January 17, 2013
Column | Korky Koroluk
Sewage an untapped energy resource
We’ve heard a lot about renewable energy in the last few years as we slowly began to realize the huge penalty we’re all going to pay for our dependence on fossil fuels.
So developers have been busy promoting and building wind and solar farms, and developing biofuels. The geothermal advocates have been busy, too, tapping the limitless energy contained in the earth beneath our feet to heat houses, motels, and assorted other commercial buildings.
But there is a source of energy that no one thought about much until recently, when an outfit called NovaThermal Energy LLC installed a pilot plant at a wastewater treatment facility in Philadelphia. Its aim: To tap sewage geothermal.
If you live in a city, as most of us nowadays do, there is a gray river of warmth flowing through the pipes under our feet.
Conventional geothermal utilizes ground-source heat pumps to heat and cool homes. There are installations that make use of a nearby lake. Instead of drilling geothermal wells down into the ground, the piping is horizontal and installed in what’s called a lake plate, which is towed into deep water, then sunk.
Well, in China, where the idea of sewage geothermal was pioneered, several large buildings have used the technology for heating and air conditioning. They include a couple of hotels, and a million-square-foot train station in Beijing. A highrise apartment building in Tianjin, China’s third-largest city, also uses sewage geothermal for heating and cooling.
Wastewater picks up heat from a number of sources, including dishwashers and laundry machines in your home, from showers, and from any number of industrial processes. There’s also what the industry delicately calls “biomatter” that still contains heat.
All that means that in many North American cities, sewage is about 15 C in the winter, and can exceed 22 C in the summer. That represents plenty of energy that can be extracted by heat pumps.
NovaThermal installed its Philadelphia pilot last spring, then later in the year but in a second, larger plant at a sewage-treatment plant across the Delaware River in Camden, N.J.
The company put its plants at treatment plants because they are public buildings with plenty of wastewater.
But a company spokesperson said that the technology could be used in any large building that’s near a major trunk sewer with a steady flow of wastewater that’s still warm from its previous use.
NovaThermal’s process taps into sewer lines and diverts some of the flow through heat exchangers.
A Swiss firm, Rabtherm Energy Systems AB, is promoting a somewhat different system. It involves replacing sewer mains with new pipe that has tubes embedded in the concrete. A solution circulating through the tubes picks up heat from passing wastewater, and moves it to nearby buildings. The company so far seems to be concentrating its activities in the French and Korean markets.
Since NovaThermal brought its technology from China, it has concentrated its efforts in the United States. As the world develops alternative, renewable energy technologies, it is apparent that there will be no single, replacement energy source to replace fossil fuels. Instead there will be a mix of wind and solar, hydro and geothermal.
And the technology for storing energy improves, we can look forward to a day when you can have solar or wind energy powering your building, even when the sun isn’t shining or the wind isn’t blowing.
But sewage is a constant, expensive to collect and expensive to treat. And as our cities grow, there will be more and more of it. If we can utilize it as one part of the renewable energy mix, though, cash-strapped cities might discover that there is money flowing through their sewer pipes.
Korky Koroluk is an Ottawa-based freelance writer. Send comments to firstname.lastname@example.org
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