Water is widely used in a wide variety of industrial processes. After industrial use, the water must be cleaned of contaminants, after which it is returned to the environment. For this purpose, complexes of treatment facilities are installed at enterprises.
The wastewater treatment procedure includes several stages. Their number and depth of purification in general are largely determined by the degree of contamination of the liquid, as well as the system of quality standards existing in a particular industry. Typically, cleaning is divided into mechanical and biological stages, followed by a physicochemical stage. Disinfection of waste water completes the process.
The mechanical stage is the preliminary treatment of water entering the treatment system. Here, the trapping and retention of harmful insoluble impurities takes place, which is important for the subsequent stage of biological treatment. The system for the retention of harmful substances consists of filter grids, sand traps, membranes, sedimentation tanks and septic tanks. This stage of the technological process allows for a rather rough primary cleaning.
Grids and sieves make it possible to retain relatively large particles of mineral origin. Everything that accumulates on the grates is crushed at a subsequent stage and disposed of together with sediments in places where industrial and domestic waste is processed. Smaller particles naturally settle in so-called grit traps. Water purified in this way passes through special membranes and enters the sedimentation tanks.
Biological wastewater treatment removes organic impurities from them: bacteria and microorganisms. Two methods of such cleaning are used - passive and active. The weighed organic matter is preliminarily settled in sedimentation tanks, which resemble massive reinforced concrete reservoirs. From here, organic compounds are sent to secondary treatment devices, where the active substances are completely neutralized.
Methods of physical and chemical purification make it possible to remove dissolved impurities and even the remaining suspension from water. The main processes of this stage are coagulation, sorption, flotation, neutralization, electrochemical purification, evaporation and crystallization. The previously formed sediment is also dehydrated, for which water is passed through special centrifuges, adding reagents.
The final stage of purification is the disinfection of wastewater by means of their disinfection. Most often, devices for ultraviolet irradiation of water are used for this purpose. After such treatment, wastewater is discharged onto the terrain or otherwise discharged into the external environment. The enterprises have special services that ensure the operation of treatment facilities and control the quality of water after their treatment.