Troublesome Waste Plastic Solved by Microorganisms [Reading Science]

Nature "US Research Team Develops Two-Stage Treatment Method Using Microorganisms"
Useful Compounds Can Be Produced from Organic Acids That Decompose Mixed Plastics

[Image source=Yonhap News]

[Asia Economy Reporter Kim Bong-su] In theory, plastic is not difficult to recycle, but in reality, various types are mixed during the collection process, making separation and cleaning costly and troublesome. There are concerns that abandoned plastics break down into microplastics in the ocean, causing fatal damage not only to ecosystems but also to humans. However, a U.S. research team has attracted attention by developing a technology that separates mixed plastics into useful chemical substances through a simple process.

According to the international journal Nature on the 18th, a research team at the U.S. National Renewable Energy Laboratory (NREL) developed a two-step process to decompose and recycle mixed plastics containing high-density polyethylene (HDPE), mainly used for food packaging films, polystyrene used in construction materials and insulation Styrofoam, and PET used in beverage bottles.

The research team first used cobalt and manganese as catalysts for oxidation to break down the polymer chains of the mixed plastics into oxygen-containing organic acid molecules. In fact, this technology had been studied before. In 2003, the multinational chemical company DuPont in the U.S. researched and developed a method to decompose a single type of chemical substance into benzoic acid and acetone for recycling purposes.

The team added one more step. They introduced a bacterium called Pseudomonas putida, a soil microorganism that feeds on small organic substances. These bacteria consumed dicarboxylic acids derived from polyethylene decomposition, terephthalic acid generated from PET, and benzoic acid from polystyrene decomposition, then produced two useful chemical substances. First, they created polyhydroxyalkanoate, a biodegradable plastic used for surgical sutures. They also produced beta-ketoadipate, a substance used as a high-quality nylon raw material.

However, commercialization still has a long way to go. The research team is struggling to find the optimal temperature for the bacteria to produce useful chemicals to increase yield. Another obstacle is that the compounds produced through this upcycling process currently have limited market demand. A team representative explained, "Regarding temperature control, much experience and knowledge have already been accumulated, so if related companies conduct full-scale research, technical know-how can be established soon," adding, "Whether to scale up the process depends on economic feasibility."

Meanwhile, more than 390 million tons of plastic waste are generated annually, but most are discarded without recycling. This has led to the formation of massive plastic islands in the Pacific Ocean, causing fish deaths and fears over microplastics.