Reverse Osmosis removes contaminants from water through semipermeable membranes. Water flows from the more concentrated side (more contaminants) from the RO membrane to the less concentrated side (less contaminants) to provide clean drinking water. The fresh water produced is called permeate. The remaining concentrated water is called wastewater or water rejection. Semipermeable membranes have small pores that block contaminants but allow water molecules to flow. In osmosis, water becomes more concentrated as it passes through the membrane to gain balance on both sides. Reverse osmosis will prevent contaminants from entering the less concentrated side of the membrane. For example, when pressure is applied to the volume of salt water during reverse osmosis, the salt is left behind and only clean water flows.
How Do Reverse Osmosis Systems Work?
The reverse osmosis system removes sediment and chlorine from water by prefiltering it before passing through a semipermeable membrane to remove dissolved solids. After the water leaves the RO membrane, it passes through the postfilter to process drinking water before going into the special tap. The reverse osmosis system has various stages depending on the number of prefilter and postfilter.
RO System Stages
The RO membrane is the focal point of the reverse osmosis system, but the RO system also includes other types of filtration. The RO system consists of 3, 4, or 5 filtration stages. Every reverse osmosis water system contains a sediment filter and a carbon filter in addition to the RO membrane. These filters are called pre filter or postfilters and consist of the following filters:
- Sediment Filter: Reduces particles such as dirt, dust and rust
- Carbon Filter: Reduces volatile organic compounds (VOCs), chlorine, and other contaminants that give water a bad taste or smell
- RO membrane: Removes up to 98% of total dissolved solids (TDS)
- When water first enters the RO system, it goes through the prefiltration. Prefiltration usually includes a carbon filter and a sediment filter to remove sediment and chlorine which can clog or damage the RO membrane.
- Next, water passes through a reverse osmosis membrane where the dissolved particles are removed.
- After filtration, water flows into a temporary storage tank. The reverse osmosis system continues to filter water until the storage tank is full and then shuts down.
- After turning on the drinking water tap, the water will come out of the storage tank through another postfilter to process the drinking water before it reaches the tap.
Why need an RO storage tank?
The RO storage tank holds RO water so that the system has a potable water supply. The RO system goes quite slowly. It takes one minute to produce two to three liters of RO water. If turning on the tap for a gallon of water at the actual membrane production rate, then we have to wait at least a few minutes for it to fill. With storage tanks, our gallons of water can be filled immediately.
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