Glycerol Supplementation Effect on Biogas Production from Cattle and Pig Manure Substrates

Abstract

Organic wastes are potential sources of biogas and high-quality bio-fertilizers. Biogas is an appealing energy product that can be used directly as a renewable alternative source of energy. Some of the most commonly used substrates for biogas production are cattle and pig manure. Technology for biogas production is an active research area. Studies on optimization of biogas production are being undertaken with a view to making the process fully cost-effective. This study was conducted to investigate the effect of glycerol supplementation on biogas yield under the respective appropriate optimum mesophilic temperatures and substrates to water dilution ratios of both cattle and pig manure substrates. Analysis of substrates and inoculum for various physico-chemical characteristics was carried out. The optimum mesophilic temperature for both cattle and pig manure substrates was determined to be 40 ºC. The optimum cattle manure substrate to water dilution ratio was established to be 17.5:7.5 (m/v) and 5:20 (m/v) for pig manure substrate, respectively. On supplementing the optimum cattle manure substrate to water dilution ratio of 17.5:7.5 (m/v) with 0.1, 0.2 and 0.3 g of glycerol, the respective percentage increases in biogas yields over the control were calculated to be 6.4, 12.5 and 21.9%. Further, for the established optimum pig manure substrate to water dilution ratio of 5:20 (m/v) supplemented with 0.03, 0.05 and 0.08 g of glycerol, the respective percentage increases in biogas yields over the control were calculated to be 10.0, 17.65 and 29.6%. The study shows that, one, the upper limit of the mesophilic range (30-40 °C) gives a higher biogas yield; two, over-diluting or under-diluting substrates with water influences biogas yields; and three, glycerol which is also a by-product of biodiesel manufacturing can be advantageously utilized as a supplement to boost biogas production. Use of optimum conditions of temperature and dilution ratios would significantly improve biogas production.