| Twenty-two organic chemicals, including organophosphate pesticides, volatile organic chemicals (VOCs), three types of herbicides (thiocarbamate, urea and triazine), and substituted benzene compounds on the U.S. EPA Contaminant Candidate List (CCL) were screened for their relative reactivity and studied for reaction rate constants and byproducts formation during batch ozonation and the O 3/H2O2 advanced oxidation process (AOP). Results of screening showed that only three organophosphate pesticides (i.e. dyfonate, terbufos and disulfoton) and 1,2,4-trimethylbenzene can be efficiently treated by ozone alone at relatively low pH levels. Most CCL chemicals can be efficiently removed by O3/H2O2 AOP or ozonation at high pH. These chemicals include organophosphates, herbicides, aromatic VOCs, 1,3-dichloropropane and substituted benzenes compounds on the CCL. RDX and aliphatic VOCs (except for 1,3-dichloropropane) are recalcitrant to the O3/H2O 2 AOP and ozonation treatment.; Results of reaction rate constants showed that except for dyfonate, terbufos, disulfoton and 1,2,4-trimethylbenzene, all other chemicals (diazinon, urea herbicides, RDX and VOCs except 1,2,4-trimethylbenzene,) showed slow reaction toward ozone during the direct reactions. On the other hand, most CCL chemicals react fast with OH radicals during the indirect reactions. These chemicals include organophosphates, urea and thiocarbamate herbicides, aromatic VOCs, nitrobenzene, terbacil and prometon. Dinitrotoluenes showed medium reactivity toward OH radicals, and RDX and aliphatic VOCs showed low reactivity toward OH radicals.; Highly toxic chemicals such as oxons and sulfoxides were identified to be the major oxidation byproducts for organophosphate pesticides. No volatile byproducts were found for the VOCs by ozonation. Generally speaking, less toxic byproducts were produced during ozonation for VOCs, herbicides and substituted benzene chemicals. |
