Membrane Superstar

The Groundwater Recovery Facility at California’s South Coast Water District achieves high uptime and long runs between membrane cleanings.
Membrane Superstar
Steve Dishon, water production supervisor at the South Coast Water District Groundwater Recovery Facility, which received the Southwest Membrane Operator Association’s 2013 Plant of the Year Award.

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If reverse osmosis systems were nationally ranked like college sports teams, California’s South Coast Water District (SCWD) might be Number 1.

The reverse osmosis (RO) system at the District’s Groundwater Recovery Facility (GRF) filters water drawn from the brackish San Juan Basin aquifer and, along with other treatment steps, delivers it to the district’s distribution system, which serves some 40,000 customers in Dana Point, South Laguna, and parts of San Clemente and San Juan Capistrano.

According to Steve Dishon, water production supervisor, the membranes (Toray Industries) were available to produce water 96.1 percent of the time during 2012-2013. The membranes have operated for more than two years between low-pH and high-pH cleanings with a special anti-scalant. That kind of performance earned the facility the 2013 Plant of the Year Award from the Southwest Membrane Operator Association.

Doing it all

The SCWD, 60 miles south of Los Angeles, is responsible for total water management in its service area: wastewater, groundwater, stormwater and drinking water. The infrastructure includes 24 treatment facilities — many of them small plants treating reservoir water — along with 147 miles of pipeline, nine pump stations and 13 local reservoirs. With the additional capacity in two regional reservoirs, the district’s water storage totals 50 million gallons, enough to serve customers for up to seven days, and 14 days under emergency water rationing.

The GRF occupies an important place in the overall water plan: It produces about 15 percent of the district’s potable water. The facility withdraws water from a single 126-foot-deep well flowing at 700 gpm. The rest of the district’s water is imported from the California State Water Project and the Colorado River. The district also operates a recycled water system for irrigation.

The brackish nature of the groundwater is not due to seawater intrusion, even though the well lies just a few hundred yards from the Pacific Ocean. The high salinity emanates from natural salt deposits. “We’re somewhat unusual here in that our groundwater is actually an underground river flowing from the Cleveland National Forest and other areas, through San Juan Creek out to the ocean,” he says. The groundwater typically contains about 2,200 ppm total dissolved solids (TDS) and 3,000 ppm electro-conductivity.

The recovery facility

At the plant, the groundwater splits into two flows. About 85 percent passes through cartridge filters and then to the RO membranes. Anti-scalant is injected with a peristaltic pump (Blue-White Industries) just ahead of the cartridge filters at 5 ppm by volume. The remaining 15 percent of the flow is treated in an iron and manganese removal system (Loprest Water Treatment Co.) with high-performance stainless steel valves (Bray International).

The two streams reblended through a decarbonator. The split flow scheme is designed to put some mineral content back into the water. To help prevent corrosion, sodium hydroxide is added to the flow using a vortex mechanical inline chemical mixer (Superior Water Technologies); sodium hypochlorite and aqueous ammonia are also added. After disinfection, the water is pumped to the distribution system.

All plant discharge, including backwash water and solids, flows to a regional ocean outfall.

The district generates sodium hypochlorite on site, using injection equipment from Process Solutions. Chloramines are produced by adding ammonia. “We have a 35-minute detention time in the clearwell,” Dishon says. “That’s an adequate contact time for the chloramines before the water is pumped to the potable water system.”

The facility can add sulfuric acid but has not done so since 2008. “By eliminating the sulfuric feed, we were able to save $160,000 per year in chemical costs,” says Dishon. That’s a considerable amount considering the plant’s operating budget is about $825,000 per year.

A bit of caustic is added to the flow after the decarbonator.

Big responsibilities

Plant processes are monitored and controlled by a Modicon Proworx SCADA system (Schneider Electric) with Wonderware software (Invensys) and a radio system. Analytical equipment has been supplied by Hach, and the GRF uses Allen-Bradley variable-frequency drives (Rockwell Automation) and Peerless vertical pumps.

“The quality of the produced water is strictly confined to match the imported water [pH, chloramines, conductivity] coming from the Metropolitan Water District of Southern California, so that there is no reaction between the produced water and the purchased water,” Dishon says.

