Aqueous Pollutants Removal By Activated Persulfate Oxidation Process

Sulfate radicals(SO4·-)-based persulfate advanced oxidation processes are promising technologies that are recently applied to degrade various refractory organic pollutants in wastewater treatment and in-situ remediation of soil and groundwater.Currently,typical methods applied for persulfate activation includes heating,cobalt(Co(II)),ferrous ion(Fe(?)),and zero-valent iron(ZVI,Fe0).Considering their characteristics of activation,this paper discusses their applications in the removal of aqueous pollutants by activated persulfate oxidation processes.Firstly,atrazine(ATZ),one of the pesticides widely used in the world,was considered as target pollutant due to its residual in various water compartments.Because heating and solution delivery are mature remediation technologies used for groundwater remediation,heat-and cobalt-activated persulfate were applied to remove ATZ.The feasibility of using these methods to treat ATZ in wastewater treatment and in-situ groundwater remediation was evaluated.Secondly,persulfate activation by ZVI and Fe(?)has attracted much attention owing to iron's safe,non-toxic and cheap properties.During the process of activation,iron will eventually be converted to precipitable ferric ions(Fe(?)),which is suitable for water treatment.Fe(?)can not only be utilized to remove phosphate by reaction with phosphate to form insoluble ferric phosphate,but also is a common coagulant capable of removing contaminants by coagulatoin.Therefore,ZVI-and Fe(?)-activated persulfate can be integrated with coagulation reaction or phosphorus removal processes.Due to variation in the removal performance of phosphorate by biological treatment of sewage treatment plant,endocrine disruptors such as bisphenol A(BPA)are poorly eliminated.Alternative methods such as chemical oxidation are often needed to deeply remove these contaminants.ZVI activation process can be used as advanced treatment process to simultaneously remove BPA and phosphorate from secondary effluent.Fe(?)activation can be integrated with traditional tap water treatment process to remove natural organic matter(NOM)by SO4·-oxidation and Fe(?)coagulation and,therefore,to reduce the production of disinfection by-products(DBPs).The following aspects are studied in detail.(1)The effective degradation of atrazine(ATZ)was observed by heat-activated persulfate(PS)process in water.Increasing the initial PS concentration or temperature significantly enhanced the degradation efficiency,and ATZ oxidation followed pseudo-first-order kinetics and Arrhenius Equation and the apparent activation energy of the reaction is 137.6 kJ·mol-1.pH value played an important role in ATZ oxidation and the highest removal rate was achieved under acid and neutral conditions.The presence of natural organic matter(NOM)decreased ATZ degradation rate,but complete removal of ATZ could still be obtained.The presence of chloride(Cl-)and bicarbonate(HCO3-)had little effects on ATZ elimination at lower concentrations(e.g.,5 mM).However,inhibitory effects were observed when concentrations of Cl-and HCO3-increased.Transformation pathways of ATZ included dealkylation,alkyl chain oxidation,and dechlorination-hydroxylation.Because solution delivery and heating are mature in-situ remediation methods,except for wastewater treatment,heat-activated PS process can also be used for groundwater remediation.(2)Cobalt catalyzed peroxymonosulfate(Co(?)/PMS)was found to be efficient for ATZ elimination in aqueous solution.Increasing the initial Co(?)or PMS concentration significantly favored the degradation efficiency.The degradation rate of ATZ increased from 37%to 100%in 45 minutes when the concentration of Co(?)increased from 1 ?M to 10 ?M.And the degradation rate of ATZ increased from 40%to 96%in 45 minutes when the dosage of PMS increased from 0.1 mM to 2 mM.ATZ oxidation followed pseudo-first-order kinetics.pH had significant impact on the degradation rate of ATZ,and higher efficiency of ATZ oxidation was observed around neutral condition.NOM,Cl-and HCO3-showed detrimental effects on ATZ degradation.Major transformation pathways of ATZ included dealkylation,dechlorination-hydroxylation,and alkyl chain oxidation.Because Co(?)and PMS solutions can be injected into groundwater via delivery wells and pipes,Co(?)/PMS can be used for wastewater treatment as well as groundwater remediation.(3)Simultaneous removal of BPA and phosphate by ZVI-activated persulfate(ZVI/PS)oxidation process was investigated.Activation of PS by ZVI mainly produces SO4·-which can efficiently degrade organic contaminants.ZVI is ultimately transformed to Fe(?)which works as a coagulant to remove phosphate.This technology can be used as an advanced treatment technology for wastewater treatment e.g.,to remove residual organic pollutants and phosphorus present in the effluent of sewage treatment plant.It was demonstrated that BPA and phosphate could be simultaneously removed in this system.The reaction rate increased with increasing ZVI and PS dosages.The removal rate of BPA increased from 30%to 91%when the dosage of ZVI increased from 0.1 g·L-1 to 0.5 g·L-1.And the degradation rate of BPA increased from 19%to 82%when the concentration of PS increased from 0.1 mM to 0.5 mM.The oxidation of BPA followed pseudo-first-order kinetics.Under acidic or near neutral conditions,the degradation of BPA is faster.The presence of NOM showed inhibitory effect on BPA degradation but had no appreciable negative effect on phosphate removal.Phosphate showed a weak inhibitory effect on BPA decomposition,and trace amounts of HCO3-exhibited no obvious influence on the removal of both phosphate and BPA.The main mechanisms of BPA degradation by SO4·-included electron transfer and hydrogen abstraction.Under the experimental conditions,the removal rates for BPA and phosphorate were 74%and 91%in real water matrix sampled from a local sewage treatment plant.(4)Fe(?)-activated persulfate(Fe(?)/PS)oxidation process was combined with the traditional tap water treatment technology.NOM that serves as an important DBPs precursor could be degraded by the oxidation of SO4·-and the coagulation of Fe(?).Without changing the original structure,pipeline and process of water utilities,Fe(?)/PS process could effectively remove NOM and thus reduce the yields of DBPs during subsequent disinfection process.All samples used in experiments are natural water samples.Under the experimental conditions,the production of halogenated methane and halogenated acetic acid decreased by 38%and 51%respectively.The removal rate of total organic carbon(TOC)was the highest when the pH value was 4,and the oxidation proceeded faster in the initial stage.The removal rate of TOC increased with increasing concentration of PS.TOC elimination rate increased from 25%to 65%when PS concentration increased from 0.1 mM to 0.5 mm.This new technology could reduce the aromaticity and decrease the molecular weight of NOM,as evidenced by UV absorption data,such as SUVA254,SUVA280 and E2/E3.The removal efficiency of fluorescent substances also increased by increasing PS dosage.There were good correlations between ultraviolet absorption(UV254),fluorescence intensity(?I),and TOC,as well as between UV254,TOC,and the formation of halogenated acetic acid.