|For the preservation of the affectivity and life span of a Reverse Osmosis (RO) installation, a sufficient pre-treatment is required. A proper selection of pre-treatment methods for feed water will improve affectivity and extend the life span of the system by preventing or minimizing biofouling, scaling and membrane plugging. |
To perform an uninterrupted and reliable pre-treatment of the feed water a special approach is used. A pre-treatment that is not geared to the installation may cause a system overload. When this occurs the system parts need cleaning much more often to restore productivity and salt retention. Cleaning costs, system performance and standstill time are very significant in that situation.
The kind of pre-treatment system that is used greatly depends on feed water quality. Consequentially, sufficient feed water pre-treatment is dependent on:
· The source of the feed water
· The composition of the feed water
· The function of the feed water
When the source of the feed water that needs treatment is specified, a complete and exact water analysis is performed. This action is an important step for the design of a pre-treatment system and the entire Reverse Osmosis system, because this often determines the type and size of the pre-treatment.
Feed water analysis
Most water types that are treated in a Reverse Osmosis system are either:
Scaling prevention and control
Scaling is the accumulation of (partially) insoluble salts in a membrane. When a Reverse Osmosis installation has a recovery of 50%, the concentration of salts in the concentrate flow is double the concentration of salts in the feed water flow. When recovery increases, the chances of scaling increase, as well. Because of this it is of great importance that the saturation limits of the (partially) insoluble salts are not exceeded.
Prevention of fouling by colloids
In Reverse Osmosis elements colloidal pollution can seriously diminish the performance by decreasing productivity. An early sign of this pollutant is usually an increasing pressure gradient. The sources of this pollution in feed water can vary greatly. They are usually bacteria, clay, and iron corrosion products.