Increased brine concentration increases nitrate reduction rates in batch woodchip bioreactors treating brine from desalination

© 2020 Elsevier B.V.This study investigated the effect of brine concentration on nitrate reduction in woodchip bioreactors treating brine from one and two-stage reverse osmosis (RO). An initial field experiment with aboveground, outdoor woodchip bioreactors tested batch experiments using one and two-stage RO brine, and a follow-up lab experiment in temperature-controlled chambers tested the same treatments and a 50:50 mix of one and two-stage brine using aged woodchips (11 months). The effect of brine concentration was greatest in the field experiment in which fresh woodchips were used, with nitrate removal rates of 20¿152 g N m¿3 of saturated woodchip d¿1. Brine concentration effect was weaker in the lab experiment with aged woodchips with lower nitrate removal rates of 2¿62 g N m¿3 of saturated woodchip d¿1. Results indicate that effect of brine concentration on nitrate reduction was dependent on carbon availability, and that brine concentration may have a smaller effect on nitrate reduction in aged woodchips not exposed to periodic unsaturated conditions. Increased brine concentration increased dissolved organic carbon in the effluent. Sustained nitrate reduction was seen over a wide range of nitrate concentration (40¿230 mg N L¿1) and salinity (12¿43 parts per thousand).