Anaerobic biodegradability of organic solid substrates by steam explosion or co-digestion

Abstract

Organic solid waste is such a dominant source which accounts for nearly 50% of the total disposal solid waste. Besides, the fossil fuels, as a main source of energy production, are running out while the global energy demand is growing rapidly. The requirement for an alternative sustainable energy source is crucial to meet this demand, while minimizing greenhouse gas emissions. Anaerobic digestion for biogas recovery from organic solid waste has become an attractive technology to solve those problems with high economic and environmental benefits. In this study, several organic solid substrates including concentrated domestic sludge, industrial sludge from slaughterhouse, spent coffee grounds, microalgae and aquatic weeds were selected to evaluate their biodegradability by steam explosion or co-digestion. Biochemical methane potential tests were conducted in batch assays to verify the biomethane production of each substrate in each strategy. The results showed that industrial sludge from slaughterhouse produced highest methane yield at 745 mL/gVS without any pre-treatment because its component consists of high proportion of lipids. The lowest methane yield was obtained for aquatic weeds mainly due to its high lignocellulosic content in the cell wall. These results supported for the assumption that lipid-rich materials may have higher methane potential in comparison with lignocellulosic materials. Steam explosion at 180°C for 30 minutes did not show a substantial improvement in the methane yield but the process promoted the methane production rate of domestic sewage sludge and aquatic weeds so that reduced the lag phase time, which further shortened the hydraulic retention time of the tests. Some inhibition processes were assessed including acceptable air content inside the vessels and the precision of the triplicates. Those assessments were important in eliminating some inhibited conditions during the digestion process as well as validating the result of biochemical methane potential test.