Compost Manufacturing Alliance – Windrow (CMA-W) Change


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As of January 1, 2024, the City of Ann Arbor and it's compost facility operator, WeCare Denali (WeCare), will no longer accept BPI​ certified material in compost carts or at the city's compost facility. Instead, only selected products identified as being certified "CMA-W", short for Compost Manufacturing Alliance - Windrow, and made of fiber material will be accepted.  A searchable list​​​​​​ (spreadsheet) of currently selected and certified CMA-W, fiber only products that will be accepted by our composting partner, WeCare. Bamboo and palm leaf products are currently excluded as they do not break down in the composting process. 

The change is necessary because​:

  • Compostable plastics can be nearly indistinguishable from traditional petroleum-based plastics, which leads to traditional plastics in the compost stream and compostable materials in the recycling stream.  

  • CMA certification adds a field test for compostability, in addition to lab testing, which ensures items break down appropriately in a real-world composting.

Compost manufacturers formed the Compost Manufacturing Alliance (CMA) in 2017 to begin researching and field testing manufactured compostable products. CMA now offers a variety of certifications to products that have ​met industry standards for properly breaking down in a myriad of ways, including compost windrows like those used at the Ann Arbor compost site. 

This change may be frustrating, especially for businesses, organizations or individuals who have stocks of this material. However, the benefits to improving our environment and in meeting the city's climate change goals are well worth the effort. 

To help the community understand this shift, the city will:

  • hold outreach and trainings to those most heavily invested in manufactured compostable products such as food businesses

  • conduct community and outreach communications via print and digital channels

​​​​​​​​​​​​​Webinar videos

The CMA-W W​ebinar slides​ (PDF) are available now.​

If your commercial property is interested in compost service, visit our Commercial Compost Collection for Food Scraps webpage. 

Frequently asked questions

Are plastic liners accepted? 

How will I know if an item is compostable? 
The CMA-W certified products are not branded as such. If the item says that it is compostable and it is Plastic, leave it out. If the item is paper or wood-based and says that it is compostable, then put it in.  

Are napkins, paper towels, paper coffee filters and cardboard acceptable?  

Are any biodegradable products institute (BPI) certified items acceptable? 
Yes,  if they are paper/fiber items and ​on the list of allowed items. These are CMA-W certified items minus plastic and bamboo and palm leaf products. Bamboo and palm leaf products do not break down in our system in a timely manner. 

Is plastic cutlery acceptable? 

Are there some plastics that are accepted in the compost? 
No. They pose a real litter problem as they are light and blow around, especially when the plastic is shredded in the grinder. 

What can I use in place of biodegradable plastic bags? 
We strongly encourage liner-less kitchen composter use and instead use a paper yard bag in the cart during the winter to prevent the materials from sticking. If a liner is a must for a kitchen composter an unlined paper one is recommended. 
When in doubt, throw it out!  

Distributors of CMA-W products​