Ozonation And Its Mechanism Of Two Typical PPCPs

Pharmaceuticals and Personal Care Products （PPCPs） raise great concern asemerging micro-organic contaminants. Both conventional wastewater and drinkingwater treatment process cannot remove PPCPs efficiently, leading to significantemissions to water environment, thus imposing potential ecology and health risk.Ozonation has been proved to be a promising process to remove PPCPs. However, dueto poor mineralization of ozonation, organic products may lead to higher risk thanparent compounds. To elucidate reaction mechanism and toxicity variation duringozonation of PPCPs, and provide technical support for practical application, we chosetwo typical PPCPs, trimethoprim and indometacin, as target compounds to carry out ourstudy.In the ozonation of trimethoprim,100%removal efficiency was achieved whenmole ratio of ozone to trimethoprim reached3, whilst no total organic carbon （TOC）was removed under this dose. Twenty one products were identified by LC-MS-MS andthe main reaction pathways were proposed to be hydroxylation, carbonylation anddemethylation. Ozone rather than hydroxyl radical plays a dominant role during thereaction. The inhibition of Photobacterium phosphoreum increased from0%to aplateau of30%as ozone dose increased. It was inferred that toxicity was contributed bysecondary products which were not identified. Vibrio qinghaiensis showed a differentresult, no inhibition was observed during the whole reaction. Software was used toestimate toxicity of trimethoprim and ozonation products to fish, daphnid and greenalgae, finding that different organisms showed totally different results.Indometacin was ozonated faster than trimethoprim, and the measured kineticconstant with ozone was5.65×10⁵M^-1s^-1，, three times higher than reported constant oftrimethoprim. Corresponding constants in anionic form was8.54×10⁵M^-1s^-1。, higherthan which of molecular form. The kinetic constants of indometacin in molecular andanionic form with hydroxyl radical were measured as6.71×10⁹M^-1s^-15.51×10⁹M^-1s^-1。, respectively. The reaction was also dominated by ozone, and majorreaction sites were methoxyl substituted benzene ring, nitrogen atom and C-C doublebond. Six products were identified by LC-MS-MS and reaction mechanisms were proposed to be cyclo-addition and electrophilic attack. Toxicity assay ofPhotobacterium phosphoreum showed that as reaction carried on, the inhibitiondecreased from50%to a plateau. The value of plateau inhibition could decrease to0%when increasing influent ozone concentration. TOC remaining was consistent withtoxicity change. Vibrio qinghaiensis showed a similar trend, but was more sensitive.Results of toxicity estimation by software were similar with which of trimethoprim, i.e.different organisms showed different results.