Reverse Osmosis Membrane Scale Inhibitors - The use of high performance RO membrane scale inhibitors is an essential component to any good reverse osmosis plant management programme. Reverse Osmosis Chemicals International offer a range of advanced technology RO scale inhibitors that have been expertly developed to meet the following criteria:

• safe to handle and safe in use.
• good scale prevention properties.
• membrane compatibility.
• stable and effective across a wide pH range.
• compatibility with other products.
• cost effectivity.

Recovery rates and the impact of salts

Reverse osmosis plant recovery rates vary from as low as 10% in the case of sea water to 90% with some low salinity brackish waters. As the water passes along the membrane surface the salt concentration increases and some sparingly soluble salts exceed their solubility products. These salts can precipitate on the membrane surface causing fouling which may reduce output and increase the product water conductivity. The two most trouble­some salts are calcium carbonate and calcium sulphate and their prevention is essential if the membrane is to work efficiently.

The use of sulphuric acid to 'de-alkalise' the feed water has been the traditional way of preventing calcium carbonate scaling. However, sulphuric acid is hazardous to handle, increases the sulphate content of the water and adds to the general corrosivity of the water on both sides of the membrane.

Calcium sulphate scale can be eliminated by lowering the recovery rate, which reduces the calcium and sulphate ion concentration in the water. Reducing the recovery rate is not always the best option as it means running the plant at lower efficiency. The best way to maintain cost effective production is to operate with recovery rates as high as possible whilst at the same time preventing membrane scaling.

Membrane scale inhibitors or antiscalants can be dosed either before or after the system cartridge filters in a typical reverse osmosis system. If iron is present in the feed water, the antiscalant can be dosed post to prevent “pick-up” of iron, or in the case of polymer antiscalants de-activation by iron. Under these circumstances a phosphonate based product with good iron sequestering properties is recommended.

The dose point for the selected antiscalant should be after the sodium bi-sulfite injection to ensure chlorine is removed (especially with high levels of free chlorine). The dose point should be sufficiently down-stream of the SBS injection point to avoid “neat” product mixing.

Membrane scale inhibitors

High performance antiscalants and membrane scale inhibitors developed to support the ROC series of products:

ROCscale 51 - high performance super-threshold membrane scale inhibitor able to stabilise a wide range of supersaturated salt solutions ... scale inhibitor >>

ROCscale 91 - membrane scale inhibitor developed for use with high silica waters. A synergistic blend of threshold antiscalants and dispersants ... scale inhibitor >>

ROCscale 95 - antifoulant for use in reverse osmosis and nano-filtration membrane systems using sea water or high salinity estuarine waters ... antifoulant >>

ROCscale 110 - super-threshold agent able to stabilise a wide range of supersaturated salt solutions ... scale inhibitor >>

Technical support and advice

Reverse Osmosis Chemicals International work closely with a diverse range of global organisations, intelligently combining advanced treatment technologies with practical solutions to resolve complex issues. If you have a project you would like to discuss, or you require technical support and assistance; or if you simply have a question about our reverse osmosis membrane scale inhibitors please contact one of our specialist advisors using our Technical Support page or call us on +44 (0) 330 223 31 31.