When the Newtown (Conn.) Wastewater Treatment Plant had trouble meeting its nitrogen limit, the plant manager, operator and mechanic worked as a team to improve nitrogen removal and dissolved oxygen (DO) control, while reducing energy costs.

“Our nitrogen limit in 2006 was 24 pounds a day, which the plant wasn’t achieving,” says plant manager Julio Segarra. “The oxidation ditch was hard to manage, since the drive for the mechanical mixers ran on high speed most of the time. What we really needed was a variable-speed drive.”

An aeration system upgrade in 2007, followed by exceptional teamwork from the plant staff, improved DO control, which in turn improved nitrogen removal and reduced electrical costs by controlling the speed of the mechanical mixer based on DO demand.

The effort paid off: In 2009, the plant was nominated by the state Department of Energy and Environmental Protection for an EPA New England Region 1 Wastewater Treatment Plant O&M Excellence Award, presented in 2010 at the New England Water Environment Association’s (NEWEA) annual conference in Boston, Mass.

 

Activated sludge plant

Built in 1997 and operated by United Water since 2004, the Newtown plant treats an average of 0.5 mgd and serves 1,126 residential and industrial customers. The influent is screened (Lakeside Equipment) and then pumped through a Jones + Attwood grit chamber (Ovivo) before activated sludge treatment in two oxidation ditches in parallel, each with a mechanical aerator (Ovivo).

A portion of the flow is recycled to a smaller anoxic tank (Ovivo) at the front of each oxidation ditch to help remove nitrogen. The wastewater flows to secondary clarifiers (Ovivo), and the secondary effluent is treated with sand filters (Ovivo), followed by Fisher & Porter UV disinfection (Ironbrook Partners) before discharge to the Pootatuck River.

A portion of the activated sludge from the secondary clarifiers is returned to the oxidation ditch, and the rest is wasted and thickened by a gravity belt thickener (Ashbrook). The biosolids are pumped to a tanker truck for off-site incineration.

Besides Segarra, the staff includes mechanic Thomas Maugeri and operation and maintenance technician Mark Byrns. Maugeri has been with the plant for five years. Byrns has been with the plant for a year and holds Class I operator, Class II collection systems, and E-2 electrical licenses.

Segarra has been with the plant seven years and holds Class IV wastewater and collection licenses, and an E-2 electrical license. He gained electrical experience from working in the steel industry and is now working on his water treatment license. In 2003, he received the NEWEA Operator Award for Excellence in Plant Operations for improved operations and maintenance at the plant.

The team oversees five pump stations, 89 simplex and 11 duplex grinder pump stations, and 23 miles of pipe. They also manage the Fairfield Hill Water Treatment Plant in Newtown, along with two wells and the distribution system.

 

Getting it done

With only three people on staff, everyone works very hard. “There is a lot of operations and hands-on involvement required to maintain quality and customer service,” says Segarra. “During disinfection season, May 1 through Sept. 30, we operate and maintain a UV disinfection system, periodically running one bank and taking the other offline so we can hand-wash and clean all the mechanical parts. The staff assists each other, and our strong point is that we are all very versatile.”

A joint training program between United Water and the town’s public works department has proven valuable in emergencies. For example, during 2011 summer storms, the public works crews cleared downed trees so United Water crews could reach the remote pump station.

When roads were closed from fallen trees, DPW directed United Water staff to clear the roadways. They also helped keep the generators fueled and operating. “It was a great collaborative effort to maintain services to the public,” says Segarra.

The plant contracts out the programmable logic controller repairs, bearing replacements and state-mandated calibrations. The Newtown staff tests for turbidity and pH, but most water samples are sent to an off-site certified lab.

Wastewater plant operators take turns driving to the water treatment plant, where they perform routine checks on pump operations, chlorine and phosphate residuals, tank levels, and plant security. They also track the amount of treated water sent to the distribution system. The plant, wells and storage tanks are monitored 24/7. The alarm service provider, Precision Alarms, receives automatic alerts if anything goes out of parameter so that they can immediately contact a plant staff member.

Staff members conduct plant tours for the community and school groups and take part in community health fairs. “We offer our plant to the local chapter of Trout Unlimited so they can conduct microinvertebrates research,” says Segarra. “They take water samples from the Pootatuck River adjacent to our plant, and they sometimes use our conference room for meetings and training.”

 

Aeration improvements

The 2007 plant upgrade, Segarra’s first project as plant manager, was a joint effort between the Newtown water and sewer authority, the public works department and director Fred Hurley, and Jason O’Brien, area manager for United Water.

