When the City of Winter Haven Utility Service Department began an aggressive cost savings program in 2012, leaders made sure the operations staff was involved. The ongoing program at the city’s two wastewater treatment plants has saved nearly $110,000 on electricity and $450,000 on chemicals.

It didn’t come easy for the operations team in this central Florida city of 34,000. “A lot of adjustments had to be made and a lot more sampling conducted,” recalls Kim Hansell, department director. “We prepared them by saying, ‘This is the vision, and this is what we want to accomplish. If you do the sampling and make the adjustments, you will see the benefits.’ Once they started seeing results, they got really excited.”

Equipment modifications and upgrades helped save chemicals and electricity, while operational changes increased efficiency. Now the utility’s 12 operators and four maintenance technicians are challenged to keep the plants running smoothly and stay on top of preventive maintenance, while monitoring and understanding how their decisions affect energy use. “It’s a question of optimizing and finding the right balance of efficiency and sustainability — for example, understanding the electrical rate and how running equipment at peak usage times affects cost,” says Hansell.

So far, the team has met the challenge. For instance, over the past year, operators at the 7.5 mgd Plant 3 enacted a process sampling program that optimized chemical dosage. The 1.7 mgd Plant 2 freed up more than a million gallons a day of drinking water by producing reclaim water for irrigation and in-plant uses.

Effluent quality is excellent, too. Plant 2 averages 3.14 mg/L BOD and 1.81 mg/L TSS; Plant 3 averages 2.05 mg/L BOD and 1.1 mg/L TSS.

Major upgrades

Plant 2 was built in 1971 and Plant 3 in 1977. Plant 1 was decommissioned and converted to a lift station in 1979. A major upgrade to Plant 2 in 1991 added sand filters (INFILCO DEGREMONT) and a chlorine contact chamber to produce reclaimed water for irrigation. Two in-ground storage tanks help meet reclaimed water peak demands. Other major equipment in use at Plant 2 includes:

• Bar screens (Huber Technology) and grit removal system (Fluidyne Corp.)
• Clarifiers (drives by WesTech Engineering)
• Anoxic basin with EMU (WILO USA)
• Aeration blowers (Hoffman & Lamson)
• Return activated sludge and scum pumps (WEMCO)
• Sludge transfer pumps (Moyno)
• Biosolids belt press (PHOENIX Process Equipment Co.) with conveyor system (Keystone Conveyor Corp.)
• Deming effluent pumps (Crane Pumps & Systems)

In 1998, the clarifier gearboxes and sweep arms were replaced to improve efficiency. Ongoing clarifier rehabilitation includes structural improvements to the walkways and added safety features. The plant operates at 62 percent of its 1.7 mgd design capacity.

Plant 3 was upgraded from an activated sludge plant to an advanced treatment plant in 2008. The process includes a post-anoxic zone with MicroC 2000 (Environmental Operating Solutions) as an alternative carbon source for denitrification, internal mixed liquor recycle, alum addition for phosphorus removal, filtration, chlorine contact, dechlorination and re-aeration.

The plant operates at 57 percent of its 7.5 mgd design capacity. Major equipment includes screening and degritting, blowers, aeration tanks, aerobic digester, biosolids thickener and belt press, clarifiers and chlorine contact chamber. Effluent is discharged to a Peace River tributary; biosolids are digested, thickened, dewatered and landfilled.

Attacking costs

The utility’s cost reduction program has yielded impressive results. Plant 3 used to operate two chlorine contact chambers with a total 380,000-gallon capacity and average contact time of 4.05 hours for 4.5 mgd. Closing one contact chamber reduced detention time to two hours, allowing less chlorine to dissipate.

