Scientists believe that humanity has come to a period when conflicts will erupt over fresh water. There is only one way to solve this problem - to find the optimal method for desalting water.
What is desalination
Any liquid in its composition has a certain share of salts, microorganisms, minerals. Purification of natural or tap water removes harmful substances from it. But sometimes it contains a large amount of salts, which make it unsuitable for consumption.
Desalination of water is a decrease in the concentration of salts dissolved in it. The procedure can be total in nature, when the liquid is deprived of any salt content or partial, when a predetermined amount of salt remains in it.
Methods
Complete desalination is carried out in the following ways:
- Distillation, thermal method.
- By ion exchange method.
- The method of electrodialysis.
- Membrane reverse osmosis.
Partial salt removal is achieved by using such methods:
- Liming.
- Barite softening.
- H-cationization.
- Freezing
Methods of water desalination require both financial and energy costs. The choice of processing method depends on the degree of salt content in the initial liquid, the performance of the installation, the costs of the components of the process (heat, electricity, reagents). Each of the methods has its advantages, disadvantages and occurs with the help of technical means.
Partial desalination
Deprived of all impurities, water is used in many production processes and is required for internal use by a very limited number of people. For domestic needs, demineralization of water to a certain extent is required. Most often, the fluid softens by cationization.
In the process, hard salts are replaced by hydrogen cations, which, in turn, react, destroy bicarbonate ions. The products form a compound that is discharged in the form of gas. The degree of purification is estimated by the amount of excreted calcium carbonate.
Water distillation
Desalting water using the distillation method is the oldest and most common method to date. The plus is its universal availability, and the minus is the high cost of the process. To obtain water without impurities, distillers are used. They are several types of evaporators, the difference between which is in the design, the type of energy used. The most common are steam and electric devices, which are distinguished by high cost and high energy consumption.
The device is a boiler (or several boilers) of low pressure, where the liquid turns into steam and separates the salt concentrate. In order for the water to receive maximum purification, a slow boiling point is reached in the apparatus. In this mode, heavy impurities do not enter the condensing distillate. One option to reduce the cost is to increase the number of steps, but such an installation entails a large initial investment.
Distillation equipment, in addition to consuming large amounts of energy, has an impressive cost for all parts. To ensure a high degree of purity can expensive pipes, fittings, heat exchangers, evaporators made of quartz or platinum. Other materials are unsuitable.
Electrochemical method
The essence of the method is the passage of water through an electric field, with the transfer of salt ions - cations are distributed towards the cathode, and anions - to the anode. The system has three compartments, which are formed using the cathode and anode diaphragms. In the middle compartment there is water prepared for desalination.
A constant electric current is passed through the stream, with the help of which the salts are sorted into the cathode and anode diaphragms. The method is very expensive in terms of equipment costs and energy costs, and therefore has not received distribution.
Ion exchange
The most reliable way that desalination of water is achieved is the ion exchange method. Precipitation of impurities in this way allows a cleaner liquid to be obtained in a short time, which is important for industrial desalination. The method is the most cost-effective and gives the best cleaning result.
The method is based on the removal of cations and salt anions from a liquid; as a result of purification, various degrees of demineralization can be achieved, 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 enters into an exchange reaction with ions of salts of the same sign. Ionites placed in an aqueous medium swell, increasing in size by 1.5–2 times.
As time passes, the ion exchangers collect the salts dissolved in the water and condense. Saturated ion exchangers regenerate, after which they are purified. Products obtained from saturated ion exchangers are called "eluates", they include solutions of salts and alkalis. Some of them are valuable substances, so they are disposed of as valuable components.
Reverse osmosis
Technological advances and the shortage of fresh water that has begun to occur are giving rise to new desalination and desalination technologies. A reverse osmosis treatment method is becoming a popular method; reliability is guaranteed by the development of membrane technologies. Industrial interest is caused by relatively low energy costs. Most devices of this principle are used for the purification of river water, where their effectiveness has been repeatedly proven.
For domestic use, water desalination plants based on the principle of reverse osmosis are suitable both in terms of energy consumption and the quality of the resulting product. The principle of reverse osmosis is based on the passage of water under pressure through a membrane that is impervious to dissolved salts and other impurities. The process of desalination of water is provided by synthetic semipermeable membranes, which cannot be retained by some gases dissolved in water (chlorine, carbon dioxide, etc.).
