Waste Not, Want Not: Heating Buildings with Sewer Water
November 26, 2013
Americans flush “350 billion kilowatt-hours of energy into the sewers each year -- roughly enough to power 30 million U.S. homes,” according to an estimate published last year by National Geographic.
Lynn Mueller is making it his life's work to do something about that.
Head of International Wastewater Systems, Mueller is described by the Vancouver Sun as “obsessed” with converting sewage into energy. He calls municipal sewage a “ubiquitous, readily accessible” energy source, though he concedes that there are some negative connotations.
“Not a lot of people shake your hand when you're in the sewage business," he joked.
'Vast' Reservoir of Warm Water Underground.
A vast potential source of heat flows every day in the sewers underneath cities, according to an article on the Informed Infrastructure website. Water used in such daily routines as showering, washing clothes, and cooking represents “the largest source of heat leakage in buildings," the article states. "Even toilet water, which is at room temperature, is warm compared to the ground.”
Genevieve Tokgoz, project engineer in the Utility Planning Department of Metro Vancouver, Canada, told Informed Infrastructure that the city is serious about finding ways to tap that resource.
“We work on many resource recovery goals, so sewer heat is just one of the potential resources we are exploring," she said. "We are also looking at opportunities to recover energy from landfill gas and from our water transmission system.”
Vancouver’s Olympic Village project now has a heating system that uses energy from city sewer lines. The Olympic Village, now called the False Creek Energy Centre, plans "to go from heating 250,000 square meters to 650,000 square meters as more nearby buildings get connected,” according to the Green Energy Futures blog.
Mueller's International Wastewater has installed three of its patented SHARC (sewer heat recovery) systems in Metro Vancouver -- one in a 60-unit North Vancouver condo complex, one in Richmond’s Gateway Theatre, and another in a 172-unit condominium project near the University of British Columbia.
Designed For Individual Buildings: A Big Plus.
One great advantage of Mueller’s system, National Geographic noted, is that it’s designed for installation in individual buildings, which doesn’t require city-owned property, “so it captures the heat from wastewater going down drains even before it leaves the building” and doesn't become a municipal issue, debated by government bodies or encumbered with bureaucratic red tape.
Mueller reports interest from dozens of potential clients in North America and other countries, saying International Wastewater could possibly sell up to $20 million worth of its patented installations in the coming year.
Informed Infrastructure calls the technology “simple and proven.” The first wastewater energy installations were built “more than 25 years ago and more than 500 wastewater heat pumps are in operation worldwide.” It can be scaled up relatively easily -- larger-scale implementations would require little additional research.
Wastewater from buildings “maintains a fairly constant temperature as it travels through sewers to the treatment plant, typically about 60°F, though this varies by geography and season,” according to the National Geographic article. A heat pump captures the warmth of wastewater and transfers it to a clean water stream flowing toward homes and businesses. Thus, “dirty water never touches the clean water.”SHARCs In The Sewers.
International Wastewater’s SHARC system separates solids from sewage and then pumps the water through a heat exchanger. The transference to clean water usage is controlled by a computerized unit.
It’s not a system that can work everywhere. National Geographic pointed to a sewage heat recovery proposal in Brainerd, Minn., a town of 13,000 north of Minneapolis, which measured the temperature of its sewage outflow “in an attempt to quantify how much energy it has at its disposal, but the project's now sitting dormant.” In that situation the numbers simply don’t work.
It’s also not a closed loop system. Electricity is needed to run a SHARC system. But Mueller told the Sun that International Wastewater can pump out “the equivalent of six times the amount of energy to heat a building -- or five times the amount if it is being used to make new hot water.”
There Are Significant Challenges Yet.
Tokgoz cautioned that converting sewage to energy poses technical challenges, such as maintenance of clogged equipment, and the impact on wastewater treatment plants, which by and large use anaerobic digestion techniques.
“There are still many unanswered questions about how much heat we can extract upstream before the inflow temperatures drop below desirable levels,” she said.
In addition to Vancouver, similar projects are underway in Oslo, Tokyo, and Beijing. National Geographic reported that a sewage heat recovery system went online in May at the James C. Kirie Water Reclamation Plant in Chicago. It uses a $175,000 system designed by a University of Chicago professor.
"We've cut our energy costs for heating and cooling [at the plant] by 50 percent," Catherine O'Connor, district director of engineering, told the National Geographic. She estimates that the system should pay for itself within three years.