Biological treatment of saline wastewater by standard active-sludge cultures typically result in low chemical oxygen demand (COD) removal efficiencies as a result of plasmolysis of cells caused by high salt content (>1%). Removal of salt from wastewater before biological treatment by reverse osmosis or ion exchange would be quite costly. However, inclusion of salt-tolerant organisms in an activated-sludge culture to improve treatment efficiency is a practical approach developed and presented in this article.
Synthetic wastewater composed of diluted molasses, urea, phosphate, and different amounts of salt (0-5% sodium chloride) was treat in an aeration tank operated in fed-batch mode. Halobacter halobium added to activated-sludge culture was used in biological treatment. And result were compered with those obtained with the activated- sludge culture alone. Halobacter addition produced significantly greater COD removal rates and efficiencies (% removal) at salt concentrations greater than 25% salt. At low salt concentrations, performances of both cultures were comparable. Result indicated that saline wastewater containing more than 2% salt can be treated effectively by halobacter-supplement, activated-slugde culture, with COD removal efficiencies greater than 85% within 9 hours of fed-batch operation.