Anaerobic digestion of sludge differing in inorganic solids content: performance comparison and the effect of inorganic suspended solids content on degradation

Abstract

High inorganic suspended solids (ISS) content of sludge in many areas (especially with combined sewage systems) results in low VS/TS (volatile solids, VS; total solids, TS) levels and raises concerns about its effect on anaerobic digestion. The performances of sludge anaerobic digestion with different feeding VS/TS levels as well as the effect of ISS content on the anaerobic degradation process were investigated in completely stirred tank reactors by semi-continuous and batch experiments. In semi-continuous experiment with sludge at VS/TS of 61.4%, 45.0, 30.0% and 15.0%, biogas yield, VS reduction and methane content decreased logarithmically with the feeding VS/TS decreasing; slightly higher volatile fatty acid concentration was observed at VS/TS 15%. Results of the batch experiments suggested that acetogenesis and methanogenesis are obviously affected by high ISS addition, while hydrolysis is less affected. The retardment of substrate conversion rate is probably attributed to decreased mass transfer efficiency at high ISS content.

Enhancement in adsorption potential of microplastics in sewage sludge for metal pollutants after the wastewater treatment process

“…Sewage sludge are composed of inorganic particles and organic matter (Wei et al 2018). The percentage of sand in sludge inorganic matter reaches up to 78.9% in China (Zhao 2015), and thus SS was selected as a representative of sludge inorganic component (Duan and Dai 2016) in the study. Sludge organic matter including protein and humic substances might affect adsorption of the MPs to metals (Wei et al 2016).…”

High-solid anaerobic digestion of sewage sludge: achievements and perspectives

“…The main reasons for this are poor management, economic limitations, and inadequate planning, as well as the characteristics of SS (i.e., low VS/TS) in China. Specifically, in many areas of China, the VS content of sludge has been found to be much lower (typically < 55% of TS) than that in developed countries (usually >70% of TS) (Duan et al, 2016;Xu et al, 2020a). HS-AD may be a viable way to solve these problems, because this SS processing technique uses a smaller reactor volume, has lower energy requirements for heating, generates less wastewater, and has a higher volumetric biogas production rate than LS-AD.…”