Desalination of water: methods and installations
Scientists believe that mankind has come to a period when conflicts for fresh water will erupt. Solve this problem only in one way - to find the best method of desalination of water.
What is water desalination?
Any liquid in its composition has a certainthe proportion of salts, microorganisms, minerals. Purification of natural or tap water removes harmful substances from it. But sometimes it has a large number of salts in the composition, which make it unfit for consumption.
Desalting of water is a decrease in concentrationdissolved in her salts. The procedure can be of a total nature when the liquid is deprived of any salt content or partial, when the prescribed amount of salt remains in it.
Complete desalination is carried out in the following ways:
- Distillation, thermal method.
- The method of ion exchange.
- Method of electrodialysis.
- Membrane reverse osmosis.
Partial salt removal is achieved when using such methods:
- Barite softening.
Methods of desalination of water requirefinancial, and energy. The choice of the treatment method depends on the degree of salt content in the original liquid, the capacity of the installation, the costs of the process components (heat, electricity, reagents). Each of the methods has its own advantages, disadvantages and occurs with the help of technical means.
Deprived of all impurities, water is used in manyproduction processes and is necessary for internal consumption of a very limited number of people. For domestic needs, demineralization of water is required to a certain extent. Most often, the liquid is softened by the cation method.
In the process, hard salts are replaced bycations of hydrogen, which, in turn, reacting, destroy bicarbonate ions. Products form a compound that is output as a gas. The degree of purification is estimated by the amount of calcium carbonate withdrawn.
Desalting water using the distillation method -the oldest and most common way to date. The plus is its universal accessibility, and the downside is the high cost of the process. To produce water without impurities, distillers are used. They are evaporators of several types, the difference between which is in the design, the type of energy used. The most common are steam and electric appliances, characterized by high cost and high energy consumption.
The apparatus is a boiler (or severalboilers) of low pressure, where the liquid turns into steam and separates the salt concentrate. In order for the water to get maximum purification, a slow boiling point is reached in the apparatus. Under this regime, heavy impurities do not enter the condensable distillate. One of the options to reduce costs is to increase the number of steps, but such an installation entails a large initial investment.
Equipment for distillation other than consumptiona lot of energy has an impressive value of all parts. High purity can be ensured by expensive pipes, fittings, heat exchangers, evaporators made of quartz or platinum. Other materials are not suitable.
The essence of the method is to allow water to pass throughan electric field, in this case, salt ions are transported - the cations are distributed to the side of the cathode, and the anions are distributed to the anode. The system has three compartments, which are formed by the cathode and anode diaphragms. In the middle compartment there is water prepared for desalination.
A constant electric current is passed through the flowthe current by which the salts are sorted into the cathode and anode diaphragms. The method is very expensive in terms of equipment costs and electricity costs, which is why it was not distributed.
The most reliable way that is achieveddesalination of water, - ion exchange method. Sedimentation of impurities in this way makes it possible to obtain a cleaner liquid in a short time, which is important in industrial desalination. The method is the most economical and gives the best cleaning result.
The method is based on removal from the liquidcations and anions of salts, as a result of purification, it is possible to achieve a different degree of demineralization, up to the complete removal of salt agents. Desalination of water by ion exchange occurs with the participation of ion exchangers, which are water insoluble polymers containing a mobile ion. Under the created conditions, the prepared polymer reacts with the ions of salts of the same sign. The ion exchangers placed in the aqueous medium swell, increasing by a factor of 1.5-2.
As time passes, the ion exchangers are collecteddissolved in water salts and compacted. Saturated ion exchangers are regenerated, after which they are purified. Products derived from saturated ion exchangers are called "eluates", and they contain solutions of salts and alkalis. Some of them are valuable substances, therefore they are disposed of as valuable components.
Technical progress and started to be observedlack of fresh water give birth to new technologies of desalination and desalination. A popular method is the method of reverse osmosis processing, reliability guarantees the development of membrane technologies. Industrial interest is caused by relatively low energy costs. Most of the devices of this principle are used for post-treatment of river water, where their effectiveness is repeatedly proved.
For household use, installations forDesalination of water, based on the principle of reverse osmosis, are suitable both in terms of energy consumption, and the quality of the product obtained. The principle of reverse osmosis is based on the transmission of water under pressure through a membrane that is impermeable to dissolved salts and other impurities. The process of desalination of water is provided by synthetic semipermeable membranes that can not hold back some gases dissolved in water (chlorine, carbon dioxide, etc.).
