A full-quantitative solidification treatment method for landfill leachate membrane filtration concentrate

Abstract

The application discloses a full-quantitative solidification treatment method for landfill leachate membrane filtration concentrated liquid, and comprises the following steps: S1, anti-salting pretreatment, adding calcium oxide and calcium chloride compound precipitation agent into the membrane filtration concentrated liquid, precipitating sulfate and chloride ions in the form of double salt at low temperature of 0-10 DEG C, and separating solid and liquid to obtain low-salt concentrated liquid; S2, heterogeneous Fenton-like oxidation, adjusting the pH of the low-salt concentrated liquid to 3.0-4.5, and introducing the low-salt concentrated liquid into a fixed bed reactor filled with porous carbon-based iron-manganese bimetallic composite catalyst, and adding hydrogen peroxide for oxidative degradation; and S3, salt-induced solidification, mixing the oxidized effluent with the salt mud obtained in S1, adding sulphoaluminate cement and phosphate stabilizer, stirring and forming, and curing to obtain a solidified body. Through the synergistic effect of low-temperature anti-salting and carbon-based catalyst, the problem of inhibition of high salinity on oxidation efficiency is solved, the calcium aluminate and Friedel salt are induced by using salt mud, and the full-quantitative harmless disposal of the concentrated liquid is realized.

Description

Technical Field

[0001] This invention relates to the fields of environmental engineering and solid waste treatment and disposal technology, specifically to a method for the full-scale, harmless solidification treatment of concentrated liquid generated after membrane filtration of landfill leachate. Background Technology

[0002] With the increasing volume of municipal solid waste disposed of through landfills and incineration, leachate treatment has become a crucial issue in environmental engineering. Currently, mainstream biological treatment combined with membrane advanced treatment processes typically generates approximately 10% to 20% of the treated water volume as membrane filtrate concentrate during operation. This concentrate is characterized by high COD, high ammonia nitrogen, high salinity (especially chloride and sulfate ions), and a high content of recalcitrant humic substances.

[0003] For the treatment of membrane filtrate concentrate, existing technologies mainly employ evaporation crystallization or traditional advanced oxidation processes. However, these existing technologies have certain limitations in engineering applications: 1) High energy consumption of evaporation process: Mechanical vapor recompression (MVR) or multi-effect evaporation (MED) processes have high equipment investment and operating energy consumption when treating high salinity wastewater, and the mother liquor generated after evaporation still needs further treatment.

[0004] 2) Traditional oxidation processes are inhibited by salt content: When treating high-salinity concentrates, traditional homogeneous Fenton or iron-carbon micro-electrolysis processes are prone to react with high concentrations of chloride and sulfate ions with hydroxyl radicals (·OH) to produce a free radical quenching effect, which leads to a decrease in the degradation efficiency of organic matter; at the same time, the strong acid reaction conditions are prone to producing a large amount of iron-containing sludge.

[0005] 3) Poor adaptability of conventional curing technologies: Existing concentrate curing technologies mostly use ordinary silicate cement. Because the concentrate contains high concentrations of chloride and sulfate ions, these ions interfere with the normal hydration reaction of the cement, resulting in lower compressive strength of the cured body, and there is uncertainty in controlling the long-term leaching toxicity of pollutants.

[0006] Therefore, there is an urgent need to develop a new process that can effectively overcome the interference of high salinity, reduce operating energy consumption, and achieve the harmless and full-scale treatment of concentrated liquid. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for the full-scale solidification treatment of landfill leachate membrane filtration concentrate.

[0008] Includes the following steps: S1 Anti-salting Pretreatment: Inorganic salt precipitation agent is added to the membrane filtrate concentrate produced after the landfill leachate is concentrated by nanofiltration or reverse osmosis membrane. The mixture is stirred and mixed at a low temperature of 0~10℃, so that sulfate ions and chloride ions in the concentrate are partially precipitated in the form of calcium sulfate and calcium chloride double salts. After solid-liquid separation, low-salt concentrate and salt mud are obtained.

