Hydrocycloning Influent, Mixed Liquor or Return Activated Sludge for Best Grit Removal and Sludge Production Reduction

This paper explores grit removal from influent and activated sludge as a means to reduce sludge production of biological wastewater treatment plants (WWTPs). Experiments were carried out on a laboratory-scale (13 mm) hydrocyclone on sludge from eight WWTPs in Quebec (Canada) with different industrial loadings and combinations of preliminary and primary treatment. Full-scale hydrocycloning (50 mm) experiments were performed on sludge from a membrane bioreactor pilot plant treating municipal wastewater in Quebec and also at the Morongo Cannibal™ WWTP (California, USA). Results indicated that hydrocyclone grit separation efficiency decreased with increasing feed solids concentration. Grit separation efficiency of the 13 mm and 50 mm hydrocyclones seemed to be comparable. The best grit removal strategy (grit chamber at the influent vs hydrocycloning sludge vs a combination of the two processes) should be evaluated on a case-by-case basis as it will depend on grit characteristics and an economic analysis, among other factors.