Ultrafiltration Fouling: Impact of Backwash Frequency and Air Sparging

Abstract

A bench-scale study was performed to optimize backwash frequency and air sparging conditions during ultrafiltration (UF) of natural surface waters in order to maximize water production and minimize irreversible fouling as well as operating and maintenance costs. Surface shear stress representing different air sparging conditions (continuous coarse bubble, discontinuous coarse bubble, and large pulse bubble sparging) was applied in combination with various backwash frequencies (0.5, 2 and 6 h) and fouling was assessed. Results indicated that air sparging with discontinuous coarse bubbles or large pulse bubbles significantly reduced the irreversible fouling rate while providing cost savings when compared to the baseline condition, which assumed a 0.5 h-backwash frequency and no air sparging during filtration. Cost savings were more pronounced at lower backwash frequencies, due to value associated with extra water produced over longer filtration times and longer membrane life resulted from fewer recovery chemical cleans because of lower irreversible fouling.

Hollow Fibers Filtration and Cleaning Processes Under Ultrasound and Gas Bubbling Combination

“…By increasing turbulence in feed side of membrane, the concentration polarization, as an important phenomenon in membrane fouling, was significantly decreased during filtration. Using two phase flow in feed side of membrane can decrease the concentration polarization by enhancing the turbulence (Ghosh 2006;Li et al 2014). Fouladitajar et al (2014) reported a higher permeation flux under gas bubbling with slug two phase flow pattern due to disruption of the concentration polarization that leads to prevent the deposition of fouling material, this mechanism was also reported by Ndinisa et al (2006) and Cabassud et al (2001) in flat sheet and hollow membrane module fiber, respectively.…”

“…Using two phase flow in feed side of membrane can decrease the concentration polarization by enhancing the turbulence (Ghosh ; Li et al . ). Fouladitajar et al .…”

“…Air bubbling has been extensively applied to prevent deposition of particles on membrane surfaces known as conventional method. The ability of air bubbling treatment to eliminate of deposited material from the membrane surface by increasing turbulence and shear stress has been investigated before (Cabassud et al 2001;Nagaoka et al 2003;Ghosh 2006;Ndinisa et al 2006;Qaisrani and Samhaber 2011;Fouladitajar et al 2014;Li et al 2014). Cabassud et al (2001) investigated the effect of air sparging in ultrafiltration hollow fibers and the relationship between flux enhancement, cake characteristics and hydrodynamic parameters.…”

Optimization of air sparging and in-line coagulation for ultrafiltration fouling control

“…UF operational and maintenance costs has been reported to be approximately three times that of conventional treatment (Chew 2016). The higher costs are largely associated with strategies to minimize the impact of fouling on production, which include coagulation, hydraulic cleaning, chemical cleaning, and membrane replacement (Chew et al, 2016;Li et al, 2014;.…”

“…The extent of fouling control is generally proportional to the shear force imparted onto the membrane, which is dependent on the bubble size and frequency (Abdullah et al, 2015;Wray et al, 2013;Ye et al, 2014). Numerous studies have reported that pulse bubbles (>100 mL) reduce membrane fouling more effectively when compared to coarse bubbles (<3 mL) (Li et al, 2014;Wray et al, 2013;Ye et al, 2014). Intermittent sparging has also been reported to result in better fouling control when compared to continuous sparging (Chan et al, 2011;Li et al, 2014).…”