To call the Peirce Island Wastewater Treatment Facility a success story is an understatement.

The plant, recently upgraded to advanced secondary treatment and nitrogen removal, is actually several success stories.

The $92 million, four-year upgrade was completed on a very small footprint without upsetting the existing primary treatment facility. Public acceptance was achieved through a comprehensive education and information campaign.

Adjoining parkland, including trails, a public swimming pool and natural areas along the Piscataqua River were not compromised nor disturbed. Effluent quality has been greatly improved, helping protect the river and the sensitive Great Bay Estuary. Construction traffic was managed to limit congestion.

As a result, the Water Environment Federation presented home city Portsmouth, New Hampshire, with a 2021 Project Excellence Award.

Significant upgrade

“Peirce Island is considered the jewel of the city of Portsmouth,” says Terry Desmarais, P.E., city engineer. The city evaluated sending all wastewater to its smaller Pease Wastewater Treatment Facility site, but that would have meant rerouting the entire collection system; it wasn’t feasible for technical and regulatory reasons.

Instead, Portsmouth built the new facility on the 3.7-acre site of the old plant, installing a space-saving BIOSTYR biological aerated filter (BAF) process from Veolia. The project also included new headworks, solids and electrical buildings, a gravity thickener and a standby electrical generator. Odor-control facilities were added, and the old biosolids processing building was converted to a laboratory and operations center.

The new facility has a design flow of 6.13 mgd and a peak of 22 mgd. It removes TSS and BOD by more than 80% over the old facility. Total nitrogen is reduced by more than 84%.

Desmarais, along with Glen Wilson, operations manager, and Peter Conroy, chief plant operator, agree that communication among all parties, especially the operations team, was the key to success.

Stepping up to secondary

While construction of the new plant took more than four years, the project’s origins go back to 2009, when the city entered a consent decree with the U.S. EPA to improve treatment. “We were one of the last plants in the country with a waiver of secondary treatment,” says Desmarais. Peirce Island had operated for more than two decades as a 4.8 mgd chemically enhanced primary treatment plant.

After comprehensive planning and public discussion, Portsmouth embarked on three technology pilots and selected the BAF system because it could achieve nitrification-denitrification in a small space. A second test of the BAF in 2014 confirmed its viability.

The system consists of upflow filters with biomass affixed to small polystyrene beads about the size of a BB. When the inlet valves are closed, the filters backwash using effluent water and the excess biomass is flushed into mudwells stacked below the filtration tanks.

Unlike the conventional three-stage nitrogen treatment common to other plants, Portsmouth uses a space-saving two-stage system. Carbon removal and nitrification take place in the first stage, while denitrification occurs in the second.

Ahead of the BAF system, wastewater is pumped to the headworks, which includes influent screens (HUBER Technology) and aerated grit chambers. The flow then passes through primary clarifiers and into a primary effluent distribution box. From there the wastewater passes through the first- and second-stage BAF tanks. Backwash water is returned to the primary clarifiers, which co-settle the excess biomass with the incoming wastewater.

Sodium hypochlorite is added ahead of the chlorine contact chambers for disinfection, followed by sodium bisulfite for dechlorination before discharge to the Piscataqua River.

To control odors, which had caused summer complaints in the past, the primary clarifier launders and aerated grit chamber are covered; exhaust air is directed to a carbon adsorption system (Calgon Carbon). A second Calgon Carbon adsorption system controls odors from solids processing.

An iFix Wonderware system monitors and controls plant operations. Maintenance is managed through JobCal (Hach) and Fiix (Rockwell Automation) work order development systems.

Co-settled filter backwash solids and influent solids are pumped from the primary clarifiers to a gravity thickener and then to storage tanks. Polymer is added before dewatering in screw presses (HUBER Technology). Trucks haul cake to landfill. Water started flowing through the new plant in January 2020, and the plant began meeting its effluent permit limits by April.

Energy and environment

In keeping with its efficient and space-saving design, the upgraded Peirce Island facility incorporates sustainability features that save energy and protect the environment. Over 18,000 cubic yards of rock had to be excavated for construction, but the waste rock was ground and used for backfill on site. That saved on disposal costs and reduced truck traffic.

High-efficiency blowers power the BAF system. Because there wasn’t room for separate blowers at each cell, four blowers feed a single header that distributes air to all the cells.

