New silica method could reduce the cost of purifying drinking water

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Source: European Commission, Environment DG

Tiny particles of coated silica could be used to purify drinking water by removing harmful pollutants and pathogens. This simple and relatively cheap technology is capable of removing contaminants from water making it safe to drink and helping ensure that drinking water meets the standards of the European Drinking Water Directive. Provision of portable water is becoming a major socio-economic issue, particularly in developing countries. Waterborne pathogens are a significant cause of disease and according to a recent UN water report, are the leading cause of diarrhoea, worm infestations and infectious diseases. In industrialised areas, organic pollutants and pathogens can also contaminate untreated wastewater derived from processes in the pulp and paper sector, the textiles and leather, and iron and steel industries and petrochemical refineries.

Water purified by traditional processes which aggregate, settle and filter the contaminants, often needs further treatment, such as chlorination, to make the water fit for drinking. Recent attention has been turned to novel methods using nanoparticles of iron or nano-sized catalysts to remove contaminants. However, these methods require sophisticated, filtering techniques to remove the nano-material, which are not always feasible in small treatment facilities.

A new Australian study has demonstrated for the first time that larger particles of silica can be engineered to remove organic pollutants simply by stirring them into contaminated water. The silica is coated with a nano-scale chemical layer which attracts contaminants that then stick to the particles. The coated silica particles can then be easily filtered off, eliminating the need for complex treatment methods and making the technology particularly suited to small, local treatment facilities. This suggests that the technology could one day be applied to schemes, such as recycling of water, that are carried out on a local level and would contribute to the creation of sustainable water systems.

As well as coating silica particles, the active chemical layer can be deposited onto other substances and structures. This suggests that the technology could be incorporated into a variety of simple water treatment designs on various scales, making it suitable for both decentralised and centralised purification processes.

The technology relies on the active layer being strongly adsorbed onto the surface of the silica particles. The layer, just one molecule thick, is made of hydrocarbon molecules which align themselves to form a self-assembled monolayer (SAM), which coats the silica particles. The researchers suggested that monolayers remove pollutants and pathogens through electrostatic attraction, which binds the organic contaminants to the surface of the SAM-coated material.

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