Recycling Waste Plastics Recovered from Landfills
Managing landfill sites is a growing issue for countries in Europe. There are over half a million sites and 90% of these were in use before the introduction of specific directives regulating safety (1999/31/EC). The responsibility for landfill sanitation and reclamation is increasingly falling to public institutions.
A new approach to waste management has led to the idea of landfills as ‘mines’ of raw resources. Landfill mining (LFM) operations involve excavating, separating, and treating waste. The benefits are both environmental (to reclaim and improve landfill sites) and economical (to recover and recycle materials) .
Enhanced Landfill Mining
Enhanced Landfill Mining (ELFM) is a powerful tool for the sustainable management of landfills. It requires innovative technologies and an integrated approach, analyzing in detail all environmental benefits and burdens.
Plastics are often a major component in landfills . Polyolefin materials such as polyethylene (PE) and polypropylene (PP) appear in large quantities, and other common polymers (such as polyvinyl chloride) are also usually present in varying amounts . Yet studies using ELFM have found that recycling of landfill materials is often limited to metals, glass, and aggregates, while plastics, as well as wood, textiles and paper, are usually converted to fuels .
This may be because there can be many challenges to face when recycling plastics into secondary raw materials. These include the requirement to separate polymers into types; contamination from soil, organic leachates and harmful substances such as heavy metals ; and material degradation brought about landfilling conditions.
This study  carried out an environmental impact assessment using life cycle anaylsis (LCA) methodology of landfill waste undergoing treatment and processing. The intention was to produce secondary plastic material in the form of PE granules. To ensure good mechanical properties in the secondary product, the team used various additives and additional manufacturing processes.
The study was based on waste plastic materials from an unregulated industrial landfill site in Italy. Mostly, the waste contained plastics with some coal (4.6%) and aluminum (1.17%). Other types of waste were cathodes and anodes, electric cables, iron, asbestos, tires and wood. Each of these represented less than 1% of total treated waste. The study used a multi-stage process, involving a patented wet-processing technology, to treat the waste, and then subjected it to processing to produce a recycled plastic. It also compared the use of two additives (maleated linear low density polyethylene (MAPE) and low density polyethylene (LDPE)) as adhesion-promoters.
The team used a range of analytical techniques to study the composition of the secondary product. One of the techniques was solid state 13C MAS NMR spectroscopy. They used a Bruker Avance II 400 spectrometer, equipped with a 4 mm MAS probe. Ground WP samples were packed into 4 mm zirconia rotors sealed with Kel-F caps and spun at 10 kHz. Cross-polarization spectra were recorded with a relaxation delay of 5 s and a contact time of 2 ms, under high power proton decoupling.
The NMR results showed that the secondary product contained high amounts of PE and very low amounts of contamination with PP, cellulose, and polystyrene. The team put this down to thorough washing in the selection process and the use of the adhesion-promotor additives. Significantly, reduced contamination meant that the mechanical properties of the secondary material compared well with virgin PE.
LCA highlighted that recovery is a sound environmental option from the point of view of both resources and emissions. The key benefit in making the secondary plastic is that it avoids the extraction of non-renewable resources (crude oil) and emissions from the crude oil refining process, which are both involved in the virgin product.
The study also considered other impacts of the process. For example, they looked particularly at grinding incoming waste, one of the main steps in the production process of secondary granules. Grinding has implications for human health as workers can inhale emissions generated during the process. However, the researchers found that placing extraction systems on each grinding machine and providing workers with personal protective equipment did an excellent job of limiting health risks.
The team concludes that improvements to the ELFM process should focus mainly on the treatment of non-recoverable waste such as cathodes and anodes, and especially sand. The non-recoverable waste needed to be transported by ship, either because it occurred in large amounts, or because of the long distance to the disposal plant. The researchers suggest that washing sand more intensively would reduce contamination and allow it to be re-used, potentially as road subfloors or, under appropriate verification of suitability, in the construction sector. This would make sand a by-product of the treatment process as well as reducing the energy costs of transporting it as non-recoverable waste.
In summary, the study uses an integrated experimental and LCA approach to show that recovering plastic waste through ELFM is feasible and environmentally sustainable, and that proper processing can increase the properties and value of the secondary products generated.
Increase Sustainability by Innovation with Integrity
Bruker offers the broadest end-to-end solution portfolio for the polymer value chain from product development via raw material qualification, process control in manufacturing and quality control of finished goods to enhanced methodologies for waste reduction in recycling processes. This approach enables our customers to transfer waste into raw materials and so closes the circle. Circular economies will make our planet a safer and healthier place to live and Bruker is strongly committed to continuously support and share this mission.
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