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

Abstract

Abstract 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-H 2 O 2 AOP, approximately 97% degradation was observed for a fluence of 700 mJ cm −2 . 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 H 2 O 2 dose, initial 2,4-D concentration, and water quality parameters, including pH (4–8), alkalinity (0–5 mM HCO 3 − ), nitrate concentration (0–1 mM as NO 3 − ), 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-H 2 O 2 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) × 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.