Long term evaluation of the effect of salinity on organic removal and ammonium oxidation in a down-flow hanging sponge reactor

The effect of salinity on organic removal and ammonium oxidation in a down-flow hanging sponge reactor was investigated by conducting a long-term continuous experiment over a period of 800 days. The DHS reactor, constructed by connecting three identical units, was fed with artificial wastewater containing 500 mg-N/L of ammonium nitrogen and 1400 mg- COD/L of phenol. Salinity of the influent was controlled by the addition of 8.0 to 25 g-Cl ^-/L of NaCl. The DHS reactor was operated at a hydraulic retention time of 12 h in a temperature controlled room at 25oC. No significant inhibition of organic removal and ammonium oxidation was observed at salinities of up to 20 g-Cl-/L, at which levels ammonium oxidation and COD removal both exceeded 90%, respectively. However, at a salinity of 25 g-Cl ^-/L, organic removal and ammonium oxidation were both severely inhibited. In addition, the ratio of effluent nitrite nitrogen to influent ammonium nitrogen increased from 3.4% at salinities of 8.0 g-Cl ^-/L to 33% at salinities of 20 g-Cl ^-/L.