Producing High-Purity Recycled Water for Industrial Applications with Microfiltration and Reverse Osmosis: Lessons Learned

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ABSTRACT
The East Bay Municipal Utility District (District), with the assistance of Black & Veatch, studied the feasibility of treating secondary and tertiary effluents using microfiltration (MF) followed by reverse osmosis (RO) to produce high-purity, recycled water for use as boiler make-up water at a local refinery. A pilot-scale test program was developed to demonstrate the ability of the MF and RO technologies to treat secondary effluent from the West County Wastewater District (WCWD), and tertiary effluent from the District’s North Richmond Water Reclamation Plant (NRWRP). The pilot-scale test systems consisted of a 25 to 40 gallons per minute (gpm) MF system and a 12 to 15 gpm RO pilot-scale system. The pilot-scale systems were operated for a total of four months. This paper summarizes the pilot test program and results, and discuses the design considerations that will be applied to the full-scale system. When treating secondary and tertiary effluents, the pilot-scale systems were able to produce permeate that met the water quality objectives of the project while operating at an overall recovery rate between 77.5 to 79 percent.

INTRODUCTION
The East Bay Municipal Utility District (District), with the assistance of Black & Veatch, studied the feasibility of constructing advanced recycled water treatment facilities at either the District’s North Richmond Water Reclamation Plant (NRWRP) or at a local refinery to produce highpurity recycled water for use in the refinery’s boiler feed water systems. Based on an evaluation of various treatment technologies it was determined that treatment of secondary or tertiary effluent with microfiltration (MF) followed by reverse osmosis (RO) was the preferred technology to consistently and cost effectively meet the established water quality goals. A pilotscale test program was developed and conducted from July 2005 through October 2005 to demonstrate the ability of the MF and RO technologies with two source waters: secondary effluent from the West County Wastewater District (WCWD) and tertiary effluent from the
NRWRP.

The following objectives were established for the pilot test program:

  • Verify that the MF and RO technologies can consistently produce high-purity recycled water that meets the established water quality goals for boiler make-up water.
  • Evaluate the operational performance of the MF and RO systems with the two sources of water to identify the preferred source water, if any.
  • Characterize the RO concentrate to assess and develop alternatives for disposal of the concentrate stream.
  • Collect sufficient data to develop design parameters and considerations for both MF and RO treatment processes.
  • Collect sufficient RO operational data to determine the cleaning frequency of the membranes and to develop warranty considers during design of the full-scale system.
  • Provide operational experience for District staff with both technologies.

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