Effect of embedding a sieving phase into the current plastic recycling process to capture microplastics

This study proposes a systematic change to the current plastic recycling process by introducing a sieving stage in between the shredding and washing units to capture the microplastics being unintentionally generated and released. The benefit of adding the sieving stage to minimise microplastics release to wash water was highlighted by comparing the findings with the case where microplastics are released to wash water and a conventional coagulation process is used to remove microplastics from water. Two coagulants, aluminium sulphate (Al 2 (SO 4 ) 3 .18H 2 O) and aluminium chloride (AlCl 3 .6H 2 O), were used to remove polyethylene terephthalate (PET) and polycarbonate (PC) from water. The size of the microplastic particles played a significant role on the removal efficiency. The maximum removal efficiency of PET by AlCl 3 .6H 2 O was 99.2 % for the particles in 1.18–5 mm range, whereas the average removal efficiency over the whole tested size range of 0.15–5.00 mm was 76.1 % for the same plastic-coagulant combination. By contrast, the addition of a 5 mm sieve between the shredding and the washing units was found to capture 96–97 % of the microplastics generated. The findings of this innovative experiment demonstrate the beneficial impact that this strategy has on capturing microplastics prior to entering water matrix. • Microplastics in wash water reduced by >95 % when shredded plastics are dry sieved. • Capturing microplastics prior to entering the water matrix reduces complications. • Dry sieving removed microplastics more effectively than traditional coagulation. • Coagulation was more effective on larger (1.18–5 mm) PET and PC microplastics. • Deformed microplastics may trap bubbles reducing coagulation efficiency.