Response of Microbial Community to Induced Failure of Anaerobic Digesters Through Overloading With Propionic Acid Followed by Process Recovery

Abstract

In order to effectively use microbial-based strategies to manage anaerobic digesters, it is necessary to distinguish between community shifts that are part of the natural dynamic of the system and shifts caused by environmental or operational disturbances. The objective of this research study was to evaluate the significance of changes in the microbial community of anaerobic digesters during failure in correlation to operational parameters such as an organic acid overload. Five continuously stirred 0.5 L reactors were set-up as semi-continuously-fed, mesophilic dairy manure digesters with a 30-day hydraulic retention time. After a 120-day stabilization period, two digesters were kept as controls, while the organic loading rates in the triplicate set were increased step-wise to ultimately provide a shock-load leading to failure using propionic acid spikes. Acidosis resulting in near cessation of biogas and termination of methane production occurred between 4 and 7 weeks, after which all the digesters continued to be fed only dairy manure. The shock loading of propionic acid led to an accumulation of mainly acetate and propionate, with low levels of iso-butyrate, butyrate, iso-valerate, and valerate. High-throughput Illumina sequencing of the V4 region of the bacterial and archaeal 16S rRNA gene in digester samples showed a significant change in the microbial community composition during propionic acid overload, followed by a return to the original composition with regular feedstock. Bacterial genera whose relative abundance decreased during the inhibition stage included Sedimentibacter, Syntrophomonas, TSCOR003.O20, and Marinilabiaceae, while the relative abundance of Lachnospiraceae, Ruminococcus, Mogibacteriaceae, Pyramidobacter, and Bacteroides increased. The relative abundance of dominant methanogens, Methanosarcina and Methanobacterium, although initially resistant, were decreased (from 91.71 to 12.14% and from 2.98 to 0.73%, respectively) during inhibition, while Methanobrevibacter and Methanosphaera that were prominent in the manure feedstock increased from 17.36 to 79.45% and from 0.14 to 1.12%, respectively. Shifts in bacterial and archaeal compositions, back to their pre-shock steady state after failure, highlight the digester’s microbial resilience and recovery potential.

Propagation of antibiotic resistance genes during anaerobic digestion of thermally hydrolyzed sludge and their correlation with extracellular polymeric substances

“…Using Spearman's rank correlation, ARG abundance, EPS components, and microbial communities were correlated with different operating conditions 36 . The correlation coefficient values ranged from − 1 to + 1, the higher positive values indicating stronger correlation and lower negative values indicating weak correlation.…”

Syntrophic propionate-oxidizing bacteria in methanogenic systems

“…Build-up of high propionate levels in anaerobic digesters is a frequently reported sideeffect of process imbalance. High propionate concentrations cause losses in methane yield and further instability, and it can be problematic to get rid of the high propionate levels once formed (Gallert and Winter 2008;Khafipour et al 2020;Nielsen, Uellendahl and Ahring 2007). In order to develop strategies to counteract this, knowledge of the causes of the accumulation would be helpful and some suggestions have been proposed.…”

“…mentioned in the section "Propionate transport across the cell membrane"), might also be of importance. Nevertheless, short exposure to extremely high propionate levels appears to be tolerated by certain SPOB, as indicated by process recovery of an anaerobic degradation reactor fed dairy manure after reaching 20 g propionate L -1 (Khafipour et al 2020). In batch trials, it has been indicated that the lag phase before initiation of propionate conversion is extended when incubation occurs at higher propionate levels (Han, Green and Tao 2020).…”

Source-Separated Industrial Wastewater Is a Candidate for Biogas Production through Anaerobic Digestion

“…Utilisation of process intensification principles and the potential efficiencies that can result may increase yields at the cost of process stability [10][11][12][13]. For anaerobic digestion to be an attractive process option at scale, a compromise must be made between yields, reactor volume, and effluent volume treated, i.e., between capital costs, operation costs, and production and treatment performance.…”