Reactor staging influences microbial community composition and diversity of denitrifying MBBRs- Implications on pharmaceutical removal

Abstract

The subdivision of biofilm reactor in two or more stages (i.e., reactor staging) represents an option for process optimisation of biological treatment. In our previous work, we showed that the gradient of influent organic substrate availability (induced by the staging) can influence the microbial activity (i.e., denitrification and pharmaceutical biotransformation kinetics) of a denitrifying three-stage Moving Bed Biofilm Reactor (MBBR) system. However, it is unclear whether staging and thus the long-term exposure to varying organic carbon type and loading influences the microbial community structure and diversity. In this study, we investigated biofilm structure and diversity in the three-stage MBBR system (S) compared to a single-stage configuration (U) and their relationship with microbial functions. Results from 16S rRNA amplicon libraries revealed a significantly higher microbial richness in the staged MBBR (at 99% sequence similarity) compared to single-stage MBBR. A more even and diverse microbial community was selected in the last stage of S (S3), likely due to exposure to carbon limitation during continuous-flow operation. A core of OTUs was shared in both systems, consisting of Burkholderiales, Xanthomonadales, Flavobacteriales and Sphingobacteriales, while MBBR staging selected for specific taxa (i.e., Candidate division WS6 and Deinococcales). Results from quantitative PCR (qPCR) showed that S3 exhibited the lowest abundance of 16S rRNA but the highest abundance of atypical nosZ, suggesting a selection of microbes with more diverse N-metabolism (i.e., incomplete denitrifiers) in the stage exposed to the lowest carbon availability. A positive correlation (p < 0.05) was observed between removal rate constants of several pharmaceuticals with abundance of relevant denitrifying genes, but not with biodiversity. Despite the previously suggested positive relationship between microbial diversity and functionality in macrobial and microbial ecosystems, this was not observed in the current study, indicating a need to further investigate structure-function relationships for denitrifying systems.

An innovative wastewater treatment technology based on UASB and IFAS for cost-efficient macro and micropollutant removal

“…This is an evidence of how hybrid systems considering different redox environments can improve the possibilities of biological reactors to enhance the biotransformation of many of the compounds present in the complex mixtures of OMPs detected in sewage [10,36,38]. In fact, although higher removal of OMPs is usually reported under aerobic than anoxic conditions, Torresi et al, [39] showed that in absence of a cometabolic limitation, the biotransformation of several OMPs can be more advantageous under anoxic than aerobic conditions.…”

Insight on the bacterial ecology in membrane bioreactor: Operational conditions effect over dominant ecological players

“…The unclassified Sphingobacteriales was found to be prevalent at short HRT and medium SRT. Sphingobacteriales ‐related OTUs have been reported as dominant phylotypes in MBBR and MBR systems and have been linked to degradation of recalcitrant organic compounds . Also, Otu0014, affiliated as Acinetobacter , was dominant at high HRT and medium SRT.…”

Microbial biomass, composition, and functions are responsible for the differential removal of trace organic chemicals in biofiltration systems

“…In previous studies, sulfite reductase was reported to catalyze the cleavage of isoxazole and piperazinyl rings (Jia et al . 2019), and nitrite reductase was correlated with the biotransformation rate constant of some compounds like sulfamethoxazole, erythromycin and trimethoprim (Torresi et al . 2018).…”

“…Dissimilatory sulfite reductase (EC 1.8.99.3) and nitrite reductase (EC 1.7.2.1) were found to be correlated to the biotransformation of carboxy acyclovir, clarithromycin, furosemide and mecoprop in our study. In previous researches, sulfite reductase was reported to catalyze the cleavage of biotransformation rate constant of some compounds like sulfamethoxazole, erythromycin and trimethoprim (Torresi et al 2018). However, more studies are needed to further support this association and to investigate whether this can be explained by any causal relationship.…”