Variation of organic halide formation potential of dyestuffs during ozonation and correlation with color

The control of the discharge of precursors to trihalometanes (THMs) derived from industrial wastewater is indicated to be important as well as the countermeasures in drinking water plants. Effluents containing various dyestuffs, intermediates and auxiliaries, which are typically biorefractory, are known to have high trihalomethane formation potential (THMFP) as well as intense color. In this study, fourteen water-soluble dyestuffs were ozonated to investigate the variations of total organic halide formation potential (TOXFP) and THMFP, and then correlated with color. Phenol was selected as a target compound because it had a fundamental molecular structure. The ratio of THMFP to TOXFP (THMFP/TOXFP) varied from 0.12 to 0.54 before ozonation. The variation patterns of TOXFP and THMFP were roughly divided into two groups: (1) compounds showing a maximum in the initial stage and (2) compounds showing a uniform decrease. In spite of the different variation patterns and initial values, long-term ozonation decreased both TOXFP and THMFP. The difference in THMFP/TOXFP became slighter after ozonation. From the relationship between TOXFP, THMFP and color, long-term ozonation, especially ozonation after decolorization was found to be necessary for the removal of organic halides.