## 3 Results and Discussion
### UV/H\({}_{2}\)O\({}_{2}\) and UV/Cl\({}_{2}\) Process in Pilot Scale  
The oxidation of geosmin and 2-MIB in the UV/H\({}_{2}\)O\({}_{2}\) and UV/Cl\({}_{2}\) processes was evaluated after the PMC coagulation process with PMC dose of 30 mg/L. For the UV based AOPs, background water characteristics are significantly important for removal efficiency of target compounds. As mentioned in Section 3.6, after coagulation process using PMC, the water quality was notably increased as follows: DOC (1.3 \(\rightarrow\) 0.8 mg/L), UV\({}_{254}\) (0.0695 \(\rightarrow\) 0.0272 cm\({}^{-1}\)), and turbidity (31.1 \(\rightarrow\) 15.6 NTU). To predict the performance of UV-based AOPs, the scavenging factor could be an indicator for \(\bullet\)OH water background demand (s\({}^{-1}\)). The scavenging factors were measured before and after the PMC treatment (Figure S1). As expected, the scavenging factor was notably decreased after PMC treatment (64998 \(\rightarrow\) 28516 s\({}^{-1}\)). The UV transmittance was increased (85 \(\rightarrow\) 4%). This could be explained by the decreased DOC and UV\({}_{254}\) after the PMC process because DOMs are the main water constituents considered in the estimation of \(\bullet\)OH scavenging rates in natural waters [16]. Moreover, removal of turbidity could increase the performance of UV based AOPs because turbidity causing particles can  
Figure 8: Concentrations of chlorophyll-a before and after coagulation using the PMC-based coagulant in the pilot-scale tests (PMC dose: 10, 20, 30, and 40 mg/L). act as a'screen' that reduces the amount of light reaching H\({}_{2}\)O\({}_{2}\) or Cl\({}_{2}\); therefore, those oxidants do not receive sufficient UV photons for \(\bullet\)OH production [12]. Figure 9: Removal of turbidity (**a**) and UV\({}_{254}\) (**b**) with varying doses of the PMC-based coagulant in the pilot-scale tests (10, 20, 30, and 40 mg/L). Since there was no geosmin and 2-MIB issue during pilot-tests, we could not verify the removal of those compounds in the PMC coagulation process. Instead, we split the PMC treated water from the main line flow (109 m\({}^{3}\)/h) into the smaller flow rate (1.8 m\({}^{3}\)/h) for the spiking test of taste and odor compounds in UV/H\({}_{2}\)O\({}_{2}\) and UV/Cl\({}_{2}\) for AOPs. Figure 10 shows the degradation of geosmin and 2-MIB by UV alone, UV/H\({}_{2}\)O\({}_{2}\), and UV/Cl\({}_{2}\) processes with varying concentrations of H\({}_{2}\)O\({}_{2}\) and Cl\({}_{2}\) (0, 2, 5, and 10 mg/L). The change in geosmin and 2-MIB concentration by UV direct photolysis was not significant, but it was significantly decreased by injection of H\({}_{2}\)O\({}_{2}\) and Cl\({}_{2}\). Interestingly, the removal efficiency of both of the compounds in the UV/H\({}_{2}\)O\({}_{2}\) process increased with increasing H\({}_{2}\)O\({}_{2}\) dose, but the UV/Cl\({}_{2}\) process had a lower removal at a higher Cl\({}_{2}\) dose. One plausible reason is the pH change by the injection of Cl\({}_{2}\). Similar to the lab test, the pH values were constant at 6.7 in the UV/H\({}_{2}\)O\({}_{2}\) process; however the pH levels of the test water after the injection of 2, 5, and 10 mg/L chlorine were 6.9, 7.5, and 7.9, respectively. As mentioned in previous Section 3.5, the performance of the UV/Cl\({}_{2}\) process is highly dependent on pH and could be decreased at the higher pH than pH 7 because of higher scavenging effect by OCl\({}^{-}\) than by HOCI. From this result, the PMC/UV/H\({}_{2}\)O\({}_{2}\) process can suggested as effective treatment process for geosmin and 2-MIB. The concentrations of geosmin and 2-MIB in the surface water were successfully reduced using the UV/H\({}_{2}\)O\({}_{2}\) process. Lower than average taste and odor threshold of geosmin and 2-MIB (10 ng/L) was achieved in the UV/H\({}_{2}\)O\({}_{2}\) process with \(>\)5 mg/L H\({}_{2}\)O\({}_{2}\). These results emphasize that UV-based AOPs are applicable at the water intake stage when algae and turbidity are successfully removed using PMC.