E.P. Jacobs

UF of pulp and paper effluent: membrane fouling-prevention and cleaning

Abstract Effluent arriving from the Mondi Kraft paper mill at Piet Retief, South Africa, was filtered through tubular poly(ether sulphone) (PES) ultrafiltration membranes under constant pressure cross-flow conditions. The effluent that was fed into the membranes and permeate produced during filtration were characterised by UV–VIS light-spectroscopy. Substances that absorbed onto membranes during filtration caused changes to the permeability characteristics of the membranes. Changes in membrane performance were monitored by pure-water and product flux (pf) measurements. A colourimetric staining technique was developed to determine the nature of foulants adsorbed onto the membranes. Membrane cleaning solutions were subsequently selected using information obtained from the characterisation studies. In addition, the anti-fouling potential of non-covalently attached coating materials was investigated as a possible membrane pretreatment technique. Results showed that foulants present in the effluent are of phenolic and hydrophobic nature. Increasing the hydrophilic characteristics of membranes prior to filtration could reduce the amount of organic foulants that adsorbed onto the membranes. Membrane pretreatment not only reduced fouling, but also improved the effectiveness of cleaning methods. Membranes were effectively cleaned by a combination of mechanical and chemical cleaning techniques.

Feed-water pretreatment: methods to reduce membrane fouling by natural organic matter

Abstract The prevention of fouling of polysulphone ultrafiltration membranes, used for the purification of natural brown water, was investigated by pretreating the feed-water prior to filtration. Natural brown water was pretreated by changing the pH of the feed solution and by coagulation with metal-ions prior to filtration. Specific characterisation techniques, developed by Maartens et al. (1998) [A. Maartens, P. Swart, E.P. Jacobs, Humic membrane foulants in natural brown water: characterization and removal, Desalination 115 (3) (1998) 215–227] and Jucker and Clarke (1994) [C. Jucker, M.M. Clark, Adsorption of aquatic humic substances on hydrophobic ultrafiltration membranes, J. Membrane Sci. 97 (1994) 37–52], were used to determine and compare the effects induced by the adsorption of natural organic matter on the permeability of capillary ultrafiltration membranes. The extent of foulant adsorption and the quality of the resultant permeate solutions were determined by UV–VIS-light spectroscopy. Results indicated that adsorption of natural organic matter can be minimised by adjusting the pH of the feed solution to 7. The findings of this investigation provides information of importance for the operation of future natural brown water ultrafiltration plants.

Enzymatic cleaning of ultrafiltration membranes fouled by abattoir effluent

Proteins and lipids are the major membrane foulants present in abattoir process effluent. The successful use of ultrafiltration (UF) to treat such effluent streams depends on the effective removal of these foulants, which are mostly hydrophobic fouling species, from the membrane surface. Lipases and proteases were used in this study to clean flat-sheet polysulphone membranes (PSMs) fouled in abattoir effluent. The lipases from Candida cylindracea, Pseudomonas mendocina and Aspergillus oryzea were used alone, as well as in combination with the proteases from Bacillus licheniformis, Protease A (a protein engineered protease specific for low temperature wash conditions) and Aspergillus oryzea. Enzyme assays were first performed to identify active bacterial proteases and lipases. The parameters used to determine the cleaning efficiencies of the enzymes used were: (i) lipid content adsorbed onto the membranes; (ii) protein content adsorbed onto the membranes; and (iii) pure-water flux (PWF) after enzymatic cleaning. The results show the ability of enzymes to remove adsorptive fouling, and indicate their usefulness in enzyme-based cleaning regimes for membranes operating on abattoir effluents.

Highly asymmetrical carbon membranes

Abstract Carbon membranes have been produced by thermo-oxidative stabilization and carbonization of polyacrylonitrile-based hollow-fibre precursors. The inner layer of coarse pores, the system of channels which penetrate through most of the wall, and the dense outer skin form the highly asymmetrical structure of the membrane. Transmission electron microscopy images of Pt/C replicas of the membranes outer surfaces revealed that the pore sizes and shapes in the outer surfaces revealed that the pore sizes and shapes in the outer skin could be altered by the use of polymers of different intrinsic viscosities as a precursor material as well as changing the stabilization atmosphere and carbonization temperature.

Humic membrane foulants in natural brown water: characterization and removal

Organic matter in natural brown water as well as humic acids from a commercial sample were characterised by ultraviolet-visible light-spectroscopy and used in ultrafiltration studies. During ultrafiltration the pure-water flux and the operational flux were measured continuously to determine the degree of membrane fouling. The natural organic matter and commercial humic acid concentrations of the feed and permeate solutions were determined spectrophotometrically. These variables were used in conjunction with conventional flux measurements, to determine the colour-removal efficiency of ultrafiltration as well as the degree of foulant adsorption onto the membranes. By calculating the ratio between the light absorbance at 465 and 656 nm, the relative sizes of the molecules in the feed and permeate solutions were monitored. Fouled membranes were cleaned with alkaline chemical agents normally used to extract natural organic matter from soil samples. The cleaning efficiency and the effect of cleaning solutions on the membrane selectivity were studied.