[0009] S2 Heterogeneous Fenton-like Oxidation: The pH of the low-salt concentrate obtained in step S1 is adjusted to 3.0~4.5, and then passed into a fixed-bed reactor filled with a porous carbon-based supported iron-manganese bimetallic composite catalyst. At the same time, hydrogen peroxide with a mass concentration of 30% is added, and a Fenton-like oxidation reaction is carried out at room temperature to degrade humic acid macromolecular organic matter and obtain oxidized effluent.

[0010] S3 Salt-induced solidification: The oxidized water obtained in step S2 is mixed with the salt mud obtained in step S1. Sulfoaluminate cement is added as a solidifying agent and phosphate as a stabilizer. The mixture is stirred and molded, and then cured at room temperature. The sulfate and chloride ions in the salt mud induce the hydration of sulfoaluminate cement to generate ettringite and Friedel salt, thus fixing the pollutants in the crystal structure.

[0011] Specifically, in step S1, the inorganic salt precipitant is a composite precipitant composed of calcium oxide and calcium chloride in a mass ratio of 1:0.5~2.

[0012] Specifically, in step S1, the total amount of precipitant added is 2% to 8% of the mass of the membrane filtration concentrate.

[0013] Specifically, in step S2, the preparation method of the porous carbon-based supported iron-manganese bimetallic composite catalyst is as follows: the biomass raw material is carbonized at 400~600℃ for 2~4 hours under oxygen-deficient conditions to obtain a porous carbon-based support. The porous carbon-based support is then immersed in a mixed aqueous solution containing iron nitrate and manganese nitrate for 12~24 hours, and then taken out and calcined at 300~500℃ for 2~4 hours under a nitrogen atmosphere.

[0014] Specifically, the biomass raw material is selected from one of straw, rice husks, and sawdust.

[0015] Specifically, the catalyst has an iron loading of 5% to 15% and a manganese loading of 2% to 8%.

[0016] Specifically, in step S2, the amount of hydrogen peroxide added is 0.5% to 2.0% of the volume of the concentrated liquid.

[0017] Specifically, in step S2, the hydraulic residence time of the fixed-bed reactor is 60 to 180 minutes.

[0018] Specifically, in step S3, the mass ratio of oxidized water to salt mud is 1:0.05~0.2.

[0019] Specifically, in step S3, the specific surface area of ​​the sulfoaluminate cement is 350~450 m². 2 / kg.

[0020] Specifically, in step S3, the phosphate is potassium dihydrogen phosphate or sodium dihydrogen phosphate.

[0021] Specifically, in step S3, the amount of phosphate added accounts for 0.5% to 2.0% of the mass of the curing agent.

[0022] Specifically, in step S3, the curing time is 7 to 28 days.

[0023] Specifically, in step S3, the 28-day compressive strength of the obtained cured body is not less than 5.0 MPa, and the chloride ion fixation rate is not less than 95%.

[0024] It has the following beneficial effects: (1) The present invention employs a low-temperature anti-salting pretreatment, which involves adding a composite precipitant to precipitate some sulfate and chloride ions in the concentrate as double salts. This pretreatment step effectively reduces the salt concentration in the liquid phase and reduces the free radical quenching effect in the subsequent Fenton-like oxidation process, thereby improving the degradation efficiency of humic acid-based organic matter.

[0025] (2) This invention employs a porous carbon-based supported iron-manganese bimetallic composite catalyst. The carbon-based support has a certain adsorption and enrichment effect on macromolecular organic matter, and the iron-manganese bimetallic component can maintain good catalytic activity over a wide pH range (3.0~4.5). Compared with traditional alumina supports or iron-carbon fillers, this catalyst exhibits improved resistance to poisoning and stability under high salt and slightly acidic conditions.

