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Plastic is ubiquitous in our lives. While most plastics are made from petroleum, some are synthesized from methane produced during wastewater treatment. An ancient bacterium called methanotroph converts methane into a molecule called poly(3-hydroxybutyrate), or P3HB. This bacterium utilizes P3HB as an energy storage mechanism. However, a biotechnology company, Mango Materials, based in California, USA, employs P3HB as a raw material, extracting it from bacteria and manufacturing it into bean-sized pellets, called nurdles. These nurdles are used in plastic production.Mango Materials is part of an ongoing effort by scientists, non-governmental organizations, and companies (both large and small) to make plastic more sustainable. However, the journey ahead is long. Mango Materials only produces about 45 tons of P3HB annually, a drop in the ocean compared to the 400 million tons of plastic generated by humans each year. As mentioned, plastic pervades every aspect of human life, from food packaging to construction materials, electronics, clothing, and beyond. The list is endless.
Plastic serves as an easily accessible material due to its affordability and practicality, particularly for those residing in remote areas with limited access to refrigeration and sanitation facilities. Moreover, its lightweight nature translates to lower energy consumption during transportation compared to other food and beverage packaging materials. Consequently, plastic has permeated every corner of the globe. Unfortunately, the minimal economic incentive to collect plastic waste in remote and secluded regions exacerbates its accumulation, especially in countries with low to moderate living standards. These regions lack serious recycling initiatives. An estimated 2 billion individuals worldwide lack access to waste management services, leading to the annual disposal of approximately 13 million tons of plastic waste into the ocean, primarily originating from areas with inadequate waste management systems. Surprisingly, a significant proportion of plastic recycling occurs in low and middle-income nations, where recycling is integrated into the informal economy, with waste collectors gathering and sorting various plastic types. However, these individuals operate in hazardous environments and lack the necessary support systems. Nonetheless, this scenario is gradually changing as they begin to engage in waste management programs, underscoring the necessity for adaptable global solutions to combat the plastic waste crisis.
Emerging Technology
Another endeavor involves the exploration of advanced recycling technologies, known as chemical recycling. Although these methods have not yet seen widespread commercial application, they are gradually being employed for plastics that cannot be recycled using conventional machinery. One such method is pyrolysis, wherein plastic is heated at high temperatures in the absence of oxygen, causing polymer chains to break down into smaller constituents. Pyrolysis can be applied to mixed plastic waste. Currently, most research on pyrolysis focuses on converting plastic into fuel—a process that consumes substantial energy and ultimately emits carbon. However, theoretically, the smaller molecules resulting from pyrolysis could reassemble to form plastic.
Another advanced recycling method involves breaking down plastic molecules into individual units, then recombining them into polymers, bypassing the polymer chain shortening process and the quality degradation that occurs during machine recycling. This could support the recycling of thermoset plastics—a type of polymer that cannot be melted and therefore cannot be machine recycled. These polymers are used to produce materials such as bakelite, melamine, and epoxy resin used in wind turbine blades. Chemical recycling also opens up the possibility of upcycling (making chemical products more valuable than plastic and difficult to manufacture using other methods).A challenge with chemical recycling is the durability of plastic polymers, which makes plastic very useful in many life applications, thus requiring a lot of energy to break these chains. Researchers are experimenting with enzymes and catalysts to reduce the energy required for the recycling process.Natural Solutions
Nature offers a treasure trove of enzymes and catalysts waiting to be discovered. The intricate polymer chains abundant in nature hold the secrets to breaking down synthetic polymers. Take, for instance, the humble mealworm (Tenebrio molitor), hailed as a miniature biological reactor. This creature can degrade plastics thanks to the bacteria in its gut. Certain bacterial strains can break down diverse plastics into similar end products, showcasing their potential in recycling mixed plastics.
Furthermore, researchers are turning to nature to bolster the sustainability and circularity of the plastics industry. The demand for plastics derived from sugarcane and corn is on the rise. However, bioplastics currently represent only a fraction of total plastic production. Scaling up bioplastics could exert significant pressure on agriculture and water resources. Yet, this pressure serves as the impetus for Mango Materials (the company mentioned earlier) to produce P3HB from methane, a much cheaper alternative. Plastics derived from methane hold far greater value than other methane-based products. Despite the promise, concerns linger about bioplastics due to their distinct polymer chains, rendering them incompatible with existing recycling systems.
