Efficiency upgrades and process improvements allow a Massachusetts water treatment plant to generate 70 percent of its own electric power.
In 2007, the Massachusetts Department of Environmental Protection (MassDEP) began an energy management pilot to help reach near net zero energy for seven water treatment plants.
One of the biggest successes was the Town of Lee drinking water treatment plant, which now produces nearly 70 percent of its own electricity, saving the community up to $34,000 a year and providing 114 kW of green power capacity. The updates account for a greenhouse gas emission reduction of 34 tons per year.
In July 2009, Lee was awarded $801,000 from the American Recovery and Reinvestment Act (distributed through the Massachusetts State Revolving Fund) to upgrade its water treatment plant, built in 1997. All updates were online as of December 2011.
A tourist destination in picturesque Berkshire County, Mass., Lee has a population of 5,200 and 2,055 water customers. The town has a single surface water plant that treats and distributes an average 600,000 gpd (2 mgd capacity). The plant draws from three reservoirs, which provide high-quality water. Two full-time operators staff the plant.
The Lee plant uses a KROFTA process that mixes raw water, aerated water, and flocculation and coagulation chemicals into a tank. Sludge is skimmed off the top, and clarified water flows through a filter bed. The finished water is disinfected and pumped to one of three storage tanks.
With goals to reduce energy use, lower greenhouse gas emissions and save money, the town performed a full audit on three key areas: electric energy, heating energy and renewable energy. Consulting engineering company CDM Smith came on board to evaluate the plant and help Lee progress toward its net zero energy goals.
Optimizing the process
The first consideration was to identify process optimizations. The plant already had a Canyon Hydro 80 kW hydroelectric microturbine system for renewable power generation, but it was being underutilized. The plant team wanted to get 15 percent more power from the turbine to enable an additional 26,000 kWh of production annually. The key was to redirect the turbine's nozzles and install automatic flow control.
"The way the water used to come into the turbines, it would slosh around and wasn't directed toward the paddles, so some of the energy wasn't getting picked up,"
says Department of Public Works director Chris Pompi. "We retooled the piping going into it and adjusted the paddles to optimize the water going through the turbine. Now, instead of waiting for two million gallons to generate the capacity power, it needs just 800,000 gallons per day."
Workers performed upgrades to the turbines in small time increments because the system couldn't be offline for longer than eight consecutive hours. "We had to keep the plant running while we did all the work, like performing open-heart surgery on a patient," says Pompi. "We can't say to 2,055 customers, 'Sorry, we couldn't get back online, so no water today.' "
More power control
To further enhance the electrical efficiency of the plant, the team retrofitted Baldor Electric premium efficiency motors onto two 25 hp air dissolving tube pumps, two 7.5 hp backwash supply pumps, two 7.5 hp plant water pumps, and two 40 hp filtered water pumps. Combined, the new motors save 11,000 kWh annually.
To reduce usage even more, the batching system was outfitted with Baldor Electric variable-speed drives that allow for a steady flow of water throughout the day and night to keep the water balanced within the system. Without those drives, the pumps would operate at top speed even when demand did not call for it.
Lighting improvements have also decreased electricity demand. The plant's sixteen 400 W high-pressure sodium light fixtures and four 400 W metal halide fixtures were replaced with 20 T-8 fluorescent fixtures (6 W to 32 W each). The lighting improvements have saved 13,000 kWh annually and have improved visibility.
"The old lighting used to take a half hour to crank on and would use a lot of energy," Pompi says. "The operators can see better in the plant now. I didn't realize the color of our sludge until they got rid of the old lighting. The sludge is lighter than I thought."
Efficient temperature control
Programmable thermostats improved heating system efficiency. The plant's HVAC system consists of an oil-fired hot-water boiler, hydronic heater, and ventilation fans. The system reduced oil consumption by 400 gallons annually, saving an estimated $1,200. The thermostats are programmed to adjust appropriately during the times of day when operators are present. Since the building is concrete and windowless, it stays relatively insulated from fluctuations in external temperatures.
Taking advantage of the plant's location with southern exposure on a hilltop, 156 solar modules from groSolar rated for 225 watts each together generate over 30,000 kWh annually. Monitoring the solar panels is simple for operators because the solar array is tied into the SCADA system. The town sees potential to save another $12,000 annually by installing more solar fields around town, supported by a public-private partnership and an enterprise fund.
Going off the grid
The goal of the plant upgrades was to reach net zero. While the plant has not yet met that goal, it did go off the grid once on a low-flow weekend. "We went off the grid for one hour when the plant was in standby mode, there were no lights on and the tanks were filled," Pompi says. "Western Massachusetts Electric sent us a check for $5, which was surprising."
To evaluate whether the plant might be a candidate for wind power, a wind profiler was installed at one of the reservoirs last November. With further optimizations, the plant may be able to get even closer to its energy goals. "The next step is to secure more money for additional work to get us 100 percent off the grid," says Pompi. "That is up to the DEP, and we hope it will be in the near future."