[0026] (3) The salt mud produced in this invention is recycled into the solidification system. The sulfate and chloride ions contained in the salt mud can act as inducing agents to promote the formation of ettringite and Friedel salt in sulfoaluminate cement in an alkaline hydration environment. This process not only realizes the recycling of internal waste, but also the specific crystal structure generated helps to fix heavy metal ions and chloride ions in the crystal lattice, thereby improving the compressive strength of the solidified body and reducing the risk of pollutant leaching.

[0027] (4) The process of the present invention uses the precipitated salt mud directly as a component of the solidification system and the oxidized water as the solidification mixing water. There is no high-salt mother liquor reflux or discharge throughout the process, which realizes the reduction and full-volume treatment of membrane filtration concentrate. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0029] Figure 1 This is a flowchart illustrating the implementation steps of a method for the full-volume solidification treatment of landfill leachate membrane filtration concentrate according to the present invention. Detailed Implementation

[0030] It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0031] The following detailed description of the implementation method of the present invention is in conjunction with the accompanying drawings. The description is only a partial embodiment and not all embodiments. For clarity, representations and descriptions unrelated to the present invention are omitted in the drawings and description.

[0032] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this invention, the following detailed description of the technical solution is provided. Obviously, the described embodiments are only a portion of the embodiments of this invention, not all of them, and should not be construed as limiting the scope of implementation of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.

[0033] Example 1 This embodiment is a specific implementation of the present invention's method for the full-scale solidification treatment of landfill leachate membrane filtration concentrate.

[0034] In this embodiment, a membrane filtration concentrate from a municipal solid waste landfill was taken, with the following water quality indicators: COD 35000 mg / L, ammonia nitrogen 1200 mg / L, conductivity 45 mS / cm, chloride ion concentration 8500 mg / L, sulfate concentration 6200 mg / L, and pH 7.8.

[0035] In this embodiment, a method for the full-volume solidification treatment of landfill leachate membrane filtration concentrate is specifically as follows: S1 anti-salting pretreatment: Take 1000 kg of the above membrane filtration concentrate, add 40 kg of composite precipitant (calcium oxide to calcium chloride mass ratio 1:1), stir and mix at 5℃ for 40 minutes, centrifuge to obtain 960 kg of low-salt concentrate and 78 kg of wet salt mud (moisture content approximately 35%). The conductivity of the low-salt concentrate decreased to 28 mS / cm, the chloride ion concentration decreased to 5100 mg / L, and the sulfate concentration decreased to 3800 mg / L.

[0036] S2 heterogeneous Fenton oxidation: The low-salt concentrate obtained from S1 was adjusted to pH 4.0 with sulfuric acid and then passed into a fixed-bed reactor filled with 50 kg of porous carbon-based supported iron-manganese bimetallic composite catalyst.

[0037] Catalyst preparation method: Rice husks were carbonized at 500℃ in an oxygen-deficient environment for 3 hours. 100g of the carbonized product was then impregnated in 500mL of a mixed solution containing 80g of ferric nitrate (Fe(NO3)3·9H2O) and 25g of manganese nitrate (Mn(NO3)2·4H2O). After impregnation for 18 hours, the product was removed and calcined at 400℃ for 3 hours under a nitrogen atmosphere to obtain a catalyst with an iron loading of 12% and a manganese loading of 5%. Reactor operating conditions: Hydrogen peroxide (30%) dosage was 1.0% of the concentrated liquid volume; hydraulic retention time was 120 minutes; ambient temperature. The effluent COD was 380mg / L, ammonia nitrogen was 980mg / L, and iron ion concentration was <5mg / L.

[0038] S3 Salt-Induced Solidification: Take 100 kg of S2 oxidation effluent, add 8 kg of salt mud obtained from S1 (approximately 5.2 kg dry basis), and add sulfoaluminate cement (specific surface area 400 m²). 2 Add 30 kg of ( / kg) potassium dihydrogen phosphate and 0.3 kg of potassium dihydrogen phosphate, stir well, and pour into a 100 mm cube mold. Cure at room temperature for 7 days. The compressive strength of the cured body after 7 days is 3.8 MPa, and the compressive strength after 28 days is 5.6 MPa. The chloride ion fixation rate is 96.2% as determined by GB 16889 method, and the ammonia release is reduced by 84% compared with direct cement curing.

