Oxidative Degradation Of Nitrogenous Pharmaceuticals And Their Effects On Disinfection Byproducts Formation Potential

The occurrence and transformation of pharmaceuticals and personal care products(PPCPs)in aquatic environment has become a research hotspot in drinking water treatment recently.The research targets were four dimethylamine-based PPCPs and four oxidants were O3,NaClO,ClO2 and KMnO4,which commonly used in drinking water treatment.PPCPs degradation kinetics,reaction mechanisms,oxidation product toxicities and N-DBPs formation potentials were researched based on the construction of detection methods.Two detection methods of trace PPCPs and N-nitrosamines in drinking water were constructed using LC-MS/MS.For PPCPs concentration of 10-500 ng/L,the recovery ratios were 97%-113%and the detection limits were 0.2-3.3 ng/L.For N-nitrosamines concentration of 4-100 ng/L,the recovery ratios were 76%-116%and the detection limits were 0.8-2.6 ng/L.The oxidative degradation effeciency of PPCPs was investigated with the pH value of 5.0-9.0.On this basis,the kinetics of pharmaceutical oxidation were studied at pH = 7.0.Ozonation achieved the highest PPCPs removal efficiency among the four oxidants and the apparent second-order rate constants for all PPCPs were more than 105 M-1s-1.The structures of oxidation products are deduced through LC-MS/MS spectrogram analysis.Furthermore,oxidation degradation mechanism is revealed.Oxygen was added to sulfur in thioether group by all four oxidants oxidation.Oxygen was added to nitrogen in tertiary amine group by ozonation.A dimethylamine group or methy group dropped off when oxidized by other three oxidants.The C-O bond was broken in ether group by ClO2 and NaClO oxidation,but not by O3 and KMnO4.The toxicities of pharmaceuticals and their oxidation products are calculated using the Ecological Structure Activity Relationships(ECOSAR)model.The NaClO oxidation product has the lowest toxicity.The toxicity of the products adding one oxygen was 1-2 order of magnitude lower than that of the original PPCPs.The toxicity of the products adding chlorine was 3 orders of magnitude less than that of the original PPCPs.The toxicity of the products losing dimethylamine group was 1 order of magnitude lower than that of the original ones.The toxicity of the products losing methyl was still at the same order of magnitude.The effect of N-DBPs formation potential by oxidation was evaluated through comparing the change patterns of N-DBPs formation potential.Ozonation can control N-nitrosodimethylamine formation potential(NDMAFP)and trichloronitromethane formation potential(TCNMFP)at the same time.TCNMFP controlled by KMnO4 oxidation was better than ozonation,but NDMAFP could not be effectively controlled by KMnO4 oxidation.One oxidant optimization scheme for drinking water treatment was proposed based on PPCPs oxidation degradation kinetics,oxidation product toxicity and N-DBPs formation potential.When considering PPCPs oxidation degradation kinetics,oxidation product toxicity and N-DBPs formation potential,ozonation was the best choice.If only focus on PPCPs removal without considering N-DBPs formation potential,O3 or ClO2 could be seleted.The research reveals the transformation patterns and N-DBPs formation potential change for oxidation of dimethylamine-based pharmaceuticals.It provides scientific reference and technical support for oxidation treatment in PPCPs removal and the control of N-DBPs formation in drinking water advanced treatment process.