Removal of 2-MIB and geosmin using UV/persulfate: Contributions of hydroxyl and sulfate radicals

2-methylisoborneol (2-MIB) and geosmin are two odor-causing compounds that are difficult to remove and the cause of many consumer complaints. In this study, we assessed the degradation of 2-MIB and geosmin using a UV/persulfate process for the first time. The results showed that both 2-MIB and geosmin could be degraded effectively using this process. The process was modeled based on steady-state assumption with respect to the odor-causing compounds and either hydroxyl or sulfate radicals. The second order rate constants for 2-MIB and geosmin reacting with the sulfate radical (SO₄^-) were estimated to be (4.2 ± 0.6) × 10⁸ M^-1s^-1 and (7.6 ± 0.6) × 10⁸ M^-1s^-1 respectively at a pH of 7.0. The contributions of the hydroxyl radical (OH) to 2-MIB and geosmin degradation were 3.5 times and 2.0 times higher, respectively, than the contribution from SO₄^- in Milli-Q water with 2 mM phosphate buffer at pH 7.0. The pseudo-first-order rate constants (k_o^s) of both 2-MIB and geosmin increased with increasing dosages of persulfate. Although pH did not affect the degradation of 2-MIB and geosmin directly, different scavenging effects of hydrogen phosphate and dihydrogen phosphate resulted in higher values of k_o^s for both 2-MIB and geosmin in acidic condition. Bicarbonate and natural organic matter (NOM) inhibited the degradation of both 2-MIB and geosmin dramatically through consuming OH and SO₄^- and were likely to be the main radical scavengers in natural waters when using UV/persulfate process to control 2-MIB and geosmin.