How to Run a Plant with Seasonal Fluctuations

The award-winning town of Hampton team finds ways to deal with substantial variations in seasonal flows and influent strength.
How to Run a Plant with Seasonal Fluctuations
The team at the Leavitt E. Magrath Wastewater Treatment Plant includes, from left, Bill Lowney, Marie Hall, Mike Dube, Mike Carle, Cliff Lavigne, Rob Pierce, Steve Aslin and Mike Moran.

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Public Works director Chris Jacobs sums up the challenges of treating wastewater in the town of Hampton, New Hampshire: “It’s like we’re trying to run a bakery, but the cake mix constantly changes.”

That’s largely because Hampton is an Atlantic beachfront tourist community of 15,000 whose population swells to as high as 30,000 in summer. On top of that, some 100,000 visitors may crowd the mile-long Hampton Beach on hot summer days. Adding to the difficulty, a brewery opened in town two years ago, and its wastewater sharply increased the BOD loading.

The job of finessing the Leavitt E. Magrath Wastewater Treatment Plant through those changes falls to a seven-member team led by Mike Dube, operations manager, and Mike Carle, chief operator. Aside from a hiccup here and there, the two have kept the plant running efficiently and in compliance with its permit since they arrived in the late 1990s.

Recent years have brought recognition for their work, in the form of a 2013 New Hampshire Water Pollution Control Association Plant of the Year award, a 2014 U.S. EPA Regional Wastewater Treatment Plant Excellence Award and a 2015 Environmental Champion Award from Aquarion, the private water company serving Hampton and nearby communities.

Ken Kessler of the New Hampshire Department of Environmental Services (DES) and Carl McMorran, operations manager of Aquarion, were instrumental in nominating the plant for two of the awards.

Dube says the awards are related to major improvements on a main oceanfront pump station and the plant’s biosolids dewatering equipment, both completed in 2013. Those projects helped the plant fulfill its role in keeping Hampton Beach among the cleanest in the country, while protecting the marsh and clam flats in the harbor.

Beach bonanza

The town of Hampton is best known for Hampton Beach, a wide expanse of state-owned oceanfront that draws visitors from a wide area. “Hampton Beach has a five-star rating as one of the best beaches around,” says Dube. “When the summer temperature gets above 90 degrees, everybody comes here to try to cool off.”

That means higher flows to the treatment plant. Design capacity is 3.9 mgd; the winter average flow is 2.2 mgd. In summer, seasonal residents push that to 2.7 mgd. On summer days when the beach is crowded, flows can spike.

“We can hit 4.5 mgd at midday, although it goes down to about 2 mgd overnight,” Carle says. “So the daily average is still below 80 percent of our design flow. We typically exceed 3.9 mgd on only a handful of days for the year, and usually those are rain events.”

The plant’s permit includes ammonia limits of 1.1 mg/L in summer and 2.7 mg/L in winter. Effluent ammonia is typically below the detection limit. “We’ve started tracking total nitrogen and are almost always below 5 mg/L,” Carle says. That parameter is not in the permit, but may be in the future, Dube observes. There is no phosphorus limit.

Refined process

The Leavitt E. Magrath plant was built in 1964 and received a major 1976 upgrade. It uses the modified Ludzack-Ettinger process. Influent enters the headworks building and passes through a bar screen (Headworks International). Rags and debris drop into a Screwpactor spiral conveyor/compactor (also Headworks) for dewatering. “It acts like a big sausage-maker,” Dube says.

The wastewater is then delivered to a bucket elevated grit chamber (Schloss) that dumps the material into a screw auger for dewatering. From there the flow goes to three wet wells, from which three Chicago pumps (Grundfos) rated for a combined 2,000 gpm deliver it to the primary clarifiers. “We typically run one primary,” says Dube. “We have two, and we put the other one on for storm surges or when work is done on the first clarifier. It’s nice having that redundancy.”

Primary effluent goes to the aeration system, first entering an anoxic zone. A recycle pump (Flygt - a Xylem Brand) delivers return activated sludge at a ratio of 1 1/2 to two times the influent flow. “We have that recycle pump hooked up to an ORP meter (Hach) at the tail end of the anoxic process,” says Carle. “The internal recycle pump used to operate at one speed.

Now the recycle rate fluctuates according to the ORP setting. That saves money on electricity.”

The anoxic zone is followed by three aerated zones. “If you picture a large square divided into four smaller squares, that’s the setup of our aeration tanks,” Carle says. “The flow goes through the tanks sequentially.”

From aeration, the flow moves on to three Tow-Bro secondary clarifiers (Evoqua Water Technologies). Two are typically online and the other is kept as a spare. Secondary effluent is disinfected with sodium hypochlorite and dechlorinated with sodium bisulfite before discharge to a tributary of the Tide Mill Creek.

Solids side

The Hampton plant sends undigested biosolids to landfill. Primary and waste activated sludges are handled separately before dewatering. Primary sludge goes through a gravity thickener (FMC) and waste activated material through a rotary drum thickener (Parkson Corp.).

From separate storage tanks, the materials are mixed in the pipeline that feeds a rotary press (Fournier). “On a blend of 20 percent secondary and 80 percent primary sludge, we produce cake at 22 to 27 percent solids,” says Carle. Plant personnel haul the material to the landfill.

In 2013, the team replaced an older four-channel dewatering press with the current six-channel unit (Fournier) at a cost of $1.3 million. “The old press didn’t have secondary-only dewatering capability because of the channel sizes,” Dube says. “So we went with smaller channels, which enable us to dewater secondary solids.

