Hypochlorite Cleaning Causes Degradation of Polymer Membranes

Abstract

Polymer membranes are often used in water treatment industry, as a reliable economic solution for purification of surface water streams. Among a variety of membrane processes the ultrafiltration (UF) membranes combine high pathogen removal ability with minimal energy consumption. Since the membranes are considered to be chemically and mechanically stable, in-place cleaning is routinely performed with strong oxidizing agents, such as hypochlorite. The results of the current study, however, clearly indicate that the mechanical strength of UF membranes deteriorates upon hypochlorite cleaning. Values of ultimate tensile strength, ultimate elongation and Young's modulus decreased as the dose (concentration · contact time) of hypochlorite was increased, with the decreases being more marked for cellulose acetate membranes than for polyethersulfone membranes. Scanning probe microscopy showed membrane aging in response to hypochlorite treatment. The aging was related to gradual chain breaking in membrane skin layer, as reflected by the disappearance of O-C-O and C-S absorbance peaks in ATR-FTIR spectra of treated cellulose acetate and polyethersulfone membranes, respectively. Since the degree of scission was linearly related to the deterioration in ultimate tensile strength, we here propose that ultimate tensile strength measurements can be used as a simple macroscopic test for periodic inspection of the degree of degradation of UF membranes exposed to in-place chemical cleaning.

The Performance and Fouling Control of Submerged Hollow Fiber (HF) Systems: A Review

“…There is a wide variety of chemical cleaning agents utilized by the industry, with the most common being sodium hypochlorite (NaOCl) because of its ready availability, relatively low price, and high cleaning efficiency. Unfortunately, such oxidants are the main causes of deterioration in the membrane integrity [316], whereby prolonged exposure causes oxidative damage to the membrane [317], which accelerates membrane ageing and degradation that in turn not only leads to discoloration of the membrane fibers, but also embrittlement of the fibers that subsequently increases the likelihood of membrane-fiber fracture [316,318,319]. The embrittlement rate for hollow fibers has been found to be four times that of flat-sheet membranes [309].…”

Impact of in situ physical and chemical cleaning on PVDF membrane properties and performances

“…The estimation of membrane lifetime could be done by examining the mechanical properties of the membrane after its contact with chemicals (Arkhangelsky et al, 2007). In this work, nominal elongation is selected as a parameter to study the alteration in the membrane mechanical stability.…”

“…The result shows both NaOH and NaOCl, performed a flux recovery of more than 75% while HCl produced a lesser result. Other than analysing the efficacy of chemical cleaning for membrane water flux recovery, the changes in polymeric membrane stability following the cleaning process was also studied (Arkhangelsky et al, 2007). It was found that the membrane exposed to hypochlorite experienced a decline in its elasticity, tensile strength, and elongation at break.…”

Influence of PVP content on degradation of PES/PVP membranes: Insights from characterization of membranes with controlled composition

“…Sodium hypochlorite is one of the most widely-used disinfecting/cleaning agents owing to its high efficiency and low cost [8][9][10]. However, it is well known that sodium hypochlorite has a strong impact on membranes properties such as structure [2,11,12], surface charge [2,13,14] and chemical composition [3,10,13,15], which directly impacts their filtration performance and their mechanical strength as well [3,15,16].…”