Cold adaptation and replicable microbial community development during long-term low-temperature anaerobic digestion treatment of synthetic sewage

Abstract

The development and activity of a cold-adapting microbial community was monitored during low-temperature anaerobic digestion (LtAD) treatment of wastewater. Two replicate hybrid anaerobic sludge bed-fixed-film reactors treated a synthetic sewage wastewater at 12°C, at organic loading rates of 0.25–1.0 kg chemical oxygen demand (COD) m−3 d−1, over 889 days. The inoculum was obtained from a full-scale anaerobic digestion reactor, which was operated at 37°C. Both LtAD reactors readily degraded the influent with COD removal efficiencies regularly exceeding 78% for both the total and soluble COD fractions. The biomass from both reactors was sampled temporally and tested for activity against hydrolytic and methanogenic substrates at 12°C and 37°C. Data indicated that significantly enhanced low-temperature hydrolytic and methanogenic activity developed in both systems. For example, the hydrolysis rate constant (k) at 12°C had increased 20–30-fold by comparison to the inoculum by day 500. Substrate affinity also increased for hydrolytic substrates at low temperature. Next generation sequencing demonstrated that a shift in a community structure occurred over the trial, involving a 1-log-fold change in 25 SEQS (OTU-free approach) from the inoculum. Microbial community structure changes and process performance were replicable in the LtAD reactors.

Microbial Community Redundancy and Resilience Underpins High-Rate Anaerobic Treatment of Dairy-Processing Wastewater at Ambient Temperatures

“…This family belongs to phylum Synergistetes, which was also observed in other reactors treating dairy wastewater (Gunnigle et al, 2015a;Keating et al, 2018;Callejas et al, 2019) and it is known to degrade peptides, proteins and amino acids. On the other hand, contrary to other studies of room/low temperature reactors treating dairy wastewater (Bialek et al, 2011(Bialek et al, , 2014Keating et al, 2018;Callejas et al, 2019), our results showed very little active presence of Firmicutes. Nevertheless, Gunnigle et al (2015a) reported a decreased in Firmicutes associated with low temperature.…”

“…In particular, there was a high relative abundance of active methanogenic species of Methanothrix, which represented up to 50% of the active microbial community and up to 25.5% of the total community. The presence in high abundance of Methanothrix species in low-temperature AD systems was observed at laboratory-scale in several studies (Enright et al, 2009;Siggins et al, 2011a,b;Bandara et al, 2012;Gunnigle et al, 2015a,b;Keating et al, 2018). Furthermore, real-time PCR results of an archaeal populations revealed that Methanosaeataceae was the dominant methanogen in the bioreactor treating dilute dairy wastewater and its numbers remained stable during the complete trial (Bialek et al, 2013), along with high numbers of Methanobacteriales and Methanomicrobiales.…”

“…Those results seem to indicate an adaption of this group to alkaline environments and may explain why they emerged following the pH shocks in our reactor. Bacteroidetes are commonly found in the microbial communities of anaerobic digesters (Werner et al, 2011;Shah et al, 2014;Guo et al, 2015;Sun et al, 2015), including low-temperature AD digesters (McKeown et al, 2009;Abram et al, 2011;Bialek et al, 2012Bialek et al, , 2013, and lowtemperature AD digeste treating dairy wastewater (Bialek et al, 2011(Bialek et al, , 2014Keating et al, 2018), which indicates their crucial role in anaerobic treatment. Their presence in abundance indicates a high hydrolytic activity in the system .…”

“…On the other hand, the phylum Proteobacteria, commonly found in dairy-treating reactors (Bialek et al, 2011(Bialek et al, , 2014Gunnigle et al, 2015a;Keating et al, 2018;Callejas et al, 2019), aside from Pseudomonas, represented 8 to 16% of the active community, although no family was highly abundant. These values are much lower than the 62% relative abundance of this phylum observed by Gunnigle et al (2015a), but more similar to the 27% observed by Callejas et al (2019).…”

“…These microorganisms also present different responses to environmental stresses, such as temperature, pH variations, substrate composition/concentration or the presence of inhibitory or toxic compounds (Shah, 2014;Venkiteshwaran et al, 2015). Several studies have focused on the development of microbial communities in laboratory-scale AD bioreactors operated at >35 • C to lower temperature conditions, with special focus on the methanogenic portion of communities (Enright et al, 2009;McKeown et al, 2009;O'Reilly et al, 2009;Abram et al, 2011;Bandara et al, 2012;Zhang et al, 2012;Gunnigle et al, 2015a,b;Keating et al, 2018). Nevertheless, very little is known about the potential development of such communities at pilot and full-scale, or how they respond under environmental stresses, such as variations in operational parameters.…”