How Contamination Disrupts Composting: Impacts on Quality, Costs, and the Environment

Compost contamination can lead to a variety of problems that affect the composting process, the quality of the final product, and even the environment. Contamination occurs when non-organic or harmful materials are mixed with organic waste during the composting process.

According to a study by the Composting Consortium, an industry collaboration managed by Closed Loop Partners’ Center for the Circular Economy, approximately a 5th of operating costs is spent on dealing with contamination. The study found that 85% of the contamination detected at composting facilities was conventional plastic.

Source: “Don’t Spoil the Soil: The Challenge of Contamination at Composting Sites” a report by the Composting Consortium, managed by Closed Loop Partners’ Center for the Circular Economy 

Below are some key contaminants found in residential green bins:

1. Plastic and Synthetic Materials

2. Glass, Metal, and Other Inorganic Materials

3. Pet Waste (cat litter and other pet feces)

4. Diapers or Sanitary Products

5. Batteries, Light Bulbs, and Hazardous Waste 

To further complicate the problem, there are differing rules from city to city on what is considered acceptable in the green bin. Some cities allow compostable plastic bags and some do not. Some allow meat and oils, some do not. Even used napkins and grease stained pizza boxes are allowed in some composting programs and not others. This will likely tighten up as more provinces and states adopt EPR legislation. In an effort

to reduce contamination in organics, Colorado company A1 Organics has reduced its acceptable materials. Other composters, like Glacial Ridge Composting Facility, are only accepting compostable packaging that is BPI-certified compostable, to reduce risk of contamination from non-compostable packaging. 

Impacts of Compost Contamination:

Below are some key impacts of contamination in the organics stream, as shared in the Composting Consortium’s research. For more details on the environmental and economic impacts of compost contamination, read the Consortium’s report.

1. Decreased Compost Quality

   1. Presence of Inorganic Waste: When plastic or other non-organic materials contaminate the compost, impacting the final product. Instead of being a nutrient-rich, natural fertilizer, the compost can have a lot of trash in it, reducing its overall quality.

   2. Nutrient Imbalance: Contaminants like plastics or metals can interfere with the natural balance of nutrients in the compost, making it less effective as a soil amendment.

2. Economic Costs

   1. Increased Processing Costs: Commercial composting operations often need to invest additional resources in sorting out contaminants or addressing any issues that arise from contamination. This increases the cost of producing compost.

   2. Product Wastage: Compost can be deemed unusable if contamination levels are too high. Resulting in wasted resources, increased landfill costs, and missed opportunities for creating high-quality compost.

3. Environmental Impact

Contaminated compost, especially when it contains chemicals or

non-biodegradable plastics, can pollute the surrounding environment. The presence of plastics in compost can contribute to the growing microplastic pollution problem. Small plastic particles may be dispersed into the soil and can enter the food chain.

Prevention and Management

Measures taken to prevent contamination and ensure a high-quality product can include:

• Strict sorting procedures: Ensuring that only organic and certified compostable materials are composted by screening out contaminants.

Education and outreach: Informing the public about what can and cannot be composted to reduce the amount of contamination in the incoming waste stream.

Contamination of commercial compost can significantly affect its quality, increase costs for producers, and pose environmental risks. Proper management, education, and stringent quality control are essential to prevent contamination and ensure that compost serves its intended purpose of enriching soil and reducing waste.