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Mixed oxidants produced by means of an electrochemical method were evaluated to confirm the presence of oxidants other than free chlorine. Inactivation rate of B. subtilis spore on the mixed oxidants were similar with that on free chlorine. Activation energy of mixed oxidants and free chlorine for B. subtilis spore inactivation at pH 8.3 were determined as 30.8 kJ·mol !1 and 34.7 kJ·mol !1 respectively. UV absorption spectrum of both free chlorine and mixed oxidants were compared. Molar extinction coefficients of free chlorine and mixed oxidants at 292 nm, which is the maximum absorption wavelength of OCl ! , were 357 M !1 cm !1 and 377 M !1 cm !1 , respectively. Disinfectant decay rate and formation rate of THM on sand filtration effluent at S WTP were compared. The disinfectant decay rate followed a first-order reaction for both mixed oxidants and chlorine. In order to evaluate the effect of secondary disinfection, the decay rate of chlorine followed by mixed oxidants was evaluated compared with chlorine secondary disinfection. The formation rate of THM on both mixed oxidants and chlorine show an insignificant difference. In consequence, most of the oxidants in mixed oxidants are hypochlorite.

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The numerical study was conducted to compare process performance depending on the pump type and process configuration. The daily monitoring data of seawater temperature and salinity offshore from Daesan, Republic of Korea was used to reflect the site-specific seawater conditions. An algorithm for reverse osmosis in constant permeate mode was developed to simulate the process in time-variant conditions. Two types of pumps with different maximum leachable efficiencies were employed to organize pump-train configuration: separated feed lines and common pressure center design. The results showed pump type and design configuration did not have a significant effect on process performance. The annual means of specific energy consumption (SEC) for every design configuration were under 2 kWh/m3, except for a worst-case. The worst-case was decided when the pump was operated out of the best operation range. The two operation strategies were evaluated to determine the optimal configuration. The permeate flow rate was reduced to 80% of the designed permeate flow rate with two approaches: feed flow rate reduction in every train and pump shutdown in a specific train. The operation mode with feed flow rate reduction was more efficient than the other. The operating pressure reduction led to a decrease in SEC.