Kinetics And Mechanisms On The Fast Degradation Of Micro-organic Contaminants By Bisulfite Activated Permanganate

With the development of social production and process of measuring and testing techniques,the frequency and species of detected micro-organic pollutants increased.The conventional water treatment process was not efficient in removing various micro-organic pollutants.Hence,the development of new strategies to deal with this concern is necessary.Surprisingly,the contaminants disappeared rapidly during the oxidaiton by permanganate when designed concentration of sulfite was added.This study systematically investigated the mechanism,kinetics,influence factors of contaminants oxidation in the PM/BS process,as well as the degradation of various contaminants and the removal of contaminants toxicity.The results showed that the organic contaminants could be degraded in the PM/BS process in the order of millisecond which were ?5 to 7 orders of magnitude faster than conventional and advanced oxidation processes for water treatment.The above results,time-resolved spectroscopy of manganese species under various conditions,the electron paramagnetic resonance spectrum,the effect of pyrophosphate on UV absorbance spectra,the acceleration of bislufite on the oxidation of contaminants by manganese dioxide,and stoichiometric analysis of pH variation suggest that the reactive intermediate?s?responsible for the extremely rapid oxidation of organic contaminants in the PM/BS process involve manganese???species with minimal stabilization by complexation.pH significantly influenced the degradation of organic contaminants in the PM/BS process,with higher reaction rate at lower pH.The concentration of organic contaminants removed in the PM/BS process decreased with pH exceeding 7.0.The in situ formed Mn???could be complexed by the ligands which decrease the reactivity of Mn???.Phenol was generated during the oxidation of benzene by Mn???,then Mn???generation-utilization model was developed by combining the generation kinetic of phenol and the reduction kinetic of permanganate.The concentration of Mn???as the function of time and the utilization of Mn???at different pH could be obtained from the model.The utilization of Mn???was similar at pH = 4.5-6.5 and decreased during increasing the pH from 6.5 to 8.0 which could be attribuated to the high rate of Mn???disproportionation at higher pH.Further,the model showed the concentration of Mn???was in the order of micromolar.Combining Mn??? generation-utilization model and competition kinetics model,the second-order rate constants of bisphenol A and aniline oxidation by soluble Mn???could be calculated which were in the range of 10⁵-10⁶ L mol^-1s^-1,much higher than that in other traditional oxidation process.Although the second-order rate constants for reaction of organic contaminants with Mn???were 3-4 orders of magnitude lower than those with hydroxyl radicals,the concentration of active oxidant,Mn???,in the PM/BS process was 10⁶-10⁸ times of that of hydroxyl radicals in advanced oxidation processes?AOPs?.Therefore,the PM/BS process could oxidize organic compounds?phenol and ciprofloxacin?with apparent reaction rates several orders of magnitude faster than AOPs.The Mn??? in the solution after PM/BS process could be partially transformed to colloidal manganese dioxide by purging air,then the residual Mn???could be absorbed to the manganese dioxide.The colloidal manganese dioxide was unstable and easily precipitated which make it easier to separate from the solution and met the drinking water standard.Ciprofloxacin?CIP?,one of the representative quinolone antibiotics,was selected as the target comtaminant to investigate the influence of reaction conditions on the oxidation of contaminants in the PM/BS process.High temperature facilitate the generation and consumption of Mn???as well as the oxidation of contaminants by Mn???.The activation energy of CIP oxidation by Mn???at pH 5.0 was higher than that at pH 6.5 which could be ascribed to the dissociation of CIP molecule.The oxidation mechanims of CIP with different species might be different.The coexisting ions did not interfere the reaction between permanganate and bisulfite at pH 5.0,while the degradation rate of CIP in the PM/BS process decreased which was due to the influence of coexisting ions on the oxidation of CIP by Mn???.Compared with that at pH 5.0,the oxidation of CIP at 6.5 was significantly depressed in the presence of NaCl,CaCl₂,MgCl₂ and Na₂CO₃.The dissociation of carboxyl group changes the properties and charge of CIP which account for the different influence of coexisting ion on CIP oxidation at pH 5.0 and 6.5.Oxidation products were identified by UPLC-QTOFMS analysis which implied that CIP was initially attacked by Mn???at the piperazinyl substituent and cyclopropyl substituent.Bacterial growth inhibition bioassays and genotoxic experiments showed that the mixture of products resulting from Mn???reactions with the CIP retained negligible cytotoxic and genotoxic potency.Therefore,the destruction of piperazinyl substituent and cyclopropyl substituent is effective for the removal of toxicity.The formation potential of bromate was quite low implying that Mn???was a comparable green oxidant.PM/BS process was effective in degrading various contaminants.Excepting caffeine and benzotriazole,other selected comtaminants with the concentration of 1 ?mol/L could be completed degraded.Contaminants competete Mn???when various contaminants were coexisted and most of Mn???was consumed by the organics which could be easily oxidized.Comparatively,the degradation of organic contaminants is complicated in real water.The organic matter and inorganic reductants consumed Mn???and depressed the oxidation of target contaminants,while some coexisting species enhanced the oxidation of contaminants.Hence,it is necessary to consider the properties of contaminants and the water quality to optimize the removal of contaminants in the PM/BS process.