A device and working method for softening leachate membrane concentrate

Abstract

The present invention relates to the technical field of landfill leachate treatment, in particular to a device and a working method for softening leachate post-membrane concentrated liquid. The device comprises a Na2CO3 solution storage tank, a Na2CO3 solution dosing pump and a second reaction tank connected in sequence, and a NaOH solution storage tank, a NaOH solution dosing pump and a first reaction tank connected in sequence. The first reaction tank, the second reaction tank and the circulating membrane tank are arranged side by side in sequence. The bottom outlets of the two reaction tanks are both connected to the sludge tank inlet. The sludge tank outlet is respectively connected to a sludge discharge pipeline and a clear liquid return pipeline through an external discharge pump. The outlet of the clear liquid return pipeline is connected to the circulating membrane tank inlet. The bottom outlet of the circulating membrane tank is connected to the sludge tank inlet. The lower outlet of the circulating membrane tank is connected to the top inlet of an ultrafiltration membrane device through an ultrafiltration water inlet pump. The top outlet of the ultrafiltration membrane device is respectively connected to the first reaction tank inlet and the circulating membrane tank inlet. Softened product water flows out of the side wall outlet of the circulating membrane tank.

Description

Technical Field

[0001] The present invention relates to the technical field of landfill leachate treatment, and specifically relates to a device and a working method for softening leachate post-membrane concentrated liquid. Background Art

[0002] Municipal waste incineration plants implement "zero emissions." The post-membrane concentrate from the final stage of leachate treatment requires disposal. Typically, waste incineration plants spray the concentrate into the flue gas section of the incineration system for flue gas cooling or directly spray it back into the incinerator for disposal. These disposal processes are associated with significant heat energy losses. To reduce the disposal cost of the concentrate, the industry currently uses high-pressure reverse osmosis membrane systems (typically DTRO systems) for concentration and volume reduction.

[0003] The leachate concentrate contains high concentrations of humic acid-based organic matter and various inorganic ions. During the process of intercepting these substances in the reverse osmosis membrane, high-valent ions such as calcium, magnesium, silicon, iron, and aluminum interact with sulfate, carbonate, and bicarbonate ions on the concentrate side, leading to the formation of scale crystals on the membrane surface. To prevent scale crystals from forming on the membrane surface, pH adjustment and the addition of scale inhibitors are typically used during reverse osmosis membrane system operation to intervene and prevent the formation of a scaling layer. (In practice, scale crystals cannot be completely prevented, but their formation rate can only be slowed down.) In actual operation, the membrane modules require chemical cleaning after a period of operation (or when parameters such as membrane module pressure and flow rate reach a threshold). Hard scale crystal particles not only severely wear the high-pressure pump, but internal scaling can also easily damage the high-pressure diaphragm, leading to membrane perforation. For high-hardness concentrates after the membrane, the high-pressure membrane system needs to increase the dosage of hydrochloric acid and scale inhibitors during operation. The frequency of chemical cleaning will also increase with increasing hardness.

[0004] There are usually two problems with chemical cleaning of membrane elements: (1) Chemical cleaning has a certain damaging effect on the membrane, and a higher cleaning frequency directly affects the service life of the membrane element; (2) Chemical cleaning cannot completely remove the scaling layer. When the scaling crystals accumulate to a certain extent and form solid particles, they can easily cause irreversible damage to the internal structure of the high-pressure pump and the diaphragm, seriously affecting the stability and service life of the entire system.

[0005] Currently, the TUF process is used to soften leachate concentrate. The specific process involves reacting the leachate concentrate with lime slurry, or with lime slurry and sodium carbonate, respectively. Under alkaline conditions, the magnesium and calcium ions in the concentrate form solid precipitates and suspended solids, which are then separated by tubular ultrafiltration (or microfiltration). This softening process has a significant softening effect on leachate concentrate.

