AWWA MTC61136

Previous articles summarized the difficult first two years of operating the microfiltration/reverse osmosis/nanofiltration (MF-RO-NF) plant in Chandler, Arizona, a Phoenix suburb. It reclaims industrial wastewater from semiconductor manufacturing to potable standards to recharge an aquifer. This update presents subsequent improvements in pretreatment and processing that have lowered operating costs, cleaning frequencies, and rate of membrane replacement. The cutting-edge, award-winning facility commenced operations in July 1996, reclaiming wastewater generated by Intel's Fab 12, one of the world's largest semiconductor manufacturing facilities. The reuse plant was designed before Fab 12 was operating, so site-specific data were not available. At start-up, it was found that the raw water would need pretreatment to protect RO from high Silt Density Index (SDI) and turbidity values. Many in the RO industry would consider these impossible operating conditions. It was difficult, but not impossible. As a temporary solution, field revisions were implemented to allow operation of the polyamide thin film composite membrane, including: lower flux, lower recovery, increased velocity across the membrane surface, lower feed pH (to address calcium phosphate scaling), frequent cleanings, and experimental cleaning methods. These were relatively successful, but, as anticipated, there were problems: chemical cleanings were required often, cartridge filter replacement rate was frequent, and service life of the spiral wound RO elements was short. Subsequent modifications included adding prefiltration by UF, replacing the UF with MF, and implementing pre-chloramination to control biofouling. Today, the plant has injected over 2.5 billion gallons of potable water. The paper summarizes the history of the plant, water quality, equipment descriptions, replacement of cartridge filters with automatic backwashable screens, cleaning methods, and current operating practices. Includes 4 references, tables, figures.