Main factors affect the Contamination of Reverse osmosis system

I. Different material of RO membrane (CAB series or CPA series)

Common RO membrane on the market can be divided as CAB series (acetate cellulose) membrane elements or (aromatic polyamide) membrane elements. For the ground water or waste water which is hard to treat, can select CAB series to replace CPA series. The advantages of CAB series are membrane surface is smooth, so can reduce the deposition of contaminants.The other advantage of CAB series is that the feed water could contain 0.3-1.0ppm free chlorine which will not break RO membarane and help to prevent the growth of bacteria. As for CPA series, it is resistant to chlorinebut can not bear the oxidation, therefore chlorine removal is necessary.

II. Product water flux

The product water flux means the product water per unit effective area of the membrane surface, can be indicated as GFD(gallons/square feet/day) or LMH (liters/square meter/hour). The product water flux of reverse osmosis system is directly proportional to the pollution rate. Lower the product water flux, lower the pollution rate. Thus can select reverse osmosis membrane with large membrane area to lower the product water flux.

III. Horizontal flow velocity

Lateral flow velocity is also an important factor affecting the rate of contamination of reverse osmosis equipment. The higher the lateral flow velocity of the surface water supply and the concentrated water produced on the membrane surface, the lower the membrane fouling rate. This is because the inflow of high lateral flow reduces the precipitation and accumulation of particulate matter on the membrane surface, and at the same time accelerates the diffusion rate of high concentration salt on the membrane surface to the main solution, reducing the risk of insoluble salt precipitation.

IV. Cleaning the reverse osmosis system

Cleaning the reverse osmosis system can effectively prevent the pollution speed of system. Main methods could be include concentrated water recirculation, low-pressure flushing during shutdown, and regular disinfection, etc. Rinse and short-term immerse the membrane element by product water can help to inhibit the growth of bacteria and dissolve the pollutants on the membrane or make it loose.

V. Element structure of reverse osmosis membrane

When design reverse osmosis sytem for well water and ground water, should select roll-type membrane element. Under varied of conditions, the roll-type membrane element is superior to the hollow fiber and plate-frame structure. Design the membrane with large membrane area can help to reduce product water flux and increase lateral flow velocity, then inhibit the system pollution speed.

If clean the system every three months or longer, then shows that the design of pre-treatment filters and reverse osmosis system are resonable. If need to clean the system every 1-3 months, then need to improve the process or increase the equipments.

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