Abstract
Gravity-driven membrane (GDM) filtration technology has been extensively in the employed drinking water treatment, however, the effect filtration mode (i.e., dead-end mode vs. cross-flow mode) on its long-term performance has not been systematically investigated. In this study, pilot-scale GDM systems were operated using two submerged filtration mode (SGDM) and cross-flow mode (CGDM) at the gravity-driven pressures 120 mbar and 200 mbar, respectively. The results showed that flux stabilization was observed both in the SGDM and CGDM during long-term filtration, and importantly the stabilized flux level of CGDM was elevated by 3.5–67.5%, which indicated that the filtration mode would not influence the occurrence of flux stability, but significantly improve the stable flux level. Interestingly, the stable flux level was not significantly improved with the increase of driven pressure, and the optimized driven pressure was 120 mbar. In addition, the GDM process conferred effective removals of turbidity, UV254, CODMn, and DOC, with average removals of 99%, 43%, 41%, and 20%, respectively. With the assistance of cross flow to avert the overaccumulation of contaminants on the membrane surface, CGDM process exhibited even higher removal efficiency than SGDM process. Furthermore, it can be found that the CGDM system can effectively remove the fluorescent protein-like substances, and the intensities of tryptophans substance and soluble microbial products were reduced by 64.61% and 55.08%, respectively, higher than that of the SGDM. Therefore, it can be determined that the filtration mode played an important role in the flux stabilization of GDM system during long-term filtration, and the cross-flow filtration mode can simultaneously improve the stabilized flux level and removal performance.
Highlights
The gravity-driven membrane (GDM) ultrafiltration has been increasingly reported in the fields of surface water treatment, rainwater reclamation, and seawater pretreatment [1,2]
The results indicated that the GDM systems effectively can remove tyrosine proteins and soluble microbial products (SMP) substances
The stable flux of CGDM was obviously higher than that of the submerged filtration mode (SGDM) system at the same driven pressure condition, since cross-flow operation could prevent the overaccumulation of contaminants on the membrane surface
Summary
The gravity-driven membrane (GDM) ultrafiltration has been increasingly reported in the fields of surface water treatment, rainwater reclamation, and seawater pretreatment [1,2]. During the GDM filtration, colloids, particles, and microorganisms, would be effectively intercepted by the ultrafiltration (UF) membrane, and thereby aggregated on the membrane surface [4] These increasingly accumulated substances would gradually develop a fouling layer on the UF membrane surface, which is determined as a “so-called” biofouling layer [5]. In such situations, the GDM system can couple the multifunctional rejection between the biofouling layer and UF membrane, enhancing the removal performance of organic pollutants (i.e., biopolymers and assimilable organic matter (AOC)) and pathogens in the feed water [6]. Four pilot-scale GDM systems were introduced to reveal the effects of the filtration mode (e.g., dead-end filtration vs cross-flow filtration) on the flux stabilization and the flux levels were analyzed. Water 2022, 14, x FOR PEER REVIEW performance improvements and practical application of GDM technology
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