A review on anaerobic co-digestion of sewage sludge with other organic wastes for methane production: Mechanism, process, improvement and industrial application

The rapid progress of urbanization strategies in China has led to a significant increase in sewage sludge production. Sewage sludge contains organic compounds, pathogens, and heavy metals, making the effective utilization of its organic components a crucial concern in sludge treatment. Anaerobic digestion is widely recognized as a viable method for converting the organic components of sewage sludge into methane, volatile fatty acids (VFAs), and soil fertilizer. Co-digestion, which involves the simultaneous digestion of sewage sludge with other organic wastes, holds great promise for renewable methane production. This review provides an overview of anaerobic co-digestion, focusing on the production of methane through the utilization of sewage sludge and other organic wastes. The kinetics and process parameters involved in co-digestion are discussed, along with the mechanisms underlying the synergistic effect on methane production. These mechanisms include the modulation of the carbon-to-nitrogen (C/N) ratio, dilution of toxic compounds, and the bioaugmentation effect on enzymes and microbial communities. Various methods for improving co-digestion, such as pretreatment and additive techniques, are explored. Furthermore, the industrial application of co-digesting sewage sludge with other organic wastes is highlighted to showcase the commercial feasibility of this technology for methane production.