Wet-mechanical processing of a plastic-rich two-dimensional-fraction from mixed wastes for chemical recycling

The recycling of source separated polyolefins (POs) (e.g., light weight packaging waste) is already state of the art. Therefore, further plastic materials contained in mixed wastes have become more important due to increasing legal pressure. Mixed commercial and municipal solid wastes contain large quantities of POs. These mixed wastes would usually be treated in waste incinerators or processed to refuse-derived fuel for cement plants. Large-scale experiments were conducted to assess the potential of such POs from these waste streams for recycling processes. The potential and applicability of a dry-mechanical and subsequently wet-mechanical (Wet-mechanical) processing with the aim of generating a PO concentrate for chemical recycling purposes was assessed. These investigations’ focus was put on the centrifugal force separator technology as the core element of Wet-mechanical processing. In addition to the input material, all output materials and process water streams were chemically and physically characterized to estimate potential treatment or recycling paths. Results demonstrate that a two-stage purification is necessary to produce POs with sufficient purity out of both wastes. Chlorine and heavy metal levels are simultaneously reduced. The increased quantity of impurities only slightly changes the density of the process waters. Process water analyses show that wastewater treatment is necessary before discharge into a receiving water or sewage treatment plant. The sediment does not fulfil any hazard-relevant properties, and different thermal treatment options are possible.

Processability of Different Polymer Fractions Recovered from Mixed Wastes and Determination of Material Properties for Recycling

To achieve future recycling targets and CO2 and waste reduction, the transfer of plastic contained in mixed waste from thermal recovery to mechanical recycling is a promising option. This requires extensive knowledge of the necessary processing depth of mixed wastes to enrich plastics and their processability in polymer processing machines. Also, the selection of a suitable processing method and product application area requires appropriate material behaviour. This paper investigates these aspects for a commercial processed, mixed waste, and two different mixed polyolefin fractions. The wastes are processed at different depths (e.g., washed/not washed, sorted into polyethylene, polypropylene, polyethylene terephthalate, polystyrene/unsorted) and then either homogenised in the extruder in advance or processed heterogeneously in the compression moulding process into plates. The produced recyclates in plate form are then subjected to mechanical, thermal, and rheological characterisation. Most investigated materials could be processed with simple compression moulding. The results show that an upstream washing process improves the achievable material properties, but homogenisation does not necessarily lead to an improvement. It was also found that a higher treatment depth (recovery of plastic types) is not necessary. The investigations show that plastic waste recovery with simple treatment from mixed, contaminated wastes into at least downcycling products is possible.

A fair CoP? MRF sampling, testing and reporting: Big problems caused by small particles. Part 2: Operational realities and financial implications

The operation of qualifying materials recovery facilities (MRFs) in England is governed by the MRF code of practice (MRF CoP), which mandates certain sampling and testing practices for the mixed wastes being processed by the MRF. The results of this testing are required to be reported to the system regulator and are then made publicly available in a register. The MRF CoP is critically examined and certain aspects of the testing methodology are shown to be invalid, resulting in inaccurate information being included in the register. The current investigation looks at the extent of these inaccuracies and shows how they have very real financial implications for commercial operators of MRFs, especially where ‘shared basket’ contracts have been entered into, typically with local authorities.

A fair CoP? MRF sampling, testing and reporting: Big problems caused by small particles. Part 1: Compliance difficulties and data validity

The Regulations governing Materials Recovery Facilities (MRFs) in England require that they report on the quality of both the incoming mixed wastes and the single-stream recyclate products, with the results being made available on a public register. In this investigation, tests were conducted on a number of mixed wastes from different suppliers being processed at a qualifying MRF to evaluate how effective the Regulations (or MRF Code of Practice (MRF CoP)) were in generating useful, meaningful information. The empirical evidence obtained showed that MRF CoP in its current form has a number of serious flaws which detract from the validity and value of the reported operational data. The statutory definition of ‘material particles’ in the mixed wastes given in the MRF CoP means that compliance with the MRF CoP is impracticable, and in order to overcome this it will be necessary to re-word the definition of ‘material particles’. Empirical evidence also invalidated the explicit assumption made in the MRF CoP that the composition of the material particles is identical to that of the bulk materials, and consequently the basis for the mandatory apportioning of the weight of the material particles has no logical foundation and apportioning leads to distortion in the reported data. Changes will be required to the present statutory requirements for reporting operational results if the recorded information is to have meaning and relevance for stakeholders in the system.

Photoreforming of food waste into value-added products over visible-light-absorbing catalysts

Food and mixed wastes are converted into H2 and organics over CdS and carbon nitride photocatalysts.