“I’ve worked in other plants, but it wasn’t as easy to make changes,” says Segarra. “The relationship we have with Newtown and its leaders is second to none.”

When the plant had trouble meeting its nitrogen limit, the water and sewer authority and United Water made the commitment to upgrade the aeration system. That meant replacing the 75 hp two-speed motor on the second oxidation ditch aerator with a variable-frequency drive (ABB Inc.) with DO control (Royce Technologies – a Xylem Brand).

Now the aerator can operate at the speed required for optimum DO in summer and winter. The variable-frequency drive results in better nitrogen removal and helps lower energy costs. Segarra and his staff spent six months fine-tuning the aeration system. To learn how to operate the new equipment, the staff read manuals and talked to the design engineers. “As can happen with new equipment startup, we had a few challenges,” Segarra says.

For example, placement of the DO probes was influenced by the mechanical mixer, which allowed high DO to bleed into the anoxic portion of the oxidation ditch. By monitoring and tweaking the probes, operators were able to reposition them and establish a set point of 0.9 mg/l to control the nitrification portion of the ditch.

“The DO probes were constantly fouling,” says Segarra. “After monitoring the situation, I made a special device to prevent materials in the wastewater from collecting on the probes, resulting in consistent DO readings and reduced maintenance.” The probe is inserted into a special PVC sleeve, which is then suspended into the oxidation ditch.

The plant meets its nitrogen limit of 19 pounds per day, with an actual output of 18 pounds. “In Connecticut, we have a nitrogen credit program,” says Segarra. “Before the upgrade, the water and sewer authority had to pay $6,000 in credits for not meeting the permit limit. Since the upgrade, they have received a check every year for $800.”

 

Energy savings

The Newtown plant has reduced energy by about 30,000 kWh per month by installing the variable-frequency drive and operating the mixer in a narrow range of +/- 15 percent speed.

The plant reduced natural gas consumption in the filter building by reducing the number of fresh air exchanges. “By resequencing our HVAC system we reduced the outside fresh air intake,” says O’Brien. “The intake had been 100 percent, but we were exhausting all the air, so we reduced the intake by 75 percent and shut off the exhaust.” United Water had OSHA come in and test the air, and they determined that it was of good quality for the employees.

Natural gas use has dropped from about 9,000 cubic feet per month during winter to less than 2,000 cubic feet. In 2008, the town public works department received the platinum award for energy conservation from the Connecticut Department of Public Utility Control for the largest energy reduction in Fairfield County.

 

Operating challenges

The plant’s greatest challenge, according to Segarra, is “balancing demands with a small staff and consistently meeting permit and effluent quality.” Weather is also a factor, as heavy rains can bring significant inflow and infiltration (I&I).

“We had some high flows in the spring of 2011, and we’ve had I&I of 0.5 mgd and as high as 2.0 mgd,” Segarra says. The water and sewer authority purchased monitoring equipment for the collection system to pinpoint the sources of I&I.

By monitoring, the plant staff was able to detect high flows and divert a portion of the influent to an offline tank to maintain the process. “It’s important to keep track of the weather and to prepare for it, because the last thing any operator wants to do is bypass; that’s our bad six-letter word!” Segarra says.

The staff prepares by communicating, planning, reviewing procedures, monitoring weather conditions, and making changes only when necessary. In some cases, they reduce solids inventory. They also watch all operational parameters, such as solids levels in the tanks, sand filters and headworks.

Another challenge is the occasional issue with industrial customers. Local industries include a paper box manufacturer, a cable communications company and a NASCAR racing team.

“We have had to stay on top of some industrial effluent,” says Segarra. “In the past, we had a copper violation and found that an industrial plant’s solids were carrying copper to our plant. Once we identified the source, we worked with the company to correct the problem.”

 

Future upgrades

The plant is scheduled for an upgrade to the 14-year-old SCADA system, which now allows alarm monitoring only. The new SCADA system will improve operations tracking and history. “As EPA rules become more stringent, we need tighter control of our operational parameters, and that’s where the SCADA comes in,” says Segarra. The project is scheduled to start in 2012.

Another planned upgrade is to radio telemetry, Ethernet and fiber optic communications, and data transfer systems that will tie into the wastewater plant, the remote wastewater pump stations, and water treatment plant. Says Segarra, “At one test location, the water and sewer authority has improved security by installing live streaming monitors directly to the police department.”

The water and sewer authority has approved a solar power project, to start in 2012, that will reduce the plant’s power use by about 30 percent. During optimal days, the plant will be 100 percent solar powered. “We’re trying to stabilize our costs over time, and the solar project will help us achieve that,” says Hurley. “We may look at wind power down the road, but that’s on hold right now.”