Membrane Development In South Africa
By Gerhard Offringa,
Water Research Commission, Pretoria, South Africa
In nature the difference between relatively simple organisms such as
bacteria and more complex organisms with many cells such as plants, ourselves
and insects is the creative use of membranes within our cells to separate
chemical processes. In science, the application of membrane technologies
frequently allows research programmes to evolve to higher levels. In society,
membranes allow many communities to benefit from things as varied as clear apple
juice, clean water and kidney machines to more cost effective, safer,
pharmaceuticals. As editors we feel this article is an important overview of
membrane technology in SA, by a man who has played a pivotal role in shaping the
development of this field into a highly effective membrane research community.
In future editions we will highlight the individual programmes outlined below.
We hope that this will allow anybody who has not yet heard of these technologies
to work out how they can be used to benefit their own futures.
This article gives a broad overview of the advances in membrane research and
development in South Africa. In particular, the more recent innovations are
discussed.
South Africa is a relatively dry country, which receives an annual rainfall
of less than 500 mm compared to a world average of 860 mm. In addition, large
areas of the country may be classified as desert or semi-desert. Therefore,
membrane development in South Africa naturally tends to focus more on the
water-related applications, although some work on gas separation is also being
done. Research and development (R&D) is being undertaken on most membrane
processes, including reverse osmosis (RO), ultrafiltration (UF), microfiltration,
(MF) and electrodialysis (ED). Research further focuses on membrane materials
(polymeric and ceramic), electroconducting membranes, membrane bioreactors,
membrane surface modification and defouling studies. Most of these technologies
have been commercialized or are on the verge of being commercialized.
The Beginnings
The earliest fundamental membrane research in South Africa started in 1953 on
ED systems and their membranes at the Council for Scientific and Industrial
Research (CSIR). This research laid the foundation for a better understanding of
the thermodynamic and physical processes involved in ED[1]. Parchment paper
membranes were developed and piloted for the low-cost desalination of brackish
gold-mine underground waters. Initial research on polymeric membranes started in
1973 at the Institute for Polymer Research (IPS), University of Stellenbosch,
leading to the establishment of the first local membrane manufacturing company
in 1979[2] In conjunction with the IPS, this company developed low cost tubular
RO and UF systems in the 1980s. The tubular UF systems were later successfully
combined with anaerobic digestion and commercialized as the "ADUF"
process. From humble beginnings the activities have grown to the current
situation where R&D on membranes is actively pursued - not only at a number
of tertiary educational institutions, but also at private companies and water
and power utilities. Some of the more recent and noteworthy research and
research products are discussed below:
UF Membranes
 In earlier work, the IPS produced an outer- skinless ultrafiltration
polysulphone membrane (see figure to the right and enter for larger image) which was specifically designed and produced for
use in membrane bioreactor related research, described further on below. With
slight modifications, the membrane also served as a low-pressure filter for the
treatment of non-saline surface and subsurface water for potable use[3].
Recently, a polysulphone UF membrane was produced with a very thin 
internal skin layer and the dimension of the voids in the substructure such that
bacteria will not pass through the membrane should the skin layer be punctured
during filtration (see figure to the right and enter for larger image). This membrane efficiently filters out very small particles,
yet still has a suitably high pure-water flux (a measure of the amount of pure
water passing through a unit of membrane in a unit time).The membrane is
intended, amongst others, for the production of potable water for small
communities.
Reverse Osmosis (RO) Developments
Reverse osmosis is a process for desalting water that uses membranes that are
permeable to water but essentially impermeable to salt. Most fundamental
research on RO has been taking place at the IPS, University of Stellenbosch.
Following the initial development work on cellulose acetate tubular RO systems,
some of their more recent developments include the following [4]:
o Ultrathin-film tubular membranes were made from poly-2-vinylimidazoline and
polyvinyl alcohol, cross-linked with 3,5-dichlorosulphonyl benzoylchloride and
were successfully housed and tested in commercially available modules.
o A coating procedure was developed for the regeneration of substandard or
degraded cellulose acetate membranes.
o Chemical oxidation-resistant fluorinated polyvinylidene fluoride was
fabricated for possible use with oxidizing chemicals such as ozone.
o Polypropylene surfaces were modified to make them more glueable with epoxy
glues.
o Novel, electroconducting, polymeric membranes have been produced for the
separation of certain gases.
