Coal-containing wastewater treatment method based on magnetic coagulation technology

Abstract

The invention discloses a coal-containing wastewater treatment method based on a magnetic coagulation technology, and particularly relates to the technical field of wastewater treatment.The coal-containing wastewater treatment method comprises the first step, the second step, the third step, the fourth step, the fifth step and the sixth step; a plurality of stirring rods used for stirring sludge are arranged in the treatment barrel, each stirring rod comprises a rod shell, a water absorption cotton rod is arranged in each rod shell, a plurality of communicating grooves penetrating through the rod shells are formed in the outer ends of the rod shells, and a detachable bottom cover is arranged at the bottom ends of the rod shells. Sludge containing water is concentrated into the treatment barrel to be stirred, the water in the sludge is absorbed by the water absorption cotton swab in the stirring process, so that the water in the sludge is separated from the sludge, and compared with static settlement, the time required by the mode is shorter, so that the sludge treatment efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for treating coal-containing wastewater based on magnetic coagulation technology. Background Art

[0002] Coal-containing wastewater refers to wastewater generated during coal mining, processing and transportation, such as coal wastewater generated by spraying in coal yards, coal wastewater from road washing, and coal-containing rainwater flowing out of the yard on rainy days.

[0003] The composition of coal-containing wastewater is complex, mainly including soluble organic matter, inorganic salts, asphaltene, phenol, acid, sulfur, etc. in coal. If it is not treated and directly discharged, the harmful substances in the wastewater will have a serious impact on the ecological environment and even human health.

[0004] In order to solve this problem, the prior art has enhanced the treatment effect through magnetic coagulation technology, so that the precipitation of harmful substances is more complete, such as a magnetic coagulation type coal-containing wastewater treatment system with publication number CN220034287U.

[0005] In the existing technology, a lot of sludge is generated in the treatment process. The sludge still contains a large amount of water. If it is directly discharged, it will cause a waste of water resources. Therefore, the conventional treatment method is to collect the sludge and then precipitate it uniformly to separate the clear liquid on the upper layer. However, this treatment method is slow, the precipitation time is long, and the treatment efficiency is low. Summary of the invention

[0006] The purpose of the present invention is to provide a method for treating coal-containing wastewater based on magnetic coagulation technology, by using an absorbent cotton swab to absorb moisture in the sludge during the stirring process, so as to separate the moisture in the sludge from the sludge. Compared with static sedimentation, this method requires less time, thereby improving the efficiency of sludge treatment.

[0007] In order to achieve the above object, the present invention provides the following technical solution: a method for treating coal-containing wastewater based on magnetic coagulation technology, the specific steps are as follows:

[0008] Step 1: Inject untreated sewage into the screen water collection well. When the sewage enters the well, due to the large water flow in the water inlet pipe, the solid matter in the sewage will naturally sink and be intercepted after being filtered by the screen, thereby removing large particles of solid impurities in the sewage. Then use the sewage lift pump to pump the treated sewage in the screen water collection well into the cyclone sand settling device. The water flow will rotate inside it. Under the combined action of buoyancy, fluid drag, centrifugal force and centripetal force during rotation, the water with low density rises and is discharged from the outlet, while the sand with high density is deposited at the bottom of the equipment and finally discharged through the sewage outlet. Through these two treatments, most of the large particles of solid suspended matter in the water are separated;

[0009] Step 2: The upper clear liquid separated in the cyclone sand settling device is injected into the water collection tank, and the high-concentration solid-liquid mixture is input into the sand-water separator through the air lift pipeline. The sand-water separator is equipped with a separation device. After the mixture enters, the separation device rotates to generate centrifugal force. Due to the action of centrifugal force, the heavier sand particles will be thrown out and settle downward, while the lighter water will be discharged through the holes or pipes of the separation device. The water separated in the sand-water separator is input into the coagulation reactor, and the water in the water collection tank is also pumped into the coagulation reactor through the sewage lifting pump, and the coagulant PAM, coagulant PAC and alkali solution are added to the coagulation reactor to produce coagulation and flocculation reactions in the sewage, thereby forming flocs to absorb suspended matter in the water. When the water in the coagulation reactor is mixed with PAC and PAM and reacts fully, the sewage and the flocs are input into the pre-sedimentation tank, and the flocs are precipitated in the pre-sedimentation tank and then separated from the water. The upper clear liquid after precipitation is discharged after meeting the requirements of the standards for connecting to the urban sewage pipe network;

