Kinetic effect of humic acid on alachlor degradation by Anodic Fenton treatment

• Published in: Journal of environmental quality 2004-11, Vol.33 (6), p.2343-2352
• Main Authors: Wang, Q, Lemley, A.T
• Format: Article
• Language: English
• Subjects: Acetamides - chemistry; Acids; Agrochemicals; Agronomy. Soil science and plant productions; Alachlor; Applied sciences; aqueous solutions; Biological and medical sciences; chemical degradation; Crop residues; Degradation; Earth sciences; Earth, ocean, space; Electrochemistry; Engineering and environment geology. Geothermics; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Herbicides; Herbicides - chemistry; Humic acids; Humic Substances; Hydrogen Peroxide - chemistry; Hydrogen-Ion Concentration; Hydroxyl radicals; Iron - chemistry; Kinetics; Models, Chemical; Oxidants - chemistry; Pesticides; Pollution; Pollution, environment geology; reaction kinetics; Reagents; remediation; Slurries; Soil contamination; Soil remediation; wastewater treatment; Water pollution; Water Purification - methods
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2004.2343

Contamination of water often results from the heavy use of agricultural chemicals, and the disposal of aqueous pesticide waste is a concern. Anodic Fenton treatment (AFT) has been shown to be a successful remediation method for pesticides in solution, but the effect of soil on the degradation kinetics of pesticides using this method has not been determined. The purpose of this study was to study the effect of humic acid, as a soil surrogate, on the degradation kinetics of alachlor [2-chloro-N-(2,6-diethylphenyl-N-(methoxymethyl) acetamide], a heavily used herbicide that has been studied in pure aqueous solution by AFT. The AFT consists of a controlled constant delivery of Fenton reagents, using an electrochemical half-cell to deliver ferrous iron. Alachlor was quickly degraded by AFT, and the kinetics were found to obey the previously developed AFT model well. Degradation of alachlor by AFT in humic acid slurry showed that when the amount of humic acid was increased, alachlor degradation was significantly slowed down and the degradation kinetics were shifted from the AFT model to a first-order model. Further experimentation indicated that humic acid not only competes with alachlor for hydroxyl radicals, reducing the degradation rate of the target compound, but also buffers the slurry at near neutral pH, blocking regeneration of ferrous ion from ferric ion and subsequently shifting the kinetics to first order. Degradation of several other pesticides in humic acid slurry also followed first-order kinetics. These results imply that higher concentrations of Fenton reagents will be required for soil remediation.