Assessing the effects of sodium hypochlorite exposure on the characteristics of PVDF based membranes

• Published in: Water research (Oxford) 2013-09, Vol.47 (14), p.5392-5399
• Main Authors: Abdullah, Syed Z., Bérubé, Pierre R.
• Format: Article
• Language: English
• Subjects: additives; Applied sciences; Chemical cleaning; chemical composition; cleaning; cleaning agents; Concentration (composition); contact angle; Exact sciences and technology; Exposure; Exposure dose; exposure duration; filtration; Fouling; Fourier transform infrared spectroscopy; Hydrophilic additive; hydrophilicity; Hydrophobic and Hydrophilic Interactions; Magnetic Resonance Spectroscopy; Membrane lifetime; Membranes; Membranes, Artificial; Microscopy, Electron, Scanning; NMR; nuclear magnetic resonance spectroscopy; Oxidation; Pollution; Polyvinylidene fluorides; Polyvinyls - chemistry; Porosity; scanning electron microscopy; Sodium hypochlorite; Sodium Hypochlorite - chemistry; Spectroscopy, Fourier Transform Infrared; wastewater treatment; Water Purification - instrumentation; Water Purification - methods; Water treatment and pollution
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2013.06.018

Sodium hypochlorite is commonly used as a cleaning agent to remove adsorbed foulants from PVDF based micro/ultra filtration membranes in water and wastewater treatment applications. Although effective for fouling control, extended sodium hypochlorite exposure can affect the physical/chemical characteristics and hinder the treatment performance of these membranes. To assess these effects, PVDF based membranes were exposed to sodium hypochlorite at different concentrations for varying periods of time, and the physical/chemical characteristics of the virgin and sodium hypochlorite exposed membranes were compared. The membranes were characterized based on chemical composition (FTIR and NMR), mechanical strength (yield strength), surface hydrophilicity (contact angle), pore size and porosity (scanning electron microscopy and challenge test), and membrane resistance (clean water permeation test). The results indicated that exposure dose and concentration of the sodium hypochlorite used have significant influence on the membrane characteristics. The impact of sodium hypochlorite exposure on the parameters investigated could be most accurately and consistently correlated to an exposure dose relationship of the form Cnt (where, C = concentration and t = exposure time) rather than the Ct relationship commonly used to define the extent of exposure to cleaning agents. For all the parameters investigated, the power coefficient n was less than 1 indicating that time had a greater impact on the changes than did the concentration of the sodium hypochlorite. The results suggest that the use of sodium hypochlorite for chemical cleaning, at concentrations that are higher than those typically used for chemical cleaning would have less of an effect on the characteristics of the membrane materials. Changes in the characteristics were attributed to the oxidation of the hydrophilic additives (HA) present in blended PVDF membranes. [Display omitted] •Exposure dose and concentration of NaOCl used affected the membrane characteristics.•The changes were attributed to the oxidation of the membrane's hydrophilic additives.•The changes could be correlated to an exposure dose relationship of the form Cnt.•Exposure time had a greater impact on the changes than did the concentration of NaOCl.•For a given exposure dose, lower concentration had greater impact on the changes.