Reverse Osmosis

Content

Reverse osmosis is a process of pumping water through a semipermeable membrane by applying adequate pressure. As a result, water is purified from dissolved contaminants, as well as from harmful bacteria and viruses. Water from various sources, including centralized supply, becomes cleaner and sometimes safer after reverse osmosis treatment.

This purification technology is highly effective and widely used both in industrial and in domestic conditions. During the process, the incoming water is divided into two fluxes – purified water (permeate) and concentrated water (filtrate). The latter is usually discarded. Operation of industrial reverse osmosis systems usually includes the following stages:

• Preliminary purification of water
• Passage of water across the membrane
• Purified water accumulation
• Purified water final treatment
• Bottling of purified water

Preliminary water purifying is necessary to increase the resources of RO systems. Mechanical filters eliminate suspended solid particles; absorbing materials remove gaseous substances from water. Such pre-treated water then passes on to the reverse osmotic membrane under appropriate pressure. The resulting water thus purified by reverse osmosis is free from organic compounds, toxic heavy metals, and pathogenic germs.

pH of Water after Reverse Osmosis

The hydrogen index, or pH, is a parameter associated with the acidity of water. Quantitatively it is related to the concentration of hydrogen ions ([H⁺]) in water, amounting to the decimal logarithm of [H⁺] taken with the opposite sign.

• pH=7 means that the water is neutral, i.e. that [H⁺] is equal to the concentration of hydroxide ions ([OH^-]) and amounts to 10^-7 mol/l.
• if pH<7, the concentration of hydrogen ions is higher, and the water has acidic reaction
• if pH>7, the water is alkaline, i.e. the concentration of hydroxide ions exceeds that of hydrogen ions

The optimum pH level of drinking water is in the interval between 6,5 and 8,5. It means that drinking water should be either virtually neutral or moderately alkaline.

It is known that water treated with reverse osmosis tends to have low values of pH. This is in part related to the removal of hydrogen carbonate ions (HCO₃^-) which account for the alkaline reaction due to their partial hydrolysis.

Reverse Osmosis – Harm or Benefit

Reverse Osmosis water purifying method implies elimination of inorganic and macromolecular impurities – heavy metals, nitrates, pesticides, herbicides, as well as viruses and other potentially harmful microorganisms. Such water will by no means become a source of, e.g., cholera, as the cholera vibrio will be detained by the membrane.

At the same time, the method of reverse osmosis has a very serious shortcoming – its lack of selectivity. The harm related to RO is related to complete (or nearly complete) removal of elements vitally important for the human organism. In the first place, removal of calcium and magnesium ions, the major contributors to water hardness. Chronic consumption of water lacking these minerals is recognized as a significant risk factor for cardiovascular diseases and musculoskeletal pathology.

Besides, water treated by reverse osmosis is totally devoid of fluorine and other essential microelements. This fact, of course, may be regarded as harm only if the initial water contained adequate amounts of these elements before RO treatment.

Reverse osmosis removes most of the hydrogen carbonate (bicarbonate) ions from water, thus reducing the pH level. Low pH of the treated water is one of the major drawbacks of RO method.

These harmful side effects of reverse osmosis can be eliminated only if a compensation method is employed to replenish the deficiency of vitally important macro- and microelements.

In some cases, the initial parameters of untreated water allow mixing a certain part of it with water after RO (the so-called “bypass”). Possible ratios of bypass are determined by different factors, including the levels of contaminants in raw water.

Very often, however, the quality of raw water excludes effective usage of bypass. In such cases, the only way to bring the hollow, void osmotic water back to life is to enrich it with mineral salts and microelements. In particular, with Severyanka^® mineral supplements specially designed for this purpose. These supplements contain only cations and anions which are normally present in any natural water; the ionic composition of the enriched water complies with the strictest sanitary rules.