Reverse osmosis water treatment systems are a very efficient method to create safe drinking water. Depending on the water quality, it is important to add on pre-treatment to the reverse osmosis water treatment system in order to maximize the system’s performance and life span. Certain elements can create fouling and scaling on the reverse osmosis membrane. This causes major problems in the reverse osmosis water treatment system and can damage the entire system if left unmaintained.
There are a few different options for pre-treatment, but those options can only be determined once a proper water quality analysis has been conducted. Depending on the quality and the actual types of contaminants in the feed water, one or a combination of the following should be added on to the reverse osmosis system: chemical injection systems, pre-filtration, and/or a water softener or deionization system.
Fouling means that there is a buildup of materials on the membrane surface. This does not alter the structure of the membrane, but it can slow down membrane performance significantly. Fouling can occur when there are high SDI (Silt Density Index) levels found in the water. This is generally needed for municipal water supplies, but very rarely needed in brackish water reverse osmosis water treatment systems because there are very low SDI levels found in well water.
Scaling occurs when inorganic salts are rejected by the RO membrane and the concentration of those salts in the concentrate become higher. This causes the salts to precipitate on the surface of the membrane, which is the scaling. This can become a large problem and must be treated right away.
There are also methods to prevent this problem in the first place. Just like preventing fouling, it is important to get a proper water analysis to find out what types of chemicals and what concentration they are in the water to find out how much pre-treatment is needed.
Pre-treatment to prevent scaling is common in all water types, but it is most important and required in sea water reverse osmosis water treatment systems. Scaling has an effect on production capacity, product quality and energy consumption. The most common types of scale-forming chemicals are calcium, sulfates, and silica. The most common and effective pre-treatment methods for a reverse osmosis water treatment system includes acid addition, dosing of antiscalant (scale inhibitors) and/or softening. Also, pH and temperature influence the precipitation of scaling compounds, and the recovery rate can be adjusted to prevent the increase in the concentration beyond the saturation limit.