Turning the Corner

Operations staff engineered a revival that changed the Tarpon Springs treatment plant from a problem facility to a multiple-award winner
Turning the Corner

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In barely 10 years, the Tarpon Springs (Fla.) Advanced Wastewater Treatment Facility has gone from “the little plant that couldn’t” to “ the little plant that can” — and does.

That’s how utilities superintendent Ray Page and director of public services Paul Smith describe the progress they’ve made at the 4.0 mgd (design) plant. They compare multiple operator-driven process improvements to the train engine in the old children’s story that found it could achieve success if it reminded itself: I think I can.

“In 1999, we were under a consent decree,” recalls Page. “But most of what we’ve done to improve treatment here, we’ve done on our own.” They’ve accomplished a lot. From developing sophisticated SCADA systems, to devising fail-safe water recycling procedures, to cutting power and staffing costs, the Tarpon Springs staff has simply redone the plant. Plagued with permit-violating conditions a decade ago, the facility now provides pure recycled water to about 1,000 customers and has garnered state and professional awards for treatment effectiveness and efficiency. Now, the Florida Department of Environmental Protection (FDEP) refers professionals from other cities and counties to Tarpon Springs for ideas and solutions to compliance issues.

Automated process

About 2 mgd on average flows into the plant from a community of 25,000 people on the Gulf of Mexico in the Greater Tampa-St. Petersburg metropolitan area. Two Myers submersible pumps and a tandem of aboveground pumps (ITT Water & Wastewater) boost water from the wet well to the headworks, which are equipped with a pair of Huber bar screens.

The pumps replaced old screw pumps that were less efficient and consumed more power. A Fluidyne vortex-type unit removes sand and grit.

An Ovivo Bardenpho process accomplishes biological treatment and nutrient removal. The system consists of a five-stage complete-mix sludge process with alternating stages of anoxic and aerobic conditions.

In the first (fermentation) stage, influent mixes with return activated sludge. After contact, the liquid moves to the anoxic zone, where it is mixed with nitrates from the nitrification zone. Nitrates are reduced to nitrogen gas in a second anoxic zone before the water passes to a reaeration zone, where mixed liquor dissolved oxygen is increased so that phosphorus is not released in the 80-foot-diameter final clarifiers.

The process is automatically controlled by the facility’s state-of-the-art SCADA system. “We’re getting good annual results,” says chief operator Rob Marcincuk. “We use a minimal amount of aluminum sulfate to aid in clarifier settling.”

Two Ovivo automatic backwash filters remove remaining suspended solids before the water passes to the chlorination-dechlorination process. The plant uses gaseous chlorine, followed by sodium bisulfite and sulfur dioxide, to meet its requirement of zero chlorine in the final effluent when discharging to the Anclote River, which flows into the Gulf of Mexico.

Page explains that the dechlorination process is redundant to ensure that the residual requirement is met consistently. “Either sodium bisulfite or the sulfur dioxide could do the job on its own,” he says. “But this way, if one doesn’t work, the other will. If we have a sulfur residual in the effluent, we’re certain there’s no chlorine.” The vertical chlorine contact chamber has been modified with a cascade aeration system to air-strip and remove trihalomethanes.

A Siemens centrifuge dewaters biosolids to cake at 20-plus percent solids at about 100 gpm, using a specific polymer blend. The centrifuge replaced an old belt press that was achieving only 12 to 14 percent solids at 40 gpm. At a loading station on site, a private fertilizer manufacturer picks up the cake for hauling it to a central processing facility.

Another Siemens technology called PRISC, controls plant odors using a combination of Odophos and concentrated hydrogen peroxide. A portable odor logger measures air quality before and after treatment. When the PRISC system was started in March 2008, influent hydrogen sulfide levels spiked as high as 240 ppm but now have been reduced to less than 12 ppm as a peak. Averages are much lower.

Using a resource

If any plant in the nation is serious about reuse, it’s Tarpon Springs. In fact, the plant won the Florida Water Environment Association Reuse Plant of the Year Award in 2010. “About 65 to 70 percent of our effluent water is reused,” says Page. “We have about 1,000 customers, including the city cemetery and the municipal golf course, which maintains an 850,000-gallon storage pond monitored and flow-controlled by remote telemetry.”