[0006] However, the current TUF system has the following disadvantages in practical applications: (1) The lime slurry preparation process is complicated, the system equipment is numerous, and the overall construction investment and operating costs are high; (2) The lime slurry has the characteristics of static sedimentation. Therefore, regardless of whether the TUF system is running or not, the lime slurry preparation and transportation system must be operated and refluxed continuously, resulting in excessive ineffective energy consumption; (3) When lime is used as an alkaline agent, excessive calcium ions are also introduced. The calcium ions will react with sulfate ions in the concentrate to form an insoluble substance - calcium sulfate, which adheres to the membrane pores and cannot be chemically dissolved. If it is removed during cleaning, the ultrafiltration membrane flux is difficult to recover; (4) The ultrafiltration of the TUF system usually adopts a tubular ultrafiltration unit, which has a high flow rate and large flow rate, and the system energy consumption is high; (5) The chemical sludge output of the TUF system is high, which not only requires the configuration of an independent sludge dewatering system, but also requires the treatment and disposal of a large amount of chemical sludge, and the overall construction cost and operation cost are high; (6) The inner wall of the hardness removal reaction tank of the TUF system is easily attached and "grown" by hardness scale crystals, causing scale blockage at the bottom of the reaction tank, the inlet and outlet pipes, and the overflow weir, which requires frequent cleaning. Summary of the Invention

[0007] The object of the present invention is to provide a device and a working method for softening the concentrated liquid after the leachate membrane.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A device for softening leachate membrane concentrate, comprising a Na2CO3 solution storage tank, a Na2CO3 solution dosing pump and a second reaction tank connected in sequence, and a NaOH solution storage tank, a NaOH solution dosing pump and a first reaction tank connected in sequence, the inlet of the first reaction tank flows into the leachate membrane concentrate, the first reaction tank, the second reaction tank and the circulating membrane tank are arranged side by side in sequence, the first reaction tank and the second reaction tank are both provided with a water baffle and a crystallization catcher, the bottom outlets of the first reaction tank and the second reaction tank are both connected to the sludge tank inlet, the sludge tank outlet is respectively connected to the sludge discharge pipeline and the clear liquid return pipeline through an external discharge pump, the outlet of the clear liquid return pipeline is connected to the circulating membrane tank inlet, the bottom outlet of the circulating membrane tank is connected to the sludge tank inlet, the lower outlet of the circulating membrane tank is connected to the top inlet of the ultrafiltration membrane device through an ultrafiltration water inlet pump, the top outlet of the ultrafiltration membrane device is respectively connected to the first reaction tank inlet and the circulating membrane tank inlet, and the side wall outlet of the circulating membrane tank flows out softened water.

[0010] Furthermore, the water baffle is located on the inner side of the crystallization catcher, and the crystallization catcher is close to the side wall of the reaction tank; the crystallization catcher includes a stainless steel mesh, a polyester fiber bundle is placed in the stainless steel mesh, the stainless steel mesh is welded into one with a stainless steel connecting rod, and a left fixed slider and a right fixed slider are welded to the left and right ends of the stainless steel connecting rod respectively, the left fixed slider is installed in the left mounting rail, and the right fixed slider is installed in the right mounting rail, and the left mounting rail and the right mounting rail are both welded to the inner wall of the reaction tank; the upper ends of the left mounting rail and the right mounting rail are both open, and a limiting bottom plate is provided at the lower end.

[0011] Furthermore, a pH online monitor is provided in the first reaction tank, a first agitator is provided above the first reaction tank, and a second agitator is provided above the second reaction tank.

[0012] Furthermore, a water hole communicating with the second reaction tank is provided on the side wall above the crystallization catcher in the first reaction tank, and a water hole communicating with the circulating membrane tank is provided on the side wall above the crystallization catcher in the second reaction tank.

[0013] Furthermore, the inner walls of the first reaction tank, the second reaction tank and the circulating membrane tank, as well as the stirring blades of the first stirrer and the second stirrer are sprayed with PTFE material.

[0014] Furthermore, the ultrafiltration membrane device has a built-in external pressure column-mounted ultrafiltration membrane with a working pressure of 0.03 MPa, and the ultrafiltration membrane is made of PTFE material; the crystallization catcher is made of PP material.

[0015] Furthermore, a sludge interface meter is provided in the sludge pool, a circulating membrane pool sludge discharge electric valve is provided at the bottom outlet of the circulating membrane pool, a sludge discharge electric valve is provided on the sludge discharge pipeline, and a clear liquid reflux electric valve is provided on the clear liquid reflux pipeline.

