THE EFFECT OF CHEMICAL BULKING CONTROL ON BIOLOGICAL NUTRIENT REMOVALIN A FULL-SCALE ACTIVATED-SLUDGE PLANT

The use of chemicals for sludge bulking control has a direct effect on the biological nutrient removal processes in activated sludge systems designed for this purpose. Chlorine has been used on full scale but I nformation on the use of ozone and hydrogen peroxide is limited to pil ot scale tests. The objective of this study was to investigate the eff ects of chlorine, ozone and hydrogen peroxide on nutrient removal proc esses when used on a continuous basis for bulking control in a full sc ale biological nutrient removal activated sludge plant. The full scale studies were conducted over a period of 39 months at the Daspoort sew age works of the City Council of Pretoria. The results indicate that a t low dosages the oxidants have limited effects on the nutrient remova l processes but at higher levels chlorine had a detrimental effect res ulting in the phosphate limit of 1 mg P.1(-1) being exceeded. It is co ncluded that chlorine is the most effective of the three oxidants for bulking control, but that it should be used with caution in order not to upset the biological phosphate removal processes. Ozone at low leve ls had a small but consistent positive effect on bulking control as we ll as on nutrient removal. The effects of hydrogen peroxide were very small except at high dosages. Copyright (C) 1996 IAWQ. Published by El sevier Science Ltd.