Pursuing Net Zero

The team at North Conway Water Precinct takes extra measures to safeguard the environment and reduce reliance on carbon-based energy.
Pursuing Net Zero
A new aeration system under construction at the North Conway facility.

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North Conway lies in the heart of the Mount Washington Valley in New Hampshire’s White Mountains. The nearby Saco River offers fishing and boating, and the local aquifer supplies drinking water. Preserving the environment of this year-round resort area is important to the North Conway Water Precinct, an independent agency that provides sewer, water and fire service.

The North Conway advanced wastewater treatment facility is doing its part to protect the environment with a five-stage Bardenpho process that discharges to infiltration beds, rather than directly to the river. The team also invests heavily in energy conservation and has set a long-term goal of reaching net zero energy — reducing demand for utility energy sources, then offsetting that with renewables. The plant already has solar panels and geothermal wells that have saved energy and reduced the plant’s carbon footprint.

The plant serves a full-time population of 5,000 that grows to more than 30,000 people in the summer. Flows average 350,000 gpd during the week and 800,000 gpd on weekends.
“When the system was installed 16 years ago, it was the only advanced wastewater plant with zero discharge,” says precinct superintendent David Bernier. “The effluent goes to rapid infiltration basins, where the water percolates through 30 feet of sand before reaching groundwater. The sand provides significant additional treatment of the secondary effluent as it percolates down to recharge the aquifer.”

A major plant upgrade, to be completed this year, will replace old blowers and associated plumbing and dissolved oxygen monitoring equipment and will add coarse bubble diffusers in the carousel. The upgrade will allow the Village of Conway to tie into the North Conway treatment plant.

Advanced treatment

Designed to protect the watershed while serving community needs, the wastewater treatment system’s Bardenpho process (Ovivo) uses the BOD in the wastewater to remove nitrogen and promote biological phosphorus removal. The system has one anaerobic zone, two anoxic zones and two aerobic zones.

Treatment also includes a UV disinfection system (TrojanUV), 12 rapid infiltration basins (8.25-acre and 4.5-acre field-constructed basins with natural stone embankments), and a two-stage odor removal and treatment system (Pepcon Systems).

Nitrogen removal is excellent in summer, but not in winter. “A combination of low seasonal flow, low organic loading, water temperatures around 46 degrees F and excessive aerobic hydraulic detention time [average of 65 hours], all contribute to a high DO environment,” says Bernier.

The plant team solves this problem by introducing an external carbon source (carbohydrate-based product) into the second anoxic zone. By making sufficient BOD available to the organisms, the process removes excess DO in the anoxic zone while leaving enough available food to reduce nitrate to nitrogen gas.

“The plant upgrade will eliminate this issue, along with the increased loadings from Conway Village tying into the plant and our latest $8.2 million sewer service expansion,” says Bernier. “The additional BOD will be sufficient to lower the DO to a manageable concentration, allowing denitrification without additional cost.”

Future upgrade

The plant upgrade was scheduled for completion in October, and Conway Village is expected to tie into the system by fall 2014. With flows expected to increase from 700,000 gpd to 1 mgd, the Precinct may need to add operators. “We’ll try to make due with the existing staff for the first year or two,” says Bernier. “We may concentrate on plant operations and contract out the pump station and yard maintenance duties.”

Once improvements are made to the aeration system, the only bottleneck will be biosolids dewatering. “With the plate-and-frame press, we are limited to how much we can dewater in an 8-hour day,” Bernier says.  “The plan is to resolve that by having the staff work four 10-hour days. That will allow time for multiple runs per day and enable a 30 percent increase in dewatering capacity.”

Bernier says the staff is excited about the four-day work week. “It also helps that we have water distribution staff co-located at the same facility, and we share vehicle and heavy equipment maintenance and collection system operations. That saves on labor costs and eliminates redundant tools and equipment.”

Grants and loans from the U.S. Department of Agriculture will fund the pipeline from the Conway Village wastewater treatment plant to North Conway. “The village’s plant is operating at capacity with outdated equipment that can’t remove nitrogen and phosphorus before discharge to the river,” Bernier explains. “In fact, the state has placed a moratorium on building permits in the village because of insufficient treatment capacity. That will be lifted once the village ties into our system.”

Highly motivated

Four staff members operate the North Conway plant: Peter LaBonte, treatment plant chief operator (Grade IV license, 15 years at the plant); Glen McDonald, operator II (Grade IV, 15 years); Aaron Bernier, maintenance supervisor (6 years); and Dennis Aikens, laborer (Grade I, 6 years). “They work well beyond what is expected, always complete the task at hand, work independently and take considerable pride in their work,” says Bernier.

