Why It’s So Hard to Recycle Plastic

There’s a soap dish for sale at a beauty products shop in São Paulo, Brazil. An off-white disc with a smooth, rounded shape like a river stone, it is just one of millions of plastic soap dishes on offer in shops around the world. But, although most plastics are made from petroleum, some of the plastic in this dish started out as methane generated by a water-treatment facility in California.

Inside a 10-metre-tall bioreactor at the facility, ancient bacteria known as methanotrophs transformed the methane into a molecule called poly(3-hydroxybutyrate), or P3HB. The bacteria use P3HB as a kind of internal battery for energy storage. But a biotechnology company called Mango Materials in Redwood City, California, uses P3HB as a raw material, harvesting granules of it from the bacteria and manufacturing them into lentil-sized pellets called nurdles. These nurdles, the common currency of the plastics industry, then became the soap dish.

Mango Materials is part of a growing effort among scientists, non-governmental organizations and companies large and small to make plastics more…