Biological treatment of saline domestic wastewater by using a down-flow hanging sponge reactor

In this study, the effect of salinity on the removal of organic matter and nitrogen concentrations in bioreactor was investigated using a hybrid bench scale down-flow hanging sponge (DHS) system for 145 days of operation. The reactor had three identical sections that were filled to 30% volume with Bio-Bact to serve as attached media. The DHS reactor was fed with domestic wastewater that was mixed with increasing concentration of sodium chloride from 0.5 to 3.0% stepwise. The influent and effluent concentrations of BOD5, CODCr, NH4+-N, and TN were analyzed to evaluate the performance of the DHS reactor during the operational period. Results indicate that when salinity was increased from 0.5 to 3.0%, the removal efficiency gradually decreased from 80.3% to 61.5% for CODCr, 76.4%–65.0% for BOD5, 64.1%–48.4% for NH4+-N, and 50%–36% for TN. Besides, the changes in biofilm characteristics with increasing salinity were observed during the operational period. The results indicate that salinity has a significant influence on the removal of organic matters and nitrogen transformation in the biofilm of the bioreactor. Even so, the DHS reactor revealed a good potential for treating saline wastewater. [Display omitted] •Effect of salinity on biological treatment of domestic wastewater was investigated.•Removal of CODCr, BOD5, NH4+-N, and TN decreased with increasing salinity.•Salinity influences the removal of nitrogen more than that of organic matter.•Morphology and biomass concentrations in media change with varying salinity.•Relationship between contaminant removal efficiencies and salinities was well-established.