Temperature Sensitivity and Composition of Nitrate-Reducing Microbiomes from a Full-Scale Woodchip Bioreactor Treating Agricultural Drainage Water

Abstract

Denitrifying woodchip bioreactors (WBR), which aim to reduce nitrate (NO3−) pollution from agricultural drainage water, are less efficient when cold temperatures slow down the microbial transformation processes. Conducting bioaugmentation could potentially increase the NO3− removal efficiency during these specific periods. First, it is necessary to investigate denitrifying microbial populations in these facilities and understand their temperature responses. We hypothesized that seasonal changes and subsequent adaptations of microbial populations would allow for enrichment of cold-adapted denitrifying bacterial populations with potential use for bioaugmentation. Woodchip material was sampled from an operating WBR during spring, fall, and winter and used for enrichments of denitrifiers that were characterized by studies of metagenomics and temperature dependence of NO3− depletion. The successful enrichment of psychrotolerant denitrifiers was supported by the differences in temperature response, with the apparent domination of the phylum Proteobacteria and the genus Pseudomonas. The enrichments were found to have different microbiomes’ composition and they mainly differed with native woodchip microbiomes by a lower abundance of the genus Flavobacterium. Overall, the performance and composition of the enriched denitrifying population from the WBR microbiome indicated a potential for efficient NO3− removal at cold temperatures that could be stimulated by the addition of selected cold-adapted denitrifying bacteria.

Comparison of microbial communities in replicated woodchip bioreactors

“…These dominant phyla included Proteobacteria, Firmicutes, Chloroflexi, Actinobacteria, and Bacteroidetes. The observation that dominant phyla include Proteobacteria, Actinobacteria, and Bacteroidetes is consistent with other studies (Grießmeier et al., 2017; Hellman et al., 2021; Jéglot, Sørensen, et al., 2021). Firmicutes have also been observed as a dominant phylum at the laboratory scale (Grießmeier et al., 2017).…”

Nitrogen Removal Capacity of Microbial Communities Developing in Compost- and Woodchip-Based Multipurpose Reactive Barriers for Aquifer Recharge With Wastewater

“…Hence, the resulting ammonium levels in the water after barrier passage is not lower in the compost barriers despite significantly higher amoA abundances. In other woodchip-based systems for N removal, it has been shown that changes in the microbial community composition appear within a few months ( Grießmeier et al, 2017 ; Aalto et al, 2020 ; Hellman et al, 2021 ; Jéglot et al, 2021 ). Given that the increase in copy numbers of nir and nosZ genes in the woodchip barrier resulted in the same genetic potential for denitrification and nitrous oxide reduction between the compost and woodchip barriers, it is plausible that in the present systems, the potentials for denitrification and nitrous oxide reduction were similar among the barriers during a substantial part of the experimental period, which contributed to the equal overall removal of reactive N. A higher temporal resolution would be needed to better understand this phenomenon.…”

Impacts of Biostimulation and Bioaugmentation on Woodchip Bioreactor Microbiomes

“…Some of them can breakdown cellulose, a major component of woodchips, and therefore, can provide more labile carbon to the environment (Jang et al, 2019). By inoculating these cold-adapted denitrifiers, it might be possible to enhance nitrate removal at cold conditions (Jéglot et al, 2021, 2022).…”