Millions flock to the Sunshine State each year for exactly that: the plentiful sunshine.

But those sun rays are not so popular at the Southwest Regional Wastewater Treatment Facility in Polk County, Florida. There, the staff uses a floating UV ball system to shield the chlorine contact chambers from the sun, reducing algae growth and evaporation and saving thousands of dollars in chlorine costs each year.

It’s just one of a number of innovations and improvements at the facility, winner of the 2018 David W. York Reuse Award from the Florida Water Environment Association and the 2018 Plant of the Year award from the Florida Department of Environmental Protection.

“We’re a 100% customer-based reuse system,” says Todd Potter, plant supervisor. “The awards recognized the work we’re doing here. We’re feeling pretty good about it.”

Multipurpose reuse

The plant, in Mulberry, serves a number of communities in Polk County, which includes Winter Haven and Lakeland. Every drop of its crystal-clear effluent is recycled through a 41-mile piping system for irrigation at more than 1,800 homes, two golf courses and a park. The plant also sells at least 0.6 mgd for power plant cooling water.

During wet weather, the plant can store up to 14 million gallons in an on-site reservoir.

Four operators run the system during the week; one is on site during weekends. Operators are on call via the plant’s SCADA and callout system. Operators are William Altman, James Hall, Andy Martin and Carlos Brito. 

Wastewater influent is screened through a Parkson Corp. bar screen, followed by a Fluidyne grit system. Then the flow passes to two channels of a four-basin Eimco oxidation ditch (Ovivo) operated in the extended aeration mode. The ditches function as a modified carousel process: The plant can control the flow to a dedicated anoxic zone.  

Four secondary clarifiers follow. Then, three Evoqua Water Technologies automatic backwash traveling bridge filters polish the effluent, and three chlorine contact chambers equipped with the UV balls disinfect the effluent with sodium hypochlorite and maintain the chlorine residual. Sodium hypochlorite also prevents algae growth on the filters.

Solids are aerobically digested, then processed through a portable centrifuge (Centrisys/CNP). Cake at 20% solids is loaded into a 25-yard roll-off container and hauled to a county landfill. “This is a huge savings for us since we do not have to pay tipping fees,” Potter says.

Big data

Data monitoring is critical to effluent quality. The chlorine residual values are recorded and stored in iFIX HMI/SCADA’s central historian systems (GE Digital). The plant staff reviews trends daily and enters the data into a Hach water information management solution for later reporting. 

The reclaim water pH is monitored continuously and recorded. Turbidity is monitored by two in-line MicroTOL HF scientific turbidity analyzers at the effluent discharge in the filter effluent common wells. All data is connected to the plant’s PLC system.

The system dates to 2007 when the plant was expanded from 2 to 4 mgd. At that point, the county shut down all but three old package plants and tied their service areas into the central system.

“Expanding our distribution system and converting the package plants to regionalize our flows was a huge cost,” Potter says. “We had to make agreements with cities to take their flow. We manage and maintain our infrastructure up to where it ties into their systems.” The remaining three package plants are landlocked and too far away to treat cost-effectively.

Substantial savings

The UV balls, also known as shade balls, have saved money and improved operations. The hollow ball system, supplied by Environmental Controls Co., floats on the surface of the chlorine contact chamber and limits the sunlight reaching the water. The county had successfully used overhead shades at its Northwest Regional plant, so there was a proof of concept. The Southwest facility purchased the balls in 2014.

Results have better than anticipated. By reducing sunlight and water temperature, while limiting evaporation via chlorine off-gas, the facility has reduced chlorine demand from 18.8 to 13.2 mg/L, saving more than $30,000 per year, with no impact on the flow pattern and only minor structural changes. Chlorine consumption dropped by 4 mg/L almost immediately at the normal chlorine dose setpoint, Potter says.

The county is using the balls at all three regional plants and has saved some $450,000 on chlorine over the past five years. There is no maintenance cost; the balls are cleaned when the tanks are cleaned. “This only cost us $4,500 for all three contact chambers, and we made that money back in the first year,” Potter says.

The Southwest facility has had similar success transitioning from dissolved oxygen to oxidation reduction potential controls, saving energy and improving ammonia control. “It has been about three years since we switched from DO control to ORP,” Potter says. “We were trying to achieve a DO setpoint under DO control; that resulted in aerators running higher than they needed to.”

Now the team can use the negative ORP values to measure and control the anoxic zones. “This allows the aerators to run at a lower speed to achieve the targeted nitrate levels while conserving energy,” Potter says. “And, we have tighter control over the process in general.”

The results show it. With the flexibility of tighter controls, the facility consistently puts out effluent with low nitrogen and almost no ammonia. The plant hasn’t had a composite or grab sample out of compliance since May 2013.

Complete reuse

Potter points to another success story: making the reuse system totally customer-based. The facility recently collaborated with Tampa Electric Co., or TECO, to supply cooling water. “With the help of many others and a lot of permitting, TECO was able to take as much water per day that we could give them,” Potter says. That has eliminated the need for wet-weather discharge and the associated discharge permits.

“Although we did keep one discharge site permitted for flexibility, we have not had to use that in more than two years,” Potter says. “We’re 100% reuse, reducing the demand on the potable water system, recharging wetlands and providing habitat for wildlife.”

An efficient plant is also a safe plant, and the Southwest facility has racked up an exemplary record. The plant received 2018 safety awards from the Florida WEA and the Florida Water and Pollution Control Operators Association.

Potter credits safety meetings conducted daily, weekly, monthly and quarterly, and he salutes the county for stressing safety. “The county has made the investment and enrolled the staff in an online monthly safety course called Pure Safety,” he says. “It allows us to get training that keeps us mindful of safety procedures and allows us to obtain CEUs toward our licenses.

“We also do monthly fire extinguisher inspections, diesel tank inspections and truck inspections; quarterly safety sign inspections; and yearly trip hazard repainting. Plus, our safety manager teaches a defensive driving class.”

Visible commitment

Visitors experience the environmental commitment of the Southwest facility’s team on arrival at the property. The grounds feature a waterfall and a fishpond, illustrating the work done at the plant. “It shows the public what we do,” Potter says. “The whole staff pitched in, dug the holes and did the work. We’re saying that we wouldn’t have clean water except for us. We’re here to protect the environment.”

The Southwest facility won’t be a repeat winner of the York Reuse Award this year because the honor is given only once every four years. So, stay tuned for 2023.