The Curbside Compost Microplastic Conundrum

Time to pay up suckers! Today’s the day New York City begins enforcing fines for buildings that don’t separate compostable food waste from landfill garbage in respective curbside bins. NYC’s program accepts pretty much any kind of food waste and “food-soiled paper” such as wrappers or pizza boxes. You can dump your food scraps directly into the compost bin, or in a clear plastic bag, but not a paper bag, which seems puzzling if they accept food-soiled paper.

But, plastic bags in compost? Isn’t that bad? Well, yes, and … probably also yes.

First, consider how curbside composting fits into the New York City’s overall recycling program, which in turn fits into the larger operations of the City of New York Department of Sanitation (DSNY). Independent news site The City (no relation) has a fulsome further explainer not just of the citizen-side details of curbside composting, but also regarding what happens to food waste once collected. Depending on where the waste comes from, it can go to the city-owned composting facility on Staten Island, the city-owned biogas plant in Brooklyn, or to a number of smaller contractors who process it in various ways.

But if we’re following the food scraps to where they become delicious dirt, Staten Island here we come!

Look at all those big piles of fertile dark Earth. Don’t you just want to roll around in there like a fat glistening grub straining for fecund release? Of course you do. Note how the Earth came to be so piled: collected food waste is run through a machine called a depackager—in DSNY’s case, a Tiger depackager—which separates organics from the aforementioned plastic bags and other contaminants.

DSNY assures us the Tiger can skim off the good from the bad and vice versa, which is why it’s OK to toss your compost in plastic bags. From the NYT story:

The machines have blades! Not a threat, merely a promise, because they also have sensors. What do the Tiger’s innards look like though?

Yep, those are blades all right: rows of opposed corkscrew auger blades in fact, horizontal and vertical. These blades grind everything to goop, which is then channeled apart by centrifugal force and screening. Out of one chute you get nutritious organic slurry, ready for composting. From the other, a savory étouffée of shredded plastic and other Bad Stuff you don’t want in your mouth.

That’s all well and good, but what about microplastics? Seems like feeding plastic bags into a giant blender would, you know, produce a lot of those. Isn’t microplastic contamination a growing concern for industrially produced compost? I’m glad you asked that question. Nobody else will be glad you asked that question. (The question was asked of DSNY, by me, but no response has yet forthcome, glad or otherwise.)

The Tiger depacker and similar machines focus on “size reduction” (via those auger blades in this case) to separate inputs into useful outputs. Which seems like an obvious recipe for creating really great amounts of microplastics in all your outputs, good and bad. But some newer approaches instead favor the “minimum fragmentation” approach, using air and water or percussive, squeezing paddles to separate organics from plastic and other contaminants. This should theoretically create fewer microplastics in the outputs. No doubt conscious of this issue with their own machines, Tiger now sells an add-on accessory that’s supposed to filter out microplastics produced by its depackers, though there’s no public data on how effective the accessory is, or if it’s in use anywhere yet. (Tiger did not respond to what I considered an extremely polite question on the matter.)

Depackaging is a pretty young industrial niche, descended from quarrying machinery and other solutions for separating stuff from other stuff. Widespread awareness of environmental microplastic contamination is even younger, and worries about microplastics in compost are younger still. And yes, we all must grapple with living in a post-contaminant world. But while environmental microplastics are as common around New York City as everywhere else, in theory the environmental contamination vector takes time to make the journey through water, soil, plants, and animals into local human bodies. Distributing city compost pre-contaminated with microplastics—compost which is then used to grow produce eaten by humans—potentially creates a much more direct path for those microplastics to take up permanent residence in your guts, blood, and/or brain. I doubt most New Yorkers are interested in having their own plastic waste fed back to them.

It would be useful to get a few bags of the official NYC compost from the Staten Island facility and test them for microplastics. But since microplastic soil testing goes for a thousand bucks a throw, such an investigation will have to originate with a better leveraged media operation than this newsletter. Ideally DSNY would make a point of addressing potential microplastics in their compost, especially given the big public campaign around curbside composting. Maybe a publication with more pull than this one can get DSNY to cough up an answer. For added color in such an editorial pitch, consider this Upton Sinclair-style stemwinder about DSNY greenwashing from an anonymous Communist sanitation worker. (The Communists did not respond to my request for contact with the author for a follow-up.)