Reverse Osmosis (RO) Plant & Scale Inhibitors

Reverse Osmosis (RO) Plant & Scale Inhibitors - This short paper considers the performance optimisation of reverse osmosis plant using scale inhibitors looking at the effects of scale build-up, good practice procedures and what to look for in an effective membrane antiscalant.

Why Should You Use a Scale Inhibitor?

This short article gives an overview of the types of problems faced by operators of reverse osmosis plant. It summarises the problems and the need for a suitable inhibitor treatment to combat problems caused by scale, all of which can be added simply to overcome the issues. Reverse Osmosis Plant & Equipment Reverse osmosis plant have at their heart a membrane that if damaged reduces output, increases costs and gives poor water quality so it is important to keep it clean and operating efficiently.

Advanced Antiscalant Technology

Most reverse osmosis membranes are formed from hollow fibre or thin film composite sheets with the membrane allowing passage of pure water and rejecting the dissolved solids contained in the water.

As water passes along the membrane surface the solids concentration increases and some sparingly soluble salts start to exceed their solubility and precipitate. When precipitated onto the membrane surface this causes fouling that may reduce output and increase product water conductivity. The worst of these solids being calcium carbonate and calcium sulphate and so the prevention of their precipitation is vital if the membrane is to function efficiently.

The traditional way to prevent this was to "de-alkalise" the water using sulphuric acid to prevent calcium carbonate precipitation. However the acid is hazardous increases the sulphates and increases the corrosivity of the water on both sides of the membrane. Reducing the recovery rate of the reverse osmosis plant eliminated calcium sulphate but this reduces the efficiency of the plant and hence increases costs.

RO Membrane Antiscalants

Effective membrane antiscalants should be:

• Safe to handle and safe to use.
• Good scale inhibitors.
• Membrane compatible.
• Effective across a wide pH range.
• Compatible with other products.
• Cost effective.

It is also normal operating practice to keep residual iron levels in the feed water as low as possible, normally below a maximum set by membrane manufacturers. Precipitated iron is a membrane foulant and adversely affects the performance of many antiscalants.

With this in mind it is important to design chemical and maintenance programs that are capable of meeting all of the above to ensure problem free running together with low operating costs.

Should you need assistance in any of these areas please contact Accepta who can help provide the requirements needed to assist with such plant, maintain their efficiency and thus reduce costs and improve plant life expectancy.

Nigel Richardson - April 2002: Nigel is CEO of Accepta

Additional Information & Technical Support

For further information about any issues raised or details of Accepta's specialist products and services please call Accepta on +44 (0) 161 877 2334 or e-mail info@accepta.com.