Three birds with one stone: Lower volatile fatty acids (VFAs) reduction, higher phosphorus (P) removal, and lower alkali consumption via magnesium dosing after waste activated sludge (WAS) alkaline fermentation

Magnesium (120 mmol/L) was dosed to investigate the effects of different methods and times on performance of waste activated sludge (WAS) alkaline fermentation. The investigation revealed that maximum soluble chemical oxygen demand (SCOD) was achieved without magnesium addition, indicating magnesium addition, regardless of dosing method or time, could constrain the sludge hydrolysis process. Fermented sludge dewaterability was improved with magnesium addition, as based on results of capillary suction time (CST) and bound water. The optimal magnesium dosage was reached following WAS alkaline fermentation, in which little volatile fatty acids (VFAs) reduction (67 mg COD/L), higher PO43--P removal efficiency (95.41%), and lower alkali consumption were achieved. Further, 682.19 mg chemical oxygen demand (COD)/L of the released protein was precipitated, suggesting that soluble protein was effectively recovered from sludge with magnesium addition after fermentation. In conclusion, dosing magnesium after WAS alkaline fermentation has multiple merits and warrants further study. (C) 2020 Elsevier Ltd. All rights reserved.