Like many municipalities in urban and suburban areas, San Bruno, Calif.’s source water comes both from its own groundwater supply and through a...
Located 50 miles northwest of Daytona Beach, Fla., the 11,000 residents of the City of Palatka derive their potable water supply from groundwater through multiple wells with varying water qualities. Like many communities in Florida, Palatka’s relatively high water table is subject to the influence of surface water, which manifests itself as elevated organics in the raw well water. Any possibility of infection from these organics is neutralized through disinfection.
Disinfecting organics in water can, however, lead to other issues. Organics can react with disinfectants, forming carcinogenic disinfection byproducts (DBPs) in the form of trihalomethanes (THMs) and haloacetic acids (HAA5).
As early as 2003, Palatka’s commissioners were aware of impending regulatory changes, and that the city was likely to be non-compliant with the EPA’s lower DBP maximum contaminant levels. The commissioners took a proactive stance and planned for the necessary improvements to the R.C. Willis Water Treatment Plant. Assisted by a consulting engineer, Hoyle Tanner & Associates, the city selected a process of air stripping for H2S removal followed by oxidation, enhanced coagulation and then ultrafiltration (UF) for manganese and TOC removal. The city piloted a Norit membrane to remove the organics, and this configuration was used to bid the membrane portion of the project.
Layne Christensen Co. was selected as the system integrator for the 6-million-gal-per-day (mgd) primary UF system with Norit XIGA membranes for potable water production along with a 1-mgd secondary system with Norit Aquaflex membranes for backwash recovery. The membrane systems were fabricated entirely by Layne’s own forces at its 40,000-sq.-ft. fabrication facility
in Lakeland, Fla.
After the award, Layne conducted an extensive pilot to validate the performance of the Norit membranes and also to dial in the process and operational parameters of the completed system. The feedwater is not easy to treat since the wells cycle on and off automatically, thus changing the feed quality. The multiple contaminants of TOC, manganese and H2S further complicate the process by requiring different pH levels, chemicals and treatment processes for their removal. The pilot study mimicked the entire process and defined the requirements for advanced monitoring and control to ensure the treated water consistently met its goals and that the final design allowed for ease of operation. Various coagulants, dosages and pH levels were evaluated before the final process was defined. The secondary UF system was also tested on backwash waste from the primary UF pilot.
The system was installed and commissioned in the fall of 2009. Based on the pilot data, the plant was configured for a coagulant dosage of 4 mg/L of alum. The plant’s performance has shown an average TOC reduction of 40%, and the four distribution system sampling points show an average DBP of 55.1 (well below the MCL of 80 µg/L), and all four measurement points are reporting below the MCL, thus achieving the city’s compliance goals for treatment of DBPs, H2S and manganese. The primary and secondary membranes run continuously, only requiring occasional chemically enhanced backwashes to maintain stable trans-membrane pressures, and do not require any offline cleanings.