A method for treating landfill leachate

Abstract

The application discloses a kind of garbage leachate processing method, belong to wastewater treatment technical field, comprising the following steps: first, adjust the pH of garbage leachate MBR effluent to weak acidity, coagulant and flocculant are added in turn stirring and standing, adjust pH to weak alkalinity, standing precipitation, obtain pretreated wastewater;Second, sodium alginate is added to water stirring and dissolving, add hydroxyl-terminated hyperbranched modified graphene, after stirring dispersion, obtain glue liquid, ferrous sulfate solution is added dropwise to glue liquid and mixed, after stirring, add reducing agent, continue stirring, dropwise to calcium chloride solution, stand, obtain spherical particle, after washing, by freeze drying, obtain catalyst;Third, catalyst is added to pretreated wastewater, adjust pH value to 3-5, add hydrogen peroxide, blast stirring, add flocculant stirring and standing, effluent.By adding self-made catalyst solves the existing H2O2 utilization rate is low, the problem of large amount of iron mud.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and specifically relates to a method for treating landfill leachate. Background Technology

[0002] Characteristics of Leachate from Waste Transfer Stations: With the continuous increase in the amount of urban domestic waste, the implementation of waste sorting, collection, and treatment is imperative. As the link between the waste generation source and the final disposal system, waste transfer stations face an unavoidable problem in compressing waste and collecting wastewater: the pollution of the surrounding environment by leachate during waste compression. Not only is the stench unbearable, but the leachate also becomes increasingly difficult to treat over time. Compared to uncontrolled leachate discharges from other stages of the waste collection and transportation system (such as garbage truck leaks and damaged garbage sheds), the leachate produced by waste transfer stations is characterized by concentrated generation and large volume. From a pollution treatment perspective, the leachate (i.e., press filtrate) generated during transfer operations has fundamentally different properties from the domestic sewage within the transfer station. Specifically, the press filtrate generated during waste compression mainly consists of moisture inherent in the waste itself and moisture from rainfall; the volume is relatively small, but the pollutant concentration is very high.

[0003] Due to the high level of organic pollution and ammonia nitrogen in leachate from waste transfer stations, there are currently three main treatment methods: biochemical-ultrafiltration (MBR) + nanofiltration / reverse osmosis (NF / RO), pretreatment + two-stage disc reverse osmosis, and two-stage A / O + ultrafiltration (MBR) + Fenton (or other advanced treatment).

[0004] The biochemical-MBR+NF / RO process combines the advantages of biochemical and membrane separation technologies. It degrades most pollutants through a series of processes, while membrane separation ensures effluent meets standards. There are numerous engineering examples, and the investment and operating costs are moderate. However, the system remains relatively complex and is highly dependent on the biodegradability of the leachate. It also suffers from late-stage instability (the accumulation of salts in the concentrate within the leachate leads to a progressively shorter membrane lifespan).

[0005] Two-stage disc reverse osmosis systems are simple, flexible in operation, easy to manage, and quick to debug. However, the operating cost of this process is relatively high, and it is only a simple material separation process, which cannot completely decompose pollutants in landfill leachate.

[0006] Fenton Process Introduction: For landfill leachate that has undergone prolonged biochemical treatment, the residual organic matter is often highly recalcitrant soluble organic matter. The most common treatment method for this type of organic matter is Advanced Oxidation Process (AOP). AOP utilizes hydroxyl radicals (standard electrode potential 2.80) generated during the reaction to oxidize the organic matter, producing highly oxidizing hydroxyl radicals. Fenton oxidation is one of the most representative types of AOP.

[0007] Advanced oxidation technologies, such as the Fenton reaction, can replace membrane processes for the full-scale treatment of landfill leachate, addressing the problems of membrane fouling and the difficulty in treating concentrated leachate generated in membrane processes. However, this technology has drawbacks such as low H2O2 utilization, difficulty in catalyst separation, large amounts of iron sludge, and easy discoloration of the effluent. Summary of the Invention

[0008] The purpose of this invention is to provide a method for treating landfill leachate to solve the problems of low H2O2 utilization and large amount of iron sludge.

