I recently had the opportunity to tag along with Nicole Berg, a program manager with the Office of Campus Sustainability (OCS), on one of her routine compost site contamination checks. During this check, we were able to visit the WeCare compost site where all of the compost from the university (and the city of Ann Arbor!) is disposed. To be honest, I didn’t really know much about what actually happens to my compost after I dispose of it, but I learned a lot about the entire composting process on my visit!
So, how does composting work?
Once the compostable material is collected, it is brought to the composting site and dumped. The waste is ground into smaller pieces and arranged in windrows—these are large rows of compost that are in the process of breaking down that you can see in the photo below. These windrows are periodically “turned” to allow oxygen in, which breaks down the organic material in compost. Turning is when a machine physically rotates the pile of compost, and we actually got to see the compost being turned during our visit! Something that I didn’t know is that the inside of the windrows is actually really warm—it lets off a bunch of steam as it’s turned.
It takes about 3 months for the compost to fully break down. Then, it’s screened to remove any small pieces of contamination (like plastic bags that accidentally get tossed into compost bins). The final product is compost that can be bought, which can be added to mulch/soil to improve its health/moisture, add some nutrients/beneficial organisms, and reduce the need for harmful pesticides. WeCare Denali produces around 10-15 thousand cubic yards of compost every year. For reference, that is about 500 garbage trucks full of compost! (For Ann Arbor residents, you can get 1 cubic yard of compost for free—learn more about WeCare’s compost here.)
What is compost contamination?
Compost contamination is when waste items that are not compostable make their way into the compost piles. This is dangerous for several reasons:
- Wildlife loves to eat the food waste from the compost bins. Before the waste is incorporated into the larger compost piles, you can see tons of birds scavenging for food. We even saw a flock of wild turkeys roaming around the site! When plastic and other non-compostable material ends up at the compost site, it poses a major health risk to wildlife.
- Small pieces of plastic in compost end up polluting the soil. The chemicals in certain plastics can damage crops, seep into groundwater, and pose a serious risk to human health. Plastic doesn’t belong in soil!
- If there is too much contamination, the entire batch of compost can be tossed out, and everything will have to go to the landfill (including all that valuable compost)! When compostable material ends up in a landfill, it doesn’t break down—because landfills aren’t designed to decompose organic matter.
The purpose of the Office of Campus Sustainability’s visits are to check the compost that comes directly from U-M, before it is incorporated into the larger compost piles. That way she can see what the major sources of contamination are on campus, and potentially stop the contamination at its source. The compost pile may not be the prettiest thing to look at, but that’s usually a good sign! A big pile of food waste means healthy compost. (However, this does not mean that food waste is necessarily good. As a whole, we should be striving to reduce our food waste, whether you’re eating at home or to-go. If you do have food waste, make sure that you are disposing of it properly so that it can get composted instead of ending up in a landfill.)
How can we prevent compost contamination?
During our visit, the main source of compost contamination were items like coffee cups and take-out containers. Items like these often cause some confusion. Most coffee cups you get from cafes here on campus are made of compostable material (and will be labeled as such). However, your typical paper coffee cup will have a plastic lining along the inside that makes it non-compostable. The majority of take-out containers need to be landfilled for the same reason.
Preventing compost contamination on campus is a complicated thing; there is not necessarily one right way to fix the issue. Among students, the main reasons for compost contamination are confusing items or accidental misthrows. Increasing signage around compost bins and education about compost may both help address these problems. This can be done by the university, but it can also be done by you! If you’re getting coffee with friends, or you see someone about to toss their take-out container in the compost bin, gently nudge them in the right direction! You can be part of the solution and help solve compost contamination at its source by informing those around you. If you are ever unsure how to properly dispose of something, check out OCS’ where to throw resource. You can type in any item, and it will tell you exactly where to throw it away! When it doubt, throw it out.