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Maximizing Recovery of Recycled Water for Groundwater Recharge Employing an Integrated Membrane System

Project: 08-10
Type: Report
Year Released: 2011

Program: Tailored Collaboration
Funding Partners: Bureau of Reclamation, California State Water Resources Control Board, Water Replenishment District of Southern California
Total Investment: $355,160.02 (Cash: $224,995.02, In-Kind: $130,165)

Principal Investigator: Christopher Yu, PhD., P.E., Psomas

Background

The Water Replenishment District of Southern California (WRD) has instituted numerous projects and programs over the years in a continuing effort to effectively manage groundwater replenishment and groundwater quality in southern California’s Central and West Coast Basins.

One of the key groundwater resources for the WRD is recycled water. The recycled water has primarily been used to replenish the groundwater basins by surface spreading and injection at seawater intrusion barriers. In view of the potential for drought conditions to strike California and uncertainty in the future availability of imported supplies, recycled water has become increasingly vital and essential as a replenishment source.

Because of the increasing costs of water for the barriers, the WRD is constantly evaluating alternatives to minimize costs, such as the reduction of pumping near the barriers, increased recycled water to offset imported water, or banking water at lower seasonal rates. One of the alternatives that the WRD is interested in is increasing the recovery at the Leo J. Vander Lans Water Treatment Facility (LVL) to produce more recycled water.

Goals and Objectives

The project evaluates whether a multistage, high-pressure membrane process, such as the one used at the LVL, can be operated at higher recovery and permeate flux, resulting in lower overall operating costs, without compromising product water quality. For this specific water reuse application, it is hypothesized that new-generation NF and LPRO membranes could be operated at higher recovery and lower operating costs, while maintaining a product quality comparable to conventional RO membranes.

Research Approach

A literature survey was first conducted to identify previous experience in operating IMS at elevated flux and recovery for water recycling applications and to explore foulants that can results in flux decline. The survey provided the guiding principles to the selection and optimization of recovery enhancement challenges at LVL.

Due to their relatively high flux rates at lower pressure and low fouling propensity, five NF membranes (NF-90, NF-270, NF-4040, TFC-S, and TFC-SR3) and one low pressure RO membranes (ESPA2) were selected for bench-scale testing. Two membranes were ultimately selected for on-site piloting at LVL. The ESPA2 membrane served as the baseline membrane as it is currently employed at the LVL. The other membrane selected was NF-270.

Findings and Conclusions

This study provides data on NF membrane treatment of recycled water, which are critical for acceptance by the regulatory authorities. It is expected that this mode of operation will allow savings in operations for utilities seeking to treat recycled water without stringent TDS removal requirements. It could also offer a proven, cost-effective option to existing facilities that use two-stage RO.

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