Ozone and hydroxyl radical (*OH) reaction kinetics were measured for 14 antibacterial compounds from nine structural families, to determine whether municipal wastewater ozonation is likely to result in selective oxidation of these compounds' biochemically essential moieties. Each substrate is oxidized by ozone with an apparent second-order rate constant, k''(O3,app) > 1 x 10(3) M(-1) s(-1), at pH 7, with the exception of N(4)-acetylsulfamethoxazole (K''(O3,app) is 2.5 x 102 M(-1) s(-1)). k''(O3,app) values (pH 7) for macrolides, sulfamethoxazole, trimethoprim, tetracycline, vancomycin, and amikacin appear to correspond directly to oxidation of biochemically essential moieties. Initial reactions of ozone with N(4)-acetylsulfamethoxazole, fluoroquinolones, lincomycin, and beta-lactams do not lead to appreciable oxidation of biochemically essential moieties. However, ozone oxidizes these moieties within fluoroquinolones and lincomycin via slower reactions. Measured k''(O3,app) values and second-order *OH rate constants, k''(*OH,app) were utilized to characterize pollutant losses during ozonation of secondary municipal wastewater effluent. These losses were dependent on k''(O3,app), but independent of k''(*OH,app). Ozone doses > or =3 mg/L yielded > or =99% depletion of fast-reacting substrates (K''(O3,app) > 5 x 10(4) M(-1) s(-1)) at pH 7.7. Ten substrates reacted predominantly with ozone; only four were oxidized predominantly by .OH. These results indicate that many antibacterial compounds will be oxidized in wastewater via moiety-specific reactions with ozone.

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The initial phase of ozone decomposition in natural water (t < 20 s) is poorly understood. It has recently been shown to result in very high transient HO* concentrations and, thereby, plays an essential role during processes such as bromate formation or contaminants oxidation. Phenols and amines are ubiquitous moieties of natural organic matter. Naturally occurring concentrations of primary, secondary, and tertiary amines, amino acids, and phenol were added to surface water, and ozone decomposition as well as HO* generation were measured starting 350 milliseconds after ozone addition. Six seconds into the process, 5 microM of dimethylamine and phenol had generated integral of HO* dt = 1 x 10(-10) M*s and 1.8 x 10(-10) M*s, respectively. With 10 microM dimethylamine and 1.5 mg O3/L, R(ct), (integral of HO*dt/ integral of O3dt) reached 10(-6), which is larger than in advanced oxidation processes (AOP) such as O3/H2O2. Experiments in the presence of HO*-scavengers indicated that a significant fraction of phenol-induced ozone decomposition and HO* generation results from a direct electron transfer to ozone. For dimethylamine, the main mechanism of HO* generation is direct formation of O2*- which reacts selectively with O3 to form O3*-. Pretreatment of phenol-containing water with HOCl or HOBr did not decrease HO* generation, while the same treatment of dimethylamine-containing water considerably reduced HO* generation.

Potentially carcinogenic bromate forms during the ozonation of bromide-containing waters. Some water treatment facilities have had to use ammonia addition and pH depression to minimize bromate formation, but these processes may prove to be insufficient to comply with upcoming regulations. The chlorine-ammonia process (Cl2-NH3), consisting of prechlorination followed by ammonia addition priorto ozonation is shown to cause a 4-fold decrease in bromate formed when compared to the ammonia-only process. Experiments revealed three key mechanisms: (i) oxidation by HOCl of Br- to HOBr and its subsequent masking by NH3 as NH2Br; (ii) decrease of HO- exposure through halogenation of Dissolved Natural Organic Matter (DNOM) by HOCI and scavenging of HO by NH2Cl; and (iii) DNOM acting as a bromine sink after oxidation of Br- to HOBr. At an ozone exposure of 6 mg/L x min and pH 8, conventional ozonation of Lake Zurich water spiked with 560 microg/L Br- formed 35 microg/L BrO3-, whereas the application of the Cl2-NH3 process resulted in 5 microg/L BrO3-. Additional pH depression to pH 6 further decreased bromate formation by a factor of 4. Trihalomethanes (THM) and cyanogen chloride (CNCl), that mayform during prechlorination and monochloramination, respectively, were well below regulatory limits. The chlorine-ammonia process holds strong promise for water treatment facilities struggling with a bromate formation problem during ozonation.