CN115636535A

CN115636535A - Industrial wastewater comprehensive treatment system and process

Info

Publication number: CN115636535A
Application number: CN202211338049.9A
Authority: CN
Inventors: 徐叶飞; 吴事浪; 黄杰; 秦梦璐
Original assignee: Sichuan Zhongqing Ruike New Energy Technology Co ltd
Current assignee: Sichuan Zhongqing Ruike New Energy Technology Co ltd
Priority date: 2022-10-28
Filing date: 2022-10-28
Publication date: 2023-01-24

Abstract

The application discloses an industrial wastewater comprehensive treatment system and a process, which comprises a physical stirring device and a chemical flocculation device which are communicated with each other, wherein the physical stirring device comprises a tank body for containing sewage, a driving mechanism and a filling mechanism for filling flocculation reagents into the tank body; the chemical flocculation device comprises a PH adjusting tank, a flocculation tank, a sedimentation tank and an aeration tank which are communicated with each other; the system and the process can effectively remove heavy metal ions in the industrial wastewater. The invention can combine the solid-liquid separation process and the flocculant adding process into one through the physical stirring device, and the flocculation reagent and the sewage can be mixed more uniformly under the stirring action of the physical stirring device, so that a large amount of flocculates can be formed in the electro-catalytic flocculation tank in a short time, and compared with the existing natural flocculation precipitation, the time is greatly shortened.

Description

Industrial wastewater comprehensive treatment system and process

Technical Field

The invention relates to the technical field of environmental protection, in particular to the technical field of an environmental protection device and a process for industrial wastewater treatment, and specifically relates to an industrial wastewater comprehensive treatment system and a process.

Background

Industrial wastewater treatment refers to the proper treatment of the water used in an industrial process for reuse in production or for proper discharge from a factory, including the management of process water and measures taken to facilitate the treatment of wastewater. Waste materials needing to be treated in the existing industrial wastewater are mainly heavy metal ions, and with the revolution of the current automobile field, manufacturers of large vehicles and enterprises gradually change from traditional fuel vehicles to new energy electric vehicles, so that the demand of power lithium batteries serving as one of core components of a power source of a pure electric new energy vehicle is increased rapidly, and the discharge pressure of the industrial wastewater generated by producing the lithium batteries reaches unprecedented pressure.

The main pollutants of the industrial wastewater generated in the manufacture of lithium batteries, which is one of the most important industrial wastewater at present, include ternary materials, lithium cobaltate, lithium iron phosphate, carbon powder, NMP solvent, deionized water solvent, and the like. The existing treatment modes mostly adopt physical filtration, flocculation precipitation, anaerobic treatment, itching relieving and other treatment modes, a plurality of ponds with very large occupied area are needed, the natural precipitation time is long, and the treatment efficiency is relatively low.

Disclosure of Invention

In order to solve the problems that the existing industrial wastewater adopts natural flocculation and precipitation and cannot continuously flow for treatment, so that the treatment time is long, the application provides an industrial wastewater comprehensive treatment system and process for replacing the existing natural flocculation and precipitation method, the continuous multi-stage treatment can be realized for the industrial wastewater containing heavy metal ions, the long-time static precipitation waiting is not needed, the industrial wastewater treatment period of unit amount is shortened, and the treatment efficiency is improved.

In order to achieve the purpose, the technical scheme adopted by the application is as follows:

the industrial wastewater comprehensive treatment system comprises a physical stirring device and a chemical flocculation device which are mutually communicated, wherein the physical stirring device comprises a tank body for containing sewage, a driving mechanism for providing stirring driving force and stirring the sewage, and a filling mechanism for filling a flocculation reagent into the tank body; the chemical flocculation device comprises a PH adjusting tank, a flocculation tank, a sedimentation tank and an aeration tank which are mutually communicated, wherein the PH adjusting tank is communicated with the water outlet through a first sewage pipe, an air inlet pipe is arranged at the bottom of the aeration tank, and a fifth sewage pipe for discharging sewage is arranged at a position, close to the top, of the aeration tank.

