Florida Treatment Plant Transitions to Sophisticated Step-Feed Biological Nutrient Removal

Upgrades and automation keep the process running smoothly and effluent in compliance for the operations team in Eustis, Florida.
Florida Treatment Plant Transitions to Sophisticated Step-Feed Biological Nutrient Removal
The Eustis Wastewater Treatment Plant team includes, front row, from left: Bill Johnston, superintendent; and Rick Houben, utility supervisor; second row: Herb McNealy, utility worker III; and Walt Linton, utility foreman; third row: Sophia Swoboda, lab manager; Jim Eaton, utility worker II; and Keith Leflore, environmental compliance inspector; back row: Michael Brundage, operator B; Jerry Johnston, operator B; Cory Savage, operator C; J.D. Styles, operator C; Luther Bodie, lift station operat

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The Eustis Wastewater Treatment Plant went online in 1959 with a 1.0 mgd trickling filter process. Fifty-seven years later, it’s a 2.4 mgd facility with sophisticated step-feed biological nutrient removal (BNR) and tertiary filtration; 100 percent of the effluent is reused for irrigation and plant processes.

Periodic upgrades have kept this central Florida plant in step with increasingly strict permit requirements. The latest upgrade in 2012 established the BNR process, controlled with advanced automation and overseen by an experienced and thoroughly trained staff of 18.

“During the upgrade we did an entire retrofit of our SCADA system and lift station monitoring,” says Rick Houben, utility supervisor. “The SCADA system now can do plant monitoring, alarm notifications and process control. It also provides notification of alarms to our standby staff by text message, enabling quicker response.”

The plant received a 2013 Domestic Wastewater Operations Excellence Award from the Florida Department of Environmental Protection (DEP) for outstanding operation, maintenance and compliance. It also won the 2015 Earle B. Phelps Award from the Florida Water Environment Association for outstanding performance and professionalism.

Maintaining stability

Eustis is an inland lake community of 23,500 about one hour north of Orlando. The treatment plant’s flow is residential except for contributions from a vegetable processor and local restaurants.

The original trickling filter plant was expanded in 1970 to its current 2.4 mgd design capacity to accommodate growth. As permit requirements tightened, it was converted in 2000 to an extended aeration process. “That process used a series of surface aerators that were troublesome to maintain,” says Houben. “We were unable to nitrify, and no denitrification system was in place to denitrify. The tertiary filters did not have the necessary modes to have a denitrification system installed.”

In 2012, the step-feed BNR process went online. Existing tanks were retrofitted for that purpose, and the surface aerators were replaced with turbine blowers and a fine-bubble diffusion system for aeration, nitrification and ammonia conversion. Tertiary filtration polishes the effluent for distribution through a reuse system that serves golf courses, parks, sports fields and residential landscapes. Relatively consistent influent and extensive automation help keep the process highly stable, ensuring consistent effluent quality.

Controlling quality

Forty-three lift stations deliver wastewater to the plant’s master pump station, equipped with four 30 hp submersible pumps (Flygt - a Xylem Brand). Pump speed is controlled with variable-frequency drives (VFDs) to keep the flow balanced through the plant. “One reason that is so critical is that we use our influent flowmeter to stabilize and adjust all our chemical feed rates, internal recycle pump rates and sludge return rates,” says Houben.

“The more even we can keep the flow, the better our process performs.”

Preliminary treatment consists of bar screens (Parkson Corp.), a cyclone de-gritter (Ovivo) and an auger (WesTech Engineering) that removes the grit for disposal. The secondary process is split into a 1.4 mgd Phase 1 and a 1.0 mgd Phase 2. At present, only Phase 1 operates as it readily handles the 1.07 mgd daily average flow. “However, we can easily divert flow to Phase 2 when required, as it has sectioned common wall construction,” Houben says.

In the BNR process, air is delivered by four VFD-equipped Aerzen TB turbo blowers through more than 700 fine-bubble diffusers (Aquarius Technologies). Inline sensors (Hach) communicate with the blowers by way of the SCADA system to keep dissolved oxygen and ORP at optimum levels. The DO ranges are maintained at less than 0.4 mg/L in the anoxic basins and 2.0 mg/L in the aerobic basins. The ORP is maintained at -100 mV to +100 mV in the anoxic basins and greater than +100 mV in the aerobic basins.

