THE MOST TECHNICALLY SIMPLE AND COST-EFFECTIVE DESALINATION PROCESS FOR SEAWATER
Alscore’s reverse osmosis plants for seawater are designed to provide drinking-quality water from high-salinity water or seawater. These water treatment units are typically designed for feeds with 35000 mg/l TDS and recovery rates between 30% and 40% and are ideal for domestic, irrigation, commercial or industrial use when the main water intake is close to shore and have a higher than acceptable salinity (see our guideline for maximum salinity levels).
Reverse Osmosis for seawater desalination is the only system capable of converting seawater into drinking water in one single pass and is also the most cost effective when seawater salinity is lower or equal than 41,000 ppm (41g/l). Considering that Australia’s surrounding Oceans have an average salinity of 31 g/l, reverse osmosis desalination plants are remarkably cheaper to build and maintain than the old heat distillation processes.
When looking for an easy water intake for seawater desalination plants in coastal Australia, Alscore always recommend the use of coastal wells, which is the simplest option for small and medium size industrial and commercial applications. Open sea extractions are also possible but will require in general higher costs and will lack the primary filtration that the ground provides naturally when using wells.
Two important aspects to consider from a pre-treatment point of view when planning a reverse osmosis plant for seawater are the existence of H2S (typical in deep seawater wells) that forms an extremely sticky get when oxidised that will foul the membranes in just a few hours, and the risk of membrane fouling by biodegradable colloidal organic matter when using continuous pre-oxidation.
From a design perspective, seawater reverse osmosis plants are simpler than reverse osmosis plants for brackish water. The reason is that plants designed for seawater are usually single-staged with low recovery as the incremental osmotic pressure makes impractical other configurations.
All our standard SWRO-series plants include a 1 micron cartridge pre-filter, but Alscore can also offer other pre-designed ready-to-use packages to pretreat and condition the permeate (product water) to make it suitable for plants and human consumers.
*(1) All data for information only and subject to change based on actual water analysis and final design parameters
Reverse osmosis membranes are very sensitive to microorganisms, small sand particles, iron, manganese and organic matter typically present in seawater.
Chlorine as NaOCl 12.5% (2-3 ppm dosing) is an excellent disinfectant and oxidant.
FeCl3 (10-20 ppm dosing) is a common coagulant good for colloids filtration.
Dechlorination by means of NaHSO3 40% (6-9 ppm) or activated carbon is required as membranes have a minimum tolerance to free chlorine.
Reverse osmosis permeate (product water) is acidic and low in calcium and magnesium. Therefore it is recommended to re-equilibrate its PH and remineralize to make it suitable for human or animal use as well as general irrigation.
Calcite filtration neutralises the PH and increases the calcium and bicarbonate content.
Desalination is the process of removing salts from the water. The salinity of the water before desalination influences how much salt can be removed.
Osmosis is a natural process where liquid will flow from a dilute source to a solution of greater concentration, across a semipermeable membrane. The semipermeable membrane only allows passage of water (solvent) and not the salts.
Osmosis can work in reverse mode if the salty solution is placed under an external pressure greater than the osmotic pressure.
In that case the water will move from the solution of greater concentration to the dilute source. As the salts cannot pass through the semi-permeable membrane they are left behind. The result is potable water on one side of the osmotic membrane, and very salty water (brine) on the other side, where the pressure was applied.
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