Preferably, actuating mechanism is including installing and being used for supporting variable speed drive in the frame of the jar body to and drive the motor and the stirring unit of connection at variable speed drive both ends respectively, the stirring unit is including sealing connection jar body bottom and variable speed drive's axle sleeve mechanism, install in the axle sleeve mechanism and run through the cavity pivot of jar body bottom, install the paddle that the multi-disc is used for stirring sewage on the free end of cavity pivot.

Further preferably, the filling mechanism comprises a medicament hose which is installed on the rack and used for filling the flocculating medicament, one end of the medicament hose is connected with a hard pipeline through an electromagnetic control valve, the hard pipeline is provided with a medicament adding opening, and the other end of the medicament hose is communicated with the tank body.

Still further preferably, the end of the medicament hose communicated with the tank body is communicated with the bottom of the hollow rotating shaft in a sealing manner through a joint, a medicament flow passage for the circulation of the medicament is arranged in the hollow rotating shaft, and a medicament discharge port for the outflow of the medicament is arranged on the side wall of the hollow rotating shaft, which is positioned in the tank body.

In order to make things convenient for the structure to overhaul, promote later stage plant maintenance's convenience, preferably, the jar is provided with the lid on the body, be provided with the water inlet that supplies sewage to get into the jar body on the lid.

Still further preferably, an overflow pipe for balancing the internal pressure of the tank body is provided on the lid body.

In order to reduce the occupied area of the flocculation equipment and improve the efficiency through continuous flocculation, preferably, the chemical flocculation device is arranged in a structure that the PH adjusting tank is communicated with the flocculation tank through a second sewage pipe, one end of the second sewage pipe is communicated with the top of the PH adjusting tank, the other end of the second sewage pipe extends to a position, close to the bottom, of the flocculation tank, one end, far away from the PH adjusting tank, of the flocculation tank is communicated with an aeration tank through a fourth sewage pipe, the fourth sewage pipe is communicated with the top of the flocculation tank, the other end of the fourth sewage pipe extends to a position, close to the bottom, of the aeration tank, a fifth sewage pipe for discharging sewage is further arranged at the position, close to the top, of the aeration tank, and an air inlet pipe for injecting air is arranged at the bottom of the aeration tank.

In order to further optimize the structure and further optimize the structural design on the premise of not influencing the treatment effect, preferably, the flocculation tank is directly communicated with the sedimentation tank, the sedimentation tank is positioned below the flocculation tank, and the bottom of the sedimentation tank is provided with a third sewage pipe for discharging sediment.

In order to treat the floating objects and realize the concentrated collection of the floating objects, preferably, a mesh electrode for electrocatalytic flocculation is arranged in the flocculation tank, an overflow port is arranged on one side of the top of the aeration tank, and a foam tank for collecting flocculation foam is arranged on the other side of the overflow port and the aeration tank.

The application also provides an industrial wastewater comprehensive treatment process which is realized by adopting the comprehensive treatment system and specifically comprises the following process flows: communicating an industrial sewage pipe to be treated with the water inlet, and checking air tightness and pipeline circulation; according to the flow of the industrial sewage pipe, determining the input flow of the flocculating agent according to a preset proportion, stirring in the tank body and synchronously inputting the flocculating agent into a PH regulating tank, and adding OH-containing water into the PH regulating tank ^- A conditioning agent to adjust the final pH to a pH of 9.5 to 10; electrifying the mesh electrode to carry out electrocatalytic flocculation, and simultaneously injecting compressed air into the air inlet pipe through the air compression equipment to increase the oxygen content in the aeration tank.

Has the advantages that:

the invention can combine the solid-liquid separation process and the flocculant adding process into one through the physical stirring device, and the flocculation reagent and the sewage can be mixed more uniformly under the stirring action of the physical stirring device, so that a large amount of flocculates can be formed in the electro-catalytic flocculation tank in a short time, and compared with the existing natural flocculation precipitation, the time is greatly shortened.

