Distribution patterns of functional microbial community in anaerobic digesters under different operational circumstances: A review

[Display omitted] •The functional microbes play critical roles in the anaerobic digestion of organics.•The shift of microbial community associated with operational factors is disclosed.•The Firmicutes and hydrogenotrophic methanogens are more adaptive in AD.•The research gaps for the evolution principles of anaerobic species are proposed. Anaerobic digestion (AD) processes are promising to effectively recover resources from organic wastes or wastewater. As a microbial-driven process, the functional anaerobic species played critical roles in AD. However, the lack of effective understanding of the correlations of varying microbial communities with different operational factors hinders the microbial regulation to improve the AD performance. In this paper, the main anaerobic functional microorganisms involved in different stages of AD processes were first demonstrated. Then, the response of anaerobic microbial community to different operating parameters, exogenous interfering substances and digestion substrates, as well as the digestion efficiency, were discussed. Finally, the research gaps and future directions on the understanding of functional microorganisms in AD were proposed. This review provides insightful knowledge of distribution patterns of functional microbial community in anaerobic digesters, and gives critical guidance to regulate and enrich specific functional microorganisms to accumulate certain AD products.