Removal Of Perfluorinated Compounds In Water By Anion Exchange And Adsorption And Activated Persulfate Oxidation

Perfluorinated compounds?PFCs?have been globally identified and subjected to be scutiny by goverments and environmental science community.Although activated carbon?AC?and ionexchange adsorption technologies have been finite applied for removal of PFCs from water,contaminant penetration and secondary pollution frequently occure duing the AC adsorption process and the ionexchange adsorption is uneconomical due to lack of efficient resin recovery technology.In addition,the investigation on sorption mechanisms of both of the two technologies are still inadequate.The effect of properties of AC and ionexchange resin and water qualities on adsorption was investigated in this research,thus the mechanism of the adorption process was also studied basing on the experiment results.Furthermore,removal of PFCs by activation persulfate?PS?oxidation was studied in this dissertation.A novel removal technology,covalent bonding chemisortion,was discovered in reaction systems with presence of AC and PS.It is a promising treatment technology which is with rapid reaction,absence of byproducts and secondary pollution,meanwhile supplies an alternative for removal of recalcitrant organic pollution from water.Basing on experiment results,the strong base ionexchange resin displayed excellent ability on PFCs removal,whereas the weak base ionexchange resin with poor effective removal.In contradiction with adsorption of PFCs by AC,a specific concentration of NOM could enhance removal of PFCs by ionexchange resin owing to increase of hydrophobic effect between ionexchange resin and PFCs.In experiment of ultrapure water,removal of PFBA by ionexchange resin was 18%,whereas 70% of initialed PFBA was removed in reaction system of natural water with 5.1 mg/L TOC.The adsorption kinetic results suggest that the intraparticle diffusion process and chemical reaction process are the major controlling factor of ionexchange adsorption,and the intraparticle is the rate controlling step.Compared with gel-type ionexchange resin,macroporous ionexchange resin possesses lager pore structure which could enhance the intraparticle diffusion to increase initial adsorption rate.According to experiment results,the mesopore volume is the major controlling factor of adsorption rate of PFCs removed by AC and BET surface area determines the adsorption capacity.The electrostatic interaction between PFCs and AC is not dominant in adsorption process,whereas the hydrophobic interaction might be the priority controlling factor.Due to the tiny effect of electrostatic interaction,ionic strength and pH condition of water are unable to affect adsorption of PFCs by AC.Natural organic matter?NOM?hindered the adsorption of PFCs by AC.Removal of PFCs with longer CF backbone in experiment of natural water with 4.8 mg/L TOC decreased 50% compared to experiment of ultrapure water,even no removal on PFCs with shorter CF backbone.For industry application of PFCs removal,a water treament process for NOM removal should be consiered to place at the front end of AC fix bed to diminish effect of NOM.The experiment results suggest the C-C bond sequential cleavage chain reaction could only initialed in reaction systems under acidic conditions.According pH various experiment results,degradation of PFCs by activation PS oxidation only existed in reaction systems under pH < 3.4.For the homogeneous reaction system under pH 8.2 and the homogeneous and heterogeneous systems under pH 13.0,due to the high concentration of OH-,SO4-· was immediately converted to OH·,which is unable to oxidize PFCs,PFOA loss was stable during the reaction process.A novel removal pathway of PFCs was observed in AC heterogeneous system with presence of PS under circumneutral pH conditions.Under these conditions,the removal of PFOA was attributable to covalent bonding chemisorption,a reaction process in which activated carbon catalyzed S₂O₈^2-decomposition and reacted with the transformation products to produce covalently bound PFOA on activated carbon.At PFOA initial concentration of 0.5 ?M and PAC concentration being between 200 and 1000 mg/L,15% to 50% of PFOA was removed by covalent bonding chemisorption.Covalent bonding chemisorption could significantly improve removal of PFCs from water.At PAC concentration 1000 mg/L and PFBA initial concentration 0.5 ?M,94% of PFBA was removed in the heterogeneous reaction system in the presence of S₂O₈^2-,whereas only 60% of PFBA was removed in homogeneous system in the absence of PS.