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. Halobacter 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‐batch operation.