These days, Arnie Bevins is even more focused on ensuring the future well-being of the treatment works and its staff than on making the monthly permit at his Town of Vernon (Conn.) Water Pollution Control Facility.

He makes sure that extensive Standard Operating Procedures are up to date and readily available, and that new people are brought on board and trained on the innovative and complex processes that make Vernon unique among treatment plants in New England and across the United States. Furthermore, the Vernon staff has been “hands-on” throughout the many improvements and upgrades to the plant.

“We were the first full-scale powdered activated carbon treatment and wet-air carbon regeneration system on planet earth,” says Bevins, assistant director of the Vernon utility and superintendent of the plant. “A lot of us grew up with this plant and the process. We want to make sure we leave it in good hands.”

It’s in good hands now, discharging pristine effluent to the Hockanum River, which includes a state-designated wild trout management area not far downstream.

The operational excellence, budget controls, customer satisfaction and employee retention exhibited by Bevins and his staff recently earned the Vernon utility the New England Water Environment Association’s outstanding wastewater utility award earlier this year. “There were six finalists,” says Bevins. “It’s great to be recognized.”

How it works

While Bevins is known for his wry sense of humor, he wasn’t kidding about his plant being the first of a kind. The facility serves the towns of Vernon, Ellington, Tolland and small parts of South Windsor and Manchester, taking in wastewater from 122 miles of sewers and seven pump stations.

At its heart is a powdered activated carbon treatment (PACT) system from Siemens Water Technologies — Zimpro that incorporates powdered activated carbon with biomass in the aeration basin to achieve biophysical treatment.

The process removes color and nutrients and produces near-drinking-water-quality effluent. Powdered carbon, with substantially more surface area than granular carbon, adsorbs pollutants and acts as a site for the microorganisms to enhance their uptake. Vernon operates the aeration basins at about 12,000 mg/l mixed liquor suspended solids, and the return activated sludge content ranges from 20,000 mg/l mlss to 25,000 mg/l mlss.

The Zimpro wet-air regeneration system recovers the carbon and essentially eliminates the need for secondary sludge removal, reducing costs by about $400,000 a year. Recovered carbon is recycled to the aeration basins through a metering system. Makeup carbon is stored in a carbon silo and added as needed.

Installed in 1979, the PACT process was the first of a number of similar systems that have been used to treat municipal wastewater as well as industrial wastes and landfill leachate over the past 30 years.

To the river

Ahead of the PACT system, a 10,000-square-foot building houses the preliminary treatment system, which includes a coarse screen followed by automatic fine screens (FMC Technologies), and a Waste Tech (A Division of Kusters Zima) and Jones & Attwood (Ovivo) Jeta cyclonic grit removal chamber. Removed solids are classified, washed, and compacted before being landfilled. The equipment is enclosed because the plant is next door to a large apartment complex. A 25,000 scfm scrubber (Xerxes and Heil Process Equipment) collects and treats odorous air.

The wastewater is then lifted by screw pumps (Siemens – CPC) to the primary clarifiers, and the overflow moves on to the PACT system. Effluent from the secondary clarifiers (Siemens – Envirex) passes through four Leopold (ITT Water & Wastewater) dual-media sand filters and is chlorinated-dechlorinated (Pulsafeeder) during warm months.

Effluent is aerated year-round to maintain a dissolved oxygen level of 7 mg/l. “Based upon Department of Environmental Protection calculations, about 85 percent of the river’s flow below our plant is treated effluent,” says Bevins. That and the downstream trout habitat explain the plant’s strict effluent requirements.

Primary sludge is thickened in a pair of 35-foot-diameter thickeners (AMWELL), then trucked to an off-site merchant incinerator. About half a million gallons of primary sludge is handled that way each year.

The regeneration process uses heat and pressure generated by Ingersoll Rand compressors and Zimpro high-pressure pumps to oxidize secondary solids amassed on the carbon and produce a reusable carbon and a small amount of ash, which is periodically blown down and landfilled with the plant’s grit and debris.

Keeping control

A 2,700-point PLC-based SCADA system (GE Intelligent Platform fed by 28 Allen-Bradley PLCs from Rockwell Automation) provides automatic control of the entire plant operation. The treatment process also handles outside high-strength wastes that haulers bring to the plant under a state waste acceptance permit. “This is wastewater that’s difficult to treat in conventional systems,” says Bevins. “We have 10,000 to 15,000 gallons a month. It more than pays for itself, plus we know where this stuff is going.”

The plant also maintains its own laboratory, and Bevins credits his lab staff with accurate sampling and analysis. “Our lab people do the bulk of the sampling and analysis, with the exception of metals,” he says. “They handle all of our process control testing. We have good consistency in our data. Our staff represents a real value to us. They know in an instant when something is not right.”