[0039] Example 2 This embodiment is a preferred implementation of Embodiment 1.

[0040] In this embodiment, the same concentrated solution as in Example 1 was used, the low temperature condition in step S1 was adjusted to 0°C, and the amount of composite precipitant added was 60 kg (calcium oxide to calcium chloride mass ratio 1:0.5).

[0041] In this embodiment, the conductivity of the low-salt concentrate was reduced to 22 mS / cm, the chloride ion concentration was reduced to 4200 mg / L, and the sulfate concentration was reduced to 3100 mg / L.

[0042] In this embodiment, the processing method is the same as in Embodiment 1.

[0043] In this embodiment, the COD of the oxidized effluent was measured to be 290 mg / L, the 7-day compressive strength of the solidified body was 4.2 MPa, and the chloride ion fixation rate was 97.5%.

[0044] Example 3 This embodiment is a preferred implementation of Embodiment 1.

[0045] In this embodiment, the same concentrate as in Example 1 was used, and the raw material for catalyst preparation in step S2 was adjusted to be wood chips, the carbonization temperature was 600°C, and the calcination temperature was 500°C, resulting in a catalyst with an iron loading of 10% and a manganese loading of 6%.

[0046] In this embodiment, the processing method is the same as in Embodiment 1.

[0047] In this embodiment, the COD of the oxidized effluent was measured to be 350 mg / L, and the compressive strength of the solidified body after 7 days was 3.9 MPa.

[0048] Example 4 This embodiment is a preferred implementation of Embodiment 1.

[0049] In this embodiment, the same concentrated solution as in Example 1 was used, and the amount of curing agent in step S3 was adjusted to 25 kg, and the phosphate was 0.4 kg of sodium dihydrogen phosphate.

[0050] In this embodiment, the processing method is the same as in Embodiment 1.

[0051] In this embodiment, the 7-day compressive strength of the cured body was tested to be 3.5 MPa, and the chloride ion fixation rate was 95.8%.

[0052] Comparative Example 1 This comparative example is an adjustment based on Example 1, and verifies the beneficial effects of the full-scale solidification treatment method for landfill leachate membrane filtration concentrate of the present invention.

[0053] In this comparative example, step S1 is omitted, and the original concentrate is directly subjected to Fenton oxidation (pH adjusted to 4.0) in step S2.

[0054] In this comparative example, the processing method is the same as in Example 1.

[0055] In this comparative example, the COD of the oxidized effluent was measured to be 1250 mg / L, and the COD removal rate was only 64.3% (compared to 89.1% in Example 1).

[0056] In this comparative example, the catalyst was found to have decreased activity by 40% after 72 hours of operation.

[0057] In this comparative example, the curing step was carried out under the conditions of Example 1. The curing body was tested and found to have a compressive strength of only 1.2 MPa after 7 days, and a chloride ion fixation rate of 82%.

[0058] Comparative Example 2 This comparative example is an adjustment based on Example 1, and verifies the beneficial effects of the full-scale solidification treatment method for landfill leachate membrane filtration concentrate of the present invention.

[0059] In this comparative example, the salt mud obtained from S1 was not used for S3 curing; S3 curing used only sulfoaluminate cement and phosphate.

[0060] In this comparative example, the 7-day compressive strength of the solidified body was tested to be 2.8 MPa, and the chloride ion fixation rate was 88%, indicating that the lack of salt mud led to insufficient formation of ettringite and Friedel salt.

[0061] In summary, the anti-salting pretreatment of the present invention can significantly reduce the inhibition of Fenton-like reactions by salt in the concentrate, the carbon-based catalyst has a better targeted degradation efficiency of humic acid than existing Fenton-like catalysts, and the salt-induced solidification utilizes the precipitated salt mud to greatly improve the strength of the solidified body and the chloride ion fixation rate. The coupling of these three factors realizes the efficient, stable, low-cost full-scale treatment of membrane filtration concentrate.

