A Seasonal Challenge

Operator motivation and teamwork help the award-winning Provincetown treatment plant deliver quality effluent despite extreme seasonal flow variations
A Seasonal Challenge
Operator Chris McKernan tests samples in the lab using a Hach DR 2800 portable spectrophotometer.

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Located on the tip of Massachusetts’ Cape Cod, Provincetown was the Pilgrims’first landing place. It is also the country’s oldest continuous arts colony and is home to numerous beaches. Between Memorial Day and Labor Day, tourists swell the population from 3,000 year-round residents to 70,000.

None of this fazes the three operators at the town’s wastewater treatment plant. “We have a commendable compliance record,” says plant manager Chris Rowe of Woodard & Curran, which operates the plant. “Our plant actually runs better during the summer when the flow is higher.”

Built in 2003, the 0.5 mgd plant requires careful monitoring and adjustment during seasonal changes. The highly trained and motivated operators do that so well that they won the 2011 New England Water Environment Association (NEWEA) Utility Management Award for operational and performance excellence.

 

Checkerboard system

Unlike other plants in the Northeast, Provincetown uses a vacuum sewer collection system (AIRVAC) — the first on Cape Cod. “It uses traditional vacuum lines in tandem with mechanical pump stations that convey sewage to the plant,” says Rowe.

Vacuum systems are suited for areas with high water tables that prevent excavating to the depths required by a gravity system. While vacuum systems are designed for flows normally found in residential areas, Provincetown’s flow varies from as low as 60,000 gpd in winter to greater than 475,000 gpd on peak summer days. A post-equalization basin helps manage peak hourly flows during high-demand seasons.

Before the plant went online in 2003, numerous residential and commercial septic systems in Provincetown failed. That led to a regulatory consent order mandating installation of a collection system and treatment facility.

Says Rowe, “Provincetown received special state permission that exempted properties in the vacuum service area from mandatory connection; only certain ‘spot’ properties had to connect. That’s why they call it a checkerboard system.”

Residences that have septic systems do not have to connect to the sewers but can join a townwide septic system inspection program. It requires a property owner either to correct septic tank deficiencies or tie into the sewer system once issues are known. The same conditions apply for real estate transactions, where a state law requires a septic system inspection with every property deed transfer.

 

Growing population

Many residents and businesses have chosen to connect to the sewers: Today, 722 properties are connected, including homes, inns, restaurants, art galleries, theaters, condominium complexes, campgrounds, comfort stations, the airport, and general businesses. The number of connections is expected to grow to around 950.

“An issue arises when people who didn’t want to be connected 10 years ago want to connect now,” says Rich Hunt, maintenance reliability manager with Woodard & Curran. “The difference between then and now is that three houses in a row may want to be connected, but not the next two, and then the next one wants to be connected, but not the next three.” The collection system was expanded in 2008, and a second expansion will be completed in 2013.

AECOM designed the treatment plant and collection system and subcontracted operation to Woodard & Curran. The activated sludge plant consists of:

• In-channel microstrainer with Sigma flowmeter (Hach Flow Meter Products & Services)

• Two sequencing batch reactors (Sanitaire – a xylem brand)

• Aeration system (Sanitaire – a xylem brand) with blowers (Aerzen) controlled by variable-frequency drives

• Recycle/post-equalization tank

• Two disc filters with cloth membranes (Aqua-Aerobic Systems)

• UV disinfection system (Infilco Degremont)

There are two 70-foot-diameter SBR tanks and both are split into two chambers. Both tanks are used between Memorial Day and mid-October. One is then taken offline for the non-peak months. “The nicer the weather, the more people are in town, and the higher the flow,” says Hunt. “When one tank is offline and there is a high flow, the second tank will be used as an equalization tank to get through a couple of days of high flows. It’s not uncommon for the flow to triple or even quadruple over a weekend.”

Sludge is processed through a rotary drum thickener (Huber Technology) and sent to a holding tank. When the tank reaches capacity, a contractor removes 9,000 gallons at a time and trucks it to a facility in Cranston, R.I., for further treatment. Effluent is discharged into the ground through five rapid infiltration basins.

 

Tweaking the system

The nature of the vacuum system, combined with seasonal flow variations, keeps operators on their toes. “Both the vacuum system and SBR process settings need to be monitored and adjusted often,” says Hunt. “There isn’t any system that you can set and forget. With each season and flow change, you can tweak the settings to get close to where it should be, but it still requires operators’ attention to evaluate and adjust.”

Rowe and operators Reid Snow and Chris McKernan make sure they stay on top of their lab testing, gravity system monitoring and spot checking, and equipment maintenance. “We do lab work and maintenance in-house,” says Rowe. “We spend about half our time on maintenance and the rest on operations, lab testing and plant aesthetics.”

They send the regulatory samples to a private lab but take daily process-related samples for pH, turbidity and TSS, plus ammonia and nitrate samples three times a week.

The operators’ greatest challenges occur in spring and fall, during the tourist season changeover. “The guys time the valve controllers to make sure they are working right when the flow starts to increase and again when it starts to decrease,” says Rowe.

System flow typically increases from 60,000 gpd in winter to 120,000 gpd in the spring, and that requires some process tweaking. Says Rowe: “Typically, these flow changes require control changes to the SBR aeration and decant cycles. They also require changes to rotary drum thickener operation, the recycle of decant from the post-equalization basin, and return activated sludge changes, including sludge hauling and chemical feed adjustments.”