The reverse osmosis method purifies water from allimpurities, there is complete demineralization, which is harmful to the human body. In most cases, the average person has to choose between tap water or treated with a filter. The lesser evil is water, devoid of all natural components.
To date, in some countries alreadyThere are factories for the production of drinking water, where for demineralization the reverse osmosis method is used, and as additional post-treatment, dissolved gases are removed from it. To give it a normal state, close to the natural, in the plants in the purified water add the necessary salts in the adjusted concentration.
Pros and cons of the main methods
Each of the methods of desalination of water has both positive and negative qualities. Having considered them in detail, it is possible to understand which of them to give preference:
- Ion exchange helps to get the most purewater, the system is reliable and does not react to the degree of mineralization of the original liquid, it requires a small expenditure on equipment. The desalination process occurs with minimal loss of water flow. The minuses of the method include the rapid pollution of the environment by harmful chemicals, the high cost of the reagents themselves, the system quickly becomes dirty and requires frequent replacement of filters. Disposal of waste and filter parts is difficult.
- Distillation. Installations for desalination of water based on the thermal method are used without the use of chemicals, demonstrate good quality of the received liquid, heat released during operation can be used for other needs. A distinctive feature of this method is the possibility of eliminating dissolved gases in water. Minuses of the method include: large energy costs, the need for water preparation, the cost of maintenance of the installation (cleaning of all parts), the high cost of equipment.
- Membrane plants are unpretentiousto the initial state of water, the process does not require chemical reagents, easy to maintain. Negative qualities are: preparation of water for processing, large volume of water to ensure the operation of devices, a large consumption of electricity, which affects the cost of the final product.
Desalting at home
Water filtration is the most accessible method of post-treatment. For desalting well or sea fluid at home there are two common ways:
- The container with water should be placed in the freezer compartment andleave to incomplete freezing. Salt with a part of the liquid does not freeze, the ice should be melt, and can be used immediately. For further cleaning, it is worthwhile to pass the melt water through any household filter. The method is called cold distillation.
- Evaporation. Take two containers of different sizes, in a large pour sea / salt water, a smaller one is left empty and placed in a large bowl. The entire structure can be put to heat on a plate or left in the sun, previously covered with a lid. It is necessary to achieve a slow boiling of salt water. Vapors devoid of salt will concentrate in an empty container. The process of evaporation in the sun will proceed much more slowly. With this method, a rather small volume of drinking water is obtained.
Desalination and desalination of water by handicraft methods is possible, but not fruitful. The best option would be to purchase a household cleaner.
For domestic needs, more often than not, systems are needed for the post-treatment of water. Water filtration can be carried out in several ways:
- The simplest and most accessible is a jug with replaceable filters.
- Nozzle with filter on the tap.
- Table filters for water.
- Embedded cleaning systemsliquids depending on the location (only in the kitchen, at the point of entry of the water supply to the house, multistage filters for cleaning water from the artesian well, etc.).
None of the household systems can fullyEliminate salt from the liquid, but soften the hard water in the state. In this case it is necessary to know what elements it is saturated with in order to select a system, water cartridges, filters or reagents. Demineralization process requires spacecraft, large area for installation, large financial investments and availability of system maintenance, which is not available to a wide range of consumers.
Types of household cleaning
To date, the following types of water treatment are widely used:
- Coal filtration. The device is a container filled with wood, activated or hard coal. The water passed through such a filter is cleared of chlorine, oily elements, pesticides, microorganisms, bacteria, etc. The filter is affordable, durable and easy to operate.
- Fine cleaning. This type of filters is divided into two types - single-function and multifunctional. At any choice maintenance is required - constantly change cartridges for water, make replacement of armature, etc.
- Coarse cleaning. Eliminate large particles of contaminants (sand, rust, sediment, etc.).
- Deep cleaning. This type of filters include systems with reverse osmosis, multistage filters, etc.
In most regions of Russia, onlyadditional water treatment, since there is enough water in the country. The only region where there may be a shortage of fresh water is Crimea, where industrial plants for desalination of sea water may be needed. All process devices have a patent. Desalination and desalination of water should be carried out on scientifically based methods with mandatory testing of results in the laboratory.