The invention can be arranged in parallel and/or communicated through a plurality of sets of treatment systems, the content of pollutants such as heavy metal in the treated sewage is reduced step by step in a step-by-step continuous treatment mode, long-time standing is not needed in the treatment process, and the treatment efficiency is improved.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without inventive exercise.

FIG. 1 is a structural isometric view of a physical agitation device.

Fig. 2 is another visual isometric view of the structure of fig. 1.

Fig. 3 is another visual isometric view of the structure of fig. 2.

Fig. 4 is a top view of fig. 1.

Fig. 5 isbase:Sub>A full sectional view of fig. 4 taken along the cut linebase:Sub>A-base:Sub>A.

Fig. 6 is a top view of a chemical flocculation apparatus.

Fig. 7 is a full sectional view of fig. 6 taken along the section symbol B-B.

In the figure: 1-a cover body; 2-tank body; 3-a water outlet; 4-a slag discharge port; 5-a frame; 6-adding medicine mouth; 7-a medicament hose; 8-a variable speed drive; 9-a motor; 10-an overflow pipe; 11-a solenoid control valve; 12-water inlet; 13-a shaft sleeve mechanism; 14-a filter screen; 15-a medicament flow channel; 16-a hollow rotating shaft; 17-medicine discharge port; 18-a blade; 19-a first sewer pipe; 20-PH adjusting tank; 21-a second sewer pipe; 22-a flocculation tank; 23-a sedimentation tank; 24-a third sewer pipe; 25-mesh electrode; 26-a fourth sewer pipe; 27-an aeration tank; 28-an air inlet pipe; 29-fifth sewer; 30-an overflow port; 31-foam pool.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, generally described and illustrated in the figures herein, can be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present application, presented in the accompanying drawings, is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.

In the description of the present application, it should be noted that if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are used for indicating the orientation or positional relationship based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship which is usually placed when the product of the application is used, the description is only for convenience and simplicity, and the indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation and be operated, and thus, should not be construed as limiting the present application. Furthermore, the appearances of the terms "first," "second," and the like in the description herein are only used for distinguishing between descriptions and not necessarily for describing or implying relative importance.

Furthermore, the terms "horizontal", "vertical" and the like when used in the description of the present application do not require that the components be absolutely horizontal or overhanging, but may be slightly inclined. For example, "horizontal" merely means that the direction is more horizontal than "vertical" and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.

In the description of the present application, it should also be noted that, unless otherwise explicitly stated or limited, the terms "disposed," "mounted," "connected," and "connected" should be interpreted broadly, e.g., as being fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present application can be understood in a specific case by those of ordinary skill in the art.

Example 1:

the embodiment provides an industrial wastewater comprehensive treatment system, which comprises a physical stirring device and a chemical flocculation device which are mutually communicated, as shown in the attached drawings of the specification 1-7, wherein the physical stirring device comprises a tank body 2 for containing sewage, a driving mechanism for providing stirring driving force and stirring the sewage, and a filling mechanism for filling flocculation chemicals into the tank body 2, a water inlet 12 is arranged on the tank body 2, the bottom of the tank body 2 is obliquely arranged and is provided with a water outlet 3 near the lower end of the bottom, a filter screen 14 is arranged between the water outlet 3 and the interior of the tank body 2, and a slag discharge port 4 for collecting and removing precipitated impurities is arranged near the filter screen 14 and is positioned at the bottom of the tank body 2; the chemical flocculation device comprises a PH adjusting tank 20, a flocculation tank 22, a sedimentation tank 23 and an aeration tank 27 which are mutually communicated, wherein the PH adjusting tank 20 is communicated with the water outlet 3 through a first sewage pipe 19, an air inlet pipe 28 is arranged at the bottom of the aeration tank 27, and a fifth sewage pipe 29 for discharging sewage is arranged at a position, close to the top, of the aeration tank 27.

