Doing It the Island Way

The reverse osmosis membrane water plant in Sanibel, Florida, thrives on autonomy in operator training, process improvements, and planned maintenance.

Doing It the Island Way

Plant operator trainee David Coleman and colleagues are strongly encouraged by the board of directors and the general manager to progress to higher-level licensing.

They don’t hire licensed operators when there’s an opening at the Island Water Treatment Plant in Sanibel, Florida.

“We take new people and train them ourselves,” says Pat Henry, production manager. “It takes a newcomer about three years to learn the water plant, depending on their mechanical ability. We’d rather have it done the Island Water way.”

The results speak for themselves. The 5.99 mgd Island Water plant, owned and operated by The Island Water Association, has used reverse osmosis membranes on brackish water for nearly 40 years. It turns out a pristine product for its 14,600 customers and regularly wins the Florida Department of Environmental Protection Operations Excellence Award for communities its size. It serves as a model for RO desalting and hosts the Southeast Desalination Association Conference every four years.

Brackish water 

Island Water, a nonprofit, member-owned potable water utility faces raw water that is high in salt and minerals. It comes to the brackish Hawthorn and Suwannee aquifers through a series of 15 wells drilled 500 to 700 feet deep. The plant draws from nine wells at any given time, rotating them monthly.

The Hawthorn aquifer can supply about 300 gpm and the Suwannee about 600 gpm. Total dissolved solids, or TDS, average about 3,000 ppm. In-line monitors from Great Lakes and GF Signet (GF Piping Systems) track pH and turbidity into the plant. Henry notes that his staff first feeds an anti-scalant to the water to keep the salts and metals in solution so they won’t precipitate onto the membrane surfaces.

After that, the raw water passes through a series of Parker Bioscience Fulflo Avasan cartridge filters to remove solids ahead of the membranes. “These are 1-micron polypropylene melt-blown filters,” Henry says. “We have 354 of them and change them out every seven to nine months.” Exiting the cartridges, the water is pumped into the RO system. The Sanibel plant has six RO trains, each containing 120 ultrathin spiral-wound Filmtec membrane modules from Dow Water & Process Solutions. Operating pressure is 176 psi.

Lower pressure, less energy

Henry says, “Originally, we ran at 300 psi, but by working with Dow and developing new technology, we’ve been able to reduce the pressure and save energy. We had a Dow test unit on one of our trains for about 10 years and collected data for them.” By running the water through the membranes in a two-pass system, Island Water can remove more and more of the dissolved solids, until the TDS in final permeate water is about 145 ppm.

Each membrane train has a two-pass 14/6 array, which means there are 14 vessels on the first pass and six on the second. The feed into each membrane train is 626 gpm, and the first pass-through does the brunt of the work, producing about 450 gpm of permeate water. The second pass produces about 50 gpm.

“The elements are hooked together so that the concentrate (reject) water from the first element feeds the second element, and so on,” Henry says. “After the first pass, the interstage TDS is about 9,500 ppm in the concentrate; the TDS in the final increases to 14,200 ppm.”

Efficient recovery

“Our recovery rate is 80 percent,” Henry says. “Eighty percent of the brackish feed water is recovered as high-quality potable water, while 20 percent is collected as concentrated brine water.” The concentrate is pumped to a deep well where it is injected along with excess reclaimed water from the Sanibel Island wastewater treatment plant. Well depth is 3,300 feet.

The operation produces an average of 500 gpm of drinking water per train. The membranes can produce up to 600 gpm, “although we haven’t needed to do that in years because of plentiful rainfall,” Henry says. Actually, the membranes do too good of a job removing contaminants. The plant blends about 6 percent of the raw water back in to stabilize the RO water, which is too aggressive and corrosive: “The membranes remove too much calcium and alkalinity.”

The final product water is pumped into a clearwell and disinfected with chlorine gas so that a residual of 1.6 ppm is maintained throughout the 101.5-mile distribution system. Just before that, a corrosion inhibitor is added that coats any copper piping in the distribution system with a zinc film for compliance with the 1991 Lead and Copper Rule. From the clearwell, the product water is pumped to two 5-million-gallon storage tanks on site and then into the distribution system at 65 to 76 psi.

“Our demand peaks around March/April, the height of the tourist season, when pools are being filled and lawns watered,” Henry says. “During the summer rainy season, we can’t give it away.” Sanibel is on year-round watering restrictions issued by the South Florida Water Management District.

To oxidize the hydrogen sulfide in the water, Island Water feeds chlorine gas into a looped system of product water that is fed back to the permeate stream. The loop goes from the plant out to the chlorine building and then back to the plant.

In addition to reducing membrane feed pressure, Island Water saves energy by recovering the pressure from the brine valves on each membrane train. “Each train’s brine pressure is fed back to an energy recovery turbine hooked up to our spare pump,” Henry says. That procedure reduces the power draw from the pump motor by about 50 percent.  

