Abstract
BACKGROUND: In this study, the inductive effect of salinity on nitrite accumulation in a downโflow hanging sponge (DHS) reactor, developed as a novel and costโeffective wastewater treatment process, was evaluated by conducting a longโterm continuous experiment lasting more than 1400 days.
RESULTS: The influent salinity was controlled by adding NaCl at concentrations ranging from 0 to 25 g Cl^โ^ L^โ1^. The effluent nitrite increased with increases in salinity, i.e. the fraction of nitrite to total nitrogen in the effluent increased from 1.6% at 0 g Cl^โ^ L^โ1^ to 87.6% at 25 g Cl^โ^ L^โ1^. Fluorescence in situ hybridization (FISH) analysis revealed that as salinity increased, the nitrifying bacterial community in the DHS changed markedly at the species level. In particular, the dominant nitriteโoxidizing bacteria changed from Nitrospiraโsublineage I at 0 g Cl^โ^ L^โ1^ to Nitrobacter spp. at 15 g Cl^โ^ L^โ1^. At 25 g Cl^โ^ L^โ1^, no nitriteโoxidizing bacteria were detected.
CONCLUSION: Our findings suggest that the DHS reactor is suitable for costโeffective nitrite production processes and that salinity control using NaCl is an effective method for inducing nitrite accumulation. Copyright ยฉ 2012 Society of Chemical Industry