The tubular RO technology was further refined and cost-optimized by a private
company near Cape Town, using a simple low-cost support system, and employing
sponge-ball cleaning to enable its application on fouling effluents. It is
currently being used in industrial applications internationally.
R&D performed by another private company in the vicinity of Cape Town led
to the discovery that the application of an electromagnetic field around the
membrane module in a very specific way resulted in a significant reduction of
the concentration polarization phenomenon[5]. The RO unit is fitted with an
electromagnetic system which, together with a flow distribution unit, constantly
removes the polarization layer - and any fouling before the layer can be formed
- thereby enhancing flux and keeping the membrane clean. The RO membrane is
employed together with their MF unit as pretreatment. No chemical pretreatment
is required when desalting sea water, since the electromagnetic field also
prevents scaling from taking place. The first commercial plant, situated close
to Port Elizabeth, South Africa, was commissioned in December 1997. The plant,
consisting of the MF unit, followed by RO, supplies 480 000 litres per day of
potable water from sea water to a small community. The plant is currently being
expanded to 1.6 million litres per day. Subsequently a number of plants have
been commissioned world-wide. A recent development includes a 400 mm (16 inch)
diameter RO module, which also has the full complement of non-fouling devices
built into the unit.
Tubular Woven Fibre Microfiltration
 Woven fibre MF technology underwent significant development at the Pollution
Research Group, University of Natal, in the 1980s, and is currently being
further refined by the ML Sultan Technikon in Durban[6]. The system consists of
two layers of a woven polymer material, stitched together to form rows of
parallel filter tubes, called a "curtain" (see figure to the right and
enter for larger image). Feed is from the
inside. Clear liquid permeates the tube wall, and runs down the outside of the
tubes as permeate. The system is used in cross-flow (ie liquid flows along the
tubes and some filters out) or dead-end (ie one end of the tube is blocked and
the only way out is through the membrane) mode in clarification applications. In
its vertical configuration, the system has been adapted successfully as a filter
press for cost-effective sludge dewatering.
Electroconducting Membranes
Research on electroconducting membranes is performed mainly at the
Universities of Stellenbosch and the Western Cape.
 At the University of Stellenbosch, research is being conducted, in
conjunction with a private company, on the cost-efficient manufacture of ozone
using membranes and anodic oxidation in- stead of the Corona discharge
method[7]. The figure to the right (enter figure for larger image) shows two different electrocatalytic ozone- generating
systems developed by the private company. On the left, there is an
ozone-generating reactor, utilising a water-soluble electrolyte which catalyses
production of high-concentration ozone (up to 25 wt %). On the right, there is a
reactor with a catalyst embedded into a membrane. This reactor uses deionised
water for ozone generation.
Other research, which has just begun at the IPS, focuses on the coating of
ceramic and other inorganic membranes with catalytic, conducting materials for
the oxidation or combustion of components in water[8]. Good conductance has been
obtained in some early experiments using the inorganic sol-gel coating and
calcination route. This research is now being taken into the next, bench-scale
phase.
At the University of the Western Cape novel proton-conducting composite
ceramic membranes are being designed for electrochemical decomposition of
organic pollutants such as phenols [9]. Reversing the polarity regenerates the
membrane. Various surface property modifiers and reactor configurations are
being investigated. Some of the systems are able to produce sodium hypochlorite
or ozone as by-products.
Supported Liquid Membranes
Research at the Department of Chemical Engineering, University of
Potchefstroom, showed that an encapsulated form of supported liquid membrane
shows potential to extract metals such as nickel from liquid streams[10]. The
institution is performing general membrane research and has recently started
working on ceramic membranes and chitosan-based adsorptive membrane systems.
