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UP-CYCLING OF MICROFIBERS INTO NANODIAMONDS
The project was funded by the Ministry of the Environment and Energy Security (Directorial Decree EC-DEC-86, dated 07/09/23), call for circular economy projects, aimed to develop technologies for the prevention, recovery, recycling and treatment of non-recyclable waste falling into categories not already served by the supply chain consortia, 2021 edition (Decree of the Ministry of Ecological Transition of 9/12/2021, n. 83). The aims were to evaluate the feasibility, life cycle, social and economic impact of the recovery/reuse of washing machine wastewater in its two components: synthetic fibres, to be transformed into carbon-based nanomaterials (nanodiamonds), in the framework of up-cycling, and wastewater treatment with a biological filter, in the framework of water circularity. The project includes the Departments of Biology (leader), Civil and Computer Engineering, Management and Law, Chemical Sciences and Technologies.
The microfibres deriving from the washing processes of synthetic fabrics represent an important fraction of waste. Currently, they are not intercepted by the management chains, so they remain dispersed in both industrial and domestic wastewater. The estimate provided by Singh et al. (2019) and confirmed by the EAA 2022 report, accounts for several hundred thousand tonnes of microfibres annually released on a European scale. So they represent the main source of primary pollution from microplastics in the oceans, with consequent significant impacts on environment and ecosystems. To face this problem, some filtration solutions have been proposed, to be added to domestic and industrial washing machines, to reduce the release of microfibres into receiving water bodies (Fig. 1).
Fig. 1 Commercial devices, such as filters or bags, for the washing of clothes made of artificial fibres.
This project proposes a solution for the management of the waste flows made up of synthetic microfibres obtained from filtration systems applied to domestic washing machines, but scalable even to industrial users. This allows the valorisation, through the up-cycling of the synthetic microfibres, via their transformation into materials with high technological content, such as micro- and nano-metric diamonds. The transformation is possible through a thermal pyrolysis process in the presence of H-reactive plasma. The hydrogen plasma effectively fragments the microfibers into small radical fragments (CH3, C2H2) and H2 which fuel the diamond formation by radical addition. This process, unlike other thermal pyrolysis techniques, has a significant advantage as it does not produce potentially dangerous wastes for the environment, thanks to the extreme reactivity of atomic H.
The issue of microplastics is currently not comprehensively regulated, and there is no incentive system to support companies to undertake measures aimed at reducing the presence of microplastics in the environment. But the European Green Deal (COM (2019) 640 final) and the Action Plan for the Circular Economy (COM (2020) 98 final) represent a fundamental driver for the start of a paradigm shift in this field. The theme is also central within the United Nations, where there are numerous initiatives, such as the United Nations global partnership on marine litter and the action plans presented by the G7 and G20. Already in December 2017, the United Nations Environment Assembly adopted a resolution on marine litter and microplastics (UNEP/EA.3/L.20).
To foster circular economy, as promoted by European Union policies, particularly important aspects that this project intends to explore and promote, are: to close the synthetic fibre cycle, by favouring the maintenance of their value, in the logic of up-cycling, and to reuse water resources, in the logic of water circularity.
The project is based on six different independent activities, interconnected to each other.
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