Behind the hoardings on the southeast corner of a busy downtown Toronto intersection sits an unnervingly deep hole, about 32 feet across and 130 feet down. It’s so deep that visitors can’t see the bottom from the sturdy guardrail around the rim. The surrounding work site is wedged between the back of a public library and a curb skirted by a streetcar line. A crane is shoehorned against the wall.
“This is all in the public right of way, all on Toronto Transportation [Services] land,” says engineer Cam Quinn, a senior project manager at Noventa Energy Partners, matter-of-factly. He peers into the pit and explains that the really tricky obstacles turned up well below ground: old pipes and something he calls “a vortex chamber, a concrete vault, built like a bank vault in the 1970s. We had to do a targeted demolition.”
None of this civil engineering, however, holds a candle to the most sensitive part of the project, which will happen later this fall, when Quinn’s team bores a few holes into the 10-foot-wide sewer main that traverses the shaft, shunting millions of litres of raw sewage toward the city’s treatment plant. For all the obvious reasons, the city’s water and wastewater officials prefer that its sewer mains aren’t perforated, but this delicate exercise in municipal laparoscopy represents a critical step in one of North America’s most ambitious renewable-energy ventures.
Noventa Energy, founded in 2018 by long-time Enwave CEO Dennis Fotinos, has partnered with the City of Toronto and Toronto Western Hospital, a sprawling 118-year-old healthcare facility located across the street from the big hole, to build a sewage waste heat recovery system that captures the heat from sewage and uses it to warm or cool the air inside.
The heart of the project is a cutting-edge heat exchanger from Huber, a German firm, that takes the thermal energy out of the sewage, concentrates it, and then uses it to replace the natural gas Toronto Western burns to run its massive boilers and chillers. The sewage travels in a closed loop out of that big main, through the heat exchanger, and then back into the sewer. The technology works in reverse in the summer, removing heat from the hospital and transferring it into the sewage. According to Noventa, which has a long-term agreement to sell the waste heat to the hospital, the venture can reduce Western’s heating and cooling needs by up to 90% while removing the equivalent of almost 2,000 cars worth of carbon each year.
The company claims it is the world’s largest wastewater energy-transfer project.
Recovering energy from warm sewage is about as elegant a circular-economy undertaking as one can imagine. Every city generates waste, which tends to be between 10 and 20°C. However, all that energy has traditionally ended up getting dumped in rivers, lakes and oceans, either directly or, more typically, after processing at a treatment plant.
A growing number of cities see this practice as a wasted opportunity. For the past dozen years, the City of Vancouver has operated a sewage heat recovery plant in False Creek, which distributes low-carbon energy for heating and hot water to 6.4 million square feet of mixed-use buildings. The facility has the capacity to generate 3.2 megawatts of power. Halifax launched a small-scale sewage heat recovery project in 2021.
In 2019, the City of Toronto asked for private-sector proposals to tap its own wastewater energy, the main conduits for which have been mapped by municipal officials. Noventa proposed a joint venture with Western, but city officials say there are so many large trunk sewers across Toronto that there’s plenty of this, well, resource to go around.
The City of Toronto estimates its sewers can produce 17 megawatts of energy, and council has approved a plan to expand to other sites – hospitals, university campuses, government buildings – now that the Western project is almost complete. “We can do about 30 projects based on the resource right now,” says Fernando Carou, energy transition leader for the City of Toronto’s environment and energy division. “It’s kind of shocking that you can actually recover [the energy for an] entire hospital campus from the sewer.”
While the idea is appealingly common-sensical, the engineering required to carry it out is complex. Quinn explains that the hospital had to replace part of its own heating system while Noventa installed banks of its Huber heat exchangers, as well as a variety of heat pumps, in a vacant building next door. The project called for a tunnel beneath the street, which carries the pipes that link the heat exchangers with that big trunk sewer. The sewage never leaves those pipes, of course, and Noventa’s technology is designed to continuously flush the interiors of the equipment so it isn’t “befouled” – a term of art in this nascent sector.
Noventa’s contract with the city and the hospital runs for 30 years, enough time, presumably, for the company to recoup the capital costs and earn a profit. Although municipal officials stress that subsequent wastewater energy-transfer sites will be available to other bidders, Noventa has secured nine other locations across Toronto and agreed to help offset the city’s energy costs by providing heating and cooling at other municipal facilities.
Edward Rubinstein, Noventa’s vice-president of business development, notes that many other cities and countries are actively looking at tapping into this energy source, especially in the U.K. “There’s a lot of work going on,” he says. The City of Berlin, for example, has mapped the entire resource through its sewer-shed. And across Europe, an earlier, but smaller-scale, version of this kind of wastewater energy-transfer system has been around for about 20 years. “It’s a proven technology, but we’re doing it at a different scale,” Quinn says. “All of the existing installations are one or two heat exchangers, and we’re doing 16.”
With the imminent completion of Noventa’s first wastewater mega-project, energy-recycling firms will be watching closely to see whether Huber’s technology delivers the goods. But as such ventures scale up, other important questions will, well, float to the surface: Who owns all this energy? Should we begin to think of the wastewater divisions of municipalities as new kinds of utilities? And can we stomach the idea of private firms profiting from the waste that each of us deposits in the toilet every day?
Regardless of how the policy details settle out, there’s no disputing the fact that the opportunity for cities to recycle something as unloved as sewer warmth is an encouraging turn in the energy transition.