LaBonte agrees: “All are very motivated people with a can-do attitude. They installed variable-frequency drives in the plant’s compressed air system, which operates all the automatic valves, HVAC control louvers and air-operated leachate and septic pumps.”

The old aeration system ran at 100 percent speed and vented excess air. Operators replaced the influent and effluent pumps with more efficient submersible pumps (Flygt) that have energy efficient motors and an updated design that minimizes electrical consumption and maintenance.

LaBonte and his staff saved considerable money by obtaining a discharge permit modification to discontinue UV disinfection before discharge to the infiltration basins. LaBonte submitted the request to the state Department of Environmental Services with references taken from the U.S. EPA Process Design Manual under Land Treatment of Municipal Wastewater, and with supplemental information from the Supplement on Rapid Infiltration and Overland Flow.

“In general, studies show that rapid infiltration in itself can be of very high quality with respect to viral and bacterial content,” says Bernier. “Since the plant effluent travels through 30 feet of sand before reaching groundwater, and because there is no on-site recovery of water for drinking, the request was granted.” The department recommended that the UV be taken offline but left operational for possible future use. The plant saves $60,000 a year on energy with the UV offline.

Operators do a little bit of everything, including lab work, maintenance, grounds work, painting and cleaning. When a job requires more people, Bernier can bring in water distribution team members. “Everyone takes great pride in the facility, and visitors always comment that the plant looks brand new,” says Bernier.

The plant promotes in-house training and provides paid continuation training. “If an operator only needs a grade II license for the job, but is willing to seek a higher level, we pay them a higher hourly rate,” says Bernier. “Not only does this improve their individual skill set, it provides opportunities down the road for promotion,” says Bernier.

Reducing costs

The North Conway plant significantly reduced energy costs with a number of measures. On the water distribution side, the team reduced electrical costs from 36 percent of budget to 12 percent by pumping water only at night when the rates are lower. “This was done seamlessly via our SCADA system and control,” Bernier says. “We have also lowered our unaccounted for water consumption from 36.6 percent to less than 11 percent over the last seven years. That means less pumping, less cost for chemicals, and less wear and tear on pumps and ancillary equipment.”

The plant has saved 50 percent on chemical costs during the past seven years by purchasing full tractor trailer deliveries. This also saves on trucking fees, as the chemicals are now delivered directly from the manufacturer.

Other savings include 5 to 8 percent in electrical costs from purchasing power directly from the wholesale supplier. “We participate in a demand response program where we are asked to self-generate our power when the New England power grid experiences excess demand,” says Bernier. “That allows us to exercise our generators under load and get paid to do it.” That makes money for the plant, which also sells renewable energy certificates from its solar array on the open market.

The plant also saves money for customers and the town by accepting and treating leachate from the local landfill. “That saves the town more $550,000 in trucking and disposal costs for the leachate,” says Bernier.

Net zero energy

Bernier would like the plant to become a net zero consumer of energy: “As environmental stewards we must set an example and reduce our dependency on carbon-based energy. The single highest cost of treatment plant operation is electricity. Eight years ago, it was 35 percent of our operating budget; today it is less than 18 percent.”

The plant has installed 744 solar panels with a capacity of 167.4 KW that generate a yearly average of 255,000 kWh — 22.5 percent of the plant’s consumption. Premium efficiency motors, many coupled with variable-frequency drives, also save energy. Plant employees did this work in-house.

“Many small or medium utilities are not willing to do this because they are afraid of the negative consequences should something go wrong or if the benefits are never realized,” says Bernier. “As a result, the municipal sector often hires engineers to design and install the improvements. I personally would back up my employees on these projects and take full responsibility for the outcome. I think they realize that, and they know I appreciate everything they do. That is part of the reason why we are successful.”

The plant uses geothermal wells for cooling in summer and heating in winter. Although there was a learning curve during the first year, minor modifications have led to a reliable and efficient system. “To help us achieve net zero, we are toying with the idea of adding more solar arrays and using effluent for geothermal,” says Bernier. “Once emerging technologies have ad-vanced enough to be cost-effective, we may consider the use of effluent and solar to extract hydrogen for possible use in fuel cells for generating power.”

It’s just another way to take care of the environment and protect a special place for local residents and visitors alike.


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