[0016] Furthermore, a measurement sampling tube and a measurement reflux tube are connected to the top of the second reaction tank, the outlet of the measurement sampling tube is connected to the inlet of the calcium ion online sampling and measuring instrument, and the outlet of the calcium ion online sampling and measuring instrument is connected to the inlet of the measurement reflux tube.

[0017] The method for softening the concentrated liquid after leachate membrane using the above device comprises the following steps:

[0018] ① Add NaOH solution into the first reaction tank, and the concentrated liquid after leachate membrane flows into the first reaction tank, Mg 2+ With OH - The reaction generates solid Mg(OH)2, and at the same time, the HCO3 in the concentrated liquid after the leachate membrane - With OH - Reacts to produce CO3 2-and H2O, CO3 2- Mg 2+ and Ca 2+ The reaction generates solid MgCO3 and CaCO3, and the Mg in the concentrated liquid after the leachate membrane 2+ and HCO3 - Almost all of them participated in the relevant reaction; the pH in the first reaction tank was controlled at 10.5-11.0;

[0019] ② After the first reaction tank, the concentrated liquid after the leachate membrane enters the second reaction tank, and Na2CO3 is added to the second reaction tank. The remaining small amount of Mg in the mixed liquid 2+ and a large amount of Ca 2+ With CO3 2- Reacts to produce MgCO3 and CaCO3;

[0020] ③ After passing through the second reaction tank, the concentrated liquid after the leachate membrane enters the circulating membrane tank. The circulating membrane tank, ultrafiltration water inlet pump, ultrafiltration membrane device, and related pipelines form an ultrafiltration system. The mixed concentrated liquid containing a large amount of solid particulate matter MgCO3 and CaCO3 is separated into solid and liquid in the ultrafiltration system.

[0021] Mg in the concentrated liquid after leachate membrane 2+ and Ca 2+ The sludge discharged from the first reaction tank, the second reaction tank, the circulating membrane tank and the ultrafiltration membrane device is basically removed and the softening treatment is completed. The sludge discharged from the first reaction tank, the second reaction tank, the circulating membrane tank and the ultrafiltration membrane device is concentrated into the sludge tank and transported to the sludge disposal terminal for treatment through the external discharge pump.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention softens the hardness of the post-membrane concentrate to remove calcium and magnesium ions from the concentrate. Softening the post-membrane concentrate not only prevents damage to the system caused by calcium and magnesium scaling crystallization, but also reduces reagent consumption and the frequency of chemical cleaning. The present invention optimizes the operating conditions of the membrane-based reduction system for post-membrane concentrate and increases the service life of the high-pressure membrane system.

[0024] (2) The present invention adopts two special designs to prevent the adsorption and growth of hardness scaling crystals on the inner wall of the reactor: ① The hardness removal reactor is lined with PTFE material to have a smooth inner surface and low charge adsorption force on scaling crystal nuclei; ② A crystallization catcher is designed with PP material that has a strong charge adsorption force on inorganic crystal nuclei to adsorb crystal nuclei. Under the dual action, the adsorption and growth of hardness scaling crystals on the inner wall of the reactor are prevented. The crystallization catcher adopts a disposable replacement and installation design.

[0025] (3) The present invention adopts a sludge interface meter in the sludge tank to realize the real-time switching between sludge discharge and clear liquid return, so that it can also have the function of sludge concentration, and the sludge concentration tank and the sludge tank are combined into one; the design of the present invention in the sludge tank also realizes that one working pump can realize both sludge discharge and clear liquid return, which simplifies the process configuration and system construction investment compared with the traditional design that requires the configuration of an overflow weir or a decanter and a separate sludge pump and clear liquid pump.

[0026] (4) After static stratification is achieved in the sludge pool, the sludge discharge and the supernatant return are separated, which reduces the moisture content of the discharged sludge and reduces the sludge disposal load and cost.

