| dc.description.abstract | In recent years, emerging pollutants have attracted widespread attention. Among them, pharmaceuticals and personal care products are used most frequently. Conventional wastewater treatment cannot remove these chemicals effectively, which leads to trace remain in water body, causing ecological and human health problems. Advanced oxidation processes (AOPs) have become a method that can remove emerging pollutants effectively, especially the UV-based AOPs. Compared with other UV-based AOPs, UV/chlorine process is more cost-effective and the degradation efficiency is more advantageous in certain pollutants. Therefore, this study used UV/chlorine process which was combined with electrochemical process to degrade salicylic acid (SA), which was a kind of emerging pollutants. Then, according to the results to optimize the operating condition and assess the feasibility of this process for degrading SA.
This research was divided into three part: First, sodium hypochlorite was added into the system to confirm the feasibility of degradation of SA by chlorine; Second, the free chlorine(including hypochlorite and hypochlorous acid) was electrochemically oxidized from chloride in the system, without adding additional oxidant. Third, the electro-generated free chlorine was irradiated by UV irradiation. In the results, the optimal operating condition of current density, chloride concentration and pH value were found to be 5 mA cm-2, 0.05M and pH 4, respectively. The SA degradation conformed pseudo first order reaction. After 60-min reaction, the SA degradation efficiency could reach 96% and the reaction constant was 0.0544 min-1. It was found that UV irradiation could enhance the degradation and reduce the activated energy because of the generation of free radicals. Also, the SA degradation by UV/chlorine conformed pseudo first order reaction. After 60-min reaction, the SA degradation efficiency could reach >99%, and the reaction constant was 0.0844 min-1. Finally, a possible degradation pathway was proposed that SA degradation initiated by substitution reaction on benzene ring by radicals. Moreover, catechol and 1,2-Benzoquinone may be form by decarboxylation and hydrogen abstraction. Then, ring opening may occur to formed unsaturated products and mineralize to CO2 and water finally. Disinfection by-product (DBP) may also be formed during the SA degradation. | en_US |