Treatment of chlorophenols in water matrix by UV/ferri-oxalate system: Part II. Degradation mechanisms and ecological parameters evaluation Original Research Article

The aim of the study was to evaluate mechanisms involved in degradation of p-CP in water matrix by UV/ferrioxalate (UV/Fe(OX)) system regarding the type of applied UV irradiation source (UV–C and UV–A). Besides the monitoring of parent pollutant degradation and the formation of its typical degradation by-products, the process effectiveness was evaluated on the basis of mineralization extent and changes in biodegradability and toxicity of p-CP model wastewater during the applied treatments. In Part I of the study, the optimal conditions for applied UV–C/Fe(OX) and UV–A/Fe(OX) were determined and used in this comparative study. Biodegradability is estimated over BOD5/COD ratio. The toxic effects were investigated on Vibrio fischeri determining EC50 value. It was found out that p-CP degradation by UV–C/Fe(OX) process occurred via synergy of direct photolysis and radical mechanism, while radicals formed through photo-induced degradation of ferrioxalates played a dominant role when UV–A/Fe(OX) process was applied. The presence of ferrioxalates strongly influenced the mineralization yield and improved biodegradability in the cases when UV–A and UV–C irradiation sources were applied, respectively. However, all applied processes yielded higher toxicity of treated water within observed treatment period presumably due to the presence of p-CP degradation by-products, which are more toxic than parent pollutant.