[0010] Step 3: Input the upper clear liquid in the pre-sedimentation tank into the magnetic coagulation equipment, and add the coagulant PAM, coagulant PAC and magnetic powder. After the three are stirred and mixed evenly with water, the magnetic powder combines with the flocs in the coagulation process to form stable flocs with magnetic powder as coagulation nuclei. Since the specific gravity of magnetic powder is 5 times that of water, the specific gravity of flocs combined with magnetic powder increases rapidly. This kind of flocs can be quickly settled within a few minutes after flowing into the sedimentation tank. The settling speed can reach 40 meters per hour, which is 20 times that of conventional coagulation sedimentation. At the same time, this process The process further improves the bridging, adsorption and capture capabilities of the coagulation and flocculation reaction, and strengthens the treatment effect. Subsequently, the water and the flocs are injected into the magnetic separator to separate the treated water and the flocs containing magnetic powder. A magnetic field is generated inside the magnetic separator to attract the flocs containing magnetic powder by magnetic force, collect the flocs, and separate them from the water to remove pollutants in the water. The separated water is output and stored in a reuse water pool. The water in the reuse water pool can meet the standards of urban miscellaneous drainage, and finally achieve the purpose of reuse.

[0011] Step 4: Solid impurities containing a small amount of water will be separated from the screen water collection well, cyclone sand settling device, sand-water separator, pre-sedimentation tank, water collection tank and magnetic separator. This part of impurities is called sludge. These sludges are collected and transported to the sludge pretreatment device to absorb the water contained in them;

[0012] Step 5: The sludge after being treated by the sludge pretreatment device still contains moisture. The sludge can be processed by a screw stacker to squeeze out the moisture in the sludge and finally make a mud cake. After the sludge is transported to the feed port of the screw stacker through a pipeline, it is squeezed through the filter gap between the fixed ring and the movable ring under the push of the spiral shaft, and the moisture is discharged. The solid sludge remains in the filter gap and gradually forms a mud cake, which can be sent back to the yard for continued use.

[0013] Furthermore, the sludge pretreatment device mentioned in step 4 and step 5 comprises a treatment cylinder, wherein a plurality of stirring rods for stirring the sludge are arranged inside the treatment cylinder;

[0014] The stirring rod includes a rod shell, a water-absorbing cotton swab is arranged inside the rod shell, a plurality of connecting grooves penetrating the rod shell are opened at the outer end of the rod shell, and the moisture in the sludge can contact the water-absorbing cotton swab through the connecting grooves. A detachable bottom cover is arranged at the bottom end of the rod shell. After removing the bottom cover, the rod shell can be opened to take out the water-absorbing cotton swab for replacement.

[0015] Furthermore, a support frame is provided at the bottom of the treatment cylinder, and two vertical plates on the support frame are respectively connected to two sides of the treatment cylinder, and the support frame plays a role in supporting the treatment cylinder;

[0016] An input channel is fixedly provided at the rear side of the treatment cylinder, and untreated sludge is input into the treatment cylinder through the input channel. A slag discharge pipe with a valve is fixedly provided at the bottom end of the treatment cylinder, and treated sludge is discharged through the slag discharge pipe.

[0017] Furthermore, a mounting frame is fixedly provided at the top of the processing cylinder, and a central tube penetrating the mounting frame is rotatably connected to the mounting frame. Two gears are provided at the bottom of the mounting frame, one of which is fixedly provided at the outer end of the central tube, and the two gears are meshed with each other. A motor for driving the other gear to rotate is fixedly provided at the top of the mounting frame.

