With Greenway incinerator set to go offline, city looks at options for sewer sludge
Usually burned, the byproduct of wastewater treatment could have commercial uses
Over the course of a typical day, about 18 trucks arrive at London's Greenway Wastewater Treatment Plant and unload some 275 tonnes of partially dried and treated human waste.
The trucks come to Greenway from London's four other wastewater treatment plants.
The cargo they haul into Greenway is sludge, a byproduct of the wastewater treatment process in use at all five of London's plants.
Once unloaded at Greenway, the sludge is "dewatered" and heated to 900 C until it becomes ash, which then goes into a landfill.
The City of London is looking at other ways to use at least some of this sludge instead of burning all of it, in part because the Greenway incinerator is about to go offline for six months so it can be replaced with a new one. Even with the new incinerator, the plant will be at capacity in about 15 years.
Kirby Oudekerk, the city's division manager of wastewater, said staff are looking at other options to handle the sludge, admitting the current process isn't optimal in a city that's declared a climate change emergency.
"Those trucks, they're always consuming diesel, so if we can find alternatives to minimize that or find alternative sources for that fuel, that would be the goal," he said.
Options include using the sludge as landfill, compost or fertilizer. Some of the options might require the city to partner with outside companies. You can read more about their plans and submit input on this city web page.
WATCH | Take a look inside the Greenway wastewater plant:
The hope is that at least some of the sludge can find some end-use instead of incineration. The city's own information describes the sludge as "nutrient-rich" which raises the question: Why can't it used as fertilizer, particularly in a city that is surrounded by farm fields?
Oudekerk said the sludge has to go through a costly preparation process before it can be used as a surface fertilizer.
"In the volumes that we're dealing with, that ends up being a very costly endeavour so as a long-term strategy, we don't feel beneficial re-use is going to be the total solution for us, but it can form a part of our solution," he said. "Incineration is a key part of our strategy."
While it does generate greenhouse gases, Oudekerk said there is some upside to burning the sludge.
A new generator has been added that uses the incinerator's heat to generate about 25 per cent of the electricity needed to run the Greenway plant. And while the initial ignition stage uses natural gas, after that the gas is turned off and the sludge effectively burns as its own fuel for the rest of the process.
Also, Oudekerk said once it reaches the ash stage, the volume of waste is greatly reduced.
Sorting out the wastewater biosolids plan comes as Greenway deals with other issues and upgrades needed to keep pace with London's growth.
A flood protection plan will get underway this year.
Oudekerk said it's needed to ensure the plant is able to keep operating during a heavy rainstorm or snow melt. Major rain storms are projected to become more frequent with climate change.
"Once you're flooded, it's very difficult to get water out of the plant," he said. "If you have lots of rain in a few hours, that's a major issue," he said. "There's over $500 million of infrastructure that we need to protect."
The work will require a diversion of traffic on the section of the Thames Valley Parkway that runs past the plant. The closure isn't scheduled to start until late this year and will last about two months.
The popular dog park close to the Greenway plant will remain open but vehicle parking will be affected.
You can read more about the city's wastewater biosolids plan here. Information about upgrades to the Greenway plant to improve its flood protection is here.
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