Effect of Thermo-photocatalytic Process Using Zinc Oxide on Degradation of Macro/micro-plastic in Aqueous Environment

More than 320 million tons of plastics are produced annually, and the rate of plastic waste generation steadily increases by 3.9% per year. Introduction of plastic waste into water bodies may lead to many adverse environmental impacts as the plastic debris is very stable and generally requires a longer time to degrade. Over a period of time, bulk plastic debris will slowly degrade into small fragments known as macroplastics (particles size >5mm) and microplastics (particles size <5mm). Accumulation of this newly emerging class of pollutants potentially decreases the efficiency of the existing water treatment system. Therefore, improvement on the existing water treatment technique is required. This study aimed at investigating the effect of using the UV-assisted thermo-photocatalytic reaction on the degradation of polypropylene (PP) macro- and microplastics in an aqueous environment for 6 hours. ZnO nanoparticles (<50 nm) were employed as the photocatalyst. 23 Full Factorial design was carried out in order to identify the correlation between the reaction temperature (35-50 o C), size of PP plastic (25-100 mm2 ) and the catalyst dosage (1–3 g/L) factors and their influences on the weight loss of macro/micro-plastics. Maximum plastic weight loss of 7.8 wt% was achieved at 50°C, 1 g/L ZnO and 25 mm2 of PP plastic. The interaction between temperature and size must be taken into consideration.