Reverse osmosis is a process of reversal of the process of osmosis. Osmosis is the process of moving a solution from a solution with low solute concentration to a solution with higher solute concentration until there is equilibrium concentration. Osmosis is a natural phenomenon, but the flow of solution can be slowed, stopped, and can even be reversed (this is known by the term "Reverse Osmosis"). Reverse osmosis is done by applying pressure on the solution with high concentration to exceed the pressure at the solution with low concentration. So the solution will flow from high concentration to low concentration. Solution transfer process occurs through a semipermeable membrane and the applied pressure is hydrostatic pressure (Shun Dar Lin, 2001).
To illustrate the events of reverse osmosis, imagine a semipermeable membrane with water on one side and a solution with high solute concentration on the other. If there is an incident normal osmosis, water will pass through the membrane into a solution with high concentration. In the event of reverse osmosis, in the solution with high concentrations given the pressure to push water molecules through the membrane into the aqueous solution (Figure). This separation process will be split between the solute on one side of the membrane and the pure solvent on the other side.
Semipermeable membrane used in reverse osmosis membrane is called reverse osmosis (RO membrane). < 1 nm (http://www.lenntech.com/membrane-technology.htm)." ae="RO membrane has a pore size <1 nm. ">RO membrane has a pore size <1 nm. Because of the size of a very small porinya, RO membrane called the membrane is not porous. RO membrane typically used for water treatment, such as drinking water treatment, seawater desalination, and wastewater treatment. Current RO membranes is also widely used in water treatment process refill. Characteristics of RO membrane fluid processing results are as follows:
In drinking water treatment, such as refilling water treatment, RO membrane is designed to pass water molecules and hold a solid, such as salt ions. RO membrane to separate and exclude solutes, organic matter, pyrogens, colloids, viruses, and bacteria from raw water. Penyisisihan efficiency of RO membranes for total solutes (TDS) and bacteria, respectively 95-99% and 99%. So at the end of the process will produce pure water
RO membrane removal efficiency of high lead allowance for the natural minerals in the raw water. These natural minerals not only provide good taste in the water but also helps the vital functions of body systems. Drinking water will be less healthy for the body if it contains less of these minerals
In other words, pure water produced by RO membranes is not healthy for the body. In addition, the RO membrane is limited in its operation, including:
Raw water pressure is between 40-70 psig (800-1000 psi).
Raw water turbidity should not exceed 1 NTU.
operating pH range from 4-11.
TDS of raw water should not be more than 35,000 ppm. Higher TDS value will decrease the speed of production.
Suspended Solid raw water; (expressed with SDI, Salt Density Index), must be less than 5.
Raw water chlorine residual should be zero (0).
Another problem that often occurs in RO membrane application is the occurrence of membrane fouling. Membrane fouling is stacked events solutes on the membrane surface or inside the membrane pores, so that the membrane performance will decrease. If membrane fouling experienced, needs to be done washing with chemical solutions or membrane replacement. This will increase operational costs
