AWWA WQTC57086

A groundwater demineralization pilot study using ultra-low pressure reverse osmosis (RO) membranes was recently completed by the Alameda County Water District (District), a Northern California public utility located in the southern San Francisco Bay Area. The District is pursuing development of a new Groundwater Treatment Facility that will provide increased pathogen protection and reduced hardness in the blended drinking water supply delivered to District customers. Objectives of the RO pilot testing program included assessment of the following issues: ability of RO membranes to remove hardness in order to meet District's distribution system hardness goals of 150 mg/L and 175 mg/L for average and maximum hardness, respectively; rejection of heavy metal species in the RO concentrate (brine) regulated by the Regional Water Quality Control Board (RWQCB) under the Basin Plan and the California Toxics Rule; toxicity of RO concentrate to aquatic species in fresh water and marine environments; and, treatability of local groundwater to establish full-scale plant design criteria and scale formation potential by sparingly soluble salts. The focus of this paper is the removal of regulated heavy metal species by the RO membranes, and the variability of rejection efficiencies demonstrated for different species. Includes tables, figures.