Microbial community changes in methanogenic granules during the transition from mesophilic to thermophilic conditions

Abstract

Upflow anaerobic sludge blanket (UASB) reactor is one of the most applied technologies for various high-strength wastewater treatments. The present study analysed the microbial community changes in UASB granules during the transition from mesophilic to thermophilic conditions. Dynamicity of microbial community in granules was analysed using high-throughput sequencing of 16S ribosomal RNA gene amplicons, and the results showed that the temperature strictly determines the diversity of the microbial consortium. It was demonstrated that most of the microbes which were present in the initial mesophilic community were not found in the granules after the transition to thermophilic conditions. More specifically, only members from family Anaerolinaceae managed to tolerate the temperature change and contributed in maintaining the physical integrity of granular structure. On the contrary, new hydrolytic and fermentative bacteria were quickly replacing the old members in the community. A direct result from this abrupt change in the microbial diversity was the accumulation of volatile fatty acids and the concomitant pH drop in the reactor inhibiting the overall anaerobic digestion process. Nevertheless, by maintaining deliberately the pH levels at values higher than 6.5, a methanogen belonging to Methanoculleus genus emerged in the community enhancing the methane production

Converting mesophilic upflow sludge blanket (UASB) reactors to thermophilic by applying axenic methanogenic culture bioaugmentation

“…The theoretical methane equivalent of intermediates (VFAs and alcohols) was determined assuming that all organic material will be converted to CH 4 and CO 2 and calculated from the following equation [23]. OTU clustering and taxonomy identification were performed using CLC Workbench software (V.8.0.2) equipped with the Microbial genomics module plugin as previously described [13]. Only…”

“…Three different bioaugmentation strategies were investigated using lab scale UASB reactors with working volume of 1.4 L. The reactor configuration was previously described by Zhu et al [13]. Briefly, the liquid feedstock was supplied from the bottom of the reactor every 6 hours according to the designed HRTs and OLRs.…”

“…The duration of bioaumentation effect of the best bioaugmentation strategy (Strategy 3) was evaluated by operating two additional UASB reactors, namely bioaugmentation and Control 2. A previous study demonstrated that, utilization of potato juice as substrate requires pH control during temperature transition from mesophilic to thermophilic operation [13]. Therefore, in this experiment bicarbonate was supplemented to the feedstock in order to maintain the pH levels within the optimum range for methanogenesis.…”

“…Recent studies based on high throughput amplicon sequencing remarked that during temperature transition, the thermophilic bacterial community evolved spontaneously in liquid phase of UASB reactors and were found inhabiting in the granular structures [12]. However, it was demonstrated that the thermophilic archaeal group grew slowly and concomitantly led to process imbalance [13].…”

Delta-Integration of Single Gene Shapes the Whole Metabolomic Short-Term Response to Ethanol of Recombinant Saccharomyces cerevisiae Strains

“…The main cost in bioethanol and other bio-products production is the substrate. Therefore, to reduce the costs, the processing of cheap materials such as energy-crops, food processing residues, agricultural and forest waste is paramount [2][3][4][5][6][7][8][9][10][11].…”