Reverse osmosis (RO)
RO is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pressure, a colligative property that is driven by chemical potential differences of the solvent, a thermodynamic parameter. Reverse osmosis can remove many types of dissolved and suspended chemical species as well as biological ones (principally bacteria) from water, and is used in both industrial processes and the production of potable water.
Reverse osmosis differs from filtration in that the mechanism of fluid flow is by osmosis across a membrane. The predominant removal mechanism in membrane filtration is straining, or size exclusion, where the pores are 0.01 micrometre’s or larger, so the process can theoretically achieve perfect efficiency regardless of parameters such as the solution’s pressure and concentration. Reverse osmosis instead involves solvent diffusion across a membrane that is either nonporous or uses nanofiltration with pores 0.001 micrometre’s in size. The predominant removal mechanism is from differences in solubility or diffusivity, and the process is dependent on pressure, solute concentration, and other conditions. Based on the raw water quality, the pre-treatment process for RO Plants may consist of all or some of the following treatment steps:
- Clarification followed by Sand Filtration for Turbidity removal
- Water disinfection with chlorine
- Hardness reduction by Softening
- Addition of scale inhibitor
- Reduction of free chlorine using sodium bisulfite/ Activated carbon filters
- Final removal of suspended particles using cartridge filters
SA Enviro Solutions designs RO plant for Industrial, Commercial, Institutional & Domestic use on small to large scale.