The effect of retention time on biogas production from slurry produced by cattle fed sugar cane.

Abstract

A study was made of different retention times employed in the anaerobic fermentation of slurry from cattle kept on slatted floors and fed sugar cane and molasses/urea. A standard 200 lib. oil drum with a plastic lining was used as a digestor. The treatments were different retention times of 10, 20 and 40 d and there were two determinations at each of these times. The slurry was obtained from the exit sluice of a feedlot with a slatted floor. The digestor was filled to the level of the overflow pipe (approximately 190 kg) with slurry. Amounts of 18.5, 9.25 and 4.62 kg fresh slurry ware added daily for the respective retention times of 10, 20 and 40 d. Each experiment lasted for a complete cycle, ie 10, 20 or 40 d according to the treatment. Daily gas production fell slightly fro. 53 to 48 litres/d, as retention time was increased from 10 to 40 d. The amounts of gee produced per unit of dry matter and per unit of organic matter entering the digestor showed a linear increase with retention time. The maximum value was 300 litres of biogas/kg organic matter entering the digestor. The air temperature during the experiment warded from 21 to 30 and the temperature of the gee at the time of measurement from 23 to 40 .