Edmonton’s Faulty Compost Digester Needs $6.7 Million Investment

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Edmonton’s long-life digestion facility needs millions of dollars in investment to keep poor-quality compost from ending up in the landfill and polluting the environment with plastic.

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The high solids anaerobic digester, which opened fully last year, needs an additional $6.7 million to build two screens and two blenders to filter waste and remove moisture, according to a staff report meeting at the municipal council on September 12. The original institution was budgeted at $30 million in 2013, but costs rose to $42 million in 2018.

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The facility uses micro-organisms to degrade waste without oxygen and produces “digestate” and biogas. The digestate is put into aeration boxes to create compost. It was designed to process up to 40,000 tonnes of waste per year.

But a business case recommending the new upgrades paints a damning picture of what the long-awaited install produces.

The digester was designed to work in tandem with the Edmonton Composting Facility (ECF). The ECF was closed in 2019 over safety concerns – it was partially closed after a roof collapsed the previous year and had suffered structural problems since at least 2017. The council voted last December to do not build a replacement.

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But without the screening provided to the ECF, the digestate now arrives at the processing site filled with waste, littering the Edmonton Waste Management Center (EWMC) site and adjacent wetlands, the business case says. The quality of the compost is so poor that it is sent to line the landfill.

“Status quo or inaction is not a practical option, as continued waste disposal at treatment sites is considered a significant environmental issue that cannot be ignored,” the business case states. .

“Compost is currently only used as a daily alternative cover for landfill as it does not meet the quality standard for other uses. This use of compost incurs a cost to waste services for the elimination.”

In addition to limiting the waste that escapes from the processing site, the improvements promise to more efficiently mix wood chips with digestate so they can be recycled instead of the city paying to dispose of them, and create a more marketable compost, according to a staff report.

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Digestate that has been screened and processed at the Edmonton Waste Campus.
Digestate that has been screened and processed at the Edmonton Waste Campus. Photo by Source: City of Edmonton, Business Case for Anaerobic Site Upgrade

Garbage Compost

Neil Kjelland, the city’s sustainable waste management manager, said the compost from the anaerobic digester is of poor quality because it’s made from organic waste extracted from the waste stream.

The city sells other high-quality composts in bulk made from organic material collected with seasonal yard waste that is much less contaminated, he said.

“As compost suitable for all applications, we are also providing limited quantities of this compost free of charge to Edmontonians at eco-stations,” he said in an emailed statement Friday. “In addition, the organic material collected in the green carts is also turned into good quality compost, as it contains much less contamination.”

Kjelland said the new mixers will improve the way all organic materials are processed.

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“This will help filter contaminants (plastics, etc.) from organic material. It will also be used to pre-treat organic waste that will be sent to processing partners, to ensure they receive contaminant-free organic waste.

The 2017 business case for three-stream source separation, said organics from green bins would be treated at the anaerobic digestion site.

Last year, an estimated 40% of waste was not diverted from landfill.

Wood chips and plastic cannot be separated at the anaerobic digestion facility.  This means that these items go together in the landfill, although the wood chips can be recycled.
Wood chips and plastic cannot be separated at the anaerobic digestion facility. This means that these items go together in the landfill, although the wood chips can be recycled. Photo by Source: City of Edmonton, Digester Upgrade Business Case

The plan was to make a profit

Producing something the town can sell for a profit was part of the original plan when the anaerobic digester was first funded by the council in 2013.

The digester captures methane gas which can be burned to generate heat elsewhere on the waste management campus, create electricity and be sold.

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The documents available on the city’s website do not indicate whether or not the digester meets expectations. The responses provided by the city did not clarify the situation.

“Some of the gas was used to generate electricity which was used in our facility, fed back into the grid or sold. The subject matter expert who can provide revenue information is not available until next week,” Kjelland said.

The 2021-2022 annual business plan shows an intention to make gradations to better understand “the biomethane potential of waste” which will make it possible to create “key performance indicators expected from the cogeneration of electricity”.

The city has earned $235,000 from bulk compost sales so far this year, Kjelland said.

The digester site was built by Maple Reinders using BioFerm technology and is operated by Veolia, formerly known as Suez.

maple reindeer’ project website said the site can handle 48,000 tonnes of waste although the city says its capacity is 40,000.

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