Treatment and utilization method of high calcium leachate nanofiltration concentrate

Abstract

The present invention belongs to the technical field of landfill leachate treatment, and specifically relates to a method for treating and utilizing high-calcium leachate nanofiltration concentrate. A three-stage ultrafiltration system is mainly used to separate and concentrate the nanofiltration concentrate at a high multiple, and a gypsum crystallization precipitation and divalent ion control system are used to efficiently remove the high-concentration calcium in the secondary ultrafiltration retentate containing scale inhibitors and the secondary ultrafiltration permeate without scale inhibitors and the tertiary ultrafiltration permeate formed during the process. 2+ and SO4 2‑ , and combined with the nanofiltration system to achieve the purpose of closed-loop treatment of high-calcium leachate and nanofiltration concentrate and utilization of humic acid resources. In order to effectively inhibit the scaling of the secondary ultrafiltration permeate formed in the process due to excessively high calcium ion concentration, the Ca 2+ <3000mg / L. This method is efficient, practical, economical, easy to operate, stable in operation and has strong adaptability.

Description

Technical Field

[0001] The invention belongs to the technical field of landfill leachate treatment, and in particular relates to a method for treating and utilizing high-calcium leachate nanofiltration concentrate. Background Art

[0002] The MBR+NF process is the mainstream technology for treating landfill leachate, but its disadvantage is that it produces nanofiltration concentrate that accounts for 10-20% of the original liquid volume. Currently, there is no recognized and fully applicable typical treatment process. The treatment process using a single multi-stage material membrane can achieve the reduction of nanofiltration concentrate (tail water recovery rate is about 75%), and the authorized invention patent "Treatment and Utilization Method of Nanofiltration Concentrate of High Sulfate Leachate" (ZL201910754284.6) also provides a method for treating high-concentration SO4 2- For feed liquids containing divalent ions such as secondary ultrafiltration permeate and nanofiltration retentate, the method of removing gypsum crystallization precipitation is adopted. The combination of the two can achieve the full treatment of nanofiltration concentrate. Therefore, the treatment process based on material membrane will gradually become the mainstream method for nanofiltration concentrate. However, the material membrane also inevitably has the problem of membrane pollution, making it difficult to achieve high-multiple separation and concentration. For the nanofiltration concentrate formed during the conventional landfill leachate MBR+NF process treatment, because it contains Ca 2+ The concentration is generally lower than 350 mg / L, and it is easy to achieve 30 to 40 times of separation and concentration. However, for the landfill leachate nanofiltration concentrate with membrane concentrate reinjection, or the leachate nanofiltration concentrate from the waste incineration power plant, the Ca 2+ The concentration is often higher than 700 mg / L. Even if the method provided by the invention patent "Treatment and Utilization Method of High Sulfate Leachate Nanofiltration Concentrate" (ZL201910754284.6) is adopted, the Ca2+ content in the secondary ultrafiltration permeate is still high due to the lack of efficient commercial scale inhibitors (membrane separation and retention). 2+ When the concentration is greater than 3000~4000mg / L, it is easy to form scales such as calcium carbonate and calcium phosphate in the membrane support layer, causing a significant increase in membrane filtration resistance and a rapid decrease in membrane flux. In addition, scaling is formed in the secondary ultrafiltration permeate delivery pipeline and the liquid contact surface of the instrument, causing pipeline blockage and instrument detection information errors. Although the membrane fouling problem can be solved by methods such as chemical cleaning, it is difficult to increase the concentration ratio, so it is impossible to achieve full treatment. Further treatment methods such as evaporation or advanced oxidation are expensive or have poor operational stability. Therefore, it is necessary to further develop a method for treating and utilizing high-calcium leachate nanofiltration concentrate that is more efficient, economical, simple to operate, and stable in operation. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for treating and utilizing high calcium leachate nanofiltration concentrate, which is aimed at the lack of commercial scale inhibitors in the permeate of material membrane separation. 2+ When the concentration is too high, membrane fouling and pipe scaling are likely to occur, which will affect the treatment efficiency of the nanofiltration concentrate. By performing gypsum crystallization precipitation on the permeate and retentate of the secondary ultrafiltration, the Ca content in the feed liquid of the process membrane system can be regulated. 2+ and SO4 2- At an appropriate concentration level, this method is efficient, practical, economical, easy to operate, stable in operation, highly adaptable, and can realize the utilization of humic acid resources.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for treating and utilizing high-calcium leachate nanofiltration concentrate comprises the following steps:

