The fouling behaviours and membrane autopsy protocol for polysulfone (PSF) ultrafiltration membrane fouled with natural organic matter source waters were studied. Samples from Ulu Pontian river which has a relatively hydrophilic NOM source water and Bekok Dam river which has a relatively hydrophobic NOM source water have been used as the case study. Fouling characteristics of the NOM source waters were assessed by filtering the feed water with an immersed hydrophobic PSF ultrafiltration membrane. The asymmetric hollow fiber PSF membrane was spun by a dry–wet phase inversion spinning process. The membrane autopsy protocol was performed to identify the nature of the deposited foulants and their relative effects on membrane characteristics. Results for the relatively hydrophilic NOM source water (Ulu Pontian river) exhibited greater flux decline but lesser NOM removal considerably due to pore adsorption, indicating that the low molecular weight, aliphatic linear structure and neutral/base organic matter contained within the hydrophilic fraction were the prime foulants. In contrast, relatively hydrophobic NOM source water (Bekok Dam water) that possessed higher charge density, greater molecular weight and bulky aromatic structure has exhibited lesser flux decline and better NOM rejection noticeably due to cake deposition, despite filtering through a hydrophobic membrane, thus suggesting that the electrostatic repulsion was more influential than the steric hindrance mechanisms. In comparison a non-charged model compound (polyethylene glycol) of similar molecular weight was used to quantify the role of electrostatic charge repulsion on NOM rejection. Moreover, analyses on the permeate characteristics revealed that the hydrophobic NOM was preferentially removed by the negatively charged PSF membrane as opposed to the hydrophilic NOM, hence, suggesting that the charge interactions, in addition to size exclusion were more crucial to NOM removal. The membrane autopsies analyses confirmed the flux decline results and permeate analyses as the filtered-membrane was mainly fouled by the hydrophilic NOM components rather than humic compounds. Distinctive changes were observed in membrane characteristics in terms of ionizable functional groups, membrane wettability and zeta potential. ATR-FTIR analysis revealed that hydrophilic components such as the polysaccharides-like substances, alcoholic compounds and aliphatic amide of protein groups as the responsible materials covering the membrane surface. Morphological analyses using SEM indicated different fouling mechanisms occur for both NOM sources associated with differences in the relative NOM constituent distributions, NOM structural variations and NOM removal mechanisms.
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"Nevertheless, among these foulants, natural organic matter (NOM) was found to have the most detrimental effects on membrane performance as it can result in fast irreversible fouling during surface water filtration . "
"Since a large number of factors must be taken into account, mechanisms associated with fouling are not yet well understood. Moreover, the nature of the organic fraction   , the properties of the solution , the hydrodynamic conditions of the filtration system  and the membrane surface properties   also appear to play key roles in the fouling phenomenon. For a better understanding of the fouling phenomenon, the characterization of membrane structure, roughness and porosity, are of particular importance. "
[Show abstract][Hide abstract] ABSTRACT: In order to provide a better understanding of the impact of flocculant used on membrane properties in drinking water production, a complete structural characterization of membranes was carried out from microscopic to macroscopic scale. New flat-sheet PES membranes with 10, 30 and 100 kDa MWCO were characterized by SEM, ellipsometry of angle resolved scattering (EARS), white light interferometry (WLI) and atomic force microscopy (AFM). It was shown that AFM is able to differentiate between membranes according to their MWCO and their manufacturing processes. The impact of flocculant filtration (PAX-XL 7A and Aqualenc F1) on flat-sheet PES 100 kDa membrane was studied. SEM and AFM characterizations revealed a modification of membrane surface state after flocculant filtration and cleaning step. AFM was finally used to characterize hollow fiber membranes after 1 and 2 years of water production. The results showed that AFM is a very interesting tool to investigate membrane ageing.
Full-text · Article · Dec 2014 · Journal of Membrane Science
"Successive fouling phases enable more NOM particles to accumulate and further adsorption could lead to constriction, filling and plugging of pores and eventually cake layer formation.  Interestingly, even though each filtration cycle started with a higher TMP, all three fouling phases ended with almost the same TMP, demonstrating similar values of total resistance at these points. This decreases the behaviour of the TMP profile from cycle to cycle. "
[Show abstract][Hide abstract] ABSTRACT: Abstract The increasing application of membrane filtration in water and wastewater treatment necessitates techniques to improve performance, especially in fouling control. Ultrasound is one promising technology for this purpose as cavitational effects facilitate continuous cleaning of the membrane. This research studied ultrafiltration of lake water in systems with constant permeate flux under medium frequency (45 kHz) ultrasound irradiation. Fouling was investigated by monitoring transmembrane pressure (TMP) using continuous or intermittent ultrasound irradiation and dead-end or crossflow operation. Best performance was observed with continuous ultrasound irradiation in crossflow mode. Intermittent irradiation reduced the rate of TMP build-up but nevertheless allowed irreversible fouling to develop.
Full-text · Article · Nov 2014 · Environmental Technology