SA faces water technology challenges
Posted on 13. Apr, 2010 by admin in News-Supply Chain, Research
With water issues being in the spotlight at the moment, Neil Stacey takes a look at some of the challenges facing the sector for finding appropriate cost-effective solutions on behalf of ManufacturingHub.co.za including nano-technology.
On Monday 15 March, the Water Research Commission (WRC) hosted a media workshop addressing the topic of nano-technology, and its role in the field of water treatment. The WRC intends to hold several such workshops each year in order to give media and interest groups access to their findings on relevant water issues.
The talks served to highlight the complex nature and broad scope of water treatment in South Africa. General perception of water treatment emphasises the purification of drinking water as the key component of water treatment, but this is only a small piece of the bigger picture. It was pointed out that the agricultural sector accounts for 50% of the country’s total water consumption, with a further 35% going to industrial usage, and only 15% allocated to Local Authorities and Water Services Institutions. The purity requirements for industrial and agricultural water are, as one might expect, substantially less stringent than those for drinking water. This means that the main consideration for water treatment in these areas is not the purification of water which is to be used, but the treatment of wastewater before it is discharged and the remediation of contaminated groundwater.
The diversity of industry in South Africa demands a wide range of treatment methods for industrial wastewater. Professor Maggy Momba of the Tshwane University of Technology outlined some of the most prevalent methods, and how nano-technology can potentially improve them. Treatment through chemical reactions that eliminate harmful contaminants is one such treatment method. Examples of this include the chemical reduction of metal ions and organic molecules such as alkanes.
Nano-technology can facilitate these chemical treatments in three ways. Firstly, catalyst particles on the nano-scale offer a higher surface area relative to their mass than larger particles, thus offering greater catalytic activity. Secondly, the reacting chemical species themselves, if produced on the nano-scale, offer larger reactive surface area relative to their weight. Thirdly, nano-reactive membranes can be produced by incorporating nano-scale catalyst particles into nano-fibres which are woven into a membrane. Fluids passing through such membranes are more effectively contacted with these catalyst particles than is the case with conventional methods.
The large scale treatment of drinking water in South Africa is relatively straightforward: sedimentation to remove large particles, flocculation with aluminium sulphate to remove colloidal particles and dissolved solids, possibly followed by disinfection with low concentrations of chlorine. However, South Africa’s widely dispersed population makes water distribution highly problematic. According to Dr. Marelize Botes of the University of Stellenbosch, decentralisation of water treatment is the most feasible approach for extending water supply to remote areas. The prevalent method for water treatment in South Africa, sedimentation followed by flocculation, is suitable primarily for large-scale treatment operations.
Alternative technologies, suitable for small scale point-of-use water treatment operations, must be pursued. A further complication is that those areas in most urgent need of improved water supplies also lack other basic infrastructure such as electricity.
Thus, to be considered as a solution to South Africa’s clean water shortage, a technology must be affordable on a small scale, operate without regular maintenance and require a minimum of expertise to set up, while also being versatile enough to cope with a wide range of contaminants.
This is a daunting set of requirements, which cannot be met by any existing technology. The pursuit of revolutionary water treatment technologies is critical if universal access to clean water is to be achieved. Nano-technology is one such avenue of research, promising a variety of options for enhanced water treatment.
Reverse Osmosis is perhaps the most promising water treatment option for purification of drinking water. Making use of a membrane with pore size sufficiently small to permit no solid contaminants, Reverse Osmosis processes are of particular interest for their versatility; they are capable of removing all solid contaminants, including viruses, as well as dissolved solids like salt. Nanofibres can be woven to produce membranes with high porosity and permeability but very small pore size, admitting high flow rates of water, while effectively removing all contaminants. The high ratio of surface area to volume of fibres on the nano-scale also results in a high removal capacity before membrane saturation occurs. The University of Stellenbosch is conducting ongoing research into the production of nano-fibres through a process called electro-spinning.
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