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How raw sewage becomes biodegradable plastic

How raw sewage becomes biodegradable plastic

Posting in Energy

The California-based company Micromidas has a two-pronged environmental mission: reuse sewage that usually ends up in landfills to create biodegradable plastic.

The California-based company Micromidas has a two-pronged environmental mission: reuse sewage that usually ends up in landfills to create biodegradable plastic. I spoke this week with Ryan Smith, the company's chief technical officer, about the process -- and the future of plastics.

Your company converts raw sewage into disposable plastics. What does the process entail?

Raw sewage, for us, means a large variety of underutilized waste streams. We focus primarily on municipal wastewater, essentially the solids. We also look at food waste and manure. We take the waste -- it's usually 5 to 10 percent solid content, the rest is water -- and run it through a typical process of anaerobic digestion. The idea is to convert the waste, or at least some fraction of it, to bio-gas or methane. In the process of doing that, there's a cascade of biological reactions that take all the constituents of that waste and break them down to methane. Partway through there -- usually the first two to three days [in a 30-day process] -- a lot of that gets broken down into a soluble form, essentially an organic acid. Those organic acids are a perfect nutrient to feed microbes we've selected.

We have a small tank that runs for a couple of days that breaks solids down into this organic acid that's soluble in water. We take that liquid stream, do a bit of processing on it and feed it to microbes. Just like we store fat for energy, these organisms store little granules of plastic. We grow them up on those organic acids until they're fat with plastic granules. We've got essentially a cell broth. We take the water out of that stream and we have a cell paste that has a lot of plastic in it. We run it through a traditional extraction process that removes the plastic from the cell debris. Then we have this nice, high-grade, clean, disposable plastic. It's converted into a disposable article [and] instead of going into a landfill for 1,000 years, it will biodegrade over the course of six to 18 months.

Do you partner with wastewater treatment plants to get the waste material?

We do. There are a lot of wastewater treatment plants we've been working with, particularly in Northern California. There's a truck that goes to various waste treatment plants throughout the week and grabs 500 to 1,000 gallons of sewage. It brings it back to our lab and we run that in a large pilot facility to demonstrate and develop the process. A next step for us is to work with one of those treatment plants and build a demo facility where we've co-located on site with them and we pipe over the sewage.

For a waste treatment plant, the solids we're using are a costly burden. It's less than 1 percent of the total volume of most waste treatment plants, but it's easily 30 to 40 percent of the total cost. The solids, for a large municipality, just accumulate. You can't burn it under most regulatory areas. You can't bury it or even use it as fertilizer because it has human pathogens in it. They end up applying an expensive drying process to it and shipping it to a landfill willing to take it. They're willing to have us come on site, pipe their sewage and reduce it substantially.

What's your goal? Why is this important?

We view the work as important for a couple of reasons. One is that these waste streams are burdensome and expensive to deal with. It's important to come up with new technologies that are capable of treating them because some of the methods used now aren't sustainable. Every container made of plastic, every plastic fork that you or I have used, is still out there somewhere. It's a jarring concept. When you throw something away, it never really goes away. Providing a substitute or alternative plastic -- and it really is a plastic -- that biodegrades is quite substantial from an environmental perspective. For us, as a business, what's exciting [is] we're actually refining waste. Making something that's good for the environment is a bonus.

You mentioned plastic utensils. Could your plastic, made from waste, actually be used to make something that touches our food?

[The plastic] is clean. There's no reason to worry about it coming in contact with food. That said, there is a certain 'ick' factor associated with running from waste streams to plastics, particularly from human waste. FDA approval for food contact use is a process in itself. As a start-up company, that's certainly a market we're looking at in the long run. In the short run, for regulatory reasons, [we're now considering] some sort of secondary packaging. Perhaps the next time you buy something from Amazon the foam peanuts are instead biodegradable. That's the kind of application we think could work. In terms of determining what applications work from a technical and adoption standpoint, we're having the plastic sent to third party labs and potential customers now to be validated. I'd also expect it to blend with more traditional plastics, as well.

Is your plastic out in the market yet?

It is in the development phase. This plastic is currently made [by other companies] and used in the market. But because it's derived by sugar sources, it is sold at a high price. It's found niche markets, like medical sutures and bio-medical implants. To really utilize the potential of the biodegradability of this plastic, it's important that it can compete at parity with petroleum plastics. By using a waste stream [rather than sugar sources], we're able to open up those markets. I wouldn't expect to see articles made of Micromidas plastic for the next at least 18 months.

What's the next step for your company?

There are a couple of next steps. One is to demonstrate the process at a commercial or pre-commercial demonstration scale that demonstrates the economics of using a waste stream to make a commodity. To do that, we're partnering with waste treatment plants and manure providers to build those first demonstration plants to prove the economics and scale this to a larger, high-volume process. Over the next 12 to 18 months, that's what we'll be doing.

In addition to that, the organisms we use utilize a lot of soluble organics, but there's still a fraction of the waste that gets unutilized by bacteria. We've got a parallel program looking at upgrading the residual solids chemically to other biochemicals. That's a program being developed probably six to eight months behind the bioplastics program.

We want to become the folks who can refine solid waste much like petroleum was refined over the last century. We're developing other technologies to utilize every piece of that waste stream and turn it into something of value.

Watch Ryan Smith's PopTech presentation

Photo: Flickr/Carol Mitchell


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Christina Hernandez Sherwood

Contributing Writer

Contributing Writer Christina Hernandez Sherwood has written for the Los Angeles Times, Newsday, the Philadelphia Inquirer, Diverse: Issues in Higher Education and Columbia Journalism Review. She holds degrees from the University of Delaware and Columbia University's Graduate School of Journalism. She is based in New Jersey. Follow her on Twitter. Disclosure