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It’s an exciting time for renewable and alternative energy. As demand grows, scientists, engineers, politicians, and others are looking beyond the staple renewable energy sources of solar and wind to other, potentially valuable sources of energy. One of these new energy sources is Waste Water Energy Recovery (WWER), a technology that has the potential to save money on heating or cooling bills. Three students from Worcester Polytechnic Institute (Erica Parker, Aimee St. Germain, and Elise St. Laurent) spent the seven weeks of their Interactive Qualifying Project (interdisciplinary applied research that connects science or technology with social issues and human needs) working with DOER to see just how valuable WWER might be, and how it might be implemented in Massachusetts.

image of waste water energy recovery system

Waste Water Energy Recovery flow diagramj

The way a WWER system works is relatively simple. As you can see in the diagram, waste water from a sewage source is separated (with solids returning to the sewage source), and then the waste water is processed through a heat exchanger. The waste water passes through a series of tubes, heating a different, clean fluid, before being returned to the sewage source. The clean fluid is then pumped through a building, carrying the heat – or removing the heat – much the way boiler and radiator systems work. This method represents a more efficient way of generating heat for a building, and at no point does any waste water actually enter the building’s own pipes.

Although heat exchanges and heat pumps have been around for a long time, the idea of using waste water as the heat source is new. Even in Europe, the oldest installation of this type is around three years old, and no installation is old enough yet for definitive cost-benefit numbers to be posted. However, the idea represents remarkable potential savings. Imagine if your business’ heating and cooling bills were cut by 50 or 75 percent. Although the technology is new, Massachusetts is interested in its potential. There are technical and financial hurdles, of course, and the concept itself is too fresh to begin widespread implementation. And, while there are indications that such projects will be able to offset their production costs over the long-term, nothing is definite thus far.

Additionally, a WWER type system is not something that can be implemented everywhere. Right now, the ratio between sewage flow and heating is somewhere around a million gallons of flow for every 100,000 square feet of building to be heated. While that level of flow is not difficult to reach, it is generally much more than a 100,000 square foot building produces, meaning that businesses wishing to use WWER as a heating system will have to tap municipal sewage systems to have access to the necessary volume. This still makes sense from an energy perspective. After all, the energy is just going ‘to waste’ otherwise. But it also raises a host of issues regarding ownership of the energy contained in the wastewater and who should be able to access this energy source.

These issues, and potential financial models to support this technology, will take plenty of discussion to resolve. However, the approach perhaps represents a revenue stream for cash-strapped municipal wastewater systems. WWER projects are interesting applications of outside-the-box thinking regarding heating and cooling. They are the types of projects we like to see – ones that find a use for what would otherwise be wasted energy and resources, and a use with the potential to save a lot of money, at that. While there has been proof-of-concept, especially in Europe, this style of project remains too recent for any systematic implementation here. Still, Massachusetts is gearing up to explore the potential for energy recovery from waste water, so stay tuned.

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Silas is in an intern working with DOER’s Green Communities Division for the 2013 fall semester. He is in his second year of graduate school, studying to get his masters in urban and environmental planning at Tufts University. A New Englander born and bred, Silas grew up in Maine before moving abroad to Scotland for four years to pursue an undergraduate degree in Sustainable Development at the University of St. Andrews. His academic focus is on climate change, with a growing emphasis on disaster preparedness, but he is still deciding on what to do with that after he graduates. Silas enjoys reading, hiking, and cooking lots of delicious things, and loves fall for the sports, the leaves, the cider, and the butternut squashes.

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