Pretreatment for RO

Pretreatment for RO

Desalination facilities for the conversion of sea water or brackish water to potable water or industrial process water typically rely on nanofiltration (NF) membranes or reverse osmosis (RO) membranes.

RSL Membranes™ are an excellent technology choice to pretreat water for this application. RO membranes are sensitive to high levels of silica which will cause fouling in both NF and RO membranes. Parameters such as aluminum, barium, iron and zinc can create fouling issues. One significant benefit of the RSL Membranes™ is their ability to absorb certain metals during the filtration process. Testing and ICP analysis has provided a data base which confirms that RSL™ Powder, used as the membrane skin layer, has consistently adsorbed:

1. Aluminum >85%
2. Barium > 70%
3. Boron >40%
4. Fe >85%
5. Si >65%

Other metals, to a lesser extent are also being adsorbed

Table 1 summarizes a study that evaluated the adsorption capability of RSL™ powders compared to conventional media (Activated Alumina and Diatomaceous Earth- DE) which are used for filter cake/dynamic membrane filtration processes.

Because the RSL Membranes™ can handle a high suspended solid load (as high as 5000 ppm), the technology replaces conventional clarifiers or DAF’s. If softening of the water is required through the use of lime or NaOH addition, calcium and magnesium can be precipitated and removed via the RSL Membrane™. Furthermore, the RSL Membranes™ have been used extensively to remove high amounts of silica with the addition of poly aluminum chloride (PACl) to cause a crystallization of the silica.

RSL Membranes™ were compared to Veolia Ceramem membranes in the first assessment of the RSL Membranes™. The technologies were evaluated for pretreatment prior to an RO membrane. RSL Membranes™ outperformed the Veolia Ceramic UF membranes. Flux rates were 10 times the ceramic membranes and produced similar quality water (SDI<3 and typically<1). In the above photo, the white trailers contain the ceramic membranes and the small blue trailer to the left contain the RSL Membranes™. As you can see the footprint impact was significant. The systems had the same flow rate and were operated for a year side by side with full time operation over a four-month period. The Ceramic membranes had fouling issues and were limited to a TSS concentration< 100ppm in the feed water. RSL Membranes™ could operate over a large range of TSS levels.