The working principle is as follows: the physical stirring device is used for rotationally stirring the sewage, and the vortex generated by stirring is utilized to intensively coagulate solid matters which are mixed in the sewage and have density higher than that of the sewage, and the sedimentation of the solid matters is controlled by adjusting the stirring rotating speed. When the rotating speed is higher, the solid matters are subjected to larger sewage action, the mass is higher, the speed of the solid matters gathered in the sewage rotational flow is higher, and the solid matters can be settled more quickly; when the rotation speed is small, the speed at which the solid matter is gathered is slower; when the rotating speed is reduced or even is static, the solid matters naturally settle to the bottom of the tank body 2 and naturally fall into the slag discharge port 4 along with the bottom of the tank body 2 which is obliquely arranged, so that the effect of collecting the solid matters is achieved, and the effect of solid-liquid separation is achieved; since the water outlet 3 will pass through the filtering screen 14 when entering the next process for treatment, the impurities which are not completely settled and enter the residue outlet 4 will be blocked by the filtering screen 14, and will also fall to the residue outlet 4 when the water flow stops, and will not enter the next process, such as a chemical flocculation apparatus, along with the sewage. The slope setting is adopted to jar body 2 bottom and is one of them structure improvement point in this embodiment, and the technological effect that this structural improvement set up is when stirring sewage, and what sewage formed in jar body 2 is the regular solid of revolution, and to the bottom of the jar body 2 that the slope set up, the sewage of lower one side will not have obvious stirring, belongs to static, does benefit to the settlement of solid impurity. Based on the setting, the continuous solid-liquid separation effect can be realized under the condition that the stirring is not stopped; simultaneously, the filling mechanism continuously adds the flocculating agent in equal proportion, so that sewage can be fully mixed and stirred before formal flocculation is carried out, and the flocculation effect is improved. After solid-liquid separation and uniform mixing of the flocculating agent, the sewage after filtration and flocculation pretreatment is sent into a chemical flocculation device through a water outlet 3 for pH value adjustment, so that the industrial sewage is in an alkaline condition, and is subjected to high-efficiency flocculation by adding electrocatalysis. In this example, the principle of electrocatalytic flocculation is consistent with the prior art.

Example 2:

this embodiment is in fact on embodiment 1 basis further combines specification attached drawing 5 to carry out configuration optimization setting to actuating mechanism, and it is shown with fig. 4 and fig. 5 to combine specification, actuating mechanism is including installing the variable speed drive 8 on the frame 5 that is used for supporting jar body 2 to and respectively the drive connection is at motor 9 and the stirring unit at variable speed drive 8 both ends, the stirring unit is including sealing connection jar body 2 bottom and variable speed drive 8's axle sleeve mechanism 13, install in the axle sleeve mechanism 13 and run through the hollow rotating shaft 16 of jar body 2 bottom, install the blade 18 that the multi-disc is used for stirring sewage on the free end of hollow rotating shaft 16. The advantage of above-mentioned structure is compared in directly adding the benefit in the sewage with news your medicament and lies in, and the medicament is from the bottom release of central point position, and diffusion all around that can be quick under the effect of rotatory centrifugal force, from inside to outside, from bottom to top abundant diffusion to sewage in, avoid adding from the surface and appear bottom blind area, mix uneven problem.

In this embodiment, the filling mechanism includes a medicament hose 7 that is installed on the frame 5 and is used for filling flocculation medicament, one end of the medicament hose 7 is connected with a hard pipeline through an electromagnetic control valve 11, the hard pipeline has a medicament adding opening 6, and the other end of the medicament hose 7 is communicated with the tank body 2.

Still further preferably, one end of the medicament hose 7, which is communicated with the tank body 2, is hermetically communicated with the bottom of the hollow rotating shaft 16 through a joint, a medicament flow passage 15 for the circulation of the medicament is arranged in the hollow rotating shaft 16, and a medicament discharge port 17 for the outflow of the medicament is arranged on the side wall of the hollow rotating shaft 16, which is positioned in the tank body 2.

