Mechanical Wastewater Treatment: Ways, Features and Scheme

To date, there are chemical-physical, mechanical and biological wastewater treatment. They differ in the nature of the processes underlying them, as well as in technological parameters. Let us further consider what are the mechanical methods of wastewater treatment.

General information

Wastewater is used as a resource for industrial water supply. To be used for production purposes, they must undergo special training. During this process, waste water is treated from mechanical impurities. Special constructions are used for this. They differ in the type of structures and other parameters.

Types of structures

At filtration are used:

1. Mechanical grilles for wastewater treatment.
2. Sandpipers.
3. Membrane elements.
4. Primary clarifiers.
5. Septic tanks.

These structures are used in a certain sequence.

Specificity of the scheme of mechanical sewage treatment

At the first stage, large-scale pollution of mineral and organic origin is seized. Grids are used for this. To maximize the removal of coarse particles, sieves are used. The maximum width of the holes in the grille is 16 mm. The components detained by it are subjected to fragmentation. Then they are sent along with the precipitation from treatment plants for processing. Also, the separated solid components can be exported to the treatment sites for industrial and domestic waste. After the primary filtration, the effluents are passed through the sand trap. Small particles of contaminants are emitted here. This, in particular, the battle of glass, slag, sand, etc. Under the influence of gravity they settle. Then the greasers are activated. With the help of these structures, hydrophobic substances are removed from the water surface by flotation. Sand, isolated when passing through the sand trap, is usually stored, and then used in road works. Membrane elements are used for deeper filtration. This technology has recently become quite widespread. Mechanical treatment of sewage by the membrane method ensures the return of raw materials to the production cycle.

Method of precipitation

Mechanical treatment of wastewater in this way can be used, for example, to eliminate suspended particles. Filtering can be organized in two ways. The first involves the use of gravity of pollution. Under its influence in the settling process, the suspended particles settle to the bottom. Another way involves the use of centrifugal force. Mechanical treatment of waste water by such methods allows to eliminate insoluble elements, the size of which is more than several hundred millimeters. In the process of preparation of raw materials for reuse in production, settling tanks of a multistage type are often used. Partially filtered raw materials are fed to the next pressure in one stage.

Flotation

Mechanical treatment of waste water in this way involves the transfer of pollutants to the surface with air bubbles. As a result of flotation, foam formations appear. The contaminants contained in them are subsequently removed with the help of scrapers. Air bubbles can be obtained by a mechanical method. For this purpose, nozzles or turbines, electroflotation, etc. are used.

Application of porous materials

This method is considered today the most common. With the help of porous materials, the sediment of mechanical cleaning of oily wastewater can be eliminated. When using filtration, grids or materials of a special structure are used. This method is relevant for cases when it is necessary to use recycled water.

Features of the sand

From the sewerage network, the drains enter the screens and screens. Here they are filtered. Large elements - kitchen waste, rags, paper and other - are retained. Subsequently, they are removed and taken out for decontamination and disinfection. The filtered effluents enter the sand trap. They are designed to protect sedimentation tanks from contamination with mineral particles. The designs of the pesos can be different. This depends on the amount of incoming sewage. Sand trap can be vertical and horizontal, as well as slotted. The first two types are used in treatment plants, and the latter - on canals. Vertical and horizontal sand pickers are installed if the incoming feed volume is more than 300 m ³ / day. Sandboxes are made in two-section. This is necessary in order that during the repair of one part the second could function. In a horizontal structure, the process of precipitation of mineral particles occurs when the fluid moves at a velocity of 0.1 m / sec. In vertical sand pickers, the release of impurities is carried out when the sewage is raised. The velocity of the fluid is 0.05 m / sec.

Sedimentation tanks

They are considered the main, and therefore the most common category of filtration structures. In the sediment bowls, horizontal or vertical movement of water may be provided. With a large volume of raw materials, continuous structures are used. If the water flow per day is not more than 50 thousand m3, vertical settling tanks are used. The work of such structures is as follows. The drains are fed along the central pipe to the bottom of the structure. The outflow moves upwards to the collecting and outgoing trays. In the process of recovery, elements with a large specific gravity fall out of the water. Also, during filtration, septic tanks of the radial type are used.

Processing Specificity

Primary and secondary settling tanks are used in industry. 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 conditions of the terrain allow the drains to be sent to water bodies, then a decontamination tank must be provided in the filtration scheme. Suspensions separated in the primary sedimentation tank, rot. The resulting mass is dried on special sites, and then used as an agricultural fertilizer.

Aerators and biocoagulators

The facilities of these types are designed for the non-reagent treatment of impurities with excess sludge by purging water with compressed air. The aerators are made in the form of rectangular tanks, in which there are partitions that extend the path of the raw material movement. These facilities contribute to increasing the level of clarification, elimination of liquid fat. In aerators, mechanical cleaning of oily wastewater is often carried out. In these facilities, raw materials are also prepared 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 pipes. Biocoagulators are made in the form of a horizontal or vertical sedimentation tank with a ring zone and a central compartment. It mixes and contacts excessively activated sludge with water. To reduce the air consumption in the corners of the central chamber, there are 4 boxes of triangular shape. In this case, horizontal containers with filter plates are installed at a depth of 2.5-3 m. Water enters the central pipe through the supply chute.

Effects of structures

The feed is introduced into the coalescer below the level of the filter plates. This prevents their clogging with coarse particles. The concentration of sludge is about 7 g / l. At the same time, its quantity should be about 1% of the discharge of waste water. Compressed air is supplied to the filter plates. With it, the activated sludge is mixed with wastewater and maintained in a suspended state. At the same time, the aeration intensity should be kept within 1.8-2 m ² / h. The liquid treated with air starts to move through the circulation boxes, which are installed at the corners of the central chamber. Its walls are longer than the tanks. In the annular zone of the coagulator, between the outer surfaces and the central chamber, a suspended silt layer is formed. Its level will depend on the consumption of waste water. This weighted layer promotes coagulation, equalization of the rate of recovery of raw materials and 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, since it allows you to prepare the liquid for the subsequent stages of filtration. Mechanical cleaning in any case can not be neglected. Otherwise, the subsequent filtration steps will be significantly hampered. Moreover, the presence of large particles of contaminants can disrupt the operation of biological treatment facilities. This, in turn, will entail additional costs for the repair or even replacement of equipment. The facilities for filtration should be selected in accordance with the specifics of the enterprise's activities, the volume of wastewater, and also the need for re-use of purified water.