Method for comprehensive utilization of domestic waste leachate concentrate

Abstract

The present application relates to waste treatment and resource utilization technical field, specifically relates to a kind of comprehensive utilization method of domestic waste leachate concentrated liquid.The present application method can realize the recovery of fulvic acid in leachate concentrated liquid by coagulation and organic solvent extraction, and simultaneously the residue after extracting fulvic acid is compounded with polyferric sulfate, and is used as coagulant, it is found in experimental exploration that the coagulant after compounding can play the same technical effect as original coagulant, realizes waste resource utilization, also effectively reduces the use amount of original flocculant, helps to reduce processing cost, more convenient for industrial application and has broad application prospect.

Description

Technical Field

[0001] This invention relates to the field of waste treatment and resource utilization technology, specifically to a method for the comprehensive utilization of leachate concentrate from municipal solid waste. Background Technology

[0002] Leachate generation is a prevalent environmental problem in the treatment and disposal of municipal solid waste. While the mainstream treatment process currently used in engineering applications, the "MBR(+UF)+NF / RO" system, can effectively treat leachate, it generates leachate concentrate (LLC), which accounts for 20-30% of the original liquid volume. This secondary pollutant has the following significant characteristics: it is essentially a high-concentration, recalcitrant organic waste liquid with poor biodegradability and complex composition; its physicochemical indicators show extremely high organic matter concentration, high salinity, dark color, and high turbidity; and its pH value is mostly distributed in the neutral to slightly alkaline range (6.5-8.5). It is noteworthy that although the pollution load of LLC is extremely high, its heavy metal content is usually at trace levels.

[0003] Current research both domestically and internationally mainly focuses on modifying process conditions to explore the removal effects of coagulants on pollutants such as TOC, COD, and color in leachate membrane concentrate. Zhang Yuechun et al. (2013) used FeSO4, Al2(SO4)3, PAC, and cationic PAM coagulation to treat leachate membrane concentrate and studied the removal rates of COD and UV254, which reached a maximum of 74.23% and 52.84%, respectively.

[0004] Numerous studies have also shown that humic substances (including humic acid, fulvic acid, and humin) are the main organic components in leachate membrane concentrates; these substances have complex and large molecular structures, making them difficult to process. Li Gongwei et al. found that the organic matter in NF membrane concentrates is mainly humic, accounting for about 82% of the total organic matter, and humic acid (FA) is the main component, accounting for about 72.2% of the total organic matter; the content of humic acid (HA) is relatively low, accounting for only 9.8%; in addition, 51.3% of the humic substances have a molecular weight of less than 1 kDa, FA is mainly composed of small molecule organic matter with a molecular weight of <1 kDa, and HA is mainly concentrated above 3 kDa.

[0005] Therefore, this invention extracts fulvic acid from the precipitate obtained by coagulation, realizing the resource utilization of waste. At the same time, this invention unexpectedly discovered that the filter residue (PFSS) after fulvic acid extraction still has a flocculation effect after treatment. The treated filter residue (PFSS) is mixed with polyferric sulfate (PFS) in a certain proportion and used for coagulation and precipitation, which can achieve the same effect as using pure PFS. This method can reduce the amount of coagulant added during coagulation and precipitation, thereby saving the amount of reagents used and reducing the treatment cost. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the comprehensive utilization of leachate concentrate from municipal solid waste, in order to solve the problem that existing methods for treating leachate concentrate often focus on the recovery of humic substances from the leachate concentrate, without comprehensively treating and utilizing the residue after the humic substances are recovered.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for comprehensive utilization of concentrated leachate from municipal solid waste, comprising the following steps:

[0008] S1. Adjust the pH of the leachate concentrate to weakly acidic, coagulate it with polyferric sulfate, let it stand, filter it, and take the precipitate obtained from the filter and dry it for later use.

[0009] S2. Mix the precipitate obtained in S1 with an organic solvent, extract fulvic acid completely, filter, and dry the filter residue for later use.