“As part of that project, we diverted the recycle water from the rotary drum thickener and the press so it goes into the wet wells instead of back through the headworks. The advantage is that we get a more accurate reading of the loadings coming into the plant.”

The other major 2013 project was a $2.4 million rebuild of the Church Street pump station serving the beach area. “The previous pump station was so old that it was registered as a historical site,” says Dube. “We had to go through all the hoops and waivers to be able to take it out. It wasn’t cost-effective to rehabilitate it.”

Carle recalls, “We had to dig down to 30 feet below the low tide mark — the contractor was essentially digging into the Atlantic Ocean. It took them several months to dewater the area. We located the new station 2 feet above the 100-year tide mark, taking into consideration the rising sea levels.” The pump station contains three Flygt premium-efficiency submersible pumps, each rated 30 hp, significantly smaller than old pumps. For the energy efficiency gains, the town received a $50,000 incentive rebate from Unitil, the local electric utility.

Adapting to change

While efficiency is important, the greater quest is keeping up with changes in influent volume and strength. For that, Carle and the team get help from the Hach Water Information Management Solution.

“Using the WIMS data, I can look up our BOD loadings coming in for the week,” Carle says. “Then I can go back two or three years if I want to and compare and say, ‘Yes, this is a spike, and this is a real difference.’ Then I can compare that to different parameters to see when the plant was running well and when it wasn’t. I can then use different process strategies, whether that be a mixed liquor suspended solids level or the food-to-microorganism ratio, and see which one correlated the best.

“One of our biggest process challenges has been the addition of the brewery. After they came into town, we saw our influent BOD loading almost triple. It took us a while to figure out how to deal with that, but since we did, it’s been fine. We recently switched process strategies to maintain a constant solids retention time of 13 days. Now on our best days, you can read a newspaper at the bottom of our 8-foot-deep chlorine contact chamber.”

When minor day-to-day problems crop up, the team addresses them with an eye toward lasting fixes. Dube recalls, “We had a chlorine violation because somebody turned a chemical feed pump off and forgot to turn it back on. We said, ‘All right, what can we do to keep that from happening again?’ We tied that pump into our SCADA system, so that if it’s not turned back on, there’s going to be an alarm.”

Never at a standstill

The Hampton team continues to face down difficult issues. One is I&I. In 2006, contractors replaced many of the aging sewer mains along the beach in a $10 million project. “We actually saw a drop in flow of a million gallons a day,” says Carle. “The trouble with being on the beach is that we have 10-foot tides here, so during springtime we would essentially be receiving the Atlantic Ocean.” More work on I&I reduction needs to be done.

“We’re also trying to add some new equipment and make more improvements at the plant,” Dube says. “That includes upgrading the septage receiving station and adding an emergency generator for our aeration blower building.”

Given the plant’s age, repairs and maintenance are daily concerns. “We’ve installed the Hach JOB CAL computerized preventive maintenance program,” says Dube. “It helps us track all of our equipment repairs and scheduled maintenance. The operators log in to look at what’s due to be checked or worked on and just go in and do it.”

While budget issues are challenging, the Hampton team faces the future optimistically. “I’m sure all treatment plants go through ups and downs,” says Dube. “Lately, we’re headed in the right direction. The elected officials we have in place now are looking out for the future of the town and making the necessary plans to improve it.”

Carle adds, “It’s a team effort here. As operators, we can’t do our jobs without the support of the people who haul the biosolids, do the lab work and do the maintenance. We try to cross-train everybody to be able to do everything.”

That’s especially important in a plant where change is always in the mix.

Little things count

It’s not just the million-dollar projects that make things better at the Leavitt E. Magrath Wastewater Treatment Plant. Sometimes it takes nothing more than a couple of sheets of paper, or the repurposing of a plastic reagent bottle.

Ideas arise constantly from a staff that totals more than 100 years of experience. The team includes:

  • Steve Aslin, maintenance technician/grease inspector (Grade 4 wastewater operator license, 19 years with the town of Hampton)
  • Rob Pierce, lab technician, Grade 2, 10 years
  • Bill Lowney, operator, Grade 1, 10 years
  • Cliff Lavigne, truck driver, Grade 1, nine years
  • Mike Moran, equipment mechanic, Grade 2, five years
  • Marie Hall, Public Works secretary, 26 years

“We have a lot of operator ingenuity here,” says Mike Dube, operations manager (Grade 4, 18 years). Mike Carle, chief operator, was recognized twice by the Water Environment Federation in its Operator Ingenuity Contest, first for a “fecal clock” and then for a makeshift but effective shield to keep an influent composite sampler from getting clogged by wipes or rags.

“We use the IDEXX test for fecal coliform,” says Carle (Grade 4, 17 years). “It’s an 18-hour test. On weekends we rotate the lab duties, so the person coming in may not know when it’s time to conclude and read the test.” The “clock” consists of a sheet of manila paper with two dials printed on it, one for indicating when the test was started and the other when to read it. “It’s a simple visual reminder,” Carle says.

Dube notes that clogging of the influent sampler used to be “a maintenance nightmare, especially when the temperature was 10 degrees outside and our people had to clean it off.” To create the sampler shield, Carle took a 500 mL bottle from a pH buffer solution, cut the bottom off and modified the neck. When fastened in place,the bottle formed a shroud over the intake. “Now the rags don’t get sucked into the intake and clog it up,” Carle says. “At best they just slide on by. At worst they get caught on the hose.”

Either way, the sampler is able to operate continuously.

Dube says, “Little things like that help us do our jobs a bit better.”


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