How do you accommodate a two-year upgrade of a treatment plant, change over to new processes, keep staff abreast and involved, and maintain effluent compliance — all while dodging contractors, engineers and equipment suppliers?

In St. Charles, Illinois, Chris Rebone, wastewater division manager, says it takes a proactive and patient approach, open communication between departments, and the willingness to make mistakes and learn from them.

He should know. From 2017 to 2019, the city’s Main Wastewater Treatment Facility underwent a game-changing renovation that added a new biological phosphorus removal process, rehabilitated the digestion and biogas systems, and added other new equipment and processes.

Rebone gives credit for the successful transition to his staff of Samantha Metallo, assistant division manager; Dan Massa, John Huver, Steven O’Neil and Steven Streich, certified wastewater operators; James Smith, wastewater technician; and Richard Wadda, laboratory technician.

“It took a lot of ingenuity on their part,” he says. “I can’t thank our people enough for their due diligence and attention to detail. They accepted the challenge and ran with it.”

Extensive upgrade

The Main Wastewater Treatment Facility is one of two at St. Charles. The Westside plant treats 0.6 mgd on average and has a 0.7 mgd design capacity. The Main facility (9 mgd design, 7 mgd average) has Muffin Monster screens (JWC Environmental) in the influent pumping stations, followed by primaries, biological treatment, final clarification and UV disinfection (TrojanUV). Effluent discharges to the Fox River.

Biosolids are stabilized in a pair of egg-shaped digesters (Walker Process Equipment, A Div. of McNish Corp.), dewatered on Alfa Laval centrifuges, stored at the Westside plant and spread on corn and soybean fields in fall. Biogas powers the plant’s Walker Process Equipment boiler and heat exchanger system.

New state-imposed phosphorus removal requirements led the city to undertake the $17 million plant upgrade to biological phosphorus removal. Rebone says it made sense to rehabilitate the digesters and biogas system while the rest of the plant was under construction: “We thought it best to do everything at once.” The project involved:

Converting to a three-stage anaerobic-anoxic-oxic (A2O) system, with aerobic, anoxic and anaerobic zones for biological phosphorus removal

Adding a new internal recycle pump station

Adding a primary sludge fermenter

Adding ferric chloride for chemical polishing

Replacing a sludge storage tank and installing a new biogas storage tank

Rehabilitating the digester piping and operation systems

Upgrading the biogas system

Clearing the hurdles

Plant management had to install these improvements on the fly. The challenge was double-edged: maintain compliant operations during construction and be able to operate the new processes once the project was complete.

“We had to operate for a long time without our full biological system available to us,” Rebone says. Day-to-day operation was maintained, and the plant continued to nitrify while the new anaerobic and anoxic zones were being installed in the existing aeration basin.

“We were upgrading our air system, as well as adding new dissolved oxygen probes and blowers so we could operate our new aerobic zone with DO control,” Rebone says. “It was the middle of summer. That made it a challenge to continue to nitrify during construction and comply with our permit. The impact of restricted airflow also had an impact on our DO levels.”

That’s where the plant’s lab was critical. “We used Hach hand-held meters to monitor DO throughout the plant,” Rebone says. “The lab staff sampled DO at the tail end of the process. The lab took a harder look at sidestreams and their impact on our influent loading. They worked hand-in-hand with our operations staff. They went above and beyond the call.”

The staff also closely managed mixer speeds to maintain the minimum ORP values and optimized sludge age to maintain the required nitrification in the face of short solids retention times. Through these and other measures, the plant met its effluent permit of 98% removal of BOD, TSS and ammonia throughout construction.

Learning curve

While the new processes returned the plant to full biological treatment capacity, they also presented the team with much to learn.

“They had to learn a completely new process,” Rebone says. “Only one or two other plants nearby use the A2O process for phosphorus removal. Our operators took part in training and helped with standard operating procedures on their own time.”

The new process includes the anaerobic zone where phosphorus is released (1.5-hour detention time), an anoxic zone (three-hour detention time) and an aerobic zone with luxury phosphorus uptake (eight-hour detention time). Mixers from Philadelphia Mixing Solutions keep the anaerobic zone solids in suspension.

The aeration system incorporates Atlas Copco blowers and new DO probes (Hach LDO with Hach SC200 controller) to enable operation of the aerobic zone with DO control. An internal recycle pump station recycles 200% of the influent flow to the anaerobic zone, optimizing peak flows and loads to balance denitrification with phosphorus removal.

At the end of the aerobic zone, ferric chloride is fed by peristaltic pumps (Blue-White Industries) to chemically polish the effluent. The final clarifiers follow, and the overflow passes on to the UV disinfection units.

The staff experimented with mixing speeds to obtain optimum ORP levels for the new anaerobic/anoxic conditions. In addition, DO had to be balanced in the aerobic zone to reduce the amount recycled with the return activated sludge.

The solids side

More lessons were learned with the new primary sludge fermenter. The unit enhances biological phosphorus removal by producing volatile fatty acids and encouraging phosphorus to be incorporated in the cell biomass and removed through sludge wasting. With a detention time of three days, the biomass undergoes hydrolysis, along with acetogenesis and acidogenesis (biological processes that enhance the production of volatile fatty acids).

It all worked. Rebone notes that the bio-P project wrapped up on time, and the plant began meeting its monthly rolling average of 1 mg/L phosphorus just two months later, ahead of permit requirement.

On the digester side, the upgrade completely refurbished both egg-shaped digesters, bringing the capacity of each to 464,000 gallons. The internal piping systems and general digester operations were upgraded. The pumping and heating systems were replaced, the biogas storage capacity was expanded, and a new Walker Process Equipment boiler and heat exchangers were added.

Close coordination

Engineers and supervisors can’t accomplish such a complex project alone. Jerry Ruth, project manager for the Trotter and Associates engineering firm, says working through the many issues in the upgrade took extraordinary effort from city management, operators and laboratory staff.

“Through it all, they kept their positive attitude, cooperative approach and, most important, compliance with their permit,” Ruth says. “The Main Wastewater Treatment Facility is changed for the better, and the staff is better for it. If any plant deserves an award, it’s this one.”

Rebone credits the city administration for “being ahead of the curve and pushing the project before it was too late. It doesn’t always happen that those above you are willing to listen and take such a proactive approach.” And he notes that upgrading on the fly requires patience and the acceptance of wrong moves.

“Almost every decision you make will be right, but it’s good to be wrong sometimes,” he says. “It forces you to relearn things and can lead you down a different road. Be confident in your treatment approach and have patience. It takes some time.”

But the operations and lab staff came in for the most credit: “They knocked it out of the park.”