Characteristics of membrane fouling by consecutive chemical cleaning in pressurized ultrafiltration as pre-treatment of seawater desalination

Abstract

Effect of chemical cleaning on pressurized UF as pre-treatment for desalination • NaOCl and oxalic acid showed the optimum results for recovering flux rate • The optimum cleaning combination was oxalic acid-NaOCl-oxalic acid. • Inorganic salts were found to adhere more on the membrane surface. • Hydrophobic foulants were removed easily by chemical cleaning on the surface.Chemical cleaning of membranes is one of the most important strategies in pressurized hollow fiber ultrafiltration (UF) as a pre-treatment for seawater desalination. Various physical cleaning strategies such as backwashing, aeration and air-scrubbing or chemically enhanced backwashing (CEB) have been investigated in order to remove foulants from the UF membrane. However, the limitation in their cleaning effects being found during long-term operation leads to the need of cleaning in place (CIP) for the recovery of membrane performance. In this study, we used oxalic acid and sodium hypochlorite as chemical cleaning agents. The cleaning in series of oxalic acid-sodium hypochlorite-oxalic acid showed the optimal cleaning efficiency and was applied for the consecutive chemical cleaning. The recovery efficiency of the CIP after first, second, third and fourth cleanings was 96.8%, 95.8%, 98.3% and 99.9%, respectively. It was almost fully recovered to the previous recovered value. However, membrane surface structure was deformed by contact with chemical cleaning agents during cleaning time, because, hydrophilic inorganic foulants are still adhered on the membrane surface even after several cleanings although hydrophobic organic foulants were removed easily by chemical cleaning. An improved CIP strategy should be developed to remove hydrophilic foulants for long-term operation of desalination plants.

Assessing the removal of organic micro-pollutants from anaerobic membrane bioreactor effluent by fertilizer-drawn forward osmosis

“…By improving its hydrophilicity, the membranes can exhibit higher water flux due to more favorable transport of water molecules through improved membrane wetting [39,40]. Hydrophilic scaling often occurs in the early stage of the scaling formation [41] which can enhance the transport of water molecules. Any slight flux decline from the increased membrane resistance due to partial scale formation on the membrane surface can thus be offset by the enhanced water flux from the improved hydrophilicity of the FO membrane surface.…”

Water desalination using graphene-enhanced electrospun nanofiber membrane via air gap membrane distillation

“…6(c) shows the FT-IR spectra of the different fabricated membranes. All neat and G/PH nanofibers showed the same absorption bands attributed to the basic structural characteristics of PVDF-HFP at 839 cm -1 , 879 cm -1 , 1072 cm -1 , 1178 cm -1 , 1269 cm -1 , and 1400 cm -1 , which correspond to CH 2 rocking and CF 2 asymmetric stretch (the β phase), CH 2 in plane bending or rocking (the α phase), C-C asymmetric stretch, C-C asymmetric stretch and CF 2 symmetric stretching, CF out of plane deformation (the β phase), and CF stretching vibrations or CH 2 wagging (the α phase), respectively [41]. Similar spectra were observed for the G/PH electrospun membranes but at lower intensities, which signify the presence of interfacial interaction (physical adsorption or weak chemical bonding) between PH and graphene particles.…”

Influence of Membrane Materials and Operational Modes on the Performance of Ultrafiltration Modules for Drinking Water Treatment

“…As shown in Figure 7(b), the backwashing channel of inside-out module was large enough to withstand water backwashing with large pressure and current; therefore, it would require no gas washing and also would not fit to gas washing because of certain restrictions on the physical strength of the membrane, which reduced energy consuming and recovery rate of water production. It should be noted that acid and alkaline resistance of inside-out membrane made by PES is appropriate for the acid-base staggered method to CEB, which can intensify the effects of backwashing by water through inorganic and organic foulants cleaning [26] and therefore replace the way of gas washing of the outsidein UF module made by PVDF and PAN to some extent. In that sense, the selection of membrane material is dependent on the operational mode of UF module in a certain degree.…”