Synergy between denitrification and calcium bridging improves dewaterability of waste activated sludge

Dewaterability of waste activated sludge was significantly improved through a mild conditioning process without energy-intensive treatment. Calcium nitrate (Ca(NO3)(2)) addition enhanced sludge dewatering performance, with a reduction in capillary suction time (CST) and cake moisture content by 58.7% and 8.5%, respectively. Ca(NO3)(2) treatment outperformed KNO3 and CaCl2 treatment by 59.1% and 6.5% regarding reduction in cake moisture content. Characterization of the sludge extracellular polymeric substances (EPS) revealed that proteins in the slime EPS (S-EPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) were decomposed by 97.7%, 89.6% and 60.9%, respectively, during the 5-day denitrification process triggered by nitrate supply, thus releasing bound water. Ca2+ addition induced charge neutralization of negatively-charged EPS functional groups and also facilitated flocculation, further enhancing the sludge filterability. This study also showed a proof-of-concept that nitrate brine (i.e. concentrated nitrification effluent) could be used to enhance sludge dewatering, which might provide a new paradigm of efficient sludge reduction for local municipal wastewater treatment facilities. (C) 2019 Elsevier Ltd. All rights reserved.