Wastewater treatment systems that provide clean water also use large amounts of energy — almost two percent of the total U.S. consumption. While wastewater treatment usually accounts for 20 to 35 percent of a municipality’s total energy costs, in many communities the cost can rise to a whopping 60 percent. Thus, wastewater facilities offer great potential for savings since the majority are typically neither designed nor operated with energy efficiency as a priority. With recent help of the University of Minnesota and the Minnesota Rural Water Association, the city of Altura is on track to save an estimated $4,680 per year, and potentially as much as $14,000 per year, while being assured that the city’s water quality is maintained.
In 2017 the city of Altura was selected to be part of a project to reduce energy use in Minnesota wastewater treatment plants funded by the U.S. DOE and executed by the University of Minnesota and several other state agencies. Altura’s inclusion in this project resulted in an engineering assessment it received, free-of-charge, from Minnesota Technical Assistance Program (MnTAP). Worth several thousand dollars, the assessment showed there was a potential for significant cost and energy savings to the city. Through cautious implementation and testing these energy-saving measures are proceeding slowly so as to assure the area’s surface-water quality.
The whole process began in February 2017 when a Winona County intern, accompanied by a Southeast Clean Energy Resource Team (CERTs) staff member, stopped by to visit Dan Horvat, Altura’s maintenance engineer. Winona County and CERTs were partnering on a grant received by the Sustain Winona Partnership to promote the use of free energy-benchmarking software for public buildings as an energy-saving tool. As Horvat listened to their presentation, he noted that what he really wished he could obtain was an engineering study for the city’s wastewater aeration system. He suspected that his plant had more capacity than what was currently needed, and that newer pumps used significantly less energy, but knew the city couldn’t afford thousands of dollars to hire an engineering firm.
Luckily, Chris Meyer, coordinator for Southeast CERTs, which is located at the University of Minnesota Extension, was aware of a university resource called MnTAP. Through MnTAP the university shares its engineering expertise by providing free assistance to communities and businesses across the state on reducing energy and water use. What the CERTs coordinator didn’t know was that same week, MnTAP had put out a call to find 10 Minnesota wastewater treatment facilities that would consider implementing cost-effective changes to reduce energy costs, the work for which would be funded by a DOE grant. Altura became one of the participants, and engineers John Vanyo and A J. Van den Berghe from the University of Minnesota were on site just weeks later. The team toured the aeration ponds, pumps, and power supply. They spent several hours sorting through files to locate the original design and recommissioning documents for the wastewater treatment plant.
Several months later the MnTAP engineers came back with a recommendation. The closure of the Altura turkey plant had left the wastewater treatment facility with excess capacity, which MnTAP felt could allow Altura to shut down six of the 10 aeration pumps at the facility’s ponds. These pumps run constantly and consume lots of energy. Shutting them down has the potential to save $14,000 annually and reduce electricity use by 173,000 Kw hours per year. But these pumps are essential to the plant’s cleanup processes, putting oxygen in the water and maintaining a fairly complex balance of elements to keep sewage eating microorganism alive.
The next part of Altura’s story comes back to the importance of clean water. Two of the pumps have been shut down, with estimated annual savings of $4,680, but the rest will be removed from service only if testing indicates that the changes will not hinder the plant’s ability to effectively clean the wastewater. Altura is a member of the nonprofit Minnesota Rural Water Association (MRWA), which provides training and technical assistance related to water and waste water systems for hundreds of Minnesota municipalities. An MRWA technician is scheduled for a free testing visit to Altura in February 2018. As Horvat described it, MWRA staff will drill into the frozen aeration pools to take samples of the sludge from the bottom of the ponds. If these tests indicate that the ponds are still properly cleaning the water, then a couple more aerators will be shut down in the spring. The process will be repeated the following February, phasing in the pump shutdowns only if testing results are satisfactory.
It may take a few years for the city to realize all potential cost savings, but these changes won’t have adverse effects on local surface waters. For communities or businesses interested in energy and cost reductions while promoting stewardship of clean water, both MnTAP and CERTs have a wealth of no-cost and low-cost of resources at their disposal. The Waste Water DOE Grant Program is now closed but MnTAP can share what was learned and still provide free assistance for other types of assessments.