VUV/UV/NaClO及UV/NaClO去除百里香酚:降解机制及水质影响因素

Degradation of thymol by VUV/UV/NaClO and UV/NaClO processes:Degradation mechanism and water quality affecting factors

采用VUV/UV/NaClO及UV/NaClO工艺去除百里香酚(Tml),对比考察pH、CO_(3)^(2-)、NO_(3)^(-)和腐殖酸(HA)等因素对Tml去除的影响,鉴定识别Tml的降解产物并推测了降解途径,探究VUV/UV/NaClO工艺中反应溶液的急性毒性变化,通过反应溶液组分毒性鉴定评估结合ECOSAR软件模拟识别了毒性较大的产物。结果表明,UV/NaClO和VUV/UV/NaClO工艺中Tml的去除拟一级反应动力学常数kobs均随着pH的增大先减少后增加,且均在pH为7时达到最小,分别为0.183 6 min-1和0.554 7 min-1;CO_(3)^(2-)的存在有利于Tml的去除,在VUV/UV/NaClO工艺中,低浓度NO_(3)^(-)对Tml的去除有轻微抑制作用,高浓度则反之;而在UV/NaClO工艺中,NO_(3)^(-)的存在有利于Tml的去除;HA对Tml的去除有抑制作用。相同条件下不同水质因素对VUV/UV/NaClO工艺的促进或抑制更为显著,约为UV/NaClO工艺的1.05~3.57倍。VUV/UV/NaClO工艺中Tml主要发生了自由基的取代、加成和氧化分解反应,生成了氯代、醌和醛类中间产物。VUV/UV/NaClO处理后的溶液毒性呈先上升后下降再上升的趋势,生成的丙酸乙烯基酯和戊醛类等小分子有机物导致了反应后期反应溶液急性毒性增加。

VUV/UV/NaClO and UV/NaClO processes were employed to degrade thymol(Tml)in aqueous solution.Effects of pH,CO_(3)^(2-),NO_(3)^(-) and humic acid(HA)on Tml removal were comparatively studied.The degradation products were identified and a possible degradation pathway was proposed.Meanwhile,the alteration of acute toxicity during VUV/UV/NaClO process was investigated,and the most toxic by-products were identified by toxicity assessment and ECOSAR software simulation.The results show that the pseudo first-order kinetic constants(kobs)for Tml removal decreased firstly and then increased with increasing pH in both UV/NaClO and VUV/UV/NaClO processes,and the minimum values were 0.1836 and 0.5547 min-1 at pH=7,respectively.The presence of CO_(3)^(2-) favors Tml degradation,while low concentration of NO_(3)^(-) demonstrates a slightly inhibiting effect but high concentration shows the opposite.HA has an inhibiting effect on the degradation of Tml.The impact of water quality on Tml degradation was more obvious during VUV/UV/NaClO process,in which kobs was about 1.05~3.57 times of that of the UV/NaClO process.Tml in the VUV/UV/NaClO process mainly showed radical substitution,addition and oxidative decomposition reactions,and chlorinated,quinone and aldehyde intermediates were generated.The acute toxicity of the VUV/UV/NaClO process treated solution had an increase-decrease-increase profile.The increase of acute toxicity in the later stage may be due to the generation of small-molecule organic compounds such as vinyl propionate and glutaraldehyde.