[0010] S3. The filter residue obtained in S2 is compounded with polyferric sulfate to replace the polyferric sulfate in S1 for coagulation of the leachate concentrate. Steps S1-S3 are repeated to realize the resource utilization of the leachate concentrate.

[0011] Furthermore, in S1, the pH of the leachate concentrate is adjusted to 5-6, and the pH adjuster includes hydrochloric acid solution.

[0012] Furthermore, in S1, the dosage of polyferric sulfate is 3-5 g / L.

[0013] Furthermore, in S2, the organic solvent is any one or more of methanol, ethanol, diethyl ether, chloroform, or acetone.

[0014] Furthermore, the volume-to-mass ratio of the organic solvent to the precipitate is 5–15:1.

[0015] Furthermore, in S3, the dosage of the filter residue and polyferric sulfate compounded together is 3-5 g / L.

[0016] Furthermore, the mass ratio of the polyferric sulfate to the filter residue is: polyferric sulfate: filter residue.

[0017] =1:0.5~3.

[0018] Furthermore, after the leachate concentrate is coagulated with a coagulant composed of filter residue obtained from S1-S2 and polyferric sulfate, the TOC content in the supernatant can be reduced by more than 75% and the color value can be reduced to below 0.01 compared with the treatment of pure polyferric sulfate.

[0019] The beneficial effects of this invention are:

[0020] 1. This invention can achieve coagulation treatment of leachate concentrate and recovery of fulvic acid. After coagulation treatment, the TOC (total organic carbon) content and color of leachate concentrate are significantly reduced, realizing effective treatment and resource utilization of leachate concentrate.

[0021] 2. This invention will make comprehensive use of the residue after extracting fulvic acid. By compounding the residue with polyferric sulfate, the same coagulation effect can be achieved while effectively reducing the amount of polyferric sulfate used, realizing further resource utilization of waste and helping to save on reagent costs. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the process flow of the present invention;

[0023] Figure 2 These are graphs showing the changes in TOC content of the supernatant before and after coagulation, and the changes in color of the supernatant after coagulation, in various embodiments of the present invention. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0025] Leachate from municipal solid waste at a waste treatment plant was taken and concentrated to obtain leachate concentrate. The pH of the leachate concentrate was tested to be 7.3 and the TOC was approximately 1260 mg / L. The leachate concentrate was used for treatment in the following embodiments of the present invention.

[0026] Example 1

[0027] Take 1L of leachate concentrate, add hydrochloric acid solution to adjust the pH of the solution to 5-6; then add 4.5g of polyferric sulfate (PFS), stir and coagulate at 200rpm for 15min, then let it stand to precipitate for 1.5h, filter, take the precipitate, and vacuum dry at 80℃ for later use.

[0028] The supernatant after filtration was analyzed, and the TOC level in the supernatant decreased to approximately 314 mg / L, a decrease of 75.08%. The color of the supernatant was also measured, with absorbance values ​​measured at wavelengths of 436 nm, 525 nm, and 620 nm. The formula for calculating the color is as follows:

[0029]

[0030] The color value of the supernatant obtained in this embodiment was found to be approximately 0.0079.

[0031] The dried precipitate was collected and anhydrous ethanol was added to it at a solid-liquid mass-to-volume ratio of 1:10. The mixture was stirred at 400 rpm for 2 hours and then filtered to extract fulvic acid. The filtered residue was dried at 105°C for later use (PFSS).

[0032] Example 2

[0033] The difference between this embodiment and Example 1 is that, in the coagulation stage, the coagulant used in this embodiment is a mixture of polyferric sulfate and the filter residue obtained in Example 1, while the rest is the same as in Example 1; in this embodiment, the mass ratio of polyferric sulfate to dried filter residue is 1:3, and the total amount is 4.5g.

[0034] After treatment with the coagulant in this embodiment, the TOC in the supernatant decreased to approximately 814 mg / L, a decrease of 35.40%; the color was approximately 0.0480.

