Reverse Osmosis Pre-treatment
Reverse Osmosis Thin Film Composite membranes are subject to fouling by many substances:
| Fouling | Cause | Appropriate Pre-treatment |
|---|---|---|
| Biological fouling | Bacteria, microorganisms, viruses, protozoan | Chlorination |
| Particle fouling | Sand, clay (turbidity, suspended solids) | Filtration |
| Colloidal fouling | Organic and inorganic complexes, colloidal particles, micro-algae | Coagulation + Filtration Optional: Flocculation / sedimentation |
| Organic fouling | Natural Organic Matter (NOM) : humic and fulvic acids, biopolymers | Coagulation + Filtration + Activated carbon adsorption Coagulation+ Ultrafiltration |
| Mineral fouling | Calcium, Magnesium Barium or Strontium sulfates and carbonates | Antiscalant dosing Acidification |
| Oxidant fouling | Chlorine, Ozone, KMnO4 | Oxidant scavenger dosing: Sodium (meta)bilsulfite Granulated Activated Carbon |
NOM, particles and colloids can be removed by so-called "conventional treatment" consisting of coagulation followed by media filtration for low turbidity water . Additional steps such as flocculation and sedimentation are added in case of very turbid shallow seawater.
The non-conventional pretreatment for NOM , particles and colloids is Ultrafiltration.
An antiscalant solution should be dosed before the reverse osmosis membranes to disperse calcium carbonate and sulfates precipitates in order to avoid scaling.
Fine filtration (5-micron) is required as a last step before the RO membranes to prevent any debris, sand particles or piping material to damage the membranes.
--> See also ULTRAFILTRATION as a reverse osmosis pretreatment <--