Abstract
Quinoline is a typical nitrogenous heterocyclic compound, which is carcinogenic, teratogenic, and mutagenic to organisms, and its wastewater is difficult to biodegrade directly. The bipolar electro-Fenton process was employed to treat quinoline solution. The process/reaction conditions were optimized through the single factor experiment. The degradation kinetics of chemical oxygen demand (COD) was analyzed. To get the degradation mechanism and pathways of quinoline, the intermediate products were identified by gas chromatograph–mass spectrometer (GC–MS). By using sodium chloride as supporting electrolyte in the electro-Fenton reaction system with initial pH 3.0, conductivity 15,800 µs/cm, H2O2 concentration 71 mmol/L, current density 30.5 mA/cm2, and applied voltage 26.5 V, 75.56% of COD was decreased by indirect oxidation with electrogeneration of hydroxyl radicals (•OH) and active chloric species in 20 min. The COD decrease of quinoline solution followed the first order reaction kinetic model. The main products of quinoline degradation were 2(1H)-quinolinone, 4-chloro-2(1H)-quinolinone, 5-chloro-8-hydroxyquinoline, and 5,7-dichloro-8-hydroxyquinoline. Furthermore, two possible degradation pathways of quinoline were proposed, supported with Natural charge distribution on quinoline and intermediates calculated at the theoretical level of MN15L/6-311G(d).
Highlights
With rapid development of economy and industry, water environment pollution has become increasingly serious
We investigated the effects of initial pH value, conductivity, H2 O2 ity, H2O2 concentration, applied voltage, current density, and reaction time on the chemiconcentration, applied voltage, current density, and reaction time on the chemical oxygen cal oxygen demand (COD) decrease rate of quinoline solution
chemical oxygen demand (COD) decrease efficiency remained stable over time
Summary
With rapid development of economy and industry, water environment pollution has become increasingly serious. Treatment of hardly-degradable organic wastewater has attracted a variety of research focuses. As an important chemical raw material, is often used in the manufacture of drugs, dyes, herbicides, and pesticides, etc. The resulting wastewater containing quinoline has become a common organic pollutant in water and soil environments. A nitrogen-containing heterocyclic aromatic compound, is carcinogenic, teratogenic, and mutagenic to organisms, and can accumulate in advanced animals along the food chain, seriously threatening human health [2]. Due to its stable structural properties and toxicity, it is difficult to directly and effectively degrade with conventional physicochemical and biological methods. Efficient treatment techniques to remove quinoline in wastewater are definitely needed
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