Improved ultrafiltration performance through dielectric barrier discharge/sulfite pretreatment: Effects of water matrices and mechanistic insights

Abstract

The feasibility of utilizing a dielectric barrier discharge (DBD)/sulfite-ultrafiltration system was investigated in various real water bodies, aiming to clarify the mechanism behind alleviating membrane fouling while synchronously degrading perfluorooctanoic acid (PFOA) during the treatment process of Yangtze River water. The results demonstrated that the DBD/sulfite pretreatment exhibited remarkable rates of membrane flux mitigation (>84.10%) and efficient degradation rates of PFOA (>85.13%), which decreased with increasing pH from 3.0 to 11.0. The presence of anions, cations, and natural organic matter slightly hindered the membrane fouling mitigation and PFOA degradation by quenching free radicals; however, the addition of SO₄²⁻ had a negligible impact. The mitigation of membrane fouling was attributed to the significant involvement of various radicals, including hydroxyl radical (•OH), sulfate radical (${\text{SO}}_4^{•-}$${\text{SO}}_4^{•-}$), electron (${\mathrm{e}}^{-}{/\mathrm{e}}_{\text{aq}}^{-}$${\mathrm{e}}^{-}{/\mathrm{e}}_{\text{aq}}^{-}$), su-peroxide anion radicals ($•{\mathrm{O}}_2^{-}$$•{\mathrm{O}}_2^{-}$), and other radicals such as ${\text{SO}}_3^{•-}$${\text{SO}}_3^{•-}$, exhibiting respective contributions of 33.25%, 28.49%, 20.56%, 11.32%, and 6.39% in a synergistic redox effect. The pretreatment effectively reduced standard blocking and cake filtration fouling mechanisms by creating a sparse fouling layer on the membrane surface while increasing its roughness. Additionally, the main active species that played a significant role in the degradation of PFOA were identified as ${\text{SO}}_4^{•-}$${\text{SO}}_4^{•-}$, •OH, and ${\mathrm{e}}_{\text{aq}}^{-}$${\mathrm{e}}_{\text{aq}}^{-}$. These species contributed approximately 43.63%, 24.39%, and 20.65% respectively to the degradation process. By employing mass spectrometry and density functional theory, a proposed pathway for PFOA degradation was established, effectively reducing the toxicity associated with its degradation byproducts. This study provides innovative insights into membrane-based water treatment technologies that effectively tackle both membrane fouling mitigation and PFOA degradation.