Identification of the temporal control on nitrate removal rate variability in a denitrifying woodchip bioreactor

• Published in: Ecological Engineering
• Main Authors: Nordström, Albin, Herbert, Roger
• Format: Article in Journal/Newspaper
• Language: English
• Published: Uppsala universitet, Luft-, vatten- och landskapslära 2019
• Subjects: Woodchip bioreactor; Modeling; Macromolecular rate theory; Selection; Temperature; Longevity; Water Treatment; Vattenbehandling; Subarctic
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-366588; https://doi.org/10.1016/j.ecoleng.2018.11.015

Nitrate (NO3−) removal rates in a denitrifying woodchip bioreactor (DWB) removing NO3− from mine water in a subarctic climate was modeled with the purpose of determining the processes controlling variability in NO3− removal rates over time. The Eyring equation was used to define the temperature dependency, while a rate law was used to describe the NO3− concentration dependency of the NO3− removal rates. The results show that the temperature and NO3− concentration dependency of the NO3− removal rates changes over time in the DWB due to the preferential selection of conceptualized NO3− - reducing bacteria favoring low temperatures, with the mean temperature optimum of the NO3− reducing consortium decreasing from 24.2 °C to 16.0 °C following the first year of DWB operations. It is suggested that the selection of the low temperature NO3− reducers in the DWB represented an increased dependence on cross-feeding between a fermentative community, producing the reactive organic carbon substrate, and a denitrifying community, consuming the organic carbon substrate, with the temporal variability in NO3− removal rates being controlled by the stabilization of the microbial community structure. It is also suggested that the life expectancy of DWBs is more related to the stability of the cross-feeding between the fermenting microbial community and the denitrifying microbial community, than to the total carbon content.