[0006] 1) The landfill leachate nanofiltration concentrate is pumped into a primary ultrafiltration system, and after membrane separation, a primary ultrafiltration retentate and a primary ultrafiltration permeate are obtained; the primary ultrafiltration retentate is pumped into a secondary ultrafiltration system, and after membrane separation, a secondary ultrafiltration retentate and a secondary ultrafiltration permeate are obtained; the primary ultrafiltration permeate is pumped into a nanofiltration system to obtain a nanofiltration retentate and a nanofiltration permeate, and the obtained nanofiltration retentate is returned to the primary ultrafiltration system for cyclic separation and concentration, and the obtained nanofiltration permeate meets the discharge standards; the secondary ultrafiltration retentate is pumped into a gypsum crystallization precipitation system to obtain a supernatant and precipitated sludge; the supernatant of the gypsum crystallization precipitation system is filtered and pumped into a tertiary ultrafiltration system, and after membrane separation, a tertiary ultrafiltration retentate and a tertiary ultrafiltration permeate are obtained; the tertiary ultrafiltration retentate is used as a raw material for humic acid liquid fertilizer or for back-spray incineration or fly ash humidification;

[0007] 2) The secondary ultrafiltration permeate and the tertiary ultrafiltration permeate obtained in step 1) are fed into a divalent ion control system to adjust the pH value of the wastewater in the reactor for reaction; after the reaction, supernatant and precipitated sludge are obtained by precipitation; the supernatant of the divalent ion control system is filtered and then returned to the primary ultrafiltration system for circulation, separation and concentration; the precipitated sludge of the divalent ion control system is mixed with the precipitated sludge of the gypsum crystallization precipitation system obtained in step 1) for dehydration treatment and disposal.

[0008] Furthermore, in step 1), the Ca content of the secondary ultrafiltration liquid is controlled. 2+ <3000mg / L.

[0009] Furthermore, in step 1), the pH value of the gypsum crystallization reaction is first adjusted to 1.0-2.5, and the reaction is carried out for 2-4 hours; then the pH value is adjusted to 4-5, and the reaction is carried out for 1-1.5 hours; the operation mode is intermittent.

[0010] Furthermore, in step 1), the operating pressure of the three-stage ultrafiltration system is 1.0-2.5 MPa, the concentration multiple is 2-4 times, the molecular weight cut-off of the ultrafiltration membrane used is 2500-5000 Da; and the operation mode is intermittent.

[0011] Furthermore, in step 2), the pH value of the wastewater in the reactor is adjusted to 2.5 using concentrated hydrochloric acid.

[0012] The significant advantages of the present invention are:

[0013] (1) Efficient and practical. When the nanofiltration concentrate contains Ca 2+ When the concentration is greater than 700 mg / L, the Ca content in the secondary ultrafiltration solution is about 30 times the actual concentration. 2+ The concentration can reach more than 3000 mg / L. It was found that the float flowmeter and the surface of the pipeline that transported the secondary ultrafiltration permeate were scaling. At the same time, the membrane flux decayed very quickly, and the chemical cleaning cycle was significantly shortened. In order to avoid scaling, the concentration multiple can only be reduced to 10~15 times. The treatment effect of the nanofiltration concentrate dropped from full amount to reduced amount, that is, a large amount of wastewater needs to be further treated, and the humic acid content in the final humic acid-containing retentate is low, which is not suitable for use as a humic acid liquid fertilizer raw material. Usually, the wastewater and the final humic acid-containing retentate need to be further treated by evaporation and other methods, and the technical stability and economy are poor. This method is used to control the Ca in the secondary ultrafiltration permeate. 2+ When the COD content is less than 3,000 mg / L, the secondary ultrafiltration system operates stably, and the COD concentration of humic acid in the final tertiary ultrafiltration retentate can reach a stable level above 60,000 mg / L, suitable for use as a raw material for humic acid liquid fertilizer. The total concentration factor can also reach 30 to 40 times. Therefore, this method demonstrates high efficiency and practicality.

