Biogas from anaerobic digestion can be a solution to current and future energy needs in South Africa. One option for improving biogas yield of anaerobic digestion of organic matter is co-digestion. Cow dung and donkey manure were co-digested together at different mixing ratios. Total Solids (TS) and volatile solids (VS), ammonia-nitrogen, pH, alkalinity, volatile fatty acids (VFA) and chemical oxygen demand (COD) were determined by using the standard methods of the American Public Health Association (ALPHA). The pressure of the biogas was measured daily by means of a pressure gauge fixed on top on the batch biogas digester. Methane and carbon dioxide contents in the biogas were sensed by non-dispersive infra red sensors. Palladium/Nickel sensors were used for sensing hydrogen and hydrogen sulphide in biogas. Highest biogas yield was obtained for a mixing ratio of 50% cow dung to 50% donkey manure, however lowest biogas yield was obtained from cow dung. For all the substrates the gas yield increased with time and then attains a constant value. However the co-digestion of cow dung and donkey manure attained maximum gas yield on 24th day while for cow dung it was on 28th day and for donkey manure it was on 26th day. Co-digestion of cow dung and donkey manure increased the gas yield by about 43%. Pure samples produced less biogas than co-digested samples. There was a strong positive relationship between gas production and % of co-substrates used (R2 = 0.999). The biogas produced from co-digestion can be a solution to lack of energy in rural areas in Eastern Cape Province of South Africa where plenty of donkeys and cattle are kept.
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