AWWA ACE63028

Zone 7 Water Agency's Patterson Pass Water Treatment Plant includes an ultrafiltration membrane process train. The pretreatment process consists of ferric chloride coagulation and solids-contact clarification. The plant has demonstrated its ability to produce high-quality water since its initial startup in the summer of 2003. However, the cellulose acetate membranes are currently deteriorating at an accelerated rate and there are numerous issues that have created operational challenges and reduced production capacity. The main issues appeared to be associated with its pretreatment process. The operation of the pretreatment process ahead of the membranes has been challenging due to stringent warranty conditions originally specified by the membrane manufacturer, particularly the iron level in the feed water, which has most likely contributed to irrecoverable loss of membrane permeability. Another factor that may have had a significant impact was the delayed initial clean-in-place cleaning. The membranes also experienced several air/water hammers in 2004 due to problems with controlling the water level in the clarifier. These issues have resulted in degraded fiber material properties, shrinking fibers, and broken fibers. Although some of the issues have been resolved, some will require further investigation and mitigation. However, regardless of these issues, the ultrafiltration membrane system consistently produced high quality finished water with less than 0.1 NTU of turbidity. Includes tables, figures.