[0014] (2) Simple operation and good economy. Compared with the invention patent "Method for treating and utilizing high sulfate leachate nanofiltration concentrate" (ZL201910754284.6), this method adds a gypsum crystallization precipitation system and a three-stage ultrafiltration system. Both adopt intermittent operation mode, and the amount of water treated by both is very small compared with the original liquid (only less than 20% of the latter). Therefore, the operation is flexible and simple, and the engineering cost and operating costs of the required system are relatively low.

[0015] (3) Strong adaptability. The newly added gypsum crystallization precipitation system in this method treats the secondary ultrafiltration retentate containing high concentrations of scale inhibitors and humic acid, which have a strong inhibitory effect on gypsum crystallization. The reaction needs to be adjusted to a lower pH value to effectively induce gypsum crystallization and achieve the removal of Ca 2+ and SO4 2-After that, the pH value is only adjusted to between 4 and 5. On the one hand, it reduces the amount of alkaline reagents used, and on the other hand, it can inhibit the formation of calcium carbonate, reduce its adverse effects on the tertiary ultrafiltration system, and improve the stability of the system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0017] The following is combined with Figure 1 , the process flow of the present invention is further described.

[0018] The entire process includes a primary ultrafiltration system, a secondary ultrafiltration system, a nanofiltration system, a tertiary ultrafiltration system, a divalent ion control system for sulfate and calcium ion reactions, and a gypsum crystallization precipitation system. The specific process is as follows: (1) 2+ (1) The leachate and divalent ion nanofiltration concentrate is pumped into the first-stage ultrafiltration system for separation and concentration to form the first-stage ultrafiltration retentate and the first-stage ultrafiltration permeate; (2) The obtained first-stage ultrafiltration retentate is pumped into the second-stage ultrafiltration system for separation and concentration to form the second-stage ultrafiltration retentate and the second-stage ultrafiltration permeate; (3) The first-stage ultrafiltration permeate is pumped into the nanofiltration system to obtain the nanofiltration retentate and the nanofiltration permeate, and the obtained nanofiltration retentate is returned to the first-stage ultrafiltration system for circulation separation and concentration, and the obtained nanofiltration permeate can meet the discharge standards; (4) The second-stage ultrafiltration retentate is pumped into the gypsum crystallization precipitation system, and the pH in the reactor is adjusted to 1~2.5, and the reaction is carried out for 2~4h, and then the pH is adjusted to 4~5, and then it is allowed to settle for 1~1.5h to obtain the supernatant and the precipitated sludge; this unit process adopts intermittent operation; (5) The supernatant of the gypsum crystallization precipitation system is discharged and pumped into the third-stage ultrafiltration system after filtration. The system has an operating pressure of 1~2.5MPa and a concentration ratio of 2~4 times. The ultrafiltration membrane used is an anti-pollution high salt permeability ultrafiltration membrane with a molecular weight cutoff of 2500~5000Da. After membrane separation, the third-stage ultrafiltration retentate and the third-stage ultrafiltration permeate are obtained. The humic acid concentration in the third-stage ultrafiltration retentate is >30g / L, which can be used as a raw material for humic acid liquid fertilizer, or for fly ash humidification and back-spray incineration. This unit adopts an intermittent operation mode. (6) The second-stage ultrafiltration permeate and the third-stage ultrafiltration permeate flow into the divalent ion control system, and then the pH of the feed liquid is adjusted to perform gypsum crystallization precipitation. After the reaction, solid-liquid separation is performed to obtain supernatant and precipitated sludge. The supernatant of the divalent ion control system is discharged, filtered, and then returned to the first-stage ultrafiltration system for re-separation and concentration. (7) The gypsum crystallization precipitation system and the precipitated sludge of the divalent ion control system are discharged and further disposed after dehydration.

