Sometimes a simple change can make a big impact. Such is the case for the drinking water treatment plant in St. Peters, Mo. By replacing old motors and installing variable-frequency drives (VFDs), the plant team reduced energy consumption by 12 percent, saving 253,500 kWh per year.

To supply water to 18,300 service connections, St. Peters draws water from the Missouri River and a groundwater wellfield. River water is treated at a plant in nearby St. Louis and sold back to St. Peters wholesale.

Water from eight wells is treated at the St. Peters plant, where it undergoes aeration, lime addition to settle out iron and manganese, carbon dioxide injection for pH adjustment, filtering through gravity charcoal and sand filters, disinfection with sodium hypochlorite, and fluoridation. The plant can process 6 mgd but averages 3.5 mgd.

The water department has a $6.2 million operating budget and a staff of six distribution system maintenance personnel, as well as 16 operators and plant maintenance technicians who split their time between the drinking water and wastewater treatment plants.

Savings opportunities

In 2009, St. Peters was invited to take part in the Missouri Water Utilities Energy Management Initiative, sponsored by the U.S. EPA and the state Department of Natural Resources. The initiative aims to help water and wastewater treatment plants reduce utility costs and minimize greenhouse gas emissions.

Bill Malach, manager of water environment services, jumped at the opportunity. “We volunteered to be one of the first communities to participate,” he says. “We are always looking for ways to be more efficient. If someone holds a workshop or conducts a study, we are always willing to partake because we benefit from it.”

Malach and other staff members attended six workshops over nine months. The meetings allowed participants to evaluate their energy consumption and share ideas on how to save. “We did a self-assessment and started with the largest power loads, which are the high-service pumps and backwash pumps at our plant,” Malach says. “We talked with the operators and maintenance staff to get their ideas, and then we discussed it with other communities at the workshops.”

The city identified several top-priority upgrades that would cost $163,800. In 2010, St. Peters received a $91,500 Energy Efficiency and Conservation Block Grant through the American Recovery and Reinvestment Act. A $38,000 Business Energy Efficiency grant came from the local electric utility, Ameren Missouri, and the rest came from the city’s water maintenance and operations budget.

Easy change-out

From August to October 2011, plant maintenance staff gradually installed five 200 hp premium-efficiency high-service U.S. Motors pump motors (Nidec Motor Corporation) to replace old motors installed in the 1970s. The pumps send finished groundwater through the 290-mile distribution system. Since only four of the five pumps ran at any time, it was simple to replace them one by one without interrupting service. Pump replacements took an average of 80 hours.

Staff members also replaced two 75 hp constant-speed pump motors used for filter backwashing with premium-efficiency motors and VFDs (ABB). “Previously, the backwash pump motors were at constant speed, and we were throttling the backwash valves to adjust the flow rate during the backwash cycle,” Malach says. “Instead of burning energy through the valve, we put VFDs on to save energy and give the operators flexibility to adjust the backwash flow.”

A local contractor installed a 30 hp transfer pump motor and VFD for moving water from a plant clearwell to a new storage reservoir. Operators had been tapping water off the main high-service pumps to bleed water into the storage tank, essentially using a 200 hp pump to fill a tank that only needed a 30 hp pump. City maintenance staff handled the piping and fittings from the transfer pump to the reservoir fill line. A system integrator programmed the city’s SCADA system to incorporate the VFDs. The entire upgraded system was online in May 2012.

Operators stay involved

Plant operators and maintenance staff were involved at all steps of the upgrade, from helping to identify the energy efficiency projects to specifying and installing the equipment. “We knew it was important to get operators involved early because they deal with the day-to-day activities,” says Rob Hamlin, plant operations foreman. “They know where energy savings can be found and what will work well. Their daily operational decisions directly affect energy costs.”

Malach and Hamlin share ongoing energy savings results with the staff to show the direct effect of their efforts. Operators track monthly electrical usage to look for more possible savings. “If we see a spike in energy, we look into what’s causing it,” Malach says. “Did we turn a pump on during a high-demand period when maybe we could have waited another hour past that demand period? Is there a failing pump causing a higher load on a motor?”

Many staff members who have worked at the plant for more than 25 years have loyalty and gratification in their work that motivates them to strive for constant improvement. “Our operators have buy-in,” Hamlin says. “We don’t have an incentive program, and there are no bonuses based on energy savings. They just take a lot of pride in knowing the system, and they have overseen the upgrades over the years. When they see one of these improvement projects come in, they take a lot of pride in it and want to see results.”