[0009] The objective of this invention can be achieved through the following technical solutions:

[0010] A method for treating landfill leachate includes the following steps:

[0011] Step 1: Adjust the pH of the landfill leachate MBR effluent to a slightly acidic state, add coagulant and flocculant in sequence, stir and let stand, adjust the pH to a slightly alkaline state, let stand and settle to obtain pretreated wastewater;

[0012] The second step involves dissolving sodium alginate in water by stirring, adding hydroxyl-terminated hyperbranched graphene, and stirring to disperse it to obtain a gel. Ferrous sulfate solution is then added dropwise to the gel and mixed. After stirring, a reducing agent is added and stirring is continued. The mixture is then added dropwise to calcium chloride solution and allowed to stand to obtain spherical particles. After washing with water, the particles are freeze-dried to obtain a catalyst. The hydroxyl-terminated hyperbranched graphene is grafted onto AB-type monomer N,N-dihydroxyethyl 3-aminopropionate using a one-step esterification condensation method to obtain hydroxyl-terminated hyperbranched graphene.

[0013] The third step is to add a catalyst to the pretreated wastewater, adjust the pH to 3-5, add hydrogen peroxide, stir with a blower, recover and separate the catalyst, add flocculant, stir and let stand, and then effluent.

[0014] Furthermore, in the first step, the pH range for weakly acidic conditions is 4.5-5, and the pH range for weakly alkaline conditions is 8.5-9.

[0015] Furthermore, the amount of catalyst added is 10-40% of the mass of the pretreated wastewater; the amount of hydrogen peroxide added is 2-4% of the mass of the pretreated wastewater.

[0016] Furthermore, the ratio of sodium alginate, water, hydroxyl-terminated hyperbranched graphene, and ferrous sulfate solution is 2g:100mL:0.1-0.2g:100mL.

[0017] Furthermore, the concentration of ferrous sulfate is 0.1-0.2 mol / L; the concentration of calcium chloride solution is 0.7-1 mol / L.

[0018] Furthermore, the particle size of the spherical particles is 2-3 mm.

[0019] Furthermore, the freeze-drying temperature is -48℃ to -50℃.

[0020] Furthermore, the reducing agent includes one of sodium borohydride and tea polyphenols.

[0021] Furthermore, the catalyst also includes magnetic particles.

[0022] The beneficial effects of this invention are:

[0023] This invention provides a method for treating landfill leachate. Pretreated wastewater obtained after conventional MBR treatment undergoes Fenton oxidation treatment. A self-made catalyst is added to address the existing problems of low H2O2 utilization and high iron sludge content. Furthermore, when adding the catalyst to the pretreated wastewater, the pH is adjusted to 3-5. Under acidic conditions, metal ions dissolve more easily, which improves the catalytic efficiency of H2O2.

[0024] In this invention, sodium alginate is used as the catalyst carrier. A colloid prepared by combining hydroxyl-terminated hyperbranched graphene fixes nano-iron inside the catalyst or fixes it on the catalyst surface in the form of iron oxide through a reduction reaction. The polar groups (carboxyl and hydroxyl groups) in sodium alginate and hydroxyl-terminated hyperbranched graphene can coordinate with iron ions to fix them, thereby better coating the nano-iron and inhibiting the loss of iron ions. At the same time, the addition of hydroxyl-terminated hyperbranched graphene not only increases the capacity of iron ions, but also serves as a skeletal support structure to prevent the catalyst surface from collapsing during the subsequent low-temperature freeze-drying process, which would lead to the destruction of the catalyst's stability.

[0025] The catalyst in this invention is dried by low-temperature freeze drying. After freeze drying, a large number of pores are generated, which increases the reaction sites of the catalyst. The increase in porosity also accelerates the adsorption and degradation reaction rate of pollutants. The added terminal hydroxyl hyperbranched modified graphene not only has a rigid framework, but its branched structure also reduces the overall brittleness of the catalyst, which is beneficial to extending its service life.

[0026] Magnetic particles can be added to the catalyst in this invention. During subsequent reuse, magnetic separation can be used to improve separation efficiency, solving the problem of difficult catalyst separation. Furthermore, the catalyst in this invention can maintain high catalytic stability after separation and recovery, meeting the application requirements. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] This embodiment provides a hydroxyl-terminated hyperbranched graphene, prepared through the following steps:

[0030] 1 mol diethanolamine, 1.05 mol methyl acrylate and 100 mL methanol were mixed and stirred at 40 °C for 3.5 h. After the reaction was completed, the remaining methyl acrylate and methanol were removed by rotary evaporation to obtain methyl N,N-dihydroxyethyl-3-aminopropionate.