[0018] Furthermore, a branch tube is fixedly provided at the top of the rod shell, one end of the branch tube is fixedly connected to the outer end of the central tube, the branch tube is communicated with the rod shell and the central tube, a secondary sponge block is placed inside the central tube, a transmission sponge strip is placed inside the branch tube, and both ends of the transmission sponge strip are respectively fixedly connected to the secondary sponge block and the absorbent cotton swab.

[0019] Furthermore, the top end of the central tube extends to the top of the mounting frame and is fixedly provided with a water purification cylinder, a primary sponge block is placed inside the water purification cylinder, and the top end of the secondary sponge block extends into the water purification cylinder and is connected to the primary sponge block.

[0020] Furthermore, an extrusion assembly is fixedly provided at the top of the mounting frame, and the extrusion assembly includes a vertical plate fixedly provided at the top of the mounting frame, the upper end of the vertical plate is bent into a horizontal state, and a hydraulic cylinder is fixedly provided at the bottom end of the horizontal portion of the vertical plate, the piston rod of the hydraulic cylinder faces downward and a mesh plate is fixedly provided at the bottom end of the piston rod, and the mesh plate is located directly above the water purification cylinder.

[0021] In the above technical solution, the technical effects and advantages provided by the present invention are:

[0022] 1. The sludge containing water is concentrated in the treatment drum and stirred. During the stirring process, the water in the sludge is absorbed by a water-absorbing cotton swab to separate the water from the sludge. This method takes less time than static sedimentation, thus improving the efficiency of sludge treatment.

[0023] 2. The water in the sludge is absorbed by adsorption, ensuring that only liquid can be transmitted along the absorbent cotton swab, transmission sponge strip, secondary sponge block and primary sponge block, so the separated water does not contain solid impurities and is purer. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0025] Figure 1 This is the overall structural diagram of the sludge pretreatment device;

[0026] Figure 2 This is the internal structure diagram of the treatment cylinder of the sludge pretreatment device;

[0027] Figure 3 This is a diagram of the stirring rod structure of the sludge pretreatment device;

[0028] Figure 4 It is a cross-sectional view of a stirring rod of a sludge pretreatment device;

[0029] Figure 5 This is a cross-sectional view of the water purification cylinder and central pipe of the sludge pretreatment device;

[0030] Figure 6 This is the structural diagram of the extrusion component of the sludge pretreatment device.

[0031] Description of reference numerals:

[0032] 1. Processing cylinder; 101. Slag discharge pipe; 102. Input channel; 2. Support frame; 3. Extrusion assembly; 301. Vertical plate; 302. Hydraulic cylinder; 303. Mesh plate; 4. Mounting frame; 5. Water purification cylinder; 501. Central tube; 502. Branch pipe; 6. Stirring rod; 601. Rod shell; 602. Connecting groove; 603. Water-absorbing cotton swab; 604. Bottom cover; 7. Motor; 8. Gear; 9. Primary sponge block; 10. Secondary sponge block; 11. Transmission sponge strip. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0034] The present invention provides a method for treating coal-containing wastewater based on magnetic coagulation technology, and the specific steps are as follows:

[0035] Step 1: Inject untreated sewage into the screen water collection well. When the sewage enters the well, due to the large water flow in the water inlet pipe, the solid matter in the sewage will naturally sink, and be intercepted after being filtered by the screen made of wire mesh or plastic fence, so as to remove large particles of solid impurities in the sewage. Then use the sewage lifting pump to pump the treated sewage in the screen water collection well into the cyclone sand settling device. When the water flows into the equipment tangentially from its water inlet, the water will rotate inside it. Due to the different densities of sand and water, under the combined action of buoyancy, fluid drag, centrifugal force and centripetal force during rotation, the water with low density rises and is discharged from the outlet, while the sand with high density is deposited at the bottom of the equipment and finally discharged through the sewage outlet. Through these two treatments, most of the large particles of solid suspended matter in the water are separated;