Membrane Bioreactors
Membrane- based bioreactor studies are being conducted by a number of
institutions in the country, with most of the studies using the outer-skinless
UF membrane as reactor - which was designed specifically for this application in
mind:
 Joint research by the IPS and the Department of Biochemistry,Microbiology and
Biotechnology, Rhodes University, demonstrated the applicability of the
outer-skinless UF capillary membranes developed at IPS for the bioremediation of
industrial wastewaters. Fungi such as Phanerochaete chrysosporium and Trametes
versicolor are established in or on the micro-tubes of the membrane (see figure
to the right and enter for larger image) and
their peroxidases utilised to break down intractable organic pollutants, such as
phenols[l11]. Certain of the fungal-based membrane bioreactor systems are
currently being commercialised for the manufacture of high-value enzymes.
In an extension of this fungal bioreactor research, a bioprobe, was developed
which comprises a material on which polyphenol oxidase is immobilised together
with a colour reagent. This system may then be used as a dip-stick-type monitor
to determine the concentration of phenols in water, at concentrations from 0 -
100 mg/l, by the intensity of the colour developed[11].
Another approach involves the immobilisation of an "activatable"
enzyme (or combination of enzymes) onto the surface of an ultrafiltration
membrane before starting the filtration process. The flux decline caused by
fouling is then alleviated "on demand" by the operator by injecting an
activator solution into the feed or during back-flush. The activator triggers
the enzyme - which has been lying dormant up to this stage - causing catalytic
degradation of the foulant layer from the inside outward[12].
Membrane Fouling Studies
Research on membrane fouling centers around three aspects: electromagnetic
defouling; enzymatic and chemical defouling; and surface modification.
Studies are continuing on the positive effect the electromagnetic device
described above has on the non-fouling properties of membranes. Visualization
experimentation has begun at the IPS to "see" the concentration
polarization layer on the membrane surface using various non-destructive
visualization techniques. Initial success has been achieved and it is now
possible to "see" how a fouling layer forms on the membrane surface,
or how the layer is removed by cleaning methods, in real time.
The Department of Biochemistry, University of Stellenbosch has achieved
success in the enzymatic and chemical defouling (and fouling prevention) of
polysulphone membranes[13]. Flowing from these studies, some useful compounds
have been synthesized to modify the membrane surface non-covalently for various
requirements and applications.
At the University of South Africa (UNISA) research is being conducted on the
modification of polysulphone membranes in order to make the surface of the
membrane less hydrophobic. The polysulphone is lithiated and
2,2'-vinylidenedipyridine is added to the lithiated polysulphone. Quaternization
of the dipyridyl-functionalised polysulphone then takes place with sulphate and
perchloric acid. Studies are continuing on various chemical surface modification
possibilities[14].
Affinity Separation
 As a spin-off from the fouling research of the Department
of Biochemistry and the IPS, University of Stellenbosch, some exciting new
developments are being followed up. These include the following[15]: A compound
is attached to the membrane surface (non-covalently) which has a short
hydrophilic "leg" and two longer hydrophobic "legs",
sticking out into the water stream (see figure to the right and enter for larger
image). The active ends of these
"legs" are modified to allow a ligand (a chemical which can bind
another chemical) to be attached to each active end. The ligands are specific
and selected to "catch" wanted substances from the water stream while
the stream is being treated. The wanted substance can easily be removed by
changing certain parameters of the water. The system has been demonstrated on
the selective removal of serum albumin (a blood protein) from abattoir effluent.
Further possibilities are being investigated, such as the recovery of valuable
trace organic compounds from effluents and the analysis of low concentrations of
organic compounds such as endocrine disruptors in surface and treated waters.
Application of Membranes
Although it has taken time, membranes are now increasingly being accepted as
a viable option in the treatment of water and effluents in South Africa and a
number of local and international companies are marketing membrane-based
technologies. Membranes are being used in a variety of applications, ranging
from potable water supply to the treatment of industrial effluents such as in
the power, petroleum, steel and paper industries. A recent application being
promoted by the Pollution Research Group of the University of Natal is to
install membrane separation systems in strategic places in the production
processes to relieve water "pinch" situations in industry[16].
