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.