Today there are chemical-physical, mechanical and biological wastewater treatment. They differ in the nature of the processes underlying them, as well as in the technological parameters. Let us further consider what mechanical methods of wastewater treatment exist.
General information
Wastewater is used as a resource for industrial water supply. For industrial use, they must undergo special training. During it, wastewater is purified from mechanical impurities. For this, special facilities are used. They vary in type of construction and other parameters.
Types of structures
When filtering are used:
- Mechanical grilles for wastewater treatment.
- Sand traps.
- Membrane Elements
- Primary sedimentation tanks.
- Septic tanks.
These structures are used in a certain sequence.
The specifics of the mechanical wastewater treatment scheme
At the first stage, the detention of large contaminants of mineral and organic origin is carried out. For this, lattices are used. For maximum removal of coarse elements, sieves are used. The maximum width of the holes in the grill is 16 mm. The components delayed by it are crushed. Then they are sent along with the sludge from the treatment plant for processing. The separated solid components can also be transported to industrial and domestic waste treatment sites. After primary filtration, the effluent is passed through sand traps. Small particles of contaminants stand out here. This, in particular, the breakdown of glass, slag, sand, etc. Under the influence of gravity, they settle. Then the fat traps are involved. Using these structures, hydrophobic substances are removed from the surface of the water by flotation. The sand released when passing through sand traps is usually stored and then used in road works. For deeper filtration, membrane elements are used. This technology has recently become quite widespread. Mechanical wastewater treatment by the membrane method ensures the return of raw materials to the production cycle.
Precipitation method
Mechanical wastewater treatment by this method can be used, for example, to eliminate suspended particles. Filtering can be organized in two ways. The first involves the use of gravity pollution. Under its influence, in the process of sedimentation, suspended particles settle to the bottom. Another method involves the use of centrifugal force. Mechanical wastewater treatment by such methods eliminates insoluble elements, the value of which is more than a few hundred millimeters. In the process of preparing raw materials for reuse in production, multi-stage sumps are often used. Partially filtered raw materials at one stage are fed to the next head.
Flotation
Mechanical wastewater treatment by this method involves the transfer of polluting elements to the surface using air bubbles. As a result of flotation, foam formations appear. The contaminants contained in them are subsequently removed using scrapers. Air bubbles can be obtained mechanically. For this, nozzles or turbines, electroflotation, etc. are used.
The use of porous materials
This method is considered by far the most common. With the help of porous materials, the sediment of mechanical treatment of oily wastewater can be eliminated. When filtering, mesh or materials of a special structure are used. This method is relevant for cases when it is necessary to use recycled water.
Sand Trap Features
From the sewer network, the effluents enter sieves and grids. Here they are filtered. Large items - kitchen waste, rags, paper, etc. - are held. Subsequently, they are removed and taken out for neutralization and disinfection. Filtered effluents go to sand traps. They are designed to protect sedimentation tanks from contamination with mineral particles. Sand trap designs may vary. It depends on the volume of incoming wastewater. Sand traps can be vertical and horizontal, as well as slotted. The first two types are used in wastewater treatment plants, and the latter on canals. Vertical and horizontal sand traps are installed if the volume of incoming raw materials is more than 300 m 3 / day. Sand traps are performed in two sections. This is necessary so that in the repair process of one part the second could function. In a horizontal design, the process of deposition of mineral particles occurs when the fluid moves at a speed of 0.1 m / s. In vertical sand traps, the separation of impurities occurs when the effluent rises. The velocity of the fluid in this case is 0.05 m / s.
Sedimentation tanks
They are considered the main, and therefore the most common category of filtration facilities. In sedimentation tanks, horizontal or vertical movement of water may be provided. With a large amount of raw materials, continuous structures are used. If the water flow per day is not more than 50 thousand m3, vertical sedimentation tanks are used. The work of such structures is as follows. Drains are fed through the central pipe to the bottom of the structure. The output stream moves up to the collection and discharge trays. During the lifting process, elements with a high specific gravity fall out of the water. Filtration also uses radial type sedimentation tanks.
Processing specifics
The industry uses primary and secondary sedimentation tanks. Some are installed in front of structures for biological filtration, others, respectively, for the clarification of effluents after them. Secondary sedimentation tanks are also contact. If the terrain allows drains to be directed into water bodies, then a disinfection tank should be provided in the filtration scheme. Suspensions isolated in the primary sump decay. The resulting mass is dried at special sites, and then used as agricultural fertilizer.
Aerators and bio-coagulators
These types of facilities are designed for the reagent-free treatment of impurities with excess sludge by blowing water with compressed air. Aerators are made in the form of rectangular tanks, in which partitions are installed that extend the path of movement of raw materials. These structures help to increase the level of clarification, the elimination of liquid fat. In aerators, mechanical treatment of oily wastewater is often carried out. These facilities also prepare raw materials for the next stage of filtration. Aeration is a process of blowing water for 10-30 minutes. Air is supplied through filters or openings in the pipes. Biocoagulators are made in the form of a horizontal or vertical sump with an annular zone and a central compartment. It mixes and contacts excessively activated sludge with water. To reduce air consumption in the corners of the Central chamber provide 4 box triangular shape. At the same time, horizontal containers with filter plates are installed at a depth of 2.5-3 m. Water enters the central pipe through the inlet tray.
Action facilities
Raw materials are introduced into the coagulator below the level of the location of the filter plates. This prevents them from clogging with large particles. The sludge concentration is approximately 7 g / l. Moreover, its amount should be about 1% of the waste water flow. Compressed air is supplied to the filter plates. With its help, activated sludge is mixed with wastewater and maintained in suspension. In this case, the aeration intensity should be kept within 1.8-2 m 2 / h. The liquid treated with air begins to move along the circulation boxes, which are installed at the corners of the central chamber. Its walls are longer than containers. A suspended sludge layer forms in the annular zone of the coagulator between the outer surfaces and the central chamber. Its level will depend on the flow of wastewater. This suspended layer contributes to coagulation, equalization of the rate of rise of raw materials and the elimination of the direction of vertical fluid movement.
Conclusion
Mechanical cleaning is the most important process in the work of an industrial enterprise. It is extremely necessary because it allows you to prepare the liquid for the subsequent stages of filtration. In no case should mechanical cleaning be neglected. Otherwise, subsequent stages of filtration will be significantly difficult. Moreover, the presence of large particles of contaminants can disrupt the operation of biological treatment plants. This, in turn, will entail additional costs for repairs or even equipment replacement. Filtration facilities must be selected in accordance with the specifics of the enterprise, the volume of effluents, as well as the need for recycling treated water.