J.L. Harris

Influence of the characteristics of natural organic matter on the fouling of microfiltration membranes

Natural organic matter (NOM) plays a significant role in fouling microfiltration membranes in drinking water treatment processes even though the NOM is retained only to a small extent. The aim of this study was to obtain a better understanding of the interactions between the fractional components of NOM and microfiltration membranes. Filtration experiments were performed using 0.22 microm hydrophobic and hydrophilic polyvinylidene fluoride (PVDF) membranes in a stirred-cell system on the NOM isolated from three Australian surface waters. As expected, the fouling rate for the hydrophobic membrane was considerably greater than for the hydrophilic membrane. Focusing on the hydrophobic membrane, it was shown that the high molecular weight fraction of NOM ( > 30 kDa) was responsible for the major flux decline. Filtration tests on the four fractions of NOM isolated on the basis of hydrophobicity and charge using non-functionalised and anionic resins revealed that the fouling potential for the three waters was hydrophilic neutral > hydrophobic acids > transphilic acids > hydrophilic charged. The low-aromatic hydrophilic neutral compounds were the main determinant of the rate and extent of flux decline. This was linked to the colloidal size fraction ( > 30 kDa) and to the selective concentration of calcium in the fraction leading to organics-Ca2+ bridging. It was also shown that the higher the aromaticity of the NOM the greater the flux decline, and the aromatics mainly resided in the hydrophobic acids fraction. Overall, the fouling mechanism controlling the flux decline involved the combined effects of adsorptive and colloidal fouling by the hydrophilic neutral fraction in the internal pore structure of the membrane.

Fouling and cleaning of membranes in the ultrafiltration of the aqueous extract of soy flour

The aqueous extract of soy flour is an emulsion/suspension of proteins, lipids and carbohydrates. The foulant deposit formed on the surface of polysulfone membranes in the ultrafiltration of this complex extract was investigated from several aspects including thickness, physical structure, chemical analysis and rheological behaviour. SEM studies showed the thickness of the foulant deposit was approximately 0.2 μm for 50000 MWCO membrane and 0.4 μm for 100000 MWCO membrane. The structure of the foulant deposit consisted of lipids in a globular form of 0.2 to 1 μm diameter adhered to, and supported by, a protein-polysaccharide matrix. Rheological measurements were conducted on a sample of the foulant deposit collected from the 100000 MWCO membrane. This foulant deposit exhibited pseudoplastic and viscoelastic properties which totally resisted the surface shear stresses in the flat-plate module. Recovery of the water flux of the fouled membranes was achieved by a four-stage cleaning procedure comprising successive stages of washing with sodium hydroxide, protease detergent, sodium hypochlorite and flushing with water.

Greywater treatment by UVC/H2O2.

Greywater treatment by UVC/H(2)O(2) was investigated with regard to the removal of chemical oxygen demand (COD). A COD reduction from 225 to 30 mgl(-1) (overall removal of 87%) was achieved after settling overnight and subsequent irradiation for 3h with 10mM H(2)O(2). Most of the contaminants were removed by oxidation since only 13% COD was removed by settlement. The removal of COD in the greywater followed a second-order kinetic equation, r=0.0637[COD][H(2)O(2)], up to 10mM H(2)O(2). A slightly enhanced COD removal was observed at the initial pH of 10 compared with pH 3 and 7. This was attributed to the dissociation of H(2)O(2) to O(2)H(-). The treatment was not affected by total concentration of carbonate (c(T)) of at least 3 mM, above which operation between pH 3 and 5 was essential. The initial biodegradability of the settled greywater (as BOD(5):COD) was 0.22. After 2h UVC/H(2)O(2) treatment, a higher proportion of the residual contaminants was biodegradable (BOD(5):COD=0.41) which indicated its potential as a pre-treatment for a biological process.

Influence of gel layer rheology on ultrafiltration flux of wheat starch effluent

Ultrafiltration flux rates of wheat starch effluent in a tubular membrane system revealed unusual values of the exponents in the mass transfer model (Sh = a Ren Scm). For turbulent flow the values of the exponent n ranged from 0.2 to 0.9 and m from 0.0 to 0.35 depending on the relative amounts of protein, pentosans and suspended solids in the wheat starch effluent. Samples of the gel layer exhibited theological behaviour ranging from pseudoplastic to Newtonian depending on the suspended solids content of the effluent. The thickness of the gel layer was evaluated for the different patterns of gel layer rheology and applied in a pressure-driven filtration model. The resistance of the gel layer was found to be the dominant resistance. The variation in the values of the exponent n was ascribed to the permeability and compaction differences of the different composition gels. Concentration runs were performed in which enzymatic hydrolysis of the concentrate with hemicellulase reduced the viscosity of the concentrate from 48 to 11 mPa-sec at 70°C and the flux rate was enhanced by 200%.

