Reliable research over the last decade has shown an ever rising number of people falling sick and dying due to consumption of unsafe water. About 1.2 billion people in the world, with 450 million living in Africa, do not have access to clean, potable drinking water. In South Africa, an estimated 5.7 million people lack access to clean water and over 18 million people live in areas without basic sanitation facilities.
In addition, researchers argue that, due to the increasing population coupled by industrial expansion, centralised traditional and conventional water purification systems are overburdened and unable to achieve optimum provision and supply of clean water. Recent advances in nanoscience and nanotechnology engineering could be regarded as a cost-effective remedy and life changing gateway in providing access to clean water.
There is no doubt that a great deal of attention has been focused on the application of nanotechnology in the development and deployment of water treatment systems globally. This attention is largely attributed to the valuable and unique physical and chemical properties offered by nanofibres and nanomembranes, providing several advantages over biocide in achieving optimum water purification.
Closer to home in South Africa the Council for Scientific and Industrial Research (CSIR) has overseen major advances in the use of nanotechnology in water purification and filtration.
Polymer and Composites Adsorbent Technologies for Water Treatment
The Polymers and Composites Competence Area within CSIR Material Science and Manufacturing has developed a range of polymeric nanocomposite-based adsorbents that serve as advanced and highly sensitive filter media for effluent and water treatment. The project is aligned with both the CSIR and national strategies in improving the quality of water in South Africa.
The adsorbents are made from renewable materials (such as clay, natural fibres and graphene oxide) which are modified with functional polymers. Functional polymers are polymers with advanced optic and/or electronic properties. The core advantages of functional polymers are low cost, ease of processing and a range of attractive mechanical characteristics for functional organic molecules.
One can adjust properties while keeping material usage low to create highly effective binding sites for adsorption of pollutants such as heavy-metals, anions and certain organics. For example, in the case of one of the adsorbents, modification of the clay sheets occurs by either intercalation (the reversible inclusion or insertion of a molecule or ion into compounds with layered structures) or exfoliation of the clay sheets by a functional polymer, with the intention of exposing inaccessible clay sites. This results in polymer-clay nanocomposites, with increased adsorption capacity for the uptake of the toxic contaminants from water.
The functionalised adsorbents are also simple to implement and can be applied in various treatment options including packed-bed column, stirred tank batch reactor, permeable barrier, fluidised bed, or alternatively magnetic separator (for magnetic adsorbents). In essence the functionalised absorbents can be applied in any difficult treatment options. The research team has also successfully demonstrated the capability of scaling up the adsorbent technology.
Key features of the functionalised adsorbents
• Highly effective: Treats and processes water down to allowable pollutant limits for discharge or for potable use.
• No chemical addition required for removal: Pollutant is removed without adding any chemicals. This means lower costs to end-users and improved user and environmental safety. Also ensures lower labour costs. Toxicity of spent adsorbent for disposal is also reduced compared to influent.
• High adsorption capacity and fast kinetics: High adsorption capacities and fast kinetics means effluent can be treated quickly, allowing longer usable life-span of the adsorbent which equates to lower cost for treatment.
• Can be used in acidic pH: Adsorbents can be used directly in processing acidic water.
• Adsorbent can be easily regenerated: Adsorbent can be easily regenerated where required e.g. by back-flushing column with a basic solution and re-used. Alternatively the low-cost adsorbents can be incinerated.
• Simple manufacturing process: Manufacturing of the CSIR adsorbents is simple and in the case of clay-based adsorbents requires only a sealed reactor and a pump.
• Simple implementation process: The adsorbents can be applied in a column, which is simple to operate. A low energy pump is required, which has lower energy needs than other processes such as membrane processes.
The Impact of the technology
The Polymers and Composites adsorbent technology has a social, economic and environmental impact. The long-term impact of this intervention would be maintaining and possibly improving the quality of our water resources. This will further reduce the burden of disease particularly in vulnerable communities, thereby alleviating the pressures on the public health care system, while improving the quality of life for all South Africans.
By Tinashe Chidanyika