[0035] Example 3

[0036] The difference between this embodiment and Example 1 is that, in the coagulation stage, the coagulant used in this embodiment is a mixture of polyferric sulfate and the filter residue obtained in Example 1, while the rest is the same as in Example 1; in this embodiment, the mass ratio of polyferric sulfate to dried filter residue is 1:2, and the total amount is 4.5g.

[0037] After treatment with the coagulant in this embodiment, the TOC in the supernatant decreased to approximately 593 mg / L, a decrease of 52.94%; the color was approximately 0.0258.

[0038] Example 4

[0039] The difference between this embodiment and Example 1 is that, in the coagulation stage, the coagulant used in this embodiment is a mixture of polyferric sulfate and the filter residue obtained in Example 1, while the rest is the same as in Example 1; in this embodiment, the mass ratio of polyferric sulfate to dried filter residue is 1:1, and the total amount is 4.5g.

[0040] After treatment with the coagulant in this embodiment, the TOC in the supernatant decreased to approximately 449 mg / L, a decrease of 64.37%; the color was approximately 0.0176.

[0041] Example 5

[0042] The difference between this embodiment and Example 1 is that, in the coagulation stage, the coagulant used in this embodiment is a mixture of polyferric sulfate and the filter residue obtained in Example 1, while the rest is the same as in Example 1; in this embodiment, the mass ratio of polyferric sulfate to dried filter residue is 2:1, and the total amount is 4.5g.

[0043] After treatment with the coagulant in this embodiment, the TOC in the supernatant decreased to approximately 312 mg / L, a decrease of 75.24%; the color was approximately 0.0079.

[0044] In summary, the technical solution of this invention can effectively treat leachate concentrate, reducing the TOC of the leachate concentrate by more than 75% and the color value by less than 0.01. At the same time, while extracting fulvic acid, the filter residue after fulvic acid extraction is further comprehensively utilized by compounding it with polyferric sulfate, which can achieve the same technical effect as pure polyferric sulfate and help reduce the cost of reagent use.

[0045] This invention is not limited to the preferred embodiments described above. Anyone can derive other forms of products under the guidance of this invention. However, regardless of any changes made in their shape or structure, any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A method for the comprehensive utilization of concentrated leachate from municipal solid waste, characterized in that, Includes the following steps: S1. Adjust the pH of the leachate concentrate to weakly acidic, coagulate it with polyferric sulfate, let it stand, filter it, and take the precipitate obtained from the filter and dry it for later use. The dosage of polyferric sulfate is 3~5 g / L; S2. Mix the precipitate obtained in S1 with an organic solvent, extract fulvic acid completely, filter, and dry the filter residue for later use. The organic solvent is any one or more of methanol, ethanol, diethyl ether, chloroform, and acetone; S3. The filter residue obtained in S2 is compounded with polyferric sulfate to replace the polyferric sulfate in S1 for coagulation of leachate concentrate. Steps S1-S3 are repeated to realize the resource utilization of leachate concentrate. The dosage of the filter residue and polyferric sulfate compounded together is 3~5 g / L; the mass ratio of polyferric sulfate to filter residue is 1:0.5~3.

2. The method for comprehensive utilization of concentrated leachate from municipal solid waste according to claim 1, characterized in that: In step S1, the pH of the leachate concentrate is adjusted to 5-6, and the pH adjuster includes hydrochloric acid solution.

3. The method for comprehensive utilization of concentrated leachate from municipal solid waste according to claim 1, characterized in that: The volume-to-mass ratio of the organic solvent to the precipitate is 5~15:

1.

4. The method for comprehensive utilization of leachate concentrate according to any one of claims 1-3, characterized in that: The leachate concentrate is coagulated by a coagulant composed of filter residue obtained from S1-S2 and polyferric sulfate. Compared with the treatment of pure polyferric sulfate, the TOC content in the supernatant is reduced by more than 75%, and the color value is reduced to below 0.01.

Images