[0036] Step 2: The upper clear liquid separated in the cyclone sand settling device is injected into the water collection tank, and the high-concentration solid-liquid mixture is input into the sand-water separator through the air lift pipeline. The sand-water separator is equipped with a separation device, which is usually a rotating cylinder or spiral device. After the mixture enters, the separation device rotates to generate centrifugal force. Due to the action of centrifugal force, the heavier sand particles will be thrown out and settle downward, while the lighter water will be discharged through the holes or pipes of the separation device. The water separated in the sand-water separator is input into the coagulation reactor, and the water in the water collection tank is also pumped into the coagulation reactor through the sewage lifting pump, and the coagulant PAM, coagulant PAC and alkali solution are added to the coagulation reactor to produce coagulation and flocculation reactions in the sewage, thereby forming flocs to absorb suspended matter in the water. PAM is passed through the sewage pump to generate coagulation and flocculation reactions, and then form flocs to absorb suspended matter in the water. Through the bridging and adsorption of its polymer chains, suspended particles, colloids and organic pollutants in the wastewater are aggregated to form larger flocs. These flocs are easy to settle under the action of gravity, thereby achieving solid-liquid separation and purifying sewage. PAC can quickly adsorb negatively charged colloids and particles in the wastewater through charge neutralization, adsorption bridging and other mechanisms, causing these particles to aggregate and grow to form flocs that are easy to settle, thereby achieving efficient removal of suspended matter and some organic pollutants in the wastewater. When the water in the coagulation reactor is mixed with PAC and PAM and reacts fully, the sewage and flocs are input into the pre-sedimentation tank, where the flocs are precipitated and then separated from the water. The upper clear liquid after precipitation is discharged after meeting the requirements of the standards for connecting to the urban sewage pipe network;

[0037] Step 3: Input the upper clear liquid in the pre-sedimentation tank into the magnetic coagulation equipment, and add the coagulant PAM, coagulant PAC and magnetic powder. After the three are stirred and mixed evenly with water, the magnetic powder combines with the flocs in the coagulation process to form stable flocs with magnetic powder as coagulation nuclei. Since the specific gravity of magnetic powder is 5 times that of water, the specific gravity of flocs combined with magnetic powder increases rapidly. Such flocs can be quickly precipitated within a few minutes after flowing into the sedimentation tank. The sedimentation rate can reach 40 meters per hour, which is 20 times that of conventional coagulation sedimentation. At the same time, this process further enhances the bridging, adsorption and capture capabilities of the coagulation and flocculation reaction, thereby strengthening the treatment effect. Then the water and the flocs are injected into the magnetic separator to separate the treated water and the flocs containing magnetic powder. The magnetic separator generates a magnetic field inside to attract the flocs containing magnetic powder by magnetic force, collect these flocs and separate them from the water to remove pollutants in the water. The suspended solids in the effluent of the conventional coagulation and sedimentation reaction are below 20 mg / l. After adding the series high-efficiency coagulation reactor and magnetic coagulation, the suspended solids in the effluent can be reduced to below 1 mg / l, ensuring better effluent water quality. The separated water is output and stored in the reuse water pool. The water in the reuse water pool can meet the standards of urban miscellaneous drainage, and finally achieve the purpose of reuse.

[0038] Step 4: Solid impurities containing a small amount of water will be separated from the screen water collection well, cyclone sand settling device, sand-water separator, pre-sedimentation tank, water collection tank and magnetic separator. This part of impurities is called sludge. These sludges are collected and transported to the sludge pretreatment device to absorb the water contained in them;

[0039] Step 5: The sludge after being treated by the sludge pretreatment device still contains moisture. The sludge can be processed by a screw stacker to squeeze out the moisture in the sludge and finally make a mud cake. After the sludge is transported to the feed port of the screw stacker through a pipeline, it is squeezed through the filter gap between the fixed ring and the movable ring under the push of the spiral shaft, and the moisture is discharged. The solid sludge remains in the filter gap and gradually forms a mud cake, which can be sent back to the yard for continued use.

