Biogas production from co-digestion of livestock manure with lignocellulosic biomass

Abstract

The research aimed to investigate how to improve the effectivity and efficiency of biogas (methane) production system from livestock manure using co- digestion with lignocellulosic biomass. The treatment includes co-digestion of cattle manure, chicken manure, rice straw, and hornwort (Ceratophyllum demersum) in mesophilic (35 °C) temperature with used frying oil as an additive. The feedstock was determined according to their availability in the environment and conflict of interest. Natural microbial consortium in existing digester processing cattle manure was used as inoculum. Potential feedstock for co-digestion was characterized for their physicochemical properties before being used as substrates. The feedstock was mixed in 14 experiments for Biochemical Methane Potential (BMP) test for 74 days at mesophilic temperature. The BMP result showed that a mixture of Cattle Manure (M), Chicken Manure (P), Rice Straw (R), and Oil (L) at proportion of M:P:R:L 45:15:38:2 had the highest methane yield at 246.02+2.14 NmL CH1/g VS, increasing 40.25% compared to that of cattle manure single digestion. From the result of the BMP test, a decision analysis was performed to determine the appropriate substrate for continuous digestion considering the BMP methane yield, sustainability, and applicability in Continuously Stirred Tank Reactor (CSTR) reactor. Due to consideration of applicability and sustainability, the M:P:R:L 45:15:38:2 could not be used, and therefore, the second highest yield substrate, the M:P:R 45:15:40 mixture which had a methane yield of 233.25±0.81 NmL CH/g VS in the BMP test or an increase of 32.97% compared to that of cattle manure mono-digestion, was used for continuous digestion instead. A single-stage CSTR digester was used in the study to determine the methane production in continuous production. The Hydraulic Retention Time (HRT) was 35 days and determined from the result of BMP test. The Organic Loading Rate (OLR) was 2 g VS/L day. The result of continuous digestion test showed that M:P:R 45:15:40 substrate mixture had a stable performance with a yield of 135.30+21.41 NmL CH/g VS in the continuous digestion or 71.28% of its BMP value. Therefore, it can be concluded that cattle manure, chicken manure, and rice straw in a proportion of 45%, 15%, and 40% respectively could be used for sustainable biogas production through anaerobic digestion process.