[0027] (5) The present invention uses liquid alkali and soda ash as softening alkaline agents, which reduces lime storage, lime powder transportation, and lime slurry preparation systems, thereby reducing construction investment and operating costs. Compared with lime slurry, liquid alkali and soda ash do not have the problem of static siltation, and material storage and transportation can be started, stopped, and adjusted at any time according to the system operation status; the agents used in the present invention do not introduce calcium ions, thus avoiding the chemical reaction of exogenous high-concentration calcium ions with sulfate ions to form insoluble calcium sulfate. The present invention uses liquid alkali and soda ash to react with calcium and magnesium ions in the concentrated solution, which will produce less chemical sludge, reducing the construction investment and operating costs of the sludge dewatering treatment system and the dewatered sludge disposal treatment.

[0028] (6) The present invention uses a built-in external pressure column-mounted ultrafiltration system for solid-liquid separation. The system has a low operating pressure (0.03 MPa) and low energy consumption. The ultrafiltration membrane is made of PTFE, which is different from the tubular ultrafiltration membrane or hollow fiber ultrafiltration membrane commonly used in the industry. Tubular ultrafiltration membranes require a large flow rate to scrub the membrane interface to reduce membrane surface fouling, which requires a high-power circulation pump. The ultrafiltration membrane used in the present invention has lower operating energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic structural diagram of the device for softening the concentrated liquid after the leachate membrane according to the present invention.

[0030] Figure 2 This is a schematic diagram of the connection between the second reaction tank and the calcium ion online sampling and measuring instrument.

[0031] Figure 3 Schematic diagram of the crystal catcher structure.

[0032] Figure 4 This is the curve of hardness changing with pH value of the first reaction tank.

[0033] Figure 5 This is the relationship curve between magnesium hardness removal and alkali dosage.

[0034] Figure 6 Remove the response curve for hardness.

[0035] Among them, 1-Na2CO3 solution storage tank, 2-NaOH solution storage tank, 3-Na2CO3 solution dosing pump, 4-NaOH solution dosing pump, 5-first reaction tank, 6-second reaction tank, 7-circulating membrane tank, 8-ultrafiltration water inlet pump, 9-ultrafiltration membrane device, 10-sludge tank, 11-efflux pump, 12-first agitator, 13-second agitator, 14-water baffle, 15-crystallization catcher, 16-sludge interface meter, 17-sludge discharge electric valve, 18-clear liquid reflux electric valve, 19-circulating membrane tank sludge discharge electric valve, 20-pH online monitor, 21-calcium ion online sampling and measuring instrument, 22-determination sampling tube, 23-determination reflux pipe, 24-stainless steel mesh, 25-left fixed slider, 26-stainless steel connecting rod, 27-right fixed slider, 28-left mounting rail, 29-right mounting rail. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] like Figure 1-Figure 2 As shown, a device for softening the post-membrane concentrate of the leachate comprises a Na2CO3 solution storage tank 1, a Na2CO3 solution dosing pump 3 and a second reaction tank 6 connected in sequence, and a NaOH solution storage tank 2, a NaOH solution dosing pump 4 and a first reaction tank 5 connected in sequence, the inlet of the first reaction tank 5 flows into the post-membrane concentrate of the leachate, the first reaction tank 5, the second reaction tank 6 and the circulating membrane tank 7 are arranged side by side in sequence, the first reaction tank 5 and the second reaction tank 6 are both provided with a water baffle 14 and a crystallization catcher 15, the bottom outlets of the first reaction tank 5 and the second reaction tank 6 They are all connected to the inlet of the sludge tank 10. The outlet of the sludge tank 10 is connected to the sludge discharge pipeline and the clear liquid return pipeline respectively through the external discharge pump 11. The outlet of the clear liquid return pipeline is connected to the inlet of the circulating membrane tank 7. The bottom outlet of the circulating membrane tank 7 is connected to the inlet of the sludge tank 10. The lower outlet of the circulating membrane tank 7 is connected to the top inlet of the ultrafiltration membrane device 9 through the ultrafiltration water inlet pump 8. The top outlet of the ultrafiltration membrane device 9 is respectively connected to the inlet of the first reaction tank 5 and the inlet of the circulating membrane tank 7. The bottom outlet of the circulating membrane tank 7 is connected to the inlet of the sludge tank 10. The softened water flows out of the side wall outlet of the circulating membrane tank 7. Among them, the water retaining plate 14 is located on the inner side of the crystallization catcher 15, and the crystallization catcher 15 is close to the side wall of the reaction tank.

