Process Disturbances in Agricultural Biogas Production—Causes, Mechanisms and Effects on the Biogas Microbiome: A Review

Disturbances of the anaerobic digestion process reduce the economic and environmental performance of biogassystems. A better understanding of the highly complex process is of crucial importance in order to avoid disturbances. This review defines process disturbances as significant changes in the functionality within the microbial community leading to unacceptable and severe decreases in biogasproduction and requiring an active counteraction to be overcome. The main types of process disturbances in agricultural biogasproduction are classified as unfavorable process temperatures, fluctuations in the availability of macro- and micronutrients (feedstock variability), overload of the microbial degradation potential, process-related accumulation of inhibiting metabolites such as hydrogen (H2), ammonium/ammonia (NH4+/NH3) or hydrogen sulphide (H2S) and inhibition by other organic and inorganic toxicants. Causes, mechanisms and effects on the biogas microbiomeare discussed. The need for a knowledge-based microbiomemanagement to ensure a stable and efficient production of biogaswith low susceptibility to disturbances is derived and an outlook on potential future process monitoring and control by means of microbial indicators is provided.