Training and safety

As for the business of hiring and training new operators, “In those first two to three years, we train an operator to obtain a Class C license and be able to help us run the plant,” Henry says.

“We’re not like a normal plant where operators just come in and sit in front of a monitor. We don’t slam them with everything at once, and we don’t just have them come in here and read manuals. We sit them down with the safety data sheets first. Then they run the boosters with one of the licensed guys. They are on probation for 90 days.

“They have to complete two home study courses using the California State University, Sacramento, Volumes 1 and 2. They must sit for their C level state exam within one year, their B level by the third year, and their A level by the fifth year.”

Even though the plant is a Class B operation, the staff is strongly encouraged by the Board of Directors and the general manager to obtain the Class A level license. “We want them to continue their education,” Henry says. The utility helps pay for the extra training as an incentive.

Also, in their first year, new operators get accustomed to shift work, rotating every month from days to nights. “They also learn all plant processes, paperwork, lab procedures, how to handle chemicals safely, and a lot of cleaning and painting,” Henry says.

Safety is a high priority, and Henry and staff pay special attention to handling chlorine components, and plant security. In fact, all staffers are trained to become certified hazmat team members. “We get everybody up to the 40-hour hazmat commander level within two to three years,” Henry says. “Island Water pays for all the hazmat training. We’re all qualified to change out our chlorine cylinders. If we get a leak, we can contain it.”

The plant is staffed by a pair of operators, 24 hours a day, with two 12-hour shifts, even though state requirements specify a minimum of 16-hour operator coverage per day. Henry explains that it’s better to have two pairs of eyes. “One ‘Oh, crap’ will cancel out 1,000 ‘Attaboys,’” he says.

Doing it in-house

The thorough training and staff expertise enable Island Water to operate efficiently and cost-effectively; the plant doesn’t have to rely on outside contractors for most work. Ron Freitag, chief operator, estimates the Island Water staff saved about $250,000 a couple of years ago by re-piping the entire chlorine system. “The old PVC pipe was getting pretty brittle,” he says. “We used new 1-, 2-, and 3-inch pipe throughout the system — in the plant, underground, and inside the chlorine building.”

The rebuild took more than three years and consisted of over 2,000 feet of piping. The staff used equipment from the engineering department, and staffers from there also handled the marking of the replacement line. “Their help was a nice part of doing this project in-house,” Freitag says.

Operators also save money and learn a lot by changing out the RO membranes. “By opening the end caps and replacing the membranes, we learn all the parts and see inside the vessels,” says Brandon Henke, assistant chief operator. Doing it in-house saves about $10,000 per train, and Island Water can offset its own costs by reselling the used membranes.

In another project, the staff replaced the entire plant air pressure system piping with OSHA-approved polypropylene pipe reinforced with an aluminum core. “It’s great hands-on learning,” Henke says.

Freitag supervises the plant’s extensive preventive maintenance program. It uses a spreadsheet to track 70 to 80 items and tasks weekly, monthly, semiannually and annually. The source of the program? In-house, of course.

Multiple awards

These improvements, along with outstanding treatment performance, have earned the Island Water plant a wall filled with operations excellence awards since the membrane plant was built in 1980. “As of today, 38 awards,” Henry says. The facility wins the Florida Department of Environmental Protection Operations Excellence Award for medium-sized communities just about every other year, most recently in 2016 and 2017: “They normally don’t award it to the same plant two years in a row.”

Why so much recognition? “We go the extra mile,” Henry says. “If you looked at the plant, you’d understand. It looks and runs like new. And our paperwork is always in order.” That reflects what he has learned after starting from scratch working nights and weekends at the utility’s old electrodialysis plant 31 years ago: “It’s better to be correct than fast.”

A productive partnership

It’s a partnership that goes back decades: Dow Water & Process Solutions and Island Water. Over that time, the relationship has produced valuable experience and data to help both parties learn more about and improve the performance of reverse osmosis.

“They’re a great group and a great plant,” says Craig Granland, senior account manager with Dow, maker of the Filmtec membranes in use at Island Water. “I’ve been to plants where treatment is just a job. But at Island Water, it feels like more. They’re very conscientious in how they operate.”

Pat Henry, Island Water production manager, returns the compliment: “They are fantastic people to deal with. If there’s an issue, they fly right down here.” Dow installed the first batch of RO membranes at the plant more than 30 years ago. The original membranes were recently replaced with Dow’s new XLE units, substantially improving energy efficiency.

“They were operating at 300 psi pressure in the beginning, and now the operating pressure is around 176 psi,” Granland says. He notes that the work with Island Water has produced data that helped advance RO knowledge and the technology of salt removal.

“It’s a good example because the source water there is fairly good quality, meaning it doesn’t change a lot but has a relatively high salt content,” Granland says. Dow has used the data from Island Water in internal papers, case studies and published articles: “We’ve always provided our latest and greatest to Island Water and have been able to generate good information on feed pressure, salt rejection, and long-term stability of our products.”


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