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How Heat in Wastewater Can Help Power Buildings

By now, you’ve probably heard that real estate has an energy problem. And by energy problem, I mean that it’s responsible for almost half of the world’s energy consumption and about one-third of global greenhouse gas emissions. The act of heating and cooling a building is a huge culprit of both, just ask any building owner with a giant electric bill. But what most building owners may not realize is that there’s a perfectly viable source of heat energy within reach that literally gets flushed down the drain.

Water is essential to human life, but wastewater, or any water that has been used and is no longer suitable for human use, is a huge source of untapped energy potential for buildings in the United States. Water gets heated as it cascades out of our shower heads and gushes out of our faucets, leaving the wastewater warmer than the regular water supply. Depending on the usage patterns and climate conditions, wastewater usually averages between 50-70 degrees Fahrenheit. While these aren’t exactly scalding hot temperatures, wastewater contains a significant amount of heat energy that can be recovered and reused. 

Water systems currently account for two percent of the U.S.’s energy consumption, resulting in 45 million tons of greenhouse gas emissions each year. As cities race to meet their decarbonization targets, there’s undeniable environmental value in reducing potable water demand by recycling wastewater. We already know that recycling wastewater prevents a variety of contaminants from being discharged into the environment, but since wastewater is at a higher temperature, it can wreak havoc on aquatic ecosystems when it’s dumped back out.

Extracting heat that would otherwise be released into an outside water source also offers a positive impact from a dollars-and-cents standpoint. Against today’s backdrop of crippling energy bills and sky-high interest rates, building owners are more incentivized than ever to opt for anything that’s going to save them money, and the cost-savings that comes with taking advantage of wastewater heat can yield quite the chunk of change. As the Department of Energy explains, municipalities and utilities can save “15 to 30 percent,” which can translate to thousands of dollars for many buildings. 

Wastewater heat recovery might sound like a jarring concept to anyone in the U.S., but abroad, it’s old news. The European Union has recognized wastewater as a renewable energy source since 2018, and sewage heat recovery systems are operational in the capital cities of Japan and Norway. Israel, a country that recycles 90 percent of its water, is also well-versed in wastewater recycling. Wastewater heat recapture, though, is still nascent concept as most wastewater recycling systems don’t utilize heat recapture, but the technology is becoming increasingly prominent as it works in tandem with wastewater recycling systems.

There are several reasons why wastewater recycling hasn’t taken hold as quickly on American soil. Water isn’t as scarce in the U.S. compared to some other countries, especially Israel. Then there’s the issue of regional climate. To continue using Israel as an example, one of the reasons Israel recycles so much of its water is because the country has a warm, arid climate, which means that there is a high demand for hot water for domestic and industrial purposes year-round. This makes wastewater heat recovery systems a more attractive option in Israel, where they can help to meet this demand and reduce energy costs. In contrast, the climate in the U.S. varies widely by region, with some areas having much colder winters, which has made wastewater heat recovery systems seem less practical in the past due to the centralized model used in the majority of the U.S. Extracting heat and reusing it at a building level eliminates that potential loss of heat as it moves to the plant because the system is decentralized and operating locally.

But for Eric Hough, Chief Commercial Officer for Epic Cleantec, a San Francisco-based company that provides onsite water reuse systems for real estate developers, property owners, and water-intensive businesses, such as wineries and breweries, wastewater recycling is anything but impractical. In fact it’s painfully simple. “When you think about your existing hot water system,” Hough explained, “you put it up through the shower and it comes right back down the drain. We can basically close the loop by capturing that heat and then providing it back to the hot water users in the building.” 

Just to give you a sense of how Epic Cleantec’s technology works, the water recapture system typically starts in the basement of a large building. Under normal circumstances, a building’s wastewater (from things like showers, sinks, toilets, etc.) streams down into the sewer system. But Epic Cleantec installs a valve that diverts the flow of wastewater into their treatment system. The system removes waste solids (which owners can use to make fertile soil blends for landscaping purposes), then moves the rest of the water through a series of biological, ultraviolet and chlorine disinfection treatments steps until it’s safe enough to be redistributed throughout the building for things like flushing a toilet, irrigation, and even laundry. But as the wastewater flows through its intensive treatment process, the system extracts heat energy from that water to reuse throughout the building. 

Hough told me that most of Epic Cleantec’s projects have been individual buildings, often larger high-rise developments in major city centers. As the rate of adoption ticks upward, the company envisions a future where smaller building-scale systems work in harmony with larger municipal systems to tackle water stress and energy use. “We’re very much like where solar was 15 years ago, where we had central energy systems and then suddenly rooftop solar panels started popping up,” said Hough, before adding before adding that owners benefit from having a more resilient water supply. “Plus there’s less need for off-site treatment,” he said, which supports urban population growth and city planning at no detriment to the municipal system infrastructure.

Hough and his company believe that there is no such thing as wastewater, only wasted water. In the context of heat, that motto absolutely rings true. Losing valuable heat energy from a building’s wastewater is both a huge environmental problem and a drain on resources. While wastewater heat recovery may not be as widely adopted as it is in other countries, the technology is available and can yield significant cost-savings for building owners. By recapturing the heat energy from wastewater, we can also reduce the strain on our water systems and prevent further damage to aquatic ecosystems. Companies like Epic Cleantec are leading the charge in bringing this technology to individual buildings, districts, and beyond. It’s time for the U.S. to realize that wastewater is a renewable heat source and take action toward a more sustainable future.

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