Desalination is a process that reduces the concentration of dissolved salts in water. Water high with a high salt concentration can come from a range of sources, with the most commonly thought of being the surface water in the ocean. Along with this, ground water sources such as bore water, mining process water, and coal seam gas associated water can all be high in salts.
The amount of salt present in water determines what it can be used for, with a general classification given in the table below1.
|Salinity status||Salinity (mg of salt/L)||Description and use|
|Fresh||< 500||Drinking and all irrigation|
|Marginal||500 – 1,000||Most irrigation, adverse effects on ecosystems become apparent|
|Brackish||1,000 – 2,000||Irrigation of certain crops only; useful for most livestock|
|Saline||2,000 – 10,000||Useful for most livestock|
|Highly saline||10,000 – 35,000||Very saline groundwater, limited use for certain livestock|
|Brine||>35,000||Seawater; some mining and industrial uses exist|
Depending on the salinity of the feed water and its intended use, a varying amount of salinity will need to be removed. Due to the large energy requirements of conventional treatment methods, desalination is a costly process. Many processes are used to reduce the concentration of salts, mainly focusing on either evaporation/condensation, or membranes/filtration.
While evaporation and condensation methods are effective at producing very pure water, they typically have high energy requirements to convert water to steam, and have lower recoveries as not all of the steam generated can be condensed into water.
Reverse osmosis (RO) is the method most commonly used, which uses semipermeable membranes and applied pressure to induce water permeation through the membrane while rejecting salts. If the feed water contains high concentrations of multivalent ions (e.g. sulphate and calcium ions), the RO process’s recovery is limited to around 70% before the ions start to form a scale on the membrane. With this in mind, muliple RO stages can be required to meet the product water specifications.
Membranes are subject to fouling and scaling during the process, with pre-treatment often required. In many cases micro-filtration is used before RO to prevent particles such as sediment, algae or large bacteria from fouling RO membranes.
Clean TeQ Water’s DESALX® (2-Stage CIF®) technology removes both the anions and cations from the water in a complimentary process, leading to desalinated water with a typical recovery greater than 90% and a smaller waste stream. The process is also fouling resistant and typically operates with lower energy requirements than RO.
Our HIROX® (High Recovery Reverse Osmosis) technology uses CIF® as a pre-treatment for RO, removing ions which limit the recovery rate of RO systems. Using HIROX®, recoveries 95-99% are usually achieved, with the added benefit of using recycled brine from the RO to regenerate the CIF® resins, reducing chemical costs. The system is also fouling resistant and requires less RO stages, operating with a lower energy requirement than RO alone.
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