After the secondary clarifiers (Ovivo), the water travels to four AquaDisk cloth media filters (Aqua-Aerobic Systems). “TSS and turbidity are analyzed before chlorination,” says Houben. “We have standardized with Hach analyzers for these and for chlorine residual measurement.” The reuse water is then highly disinfected using bleach (Odyssey Manufacturing) in two chlorine contact chambers to ensure that disinfection reaches the farthest residential user.

Waste activated sludge from the clarifiers (about 25,000 gpd) is pumped to two aerobic digesters and then to a belt press (Alfa Laval Ashbrook Simon-Hartley) that dewaters the biosolids to 14 to 16 percent solids. That material is trucked in 30-cubic-yard trailers to a contractor for composting and other beneficial uses.

The step-feed process

The Eustis plant’s step-feed process responds to a total nitrogen permit limit of 10 mg/L. Wastewater alternates between anoxic and oxic zones. Low-speed mixers (WILO USA) are installed where the former aeration basins were converted to anoxic basins.

Internal recycle pumps (dry-pit submersibles, WILO USA) were added to recirculate highly nitrified mixed liquor back to the anoxic tanks at a flow ratio of 2-to-1 (recycle-to-influent) for denitrification and to stabilize metabolic rates. A swing zone between the aeration basins further denitrifies the mixed liquor. The recycle rate is regulated automatically based on the influent flowmeter reading.

“It’s the same thing with the return activated sludge (RAS) coming from our clarifiers,” says Houben. “We use the same type of dry-pit submersible pumps for our activated sludge, which we return at a 1-1 ratio to the influent flow rate, based on the influent flowmeter output.

“We added VFDs to the internal recycle pumps and the RAS pumps to enhance functionality and to meet the return flow ratios required for denitrification and biological processes. The combination of the new pumps, turbo blowers and VFDs has reduced our overall electrical consumption by about 30 percent per year. It has also improved our effluent quality to far below permit requirements for nutrients, CBOD and TSS.

“An added benefit from updating our process is that the waste sludge is much more concentrated. The mixed liquor suspended solids inventory operates at 4,000 mg/L, rather than the 2,000 mg/L range we used when operating an extended aeration plant. That has increased the waste activated sludge concentration introduced to the digesters to 8,000 to 9,000 mg/L.

“As a result, we enhanced dewatering capabilities on the belt press, reducing our polymer consumption by 50 to 60 percent. In the past, we used two to three 55-gallon drums of polymer per month, at a cost of about $560 per drum. Now we use about half a drum per month for a monthly savings of about $1,000.”

Dan DeLeon, lead operator, notes that the process includes a backup carbon source feed system, which to date has not been used.

Making the transition

A key to adapting to the step-feed process was training the team. “Most of the operators at the time were new and had never run a facility before,” says Houben. “Training them up from extended aeration to a more advanced process and getting them comfortable with the new equipment and process controls was a pretty good challenge. They have adapted well, and they’re progressing readily on their advanced certifications.”

Senior personnel, notably DeLeon, laboratory manager Sophia Swoboda and utility foreman Walt Linton, led the in-house training and worked side by side with the newer people while they mastered the processes. The city also sent operators to training classes offered by the University of Florida’s TREEO Center, the Florida Water and Pollution Control Operators Association, and the Florida Rural Water Association.

The plant’s automated systems helped the team adjust quickly. The new SCADA system uses Evolution iFix 32 software (GE Intelligent Platforms). “Technically, we are supposed to be staffed 16 hours every day, but because of our SCADA controls, the DEP granted a variance to be staffed one shift per day, seven days a week,” Houben says. “The plant is monitored by SCADA from beginning to end. We have a SCADA room where the operators can monitor the process, and we do two physical walk-throughs per day.”

A Sci-Text system (Sanders Company) monitors the lift stations and other outlying facilities, including the water reuse distribution network. That system automatically sends alarms by text message to operators’ smartphones. They can then dial in to the system for more details about the issue.

In addition, supervisors and operators on standby duty have laptop computers that enable them to make equipment and process adjustments remotely.

“We were among the first plants in the state to employ something this unique, whereby we get alarms sent to each individual who is on call as a text message,” says Bill Johnston, plant superintendent. “It has been a big plus for us.”