[0031] 0.2 g of graphene oxide and 1 g of N,N-dihydroxyethyl-3-aminopropionate methyl ester were added to 30 mL of acetone and ultrasonically dispersed. Then, 0.01 g of p-toluenesulfonic acid was added and dispersed. The mixture was heated to reflux and stirred for 30 min. The reflux was then removed, and after the acetone had evaporated, the temperature was raised to 120 °C. The mixture was stirred and reacted for 10 h under nitrogen protection. The resulting product was washed with chloroform to obtain hydroxyl-terminated hyperbranched graphene.

[0032] Example 2

[0033] This embodiment provides a magnetic particle prepared by the following steps: Under mechanical stirring at room temperature, 10g of Fe3O4 colloid, 10mL of deionized water, 10mL of anhydrous ethanol and 10mL of tetraethyl orthosilicate are added, followed by the addition of 10mL of ammonia (25% by mass) to catalyze the hydrolysis and condensation of tetraethyl orthosilicate. After reacting for 12 hours, the product is magnetically separated and washed multiple times with ultrapure water to thoroughly remove unreacted raw materials, thus obtaining the magnetic particle.

[0034] Example 3

[0035] This embodiment provides a method for treating landfill leachate, including the following steps:

[0036] Step 1: Adjust the pH of the landfill leachate MBR effluent to 4.5 with dilute sulfuric acid. Add coagulant (polyferric sulfate) and stir to dissolve. Then add flocculant (0.2% cationic polyacrylamide by mass) and stir to disperse. Let stand for 10 minutes, adjust the pH to 8.5, and let stand for 10 minutes to obtain pretreated wastewater. The dosage of polyferric sulfate and cationic polyacrylamide in the landfill leachate MBR effluent is 1.5 g / L. The COD of the landfill leachate MBR effluent is 1900 mg / L, and the ammonia nitrogen is 2000 mg / L.

[0037] Step 2: Dissolve 2g of sodium alginate in 100mL of water by stirring. Add 0.1g of the terminal hydroxyl hyperbranched modified graphene prepared in Example 1. After stirring and dispersing, a gel solution is obtained. Add 100mL of 0.1mol / L ferrous sulfate solution dropwise to the gel solution and mix. After stirring for 5min, add the reducing agent and continue stirring for 20min. Add the obtained reactants dropwise to 0.7mol / L calcium chloride solution and let stand to obtain spherical particles of 2-3mm. Take out the spherical particles, wash them with water, and freeze-dry them at -48℃ to -50℃ to obtain the catalyst. The reducing agent is sodium borohydride (the molar ratio of ferrous sulfate to reducing agent in the ferrous sulfate solution is 1:2.5).

[0038] Step 3: Add catalyst to the pretreated wastewater, adjust the pH to 3 with dilute sulfuric acid, add hydrogen peroxide, stir with forced air for 2 hours, recover and separate the catalyst, add flocculant (0.2% anionic polyacrylamide by mass), stir and let stand, then effluent. The amount of catalyst added is 10% of the mass of the pretreated wastewater; the amount of hydrogen peroxide added is 2% of the mass of the pretreated wastewater; and the amount of anionic polyacrylamide added is 1.5 g / L.

[0039] Example 4

[0040] This embodiment provides a method for treating landfill leachate, including the following steps:

[0041] Step 1: Adjust the pH of the landfill leachate MBR effluent to 5 with dilute sulfuric acid. Add coagulant (polyferric sulfate) and stir to dissolve. Then add flocculant (0.2% cationic polyacrylamide by mass) and stir to disperse. Let stand for 10 minutes, adjust the pH to 9, and let stand for 20 minutes to obtain pretreated wastewater. The dosage of polyferric sulfate and cationic polyacrylamide in the landfill leachate MBR effluent is 1.5 g / L. The COD of the landfill leachate MBR effluent is 1900 mg / L, and the ammonia nitrogen is 2000 mg / L.