[0040] The present invention also includes the sludge pretreatment device mentioned in step 4 and step 5, such as Figure 1-Figure 6 , comprising a treatment cylinder 1, wherein a plurality of stirring rods 6 for stirring sludge are provided inside the treatment cylinder 1;

[0041] The stirring rod 6 includes a rod shell 601, and a water-absorbing cotton swab 603 is arranged inside the rod shell 601. A plurality of connecting grooves 602 penetrating the rod shell 601 are opened at the outer end of the rod shell 601. The moisture in the sludge can contact the water-absorbing cotton swab 603 through the connecting grooves 602. A detachable bottom cover 604 is provided at the bottom end of the rod shell 601. After removing the bottom cover 604, the rod shell 601 can be opened to take out the water-absorbing cotton swab 603 for replacement.

[0042] After the water-containing sludge is input into the treatment barrel 1, the stirring rod 6 is driven to rotate inside the treatment barrel 1 to stir the sludge. During the stirring process, the sludge and the water contained therein can contact the absorbent cotton swab 603 through the connecting groove 602, and the water is absorbed by the absorbent cotton swab 603. After a period of stirring, most of the water contained in the sludge is sucked out, and the stirring is performed until there is no obvious water accumulation on the surface of the sludge visually.

[0043] like Figure 1 and Figure 2 As shown, a support frame 2 is provided at the bottom of the treatment cylinder 1, and two vertical plates on the support frame 2 are respectively connected to both sides of the treatment cylinder 1. The support frame 2 plays a role in supporting the treatment cylinder 1. The support frame 2 can be fixed on the ground to improve the overall stability of the pretreatment device;

[0044] An input channel 102 is fixedly provided at the rear side of the treatment cylinder 1 , and untreated sludge is input into the treatment cylinder 1 through the input channel 102 . A slag discharge pipe 101 with a valve is fixedly provided at the bottom end of the treatment cylinder 1 , and treated sludge is discharged through the slag discharge pipe 101 .

[0045] In order to drive the stirring rod 6 to rotate, Figure 2-Figure 5 As shown, a mounting bracket 4 is fixedly provided on the top of the treatment cylinder 1, and a central tube 501 penetrating the mounting bracket 4 is rotatably connected to the mounting bracket 4. Two gears 8 are provided at the bottom of the mounting bracket 4, and one of the gears 8 is fixedly provided at the outer end of the central tube 501. The two gears 8 are meshed with each other. A motor 7 for driving the other gear 8 to rotate is fixedly provided on the top of the mounting bracket 4. The motor 7 drives the gear 8 at one end of its output shaft to rotate, and driven by the gear 8, the gear 8 at the outer end of the central tube 501 rotates accordingly and drives the central tube 501 to rotate.

[0046] A branch pipe 502 is fixedly provided at the top of the rod shell 601, one end of the branch pipe 502 is fixedly connected to the outer end of the central tube 501, the branch pipe 502 is communicated with the rod shell 601 and the central tube 501, a secondary sponge block 10 is placed inside the central tube 501, a transmission sponge bar 11 is placed inside the branch pipe 502, both ends of the transmission sponge bar 11 are respectively fixedly connected to the secondary sponge block 10 and the absorbent cotton swab 603, when the central tube 501 rotates, it drives the branch pipe 502 at its outer end to rotate, and the branch pipe 502 drives the stirring rod 6 to rotate, so that all the stirring rods 6 rotate around the central tube 501, thereby achieving the purpose of stirring the sludge.

[0047] The top end of the central tube 501 extends to the top of the mounting frame 4 and is fixedly provided with a water purification cylinder 5, a primary sponge block 9 is placed inside the water purification cylinder 5, and the top end of the secondary sponge block 10 extends into the water purification cylinder 5 and is connected to the primary sponge block 9. The absorbent cotton swab 603, the primary sponge block 9, the secondary sponge block 10 and the transmission sponge strip 11 all have strong water absorption.

