Progress in inhibition mechanisms and process control of intermediates and by-products in sewage sludge anaerobic digestion

Anaerobic digestion is an effective waste treatment method both for the pollution control and energy recovery, such as treating many agricultural and industrial wastes which contain high level of easily biodegradable substances. However, there are also many problems to be resolved, such as low methane yield, long retention time and process instability, preventing this technique from being widely applied. Variety of inhibitory substances and intermediate products are the primary cause of anaerobic digester upset or failure, including free ammonia (FA), volatile fatty acids (VFAs) and sulfide/sulfate, though they are essential nutrients for bacterial growth and anaerobic digestion process. Many researches have been conducted to investigate the inhibition mechanisms and the controlling factors during the overall anaerobic digestion process. In this paper, a detailed summary of the researches was discussed on the inhibition of the anaerobic digestion process. Furthermore, the controlling and recovery of the inhibitors as valuable products were also reviewed in detail. Co-digestion with other wastes, acclimation of microorganisms, and incorporation of methods could significantly improve the efficiency of sewage sludge anaerobic digestion.