CN110330179A - Couple the advanced treating method of landfill leachate of nanofiltration concentrate humic acid extraction and application - Google Patents

Abstract

The invention discloses a novel advanced treatment method for landfill leachate which is coupled with nanofiltration concentrate for extraction and utilization of humic acid. The nanofiltration unit with advanced treatment in the process constitutes a new advanced treatment process for leachate. Among them, the two-stage ultrafiltration unit mainly plays the role of high-efficiency separation of humic acid and inorganic salts in the nanofiltration concentrate, and makes the obtained final concentrate meet the index requirements as raw materials for humic acid-containing water-soluble fertilizers; the gypsum crystallization unit can reduce the two-stage ultrafiltration rate. The concentration of calcium and sulfate ions in the feed liquid of the filtration system; and it circulates the generated tail water back to the nanofiltration unit in the leachate treatment system, so that the effluent reaches the standard. The method is advanced, practical, economical, stable in operation, simple in operation, small in land occupation, free from secondary pollution, and can realize resource recycling.

Description

Advanced treatment method of landfill leachate for extraction and utilization of humic acid from coupled nanofiltration concentrate

technical field

The invention belongs to the technical field of landfill leachate treatment, and in particular relates to a novel advanced treatment method for landfill leachate which is coupled with nanofiltration concentrated solution for extraction and utilization of humic acid.

Background technique

Landfill leachate is extremely difficult to treat due to the complex and changeable water quality. After decades of technology research and development and engineering practice, the MBR+NF+RO combined process has become the mainstream process for leachate treatment, of which NF+RO is the advanced treatment craft. Under the condition of normal operation and good function of biological denitrification in the main biological treatment process, if only the treated effluent is considered to meet the standard, the leachate can be fully achieved after passing through MBR and then passing through the NF unit, without the need to pass through the main effluent. The RO unit that meets the standards and is reused can eliminate the investment and operating costs of the RO unit, and more importantly, it can eliminate the RO concentrate that mainly relies on high-cost desalination technology (such as evaporation process). However, the NF unit will inevitably produce nanofiltration concentrate that accounts for 10-20% of the volume of the original solution. At present, there is still a lack of efficient and economical pollution control technology. Therefore, the leachate cannot be treated in full. This has become a pain point that plagues leachate treatment companies and competent authorities at all levels, and is also a difficult and hot spot for related technology research and development.

At present, there are some methods or processes for harmless treatment and resource utilization of nanofiltration concentrates alone, such as the authorized invention patent "Humic Acid Extraction Method" (ZL201110272483.7), "Landfill Leachate Advanced Treatment Process and Special Equipment” (ZL102951741A) and “Humic Acid Separation and Recovery Process in Landfill Leachate MBR+NF Concentrate Containing High Concentration SO ₄ ^2- ” (ZL201410633759.3) and the patent application for “High Concentration Divalent Salt Ion Leachate MBR+ "Method for extracting humic acid from NF concentrate" (application number 201410689333.X) and "method for extracting humic acid from low-concentration divalent salt ion leachate MBR+NF concentrate" (application number 201710843650.6), etc., these patents are provided with Independent of the nanofiltration system outside the advanced treatment nanofiltration unit in the Leachate Treatment MBR+NF process, the investment, land occupation and process of the nanofiltration system need to be increased accordingly. However, if the nanofiltration unit in the leachate treatment process is directly used, there is usually a margin in the design, and the water treatment capacity or capacity can be improved simply by increasing the operating pressure, so it can meet the requirements of the nanofiltration concentrate humic acid extraction system to produce tail water. processing load needs. This full utilization method has better technical economy, such as better effluent quality of nanofiltration unit, more stable operation, and lower investment and operating costs. However, there is no harmless treatment and resource utilization method of nanofiltration concentrate directly coupled with the mainstream treatment process of leachate, that is, the advanced treatment process of leachate coupled with humic acid extraction and utilization of nanofiltration concentrate. In some patents, innocuous treatment facilities for nanofiltration concentrates are separately set up to achieve full compliance with leachate treatment standards and pollution control. Therefore, the advanced treatment method that can be coupled in the overall leachate treatment process to realize the resource utilization of nanofiltration concentrate and the comprehensive treatment of leachate will have obvious advantages and broad application prospects.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a novel advanced treatment method for landfill leachate coupled with nanofiltration concentrated solution for extraction and utilization of humic acid. The advanced treatment nanofiltration unit in the NF process constitutes a new advanced treatment process for leachate. The method is advanced, practical, economical, stable in operation, simple in operation, small in land occupation, free from secondary pollution, and can realize resource recycling.