[0042] Step 2: Dissolve 2g of sodium alginate in 100mL of water by stirring. Add 0.2g of the hydroxyl-terminated hyperbranched graphene prepared in Example 1. After stirring and dispersing, a gel solution is obtained. Add 100mL of 0.2mol / L ferrous sulfate solution dropwise to the gel solution and mix. After stirring for 6min, add the reducing agent and continue stirring for 30min. Add the obtained reactants dropwise to 1mol / L calcium chloride solution and let stand to obtain spherical particles of 2-3mm. Remove the spherical particles, wash them with water, and freeze-dry them at -48℃ to -50℃ to obtain the catalyst. The reducing agent is sodium borohydride (the molar ratio of ferrous sulfate to reducing agent in the ferrous sulfate solution is 1:2.5).

[0043] Step 3: Add catalyst to the pretreated wastewater, adjust the pH to 5 with dilute sulfuric acid, add hydrogen peroxide, stir with a forced air for 3 hours, recover and separate the catalyst, add flocculant (0.2% anionic polyacrylamide by mass), stir and let stand, then effluent. The amount of catalyst added is 30% of the mass of the pretreated wastewater; the amount of hydrogen peroxide added is 3% of the mass of the pretreated wastewater; and the amount of anionic polyacrylamide added is 1.5 g / L.

[0044] Example 5

[0045] This embodiment provides a method for treating landfill leachate, including the following steps:

[0046] Step 1: Adjust the pH of the landfill leachate MBR effluent to 5 with dilute sulfuric acid. Add coagulant (polyferric sulfate) and stir to dissolve. Then add flocculant (0.2% cationic polyacrylamide by mass) and stir to disperse. Let stand for 15 minutes, adjust the pH to 9, and let stand for 20 minutes to obtain pretreated wastewater. The dosage of polyferric sulfate and cationic polyacrylamide in the landfill leachate MBR effluent is 1.5 g / L. The COD of the landfill leachate MBR effluent is 1900 mg / L, and the ammonia nitrogen is 2000 mg / L.

[0047] Step 2: Dissolve 2g of sodium alginate in 100mL of water by stirring. Add 0.2g of the hydroxyl-terminated hyperbranched graphene prepared in Example 1. After stirring and dispersing, a gel solution is obtained. Add 100mL of 0.2mol / L ferrous sulfate solution dropwise to the gel solution and mix. After stirring for 6min, add the reducing agent and continue stirring for 30min. Add the obtained reactants dropwise to 1mol / L calcium chloride solution and let stand to obtain spherical particles of 2-3mm. Remove the spherical particles, wash them with water, and freeze-dry them at -48℃ to -50℃ to obtain the catalyst. The reducing agent is sodium borohydride (the molar ratio of ferrous sulfate to reducing agent in the ferrous sulfate solution is 1:2.5).

[0048] Step 3: Add catalyst to the pretreated wastewater, adjust the pH to 5 with dilute sulfuric acid, add hydrogen peroxide, stir with a forced air for 3 hours, recover and separate the catalyst, add flocculant (0.2% anionic polyacrylamide by mass), stir and let stand, then effluent. The amount of catalyst added is 40% of the mass of the pretreated wastewater; the amount of hydrogen peroxide added is 4% of the mass of the pretreated wastewater; and the amount of anionic polyacrylamide added is 1.5 g / L.

[0049] Comparative Example 1

[0050] Compared with Example 5, this comparative example replaces the terminal hydroxyl hyperbranched graphene with graphene oxide, while the other raw materials and preparation process remain the same as in Example 5.

[0051] Comparative Example 2

[0052] Compared with Example 5, this comparative example does not add terminal hydroxyl hyperbranched graphene, while the other raw materials and preparation process remain the same as in Example 5.

[0053] The landfill leachate treated in Examples 3-5 and Comparative Examples 1-2 was tested, and the COD was determined using the dichromate method of HJ 828—2017 "Determination of Chemical Oxygen Demand in Water".

[0054] The test results are shown in Table 1 below:

[0055] Table 1

[0056] project Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 COD removal rate / % 58.6 67.8 72.2 67.1 61.2

[0057] The higher the amount of catalyst added, the higher the COD removal rate. As shown in Table 1, the addition of terminal hydroxyl hyperbranched graphene to the catalyst in this invention is beneficial to improving the catalytic effect. The catalyst in this invention forms a large number of pores after freeze-drying, which is beneficial to improving the catalyst's treatment effect. However, the low-temperature freeze-drying process can cause the catalyst framework to collapse, resulting in an unstable overall structure and affecting the catalyst's performance.

