Microplastics or Methane?

Martha Walden, 11th Hour

By 2024 at the latest most Humboldt residents and businesses will be obliged to separate their food waste and other organic matter from their trash. Most of California already does so in accordance with SB 1383, the sweeping law targeting methane. And as we all know, methane is a powerful greenhouse gas — eighty times worse than CO2 — that results from organic matter in landfills. 

Recology and other haulers are working to procure the extra trucks and bins to do the pickup. Then what? That’s been the burning question for Humboldt Waste Management Authority and the Solid Waste Local Task Force. Shall we build an industrial composting facility here in Humboldt? How long will we have to truck the stuff to Oregon, the closest composting facility?

Another possibility is to turn our garbage into biogas.  Miranda Dairy is setting up a biodigester operation in Ferndale. Biodigesters anaerobically break down organic matter and capture the methane. This gas can be refined to various degrees and used for various purposes — to fuel vehicles or to spin turbines at a gas power plant. 

Biodigesters have become more common during the last ten years or so as California works to reduce its GHG emissions. Dairies, in particular, invest in biodigesters as a way to capture the methane from cow manure. The technology planned for Ferndale is a co-digester, meaning that it can use both manure from its dairy cows and food waste as feedstock. In fact, it can handle a hundred tons of food waste per day, which is roughly the same estimated amount that Humboldt will be collecting by 2024.

Making biogas has drawbacks. Methane leaks and nitrous oxide emissions can severely undercut any GHG reductions—especially if dairies expand their herds in order to have even more manure to feed the digester. So they increase the initial supply of methane in order to capture most of it. This makes the operation more profitable, even lucrative—thanks to California incentives — but it’s also more difficult to calculate actual benefits for the climate.  Also, neighbors complain about increased odor, fumes and traffic. 

Adding food waste to this scenario complicates it more. Much food sent off by grocery stores and food manufacturers to be biodigested are packaged in plastic. Depackaging machines separate the food from the packages by squishing the food out. Even if that gets rid of 95% of the plastics, the rest is churned up into microplastics that wind up in a byproduct of the biodigestion process. This residue, called digestate, is spread on fields as a soil amendment. Microplastics in soil are an increasing problem.

Separating food from packaging by hand at the source is better but not perfect. In fact, biogas operations typically run source-separated foods through a depackaging machine anyway because they are sometimes contaminated. It would be better to use a different screening method for this waste stream. Packaged foods that are sorted by package type create less of a problem, but biodigester operators just want to throw everything together into the machine. In most states the packaged foods are simply thrown away.  Now we’re back to where we started with methane wafting from the landfill. 

In the new wise world of the future, we won’t gratuitously package everything — especially not in plastic. Totally biodegradable materials will contain foods that must be contained. Meanwhile, we’re in a plastic-wrapped pickle.