The term “wastewater” may become a misnomer—or at least the “waste” part. The City of Brainerd investigated the possibility of using its wastewater as a resource to produce energy for municipal buildings. With the help of an Energy Efficiency and Conservation Block Grant (EECBG) of $45,000 to conduct research on the topic of untapped energy in wastewater streams, Brainerd is now at the forefront in this field of renewable energy research.
In 2010, a research partnership between the City of Brainerd, Brainerd Public Utilities, the Brainerd School District and an area firm called Hidden Fuels looked into the potential to heat and cool schools and other public buildings by extracting energy from the wastewater stream.
Hidden Fuels is a renewable energy company providing services and products to efficiently capture and distribute unused energy from waste—domestic waste, municipal wastewater, and biomass wastes. “Given the need for both energy independence and better wastewater treatment methodologies in the United States and abroad, technologies capable of harnessing usable energy from waste are in demand,” the company’s website states.
From October 2010 to January 2012, the research team collected data using geographic information systems and monitoring at lift stations to examine flow and temperature of the wastewater stream. While the study originally aimed to determine how much energy could potentially be used to heat and cool homes and municipal buildings in Brainerd, the group eventually focused its attention on three municipal buildings that could benefit from wastewater energy: Brainerd High School (BHS), the Brainerd Police Department, and the North Star High Rise building.
Estimated savings on heating costs could be up to $17,300 for BHS, $8,300-$9,000 at the Brainerd Police Department, and $6,000-$8,100 at the High Rise, and as natural gas prices rise, alternative energy sources become even more economical.
“If the final results of this study show that the application of heat extraction technology is feasible and cost-effective, these rewards can be significant for the community,” Hidden Fuels reported. “The City of Brainerd and Brainerd School District could expect to find a significant reduction in both heating and cooling costs for many buildings.” There is also the potential for reduced fossil fuel use and decreased greenhouse gas emissions.
The study included over 1 million data points throughout Brainerd and revealed information about the flow and temperature of the stream. This data proved that the potential exists to extract heating and cooling energy from the waste stream, but the technology to perform this feat does not yet exist. Until the right technology is developed, this energy in the sewer system will continue to flow as unusable waste.
Geothermal technology could hold some clues as to how to extract heat from sewage flows. The next step in the research will be to investigate methods of energy extraction, with the eventual goal of finding a proper technology to efficiently derive as much energy from the waste stream as possible.
While there are still some uncertainties regarding who owns the energy and how it will be used, there is no doubt that thermal energy from wastewater could offset many heating and cooling costs for the City of Brainerd. Data collected in Brainerd has been synthesized and will hopefully help guide similar research projects in other locations.
If harvested to its full potential, Brainerd’s wastewater could provide enough energy to heat 450 homes annually. The research partners believe this is the first project of its kind to be carried out on a community-wide scale. If it is determined that it is feasible to extract the energy from the wastewater stream, the technology developed in Brainerd could potentially save communities across the nation significant sources of money and energy.
Despite the potentially promising economics, a number of questions remain, including: how do we capture, store, and disperse this currently-squandered source of energy?
Much of the content in this project summary has been drawn from: “Could waste heat in sewers heat buildings? Untapped energy flowing under Brainerd,” by Ann Schwartz and “Tapping Wastewater: Probing Hidden Depths for Energy,” by Renee Richardson, Brainerd Dispatch.
