Water Purification

Water intended for human consumption is universally expected to be free from chemical substances and micro-organisms in amounts which would be a hazard to health. Absence of turbidity, colour and disagreeable or detectable tastes and odors is important in water-supplies intended for domestic use. Lack of safe drinking water is a major and urgent concern in many countries and is also a huge issue in some parts of Sri Lanka. Approximately 75% of the Sri Lankan population live in rural environments, obtaining their drinking water directly from local sources such as wells, hand pump tube wells, rain water harvesting tanks, canals, streams and springs where the quality of the water can vary significantly. Currently the high level of metal ions in drinking water is a cause of the growing suspicion in a number of health problems reaching epidemic levels being reported in the country. In some areas of Sri Lanka, ground water can be found with excessive levels of Calcium, Magnesium, Sodium and Potassium. Also contamination of these water sources, by industrial and agricultural waste, results in high levels of heavy metal ions. Another concern in the dry zone of Sri Lanka is the discovery of high concentrations of fluoride ions. These ions, if present in supplies of drinking water at concentrations above certain levels, can give rise to dangers to human health. Therefore, it is important to find out effective as well as affordable means of providing safe drinking water. Currently, distillation, chemical treatment and filtration are the most commonly used water purification methods in Sri Lanka. However, the extents of ion removal from these methods remain questionable. More effective approaches such as electrochemical separation and reverse osmosis are employed in other countries. SLINTEC aims to carry out research directed at exploiting new nanotechnology based approaches to water purification. This will not only be aimed at removing contaminants such as heavy ions and fluorides from drinking water but also biological agents such as bacteria and virus strains.

1) Developing Nanomaterials for water purification

SLINTEC will explore the possibility of using nanomaterials (such as activated carbon, nano sorbents, nanoparticles, nano membranes) in water purification. These materials can be targeted to be used in filters or as chemical additives. However, direct use of these nanomaterials, which can be very effective in terms of water purification, needs detailed characterization and analysis as the nanomaterial itself can become the source of secondary contamination. Due to this, SLINTEC will focus on anchoring these nanomaterials in a matrix approach rather than direct use. Research at SLINTEC to date has shown the potential use of iron oxide and zinc oxide nanoparticles impregnated in activated carbon and clay materials, for heavy metal removal, which can be deployed for improving the drinking water quality in some areas in Sri Lanka as well as the in the region (e.g. Bangladesh). Activated carbon is one of the most effective materials for removing a wide range of contaminants from industrial and municipal waste waters, landfill leachate and contaminated groundwater. The production and export of activated carbon is a major industrial sector in Sri Lanka. Given that it is the most powerful adsorbent available, it can cope with a wide range of contaminants and is a base material used in water purification worldwide. Recent changes in water discharge standards regarding toxic pollutants have placed additional emphasis on developing the activated carbon based purification technology further. SLINTEC’s approach is to subject the total water flow to a single filtration stage which is comprised of a multi-component activated carbon composite which comprises a number of zero valent metal nanoparticles and their oxide nanoparticles. SLINTEC will focus on extending its work on heavy ion removal to address the issue of natural water pollution due to various effluents, in particular, textile waste effluents which is a problem in Sri Lanka due to industrial growth and development. Typically, effluents from textile dyeing and processing plants contain highly toxic dyes, salts, acids, alkalis and bleaching agents. Heavy metals such as cadmium, copper, zinc, chromium and iron have also been found in the dye effluents. SLINTEC aims to develop a filtration based on an activated carbon composite which is specifically aimed at the problem of textile dyeing.

2) Carbon nanotubes (CNTs) for water purification

Having a diameter of about 1nm, only water molecules can penetrate through CNTs while all other common pollutants are confined outside the CNT walls. CNTs can in principle allow the removal of almost all the impurities in water including organic, inorganic and biological contaminants. Therefore this can be thought of as the smartest water purification technique to emerge. A possibility of an activated carbon/CNT nanocomposite as a smart material for water purification will be explored as part of the strategic research theme.

3) Electrochemical methods for water purification

Hardness, high fluoride content and the presence of heavy metals are problems which arise due to metallic impurities in water in the North Central, North Western and Uva Provinces in Sri Lanka. Capacitive deionization is a method presently used for water desalination. Carbon-based materials (activated carbon, CNT) are used as the electrode material in such electrochemical cells. SLINTEC research aims to use nanomaterials in to the electrode carbon matrices to form nanocomposites. With nanocomposite based electrodes, capacitive deionization can be extended to cover a wider range of contaminant removal. This will be beneficial not only for Sri Lanka, but also for many other countries in the region having ionic impurity related water issues.

4) Developing sensors for testing water quality

Nano-enabled detection and sensing systems can significantly improve the sensitivity of pollution sensors, by detecting even a few ions of a chemical or biochemical pollutant. Additionally miniaturization could enable highly accurate, sensitive, simple and affordable field testing of water sources for acidity and presence of biological and non-biological pollutants. This is one of the future applications of nanotechnology for water purification which SLINTEC aims to research and develop with a special focus on contaminants and biological agents which are relevant to Sri Lanka.