SETUP OF THE FILTERING SYSTEMS, ANALYSIS OF THE COLLECTED MICROFIBERS AND ECODESIGN OF THE FILTER
The development and validation of an innovative filter with dimensions between 80 and 5 μm, including a control system designed to evaluate the degree of filter saturation, is the first objective of the project: an intelligent filter equipped with a sensor capable of evaluating the amount of fibres retained and therefore signalling their saturation. The sensor is based on printed electrodes (screen printed electrode – SPE), applied in strategic positions, capable of determining the quantity of retained microplastic, and giving an estimate of its degree of saturation and when it needs to be changed/cleaned. This estimate is carried out by the electrodes through impedance measurements, i.e. the change in charge transfer at the electrode interface, when a small Alternating Current signal is applied to the interface with a constant DC offset (Impedance Spectroscopy - EIS). The frequency of the most appropriate alternating voltage will be identified which, once applied, is capable of quantifying the adhered microplastic in a proportional manner to the increase in charge transfer resistance on the surface of the SPE electrodes. Furthermore, this type of measurement is carried out in a differential manner (difference between a zero point - no microplastic - and the point at which the microplastic interacts) and will also allow to define the maximum load of the filter and its saturation (i.e. when it must be changed) . The microfibers collected by the filter will be characterized from a morphological (size distribution) and compositional point by using spectroscopic techniques. The system will allow the evaluation of yields and quality of the different microfibre fractions recovered from the wastewater filtering system, obtained by washing synthetic fabrics. This information, in turn, will allow us to evaluate the yield and quality of the diamonds and the scalability of the proposed up-cycling process. This will hopefully allow us to identify and characterize in qualitative and quantitative terms a microfibre recovery chain, in the due time to manage a waste flow that in a few years will certainly become very relevant for domestic users, but potentially also for industrial ones.
Overall, the research involves the creation of a laboratory prototype of the filtering system comprising two sequential objects: the mechanical filter, a cartridge to trap macro- and micro- fibres (organized into two phases of approximately 80 microns and 5 microns) and the biofilter, containing a microbial consortium, to mineralize/degrade nutrients and contaminants. The system will be designed to simplify the self-cleaning operations of the 80 micron filter, the recovery of the plastic microfibre fractions and the collection of the consortium biomass. Both filters will be designed following the principles of Life Cycle Design, based on minimization of resources, choice of recyclable materials with low environmental impact, optimization of product life, lengthening of the material life and facilitation of disassembly at the end of the cycle.