Reverse osmosis (RO) uses pressure to drive water through semi-permeable membranes while rejecting most dissolved salts. Reliable RO operation depends as much on pretreatment and monitoring as on the membrane elements themselves.
1. Feedwater intake and screening
The process begins with the available water source. Coarse solids are removed and feed conditions are stabilized where required.
2. Pretreatment
Pretreatment is designed around the source water. It may include clarification, multimedia filtration, ultrafiltration, cartridge filtration, softening or chemical conditioning. The objective is to control suspended solids, biological fouling and scaling precursors before the membranes.
3. Chemical conditioning
Depending on design, antiscalant, acid, sodium metabisulfite or other chemicals may be dosed. Every chemical should have a defined purpose and control method. For example, dechlorination protects chlorine-sensitive polyamide membranes.
4. Cartridge filtration
Cartridge filters provide final protection against particulate ingress and upstream media carryover. A rising differential pressure is a useful warning sign.
5. High-pressure pump
The pump raises feed pressure above the osmotic pressure and provides the driving force for permeation. Required pressure depends strongly on feed salinity, temperature and recovery.
6. Membrane pressure vessels
Feed enters the membrane elements and separates into permeate and concentrate. Staging and element arrangement are selected to balance recovery, flux and crossflow.
7. Permeate handling
Permeate may require pH adjustment, remineralization, disinfection or polishing depending on final use.
8. Concentrate management
Reject water contains the salts removed from the permeate plus any non-permeating species. Disposal or reuse must be considered during design.
Key operating indicators
Trend normalized permeate flow, salt passage, differential pressure, recovery, feed pressure and water temperature. Slow changes often reveal fouling before production loss becomes severe.