AWWA QTC97078

The primary objective of this study was to enhance the removal of Cryptosporidium oocysts in the Metropolitan Water District of Southern California's washwater reclamation plants (WWRPs) through optimization of coagulation/sedimentation processes. Coagulants selected during previous bench-scale studies were evaluated in pilot-scale seeding studies at various flow rates and dosages. Turbidity, Cryptosporidium oocyst, aerobic spore former (ASF), and particle count analyses were used to evaluate coagulant performance. Seeding studies were conducted with inactivated Cryptosporidium oocysts in spent filter backwash water to determine whether turbidity, ASF and particle removals can be used as indicators of Cryptosporidium oocyst removal in coagulation/sedimentation studies. A cationic PAM polymer effected the best removal of all the evaluated constituents. Preliminary results indicate that ASF and total particle (>2 microns) removal significantly correlated with Cryptosporidium removal and may potentially be useful surrogates. Cryptosporidium removal through sedimentation ranged from 0 to 0.98 logs in preliminary tests conducted under no polymer, non-optimized and optimized coagulant conditions.