There is currently no single universal method. The selection of a suitable wastewater disinfection method depends on the results of preliminary laboratory tests. Various methods are used in private, industrial and public drains.
Necessary degree of cleaning
In some cases, it is enough to filter the water to a technical level. Certain industries can simplify cleaning mechanisms. This usually happens in factories where the level of biological pollution is not critical. The initial filtration procedures, regardless of the object and the final purpose of the water as a whole, are of the same type. Differences begin only in the final stage, when the necessary degree of purification is determined.
For example, completely different requirements today are imposed on the disinfection of wastewater when converting domestic wastewater and liquids from natural sources to clean drinking water. A number of mandatory sanitary rules and norms are already observed here. In general, the procedure becomes an order of magnitude more complicated and more expensive. For this reason, each city or industrial treatment plant has its own laboratory, experts in which regularly monitor the quality of water filtration.
Current methods
The purpose of these procedures is to reduce the risk of massive infectious diseases, as well as to eliminate the prerequisites for a negative impact on human health. All wastewater disinfection methods can be divided into four large groups.
- Physical cleaning. Includes exposure to water by electromagnetic radiation or electricity.
- Chemical cleaning. The main work is done through the introduction of various elements and compounds.
- Physico-chemical cleaning. It implies the use of joint filtering methods.
- Biological treatment. It is represented by methods of natural and artificial biocenosis.
As practice shows, the sequential use of various cleaning methods is most effective. If there is a need, then not only the water itself is disinfected, but also objects that came into direct contact with it, for example, surgical equipment, materials and devices in the food and biochemical industry. For technical needs, more stringent cleaning methods are allowed.
Physical radiation disinfection
This group of options is considered quite simple and inexpensive to operate. The most commonly used infrared and ionizing systems, as well as UV emitters. Wastewater disinfection using the last of the listed types of equipment directly affects the DNA of microorganisms living in the liquid. Ultraviolet radiation is invisible to the human eye, however, the directed influence of waves with a length of about 255 nm destroys the structure of all potentially dangerous bacteria and viruses.
Of the advantages of this method, the absence of negative residual effects can be noted. The low cost of equipment has led to the fact that this method of cleaning has become one of the most popular in the industry. In some cases, UV wastewater disinfection is combined with exposure to direct sunlight. Forced aeration in open-air reservoirs also helps to stop the growth of microorganisms and destroy them.
Infrared radiation is considered an indirect method, since it does not have a bactericidal effect. Liquid disinfection occurs due to the heating of physical objects and various accumulations of contaminants. Ionizing radiation is used only in situations where other options do not bring the desired result. The method is very expensive and difficult to use.
Features of wastewater disinfection with ultraviolet
Using the example of this method, we can consider the main installation device and the principle of use. In any design, there is a main unit - an ultraviolet camera or a disinfection chamber. Spectral electromagnetic waves of a certain frequency are generated inside the device. The material of the chamber is stainless steel, which is suitable for use in the food industry. The ballasts themselves are located in the so-called electronic ballasts. Automation is provided by the control system unit, and the chemical washing unit for quartz covers is responsible for the smooth operation.
The UV wastewater disinfection unit is suitable in almost all cases. However, turbid and heavily contaminated liquids can be treated slightly worse. Such water is preliminarily prepared by other methods for subsequent treatment with ultraviolet radiation. Preliminary purification of the fluid from various mechanical impurities, stained elements, fungi and cell walls can increase the effectiveness of UV exposure. The environmental friendliness and safety of this processing method makes the liquid safe for human consumption, since the chemical and organoleptic characteristics remain unchanged.
Other physical cleaning methods
The options below are often combined with ultraviolet disinfection of wastewater. Among other physical cleaning methods, heat exposure, electric currents of high and ultrahigh frequencies, as well as ultrasound, are distinguished. The latter, for example, due to the high oscillation frequency of the supplied signal destroys the cell walls of viruses and bacteria. Ultrasonic devices work most effectively in combination with bactericides added to water.
The following method is familiar to everyone at the household level: the thermal effect works with simple boiling water in the kettle. The complete death of all possible microorganisms occurs only after 30-40 minutes of their being in boiling liquid. Moreover, this method is too costly from a financial point of view. To heat a large volume of water requires a lot of energy. Viruses, bacteria and their spores are able to survive for a short period of time successfully in boiling water.
The functioning of the installations of electric currents of high and ultrahigh conductivity in many ways resembles the previous method. Here, the pathogenic microorganisms are also affected by heating the liquid. This type of wastewater disinfection unit works like a conventional microwave oven. Ultra-high frequencies of electromagnetic field oscillations adversely affect the cellular structure of bacteria and viruses.