The reverse osmosis method purifies water from all impurities; complete demineralization occurs, which is harmful to the human body. In most cases, the average person has to choose between tap water or treated with some kind of filter. The lesser evil is water, devoid of all natural components.
Today, in some countries, there are already factories for the production of drinking water, where the reverse osmosis method is used for desalination, and dissolved gases are removed from it as additional purification. To give it a normal state, close to natural, at the enterprises in the purified water add the necessary salts in a verified concentration.
Pros and Cons of Basic Methods
Each of the desalination methods of water has both positive and negative qualities. Having examined them in detail, you can understand which one to give preference to:
- Ion exchange helps to get the cleanest water, the system is reliable and does not respond to the degree of mineralization of the initial liquid, requires little equipment. The desalination process occurs with minimal loss of water flow. The disadvantages of the method include the rapid pollution of the environment with harmful chemicals, the high cost of the reagents themselves, the system is quickly contaminated and requires frequent replacement of filters. Disposal of waste and filter parts is difficult.
- Distillation. Thermal desalination plants based on the thermal method are used without the use of chemicals, demonstrate the good quality of the liquid obtained, the heat generated during operation can be used for other needs. A distinctive feature of this method is the ability to eliminate gases dissolved in water. The disadvantages of the method include: high energy consumption, the need for water treatment, the cost of maintaining the installation (cleaning all parts), the high cost of the equipment.
- Membrane plants are unpretentious to the initial state of water, the process does not require chemical reagents, easy to maintain. Negative qualities are: preparation of water for the treatment process, a large amount of water to ensure the operation of the apparatus, high energy consumption, which affects the cost of the final product.
Desalination at home
Water filtration is the most affordable way of post-treatment. To desalinate a well or sea fluid at home, there are two common ways:
- Place a container of water in the freezer and leave until incomplete freezing. Salt with part of the liquid will not freeze, the ice should be melted, and you can use immediately. For additional cleaning, it is worth letting melt water through any household filter. The method is called cold distillation.
- Evaporation. Take two containers of different sizes, pour sea / salt water into a larger one, leave the smaller one empty and place in a large bowl. The entire structure can be placed for heating on a stove or left in the sun, having previously closed the lid. It is necessary to achieve a slow boiling of salt water. Salt-free vapors will be concentrated in an empty container. The process of evaporation in the sun will be much slower. With this method, a rather small amount of drinking water is obtained.
Desalination and desalination of water by artisanal methods is possible, but ineffective. The best option would be to purchase a household cleaning plant.
Domestic installation
For domestic needs, water treatment systems are most often needed. Water filtration can be carried out in several ways:
- The simplest and most affordable is a jug with replaceable filters.
- Filter nozzle for crane.
- Bench-top water filters.
- Embedded systems that clean the liquid depending on the location (only in the kitchen, at the point of entry of the water supply to the house, multi-stage filters for cleaning water from an artesian well, etc.).
None of the household systems can completely remove salts from the liquid, but soften hard water in a state. In this case, you need to know what elements it is saturated with in order to choose a system, cartridges for water, filters or reagents. The desalination process requires large-sized apparatuses, a large area for installation, large financial investments and the availability of system maintenance, which is not available for a wide range of consumers.
Types of household cleaning
Today, the following types of water treatment are widely used:
- Coal filtration. The device is a container filled with charcoal, activated or coal. Water passing through such a filter is cleaned of chlorine, oil-containing elements, pesticides, microorganisms, bacteria, etc. The filter is affordable, durable and easy to use.
- Fine cleaning. This type of filter is divided into two types - single-function and multi-function. With any choice, maintenance is required - constantly change water cartridges, replace valves, etc.
- Rough cleaning. Eliminate large particles of pollution (sand, rust, sediment, etc.).
- Deep cleaning. This type of filter includes reverse osmosis systems, multi-stage filters, etc.
In most regions of Russia, only additional water treatment is required, since there are enough water resources in the country. The only region where there may be a shortage of fresh water is the Crimea, which may require industrial plants for desalination of sea water. All devices for carrying out processes have a patent. Desalination and desalination of water should be carried out using scientifically sound methods with mandatory testing of the results in laboratory conditions.