AWWA WQTC58994

Ultra-low pressure reverse osmosis (RO) membranes were used for groundwater softening during a3.5-month pilot evaluation conducted by a Northern California water district. Completed in January2002, this predesign-focused pilot study was performed as one component of the District'scomprehensive hardness reduction program. RO membranes were chosen as the most appropriatehardness reduction technology for a number of reasons including the benefit of pathogen protectionprovided by membrane separation.The primary objectives of the RO pilot testing program included assessment of the following issues:ability of RO membranes to remove hardness in order to meet the District's production waterhardness goals;rejection of heavy metal species in the RO concentrate (brine) regulated by the Regional WaterQuality Control Board (RWQCB) under the San Francisco Bay Basin Water Quality ControlPlan (Basin Plan) and the California Toxics Rule;toxicity of RO concentrate to aquatic species in freshwater and marine environments; and,treatability of local groundwater to establish full-scale plant design criteria and scale formationpotential by sparingly soluble salts.The focus of this discussion will be: the determination of the maximum viable system recoverythat the RO membranes in this study could achieve without evidence of scale formation; and, theevaluation of the need for pH adjustment via acid addition for control of calcium carbonate scalingand anti-scalant addition for control of barium sulfate scale. Testing was conducted over a range ofRO system recoveries in order to challenge the limits of conventional RO design. Specifically, thepilot study system recoveries and experimental conditions were adjusted to evaluate the edge offailure with respect to anti-scalant addition, pH depression, and precipitation of scaling salts. Includes tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/02/2003

Number of Pages:

9

File Size:

1 file , 290 KB