Anaerobic Co-Digestion Of Multiple Feedstocks For Biomethane Recover- The Impact Of Lipids:Proteins:Carbohydrates Ratio

Municipalities are facing increasing challenges regarding management and disposal of solid waste. Anaerobic digestion (AD) of municipal biowaste enables waste reduction and biogas production that can be utilized as a renewable source of energy for heat and power generation. Anaerobic co-digestion (AnCoD) enhances the performance of conventional mono-digestion. The mixing ratio of the feedstocks is an important criterion in AnCoD design which is typically determined based on the optimum carbon to nitrogen (C:N) ratio within the range of 25-30 or COD:N ratio in the range of 50-140. However, literature has shown contradictory results for the optimum C:N and COD:N ratios.

Therefore, the main objective of this study was to primarily investigate the influence of the mixing ratio of the feedstocks including thickened waste activated sludge (TWAS), manure and source separated organics (SSO) on improving biomethane production and introducing a new methodology for optimizing the mixing ratio in AnCoD based on the lipids, proteins, and carbohydrates contents as the three main compounds existing in biowaste. The hydrolysis/acidification performance in AnCoD of manure, TWAS and SSO individually and in different combinations was also investigated. This study has introduced an empirical model to explain the relationship between the biomethane production and lipids: proteins: carbohydrates ratio of the feedstocks in anaerobic co-digestion of TWAS, manure and SSO. Among the binary ad ternary combinations, the ternary co-digestion of TWAS/manure/ SSO at the mixing ratio of 2:4:4 and lipids: proteins: carbohydrates ratio of 1:3:12 resulted in the maximum ultimate methane production. The maximum methane yield of 363 ml CH4/g COD added corresponded to co-digestion of manure/SSO at the mixing ratio of 7:3. The maximum hydrolysis rate corresponded to the co-digestion of TWAS/manure at the ratio of 9:1. Overall, the best performance in both hydrolysis and methanogenesis was achieved by the co-digestion of TWAS with SSO at the ratio of 3:7 as well as TWAS/manure/SSO at the ratio of 2:4:4 compared to other feedstock mixes. It was observed that the proposed second order polynomial model could describe the relationship between biomethane production and lipids, proteins, and carbohydrates content of the feedstock.