Operations funding comes from an Enterprise Fund administered by the Vernon Water Pollution Control Authority, matching rates to expenses. Bevins likes that approach, because “It takes the politics out of it. We bill against water consumption.” He says the rates are “normal” for his area at about $5.60 per thousand gallons.

Making things better

As with all newer processes, the treatment train at Vernon has undergone a number of modifications and improvements in the 30-plus years since its initial operation, with substantial help from the plant’s 20 employees.

“All the other PACT systems out there use coarse-bubble diffusers in the aeration basin,” says Bevins. “We were spending about half our yearly energy budget on the aeration system.”

To reduce costs, Vernon investigated fine-bubble diffusers with automated controls and decided on Environmental Dynamics International fine-bubble tubular membrane diffusers with controls from Dresser Roots.

“Tom Jenkins is their main controls guy, and he helped us implement three zones in the aeration tanks,” says Bevins. “The header in each zone was upgraded with an automatic control valve and airflow meter.” The system automatically moves air around based on both DO levels and mixing air requirements, and reduces air when it’s not needed. “The control system alone is saving us $50,000 a year,” says Bevins.

The diffusers also save energy and money, since Connecticut Power and Light has a program that reimburses customers for 50 percent of the cost of energy-saving projects. “That was a big deal for us because they paid us $365,000 based on our project cost (for new diffusers and controls) of $730,000,” says Bevins. “As a result we trimmed our overall energy expense by about $200,000 per year.”

In addition, fine-bubble aeration has reduced turbidity to negligible levels. “We always had some turbidity here, but two days after going to fine-bubble, our turbidity dropped to as low as 0.5 NTU,” Bevins reports.

Foaming was another challenge. A 1992 design included a chlorinated spray system to beat down foam, but after analyzing the process dynamics relative to the plant’s nitrification requirement, the Vernon crew put more tankage online and gradually ramped up sludge age, taking the plant through the point where filamentous proliferate — 23 to 24 days sludge age. As a result, the plant no longer experiences foaming.

“We don’t make sudden changes, so this was a major leap of faith,” Bevins recalls. “It’s not for every PACT plant, but it certainly worked for us.”

Other important changes implemented by Team Vernon include modifying the original two-stage aeration setup to a single-stage plug flow operation and raising the walls in the lower tank so that all tank contents are on the same level. “By making all our surface elevations consistent, we get better distribution and it’s more cost effective,” says Bevins.

The plant has also eliminated chlorine gas, converting the disinfection step to liquid hypochlorite, followed by dechlorination and post-aeration.

Regenerating the regen unit

The wet-air regeneration unit is critical to treatment at Vernon because the process regenerates the spent powdered carbon while oxidizing the secondary sludge. Without it, the plant would pay much more for fresh carbon and secondary solids handling.

Bevins and the team have taken special care of the system over its 30-plus years of hard work. “When we rebuilt the unit, we sole-sourced the manufacturer and worked with the same technical specialists who helped us install the system in the first place,” he explains.

Operational experience indicated that the original system did not have enough heat exchanger area, and that prevented autothermal operation, which requires no ongoing fuel source. The manufacturer (Siemens) supplied a new heat exchanger bundle, essentially doubling heat exchanger capacity, and worked with Vernon to rebuild the high-pressure pumping system with new balls and seats along with significant improvements to the process controls.

In another modification, Vernon uses an equalization tank to hold the recycle stream from the regeneration step, which is high in BOD and ammonia. The recovered carbon is metered from the tank back to the PACT system, and the distribution of the liquid back to the head of the treatment works can be controlled.

Looking ahead

The managers at Vernon have worked hard to get the treatment plant performing at an outstanding level, and they want to make sure the next generation of operators and managers does the same. Bevins is constantly on the lookout for potential operators who can be recruited and trained to run the plant.

Newly hired operators-in-training are required to take the Sacramento State University wastewater courses, volumes I and II, and earn their Connecticut certification within their first year on the job, an approach Bevins says is working out well. “It gets them up to speed,” he says. “Basically, we’re replacing ourselves.”

The staff members also get plenty of practical experience and intimate knowledge of the plant because they’ve been heavily involved in the process improvements. “When we make changes, we don’t rely solely on consultants to make our decisions for us,” says Bevins.

“When we began design on our last $38 million upgrade, we took our guys and effectively locked them in a room with pizza and soda and had them write down what they felt was wrong on sheets of paper. These were labeled by unit processes, and we worked with them to determine the things that they felt needed to be changed. Then we would look at their ideas and proposals and decide whether to address them and incorporate them into the new plan.”

It’s an approach that helps Bevins feel confident about the future of wastewater treatment in his town. He recalls one of the early process improvement projects that went to a low bidder and didn’t turn out so well. “You have to fight for what you believe you need,” he tells his new team of operators. “You’re left with what you’re left with, and you’ve got to make it work. Make sure you get the equipment that you have to have.”