Influence of various reaction parameters on 2,4-D removal in photo/ferrioxalate/H2O2 process

The influence of various reaction parameters on herbicide 2,4-dichlorophendxyacetic acid (2,4-D) removal were examined in the photo/ferrioxalate/H2O2 system, with regard to: (1) sulfate, phosphate, and (OH)-O-. scavenger, as solution constituent; and (2) light intensity, ferrioxalate, H2O2, and oxalate concentration, as operating parameter. In terms of 2,4-D removal, the photo/ferrioxalate/H2O2 System has always been superior to the photo/Ferric ion/H2O2 system, despite the high presence of anions (sulfate 100 mM, phosphate 1 mM) or (OH)-O-. scavenger. Not only the rate of 2,4-D removal, but also the decomposition rate of H2O2 and oxalate proportionally increase with light intensity. The ferrioxalate concentration determines the light absorption fraction, and thus, controls the rates of 2,4-D removal, and the decomposition of H2O2 and oxalate, are predicted from kinetic formulations. The optimal concentration of H2O2 and oxalate, according to the extent of the (OH)-O-. scavenging reaction with these reagents, has been demonstrated for 2,4-D removal. It was found that an increasing oxalate concentration, which bears the burden of increased dissolved organic carbon (DOC), does not occur. This is because its decomposition, as a result of the photochemical reduction of the ferric oxalate complex, results in a decrease of the equivalent DOC. The importance of the key reaction factors to be considered, when applying this system to real wastewater treatment, is also discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.