 

Training helps

When the new system came online, the operators received classroom and hands-on training on the vacuum system. “Someone from AIRVAC came to the plant and answered our questions about the system, since every system is a little different,” says Rowe. “Reid and I went to the five-day operators’ school at the AIRVAC factory where they ran us through mock drills on a full-scale system. But I also learned a lot on the job.”

AECOM asked the major equipment vendors to perform startup training, including troubleshooting techniques. Operators took in-house training on the sophisticated SCADA system, designed by Woodard & Curran.

“We learned how to operate the system on site, and the technical representatives who designed it could log onto the computer and walk us through the steps,” says Rowe. “They also visited our site if we needed hands-on help.”

Operators recently began using portable devices such as smartphones and tablets to monitor and access the SCADA system, which has more features than typically found with a vacuum system. The system allows for more precise troubleshooting so that collection system and treatment plant issues can be corrected quickly. Says Hunt, “Being able to access the SCADA remotely is huge when you’re in the street chasing a problem and you need to control a valve or pump back at the vacuum station.”

Rowe adds, “I can’t imagine if we didn’t have this system. It makes our lives ten times better. When there’s an alarm, the system calls the house, and I use my tablet to pull up the information. The system gives me the alarm number and description. For example, ‘Alarm 112, decanter failed to cycle properly, press 2 to acknowledge.’ I can then decide if the problem must be fixed right away or if it can wait.”

The SCADA system also allows process trending. “We trend everything from incoming to outgoing flow and everything in between,” says Rowe. “It’s a good maintenance tool. If there is a vacuum leak, I can go to the plant, turn on the PC, go to the vacuum line, and diagnose the problem online.”

 

System improvements

The plant has completed a few upgrades, including moving the recycle line from upstream of the flowmeter to downstream. “We recycle water from the rotating drum thickener and plant waste discharge,” explains Hunt. “So, we’ve improved the accuracy of the influent flow, since we don’t have to use the SCADA to subtract the recycle flow.”

Other improvements:

• Dissolved oxygen, pH and ORP sensors for the SBRs in 2008. These were connected to the SCADA and allowed control of the blowers and mixers for the biological process.

• Increased aeration in each SBR in 2010 by additon of 35 percent more diffusers, upgrading of the blower motors 30 hp to 50 hp and addition of variable-frequency drives to each blower. The VFDs are controlled by the SCADA to run at a set time and airflow, or to run at a dissolved oxygen set point.

• Seven additional vacuum monitoring points along the three main vacuum lines.

• Controller towers on the vacuum valve pits, making them more service friendly.

• Valve alarm boxes with an illuminated alarm if the vacuum valve stays open for more than 30 seconds. This keeps vacuum pumps from running more often than they should and causing a low vacuum condition.

• Installation of gravity lines and grinder pumps, and four new pump stations.

AECOM is designing a plant expansion to 0.75 mgd. A pre-equalization basin will be built to buffer the peak hourly hydraulic flows and loadings, complete with an air scrubber or blower system.

Using the same footprint as the existing facility, a Bio-Mag treatment and recovery system (Cambridge Water Technology, now part of Siemens Water Technologies) will be installed for advanced sludge settling. “We anticipate using this system during peak summer months or possibly only during extreme peak flows July 4, Memorial Day and Labor Day weekends,” says Hunt.

 

Motivated team

Operator morale is high. “We’re a small group, and we all get along and don’t step on each other’s toes,” says Rowe. “We help each other out. Whatever I know, they know, and whatever I don’t know, we all learn together.”

Rowe was an operator at the plant before becoming plant manager. “I’m just one of the group,” he says. “Reid and Chris do a great job maintaining the collection system — running the vacuum pumps, changing the oil. They know what’s going on with every piece of gear, and they can just walk by a pump and tell if something sounds funny.”

Team members are also motivated to continue their education. Rowe has earned his Grade 5 wastewater license. Snow is Grade 2 certified in wastewater and collections and plans to advance his licensure. McKernan, the newest employee, is working toward his certification.

 

Future challenges

As more residents connect to the sewer system, the challenges will increase for the plant’s operators. Keeping energy costs down is a goal. “We check energy use with the SCADA system, and we check our energy bill religiously,” says Rowe.

Maintaining a strict maintenance schedule will be key as equipment ages, as will ensuring an adequate spare parts inventory. “Woodard & Curran uses a computerized maintenance software program (SEMS Technologies) for tracking routine and corrective maintenance on all our equipment,” says Hunt. “We maintain inventory of critical spare parts, and perform a thorough cost analysis for each piece of equipment so that staff can decide whether it’s more cost effective to replace or repair equipment.”

Other challenges include monitoring and tweaking the SBR and vacuum system processes during the peak season. “Peak hourly flows and loadings will continue to be challenging, and so will public outreach and education for tourists and property owners,” says Rowe. “There are many do’s and don’ts that they should know about to maintain the integrity of the system.”

At the opposite extreme, things can slow down in the off-season. “In the dead of winter, our flow might drop as low as 86 to 115 gpm, and there are days where you can watch the paint dry,” says Rowe. “But, as I tell my guys, you can always go and study, and learn something new.”



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