as waste-to-energy technology, and is widely used in the treatment of different organic wastes. The study was carried out for biogas production from co-digestion of cow dung, horse dung and chicken feather in producing biogas through anaerobic co-digestion with chicken feathers. This is achieved by constructing twelve (12) local digesters and gas collection systems mounted at the premises of Department of Water Resources and Environmental Engineering, Ahmadu Bello University Zaria. The digesters were used to digest the mixture of cow dung (CD), horse dung (HD) and chicken feathers (CF) at different percentage ratios for a period of thirty seven (37) days retention time until the biogas reduced significantly. Inflammability test was conducted to determine the quality of biogas produced. Proximate analysis such as nitrates, sulphates, carbon to nitrogen ratio and phosphates were determined before and after anaerobic digestion to rank the substrates in order of their biogas production capacity. The total volumes of the gas produced were 2.51E-01m3, 1.71E-01m3,1.38E-01m3, 1.33E-01m3,1.04E-01m3, 9.43E-02m3, 9.43E-02m3, 5.30E-02m3, 3.59E-02m3, 5.93E-02m3, 3.59E-02m3 and 3.04E-04m3 for 25%CD-75%HD, 100%CD, 50%CD-50%HD, 100%HD, 75%CD-25%HD, 75%CD-25%CF, 75%HD-25%CF, 50%HD-50%CF, 25%HD-75%CF, 50%CD-50%CF, 25%CD-75%CF and 100%CF respectively. These implied that the mix ratio of 25%CD-75%HD produced highest biogas production. The results of carbon to nitrogen ratio for anaerobic digestion were determined at optimum range of 20:1 to 30:1. The nitrates, sulphates and phosphates determined shown an increase after digestion for the cow dung, horse dung and chicken feather with percentage values of 15.1%, 9.7% and 3.2% respectively, which could be a good source of biofertilizer. The average temperatures of the digesters recorded in the morning, afternoon and evening range from 26ÂC-43ÂC under mesophilic condition, and the average ambient temperature observed during the study was 34ÂC, the pH values of the media in all the substrates digested were found almost in the optimal limits of methanogenic bacteria of 6.0-7.4. The modified Gompertz equation was used to adequately describe the cumulative biogas production from these digesters and also to assess the kinetics of the biodegradation process. It was observed that the rates of substrate biodegradability were obtained. The constants were determined using the nonlinear regression approach with the aid of the solver function of the Microsoft Excel tool pack. Biogas production was found to be feasible from the other wastes, but CF was regarded as failed digester as it does not produce significant amount of biogas because of inhibiting factor such as high keratin content. The inflammability test conducted during anaerobic digestion was found to be efficient. Biogas productions from organic wastes are having prospects in contributing towards solving the national energy crisis of most countries.
