Co-digestion of wastewater treatment sewage sludge with various biowastes: A comparative study for the enhancement of biogas production

Abstract

The objective of the present study is to improve the anaerobic digestion of sewage sludge viaco-digestionwith biowastes. In the study, anaerobic co-digestion of sewage sludge and six organic waste materials as possible co-substrates for enhancement of bio-methane potential were carried out. Furthermore, the possible impact of the co-digestion on digested sludge content in terms of volatile solids (VS), Chemical oxygen demand (COD), and total solids (TS) were examined. Firstly, physicochemical characterization of sewage sludge as the anaerobic digestion feedstock was carried out before anaerobic digestion to obtain their composition. Characterizations such as proximate and ultimate analysis were carried out using a Hach spectrophotometer, a laboratory oven, and a furnace. The characterization feedstock results showed that the sludge contains a reasonable amount of COD, organic matter, TS, and VS along with the inhibitory compounds which shows potential for a high yield of methane in biogas production, as long as the stability of anaerobic digestion is maintained throughout the process. The results show that the sewage sludge has great methane potential during biogas production quantified as 28.6 g CH4/kg feed. When compared to sewage sludge mono digestion, biomethane yield was increased by 3–6 times when thick co-substrates were used. Although high solid content co-substrates generated significantly more methane gas, they also increased the risk of organic overloading. Co-substrates such as molasses, food waste, animal manure, and fresh produce waste performed well at 25% co-digestion ratios. Furthermore, all other solid co-substrates co-digestion resulted in increased VS and COD residuals in digested sludge, withexception of manure. Most of the liquid co-substrates studied here, on the other hand, had a significant synergistic effect, enhancing the removal of TS, VS, and COD during anaerobic digestion.