Anaerobic co-digestion of fresh water hyacinth and fish waste in batch cultures.

Methane production potential of individual and mixed fractions of fresh water hyacinth and fish waste was studied in batch cultures. The study also established viable counts of selected pathogens and investigated the effects of anaerobic digestion on their reduction. The fish waste contained 32%TS, 91%VS, and a C:N ratio of 6:1. The fresh water hyacinth contained 7%TS, 79%VS (dry weight), and a C:N ratio of 23:1. The substrate concentration of S.8 to 46.6 gVS per litre of fermenter volume for the fish waste was degraded by 30 to 4S% and gave methane yields in the range of 19 to 3S ml per gram of VS digested. The substrate concentration of 1.16 to 16.6 gVS per litre of fermenter volume for fresh water hyacinth was degraded by 21 to 72% and gave methane yields in the range of 29 to S6 ml per gram of VS digested. Codigestion of fish waste and fresh water hyacinth at a ratio of 1:4 parts gave the highest methane yield of about 20 ml per gram of volatile solids digested and were degraded by 2S%. This yield is lower by 42 and 64% than that obtained for the anaerobic digestion of individual fractions of fish waste and fresh water hyacinth, respectively. The effect of anaerobic digestion on the reduction of total coliforms, fecal coliforms, Clostridium perfringes and Salmonella species was investigated at mesophilic temperature of 30 °C, in the mixture of fish waste and fresh water hyacinth for 21days. Anaerobic stabilization of the mixture of fish waste and water hyacinth resulted into total destruction of fecal coliforms, and Salmonella species. The total coliforms was reduced by 87 °lo and Clostridium perfringes was reduced by 67%. This study demonstrates that there is a need for optimizing the anaerobic digestion of the combined fractions to improve their yields, and that the mesophilic temperature of 30 °C is effective in reducing the counts of pathogens in the mixed fractions of these substrates.