Keeping Up With Disinfection Demands

July 15, 2010

About the author: Daryl Weatherup is global product manager for disinfection for Siemens Water Technologies. Weatherup can be reached at [email protected] or at 949.274.5284.

California mountain town doubles up on disinfection

In the summer, vacation traffic along California Highway 108—also known as the Sonoran Pass Highway—can get thick with urban vacationers winding their way up to campgrounds in the Sierra Nevada. They have no idea what impact they have on the wastewater treatment plant (WWTP) or its difficulty in keeping up with the disinfection demands to protect the environment.

A number of these campgrounds lie in or near Pinecrest, Calif., a remote mountain resort community on Pinecrest Lake midway between Yosemite National Park and Lake Tahoe. At an elevation of about 5,600 ft, the area features a national forest, state park, ski resort and numerous recreational areas.

Census figures list Pinecrest’s population at 232, boosted by 400 cabins and condominiums for part-time residents. But the state shuts down Highway 108 when it snows, limiting travel in the remote area, so in winter, it has only about 25 permanent residents.

From June through August, though, the real population blossoms to between 8,000 and 11,000 on any given week due to the cabins, campgrounds and other outdoor amenities. The vacationers put a tremendous demand on the only WWTP in the area, according to Pat Smith, operations manager for the Pinecrest Community Assn.

Heavy Load for Aging System
A jack of all trades, Smith runs two potable water facilities as well as the wastewater plant, which consists of a screening system, rotating biological contactor (RBC), clarification pond and percolation and evaporation pond.

“I’m general manager. I also run the distribution system. And we’re a fire department, too. We do a little bit of everything,” Smith said. “Up here in the mountains, you have to have a lot of expertise on everything—and a lot of backup parts on hand for everything. That’s why we like to have a unit where you can turn it on and you don’t have to worry about it. You don’t want to deal with a lot of breakdowns and things like that.”

With part-time demand augmented by snowmobilers and winter sport enthusiasts who come to sled at snow parks or ski at the nearby Dodge Ridge Ski Resort, the WWTP has a flow capacity for discharges of about 30,000 gal per day (gpd) in colder months. In the summer, Smith said, that jumps to 174,000 gpd.

Complicating matters a few years back was an aging electrochlorination system that required more maintenance and could not keep up with disinfection demands of the wastewater treatment plant. The system was about eight years old, and efficiency had decreased to where it was using three or four truckloads of salt a year.

“It worked way too hard because it was only a 100-lb-per-day unit,” Smith said. “Through the
summertime, it was going 24 hours a day.

Limited Space & Quick Turnaround
The challenge was to replace the existing system in an environmentally sensitive ecosystem and conscientious community with the added constraints of limited space, limited access to deliveries—particularly in the winter—and a quick installation.

Originally seeking a capacity of 125 lb per day hypochlorite, the Pinecrest Community Assn. asked for pricing from the provider of its previous system as well as from Siemens Water Technologies. Siemens manufacturer’s representative Mark Knudsen of G3 Eng., Inc. proposed a new unit being introduced
by Siemens: the OSEC B-Pak onsite electrolytic chlorination system.

With standard capacities from 250 lb/day to 1,500 lb/day of equivalent chlorine, it generates a 0.8% sodium hypochlorite solution through electrolysis of brine, consuming only water, salt and electricity. It also could produce 250 lb/day of chlorine for a better price than the competitor’s smaller 125-lb/day system.

“We took a different approach than what the owner initially was looking for and offered it to them, convincing them that they’ll get a lot longer life out of this by going with a bigger unit,” Knudsen said. “It went beyond the flexibility and capacity that they need now, but would certainly have the capability of generating enough sodium hypochlorite for any situation they may encounter in the foreseeable future.”

The payoff was the added ability and assurance of producing more hypochlorite. With the high-efficiency OSEC system, salt consumption and operation and maintenance costs were reduced, as was the sodium discharge to the environment. Furthermore, reduced cycling of the equipment saves on energy costs and prolongs system life dramatically.

“By having the larger unit in there,” Knudsen said, “you’d get a lot longer life out of the plates, the cathodes and anodes. The coating on those needs to be replaced every so often. And you’ll get a system that’s twice the capacity. You’ll run it half the time or less. And you’ll double the life expectancy of the overall system itself.”

Because peak demand was seasonal for the plant, the retrofit needed to be performed during the winter and be ready for the spring runoff and summer travelers, requiring a quick turnaround on the contract. After speaking with the client in early November 2006, Knudsen gave a quote on the system in mid-November, received a purchase order in early December, and the equipment was installed and started up in one day by Siemens in April 2007.

Same Space, Twice the System
Now, instead of running around the clock like the old system, the OSEC B-Pak system runs about three hours a day in summer and once a week in winter. The only issue with the system was that the original heater had to be replaced with a larger unit to make it run better because of how cold the water gets—about 39°F—in winter.

“It’s basically run pretty flawlessly ever since. We haven’t even had to clean it yet, and it’s been going on three years. We haven’t run it through a clean cycle, and it hasn’t looked like it needed it either yet,” Smith said.

Even though the new system is only slightly larger than the old one, the association built a new 600-sq-ft building to house the unit and store salt, which it prefers to buy once a year because travel is restricted when it snows.

Smith noticed a significant decrease in salt consumption with the new system—from four truckloads of salt (each with 19 pallets, 49 bags on a pallet)—down to one truckload with the Siemens system. And one truckload has lasted longer than a year.

In addition, the “plug-and-play” aspect of the new system was underscored by how seamlessly it fit in with the existing metering and monitoring technology.

“We had these ultrasonic meters for not only our brine storage tank, but our other storage tank for product—and they tapped into the unit really easily,” Smith said.

Broadening the Base
Today, there are close to 1,000 OSEC systems installed globally, with more than 200 of those in the U.S. Most are installed in urban drinking water systems, but they are used in wastewater applications as well.

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About the Author

Daryl Weatherup

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