[0048] During the stirring process, after the absorbent cotton swab 603 absorbs the water in the sludge, the absorbent cotton swab 603 is soaked with water. After the absorbent cotton swab 603 is completely soaked, the water will extend upward to soak the transmission sponge bar 11. After the transmission sponge bar 11 is soaked, the water continues to spread and soak the secondary sponge block 10, and finally soak the primary sponge block 9.

[0049] The absorbed water must eventually be discharged, such as Figure 1 , Figure 2 , Figure 5 and Figure 6 As shown, an extrusion assembly 3 is fixedly provided at the top of the mounting frame 4, and the extrusion assembly 3 includes a vertical plate 301 fixedly provided at the top of the mounting frame 4, and the upper end of the vertical plate 301 is bent into a horizontal state, and a hydraulic cylinder 302 is fixedly provided at the bottom end of the horizontal part of the vertical plate 301, and the piston rod of the hydraulic cylinder 302 faces downward and a mesh plate 303 is fixedly provided at the bottom end of the piston rod, and the mesh plate 303 is located directly above the water purification cylinder 5.

[0050] During stirring, when the primary sponge block 9 is fully soaked, the hydraulic cylinder 302 can extend downward and push the mesh plate 303 to move downward. After the mesh plate 303 moves downward, it enters the water purification cylinder 5 and squeezes the primary sponge block 9, thereby squeezing out the water adsorbed in the primary sponge block 9. The squeezed water can pass through the mesh plate 303 and spread to the top of the mesh plate 303. Then, the water squeezed out from the inside of the water purification cylinder 5 is extracted to obtain water separated from the sludge. After the water is extracted, the hydraulic cylinder 302 contracts and drives the mesh plate 303 to move upward back to its original position, so that the primary sponge block 9 rebounds. The cotton block 9 regains its water absorption due to the water being squeezed out, so it can continue to absorb water until it is fully soaked, and this cycle repeats to continuously squeeze out water; after the water in the primary sponge block 9 is squeezed out, it will absorb water from the secondary sponge block 10 again, and after the secondary sponge block 10 absorbs water, it will absorb water from the transmission sponge bar 11 again, and similarly, the transmission sponge bar 11 will absorb water from the absorbent cotton swab 603 again, and the absorbent cotton swab 603 will continuously absorb water from the sludge. Therefore, after the water absorption of the primary sponge block 9 is restored, the water in the sludge can be continuously transported to the primary sponge block 9;

[0051] In this way, the water in the sludge is continuously absorbed during the stirring process of the sludge, and the time required is shorter and there is no need for long-term standing sedimentation, so the treatment efficiency is higher. Secondly, if the water in the sludge is separated by traditional sedimentation, the separated upper clear liquid is difficult to keep pure, because the bottom of the upper clear liquid is in direct contact with the sludge. If this part of the sludge is directly extracted, it is very easy to bring out a lot of impurities. Since only liquid can soak the absorbent cotton swab 603, the transmission sponge strip 11, the secondary sponge block 10 and the primary sponge block 9 in turn, the water obtained by adsorption is equivalent to being filtered once by the above four respectively. The treated water does not contain solid impurities and is purer.

[0052] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for treating coal-containing wastewater based on magnetic coagulation technology, characterized in that: The specific steps are as follows: Step 1: inject untreated sewage into the screen water collection well, and then use the sewage lifting pump 1 to pump the treated sewage in the screen water collection well into the cyclone sand settling device. Through these two treatments, most of the large particles of suspended solids in the water are separated; Step 2: The supernatant separated in the cyclone sand settling device is injected into the water collection tank, and the high-concentration solid-liquid mixture is input into the sand-water separator through the air lift pipeline. The water separated in the sand-water separator is input into the coagulation reactor, and the water in the water collection tank is also pumped into the coagulation reactor through the sewage lifting pump, and the coagulant aid PAM, coagulant PAC and alkali solution are added to the coagulation reactor. When the water in the coagulation reactor is mixed with PAC and PAM and reacts fully, the sewage and floccules are input into the pre-sedimentation tank, and the floccules are precipitated in the pre-sedimentation tank and then separated from the water; Step 3: The upper clear liquid in the pre-sedimentation tank is input into the magnetic coagulation equipment, and the coagulant PAM, coagulant PAC and magnetic powder are added thereto. After the three are stirred and mixed evenly with water, the magnetic powder combines with the flocs in the coagulation process to form stable flocs with the magnetic powder as the coagulation nucleus. Subsequently, the water and the flocs are injected into the magnetic separator to separate the treated water and the flocs containing the magnetic powder. The separated water is output and stored in the reuse water pool; Step 4: Solid impurities containing a small amount of water, namely sludge, will be separated from the screen water collection well, cyclone sand settling device, sand-water separator, pre-sedimentation tank, water collection tank and magnetic separator. The sludge will be collected and transported to the sludge pretreatment device to absorb the water contained therein; Step 5: The sludge in step 4 is processed by a screw stacker to squeeze out the water in the sludge to form a mud cake.