[0038] like Figure 3As shown, the crystallization catcher 15 includes a stainless steel mesh 24, in which polyester fiber bundles are placed. The polyester fiber bundles react with the crystal nuclei by adsorption. The stainless steel mesh 24 is welded to a stainless steel connecting rod 26. The left and right ends of the stainless steel connecting rod 26 are respectively welded to a left fixed slider 25 and a right fixed slider 27. The left fixed slider 25 is mounted on a left mounting rail 28, and the right fixed slider 27 is mounted on a right mounting rail 29. The left mounting rail 28 and the right mounting rail 29 are both welded to the inner wall of the reaction tank. The upper ends of the left mounting rail 28 and the right mounting rail 29 are open, and a limit base is provided at the bottom to prevent the left and right sliders from sliding out of the bottom ends of the rails. When installing the crystallization reactor 15, the left fixed slider 25 and the right fixed slider 27 are simultaneously inserted into the left mounting rail 28 and the right mounting rail 29 from the upper end, and the stainless steel connecting rod 26 is pushed downward to the limit base position at the bottom of the slide rail to complete the installation; conversely, when disassembling the crystallization reactor 15, the stainless steel connecting rod 26 is lifted upward until the slider is separated from the slide rail to complete the disassembly.

[0039] A pH online monitor 20 is provided in the first reaction tank 5 , a first stirrer 12 is provided above the first reaction tank 5 , and a second stirrer 13 is provided above the second reaction tank 6 .

[0040] A water hole is provided on the side wall of the first reaction tank 5 above the crystallizer catcher 15, communicating with the second reaction tank 6. A water hole is provided on the side wall of the second reaction tank 6 above the crystallizer catcher 15, communicating with the circulating membrane tank 7. A water baffle 14 separates the stirring zone from the overflow zone; otherwise, stirring would disturb the flow of water flowing through the overflow hole.

[0041] The inner walls of the first reaction pool 5, the second reaction pool 6 and the circulating membrane pool 7 as well as the stirring blades of the first stirrer 12 and the second stirrer 13 are all spray-coated with PTFE material. The crystallization trap 15 is made of PP material.

[0042] The ultrafiltration membrane device 9 has a built-in external pressure column-mounted ultrafiltration membrane with a working pressure of 0.03 MPa. The ultrafiltration membrane is made of PTFE material.

[0043] A sludge interface meter 16 is installed in the sludge tank 10 to control the real-time switching between sludge discharge and clear liquid return. A circulating membrane tank sludge discharge electric valve 19 is installed at the bottom outlet of the circulating membrane tank 7. A sludge discharge electric valve 17 is installed on the sludge discharge pipeline, and a clear liquid return electric valve 18 is installed on the clear liquid return pipeline.

[0044] The top of the second reaction tank 6 is connected to a measurement sampling tube 22 and a measurement reflux tube 23 . The outlet of the measurement sampling tube 22 is connected to the inlet of the calcium ion online sampling and measuring instrument 21 , and the outlet of the calcium ion online sampling and measuring instrument 21 is connected to the inlet of the measurement reflux tube 23 .

[0045] Working mechanism of crystallization trap: In the first reaction tank and the second reaction tank, Mg 2+ and Ca 2+ During the precipitation reaction, Mg(OH)2, MgCO3, and CaCO3 will form crystal nuclei and grow into crystals within the reactor. The surfaces of the crystal nuclei and crystals of Mg(OH)2, MgCO3, and CaCO3 have a positive potential. A rough polyester fiber bundle with a negative surface potential placed within the crystallization catcher is used to adsorb free crystal nuclei and microcrystals onto the polyester fiber bundle within the crystallization catcher by utilizing the attraction of positive and negative potentials. At the same time, the inner walls of the first and second reaction tanks, the circulating membrane tank, and the first and second agitators are spray-coated with PTFE material to render their surfaces charge-neutral, thereby preventing and reducing the attachment and "growth" of crystal nuclei and microcrystals to the inner walls of the reactor. The crystallization catcher is a one-time replacement and will be disassembled and replaced in actual use according to the crystallization situation. Working mechanism of ultrafiltration system: The ultrafiltration system used in the device of the present invention is different from the existing tubular ultrafiltration or immersed hollow fiber ultrafiltration. Its ultrafiltration membrane assembly is composed of an ultrafiltration housing, an end cap, a manifold and ultrafiltration membrane filaments. For example, the Enwei series ultrafiltration membrane assembly of Shanghai Cheran Environmental Protection Technology Co., Ltd. can be used. The ultrafiltration membrane assembly used in the present invention is provided with pressure by an ultrafiltration water inlet pump, and uses an external pressure working mechanism to realize that the water phase in the mixed concentrate passes through the surface membrane cavities of the ultrafiltration membrane filaments into the interior of the membrane filaments and flows to the top manifold to be discharged from the ultrafiltration membrane assembly; the solid phase is intercepted by the membrane filaments into the membrane assembly and refluxes to the circulating membrane tank through the circulation pipeline.