Lab analysis also helps keep the process in control. Swoboda heads a nationally accredited lab that performs all analytical functions including chemical and microbiological testing. The lab also analyzes groundwater samples taken from wells around a sprayfield where excess final effluent was applied before demand for reuse water reached 100 percent of supply.

“We follow TNI standards (The National Environmental Laboratory Accreditation Conference Institute) which are based on the ISO 9000 international quality-control manual,” says Swoboda. “The quality-control requirements are substantial. We perform quality-control checks daily, weekly and monthly.”

Effective team

Houben credits his staff for the plant’s success. Besides DeLeon, Swoboda, Linton and Johnston, they include:

  • Operators: Ray Richardson, Class A; Jerry Johnston and Michael Brundage, Class B; Cory Savage and J.D. Styles, Class C
  • Lift stations: Luther Bodie and Pete Cyr, operators; Dana Marshall, mechanic
  • Utility: Jim Eaton and Herb McNealy, utility workers
  • Laboratory: Kathy McDonald, technician
  • Environmental compliance inspector: Keith Leflore
  • Administrative assistant: Vicky McGhee

“Through the years, I’ve tried to give operators ownership of their process,” says Houben. “Once we instill the knowledge they need to control the plant, I let them do their job. Even though they may make a slight error, I let them do it so they can learn from it. Having ownership gives them pride in their work.”

The city encourages team members to pursue higher state certifications from Class C (lowest) to Class A. “For each one of those licenses, we increase their pay,” says Houben. “That gives them incentive to increase their knowledge. And eventually as us older guys retire, they’ll have the training and better ability to fill our positions, so that’s another incentive.”

Challenges lie ahead for the team. Johnston notes that a solar biosolids drying process may be in the city’s future. Meanwhile, Houben expects demand for reuse water to exceed supply, which may warrant exploring the addition of stormwater to the reuse system: “That would take some further treatment, but it would give us the possibility of additional supply.”

A stricter total phosphorus limit — possibly 1.0 mg/L — may be in the offing for the next permit, to be issued in 2018. Meeting that likely would mean some form of chemical treatment. Whatever may come, Houben has confidence in his team.

“You don’t have to give them a list of tasks and work orders,” Houben says. “They find the work themselves. They’ll do the job as they see what comes up. We don’t have a mowing crew, but we have acreage that needs mowing. The staff has no problem using equipment to maintain the grounds on their own initiative. They’ll pressure-clean tanks, do maintenance on equipment, whatever is required. They perform very professionally.”

Delivering the water

The City of Eustis, Florida, operates an extensive distribution system for tertiary-treated effluent from its wastewater treatment plant. Initially, reuse water supplied irrigation for golf courses, and excess effluent was applied to a 264-acre sprayfield.

Effluent was delivered to lined receiving ponds. “For golf course irrigation, the water really didn’t have to be as high in quality,” says Rick Houben, utility supervisor. “But an open pond allowed a lot of contaminants to degrade the water quality.”

As irrigation expanded to include residential properties, it became more important to protect the reuse water. Two years ago, the city installed a 2-million-gallon inground storage tank about 1.5 miles from the treatment plant to replace the ponds. Now all the reuse water first goes there, except for what treatment plant personnel use on site.

From that point, a system of distribution pumps and hydropneumatic tanks maintains pressure to serve nearby ball fields and residential neighborhoods. A second storage tank holding 1/2 million gallons serves homes and golf courses farther from the treatment plant.  

“We keep the effluent chlorine residual relatively high, at about 5 ppm, to eliminate any possibility of pathogens,” Houben says. “Because our system extends close to 10 miles, we need to ensure that our residential users have adequate residual chlorine at the point of use.” The effluent residuals are measured by Hach CL17s chlorine analyzers.

From the chlorine contact chambers, an effluent pumping station with four Deming vertical turbine pumps (Crane Pumps & Systems) sends the reuse water into the distribution system.

A side benefit of increased reuse water demand is reduction in the size of the sprayfield, notes Bill Johnston, treatment plant superintendent. “We’ve just started leasing 200 acres of the sprayfield for cattle grazing,” he says. “It was a large area that had to be mowed, and that cost a lot of money.

Now we’re getting paid for use of the land, and it’s being grazed for us.” Revenue amounts to $15,000 a year, on top of $20,000 savings on mowing expenses.


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