Effects of salinity on simultaneous reduction of perchlorate and nitrate in a methane-based membrane biofilm reactor

Abstract

This study builds upon prior work showing that methane (CH₄) could be utilized as the sole electron donor and carbon source in a membrane biofilm reactor (MBfR) for complete perchlorate (ClO₄⁻) and nitrate (NO₃⁻) removal. Here, we further investigated the effects of salinity on the simultaneous removal of the two contaminants in the reactor. By testing ClO₄⁻ and NO₃⁻ at different salinities, we found that the reactor performance was very sensitive to salinity. While 0.2 % salinity did not significantly affect the hydrogen-based MBfR for ClO₄⁻ and NO₃⁻ removals, 1 % salinity completely inhibited ClO₄⁻ reduction and significantly lowered NO₃⁻ reduction in the CH₄-based MBfR. In salinity-free conditions, NO₃⁻ and ClO₄⁻ removal fluxes were 0.171 g N/m²-day and 0.091 g/m²-day, respectively, but NO₃⁻ removal fluxes dropped to 0.0085 g N/m²-day and ClO₄⁻ reduction was completely inhibited when the medium changed to 1 % salinity. Scanning electron microscopy (SEM) showed that the salinity dramatically changed the microbial morphology, which led to the development of wire-like cell structures. Quantitative real-time PCR (qPCR) indicated that the total number of microorganisms and abundances of functional genes significantly declined in the presence of NaCl. The relative abundances of Methylomonas (methanogens) decreased from 31.3 to 5.9 % and Denitratisoma (denitrifiers) decreased from 10.6 to 4.4 % when 1 % salinity was introduced.

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