Reverse Osmosis Units

The Merlin^TM Reverse Osmosis (RO) Drinking Water System is a water treatment unit. It uses water pressure to reverse a natural physical process called osmosis. Water, under pressure, is forced through a semi-permeable membrane to filter out minerals and impurities. Clean drinking water goes to the tap. Minerals and impurities are sent to the drain with RO wastewater.

The system includes replaceable filters and membrane elements. The prefilter removes sand, silt, dirt, rust particles, and other sediments, and chlorine from the water supply before they enter the RO membrane elements. The post filter removes any tastes and/or odours that may remain in the water after passing through the RO membrane elements.

Reverse Osmosis in more detail
Reverse osmosis is a pressure driven process for separating salts and macromolecules from water or other aqueous streams. It is capable of removing particles that are as small as 0.1 nanometers. This includes viruses, bacteria and dissolved salts. The osmosis process is used in a wide range of applications. This includes wastewater treatment, production of pure water for industries [e.g. wafer fabrication], and removal of salts from salty or seawater [desalination].

Let us start with the normal osmosis process. Consider a semi-porous membrane that separates equal volumes of liquid into two compartments. In one compartment is water, and the other dilute salt solution [see diagram below]. Due to the effect of osmosis, water flows from side containing water to the side with the salt solution. Water flows over because it is trying to dilute the salt solution. This continues until an equilibrium state is reached.

For reverse osmosis, the aim is not to dilute a salt solution, but to purify water by removing salts and other contaminants. This is done by applying a pressure to the side containing the salt solution. It causes water to flow to the other side of the membrane [see diagram below]. This purifies the water, since the membrane prevents salts and other particles from passing through.

A typical reverse osmosis membrane has 2 layers:

• A dense top layer of less than 1µm think
• A porous sub layer of 50-150µm thick, for supporting the top layer