As much as 30 to 40 percent of residential waste in North America is organic, equaling more than 20 pounds of food per person per month. While some of it is composted, the majority of it usually winds up in landfills where it does no one any good.
Clearly we should be composting much more of those leftover food scraps, but we also need it to be more efficient. Now a new study from Concordia University has identified the best method of composting that could yield high quality compost and high value by-products — and all with the help of worms.
The study’s lead author, Louise Hénault-Ethier, experimented with different methods of vermicomposting to see whether they could sufficiently inactivate certain bacteria for safe public use of the compost.
Note: The vermicomposting process uses various species of earthworms — such as red wigglers — to create a mixture of decomposing vegetable or food waste, bedding materials, and vermicast, which is the end-product of the breakdown of organic matter by an earthworm. These castings have been shown to contain reduced levels of contaminants and a higher saturation of nutrients than do organic materials before vermicomposting.
“Centralized composting, which is one of the fastest growing industrial composting methods, has strict governmental guidelines, requiring thermal sanitation to prevent the survival of harmful bacteria,” said Hénault-Ethier, who carried out her research while pursuing a master’s from what is now Concordia’s Individualized program.
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The guidelines require that the compost reaches and maintains a heat of 55 degrees Celsius over a period of three days in a self-heating process driven by decomposer microorganisms found in the compost.
“But in our case, worms graze on the decomposer community, preventing the onset of high temperatures. We wanted to see if vermicomposting, which proceeds at room temperature, could still get rid of harmful bacteria.”
Note: Did You Know: An earthworm can eat up to one third its body weight in a single day. For a 150 pound human, that would mean 50 pounds of food per day!
Together with Concordia chemistry professor Yves Gélinas and biology professor Vincent Martin, Hénault-Ethier examined the impact of vermicomposting on E. coli, which can be found in fecal matter and can easily make its way into organic waste.
For the study, the researchers conducted three experiments to monitor the presence of E. coli, testing whether the size of the batch of compost, the amount of naturally occurring compost microbes and the rate at which the compost was fed would affect the survival of the pathogen.
In every single experiment, the worms proved effective and produced compost that respected the regulatory bacterial count limits.
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“We found that the compost batches take on average 18 to 21 days to fully degrade the E. coli to levels well below the legal limit,” explained Gélinas, who worked closely with Hénault-Ethier to examine how the chemicals — such as Carbon, Nitrogen or sugars — present in the compost materials would affect the bacteria’s survival. “While that’s slower than traditional composting methods, it’s not a prohibitive amount of time.”
For Hénault-Ethier, it’s the added benefits of vermicomposting that are most important.
“The compost it produces may lead to higher plant yields when used as a fertilizer, and — even more surprising — the red wigglers themselves could then be reused as feed for other animals on the food chain,” she said, referring to what’s called “upcycling” — which means to generate something more valuable than the initial waste product..
“This study suggests that upcycling technologies like vermicomposting can be more widely developed for commercial use,” Hénault-Ethier said.
The results show that vermicomposting is a promising method in the sanitation of organic waste, which would allow for producing proteins for animal feed.
That said, while the E. coli inactivation observed in the current study is promising, Hénault-Ethier cautions that further research on a more diverse array of pathogens is still required.
Based on material provided by Concordia University. This study was funded in part by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Fonds de recherche du Québec – Nature et technologies. Results are published in the journal Waste Management.
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