Demineralisation describes the removal of nitrates and minerals from water. Ion exchange, electrodialysis and reverse osmosisare just some of the water treatment technologies often used for commercial water filters and wastewater treatment in effluent treatment plants. Ion exchange is primarily used for water demineralisation,as it can remove ions such as magnesium and calcium which cause hardness.
Reverse Osmosis (RO) is one of the most commonly found processes for demineralisation of brackish water in industrial filtration.Various studies have proven RO to be the most cost-effective technology for demineralisation, providing the total solute content of input water is above 200mg per litre.The Ro systems are found worldwide, being used in an impressively diverse array of situations. These can range fromthe purification of rain and ground water for crop irrigation, to the need for extensively purified water for industrial use. These processes are even found in medicine where systems based on the same concepts are used in the treatment of patients with renal insufficiencies.
Reverse Osmosis Systems
RO systems usually consist ofvarious steps to guarantee success. Utilisation of reverse osmosis further upstream of demineralisation processes can reduce the potential for dissolved minerals by up to 98%. This ensures that acid and caustic consumption is also reduced by up to 90%.
Before the RO stage is reached, filtration through active carbon reduces smaller particle levels, including chemicals such as chlorine. This step may be vital in some areas to preserve the RO membrane in a useable condition. RO filters can generally remove polluting particles which have a greater size then 0.1nm. This is classified as hyper-filtration. After the RO process there may be an additional carbon filter, followed by exposure to UV light which ensures the removal of microbes and any remaining chemicals.
Reverse Osmosis Plants
Some plants and power generating facilitiesrequire demineralisation of the input water to remove various minerals (such as silica) that may be retained invapourwhich can result in undesirable plating on turbines. There are various chemical techniques available to reduce fouling of industrial filters. For example, lime softening consists of reducing the hardness of the wastewater. Lime, soda, ash, and NaOH are used to convert soluble calcium and magnesium to insoluble calcium carbonate and magnesium hydroxide. Magnesium hydroxide also has the property of absorbing silica and preventing the scaling mentioned. Fouled demineralisers are typically regenerated usinga liquid caustic and sulphuric acid.