Insight into the effect of UVC-based advanced oxidation processes on the interaction of typical microplastics and their derived disinfection byproducts during disinfection

10 μm polystyrene (PS) and polyethylene-terephthalate microplastics (PET MPs), prevalent in finished drink water, were employed to investigate the effect of normal dosage UVC-based-advanced-oxidation-processes (UVC-AOPs) on the interaction between MPs and their derived disinfection-byproducts (DBPs) during subsequent chlorination-disinfection, in the presence of Br-, for the first time. The results indicated that UVC/H2O2 caused higher leaching of microplastic-derived-organic-matter (MP-DOM), with smaller and narrower molecular-weight-distribution than UVC and UVC/peroxymonosulfate (UVC/PMS). The trihalomethanes (as dominant DBPs) molar-formation-potentials (THMs-MFPs) for MP-DOM leached in different UVC-AOPs followed the order of UVC/H2O2>UVC/PMS>UVC. The adsorption of formed THMs, especially Br-THMs, back on MPs was observed in all MPs suspensions with or without UVC-AOPs pre-treatment. The Cl-THMs adsorption by MPs is more sensitive to UVC-AOPs than Br-THMs. The adsorption kinetic, isotherm and thermodynamic experiments indicated that UVC-AOPs reduce the capacity but increase the rate of THMs adsorption by MPs, suggesting the halogen and hydrogen bonding forces governed the THMs adsorption-rate while hydrophobic interaction determines their adsorption-capacity. The UVC-AOPs pre-treatment sharply increased the total yield of THMs via both indirectly inducing MP-DOM leaching and directly increasing the THMs-MFPs of MPs by oxidation. 21.36-41.96% of formed THMs adsorbed back on the UVC-AOPs-pretreated MPs, which might increase the toxicity of MPs. Microplastics (MPs) through Conventional-Drinking-Water-Treatments can cause the leaching of MP-derived dissolved-organic-matter (MP-DOM) during subsequent ultraviolet advanced oxidation processes (UV-AOPs) and increase the disinfection byproducts (DBPs) formation during disinfection in Drink-Water-Treatment-Plants. This study first investigated the MP-DOM leaching during UV-AOPs, the DBP formation during disinfection, and the MP-DOM derived-DBPs adsorption on UV-AOP treated MPs. In UV-AOPs, smaller-sized MPs released more MP-DOM, whereas bromine could increase DBP formation during disinfection by generating more Br-DBPs which were adsorbed by MPs more than Cl-DBPs. The findings could provide valuable information for the safety of drinking water treatment as MPs are present.