Fabrication, fouling and foulant analyses of asymmetric polysulfone (PSF) ultrafiltration membrane fouled with natural organic matter (NOM) source waters
ABSTRACT 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.
- Journal of Environmental Engineering-asce - J ENVIRON ENG-ASCE. 01/2003; 129(1).
Article: Humus ChemistryNature 01/1973; 245(5420):109-109. · 38.60 Impact Factor
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ABSTRACT: Surface waters contain colloids and natural organic matter, largely composed of humic substances. In this work the effect of natural organic matter (NOM) and humic substances (IHSS stream humic and fulvic acid reference material) on the deposition and rejection of inorganic colloids (hematite) by GVWP and GVHP microfiltration (MF) membranes was studied. Parameters of interest were solution pH, ionic strength, calcium concentration, primary colloid size (75, 250 and 500 nm), organic-type and concentration, as well as membrane-type and hydrophobicity, aggregate structure and colloid stability.The method of preparation of the equilibrated suspensions, and thus their aggregation state, had a large influence on the rejection of colloids and their aggregates, as well as the association of particles with the membrane material and flux decline.The systems studied were grouped into (a) organics in the absence of inorganic colloids, (b) stable primary particles, (c) primary particles at pH extremes with organics, (d) particles pre-aggregated in electrolyte solution prior to adsorption of organics (SPO), and (e) particles stabilised with organics (OPS).Extreme pH conditions and pre-adsorption of organics onto the particle surface created very stable systems (colloids retained their primary particle size) and the deposition of the colloids at the membrane surface was reduced significantly. This led to a penetration of the particles into the pores and adsorption on the pore walls leading to full rejection in the absence of organics. Flux decline was, in this case, dependent on colloid size, with the size closest to the membrane pore size causing the greatest flux decline. In the presence of organics, membrane–colloid charge interaction and adsorption were reduced and rejection decreased to near-zero for these stable colloid systems.For aggregates the presence of organics led to a greater flux decline. Rejection of colloids was complete, now determined by the large size of the aggregates formed, which also indicates great mechanical stability of these aggregates.Calcium played a key role in the flux decline of all systems. In the absence of hematite, calcium contributed to organic aggregation and increased flux decline. Calcium led to an increased flux for hematite aggregates (SPO) presumably due to the formation of looser aggregates and a decreased flux for stable colloid–organic systems (OPS) due to destabilisation of these systems.Journal of Membrane Science. 01/2000;