Degradation of 2,4-dichlorophenoxyacetic acid by UV 253.7 and UV-H2O2: Reaction kinetics and effects of interfering substances

摘要

This work investigates the degradation of 2,4-dichlorophenoxy acetic acid (2,4-D) using UV irradiation and the UV-Hsub2/subOsub2/sub advanced oxidation process (AOP). For UV irradiation at 253.7?nm, ～66% degradation was observed for a fluence of 20?J?cmsup?2/sup and the apparent fluence-based, pseudo-first-order rate constant for 2,4-D was 5.77 (±0.66)?×?10sup?5/sup?cmsup2/sup?mJsup?1/sup. With the UV-Hsub2/subOsub2/sub AOP, approximately 97% degradation was observed for a fluence of 700?mJ?cmsup?2/sup. Due to production of hydroxyl radicals, the apparent fluence-based rate constant was 100 times higher than that for direct UV photolysis. The effects of Hsub2/subOsub2/sub dose, initial 2,4-D concentration, and water quality parameters, including pH (4–8), alkalinity (0–5?mM HCOsub3/subsup?/sup), nitrate concentration (0–1?mM as NOsub3/subsup?/sup), and ionic strength (0–17?mM 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-Hsub2/subOsub2/sub system was also examined in a real surface water. The observed fluence-based rate constant in the surface water matrix was 2.6 (±0.3)?×?10sup?3/sup?cmsup2/sup?mJsup?1/sup, and this value was similar to a distilled water matrix containing the same alkalinity and pH. In addition, the biodegradability of UV and UV-Hsub2/subOsub2/sub treated wastewater increased with irradiation time, suggesting that transformation products can be degraded by biological processes. Based on this study, the UV-Hsub2/subOsub2/sub process represents a viable treatment method to transform 2,4-D into benign products.