Talk about taking the bull by the horns. In Massena, N.Y., recurring combined sewer overflows (CSOs) were creating havoc. But rather than spend money on consultants and shelf-bound studies, plant superintendent Nick Zappia and his staff took matters into their own hands.

 

With the help of the New York Department of Environmental Conservation (DEC), they devised a plan and made several changes in their treatment plant. Results? They’ve reduced the number of overflow events from 40 a year to fewer than five. Here’s what they did:

• Increased maximum flow through the plant from 6.8 to 10 mgd.

• Reduced the duration of bypasses by modifying the emergency bypass bar screen.

• Improved control of sludge settleability by enhancing the process-control program.

 

Even with such dramatic improvement, superintendent Zappia remains modest. “We couldn’t have done this without the support of our treatment plant staff, the DEC, and my boss, Hassan Fayad, public works superintendent,” he says.

 

Counters Tim Miller who worked on the project for the DEC, “It’s not what we do. It’s the operators. Nick and his staff worked hard to make this happen.”

 

Wicked winters

Massena lies on the far northern edge of New York State, three miles from the Canadian border. Summers are temperate, but the winter thermometer can fall to as far as 20 below zero. Snowmelt and rainfall are abundant.

 

The Massena Village Wastewater Treatment Plant serves a population of about 11,000. It was built in 1959 and improved through major upgrades in 1980 and 1998. Today, an average daily flow of 3.3 mgd passes through primary treatment, an activated sludge system that operates in the contact-stabilization mode, final clarifiers, and a Trojan Technologies UV light disinfection system. Treated effluent flows to the Grasse River, a tributary of the St. Lawrence River.

 

Plant design is for 4.8 mgd, with limits of 30-mg/l BOD and 45-mg/l TSS. Fecal coliform requirements are 200/100 ml on a 30-day basis, and 400/100 ml per seven-day period. In addition, plant staff tests for zinc, ammonia, and phenolics. The plant maintains an overflow retention facility (ORF) that must be monitored for BOD, TSS, SS, pH, temperature, ammonia and phenolics, and seasonally for fecal coliform during overflows.

 

An anaerobic digester stabilizes biosolids, and a belt press dewaters the material to a cake that is hauled away by a private contractor for landfilling.

Zappia and six operators are dual-licensed, responsible for the wastewater plant, the drinking water plant, and six pumping stations. They rotate tasks each week to keep personnel fresh and up-to-date on all skills in the department.

 

Sometimes overwhelmed

As with many communities in the northeastern United States, sanitary and storm sewers are combined in Massena. A total of ten combined sewer overflow outfalls exist within the collection system, and two more are located within the treatment plant itself:

• The ORF, located just before the aerated grit chamber, can provide primary settling and disinfection before direct discharge through a separate outfall.

• An emergency bypass ahead of the influent pumps provides another outfall. Any flow exceeding the capacity of the influent pumps is discharged through the bypass.

 

At a wet-weather peak design of only 6.8 mgd, the Massena plant was frequently overwhelmed. In fact, during a 15-month period from January 2003 to April 2004, the plant experienced 23 ORF discharges totaling more than 13 million gallons, and four emergency bypass discharges lasting more than 17 hours total.

 

Then, in 2004, a new requirement in the plant’s SPDES permit called for maximization of flows through the treatment plant as a best-management practice. “We had to submit a hydraulic capacity evaluation of our collection system to the DEC,” recalls Zappia. “I talked with Joe Kuta, my DEC contact in Region 6, and he pointed me to Tim Miller in the DEC facility operations assistance section.”

 

Zappia notes that operators might not be familiar with the assistance section, which offers free advice and help to treatment plants facing situations like Massena’s. “Tim Miller stepped in and offered help,” Zappia says. “Had we farmed this out, I’m sure it would have cost us thousands.”

