This schematic drawing of a typical

This schematic drawing of a typical Reverse Osmosis (RO) system is included in handout 2-2-10. Use it to explain the pathway of water through a two-stage RO.

Softened water enters the 1st stage buffer tank and is passed under pressure (achieved by a series of hygienic pumps) across the membrane in the first stage cartridge. The first stage filtrate feeds into the 2nd stage buffer tank. The 1st stage reject water is discarded, or can be collected and used, for example, for washing floors and walls. Water from the 2nd stage buffer tank is forced under pressure across a 2nd series of membranes in the second stage RO cartridge. The 2nd stage filtrate (also called the permeate) can be used for pharmaceutical manufacturing. It should be re-circulated through the distribution system and back to 1st stage buffer tank. The 2nd stage reject water is also returned to the 1st stage buffer tank.

In-line filters in both stages remove particulates. However, the membrane may still foul, and so has to be back-washed periodically, usually on an automatic cycle. Bacteria can grow in the system, as well as on and through the membrane, so the RO system needs to be periodically sanitized. Because of the plastics used (eg. in the membrane), heat is usually not an option. Some RO membranes can, however, be heat sanitized. Peroxygen products (such as hydrogen peroxide or peracetic acid) are preferred, but some membranes are able to tolerate chlorine.

Inspectors should ask for back-wash and sanitation records.