Mechanism Of The Impact Of Inorganic Anions On Typical Organic Contaminant Degradations By ^·OH And SO₄^·-

There is an increasing need for techniques to treat brakish wastewaters from industries（i.e., oilfield operations and shale gas operations） and reverse osmosis process of water reclamation facilities. Because the organic contaminants in brakish wastewaters have toxicological potential to the receiving water ecosystems, there have been concerns about the removal of organic contaminants before discharge. Hydroxyl radical（^·OH）-based and sulfate radical(SO₄^·-)-based Advanced oxidation processes（AOPs） have been widely used for broad-spectrum removal of organic contaminants in drinking water treatment plants and wastewater treatment plants. Due to the reactions between halides and ^·OH or SO₄^·- to generate halogen radicals, the efficiency of organic contaminant degradations by AOPs in brakish wastewater decides the real application of AOPs. This research seeks to investigate the effects of halides on organic contaminants degradations by ^·OH-based and SO₄^·--based AOPs. In particular, the pathway of halogen radical formation will be elucidated. Additionally, the evaluation of scavenging capacity of ^·OH or SO₄^·- will be developed. Further, the mechanism of reactivity of inorganic radicals to organic contaminants will be proposed. Finally, simultaneous generation of ^·OH and SO₄^·- by the reaction of ozone（O3） with peroxymonosulfate（PMS） has been proposed and experimentally verified.The effects of halides on organic contaminant destruction efficiency was compared for UV/H2O2 and UV/PDS AOPs in this study. The conversion of ^·OH and SO₄^·- radicals to less reactive halogen radicals in the presence of seawater halides favored attacked on highly reactive reaction centers represented by the alkene group and the aromatic group. The UV/PDS AOP was more affected by Cl- than the UV/H2O2 AOP, because oxidation of Cl- is more favorable by SO₄^·- than ^·OH at p H 7. Despite relatively low concentration of Br- in brackish waters compared to Cl-, Brwas particularly important. Br- promoted halogen radical formation for both AOPs resulting in Cl Br·-, Br2·-, and CO3·- concentrations orders of magnitude higher than ^·OH and SO₄^·- concentrations, and reducing differences in halide impacts between the two AOPs. Kinetic modeling of the UV/H2O2 AOP indicated a synergism between Brand Cl-, with Br- scavenging of ^·OH leading to Br OH·-, and further reactions of Cl- with this and other brominated radicals promoting halogen radical concentrations.Based on realizaiont of effect of halides and carbonate on organic contaminant destruction by AOPs, in the second section, the efficiency of pharmaceutical destructions in reverse osmosis brines from wastewater reuse plants was investigated. UV/H2O2 and UV/PDS AOPs were compared for degradation of five pharmaceuticals spiked into brines obtained from two reuse facilities and the RO influent from one of them. For UV/H2O2, Ef OM scavenged ⁷5% of the ^·OH, reducing the degradation efficiency of the target contaminants to a similar extent; halide and carbonate scavenging and the reactivities of associated radicals were less important. For UV/PDS, anions（mostly Cl-） scavenged ⁹3% of the SO₄^·-. Because halogen radicals contributed to contaminant degradation, the reduction in contaminant degradation efficiency was only ⁷5%-80%, with the reduction driven by halogen radical scavenging by Ef OM. Conversion of SO₄^·- to more selective halogen and carbonate radicals resulted in a wider range of degradation efficiencies among the contaminants. For both AOPs, 250 m J/cm2 average fluence achieved significant removal of four pharmaceuticals. Additionally, comparing AOP application to the RO influent or brine, equal or greater removal was achieved for brine treatment for comparable energy input.The degradation efficiency of sulfamethoxazole（SMX） and propranolol（PPL） were different by inorganic radicals in the second section. In third section of this research, the formation of oxidation products by inorganic radicals were investigated. The forms of organic compounds affect the second order rate constants of SO₄^·-. SO₄^·-always exhibited high reactivity to anion forms with faster reaction rate than neutral forms（e.g., SMX）. When the reaction rate are diffusion rate constant controlled, the rate constant of anion forms are lower for the electrostatic repulsion of negative charge（e.g., PPL）. The reaction rate constants of ^·OH shows no significant different among the forms of organic compounds. ^·OH oxidation resulted in hydroxylation of aromatic ring and addition to double bond. However, SO₄^·- was prone to react with primary amine（e.g, SMX） and secondary amine（e.g., PPL） to form hydroxylamine, which further formed nitroso and nitro derivatives. Because CO3·- and Cl2·- react with organic compounds by electron transfer mechanism, similar with SO₄^·-, the oxidation products by CO3·- and Cl2·- were the same as by SO₄^·-.Considering the adavantages of ^·OH and SO₄^·- on micropollutent degradations, a novel AOP, O3/peroxomonosulfate（PMS） was proposed. The reaction between the anion of PMS（i.e., SO52-） and O3 was demonstrated primarily responsible for driving O3 consumption with a measured second order rate constant of（2.12 ± 0.03） × 104 M-1 s-1. The formation of both ^·OH and SO₄^·- from the reaction between SO52-and O3 was confirmed directly by EPR experiment, and indirectly by chemical probes(i.e., nitrobenzene for ^·OH and atrazine for both ^·OH and SO₄^·-). The yields of ^·OH and SO₄^·- were determined to be 0.43 ± 0.1 and 0.45 ± 0.1 per mol of O3 consumption, respectively. An adduct,-O3SOO- + O3 â†'-O3SO5-, is assumed as the first step, which further decomposes into SO5·- and O3·-. The subsequent reaction of SO5·- with O3 is proposed to generate SO₄^·-, while O3·- converts to ^·OH. A definition of R,? and R,? was adopted to quantify relative contributions of ^·OH and SO₄^·-. Increasing p H or PMS does lead to increases in both values of R,? and R,?, but does not significantly affect the ratio of R,? to R,?（i.e., R,? /R,?）. Humic acid promotes O3 consumption to generate ^·OH and thus leads to an increase in the R,? value in the O3/PMS process, while humic acid has negligible influence on the R,? value. This discrepancy is reasonably explained by the negligible effect of humic acid on SO₄^·- formation and a lower rate constant for the reaction of humic acid with SO₄^·- than with ^·OH.