 

Miller explains, “Our objective was to figure out how to get more (flow) through this treatment plant. We determined that the Massena operators could handle it, and we set up a cooperative technical assistance plan in 2004.”

 

Taking a look

The first step was to review the plant’s wet-weather operating plan, and examine the process-control program. “The operators had an excellent operation in place to maximize wet-weather capacity,” Miller says. “The plant is always in contact-stabilization mode, which allows solids to be stored in the stabilization tank away from the influent flow. The staff had target values set for mixed liquor suspended solids (MLSS) concentrations in the contact and stabilization tank.”

 

Next, Massena and the DEC conducted a desktop evaluation of the aeration tank and the clarifier to see if the plant could treat additional flow. The team concluded that since wet-weather events add only groundwater and surface runoff to the incoming wastewater, there would be no significant BOD loading changes with the additional flow.

 

Further, they determined that clarifier design enhancements at Massena (15-foot depth, inboard launder, and baffling) probably could handle the suspended solids removals that higher flow rates would require.

 

“The Massena design improves suspended solids capture by preventing an updraft wall effect that can increase effluent solids during high flows,” Miller says. “The Water Environment Federation’s MOP 8 confirms the benefits of weir location and baffling.”

 

To the test

The team concluded the existing system could indeed handle hydraulic flow rates up to 10 mgd with no loss of effluent quality. But desktop analysis is just that. To prove their theories, Massena and the DEC developed a protocol to evaluate the plant at flows greater than 6.8 mgd using four high-flow stress tests.

 

“If the plant demonstrated any instability, we could stop the test before any effluent violations occurred,” says Zappia. The team ran the tests at flow rates of 7.3 mgd and 9.2 mgd, and simulated 10 mgd and 10.8 mgd with good results. “The tests show that the activated sludge process and UV units could treat short-term flows up to 10 mgd,” says Miller.

 

But to treat these higher flows reliably, it was essential to maintain the proper sludge quality. Therefore, the village purchased a portable suspended solids meter to provide daily monitoring of MLSS levels in the aeration tanks. In addition, the plan called for an increased return sludge flow during wet-weather conditions. DEC and the operations staff felt the best approach was a steady return sludge, using the clarifier and stabilization tank to store solids during wet weather.

 

Based on the stress tests, the plant staff has set the weir in the distribution box to allow 9.2 mgd to be directed to the biological process using three pumps at full output. If the fourth pump comes on, the remaining flow is split between the biological process and the ORF.

 

Bypass protocol

Next, the Massena operators turned to the emergency bypass. During intense rains, the flow would rise rapidly in the influent channel and potentially go out the emergency bypass, even when capacity through the secondary process and/or ORF unit was still available.

 

They fabricated a new bar screen for the bypass, getting input from the Massena public works department welders, and included a channel in front of the screen. Then, by adding three 2- by 6-inch stop boards in the channel, they increased the storage capacity there by 16.5 inches.

 

“That allows us to direct more flow to the plant and less out the emergency outfall,” explains Zappia. Using the plant SCADA system, the staff also implemented a monitoring program at the influent channel to identify and correct any influent pump plugging problems. “Once a week we run our pumps at 100 percent capacity,” says Zappia. “We know what the maximum flow is, so if the pumps are obstructed, we can back-flush, or open them up and inspect and clean them.

 

“Tim helped us establish a baseline by bringing in a flowmeter. We spent a day flow-testing all four of our pumps and establishing baselines for every possible combination (e.g. one pump running, two pumps running).”

 

These days the rains (33 inches a year) and spring runoffs (from 70 inches of snowfall) continue in Massena, and the old combined sewer system still delivers high flows to the treatment plant. But the water quality of the Grasse River doesn’t suffer as before, thanks to a very effective team effort.

 

“DPW superintendent Fayad gave us the green light and was always supportive of our actions,” says Zappia. “And as far as who did what, whoever was in the maintenance slot for that week would work directly with Tim. Everyone had a hand in it.”