Research and analysis

Contamination at Composting Facilities

Contamination is a systemic issue, and one of the greatest challenges that composters face. More data is needed to understand how much contamination exists in feedstock and finished compost.

To support the industry in addressing contamination at scale, the Consortium conducted an in-field study with 10 U.S. compost manufacturers to measure and characterize contamination across different points of the composters’ processes––and analyzed the financial cost to composters to handle contamination. The study examines five commonly held assumptions about contamination and compostable packaging, and breaks down in-field realities in a data-backed and easy-to-follow format. 

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How Did We Measure Contamination?

Our field team conducted sampling at three points in the composting process––examining food-waste feedstock, overs and unders––to assess contamination rates throughout composting operation.


Snapshot of How Our Findings Stack Up Against 5 Common Beliefs About Contamination

  • Common Belief Tested #1: Is conventional plastic the most common contaminant received by composters?

    Findings Suggest: Yes. On average, 85% of the contamination that composters receive is conventional plastic, by volume. 

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  • Common Belief Tested #2: Does allowing compostable packaging in the organics streams lead to higher contamination rates?

    Findings Suggest: Not necessarily. Most composters had contamination, irrespective of whether or not they accept compostable packaging. Several factors contribute to the levels of contamination that a facility receives.  

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  • Common Belief Tested #3: Contamination is a nuisance, but does it negatively impact a compost manufacturer’s bottom line?

    Findings Suggest: Yes. On average, 21% of composter operating costs are spent on contamination removal. 

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  • Common Belief Tested #4: Does conventional plastic impact the quality of composters’ finished product, threatening their businesses and our environment?

    Findings Suggest: Yes. Four out of 10 composters in our study had trace amounts of conventional flexible plastic in their finished compost. 

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  • Common Belief Tested #5: Doesn’t compostable packaging not break down and end up in finished compost?

    Findings Suggest: Sometimes. Eight out of nine composters who accept compostable products had no detectable amounts of compostable packaging in their finished compost. 

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