Plant Shut-Down - Shutting-down a reverse osmosis plant system is an important operation and one that must be completed correctly. If this operation is not done correctly then water quality and performance issues may be affected once the system is restarted.

Permeate flush

Immediately prior to shut-down it is likely that the concentration of salts in the feedwater may have increased and possibly exceeded their solubility during operation. These salts should therefore be removed by rinsing out prior to commencing any shutdown procedure (usually rinse out for at least 15 minutes). This rinsing of the RO membranes with permeate water on shut will also aid the flushing of colloids and bacteria from the membrane surface.

The flow rate during system flushing should be based on the recommended cleaning instruction flow rates recommended by the membrane manufacturers. This is normally 30 – 40 gpm (6.8 – 9.1 m3 /hr) per pressure vessel.

The flushing time should be long enough for the conductivity out to equal the conductivity in. This is typically between 15 and 20 minutes.

If the permeate flush is unavailable, feed water can be used by allowing low-pressure water to replace the water within the system by delaying the closing of the inlet valve. The introduction of any scale inhibitor chemicals should be turned OFF during the permeate flush. If the water temperature in the membranes exceeds 115^oF, the flush water should be continuously passed through the system to prevent membrane degradation.

Biological growth

For system shut downs of longer than 24 hours, biological growth in the reverse osmosis system must be carefully controlled. To control the biological growth will require the introduction of a suitable chemical disinfectant or biocide to kill bacteria and prevent re-growth. Any biocides or disinfectants must be fully rinsed from the RO system before it is re-started.

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 technology solutions please contact one of our specialist advisors using our Technical Support page or call us on +44 (0) 330 223 31 31.