The Impact of Alum on the Bulking of a Full Scale Activated Sludge Plant

The activated sludge plant (ASP) is one of the main wastewater treatment processes in the UK.With the increasing stringent requirement for effluent quality, there has been a considerable increase in the use of chemicals for phosphorus precipitation in ASPs to achieve effluent consents.Alum is one of the most widely used chemicals in the treatment of wastewater.In this study, we examine the impact of varying concentrations of alum on the bulking and settleability of a full-scale activated sludge plant with simultaneous co-precipitation.The results showed an improvement in the settleability of the activated sludge with the initial stirred sludge volume index (SSVI) before alum dosing dropping from 105 to 85 after one sludge age.The SSVI increased to 155 with the settleability and floc compactability deteriorating at a dose rate of 145mg/L of alum.The bulking of the sludge was caused by a combination of the filaments present and the surface chemistry of the activated sludge flocs.