Anaerobic Treatment of Cattle Manure for Biogas Production

Feedlot farming with abattoir integration in Malaysia is relatively new; therefore its waste management needs to be carefully administered. Although the cattle are only stored for 3 months cycle to be fatten up before being slaughtered, the manure and waste from abattoir can be as much as 200-300 tons per day. Batch anaerobic digestion of cattle manure was studied in 10 L bioreactor at 53oC and controlled at pH 6.95. Palm oil mill effluent activated sludge at ratio of 1 to 5 was used as seed sludge. The initial COD of the mixture was 42.5 g/L and reduced by 51%. The biogas production is 207 L/kg VS at hydraulic retention time of 19 days with ultimate methane yield of 184 L/kg VS. The biogas production dipped slightly on day 10 due to the availability of nutrient that has decrease tremendously. Increased N-NH3 concentration above 1 mg/L may also have inhibitory effect on the biogas production. Methane content is between 58-83% throughout the culture. The H2S concentration is low below 0.26 ppm therefore no further treatment is needed. Effluent on the final days was found to be high in COD (8.75 mg/L) and N-NH3 (260 ppm) unsuitable for irrigation in Malaysian water standard. Further treatment such as post-digestion or chemical/physical treatment is needed.