AWWA WQTC64169

Zone 7 of Alameda County Flood Control and Water Conservation District owns and operates the Patterson Pass WTP. The conventional plant's process consists of upflow clarification followed by dual media filtration, with a maximum design capacity of 13.5 mgd. In an effort to increase the plant's capacity, it was expanded by adding a solids contact clarifier and an Aquasource membrane filtration system. The 8 mgd addition (UF WTP) began operating in 2003. Although the UF plant has consistently produced an effluent of acceptable quality, the system has experienced difficulties related to operation and meeting its capacity. An evaluation was conducted to identify options to optimize the UF WTP operation and to more reliably meet its 8 mgd capacity, and to identify alternatives for increasing the capacity to 10-12 mgd. The evaluation consisted of reviewing operating data and conducting a site visit to gather information about the plant operating procedures and past performance. Issues were identified that create operating difficulties and ultimately restrict the ability of the system to reliably meet its 8 mgd design capacity. One of the key issues identified is failure of the water quality from the pretreatment unit to meet the membrane feed water quality requirements, primarily the iron concentrations which exceed the membrane warranty limits. In addition, issues such as diurnal pH fluctuations, algae growth, and return of neutralized citric acid cause process upsets that increase the iron and particle loading on the membranes. Analysis of the membranes has shown irrecoverable fouling (loss of permeability) and accelerated aging of the membranes, which have been linked to elevated iron concentrations. Includes tables, figure.