When people talk about what is osmosis they are usually referring to a system of plumbing in which water is removed from the pores of a semi-permeable membrane. There is no practical difference between what is either reverse osmosis or multi-stage osmosis. In both systems the purpose is the same. Osmosis is a method of removing what is soluble from water. This removal results from a change in the solute concentration on both the interior and exterior of the semi-permeable membrane.
The system of what is osmosis was developed by Louis Pasteur over a century ago to be used in his research on plant cell respiration. The process involved in his research was how water moved through plants as part of their chemical processes. What he found out was that certain plants had a lower solute concentration in their urine than others, and that the plants with the highest concentration of dissolved matter had a lower water/solute pressure than other plants in the same type of soil.
One of the outcomes of Pasteur’s work was what is now known as the Pasteur Law. Basically what this means is that a material will retain most of its electrical charges if its external environment is nutrient rich but free of salt particles. That is why it is so important to properly install and maintain an under-salt water-pumping system in a household. It is also important to understand that a properly installed and maintained multi-stage or parabolic membrane filter will prevent most salt particle build-up from occurring.
When what is osmosis is used for the removal of salt and other dissolved organic compounds (LDOs), the process involves a membrane with multiple stages. The lower and higher concentration solvents that are used in the process of osmosis will be separated by the membranes, which are usually made of synthetic polymers. In the process of osmosis, the membrane separates water across it in a process called osmotic pressure.
A hypertonic solution, such as a de-mineralized water or de-potable water, has a lower concentration of dissolved solutes than do minerals. Hypertonic solutions are more dense than de-mineralized solutions. Generally, the higher the concentration of dissolved solutes in a solution, the higher the osmotic pressure, and the lower the solute concentration and the greater the acidity of the resultant compound. An example of a hypertonic compound is sodium chloride. If you add more of it to an alkaline solution, it will raise the alkalinity even further.
There is a very close relationship between the concentration of salt in a solution and the osmotic pressure. When more salt than water is present in a solution, the pressure increases. If more water than salt is present, the pressure decreases. It is a simple, although not particularly pleasant, concept. It is one reason why we do not want to sit and take the water from our gardens and drinking it, because we may end up with too much pressure.
Osmotic pressure is a function of the total molecular weight of the solvent and the semi-permeable surface area of the membrane. A higher value of the semi-permeable surface area will cause the solvent to percolate more efficiently through the semipermeable membrane. The actual value of the permeability is not known, since it is dependent upon the total molecular weight and the concentration of solutes in the solvent. Some of the most commonly used solutes, including water, are of relatively low molecular weights. These substances, when exposed to high pressure, do not pass through the membranes of the devices used to perform this process.
One of the functions of the semi-permeable membrane is to act as a guard cell. The guard cell, if present, will trap larger molecules, such as in the case of organic compounds, rather than allowing those molecules to pass through the cell. This will keep the organic compound in its place, so that it does not contaminate the rest of the medium or be destroyed by contact with smaller compounds that would ordinarily enter the system. This is important in both industrial and residential settings, since biological hazards, such as those resulting from inhalation of chemical fumes or vapors, can be greatly reduced by using such a system. A properly installed and maintained semi-permeable membrane can also trap large particulates, such as dust, that would otherwise become airborne, without allowing them to pass through the membrane to the outside environment.