The Future
In order to address the future requirements for membrane research in South
Africa, the Water Research Commission (as the main research funding agency) with
the assistance of stakeholders in the membrane field, compiled a Strategic Plan
for future water-related membrane research in South Africa. One of the major
priorities is to assist in the affordable and sustainable supply of water to
small rural communities using membrane systems. In this regard the IPS,
Environmentek (CSIR) and the ML Sultan Technikon are assuming leading roles
Further, cutting edge and innovative research is also continuing at various
institutions. The Strategic Plan is available on the WRC website at
www.wrc.org.za
Acknowledgements
The concerted and continuous contributions of the membrane community in South
Africa to the general development and promotion of membrane technology are
hereby acknowledged with pride.
References
(Note: References could be left out and people only referred to me
if so preferred)
1. Wilson JR (Ed.) Demineralization by electrodialysis. Butterworths
Scientific Publications, London.
2. SA Waterbulletin (1996) WRC 25 Years 1971 -1996. Water Research
Commission, PO Box 824, Pretoria, South Africa.
3. Jacobs EP, Botes JP, Bradshaw SM and Saayman HM (1997) Ultrafiltration in
potable water production. Water SA 23 (1) 1-6.
4. Hurndall MJ, Sanderson RD, Morkel CE, Van Zyl PW and Burger M (1997)
Preparation of Tolerant Membranes. WRC Report No 619/1/97. Water Research
Commission, PO Box 824, Pretoria, South Africa.
5. Furukawa DH (1999) New developments in desalination. Proceedings of the
1st International Symposium on Safe Drinking Water in Small Systems, Washington
DC, USA. May 10-13.
6. Pillay VL (1998) Development of a Crossflow Microfilter for Rural Water
Supply. WRC Report No 386/1/98, Water Research Commission, PO Box 824, Pretoria,
South Africa.
7. Bessarabov DG (1999) Membranes help to produce high-concentration ozone:
new challenges. Membrane Technology/International Newsletter 114 5-8.
8. Grimm JH, Bessarabov D, Simon U and Sanderson RD (1999) Kinetic studies of
novel Ti/SnO2 /Sb2O5 and Ebonex/PbO2 electrodes for the oxidation of organic
pollutants in water. Paper presented at the International Congress on Membranes
and Membrane Processes, ICOM'99, Toronto, Canada. June 12-18.
9. Linkov VM and Belyakov VN (1999) New low temperature proton conducting
membranes for hydrogen separation and water treatment. Paper presented at the
International Congress on Membranes and Membrane Processes, ICOM'99, Toronto,
Canada. 12-18 June.
10. Smit JJ and Koekemoer LR (1996) The extraction of nickel with the use of
supported liquid membrane capsules. Water SA 22 (3) 249-256.
11. Burton SG, Boshoff A, Edwards W, Jacobs EP, Leukes WD, Rose PD, Russel
AK, Russell IM and Ryan D (1998) Membrane-based Biotechnical Systems for the
Treatment of Organic Pollutants. WRC Report No 687/1/98, Water Research
Commission, PO Box 824, Pretoria, South Africa.
12. Leukes WD, Buchanan K and Rose PD (1999) Defouling of Ultrafiltration
Membranes by Linkage of Defouling Enzymes to Membranes for the Purpose of Low
Cost Low Maintenance Ultrafiltration of River Water. WRC Report No 791/1/99,
Water Research Commission, PO Box 824, Pretoria, South Africa.
13. Maartens A, Swart P and Jacobs EP (1999) Feed-water and membrane
pretreatment: Methods to reduce fouling by natural organic matter. Journal of
Membrane Science 163 51-62.
14. Summers GJ (1998) The synthesis of aromatic carboxyl functionalized
polymers by atom transfer radical polymerization. Paper presented at the World
Polymer Congress Macro '98, Brisbane, Australia. 12-17 July.
15. Buckley CA (1999) Innovative clean technology. Paper presented at the
Environmental Malaysia '99 Conference, Kuala Lumpur, Malaysia. 15-16 July.
For more information please contact:
Dr G Offringa Tel: +2712 330 0340 Research Manager: Membrane Technology Fax:
+2712 331 2565 Water Research Commission E-mail: offringa@wrc.org.za
PO Box 824
Pretoria 0001 South Africa
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