Effects of high sodium chloride concentrations on activated sludge treatment

The performance and kinetics of the activated sludge process treating wastewaters of freshwater and salinewater (10 g/l NaCl and 30 g/l NaCl) origin were investigated using bench-scale, completely mixed reactors operated at different biological solids retention times (BSRT's) in the range of 3 to 20 d and organic loadings in the range of 0.5 to 2.0 kg COD/kg VSS.d. It has been found that the organic (COD or TOC) removal efficiency and the effluent quality of the activated sludge system were not deteriorated as a result of constant application of NaCl to acclimated biomass. However, the salinity of the effluent increased. The salt did not inhibit biomass growth under the experimental conditions studied but rather increased the biomass concentration in the reactors due to selection of salt tolerant microbial species. It has been demonstrated that kinetic models developed for the freshwater activated sludge system can be used successfully for the salinewater system. Biokinetic coefficients were determined which can be used for process design.