Until now, plastics have primarily been collected as part of mixed municipal solid waste and are, therefore, subsequently disposed of at municipal solid waste incineration plants. This situation is slowly changing, as in addition to the system for PET bottle recycling, which will soon celebrate its 30th birthday, collection systems for other polymers such as polyethylenes and polypropylenes have been under development for a number of years. So-called monomaterials, i.e. products that comprise only one polymer or those that can easily be separated into individual polymers, are especially attractive from an environmental perspective. At present, the material qualities of the collected waste usually only permit use in low-quality applications. As the supply of secondary polymers is still currently very small, they can nevertheless be sold and replace primary materials. In the event of a marked increase in recycling rates, this will only continue to be possible if, in parallel to this development, a greater focus is placed on separate collection (as individual polymer types) and if the markets for secondary materials are developed in a targeted manner.
The financing of plastic recycling systems also needs to be clarified as current findings suggest that the revenues generated do not cover the associated costs.Project “Economics of waste-to-energy systems” At present, the still very small systems are either financed through pay-per-bag fees or cross-subsidisation. For PET bottle recycling, an advanced recycling fee has been charged per bottle upon purchase for a number of years. Whether such structures are also appropriate for other plastics needs to be examined.
For low-quality plastics and many composite materials, thermal utilisation is the most suitable utilisation form from an environmental and energy perspective.Haupt, M., T. Kägi, and S. Hellweg. 2018. Modular life cycle assessment of municipal solid waste management. Waste Management 79: 815–827. Wherever possible, this should take place at a cement kiln where plastics usually replace CO2-intensive coal as a fuel. In a MSWI plant, on the other hand, a less CO2-intensive mix comprising non-renewable and renewable energy sources such as gas, wood and crude oil is substituted. What is important for the co-incineration of plastics at cement kilns is that the material does not contain any inorganic pollutants or halogens as in the case, for example, of PVC.
