Use of halophilic bacteria in biological treatment of saline wastewater by fed-batch operation

Biological treatment of saline wastewater by standard activated-sludge cultures typically results 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 to 5% sodium chloride) was treated in an aeration tank operated in fed-batch mode. Halobacter halobium added to activated-sludge culture was used in biological treatment, and results were compared with those obtained with the activated-sludge culture alone. Hulobacter addition produced significantly greater COD removal rates and efficiencies (% removal) at salt concentrations greater than 2% salt. At low salt concentrations. performances of both cultures were comparable. Results indicated that saline wastewater containing more than 2% salt can be treated effectively by Halobacter-supplemented, activated-sludge cultures, with COD removal efficiencies greater than 85% within 9 hours of fed-hatch operation.