In order to facilitate the structural overhaul and improve the convenience of later-period equipment maintenance, in this embodiment, the tank body 2 is provided with the cover body 1, and the cover body 1 is provided with the water inlet 12 for sewage to enter the tank body 2. The cover body 1 is provided with an overflow pipe 10 for balancing the internal pressure of the tank body 2, so as to avoid the problem that the flocculation reagent cannot be filled in a sufficient amount due to the overpressure of the pressure of the tank body 2 caused by the overlarge water.

Example 3:

in order to reduce the occupied area of the flocculation apparatus and improve the efficiency through continuous flocculation, as shown in fig. 6-7 of the specification, the chemical flocculation apparatus is configured as follows, specifically, the PH adjustment tank 20 is communicated with the flocculation tank 22 through a second sewage pipe 21, one end of the second sewage pipe 21 is communicated with the top of the PH adjustment tank 20, the other end of the second sewage pipe 21 extends to a position of the flocculation tank 22 near the bottom, one end of the flocculation tank 22 far from the PH adjustment tank 20 is communicated with an aeration tank 27 through a fourth sewage pipe 26, the fourth sewage pipe 26 is communicated with the top of the flocculation tank 22, the other end extends to a position of the aeration tank 27 near the bottom, and a fifth sewage pipe 29 for discharging sewage is further disposed at a position of the aeration tank 27 near the top, and an air inlet pipe 28 for injecting air is disposed at the bottom of the aeration tank 27.

In order to further optimize the structure and further optimize the structural design without affecting the treatment effect, preferably, the flocculation tank 22 is directly communicated with the sedimentation tank 23, the sedimentation tank 23 is located below the flocculation tank, and the bottom of the sedimentation tank 23 is provided with a third sewage pipe 24 for discharging sediment.

In order to treat the floating objects and realize the concentrated collection of the floating objects, a mesh electrode 25 for electrocatalytic flocculation is arranged in the flocculation tank 22, an overflow port 30 is arranged on one side of the top of the aeration tank 27, and a foam tank 31 for collecting flocculation foam is arranged on the other side of the overflow port 30 and the aeration tank 27 on the same wall.

Example 4:

the application also provides an industrial wastewater comprehensive treatment process which is realized by adopting the comprehensive treatment system and specifically comprises the following process flows: communicating an industrial sewage pipe to be treated with the water inlet 12, and checking air tightness and pipeline liquidity; according to the flow of the industrial sewage pipe, the flocculant input flow is determined according to the preset proportion, stirred in the tank body 2 and synchronously input into the PH regulating tank 20, and OH-containing water is added into the PH regulating tank 20 ^- A regulator, which ensures that the adjusted final pH value is pH9.5-pH10; the mesh electrode 25 is electrified to carry out electrocatalytic flocculation, and simultaneously, compressed air is injected into the air inlet pipe 28 through an air compression device to increase the oxygen content in the aeration tank 27.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. Industrial waste water integrated processing system, including physical agitating unit and chemical flocculation device that communicate each other, its characterized in that: the physical stirring device comprises a tank body (2) for containing sewage, a driving mechanism for providing stirring driving force and stirring the sewage, and a filling mechanism for filling flocculating agents into the tank body (2), wherein a water inlet (12) is formed in the tank body (2), the bottom of the tank body (2) is obliquely arranged, a water outlet (3) is formed in the position close to the lower end of the bottom, a filter screen (14) is arranged between the water outlet (3) and the inside of the tank body (2), and a slag discharge port (4) for collecting and discharging precipitated impurities is formed in the position close to the filter screen (14) and at the bottom of the tank body (2);

the chemical flocculation device comprises a PH adjusting tank (20), a flocculation tank (22), a sedimentation tank (23) and an aeration tank (27) which are communicated with each other, wherein the PH adjusting tank (20) is communicated with the water outlet (3) through a first sewage pipe (19), an air inlet pipe (28) is arranged at the bottom of the aeration tank (27), and a fifth sewage pipe (29) for discharging sewage is arranged at the position, close to the top, of the aeration tank (27).