Stormwater drainage from the site flows to a rain garden. Excess storm flow passes through catch basins to trap debris and floatables so they won’t be discharged to the river. Solar panels provide water heating and warm up external air for building heating. In-plant heating and lighting systems are all high-efficiency.

Effluent is recycled for in-plant uses. Natural stone was used for revetments around the plant property; concrete would have been unsightly and less effective. The stone matches the outcroppings on the island and provides stability for the sloped shorelines around the plant.

On the fly

Building a new plant on the site of an operating system is nothing new in wastewater treatment, but each overlay presents unique challenges and requires ingenuity and flexibility. According to Conroy, the keyword at Peirce Island was “temporary.”

For example, the new gravity sludge thickener structure was used as the primary sludge pumping station — temporarily. A temporary electrical system was rigged overhead to keep the old treatment system linked together as the old underground electrical duct banks were demolished.

All of this occurred while maintaining treatment to meet the interim effluent permit limits stipulated in the consent decree. This required significant planning for construction phasing because the facility receives significant wet-weather flows.

Perhaps the most significant adjustment was temporary relocation of all the operators, laboratory, engineering and management staff to a cluster of trailers near the construction site. “It was not easy,” says Desmarais, “Because the displacement of personnel from their normal workplaces lasted for more than three years. I am extremely proud of the staff and their patience with the inconvenience, especially during the COVID pandemic.”

Let’s talk

With so many teams working in a small space at the same time, it was critical for communications to remain clear and open to everybody. “Maintaining communications, especially during wet weather events, presented challenges,” says Desmarais. “Our operators were up to the challenge and did an amazing job. It was what made this project successful.”

Conroy adds, “Staff morale was an obvious concern. We had to make the extra effort to keep our team together as best we could. Besides Conroy and Wilson, the Peirce Island staff includes Jake Rogers, assistant chief plant operator; and operators Kevin Daley, Kathy Sanborn and Eric Gulbicki. One operator position was open as of December 2021.

The staff is onsite for one daily eight-hour shift a day, Monday through Friday; one person is on on-call for the remaining hours. Conroy says it was critical for the engineering team of AECOM and the contracting crew of Methuen Construction to work with the operations team so that operators knew what to expect: “It was important that we not wear out our staff with unanticipated changes or interruptions.”

Face-to-face meetings were the most effective means of communication, Desmarais believes: “We met every morning. We talked about what was going on that day. It was always a challenge to make sure there wasn’t a loss of communication.”

There were hundreds of meetings, and they involved all parties involved in the project, even down to the contract haulers. “The group worked as a solid team with the engineers on site, working closely with the contractor and all communicating with the city’s operators,” Desmarais says. “We were lucky to have the team we did for this project.” 

Training on the new processes was just as important. “We did a lot of training; it was a whole new process for us,” says Conroy. “We did it one building at a time, starting with headworks.” COVID had an impact because of travel restrictions, and manufacturers often had to offer training remotely via Facetime, Zoom calls or email checklists.

That puts more burden on the staff because it’s easier to do troubleshooting when manufacturers’ representatives are onsite, says Conroy. “A lot of the time they’d have to ask us what we were seeing. But they did readjust and support us well.” The plant had only minor deviations from its permit, usually related to construction, or when a process unit was taken out of service and replaced with a new system.

A happy ending

The Peirce Island upgrade was the biggest capital project the city of has even undertaken. Did it deliver a bang for their buck? A look at the effluent numbers and the quality of the water in the Great Bay Estuary clearly says the answer is yes.

BOD and TSS average less than 10 mg/L, and total nitrogen, restricted to no more than 8 mg/L in the consent decree, averages 3-4 mg/L. Desmarais observes, “We went with a conservative design because, even though we had no specific nitrogen limit for the new plant at the time of design, we knew what may be coming.”

The water quality on the New Hampshire coast and throughout New England is critical for several reasons, Desmarais notes. The estuary is listed as “significant” by the EPA and is part of the National Estuary Program.  

“Fishing, lobstering, boating, diving, all are dependent on clean water in the estuary. Just off the point where our plant is located are reefs containing rare red-gilled nudibranchs (sea slugs), and divers go down to get a look at them when they open up and change color in the winter months.”

Operations manager Wilson may best summarize the success: “When you compare what was going out to the river before, when the facility was a chemically enhanced primary plant, and what’s going out now, the difference is dramatic. It’s a great benefit to the environment.”