[0058] Example 6

[0059] Based on Example 5, magnetic particles were added. The preparation process of the catalyst in this example differs from that in Example 5. The specific steps are as follows:

[0060] 2g of sodium alginate was dissolved in 100mL of water by stirring. 0.2g of the terminal hydroxyl hyperbranched modified graphene prepared in Example 1 was added and stirred to disperse, resulting in a gel. 100mL of 0.2mol / L ferrous sulfate solution was added dropwise to the gel and mixed. After stirring for 6min, a reducing agent was added, and stirring was continued for 30min. Magnetic particles accounting for 10% of the gel mass were added, and then added dropwise to a 1mol / L calcium chloride solution. After standing, spherical particles of 2-3mm were obtained. The spherical particles were removed, washed with water, and freeze-dried at -48℃ to -50℃ to obtain the catalyst. The reducing agent was sodium borohydride (the molar ratio of ferrous sulfate to reducing agent in the ferrous sulfate solution was 1:2.5).

[0061] Example 7

[0062] Compared with Example 6, the amount of magnetic particles added in this embodiment is changed to 20%, while the remaining raw materials and preparation process remain the same as in Example 6.

[0063] The catalysts in Examples 6 and 7 were magnetically recovered. The recovered catalysts were repeatedly tested, and regenerated by rinsing them 2-3 times with deionized water at room temperature. The COD removal rate (%) was compared and recorded in Table 2 below.

[0064] Table 2

[0065] Number of regenerations / times 1 2 3 4 5 6 7 8 Example 6 70.3 69.5 65.8 65.4 66.8 61.2 60.4 62.4 Example 7 71.0 69.1 66.1 66.5 63.4 65.0 62.4 63.1

[0066] As shown in Table 2, the catalyst can still maintain high stability after multiple regenerations. However, after multiple regenerations, the active sites on the catalyst surface will be occupied, and the catalytic performance will decrease to some extent, but the overall catalytic effect can still remain stable.

[0067] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for treating landfill leachate, characterized by, It comprises the following steps: The first step is to adjust the pH of the landfill leachate MBR effluent to weak acidity, add coagulant and flocculant in sequence, stir and stand, adjust the pH to weak alkalinity, stand and precipitate, and obtain pretreated wastewater; The second step is to add sodium alginate to water and stir to dissolve, add hydroxyl-terminated hyperbranched modified graphene, stir and disperse to obtain a glue solution, add ferrous sulfate solution to the glue solution, stir, add a reducing agent, continue to stir, add calcium chloride solution, stand, obtain spherical particles, wash with water, freeze-dry, the freeze-drying temperature is-48℃~-50℃, and obtain a catalyst; The catalyst also includes magnetic particles; The hydroxyl-terminated hyperbranched modified graphene is obtained by grafting polymerization of graphene oxide as a central reaction nucleus and AB monomer N,N-dihydroxyethyl-3-aminopropionic acid methyl ester by one-step esterification polycondensation method; The third step is to add the catalyst to the pretreated wastewater, adjust the pH to 3-5, add hydrogen peroxide, stir with air blowing, recover and separate the catalyst, add a flocculant, stir and stand, and discharge the effluent.

2. The method of claim 1, wherein the method is characterized by, The pH range of weak acidity in the first step is 4.5-5, and the pH range of weak alkalinity is 8.5-9.

3. The method of claim 1, wherein the method is characterized by, The addition amount of the catalyst is 10-40% of the mass of the pretreated wastewater; The addition amount of hydrogen peroxide is 2-4% of the mass of the pretreated wastewater.

4. The method of claim 1, wherein the method is characterized by, The amount ratio of sodium alginate, water, hydroxyl-terminated hyperbranched modified graphene and ferrous sulfate solution is 2g:100mL:0.1-0.2g:100mL.

5. The method of claim 1, wherein the method is characterized by, The concentration of ferrous sulfate is 0.1-0.2mol / L; The concentration of calcium chloride solution is 0.7-1mol / L.

6. The method of claim 1, wherein the method is characterized by, The particle size of the spherical particles is 2-3mm.

7. The method of claim 1, wherein the method is characterized by, The reducing agent includes one of sodium borohydride and tea polyphenol.