Inactivation of pathogens in anaerobic digestion systems for converting biowastes to bioenergy: A review

Abstract

Biosafety of digestate remains one of the major concerns for anaerobic digestion, which affects the downstream management and may determine the success of anaerobic digestion. Inactivation of pathogens during anaerobic digestion has been reported by various studies, but most of them focus on single specific pathogen and/or operation condition, with the overall pictures absent. In this review, a systematic analysis was conducted to assess the effects of different factors on the inactivation of various pathogens during anaerobic digestion, including pathogen types, resistance mechanisms, operation conditions, intermediate products and kinetic models. Statistical analysis was performed to determine the significant influencing factors based on 141 published studies. The results indicated that pathogen types, temperatures and operation modes affected inactivation efficiencies significantly (P < 0.01). The resistances of pathogens are in the order of spore forming Gram-positive bacteria > non-spore forming Gram-positive bacteria > nematode ≥ Gram negative bacteria ≥ viruses. Thermophilic temperature can inactivate most pathogens effectively, with ambient and mesophilic temperatures not effective. Intermediate products, e.g. volatile fatty acids (VFAs)/ammonia, can contribute to the inactivation of pathogens, and dry anaerobic digestion might be a promising strategy due to the accumulation of VFAs/ammonia. Analysis on eleven commonly used kinetic models showed that Weibull, log-logistic and biphasic models were preferable for simulating the inactivation of most pathogens. Operation conditions of anaerobic digestion need to be optimised for mutually benefiting energy recovery, pathogen inactivation, economic feasibility and biowaste stabilization.