Structural features of contaminants of emerging concern behind empirical parameters of mechanistic models describing their photooxidative degradation

Abstract

The aim of this study is to assess the knowledge on system behavior of photooxidative degradation of contaminates of emerging concern (CECs). In that purpose, experimental studies including photooxidative degradation of 17 selected CECs by UV-C/H2O2 and UV-C/S2O82- and simultaneous monitoring of parent CECs conversion, organic content mineralization, oxidant consumption and changes of pH were applied. The obtained results were used to describe and predict system behavior using modeling approaches combining mathematical-mechanistic (MM) and quantitative structure activity/property relationship (QSAR/QSPR). By MM system behavior including kinetics and occurring chemical phenomena were described along with simultaneous determination of empirical parameters, which were correlated with the structural characteristics of parent CECs using QSAR/QSPR modeling. Both modeling schemes yielded accurate prediction of chosen end-points. Hence, photooxidative degradation of CECs according to chosen process parameters is accurately described by MM. QSPR enabled elucidation of CECs structural characteristics determining kinetics of their photooxidative degradation. Descriptors correlated with empirical parameters describing degradation kinetics of CEC by-products are in accordance with preferable degradation mechanism; H-abstraction and electron transfer by hydroxyl and sulphate radicals, respectively. Other two empirical parameters, describing the ratio of “slow” and “fast” mineralizing byproducts were found to be dependent on features of parent CEC’s; e.g. compact/linear structure and molecule symmetry.