Effects of sodium chloride on the performance of a sequencing batch reactor

In this study, we investigated the effects of sodium chloride (concentrations ranging from 0 to 60 g/L) on the performance of sequencing batch reactors (SBRs) using a microbial culture developed from a domestic sewage treatment plant. The lab-scale SBRs were fed with synthetic wastewater (acetate as the organic substrate) containing either sodium chloride solution or seawater to ensure consistency in feed composition. It was found that sodium chloride concentrations of up to 10 g/L stimulated substrate removal. The organic removal efficiency decreased from 96%, when no sodium chloride was added, to 86% when 60 g/L of sodium chloride was introduced into the influent wastewater. Effluent turbidity increased significantly when the sodium chloride concentration in the wastewater was equal to or above 30 g/L even though the sludge volume index (SVI) decreased. The increase in effluent turbidity could be caused by the release of nondissolved cellular components due to plasmolysis of microorganisms as observed by scanning electron microscopy. Experiments involving seawater (with 20 g/L total dissolved solids) showed that organic removal efficiency improved from 87 to 95% while effluent turbidity and SVI values were lowered when the loading rate parameter ([L.sub.i]) was lowered from 0.6 to 0.3 mg total chemical oxygen demand (mg VSS day). Optical microscopy and scanning electron microscopy indicated morphological changes in the microbial population. From this study, it was concluded that microbial culture from domestic wastewater facilities could be acclimated in a SBR to treat wastewater containing sodium chloride concentrations of up to 60 g/L. DOI: 10.1061/(ASCE)0733-9372(2005)131:11(1557) CE Database subject headings: Reactors; Dissolved solids; Chloride; Sea water; Sludge; Turbidity.