Reverse osmosis (RO) is a water purification technology that uses a semipermeable membrane to separate water molecules from dissolved salts and other impurities. Here's how it works:
1. Pressure Application:
- High pressure is applied to the feed water on one side of the membrane.
2. Membrane Selection:
- The membrane is carefully chosen to allow water molecules to pass through while blocking most dissolved impurities. These membranes are typically made of thin-film composite materials, with a dense, selective layer on top of a porous support layer.
3. Water Molecule Passage:
- Due to the applied pressure, water molecules are forced through the membrane's pores. The smaller water molecules can pass through, but larger dissolved salts, bacteria, viruses, and other contaminants are rejected.
4. Concentrate Rejection:
- The rejected impurities are concentrated on the high-pressure side of the membrane, forming a concentrated brine stream.
5. Permeate Production:
- The purified water that passes through the membrane is called permeate. It is collected on the low-pressure side of the membrane.
Key Features of RO Membranes:
* Semipermeable: Allow the passage of water molecules while rejecting dissolved salts and other impurities.
* Selective: The membrane's pore size and material properties determine its selectivity for specific molecules.
* Thin-film composite: Modern RO membranes are often made of thin-film composite materials that offer high performance and durability.
* Pressure-driven: RO membranes rely on pressure gradients to force water through the membrane.
Factors Affecting Membrane Performance:
* Membrane material and pore size: These determine the membrane's selectivity and water permeability.
* Operating pressure: Higher pressure leads to higher permeate flow, but also increases energy consumption.
* Feed water quality: Contaminants and their concentration in the feed water can affect membrane performance and lifespan.
* Temperature: RO membranes work best at moderate temperatures.
Overall, RO membranes act as a barrier, separating water molecules from impurities. The applied pressure forces water molecules through the membrane, leaving behind the unwanted contaminants, resulting in purified water.
