Many types of water purification devices offered in the contemporary market often bewilders the consumer when choosing the device you need. Meanwhile, this problem can be solved relatively easy if taking into account all the required parameters such as:
1) origin and composition of source water, in particular it is necessary to determine what contaminants should (or preferably) the water be purified from.
This part of the problem is solved by the chemical analysis of the water to be purified;
2) the quantity of purified water required by the consumer (purification system performance);
3) after determining the objective pursued by the water purification, one should pay attention to the fact that the different devices normally use a number of physical and chemical principles of purification and improvement of the water properties, different in both varying effectiveness on certain parameters of the water and technological characteristics:
• surplus pressure of water needed for work
• need and frequency of regeneration
• cyclical or continuous character of operation
• price, etc.
It is necessary to pay attention to the availability of certificates a) hygienic one confirming harmlessness and effectiveness of the device, and b) for compliance with the requirements set.
Below is a brief instruction on the principles of operation of various types of water purification devices.
1. Filtration - water purification from mechanical impurities, such as sand, rust particles etc. Implemented by filtering the water through the porous or fibrous materials with different effective diameter of the pores (100 to 0,045 microns). The degree of water purification filter performance depends naturally on the ratio between the sizes of pollutant particles and the pore diameter. It should also be borne in mind that the filters with a pore diameter of 0.45 microns or less provide a reliable disinfection of water through entrapment of bacterial particles.
2. Sorption - removal of unwanted chemicals (mostly organic, some heavy metals), thus achieving improved taste, eliminating odour by binding these substances due to intermolecular forces. The most commonly used sorbent is activated carbon of various origin, or some other natural materials. Sorption efficiency depends on the interaction surface. In order to prevent fouling of microorganisms coating with carbon particles of silver ions, iodine and other disinfecting agents are sometimes used. Devices operating according to the sorption principle characterized by the concept of "capacity" - a certain amount of certain contaminants that can be absorbed by a given amount of sorbent. After exceeding this resource the efficiency of the device decreases, and pollution of water with the substances previously absorbed by the sorbent is possible.
3. Ion exchange - replacement of one (unwanted) ions with other ions (neutral), for example, calcium and magnesium - with sodium in case of water softening. Ion exchange is often used to remove specific contaminants such as heavy metals, fluorides, etc., as well as to introduce certain substances in the water, where necessary, (fluoride, iodine). Devices operating according to this principle require periodic regeneration, and accordingly, the flow rate of certain reagents. Check with the representative of the manufacturer or vendor the possibility for purchasing these reagents, as well as regeneration mode, the ability to automate this process.
4. Reverse osmosis – water purification by filtration through a semipermeable membrane with a molecular pore size (from 10 to 500 nm). Such filtering typically requires high water pressure, which is created by special pumps, providing, depending on the pore diameter, the partial or substantial complete removal of all impurities, including mineral components. These devices are often used for desalination. Reverse osmosis devices of high performance are quite expensive, so they are often used in water supply systems for final purification of the water used for drinking only.
5. For water disinfection, ultraviolet irradiation, the water treatment with ozone, active chlorine compounds, silver ions or iodine are used. Typically, after disinfection by particular way an additional treatment is required through passing water through a filter containing activated carbon for the removal of microorganism decay products and ions used for disinfection.