Ozonation of the algaecide irgarol: Kinetics, transformation products, and toxicity.

The degradation of irgarol, a frequently detected algaecide in the aquatic environment, by ozonation was investigated in this study. The second-order rate constants for the reaction of irgarol with ozone (O3) and hydroxyl radical (OH) were determined to be 505 M-1 s-1 and 4.96 × 109 M-1 s-1, respectively. During ozonation, sixteen transformation products (TPs) of irgarol were proposed using an electrospray ionization quadrupole time-of-flight mass spectrometer. Most of the TPs are ozone-refractory compounds and therefore could only be further transformed by oxidation with OH generated from O3 decomposition during ozonation. Toxicity analysis using the ecological structure activity relationship class program indicates that some of the TPs (e.g., irgarol sulfoxide) still exhibit high acute or chronic toxicity to aquatic organisms (fish, daphnia, and algae) as the parent compound. With a typical ozone dose applied in water treatment (2 mg/L, corresponding to a specific ozone dose of 0.8 mg O3/mg dissolved organic carbon), irgarol could be completely abated in a selected surface water by ozonation. However, most of the TPs persisted in the ozonation effluent because of their low ozone reactivity. The results of this study suggest that ozonation with typical ozone doses applied in water treatment may not be able to sufficiently reduce the ecotoxicological effects of irgarol on aquatic organisms. More effective treatment processes such as ozone-based advanced oxidation processes may be required to enhance the removal of toxic TPs of irgarol in water treatment.

Pilot-scale evaluation of micropollutant abatements by conventional ozonation, UV/O3, and an electro-peroxone process.

The electro-peroxone (E-peroxone) process is an emerging ozone-based advanced oxidation process (AOP) that has shown large potential for micropollutant abatement in water treatment. To evaluate its performance under more realistic conditions of water treatment, a continuous-flow pilot E-peroxone system was developed and compared with conventional ozonation and a UV/O3 process for micropollutant abatements in various water matrices (groundwater, surface water, and secondary wastewater effluent) in this study. With a specific ozone dose of 1.5 mg O3/mg DOC, micropollutants that have high and moderate reactivity with ozone (O3) (diclofenac, naproxen, gemfibrozil, and bezafibrate) could be sufficiently abated (>90% abatement) in the various waters by all three processes. However, ozone-resistant micropollutants (ibuprofen, clofibric acid, and chloramphenicol) were abated only by ∼32-68%, 68-91%, and 73-90% during conventional ozonation of the selected groundwater, surface water, and secondary wastewater effluent, respectively. By electro-generating H2O2 or applying UV irradiation to enhance O3 transformation to •OH during ozonation, the E-peroxone and UV/O3 processes similarly enhanced the abatement efficiencies of ozone-resistant micropollutants by ∼15-43%, ∼5-15%, and ∼5-10% in the groundwater, surface water, and secondary wastewater effluent, respectively. In addition, the E-peroxone and UV/O3 processes significantly reduced bromate formation during the treatment of the three waters compared to conventional ozonation. Due to its higher efficiency, the E-peroxone process reduced ∼10-53% of the energy consumption required to abate the concentration of chloramphenicol (the most ozone-resistant micropollutant spiked in the waters) by 1 order of magnitude in the three waters compared to conventional ozonation. In contrast, the UV/O3 process consumed approximately 4-10 times higher energy than conventional ozonation. This pilot-scale study demonstrates that the E-peroxone process can provide a feasible, effective, and energy-efficient alternative for micropollutant abatement and bromate control in water and wastewater treatment.