The Enrichment Of Per-and Polyfluoroalkyl Substances At Air-water Interface And Enhanced Removal By Air Bubbles

Per-and polyfluoroalkyl substances(PFASs)are a kind of organic pollutants with high chemical stability,which are ubiquitous in the aqueous environments.However,the important interfacial behavior of PFASs has been overlooked for quite a long time.This study investigated the enrichment of PFASs at air-water interface in different systems,and the enhanced removal of PFASs by air bubbles.The research contents and results are listed as following:The partition of PFASs in oil-water systems and the enrichment of PFASs at the surface of sea spray aerosol(SSA)were investigated to study the enrichment of PFASs at air-water interface.The study suggests that air plays an important role in the partition of perfluorooctane sulfonate(PFOS)in oil-water systems.In the hexane/octanol-water systems,the PFOS could only emulsify the oil-water systems with the assistance of air,while the existence of air made no difference to octane sulfonate(OS)under the same condition.Due to the oleophobicity of the C-F chain,PFOS prefers to accumulate at the air-water interface,instead of accumulating at the oil-water interface.The SSAs were formed by simulating the wave splashing in an impactor,and the SSAs were then collected by size via a low pressure impactor.It was discovered that the enrichment of PFASs on the SSAs increases significantly with the decreasing of the particle size of SSAs and the increasing of chain length of the PFASs.Comparing to perfluorinated carboxylic acid(PFCAs),perfluoroalkyl sulfonic acids(PFSAs)shows higher enricnments on the SSAs.The enrichment factor of perfluorodecanoic acid(PFDA)and PFOS could reach 210000 and 890000 on the SSAs with a particle size smaller than 0.15 ?m.Based on the preference of PFASs at air-water interface,the high enrichment of PFASs on the SSAs may contribute to the long-range transportation of PFASs.Three remediation strategies including aeration,adsorption and adsorption combined with aeration were investigated to study the influence of air-water interface on the remediation of PFASs.An aeration-foam collection method was developed based on the preference of PFOS at air-water interface.The PFOS removal could reach 99% after aeration for 2 h,with an aeration flow rate of 75 m L/min,and the PFOS concentration in the collected foam was as high as 6.5 mmol/L.The PFOS removal from a kind of practical aqueous film-foaming foams(AFFFs)wastewater could reach 99% after aeration for 90 min,suggesting that this method was practically efficient.An efficient aminated polyachrinitrile fiber(APANF)was prepared,which showed the highest adsorption capacity for PFOS of 15 mmol/g at p H 3.It was proved that the air bubbles formed during the shaking or originally in the solution were beneficial for the adsorption of PFOS.The contribution of air bubbles to the PFOS adsorption was larger when the concentration of PFOS was lower or under a basic solution.PFOS could be adsorbed by accumulating at the surface of air bubbles,with the C-F chain ctretching into the air bubbles and the ionic group stay in the solution.Based on the contribution of air bubbles to the adsorption of PFASs,a remediation strategy combined with aeration and activated carbon was developed.By adding aeration during the ac adsorption,the removal of PFDA by 2 kinds of activated carbon were increased by 115% and 75%,respectively.The removal of perfluorooctanoic acid(PFOA),perfluorononanoic acid(PFNA)and PFOS were all improved by 50% to 90%.The aeration increased the air-water interface,which was favorable for the enrienment of PFASs in the solution,which could then be adsorbed by the activated carbon.The aeration showed a larger influence of the adsorption of long-chain PFASs and linear PFASs,due to their higher surface activity comparing to shorter-chain PFASs and branched isomer PFASs.