Optimization of a UV/H₂O₂ AOP System Using Scavenger Radicals and Response Surface Methodology

Abstract

The wastewater produced by industrial processes contains many dissolved hazardous chemicals. The removal of these hazardous chemicals is a requisite for ethical environmental practices. The advanced oxidation process (AOP) is the typical technology used for the removal of these hazardous chemicals. Water treatment via photo-assisted AOP results in the production of hydroxyl radicals (HO center dot). Hydroxyl radicals are high reactive radicals and they react non-selectively with strong oxidation potential. The hydroxyl radical not only reacts with major contaminants but also with scavenger radicals (HCO31-; CO32-; HO21-; NH2Cl; free chlorine, and dissolved organic carbon (DOC)) that are present in the wastewater. Normally, water treatment is focused on a single contaminant, neglecting scavenger radicals, which results in the underprediction of the contaminant concentration after treatment. A well-proposed optimization problem that considers scavenger radicals is proposed in this work. Moreover, in an ultraviolet hydrogen peroxide (UV-HP) AOP reactor, two process inputs (lamp power and molar ratio of H2O2 to organic contaminant) are crucial. A response surface optimization methodology that optimizes these process inputs is also proposed in this research. Methylene blue (MB) was used as the major contaminant. It was observed that the overall contaminant concentration at the reactor outlet was strongly dependent upon the scavenger radicals and the lamp power. It was perceived that after a certain limit, increasing the hydrogen peroxide concentration in the wastewater matrix results in an inhibitory effect of hydrogen peroxide. The accuracy of the proposed model was validated through experimental results. The approach used in this work not only improves the existing UV-HP reactor optimization approach but also provides a better way to model other major contaminants that are present in wastewater.