The overlooked multidimensional roles of filtration pressure in improving ozonation: A study in a O₃/pressurized...

The integrated process of in-situ ozonation and ultrafiltration (UF) process has been widely used in drinking water treatment, in which the roles of filtration pressure (FP) in controlling membrane fouling and improving purification efficiency by in-situ ozonation have not yet been clearly understood. This study thus systematically investigated the roles of FP in a O₃/pressurized cell-side feeding PVDF UF/BAC (O₃/UF/BAC) system to treat surface source water. The results indicated that FP in UF reactor could multi-dimensionally improve the ozonation efficiency, leading to the excellent anti-fouling and water purification performance. With FP, the ozone solubility was increased by 2 times firstly, which sequentially enhanced the interaction of dissolved ozone with the containing aromatic rings substances, such as lignin/carboxylic rich alicyclic molecule (CRAM)-like substances and aromatic structures, forming the higher concentration of •OH. Meanwhile, the chain length (n) of the •OH chain propagation reaction was also increased from 3.2 to 6.6. Furthermore, on the pathway to go through the foulant layer, the dissolved ozone intensely reacted with and diminished the deposited foulants near the membrane surface, as evidenced by Tof-SIMS analysis. Then, the dissolved ozone permeated into the membrane pores and interacted with the natural organic matter (NOM), reducing the pore clogging. Finally, the residual ozone further passed into the following BAC unit, which reacted with the loaded activated carbon forming •OH and promoting the pollutant degradation. Based on all these benefits, as compared with the UF/BAC, the R_r and R_ir (reversible and irreversible membrane fouling resistance) reduced by 63 % and 89 %, and COD_Mn and DOC in the O₃/UF effluent decreased by 48 % and 30 % and by 86 % and 61 % in the O₃/UF/BAC effluent, respectively. Thus, FP in the cell-side feeding UF reactor created multiple synergistic beneficial effects that guaranteed superior NOM removal and membrane fouling control performance of the O₃/UF/BAC system.