Chemical disinfection methods
There are a large number of elements that could with high efficiency destroy all the organics that live in the liquid. These include bromine and iodine compounds, ozone and hydrogen peroxide. However, first of all, chemical disinfection of wastewater with chlorine comes to mind. This substance is used much more often than others. Chlorine gas, calcium or sodium hypochlorite, chlorine dioxide, bromine chloride, nirtan, chloramine or bleach may be used. The main problem is that all of these substances harm the human body. For this reason, additional disinfection of water after the use of chlorine is required.
A gentle cleaning option is also allowed. The least harmful to humans chlorine dioxide copes with the destruction of viruses and bacteria somewhat worse than analogues. If we talk about other elements and compounds for disinfecting wastewater, we can only recall potassium permanganate, peracetic acid and similar chemical disinfectants. However, very weak bactericidal properties do not allow them to compete with chlorine and its derivatives. Sometimes certain metals are used, for example, copper compounds and silver. They are capable of secreting ions with bactericidal properties. The effectiveness of metal disinfection is quite low, and therefore the method is used only as an additional one.
Features of the use of iodine and bromine
These bactericidal agents have long been used for various medical purposes. Nevertheless, the same iodine is poorly distributed in liquids on its own, which is why it is necessary to use organic compounds of this element in the treatment and disinfection of wastewater. After the procedures, a very specific smell remains. For this reason, it is advisable to use iodine only for industrial water, but not for drinking. In large industrial volumes, such compounds are impractical due to their low distribution. Iodine is not resistant to sunlight and does not react with ammonia, like the same chlorine.
Bromine appears in a more favorable light. It is non-toxic, devoid of any characteristic odor and completely harmless to humans. With all its advantages, bromine requires the use of higher concentrations for the same amount of liquid compared to iodine. High bactericidal rates are achieved due to the oxidation of the substance. Experts advise adding bromine or iodine in places where the same water is used many times. The high toxicity values of the by-products formed during the work still do not allow the use of these inexpensive elements everywhere.
Ozone disinfection
The method is actively used by enterprises in Europe and North America. Ozone compounds easily cope with a wide range of harmful viruses, bacteria, fungi and other pathogenic microorganisms. If we talk about integrated wastewater disinfection systems, then this method can be called final or finish. During ozonation, the liquid has already been carefully filtered and processed using other physical and chemical cleaning methods. Among the negative aspects of using this method, the poor solubility of this modification of oxygen in water, the risk of explosion of components, and the increased level of released toxins can be noted. By-products that result from the cleaning process can harm humans and the environment.
The device diagram consists immediately of six main blocks. A complete list is given below:
- Ozone generators. Located directly in front of the primary processing tank. Provide the remaining blocks with this element.
- Compartments of primary and secondary ozonation.
- Block for accumulation of sludge.
- Special sand filter. It is usually located between the primary and secondary ozonation compartments.
- UV processing unit.
- Sorption filter.
Physicochemical methods of disinfection
In the general case, it can be said that the qualitative level of various effects on the liquid often rises due to the addition of any substances and elements that have the necessary bactericidal properties. Sometimes a direct electric current is also used in a special wastewater disinfection unit. The discharge is perfectly in contact with viruses and bacteria in the liquid. The addition of certain chemical elements to water, which is subjected to a constant electric current, can cause the molecules to dissociate into ions. Experts attribute this cleaning method to physicochemical.
Effective destruction of cells of pathogenic microorganisms is achieved due to the participation of the viruses and bacteria themselves in the process of dissociation of cells. Often, hydrolysis and ionization of water are also carried out. The joint work of physical and chemical methods can also be traced by heating the liquid. For a better level of wastewater disinfection, high temperatures are combined with the addition of certain ingredients, such as simple soap or alkali. In more complex cases, special disinfectant formulations developed and tested in laboratories are already in use.
The use of biocenoses for cleaning
A relatively new method. Disinfection of sewage sludge occurs due to anaerobic and aerobic bacteria, for which various biological contaminants serve as food. Special enzymes allow you to break down pathogenic microorganisms into simple chemical compounds. After that, the bacteria absorb all the organics found. Specialists artificially cultivate the culture of such "cleaners", creating suitable conditions for their existence and reproduction. The habitat of bacteria is as close to natural as possible. Typically, this method is used one of the last, when the water has already been sufficiently treated with ultraviolet radiation, chlorination, ozonation or ultrasound.
It is simply impossible to choose the best cleaning method that would be considered universal. For the most part, it all depends on the specific purpose of the disinfected water, as well as the results of chemical and bacteriological laboratory analysis. Basically, two to three of the most effective methods are selected. An interesting nuance is that bacteria and viruses can adapt over time and gain immunity to certain influences. That is why specialists regularly take samples of wastewater and check it for a sufficient level of purification from pathogenic microorganisms.