[0062] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for the full-volume solidification treatment of landfill leachate membrane filtration concentrate, characterized in that, Includes the following steps: S1 Anti-salting pretreatment: An inorganic salt precipitant is added to the membrane concentrate produced after nanofiltration or reverse osmosis of landfill leachate. The mixture is stirred and mixed at a low temperature of 0-10℃, causing sulfate and chloride ions in the concentrate to partially precipitate as calcium sulfate and calcium chloride double salts. After solid-liquid separation, a low-salt concentrate and salt sludge are obtained. S2 Heterogeneous Fenton-like oxidation: The pH of the low-salt concentrate obtained in step S1 is adjusted to 3.0-4.5, and then passed through a fixed-bed reactor filled with a porous carbon-based supported iron-manganese bimetallic composite catalyst. In the reactor, hydrogen peroxide with a mass concentration of 30% is added simultaneously, and a Fenton-like oxidation reaction is carried out at room temperature to degrade humic acid macromolecular organic matter and obtain oxidized effluent; S3 Salt-induced solidification: The oxidized effluent obtained in step S2 is mixed with the salt mud obtained in step S1, sulfoaluminate cement is added as a solidifying agent, and phosphate is added as a stabilizer, and the mixture is stirred and molded. It is then cured at room temperature. The sulfate and chloride ions in the salt mud induce the hydration of sulfoaluminate cement to generate ettringite and Friedel salt, which fix the pollutants in the crystal structure.

2. The method for full-volume solidification treatment of landfill leachate membrane filtration concentrate according to claim 1, characterized in that: In step S1, the inorganic salt precipitant is a composite precipitant composed of calcium oxide and calcium chloride in a mass ratio of 1:0.5~2; the total amount of the precipitant added is 2%~8% of the mass of the membrane filtration concentrate.

3. The method for full-volume solidification treatment of landfill leachate membrane filtration concentrate according to claim 1, characterized in that: In step S2, the preparation method of the porous carbon-based supported iron-manganese bimetallic composite catalyst is as follows: the biomass raw material is carbonized at 400~600℃ for 2~4 hours under oxygen-deficient conditions to obtain a porous carbon-based support. The porous carbon-based support is immersed in a mixed aqueous solution containing iron nitrate and manganese nitrate for 12~24 hours, then removed and calcined at 300~500℃ for 2~4 hours under a nitrogen atmosphere.

4. The method for full-volume solidification treatment of landfill leachate membrane filtration concentrate according to claim 3, characterized in that: The biomass raw material is selected from one of straw, rice husk, and sawdust; the catalyst has an iron loading of 5% to 15% and a manganese loading of 2% to 8%.

5. The method for full-volume solidification treatment of landfill leachate membrane filtration concentrate according to claim 1, characterized in that: In step S2, the amount of hydrogen peroxide added is 0.5% to 2.0% of the volume of the concentrate; the hydraulic residence time of the fixed-bed reactor is 60 to 180 minutes.

6. The method for full-volume solidification treatment of landfill leachate membrane filtration concentrate according to claim 1, characterized in that: In step S3, the mass ratio of oxidized effluent to salt mud is 1:0.05~0.2; the specific surface area of ​​the sulfoaluminate cement is 350~450 m². 2 / kg.

7. The method for full-volume solidification treatment of landfill leachate membrane filtration concentrate according to claim 1, characterized in that: In step S3, the phosphate is potassium dihydrogen phosphate or sodium dihydrogen phosphate; the amount of phosphate added accounts for 0.5% to 2.0% of the mass of the curing agent.

8. The method for full-volume solidification treatment of landfill leachate membrane filtration concentrate according to claim 1, characterized in that: In step S3, the curing time is 7 to 28 days; the 28-day compressive strength of the obtained cured body is not less than 5.0 MPa, and the chloride ion fixation rate is not less than 95%.

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