[0019] Example 1

[0020] The present invention is further illustrated below by taking the treatment and utilization of the nanofiltration concentrate produced by the mixed leachate treatment project of a domestic waste incineration power plant and a landfill in a circular economy ecological industrial park as an example.

[0021] The scale of the mixed leachate treatment project of the municipal solid waste incineration power plant and landfill is 1,300 tons / day, and it adopts a two-stage A / O+UF (MBR)+NF combined process. The treatment project produces about 240 tons of nanofiltration concentrate per day, and its water quality is as follows: pH 6.5-7.1, COD between 1500-3000mg / L, conductivity between 13-17mS / cm, SO4 2- Between 2500~4000mg / L, Ca 2+ The concentration range is 500~1000mg / L, which is significantly higher than the Ca content in the nanofiltration concentrate of the conventional landfill leachate. 2+ The concentration is generally lower than 350 mg / L, making it difficult to use the method provided in the invention patent "Method for the Treatment and Utilization of Nanofiltration Concentrate of High Sulfate Leachate" (ZL201910754284.6) for high-multiple separation and concentration (less than 20 times). The nanofiltration concentrate is pumped from the collection pool into the first-stage ultrafiltration feed barrel. After the pH is adjusted to between 6.0-6.5, it is pumped into the first-stage ultrafiltration system for 4-7 times separation and concentration. The resulting first-stage ultrafiltration retentate is first collected in the intermediate barrel and then pumped into the second-stage ultrafiltration system for 3-7 times separation and concentration. The resulting first-stage ultrafiltration permeate is also first collected in the intermediate barrel and then pumped into the nanofiltration system for 2-4 times separation and concentration. The resulting nanofiltration permeate meets the requirements of the "Pollution Control Standards for Municipal Waste Landfills" (GB16889-2008) and can be discharged directly. The nanofiltration retentate produced by the nanofiltration system is returned to the first-stage ultrafiltration system feed barrel for re-separation and concentration. The Ca content in the second-stage ultrafiltration retentate produced by the second-stage ultrafiltration system is 0.01%. 2+ Concentrations above 5000mg / L (SO4 2- The concentration reaches 13000mg / L or above) is first collected in the middle barrel and then pumped into the gypsum crystallization precipitation system. The pH of the wastewater in the reactor is adjusted to 1.8~2. The gypsum crystallization reaction is 3h, and then the pH value is adjusted back to 4.5. Then it is settled for 1h to obtain the supernatant and precipitated sludge. This system adopts intermittent operation to improve operational flexibility. The gypsum crystallization precipitation system has a great influence on the Ca 2+The removal rate can reach 40~60%, and the loss rate of organic matter retained in the supernatant due to adhesion to the sludge during crystallization and precipitation is less than 10%. The dosage (volume ratio) of concentrated hydrochloric acid and 40% sodium hydroxide solution for adjusting pH is 1.5~2% and 1~1.5% respectively; the supernatant is sucked by the pump and filtered, first collected in the intermediate material barrel, and then pumped into the three-stage ultrafiltration system. The molecular weight cutoff of the ultrafiltration membrane of this system is 2500~5000Da, the operating pressure difference is 1~2.5Mpa, and the concentration times is 2.5~3. The number is 2 to 4 times. After membrane separation, the COD of the tertiary ultrafiltration retentate reaches 60,000 to 100,000 mg / L, the conductivity is 27 to 33 mS / cm, the humic acid concentration is about 34,000 to 50,000 mg / L, and the color is black. It can be used as a raw material for humic acid liquid fertilizer, or for fly ash humidification and back-spray incineration. This unit also adopts intermittent operation to improve operational flexibility and adapt to poor water quality such as high concentrations of humic acid and divalent ions in the feed liquid and possible frequent chemical cleaning. The Ca content in the secondary ultrafiltration permeate and tertiary ultrafiltration permeate produced by the secondary ultrafiltration system and the tertiary ultrafiltration system is 2 to 4 times. 2+ The concentrations were 2200~3000mg / L and 2900-4000mg / L (SO4 2- The concentrations reach 8,000-13,000 mg / L and 15,000-25,000 mg / L, respectively), and both flow into the divalent ion control system to adjust the pH of the feed liquid to 2-3. After reacting for 3-4 hours, the mud and water are separated to obtain a supernatant and precipitated sludge. The supernatant of the divalent ion control system is discharged into the intermediate material barrel and, after filtration, is also returned to the first-stage ultrafiltration water inlet barrel to be mixed with the nanofiltration concentrate (mixed liquid) as the first-stage ultrafiltration feed liquid. The precipitated sludge of the gypsum crystallization precipitation system and the divalent ion control system is discharged and further landfilled after mechanical dehydration. This method is used to separate and concentrate the nanofiltration concentrate of the mixed leachate from the municipal solid waste incineration power plant and landfill by 30-40 times, realizing full treatment.