2. The method for treating coal-containing wastewater based on magnetic coagulation technology according to claim 1, characterized in that: The sludge pretreatment device mentioned in step 4 and step 5 comprises a treatment cylinder (1), wherein a plurality of stirring rods (6) for stirring the sludge are arranged inside the treatment cylinder (1); The stirring rod (6) comprises a rod shell (601), a water-absorbing cotton stick (603) is arranged inside the rod shell (601), a plurality of connecting grooves (602) penetrating the rod shell (601) are arranged at the outer end of the rod shell (601), and a detachable bottom cover (604) is arranged at the bottom end of the rod shell (601).

3. The method for treating coal-containing wastewater based on magnetic coagulation technology according to claim 2, characterized in that: A support frame (2) is provided at the bottom of the treatment cylinder (1), and two vertical plates on the support frame (2) are respectively connected to two sides of the treatment cylinder (1); An input channel (102) is fixedly provided at the rear side of the processing cylinder (1), and a slag discharge pipe (101) with a valve is fixedly provided at the bottom end of the processing cylinder (1).

4. The method for treating coal-containing wastewater based on magnetic coagulation technology according to claim 2, characterized in that: A mounting frame (4) is fixedly provided at the top of the treatment cylinder (1), and a central tube (501) penetrating the mounting frame (4) is rotatably connected to the mounting frame (4). Two gears (8) are provided at the bottom of the mounting frame (4), one of the gears (8) is fixedly provided at the outer end of the central tube (501), and the two gears (8) are meshed with each other. A motor (7) for driving the other gear (8) to rotate is fixedly provided at the top of the mounting frame (4).

5. A method for treating coal-containing wastewater based on magnetic coagulation technology according to claim 4, characterized in that: A branch tube (502) is fixedly provided at the top of the rod shell (601), one end of the branch tube (502) is fixedly connected to the outer end of the central tube (501), a secondary sponge block (10) is placed inside the central tube (501), a transmission sponge strip (11) is placed inside the branch tube (502), and two ends of the transmission sponge strip (11) are respectively fixedly connected to the secondary sponge block (10) and the absorbent cotton swab (603).

6. The method for treating coal-containing wastewater based on magnetic coagulation technology according to claim 5, characterized in that: The top end of the central tube (501) extends to the top of the mounting frame (4) and is fixedly provided with a water purification cylinder (5), a primary sponge block (9) is placed inside the water purification cylinder (5), and the top end of the secondary sponge block (10) extends into the water purification cylinder (5) and is connected to the primary sponge block (9).

7. A method for treating coal-containing wastewater based on magnetic coagulation technology according to claim 6, characterized in that: An extrusion assembly (3) is fixedly provided at the top of the mounting frame (4), and the extrusion assembly (3) comprises a vertical plate (301) fixedly provided at the top of the mounting frame (4), a hydraulic cylinder (302) is fixedly provided at the bottom end of the horizontal portion of the vertical plate (301), the piston rod of the hydraulic cylinder (302) faces downward and a mesh plate (303) is fixedly provided at the bottom end of the piston rod, and the mesh plate (303) is located directly above the water purification cylinder (5).

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