Study On Removal Of Acesulfame From Raw Water By The Combined Persulfate Catalytic Oxidation And Enhanced Coagulation

Artificial sweetener is a kind of sucrose substitute synthesized artificially or extracted from natural substances,which is almost indigestible in human body.Artificial sweetener is featured by high polarity,stable molecular structure and non-biodegradability.High detection rate is observed in source,threatening the healthness of drinking water.Conventional water treatment process is ineffective to remove artificial sweetener.The problem of micro-pollution of raw water needs to be solved urgently.The effective combination of advanced oxidation process and coagulation process is a common means to enhance coagulation,improving the removal of emerging pollutants.A waterworks in Zhengzhou adopts polyaluminum chloride（PAC）and polyferric sulfate（PFS）as coagulants.In this experiment,enhanced coagulation by catalytic oxidation of persulfate is proposed to remove new organic compounds in water by referring to the type and dosage of coagulants in the waterworks,including（1）Fe（II）activated persulfate catalytic oxidation-enhanced coagulation treatment,and（2）active coke activated persulfate pre-oxidation-coagulation treatment.Fe（Ⅱ）（Fe SO₄·7H₂O）is used as a substitute for PFS.For Fe（Ⅱ）activated persulfate catalytic oxidation-enhanced coagulation process（PDS-PAC/Fe（Ⅱ）system）,it can not only reduce the use cost of coagulant,but also replace ferrous coagulant with lower price ferrous coagulant.This can undergoes the combination of simultaneous in-situ oxidation and coagulation.At the same time,activated coke（ACO）is a kind of activated carbon-like material produced from coal,which is rich in pore structure and surface functional groups.ACO has higher chemical stability and mechanical strength but lower price than activated carbon,so it has been successfully applied to the actual water treatment process.The application of ACO in the persulfate pre-oxidation-coagulation process,will contribute to the removal of emerging pollutants.In this study,artificial sweetener acesulfame（ACE）was used as the target pollutant,the enhanced coagulation removal of ACE was achieved by combining the above two kinds of persulfate catalytic oxidation process.The main conclusions are as follows:（1）In the process of Fe（Ⅱ）activated persulfate catalytic oxidation-enhanced coagulation,the first-order kinetic K_app value of PDS-PAC/Fe（Ⅱ）system is 1.8×10^-2 min^-1.The K_app values of single PDS oxidation and PAC/Fe（Ⅱ）coagulation processes are 8.9×10^-4 min^-1 and 3.3×10^-3min^-1,respectively.The K_app value of PDS-PAC/Fe（Ⅱ）is 4.4 times that of the total of single PDS oxidation and PAC/Fe（Ⅱ）coagulation process,indicating a significant synergetic effect.PDS is superior to PMS in the process.Elevation of reaction temperature is favorable for ACE degradation and activation energy of the reaction is 37.1 k J/mol.The highest degradation rate is the initial p H of 5.0,and the degradation rate is moderate under the original p H.Through the response surface optimization,the optimized reaction conditions are predicted as follows:Fe（Ⅱ）dosage 10.6 mg/L,PDS dosage 61.2 mg/L,solution initial p H 4.9,which is verified by practical experiments.The oxidizing species capture experiment investigated the degradation behavior of PDS-PAC/Fe（Ⅱ）under neutral p H and initial p H 5.0.It was found that there were both free radical and non-free radical pathways.·OH、SO₄^-·、O₂^-·、¹O₂and h⁺were formed in the system.The order of inhibition of anions and natural organic compounds on catalytic-coagulation process is NO₃^->SO₄^2->HA>Cl^-.PDS-PAC/Fe（Ⅱ）system can effectively degrade ACE in surface water simulation experiment,and the removal of surface water turbidity is higher than 99.9%.（2）In the ACO activated persulfate pre-oxidation-coagulation treatment process,the K_appvalues of ACO adsorption,PDS oxidation alone and ACO/PDS catalytic oxidation system were 1.3×10^-2 min^-1,1.0×10^-3 min^-1 and 2.8×10^-2 min^-1,respectively.The K_app values of ACO/PDS catalytic oxidation is 2 times that of the total of single PDS oxidation and ACO adsorption process,indicating a significant synergetic effect.The removal rate of ACO/PDS-PAC/PFS system is the highest under the conditions of 5 mg/L ACE,60 mg/L PDS,200 mg/L ACO,67.5 mg/L PAC,40 mg/L PFS and pre-oxidation time is 30 min,and the increase of temperature promotes the degradation of ACE.Through the response surface to optimize the pre-oxidation process,the optimized reaction conditions are predicted as follows:ACO dosage 368 mg/L,PDS dosage 62.5 mg/L,solution initial p H 3.9,the experimental results show that the ACE degradation rate is 91.5%under this experimental condition.Through the oxidizing species capture experiment,it is confirmed that there are both free radical and non-free radical mechanisms in the pre-oxidation process,resulting in the formation of SO₄^-·、·OH、O₂^-·、¹O₂ and h⁺.NO₃^-has obvious inhibitory effect on the pre-oxidation-coagulation process,while Cl^-,SO₄^2-and HA have little effect on the pre-oxidation-coagulation process.ACO can be recovered and reused.The effect of surface water is similar to that of laboratory water,while the pre-oxidation-coagulation process is less affected by water quality fluctuation,and the removal of surface water turbidity is higher than99.9%.Through the study of Fe（Ⅱ）activated persulfate catalytic oxidation-enhanced coagulation treatment and ACO activated persulfate pre-oxidation-coagulation treatment,the feasibility and scientificity of the two persulfate catalytic oxidation and enhanced coagulation approaches are testified.This will provide technological support for the removal of emerging pollutants.