摘要
This work investigates the degradation of 2,4-dichlorophenoxy acetic acid(2,4-D)using UV irradiation and the UV-H_(2)O_(2) advanced oxidation process(AOP).For UV irradiation at 253.7 nm,~66%degradation was observed for a fluence of 20 J cm^(-2) and the apparent fluence-based,pseudo-first-order rate constant for 2,4-D was 5.77(±0.66)×10^(-5) cm^(2) mJ^(-1).With the UV-H2O2 AOP,approximately 97%degradation was observed for a fluence of 700mJ cm^(-2).Due to production of hydroxyl radicals,the apparent fluencebased rate constant was 100 times higher than that for direct UV photolysis.The effects of H2O2 dose,initial 2,4-D concentration,and water quality parameters,including pH(4e8),alkalinity(0e5mM HCO3),nitrate concentration(0e1mMas NO3),and ionic strength(0e17mM as NaCl),were studied.The observed rate constants were dependent on pH,alkalinity,and nitrate concentration.The degradation of 2,4-D by the UV-H2O2 systemwas also examined in a real surface water.The observed fluence-based rate constant in the surface water matrix was 2.6(±0.3)×10^(-3) cm^(2) mJ^(-1),and this value was similar to a distilled water matrix containing the same alkalinity and pH.In addition,the biodegradability of UV and UV-H_(2)O_(2) treated wastewater increased with irradiation time,suggesting that transformation products can be degraded by biological processes.Based on this study,the UV-H_(2)O_(2) process represents a viable treatment method to transform 2,4-D into benign products.
基金
The authors acknowledge the Technical Education Quality Improvement Programme-III for providing High Performance Liquid Chromatography in the Environmental Engineering Laboratory which was used to detect 2,4-D.