Enhanced ultrafiltration flux rates by enzymatic hydrolysis in protein recovery from wheat starch effluent

Abstract Wheat starch effluent contains several polysaccharide species which contribute to the formation of a viscous gel layer in the ultrafiltration of wheat starch effluent. Viscosity reduction tests with various hydrolytic enzymes on a wheat starch effluent concentrate revealed a commercial pentosanase, “Brew-N-Zyme Pentosanase” (Naarden), which was very effective at low doses (0.05 wt.% dry solids basis), was thermally stable at the ultrafiltration temperature of 70°C and had no proteolytic activity. Enzymatic hydrolysis considerably increased the permeate flux rate and the maximum achievable concentration in the ultrafiltration of wheat starch effluent from 9 to 18 wt.% solids. Flux-concentration profiles for wheat starch effluent and enzymatically hydrolyzed wheat starch effluent were closely fitted by modified mass transfer and pressure-driven models. The main resistance to permeate flux at the initial wheat starch effluent concentration was caused by adsorption of macromolecules on the surface of the membrane. This accounted for 57% of the total resistance for wheat starch effluent and 78% for enzymatically hydrolyzed wheat starch effluent. Enzymatic hydrolysis reduced the viscosity of the gel layer which was thus more easily removed by shear stress. Reduction of the thickness of the polysaccharide gel layer exposed the membrane to greater adsorption of macromolecules. At the final ultrafiltration concentration the reverse situation applied. The gel layer formed the most significant resistance accounting for 93% of the total resistance for wheat starch effluent and 80% for enzymatically hydrolyzed wheat starch effluent. In both systems, wall shear stress performed the important function of removing the mass flux of macromolecular material which impacted onto the surface of the gel layer.

Shear controlled model of the ultrafiltration of soy suspensions

Abstract The ultrafiltration of the aqueous extract of full-fat soy flour was investigated as a complex suspension of proteins, lipids and carbohydrates where the foulant layer is the major resistance. Ultrafiltration was performed on both homogenised and unhomogenised soy extracts using a flat plate module and two polysulphone membranes. The permeate flux profiles for constant recirculation flow exhibited a combination of falling-flux and constant-flux regions. The mass transfer model was not applicable to these profiles. Both regions were modeled by the shear controlled model J=Jiτrnae−bC. The model was also effective in correlating the flux where the retentate flow was reduced for increasing concentration at constant pressure drop over the module. Wall shear stress had a larger effect on the permeate flux for the homogenised extract (n = 0.7) than for the unhomogenised extract (n = 0.5). The wall shear stress was shown to have minimal effect on displacing the foulant layer. The major effect of the wall shear stress was to sweep away the gel layer preventing it from binding to the foulant layer.

Identification of key water quality characteristics affecting the filterability of biologically treated effluent in low-pressure membrane filtration

There are many water quality characteristics which could influence the filterability of biologically treated effluent from Melbournes Western Treatment Plant (WTP). Statistical correlation was used to identify the key water characteristics affecting the microfiltration (MF) and ultrafiltration (UF) filterability in terms of permeate volume of the treated effluent. The models developed showed that turbidity, dissolved organic carbon (DOC) and total suspended solids (TSS) were the key factors which influenced the MF and UF filterability. Turbidity was the dominant factor affecting the accuracy of the model for MF filterability while DOC was the major factor affecting the accuracy of the model for UF filterability. A prediction accuracy of 85% was obtained for MF and 86% for UF filterability of the WTP effluent. The characteristics of the organic components of the wastewater were demonstrated by EEM spectra to have seasonal variation which would have reduced the prediction accuracy. As turbidity, DOC and TSS can be determined on-line, the models would be useful for rapid prediction of the filterability of WTP effluent and this may assist the control of low-pressure membrane filtration processes.

Improved Extraction and Ultrafiltration Process for Protein Recovery from Soy Flour

By using a feedstock of dry milled enzyme-active full-fat soy flour, median particle size of 50 microns, an extraction process was developed which gave high solids and protein recovery. Aqueous extraction for 10 min at 80°C, and homogenization at 10 MPa followed by filtration gave 95.6% solids recovery and 86.9% protein recovery with a nitrogen solubility index of 93%. The native lipoxygenase was inactivated and the activity of trypsin inhibitors was lowered by 50%. The extract was concentrated to 20 wt% solids by ultrafiltration. The concentrate changed from dilatant to pseudoplastic behaviour at 14–15 wt% solids.