[0046] The system's sludge discharge mechanism: The circulating membrane tank is equipped with an online sludge concentration meter, which is interlocked with the sludge discharge valve. When the sludge concentration reaches the set discharge concentration, the sludge discharge valve opens and sludge discharge is initiated until the set discharge level or concentration is reached. The sludge discharge process is programmed during the automatic cleaning of the ultrafiltration membrane. Once the automatic cleaning is complete, the sludge remaining in the ultrafiltration membrane housing is discharged through the sludge discharge valve. The sludge in the circulating membrane tank and ultrafiltration membrane assembly is discharged into the sludge tank and then transported to the sludge disposal terminal via a sludge pump.

[0047] The mechanism of the effect of the ultrafiltration system returning to the first reaction tank: the mixed liquid returning from the ultrafiltration system still contains a certain concentration of OH - ions, which flow back to the first reaction tank to provide OH for the magnesium removal reaction - , thereby reducing the consumption of NaOH.

[0048] The mechanism of the effect of the ultrafiltration system flowing back to the circulating membrane pool: the mixed liquid containing solid particles in the ultrafiltration system flows back to the circulating membrane pool, providing dispersed crystal nuclei for the supersaturated solution, accelerating the precipitation of Mg(OH)2, MgCO3 and CaCO3 in the supersaturated solution and the growth of crystals.

[0049] Working mechanism of reaction process control: The pH value of the first reaction tank is set to 10.5-11.0, and is controlled online through the NaOH solution dosing pump; the second reaction tank measures the calcium ion concentration of the mixed liquid in the reaction zone through the calcium ion online sampling and measuring instrument set therein, and its data is controlled online through the Na2CO3 solution dosing pump; an online sludge concentration meter and liquid level meter are set in the circulating membrane tank to monitor the sludge concentration and actual liquid level in the circulating membrane tank online respectively, and the monitoring data is controlled online through the circulating membrane tank sludge discharge electric valve.

[0050] The automatic switching mechanism for supernatant return and sludge discharge in the sludge tank works as follows: After the solid-liquid mixture has been allowed to stand for 20 minutes, a distinct interface stratification will form between the clear liquid and the sludge. A sludge interface instrument installed in the upper portion of the sludge tank performs online monitoring. When the interface layer height reaches set value ① (sludge discharge value), the sludge (clear liquid) discharge pump and sludge discharge electric valve are activated to initiate sludge discharge. As the sludge is discharged, when the interface layer height drops to set value ② (liquid discharge value), the sludge discharge electric valve is closed and the clear liquid return electric valve is opened, returning the clarified supernatant to the circulating membrane tank.

[0051] The working method for softening the concentrated liquid after leachate membrane using the above device comprises the following steps:

[0052] ① Add NaOH solution into the first reaction tank, and the concentrated liquid after leachate membrane flows into the first reaction tank, Mg 2+ With OH - The reaction generates solid Mg(OH)2, and at the same time, the HCO3 in the concentrated liquid after the leachate membrane - With OH - Reacts to produce CO3 2- and H2O, CO3 2- Mg 2+ and Ca 2+ The reaction generates solid MgCO3 and CaCO3. The pH in the first reaction tank is controlled at 10.5-11.0, and the Mg in the concentrated liquid after the leachate membrane is 2+ and HCO3 - Almost all of them participated in the relevant reactions, resulting in a higher removal rate; Ca 2+ It has also been removed to a certain extent;