Customers include homes, commercial ventures and developers. “They pay 95 cents per thousand gallons,” says Page. “The water is pressurized and pumped to them through a separate distribution system. Their participation is voluntary.” The treatment facility itself uses some of the reclaimed water for processes such as makeup of the chlorine solution.

The system was developed through a cooperative funding program with the Southwest Florida Water Management District through a 50/50 money match. The way Tarpon Springs collects, stores and monitors the water to be reused is unique, and it’s a homegrown solution.

“In the old days, we had a single reuse tank for our recycled water,” says Marcincuk. “If effluent was out of spec, we had no other alternative but to release it to the river. We were letting a valuable commodity go to waste.”

Today, the plant operates two recycle tanks with a combined 4-million-gallon capacity. If effluent is out of spec, it is captured in a dedicated tank and then directed back through the plant for retreatment. The second tank holds water available for reuse. The SCADA system [Citect software (Schneider Electric) paired with Allen-Bradley (Rockwell Automation) PLCs and developed with integrator McKim & Creed of Tampa] is tied into the tanks so the staff can monitor water quality and the level in each tank.

“Rob and Ray developed the two-tank system and the SCADA feature,” says Smith. “We were the first system in the state to be permitted to operate our reuse system this way. The progressive outlook of the Florida DEP and the Southwest Florida Water Management District are what made it possible.”

Over the top

As critical as these process improvements have been to the facility’s performance, the staff had to work even harder to push Tarpon Springs over the top. Staff-driven innovations are saving electricity and operating costs.

Before, all of the facility’s big pumps were either on or off, draining power unnecessarily and creating surges in plant flow. “We’ve installed variable-frequency drives (VFDs) on all intermediate pump stations,” Page says. “That smooths out the flow and prevents the big swings we used to experience in chlorine usage, for example.”

The Tarpon Springs staff has also installed VFDs on the aerators, where speed is based on achieving dissolved oxygen set points; on the chlorine feed to avoid peaks and valleys; and in the wet wells to control pump station flow rates.

Through the use of pump integrators, the staff can obtain maximum pump capacity more efficiently. Before, pumps would run at 100 percent capacity all the time. Now they’re coupled with a lag pump to produce the same capacity with less energy. “By pairing the pumps at their most efficient point, we get maximum pumping capacity and efficiency,” Page says. About 20 pumps around the facility are set up this way.

In addition, the facility has switched to premium-efficiency motors, which are “the most efficient you can get,” Page says.

Staffed to succeed

With energy efficiency and process perfection as daily objectives, the Tarpon Springs team has made sure to maintain the required in-house expertise. An electrician is on site, and the facility maintains its own electrical and mechanical shop — a 20- by 30-foot building alongside the solids handling facility.

“We have experienced welders on staff,” says Smith. “When we hire, we’re looking for mechanical and electrical skills. We try to do as much as we can ourselves and reduce our costs for outside contractors. All staff members are responsible for our success on a daily basis.”

The facility maintains a stock of spare parts for every piece of equipment. And staffing is handled with an eye to economy, as well. “We used to operate with two people, around the clock,” says Smith. “Now, with our SCADA system, we can operate with one person on the afternoon and midnight shifts. We haven’t fired anyone because of this, but we’ve reduced staff where possible as people retire or leave for other jobs.”

Seeing the light

The Tarpon Springs plant has done such a good job of improving efficiency and saving money that other organizations have noticed and are taking advantage of the facility’s money-saving programs.

The facility’s SCADA system controls the lighting at local athletic fields operated by the city. The program keeps tabs on who is using the lights and how long they’re on. Charges are then based on actual use, promoting conservation. “It’s more accountable,” says Smith. “It provides a paper trail showing how the lights are used. It’s a lot better than simply turning the breaker on and off.”

The facility even applies energy efficiency to transportation. Known to staffers as the Green Bean, one of the plant vehicles operates on batteries powered by solar panels that cover its entire roof. The Bean is similar to a four-seat golf cart and is certified to DOT standards. It is equipped with lights, turn signals, safety belts and other required items and is registered as a car. Staffers drive the Bean around the facility and along the half-mile road to the river outfall.

Top speed is 21 miles per hour — perhaps about the same as that little engine as it crested the hill and headed down.



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