مهندسی عمران شریف (Feb 2022)
Assessment of inoculum to substrate ratio’s effect on dry anaerobic digestion process performance
Abstract
Nowadays, the world’s population growth and improved standards of living have given rise to increased global waste production. This rate is even higher in developing countries. For example, in Iran’s capital, Tehran, about 7,000 tons of waste is generated daily. Improper management of these massive amounts of solid waste causes many serious human health and environmental issues. According to statistics, 60% of municipal waste in most developing countries is made up of biodegradable organic materials. Anaerobic digestion (AD) is one of the most common waste management techniques which have been utilized for several decades to manage municipal wastes. Additionally, AD benefits society by producing bioenergy and biosolids that can be used as fertilizers. Today, dry anaerobic digestion (DAD) has gained much more attention in comparison to liquid anaerobic digestion due to its lesser water requirement, smaller reactor volume, and higher biogas production. Since DAD is a biological process, the inoculum to substrate ratio (I/S) is an effective parameter in AD-based processes. In this regard, the effect of the I/S ratio on the DAD of organic waste with fruit and vegetable waste provided by the Tehran fruit and vegetable market at mesophilic conditions was investigated in this study. Experiments were conducted at four different I/S ratios (0.25, 0.5, 1, 2) in bench-scale reactors using the sludge supplied from the South Tehran wastewater plant. Different operational and controlling parameters including pH, chemical oxidation demand (COD), oxidation-reduction potential (ORP), volatile fatty acids (VFAs) concentration, and the composition of the biogas were assessed in the experiments. According to the results, when the I/S ratio was below one, the volume of the biogas decreased due to the accumulation of VFAs. The best result was gained when the I/S ratio was 2 resulting in 0.35 lit CH4/g VS production and 77% removal of Volatile solids (VS).
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