The plant team also installed new sodium bisulfate injectors in the re-aeration basin to allow more complete mixing. “This has lowered our sodium bisulfate use and allowed us to turn off the re-aeration blower when the dissolved oxygen is above 6.0 mg/L,” says Carlos Brito, the plant’s chief operator. “Our limit is 5.0 mg/L.” Plant 3 also reduced chemical costs by:

• Manually adjusting alum and acetic acid based on in-house process control grab sample results.
• Adding nitrate and phosphate analyzers for automatic chemical adjustment.
• Updating the SCADA PLC with a trim factor that automatically adjusts the chlorine and sodium bisulfate dosage by up to 50 percent based on the chlorine residual.
• Switching from acetic acid to MicroC 2000, saving 65 percent annually.
• Tying the sand filter chlorine pumps to the SCADA so they are controlled by effluent flow. This has reduced liquid chlorine use by about 100 gallons.

The utility has reduced electrical costs by:

• Turning off three air conditioning units in the electrical building on cooler days.
• Updating the PLCs for effluent pump variable-frequency drives so they come on one at a time rather than two at a time.
• Shutting off the digester blowers during the day.
• Using only one aeration blower from winter to late spring.

“Last winter we found that we only needed one aeration blower, because the colder temperature lowers the wastewater a few degrees and allows the water to hold more oxygen,” says Hansell. “That helps with energy efficiency in the winter.”

Priming the process

The utility has also saved money with other process enhancements, including:

• Sending scum from the scum pits to the thickener instead of the digester.
• Turning off the return activated sludge pumps for an hour before wasting when the sludge blanket is less than 2 feet. This allows a thicker blanket to build so that less water is pumped and more solids are wasted into the thickener.
• Decanting the biosolids thickener so that less phosphorus in the supernatant is recycled back to the plant, saving on chemicals.
• Decanting the digester to use space more efficiently for biosolids treatment.
• Running the belt press on second and third shifts to use cheaper off-peak power.

Operators use a customized program to track nutrient values and optimize chemical dosage. “It gives us the daily, monthly and yearly highs and lows of nutrient readings in each BNR section,” says Brito. “That allows us to monitor seasonal changes in the wastewater.” That in turn allows operators to respond before problems occur.

“We can monitor phosphorus, nitrate and nitrite levels from 10 sample spots,” Brito adds. “We have about a year and a half of data.”

Reclaiming the water

Beyond cost savings, a major process improvement involves wastewater reclamation. In 2013, Plant 2 used some 3.3 million gallons per month of reclaim water for washdown, clarifier and belt press sprays, and plant site irrigation. More was distributed as irrigation water for homeowners, golf courses, crops and public access areas. Plant 3 plans to start producing reclaim water for irrigation in 2015. “We have made the necessary equipment upgrades, and our pumping and storage facility is under construction now,” says Brito.

An industrial pretreatment program involving three major customers is working well under the watchful eye of Terry Carver, chief operator at Plant 2. A fats, oil and grease program helps prevent sanitary sewer overflows and plant process upsets. “We instruct restaurants on best management practices to help reduce grease trap pumping frequency,” Hansell says. “That saves them money in hauling costs while preventing grease from entering the sewer system.

“The city is aggressively tackling this issue by maintaining communication between the city, businesses and haulers so everyone can stay in compliance. This allows all involved to focus on their business rather than on clogged pipes and overflows.” Inspections, enforcement and a preferred hauler program contribute to success.

Experienced team

Most of the plant operators have been with the utility for at least 10 years and were there during the Plant 3 upgrade. “Carlos came to us with experience at a similar plant, so he has been able to help train the operators on the process,” says Hansell. “The most difficult piece for them to learn was the new PLC and how it can be used to optimize the process.” They learned as they went with training support from the device vendor.

The utility plans to continue the cost reduction program. “The more we can reduce our costs, the better,” says Hansell. “Meanwhile, our goal is to beneficially reuse treated effluent in innovative and environmentally sensitive ways. In all that we do, our focus is on environmental stewardship and being the leaders in our community. Solar energy is an option we plan to consider and evaluate in the very near future.”

She would also like to look at producing Class AA biosolids: “It is expensive to haul biosolids away to the landfill. We own 400 acres, so we just need to figure out how to make biosolids management cost-effective and what the payoff is.”