Biogas production from anaerobic co-digestion of waste activated sludge: co-substrates and influencing parameters

Abstract

Anaerobic digestion is a versatile biotechnology to treat waste activated sludge (WAS), the main by-products of biological wastewater treatment, because it can achieve simultaneously energy recovery (biogas) and pollutant reduction (organic matter, pathogens). However, the potential of biogas production from mono-digestion of WAS is usually limited by the imbalance carbon to nitrogen (C/N) ratio of WAS and ammonia accumulation. Anaerobic co-digestion, simultaneous digestion of two or more substrates, should be a feasible option to resolve these disadvantages. The abundant organic wastes from municipal, industrial, and agricultural field have been the ideal co-substrates because they not only can balance the substrate nutrient to obtain the optimal C/N ratio, but also can adjust pH and dilute the toxic materials to mitigate the inhibition to methanogens, consequently improving the yield of biogas, especially methane. This paper classified the main organic co-substrates according to their source and reviewed their application in anaerobic co-digestion of WAS. Then the influence of temperature, pH, organic loading rate, hydraulic retention time, C/N ratio, digester type and pretreatment method on biogas production was extensively discussed. Finally, this review brought forward the challenges and outlooks of anaerobic co-digestion in the future.