The basic idea is straight forward: Lots of the water that goes down the drain is hot. Every bit that is harvested and put to use is a bit that need not be generated.
Lynn Mueller, the CEO and founder of International Wastewater Systems, told Energy Manager Today that the first step is to pass the raw sewage through its Sharc or Piranha systems, where the solids are removed. “The heat exchanger then extracts or rejects heat to this flow of clean sewage water via some very efficient heat pumps to provide heating, cooling and domestic hot water heating for the building. The warm sewage flow provides an excellent, dependable and very efficient medium for heat exchange.”
It appears that interest in various ways to extract energy efficiency through sewage or wastewater is growing.
The State University of New York at Geneseo is considering a project in conjunction with the establishment of a microgrid, according to Livingston County News. The story, which was posted today, doesn’t offer much detail on implementing wastewater heat recovery, but Daniel DeZarn, the school’s Director of Sustainability, is quoted in the piece saying that it is a possibility.
Last week, Energy Manager Today sister site Environmental Leader reported that a wastewater heat recovery center will be built by PurposeEnergy for Kona Brewing’s new brewery in Kailua-Kona, Hawaii. The story says that the plan is to “allow the brewery to recycle its wastewater and other brewing byproducts to produce electricity, heat and clean water for the brewery. Kona Brewing says the resource recovery center will help it reduce its water usage to less than half what typical craft breweries use”
Many of the projects are outside of the United States. In December, Borders College in Galashiels, Scotland implemented a Sharc system. The story at Energy & Environment Management says that the platform is providing the school with 95 percent of its heat. The approach is straightforward:
Backed by investment from Equitix and the UK Green Investment Bank, the system intercepts waste water from a sewer close to the local treatment works operated by Scottish Water, and uses a heat pump to amplify its natural warmth. The heat produced is being sold to the college under a 20-year purchase agreement, producing savings in energy, costs and carbon emissions.
In Barcelona, a European Union LIFE is looking at using urban wastewater to generate energy. The initial goal seems to be to develop wastewater plant redesigns that make them energy self-sufficient in performance of their core task. The piece suggests that at some point there may be a surplus of energy produced.
This new WWTP will use all organic matter in the wastewater to produce biogas, a combustible gas made up principally of methane, which can be used to obtain heat and electricity. In addition, the nitrogen in the wastewater will be eliminated autotrophically, i.e. without the need for organic matter, by means of a new technology based on two biological stages: an aerobic partial-nitritation reactor and an anammox reactor. The scientists expect this new technology to significantly lower the costs of aeration in comparison with present-day urban WWTPs.
International Wastewater Systems’ Mueller says that the company’s product – and, likely, others that go down the same path, can be a key link in the complex, multistep energy ecosystem. “The unique ability to operate as both a heat source and heat sink offers a tremendous opportunity for district energy systems to save energy and water while gaining efficiency.”