Dishon and Paul Zents and Michael Buhl, senior operators, are responsible for the GRF and 13 other facilities, including the Orange County Poche Clean Beach Project filtration and UV plant, and the Salt Creek Ozone Treatment Facility, which provides filtration and ozone disinfection and is owned by the City of Dana Point.

“We work four days per week from 7 a.m. to 5:30 p.m. and rotate the on-call duty every third week,” says Dishon. “In compliance with our permit, the plant is monitored every day it is in operation. Reads are taken, grab samples processed and forms filled out.”

The three operators work for Joe McDivitt, director of operations, who has been a strong supporter since the district took over plant operations soon after the facility was commissioned. “Joe has given us the freedom to make the changes necessary to make the facility more efficient and more reliable,” Dishon says.

Specialized membranes

The RO membranes are designed and manufactured by Toray for brackish water. They are spiral-wound, cross-linked polyamide composite, 8 inches in diameter. Dishon’s team operates a single train consisting of two banks, each with 147 40-inch long membrane cylinders.

The membranes use a split-ring seal. The operators prefer that design to more conventional rubberized brine seals, which Dishon says tend to roll during installation or when removed and repositioned during service. “If the seal rolls, then you have a high risk of bypassing the filter,” Dishon says.

“Plus, with rubberized seals you have to push all the membranes in the same direction in order to get at one for service or replacement. With the split-ring seal, it’s much easier to remove a membrane. You don’t need lubrication, and you can remove a membrane in either direction.”

That’s important at the GRF, because the membranes are a tight fit in the building and there isn’t enough room on one side of the membrane train to remove an individual unit.

“We were one of the first plants to have split-ring seals on the entire membrane system,” Dishon says. “It will be three years in March since we installed the membranes, and the seals are doing well.” For clean-in-place membrane cleaning, the staff uses K-1000 acid solution and K-2000 caustic solution (King Lee Technologies).

Getting the water

One goal of the South Coast Water District is to reduce reliance on imported water by delivering more from local sources. That makes the successful operation of the GRF more and more important in the future outlook.

The district relies heavily on imported water to meet the needs of the community and more than two million visitors each year. At present, about 75 percent of the water is imported from hundreds of miles away — from the Colorado River and from northern California. Drought, climate change, population growth, changing government policies and ecosystem challenges are all working to reduce those supplies and to make them uncertain.

In response, the district is investing millions of dollars in the continuing development of reliable and drought-proof local supplies. This work includes:

Improvements to the recycled water supply for irrigation to save more water for drinking.

Participation in the proposed Doheny Ocean Desalination Project and possibly other desalination projects.

Installation of a second well at the GRF to ensure sustainable water production.

Dishon says the second well is nearing completion and will be equipped and operating soon. Increased water production from the San Juan Basin aquifer will help the district continue to supply its customers and will have an economic benefit as well.

“While we are limited in how much water we can produce by well extraction from the basin by our California Water Resources Control Board permit, for every acre-foot [325,850 gallons] of water we produce from our local groundwater source, we receive a $250 credit from the Metropolitan Water District,” says Dishon. “It’s an incentive to produce as much water locally as possible.”

More Information

Blue-White Industries - 714/893-8529 - www.blue-white.com

Bray International, Inc. - 281/894-5454 - www.bray.com

Hach Company - 800/227-4224 - www.hach.com

Invensys Operations Management - 949/727-3200 - www.iom.invensys.com

King Lee Technologies - 800/800-9019 - www.kingleetech.com

Loprest Water Treatment Co. - 888/228-5982 - www.loprest.com

Peerless Pump Company - 800/879-0182 - www.peerlesspump.com

Process Solutions, Inc. - 888/774-4536 - www.4psi.net

Rockwell Automation - 414/382-2000 - www.rockwellautomation.com/industries/water

Schneider Electric - 888/778-2733 - www.schneider-electric.us

Superior Water Technologies, Inc. - 949/241-2096 - www.superiorwatertechnologies.com

Toray Membrane USA - 858/218-2390 - www.toraywater.com



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