AWWA WQTC57016

AWWA WQTC57016 Treatment of Microfiltration Residuals Using Clarification and Additional Membranes
Conference Proceeding by American Water Works Association, 11/01/2002

Narasimhan, Ramesh; Durbin, Herbert

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The City of Phoenix conducted the Lake Pleasant Water Quality and Testing Study Project to assess the viability of various advanced treatment processes to meet anticipated drinking water regulations. Lake Pleasant is a man-made storage facility that stores Colorado River Water delivered via the Central Arizona Project (CAP) Canal. The water from the lake is released during the summer season to meet the peak water demands of the Phoenix Metropolitan area. Many water treatment facilities are being served by the CAP Canal and Lake Pleasant, including the City of Phoenix' existing Union Hills Water Treatment Plant (UHWTP) and the proposed Lake Pleasant WTP. The City conducted pilot and demonstration scale testing of various processes such as conventional treatment, microfiltration (MF), ultrafiltration (UF), granular activated carbon, nanofiltration, ballasted flocculation, and several preoxidants. These unit processes were configured in alternative treatment trains to optimize removal of turbidity, pathogens, disinfection byproduct (DBP) precursors, and taste and odor compounds. The project will include potential stress testing of the treatment processes with simulated high algae and/or high turbidity raw water, during periods of lake releases. A significant component of this testing program was the assessment of residuals handling systems to treat waste streams from these various water treatment processes. Membrane treatment options were evaluated as a possible alternative to commonly used residual treatment processes like clarification. The membrane treatment residual treatment options evaluated include ultrafiltration of the decant stream obtained after settling of the microfiltration backwash residual stream. The recovered water from this process can be recycled without risking microbial contamination. Another innovative process that was evaluated was the treatment of microfiltration backwash using tubular UF membranes operated in hybrid mode. It was found that the hybrid mode operation of the UF system allows the backwash to be directly sent to the membrane without any settling, resulting in cost savings. This is compared to treatment of MF backwash by settling and subsequent treatment of the decant through a hollow fiber UF system. Includes tables, figures.