[0022] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for treating and utilizing high calcium leachate nanofiltration concentrate, characterized in that: The steps include: 1) Pumping the landfill leachate nanofiltration concentrate into a primary ultrafiltration system to obtain a primary ultrafiltration retentate and a primary ultrafiltration permeate after membrane separation; pumping the primary ultrafiltration retentate into a secondary ultrafiltration system to obtain a secondary ultrafiltration retentate and a secondary ultrafiltration permeate after membrane separation; pumping the primary ultrafiltration permeate into a nanofiltration system to obtain a nanofiltration retentate and a nanofiltration permeate, and the obtained nanofiltration retentate is refluxed into the primary ultrafiltration system for cyclic separation and concentration, and the obtained nanofiltration permeate meets the discharge standards; The secondary ultrafiltration retentate is pumped into the gypsum crystallization precipitation system to obtain supernatant and precipitated sludge; the supernatant of the gypsum crystallization precipitation system is filtered and pumped into the tertiary ultrafiltration system to obtain the tertiary ultrafiltration retentate and tertiary ultrafiltration permeate after membrane separation; The tertiary ultrafiltration retentate is used as the raw material of humic acid liquid fertilizer or for back-spray incineration or fly ash humidification; 2) the secondary ultrafiltration permeate and the tertiary ultrafiltration permeate obtained in step 1) are introduced into a divalent ion control system, the pH value of the wastewater in the reactor of the divalent ion control system is adjusted to 2 to 3 for reaction, and after the reaction, a supernatant and precipitated sludge are obtained by precipitation; The supernatant of the divalent ion control system is filtered and then returned to the primary ultrafiltration system for circulation separation and concentration; The sludge precipitated from the divalent ion regulation system is mixed with the sludge precipitated from the gypsum crystallization precipitation system obtained in step 1) and subjected to dehydration treatment and disposal; wherein step 1) the landfill leachate nanofiltration concentrate Ca 2+ The concentration range is 500~1000mg / L. The Ca content in the secondary ultrafiltration solution in step 1) is controlled. 2+ <3000mg / L.

2. The method for treating and utilizing high-calcium leachate nanofiltration concentrate according to claim 1, characterized in that: In step 1), the pH value of the crystallization reaction in the gypsum crystal precipitation system is first adjusted to 1.0-2.5 and reacted for 2-4 hours; then the pH value is adjusted to 4-5 and settled for 1-1.5 hours.

3. The method for treating and utilizing high-calcium leachate nanofiltration concentrate according to claim 1, characterized in that: In step 1), the gypsum crystallization precipitation system is operated in an intermittent manner.

4. The method for treating and utilizing high-calcium leachate nanofiltration concentrate according to claim 1, characterized in that: The operating pressure of the three-stage ultrafiltration system in step 1) is 1.0 to 2.5 MPa, and the concentration multiple is 2 to 4 times.

5. The method for treating and utilizing high-calcium leachate nanofiltration concentrate according to claim 1, characterized in that: Step 1) The ultrafiltration membrane used in the three-stage ultrafiltration system has a molecular weight cutoff of 2500 to 5000 Da; the operation mode is intermittent.

6. The method for treating and utilizing high-calcium leachate nanofiltration concentrate according to claim 1, characterized in that: In step 2), the pH value of the wastewater in the reactor in the divalent ion control system is adjusted using concentrated hydrochloric acid.

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