2. The integrated industrial wastewater treatment system according to claim 1, wherein: actuating mechanism is including installing and being used for supporting variable speed drive mechanism (8) on frame (5) of the jar body (2) to and respectively the drive connection motor (9) and the stirring unit at variable speed drive mechanism (8) both ends, the stirring unit is including sealing connection axle sleeve mechanism (13) of jar body (2) bottom and variable speed drive mechanism (8), install in axle sleeve mechanism (13) and run through cavity pivot (16) of jar body (2) bottom, install blade (18) that the multi-disc is used for stirring sewage on the free end of cavity pivot (16).

3. The industrial wastewater integrated processing system according to claim 2, characterized in that: the filling mechanism comprises a medicament hose (7) which is installed on the rack (5) and used for filling the flocculating medicament, one end of the medicament hose (7) is connected with a hard pipeline through an electromagnetic control valve (11), the hard pipeline is provided with a medicament adding port (6), and the other end of the medicament hose (7) is communicated with the tank body (2).

4. The integrated industrial wastewater treatment system according to claim 3, wherein: the one end of the medicament hose (7) and the jar body (2) intercommunication pass through the joint with the airtight intercommunication in bottom of cavity pivot (16), be provided with in cavity pivot (16) and supply medicament circulation's medicament runner (15), cavity pivot (16) are located and are provided with row's medicine mouth (17) that supply the medicament to flow on the lateral wall of jar body (2) inside.

5. The integrated industrial wastewater treatment system according to any one of claims 1 to 4, wherein: the tank is characterized in that a cover body (1) is arranged on the tank body (2), and a water inlet (12) for sewage to enter the tank body (2) is formed in the cover body (1).

6. The integrated industrial wastewater treatment system according to claim 5, wherein: an overflow pipe (10) used for balancing the internal pressure of the tank body (2) is arranged on the cover body (1).

7. The integrated industrial wastewater treatment system according to claim 6, wherein: the PH adjusting tank (20) is communicated with the flocculation tank (22) through a second sewage pipe (21), one end of the second sewage pipe (21) is communicated with the top of the PH adjusting tank (20), the other end of the second sewage pipe (21) extends to the position, close to the bottom, of the flocculation tank (22), one end, far away from the PH adjusting tank (20), of the flocculation tank (22) is communicated with an aeration tank (27) through a fourth sewage pipe (26), the fourth sewage pipe (26) is communicated with the top of the flocculation tank (22), the other end of the flocculation tank extends to the position, close to the bottom, of the aeration tank (27), and the position, close to the top, of the aeration tank (27) is further provided with a fifth sewage pipe (29) for discharging sewage and an air inlet pipe (28) arranged at the bottom of the aeration tank (27) and used for injecting air.

8. The integrated industrial wastewater treatment system according to claim 7, wherein: the flocculation tank (22) is directly communicated with the sedimentation tank (23), the sedimentation tank (23) is positioned below the flocculation tank, and a third sewage pipe (24) for discharging sediment is arranged at the bottom of the sedimentation tank (23).

9. The integrated industrial wastewater treatment system according to claim 8, wherein: a mesh electrode (25) for electrocatalytic flocculation is arranged in the flocculation tank (22), an overflow opening (30) is arranged on one side of the top of the aeration tank (27), and a foam tank (31) for collecting flocculated foam is arranged on the other side of the overflow opening (30) and the aeration tank (27) on the same wall.

10. The comprehensive treatment process of industrial wastewater is characterized by comprising the following steps: the integrated processing system of claim 9, which comprises the following steps: communicating an industrial sewer pipe to be treated with the water inlet (12), checking the air tightness and the pipeline circulation; according to the flow of the industrial sewage pipe, the flocculant input flow is determined according to a preset proportion, stirred in the tank body (2) and synchronously input into the PH adjusting tank (20), and OH-containing water is added into the PH adjusting tank (20) ^- A regulator, so that the adjusted final pH value is 9.5-10; electrifying the mesh electrode (25) to carry out electrocatalytic flocculation, and simultaneously injecting compressed air into the air inlet pipe (28) through an air compression device to increase the oxygen content in the aeration tank (27).