Process optimization using a kinetic model for the ultraviolet radiation-hydrogen peroxide decomposition of natural and synthetic organic compounds in groundwater

This paper discusses the application of ultraviolet radiation-hydrogen peroxide (UV-HP) process as an advanced oxidation process (AOP) in the treatment of source waters containing natural organic matter (NOM) and contaminated with a synthetic organic chemical (SOC) exemplified by alachlor, an acetanilide pesticide. Alachlor was chosen as the model compound owing to its hydrophobicity and propensity to complex with NOM, besides its classification as an endocrine disrupting chemical (EDC). The study examines the general principles, free-radical chemistry and reaction mechanisms of the UV-HP process from a kinetic modeling standpoint, and provides a systematic approach combining experimental data acquisition with modeling techniques for evaluating the influence of NOM and other free-radical scavengers such as the carbonate species on the contaminant degradation efficiency. The study proposes a kinetic model for predicting and/or simulating the UV-HP decomposition of alachlor in the presence of NOM and other free-radical scavengers under different water quality and operating conditions. The model incorporates additional and descriptive features such as pH decrease during oxidation (due to mineralization of NOM and SOC), and uses UV absorbance at 310 nm (UVA310) as a surrogate parameter for NOM, accounting for changes in NOM structural composition attributable to hydroxyl radical attack and direct photolysis. The experimental data provide model validation and verification for alachlor degradation kinetics for NOM-free and NOM-containing waters. Although the model slightly overestimates the UV-HP process reaction rates for water containing NOM at low pH, it provides insight into the complex free-radical reactions, mechanisms and kinetics for process optimization toward economical and efficient decontamination.