[0053] ② After the first reaction tank, the concentrated liquid after the leachate membrane enters the second reaction tank, and Na2CO3 is added to the second reaction tank. The remaining small amount of Mg in the mixed liquid 2+ and a large amount of Ca 2+ With CO3 2- Reacts to produce MgCO3 and CaCO3;

[0054] ③ After passing through the second reaction tank, the leachate concentrate enters the circulating membrane tank. The circulating membrane tank, the ultrafiltration feed pump, the ultrafiltration membrane device, and the related pipelines form an ultrafiltration system. The mixed concentrate containing a large amount of solid particulate matter (MgCO3 and CaCO3) is separated into solids and liquids in the ultrafiltration system.

[0055] Mg in the concentrated liquid after leachate membrane 2+ and Ca 2+ The sludge discharged from the first reaction tank, the second reaction tank, the circulating membrane tank and the ultrafiltration membrane device is basically removed and the softening treatment is completed. The sludge discharged from the first reaction tank, the second reaction tank, the circulating membrane tank and the ultrafiltration membrane device is concentrated into the sludge tank and transported to the sludge disposal terminal for treatment through the external discharge pump.

[0056] Application Examples

[0057] The present invention's device for softening post-membrane leachate concentrate was used in a research and development project to soften the leachate concentrate mixture at a waste incineration power plant in Ningbo, Zhejiang Province. Construction and operational studies of the pilot system have been completed on-site. Field operation has demonstrated significant economic efficiency and hardness removal efficiency in softening the leachate concentrate mixture, achieving unattended automated operation. The pilot system is designed to process 10 tons per day and is configured for 20 hours of operation per day.

[0058]

[0059] The direct operating cost of the TUF softening system used in domestic waste incineration plants is generally RMB 13-14 per ton. By comparison, the present invention has been verified to save about 27% of the operating cost through actual operation.

[0060] The operating parameters of the built-in external pressure column-mounted ultrafiltration system (Enwei series ultrafiltration membrane components of Shanghai Cheran Environmental Protection Technology Co., Ltd.) are shown in the following table.

[0061]

[0062] Figure 4 This is the curve of hardness changing with pH value of the first reaction tank. Figure 5 This is the relationship curve between magnesium hardness removal and alkali dosage. Figure 6 Remove the response curve for hardness.

[0063]