Formation of an externally unskinned polysulfone capillary membrane

The production protocol of internally skinned ultrafiltration membranes with no exterior skin layer was rationalized. The membranes were intended for use in bioreactor and filtration operations. The unique substructure morphology was designed to have low resistance to liquid transport and a large external surface area. The polysulfone and polyethersulfone membranes that were produced had well-defined internal skin layers, integrally part of a substructure that consisted entirely of closely packed and narrow-bore microvoids that extended from just below the internal skin layer of the membrane to the periphery. The regularly shaped microvoids open into the membrane periphery as there is no outer skin layer to bridge the cavities. The structures formed may be the result of rapid demixing of the internal skin layer, followed by nucleation and growth of the polymer-lean phase, coupled with coalescence at the membrane periphery.

An enzymatic approach to the cleaning of ultrafiltration membranes fouled in abattoir effluent

Abstract Membrane fouling severely curtails the economical and practical implementation for the purification of biologically related process streams such as abattoir effluent (Jacobs, WRC Report no. K5/362, 1991, Pretoria, South Africa [1]). Mechanical and chemical removal of foulants usually lead to membrane damage and additional pollution. Enzymes, specific for the degradation of proteins and lipids, were tested as key components of biological cleaning regimes for membranes fouled in abattoir effluent. Fouling of polysulphone membranes was assessed as previously described by Maartens et al. (J. Membrane Sci., 119 (1996) 1 [2]) and optimal enzyme concentrations and incubation times were determined for the different preparations. The ability of each cleaning agent to remove adsorbed protein and lipid material, as well as their ability to restore the water-contact angle and the pure-water flux of the fouled membranes, were determined and compared. These variables were also used to compare the cleaning efficiency of enzymatic cleaning agents with conventional chemical agents under optimal conditions. The enzymes and enzyme detergent mixtures were effective cleaning agents and the pure-water flux of statically fouled membranes could be restored by treatment with these agents.

Polyvinyl alcohol and modified polyvinyl alcohol reverse osmosis membranes

Abstract A study was conducted on the insolubilization of polyvinyl alcohol. Polyvinyl alcohol was regarded as a stable material for the formation of gel layer base membranes, which could then be further modified to produce RO membranes with good salt retention. This paper reports the study of the in situ insolubilization of polyvinyl alcohol membranes. Laboratory and field trial experiments were conducted with some of these membranes, and the results are reported on. Some results of the first chemically modified polyvinyl alcohol membranes are also given.

A low pressure ultrafiltration membrane system for potable water supply to developing communities in South Africa

Three pilot studies were performed in different areas of South Africa, demonstrating that particulate and colloidal turbidity can be reduced to acceptable levels. By operating at a static manifold pressure of between 100 and 140 kPa and a constant flux of 30–40 l/m2.h, up to 85% removal of NOM and >90% reduction in colour was observed. No microbiological indicator organisms were detected in any of the permeate samples analyzed. During the operation of the membranes for more than 3 years, a loss of only 5% of membrane area was experienced, and a membrane life of >5 years can therefore be expected. The use of polysulphone ultrafiltration capillary membranes at a low operating pressure is able to remove natural organic matter, reduce organic colour (humic and fulvic substances) and partially disinfect the water. Ultrafiltration provides a simple and effective means for the production of potable water for small communities.

Poly(vinyl alcohol) gel sub-layers for reverse osmosis membranes. II: Insolubilization by crosslinking with poly(methyl vinyl ether-alt-maleic anhydride)

Abstract Composite reverse osmosis (RO) membranes were prepared by depositing aqueous compatible blends of poly(vinyl alcohol) [PVA] and poly(methyl vinyl ether- alt -maleic anhydride) [MVE- alt -MAH] on flat-sheet asymmetric poly(arylether sulphone) [PES] substrate membranes. Insolubilization of the polymer blend films was accomplished by the formation of interchain ester crosslinks during heat treatment. The crosslinked films were intended to serve as hydrophilic gel sub-layers on which ultrathin salt-retention barriers could ultimately be formed by interfacial polycondensation. The RO properties (salt retention, permeate flux) of PVA-based membranes prepared in the absence and presence of H 2 SO 4 catalyst were measured at various pH values of the feed solution (2,000 mg/l NACl). The highest permeate fluxes were obtained when membranes were cured in the presence of acid catalyst. The salt-retention and water permeability characteristics varied with the pH of the feed solution. This was attributed to the different degrees of ionization of the first and second carboxyl groups of the maleic acid residues in hydrolysed MVE- alt -MAH at different pH values. Different ratios of PVA and MVE- alt -MAH were evaluated. A PVA: MVE- alt -MAH molar ratio of 3.5: 1 resulted in gellayer membranes with sufficiently high water permeabilities for application as gel sub-layers in RO membranes.