Monochlorophenols degradation by UV/persulfate is immune to the presence of chloride: Illusion or reality?

Abstract

The efficiency and, accordingly, the success of the advanced oxidation processes (AOPs) has generally been evaluated on the basis of degradation kinetics. In practice, chloride in saline wastewater is often found to inhibit degradation processes. Therefore its highly desirable to develop more effective processes which are not affected by chloride. In this study, no significant interference of chloride with monochlorophenols (MCPs, e.g. 2-CP, 3-CP and 4-CP) degradation by the UV photoactivated persulfate (UV/PS) process has been observed. This indicated the "illusion" that the UV/PS process might have been an appropriate technology working under saline conditions. To further evaluate its applicability, the generation of reaction intermediates, of adsorbable organic halogen (AOX) accumulation and of acute toxicity of MCPs in the UV/PS system were examined. In reality, several aromatic chlorinated compounds (number of chlorine atoms ≥ 2), such as dichlorophenols and 2,3,5,3',5'-pentachloro-biphenyl, were identified and quantified. An accumulation and relative increase of AOX with reaction time was observed in the UV/PS/Cl system. The acute toxicity tests with Photobacterium phosphoreum indicated that the inhibition effect of UV/PS reactions increased with reaction time regardless of the presence of chloride or not. The results of this study might be helpful for assessing the PS-based technologies for saline wastewater treatment.

Impact of Chloride Ions on UV/H2O2 and UV/Persulfate Advanced Oxidation Processes

“…In the UV/PS reaction of organic compounds that react with SO 4 – ·, HO·, and Cl·, Cl – has been reported to inhibit the degradation of biphenyl, polychlorinated biphenyls, azathioprine, humic acid, sulfamethoxazole, propranolol, carbamazepine, acyclovir, lamivudine, chloramphenicol, acetaminophen, atrazine and atenolol, 1,4-dioxane, diclofenac, and diethyl phthalate . However, Cl – has less of an inhibitory effect on 2,4,6-trichloroanisole, monochlorophenols, and trichloroethylene . This is because they have very high second-order rate constants with Cl· (e.g., TCE is 4.88 × 10 10 M –1 ·s –1 ) .…”

A Review on Adsorbable Organic Halogens Treatment Technologies: Approaches and Application

“…UV/TiO 2 oxidation Dye wastewaters, pulp and paper mill wastes [6,160] UV/ozone oxidation process Wastewaters [161] Adsorption on activated carbon 4-chlorophenol, 4-bromophenol, 4-iodophenol, 2,4,6-trichlorophenol, landfill leachates [162][163][164] Biochar remediation Degradation of halogenated organics [165] Al(III) coagulation/carbon adsorption process Dye wastewaters [166] H 2 O 2 /UV oxidation Pharmaceutical wastes [65,76,167] Mechanochemistry Wastes [168,169] Thermally activated persulfate by microwave heating (S 2 O 8 2-/MW) Secondary waste sludge [170] Anionic exchanger DEAE-cellulose Drinking water [171] Supercritical water oxidation (SUWOX) Industrial wastes [172] Magnetically re-extractable nanoscale Pd-on-magnetite catalyst (Pd/Fe 3 O 4 ) Wastewaters [173] Multi-barrier treatment Municipal wastewaters [174] Photo-Fenton process UV/H 2 O 2 /Fe 2+ Pulp mill effluents [40] UV/persulfate oxidation process Saline wastewater [175] UV/TiO 2 /Ru x Se y oxidation system Paper industry wastes [123] Pd/AC catalyst Kraft pulp bleaching wastes [176] UV/TiO 2 /granular activated carbon 4-halogenophenols [177] UV/H 2 O 2 /TiO 2 system Pulp and paper wastes [178] UV/sodium hypochlorite Phenol's degradation [179] Physical Hot water extraction of hemicellulose Paper and pulp industry wastewaters [58,180] Distillation and membrane processes Pharmaceutical wastes [34] Distillation Chemical wastes [181] Centrifugation and drying Sludge [97] Nanofiltration Paper and pulp industry wastes [182] Biochemical Xylanase and laccase enzymes (obtained from Bacillus pumilus and Ganoderma sp., respectively)…”

“…Coagulation, anion exchange, and ultrafiltration processes, followed by physical treatments, are also utilized. For the treatment of saline wastewater, the UV/persulfate oxidation process is suitable due to its stability at high chloride concentrations and the independence of oxidation rate on chloride levels [175]. Moreover, mechanochemistry has proven to be an effective destruction process for halogenated organic compounds.…”

Activation of periodate using ultrasonic waves and UV radiation for landfill leachate treatment

“…All tests were done in a closed reactor in different steps. In this investigation, the variables were included leachate pH (3)(4)(5)(6)(7)(8)(9)(10)(11), ultrasonication time (30-120 minutes), concentration of periodate (0.5-5 mM), and leachate concentration (25-100%). To optimize each variable, only one variable in each part of the experiment was considered and the rest of the variables were kept constant.…”

“…Comparing these cases with UV 254 absorption percentage in the whole system shows the reduction of pollutants and aromatic degradation in the whole system. In addition, the direct use of UV and the activation of free radicals are also effective in this reduction (Fang et al, 2017;Iskander et al, 2018). In the ultrasound system alone, the main mechanism for the growth and collapse of microbubbles in the liquid is the result of an unusual environmental reaction inside and near the bubble.…”