Anaerobic co-digestion of the organic fraction of municipal solid waste with several pure organic co-substrates

A strategy to improve the operation of working anaerobic digesters treating the organic fraction of municipal solid wastes (OFMSW) to increase the biogas production is studied. It consists of increasing the organic loading rate of the digesters by adding extra organic matter from some problematic organic wastes. Vegetable oil (VO), animal fats (AF), cellulose and protein (protein) were used as pure co-substrates and the co-digestion anaerobic process was analysed in terms of the ultimate methane production, the methane production rate and the hydraulic residence time. The analysis of methane or biogas production led to different conclusions when expressing this parameter on a volatile solids basis or on a reactor volume basis. The need for a combined analysis is highlighted. In addition a new model to predict the biodegradability rate and evaluating the organic matter fraction susceptible to biodegradation was developed and proved to be suitable for assessing anaerobic digestion processes. All four co-substrates used led to some operative improvements. Vegetable oil is the most suitable co-substrate to be anaerobically digested with the OFMSW since all the parameters evaluated were greatly improved compared to the OFMSW digestion. ► Anaerobic digestion of the organic fraction of municipal solid wastes has been studied. ► Several pure co-substrates have been co-digested to enhance the biogas production. ► Animal fat and vegetable oil have shown the best results in the process performance. ► A new model based on the remaining total organic carbon has been validated. ► The results are useful for the design and economics of full-scale anaerobic digesters.