[0064] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for softening and treating a leachate concentrate after membrane treatment, characterized in that: The device for softening the post-membrane concentrate of the leachate comprises a Na2CO3 solution storage tank (1), a Na2CO3 solution dosing pump (3) and a second reaction tank (6) connected in sequence, and a NaOH solution storage tank (2), a NaOH solution dosing pump (4) and a first reaction tank (5) connected in sequence, the inlet of the first reaction tank (5) flows into the post-membrane concentrate of the leachate, the first reaction tank (5), the second reaction tank (6) and the circulating membrane tank (7) are arranged side by side in sequence, the first reaction tank (5) and the second reaction tank (6) are both provided with a water baffle (14) and a crystallization catcher (15), the first reaction tank (5) and the second reaction tank (6) are The bottom outlets of the reaction tank (6) are connected to the inlet of the sludge tank (10), and the outlet of the sludge tank (10) is respectively connected to the sludge discharge pipeline and the clear liquid return pipeline through the external discharge pump (11), and the outlet of the clear liquid return pipeline is connected to the inlet of the circulating membrane tank (7), and the bottom outlet of the circulating membrane tank (7) is connected to the inlet of the sludge tank (10), and the lower outlet of the circulating membrane tank (7) is connected to the top inlet of the ultrafiltration membrane device (9) through the ultrafiltration water inlet pump (8), and the top outlet of the ultrafiltration membrane device (9) is respectively connected to the inlet of the first reaction tank (5) and the inlet of the circulating membrane tank (7), and the softened product water flows out of the side wall outlet of the circulating membrane tank (7); The water retaining plate (14) is located on the inner side of the crystallization catcher (15), and the crystallization catcher (15) is close to the side wall of the reaction tank; the crystallization catcher (15) is made of PP material; The crystallization catcher (15) includes a stainless steel mesh (24), a polyester fiber bundle is placed in the stainless steel mesh (24), the stainless steel mesh (24) and the stainless steel connecting rod (26) are welded into one body, and the left fixed slider (25) and the right fixed slider (27) are welded to the left and right ends of the stainless steel connecting rod (26), respectively, the left fixed slider (25) is installed in the left mounting rail (28), and the right fixed slider (27) is installed in the right mounting rail (29), and the left mounting rail (28) and the right mounting rail (29) are both welded to the inner wall of the reaction tank; the upper ends of the left mounting rail (28) and the right mounting rail (29) are both open, and the lower ends are provided with a limit bottom plate; The softening treatment method comprises the following steps: ① Add NaOH solution into the first reaction tank, and the concentrated liquid after leachate membrane flows into the first reaction tank, Mg 2+ With OH - The reaction generates solid Mg(OH)2, and at the same time, the HCO3 in the concentrated liquid after the leachate membrane - With OH - Reacts to produce CO3 2- and H2O, CO3 2- Mg 2+ and Ca 2+ The reaction generates solid MgCO3 and CaCO3, and the Mg in the concentrated liquid after the leachate membrane 2+ and HCO3 - All participate in the relevant reaction; the pH in the first reaction tank is controlled at 10.5-11.0; ② After the first reaction tank, the concentrated liquid after the leachate membrane enters the second reaction tank, and Na2CO3 is added to the second reaction tank. The remaining small amount of Mg in the mixed liquid 2+ and a large amount of Ca 2+ With CO3 2- Reacts to produce MgCO3 and CaCO3; ③ After passing through the second reaction tank, the concentrated liquid after the leachate membrane enters the circulating membrane tank. The circulating membrane tank, ultrafiltration water inlet pump, ultrafiltration membrane device, and related pipelines form an ultrafiltration system. The mixed concentrated liquid containing a large amount of solid particulate matter MgCO3 and CaCO3 is separated into solid and liquid in the ultrafiltration system.

2. The method for softening the post-membrane concentrate of leachate according to claim 1, characterized in that: Mg in the concentrated liquid after leachate membrane 2+ and Ca 2+ The sludge discharged from the first reaction tank, the second reaction tank, the circulating membrane tank and the ultrafiltration membrane device is concentrated into the sludge tank and transported to the sludge disposal terminal for treatment through the external discharge pump.

3. The method for softening the post-membrane leachate concentrate according to claim 1, characterized in that: The first reaction tank (5) is provided with a pH online monitor (20), a first agitator (12) is provided above the first reaction tank (5), a second agitator (13) is provided above the second reaction tank (6), a water hole communicating with the second reaction tank (6) is provided on the side wall above the crystallization catcher (15) in the first reaction tank (5), and a water hole communicating with the circulating membrane tank (7) is provided on the side wall above the crystallization catcher (15) in the second reaction tank (6).

4. The method for softening the post-membrane concentrate of leachate according to claim 3, characterized in that: The inner walls of the first reaction tank (5), the second reaction tank (6) and the circulating membrane tank (7), as well as the stirring blades of the first stirrer (12) and the second stirrer (13) are all spray-coated with PTFE material.

5. The method for softening the post-membrane concentrate of leachate according to claim 4, characterized in that: The ultrafiltration membrane device (9) has a built-in external pressure column-mounted ultrafiltration membrane with a working pressure of 0.03 MPa. The ultrafiltration membrane is made of PTFE material.

6. The method for softening the post-membrane leachate concentrate according to claim 5, characterized in that: A sludge interface meter (16) is provided in the sludge pool (10), a circulating membrane pool sludge discharge electric valve (19) is provided at the bottom outlet of the circulating membrane pool (7), a sludge discharge electric valve (17) is provided on the sludge discharge pipeline, and a clear liquid return electric valve (18) is provided on the clear liquid return pipeline.

7. The method for softening the post-membrane concentrate of leachate according to claim 6, characterized in that: The top of the second reaction tank (6) is connected to a measurement sampling tube (22) and a measurement reflux tube (23), the outlet of the measurement sampling tube (22) is connected to the inlet of the calcium ion online sampling and measuring instrument (21), and the outlet of the calcium ion online sampling and measuring instrument (21) is connected to the inlet of the measurement reflux tube (23).

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