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

Abstract

Disturbances of the anaerobic digestion process reduce the economic and environmental performance of biogas systems. 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 biogas production and requiring an active counteraction to be overcome. The main types of process disturbances in agricultural biogas production 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 microbiome are discussed. The need for a knowledge-based microbiome management to ensure a stable and efficient production of biogas with low susceptibility to disturbances is derived and an outlook on potential future process monitoring and control by means of microbial indicators is provided.

Air‐side ammonia stripping coupled to anaerobic digestion indirectly impacts anaerobic microbiome

“…Recent studies have reported the dominance of Bacteroidetes group under low-ammonium conditions, while under high concentrations the phylum Cloacimonetes disappears and the Firmicutes phylum, in particular Clostridiales and Lactobacillales orders, dominates the community (Werner et al, 2014;Vrieze et al, 2015;Regueiro et al, 2016;Westerholm et al, 2018). When high ammonia levels inhibit obligate acetoclastic methanogens, the microbial community shifts towards syntrophic acetate oxidation pathway (Westerholm et al, 2016) although the keystone taxa responsible for the function are unclear (Werner et al, 2014;Theuerl et al, 2019).…”

The Future Agricultural Biogas Plant in Germany: A Vision

“…Anaerobic digestion is a highly sensitive process exclusively carried out by microorganisms that are interdependently associated in a complex community and reside in a closed technical system with an environment controlled by the biogas plant operator [30]. Hence, it is crucial to understand how the biogas microbiomes respond to management measures and how this response affects the digestion process.…”

“…In future biogas plants the microbial communities will be subjected to frequently varying process conditions while ensuring an overall stable digestion process with low susceptibility to disturbances. Process disturbances have manifold causes with different underlying mechanisms (e.g., unfavorable process temperature, fluctuating nutrient availability, overload of the degradation potential, accumulation of process inhibiting metabolites, and many others) [30]. Digester design and operation have to be aligned after the requirements of the microbiome in the sense of a microbial-based management [31], which is a precondition to improve stability and efficiency of the digestion process.…”

“…as well as reliable process monitoring and control (Section 3.2.3). Rapid changes in feedstocks and/or temperature bear the risk of process disturbances [30], limits of flexible feeding need to be well known and considered. Model-based predictive process control [180] (Section 3.2.4) and specific digester configurations [182] can increase process stability and help to enhance flexibility, while maintaining stable conditions and thus need to be further developed.…”

Effect of a Profound Feedstock Change on the Structure and Performance of Biogas Microbiomes

“…Consequently, plant operators will be forced to use a broad range of different feedstocks which are chemically very heterogeneous, variable over time, and often available only in small quantities. This will lead to a more inhomogeneous feedstock supply and sometimes to rapid feedstock changes, which might cause problems for the microbial community in the biogas reactors as the available nutrients and the bioaccesibility may differ [1,7].The production of biogas is a complex process where several different microorganisms using different metabolic pathways work together to degrade organic matter into biogas. The process can be divided into four main steps: the hydrolysis, the acidogenesis, the acetogenesis, and the methanogenesis.…”