BENCH-SCALE EVALUATION HELPS IDENTIFY OPTIMAL TREATMENT PROCESS FOR NEW WATER RECLAMATION FACILITY

A bench scale study was conducted at the Watsonville wastewater treatment plant (WWTP) to help identify the optimal treatment processes for a new water reclamation facility. This facility would need to produce a disinfected, tertiary recycled water that satisfies the Title 22 California Water Recycling Criteria (CWRC) (i.e., turbidity limit of 2 NTU, and a total coliform limit of 2.2 MPN / 100 mL). The WWTP receives seasonal food processing discharges that historically have influenced effluent turbidity during the peak food processing season (August – October). The WWTP secondary effluent can exhibit turbidity levels ranging between 10 NTU and 20 NTU. A previous pilot study had demonstrated that neither contact granular media filtration nor microfiltration, (without prior coagulation and flocculation) could consistently meet the Title 22 CWRC turbidity limits during the peak food processing season. UV disinfection was also found to be inconsistent in meeting the Title 22 CWRC disinfection requirements. This bench scale study was initiated to obtain a better understanding of the fundamental factors impacting filtration and disinfection performance at the WWTP. The study was conducted utilizing a combination of different bench scale units – a coagulation/flocculation unit, a cloth media filter (CMF), and a UV collimated beam apparatus. Particle size distribution (PSD) and zeta potential analyses were used to help characterize the variability in secondary effluent water quality that occurred throughout the peak food processing season, and to determine how these parameters would affect the performance of different treatment processes of the water reclamation facility. Based on the results of this study a treatment process consisting of coagulation, flocculation, filtration, and UV disinfection was identified that could satisfy the Title 22 turbidity and disinfection limits at all times.