Recycling the Organics in Our Garbage Bags

Is recycling of leftover organic waste in our garbage bags really a good idea? European information suggests that this end product is a low quality product and potentially compromises the market for higher quality compost.

Mechanically sorted organic material from residential garbage in a mechanical biological treatment process.

Mechanically sorted organic material from residential garbage in a mechanical biological treatment process.

In our desire to achieve our landfill reduction goals and work towards zero waste, many communities are considering extracting remaining organic material from our garbage in material recovery facilities. In Europe, the process is called mechanical biological biological treatment. The “organic material” is mechanical separated from the garbage, then treat it biologically. There are three options (DEFRA 2013)

1. aerobic biodrying/biostabilization

2. aerobic in-vessel composting

3. anaerobic digestion for energy recovery with the organic fraction going to options 1 or 2.

To compost this material, additional bulking agent may be required because of the high moisture content of the separated fraction. This adds additional material that may be potentially contaminated with the non-organic material in the compost.

Although anaerobic digestion followed by composting sounds like a great idea, either “wet” or “dry” anaerobic digestion requires additional water or bulking agent. The resulting product is simply more of a potentially contaminated product, plus a water fraction that may cost money to dispose of.

Eunomia Research and Consulting (2003) concluded that:

“Experiences with attempts to derive ‘compost’ from mechanical separation of mixed residual waste have tended to reveal two things;

1. the end product is generally of a low quality, and has led to problems (and rejection) when attempts have been made to use the material on land. Typical contaminants are heavy metals, glass and plastics,

2. the attempt to market such materials can severely compromise the market for materials of higher quality, derived from source-separated materials.”

Read and Godley (2011) concluded that composting the biological fraction presented “higher environmental risks because of possible contamination from other components in the residual waste, and anaerobic digestion of this material “produce liquid effluents that can be difficult to dispose of.”

In the UK, DEFRA (2013) concluded that “the use of compost-like output (CLO) from mixed MSW on agricultural and is currently not permitted by the Environmental Agency. If an outlet cannot be found for the CLO, then it may have to be disposed to landfill”. They noted that it could potentially be used for capping the landfill.

My recommendation is that this material be simply “biodried” to remove moisture and some of the carbon, followed by landfilling. This process may achieve up to 80% weight reduction during the process, and will not require extensive post processing to remove contaminants. This would also be much more cost effective than attempting to capture energy during anaerobic digestion. The biodried material could also potentially be a feedstock for an energy recovery facility.

Post processing technology requirements to attempt to "clean up" organic material from an MBT process are extensive

Post processing technology requirements to attempt to “clean up” organic material from an MBT process are extensive

Our own community is planning to do this exact process (see http://www.abbynews.com/news/236040081.html), where we read:

“The district also plans to establish the Fraser Valley’s first mixed waste materials recovery facility (MRF). The high-tech centre would break open the garbage bag by removing recyclable and compostable material from waste otherwise destined for the landfill. While there are facilities that can process organics and recyclables separately, there are none currently in the Fraser Valley than can remove a large percentage of these items from a mixed bag.”

I have to agree with Read and Godley’s conclusions (2011), that the mechanical biological treatment process may not be as green as it first appears.

References

DEFRA 2013 (Department for Environment Food & Rural Affairs). Mechanical Biological Treatment of Municipal Solid Waste. www.defra.gov.uk

Eunomia Research and Consulting. 2003. Economic analysis of options for managing biodegradable municipal waste. Final Report to the European Commission.

Read, A, and A. Godley, 2011. How Green is Mechanical Biological Treatment? http://www.waste-management-world.com/articles/print/volume-12/issue-2/features/how-green-is-mechanical-biological-treatment.html

 

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