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

A novel advanced treatment method for landfill leachate for extraction and utilization of humic acid from a coupled nanofiltration concentrated solution, characterized in that it comprises the following steps:

1) The leachate MBR effluent is pumped into the nanofiltration unit, the operating pressure is 0.5~1.5MPa, the concentration ratio is 8~20 times, and the nanofiltration membrane used is an anti-pollution high monovalent ion permeability nanofiltration membrane, which intercepts The molecular weight is 150~300Da, and the nanofiltration permeate and nanofiltration concentrate are obtained; the COD concentration of the obtained nanofiltration concentrate reaches more than 2500mg/L, and the obtained nanofiltration permeate can meet the industry emission standard limits after testing. , it can be directly discharged; the produced nanofiltration concentrate is pumped into the primary ultrafiltration system, its operating pressure is 0.6~2.5MPa, the concentration ratio is 4~12 times, and the ultrafiltration membrane used is anti-pollution and high salt permeability Ultrafiltration membrane, its molecular weight cut-off is 500~2500Da; after membrane separation, first-grade ultrafiltration retentate and first-grade ultrafiltration permeate are obtained; the COD concentration of first-grade ultrafiltration retentate reaches more than 20000mg/L;

2) Pump the first-stage ultrafiltration retentate obtained in step 1) into the second-stage ultrafiltration system, the operating pressure is 0.5~2.0MPa, the concentration ratio is 3~10 times, and the ultrafiltration membrane used is anti-pollution and high salt permeability. The filter membrane has a molecular weight cut-off of 1000~5000Da; after the membrane separation, the secondary ultrafiltration retentate and the secondary ultrafiltration permeate are obtained; the humic acid concentration in the secondary ultrafiltration retentate reaches more than 30g/L, which can be used as Raw materials for water-soluble fertilizers containing humic acid;

3) The secondary ultrafiltration permeate obtained in step 2) is pumped into the gypsum crystallization system, so that the calcium ions and sulfate ions contained in it are crystallized and precipitated at 25-40° C. and pH 1.8-3 for 4-6 hours. After the mud and water are separated, the supernatant and the sediment are obtained; the supernatant is filtered and then circulated back into the primary ultrafiltration system for separation and concentration; the sediment is dehydrated and disposed of together with the remaining sludge after MBR treatment;

4) The first-stage ultrafiltration permeate obtained in step 1) is recycled back into the leachate treatment nanofiltration unit, and treated together with the leachate MBR effluent.

The significant advantages of the present invention are:

(1) The processing capacity of the nanofiltration unit in the existing invention patents is usually close to the total water volume of the nanofiltration concentrate, so the investment and land occupation are large. The method of the invention taps the potential and utilizes the nanofiltration unit in the leachate MBR+NF treatment system, saves the investment, land occupation, process and operation workload required for independent reconstruction of the nanofiltration system in the prior art, and can greatly reduce investment, Save land and labor.

(2) The water quality of nanofiltration concentrates varies greatly. Generally, COD and electrical conductivity can fluctuate between 800~9500mg/L and 8~27ms/cm, respectively. Therefore, corresponding treatments are currently given for different water quality nanofiltration concentrates. and resource utilization methods, such as the patent "Humic acid extraction method in high concentration divalent salt ion leachate MBR+NF membrane retentate" (application number 201410689333.X) and the patent "low concentration divalent salt ion leachate MBR+NF concentration Extraction method of humic acid in liquid” (application number 201710843650.6), etc. The method of the invention includes various systems with comprehensive functions (the two-stage ultrafiltration unit can efficiently separate humic acid and inorganic salts in the nanofiltration concentrated solution, and the second-stage ultrafiltration retentate can be used as a raw material for humic acid-containing water-soluble fertilizer; gypsum The crystallization unit reduces the concentration of calcium and sulfate ions in the feed liquid of the two-stage ultrafiltration system, so that the ultrafiltration and other membrane systems can operate stably for a long time; Return to the nanofiltration unit in the leachate MBR+NF treatment system to achieve all effluent standards), so it is suitable for humic acid extraction and utilization of various nanofiltration concentrates and comprehensive treatment of leachate.

(3) Some of the existing related invention patents have the following deficiencies or unreasonable points: the nanofiltration permeate in the "extraction method of humic acid" (ZL 201110272483.7) should be returned to the leachate MBR+NF treatment system or treated by The discharge after advanced oxidation is unreasonable _; BaCl ₂ is ^{used to remove SO 4 2-} _ions ^and the The sediment BaSO ₄ is eluted, and there are complicated procedures, high costs and labor safety risks; the concentrated liquid produced by the NF system in the "Advanced Treatment Process and Special Equipment for Landfill Leachate" (ZL 201210289032.9) is returned to the leachate treatment biochemical system. It will cause the flux of the membrane system to decrease and occupy its processing capacity; "The extraction method of humic acid in the retentate of low-concentration divalent salt ion Leachate MBR+NF membrane" (application number 201710843650.6) points out that the first-level ultrafiltration permeate needs to be It is discharged up to the standard after further treatment, but no specific treatment method or technology is specified; "Extraction method of humic acid in high-concentration divalent salt ion leachate MBR+NF membrane retentate" (Application No. 201410689333.X) in the NF concentrate After being treated by Fenton, the supernatant is mixed with the effluent of the leachate MBR+NF process and then discharged up to the standard, which has disadvantages such as complicated operation and maintenance, high cost and large sludge volume. Therefore, compared with these patents, the method of the present invention is advanced, practical, economical, stable in operation, simple in operation, less in land occupation, free from secondary pollution, and can realize resource recycling. Leachate treatment The advanced treatment method of the present invention can achieve the full amount of nanofiltration concentrate treatment and resource utilization, and realize the comprehensive treatment standard and pollution control of the leachate, which will promote the general application of the MBR+NF combined process in the leachate treatment, and further establish its mainstream status.

Description of drawings

Fig. 1 is a process flow diagram of the present invention.

Detailed ways

The novel advanced treatment process of landfill leachate for the extraction and utilization of humic acid from the coupled nanofiltration concentrated solution of the present invention will be further described below with reference to FIG. 1 .

First, the general idea of the present invention will be explained. At present, the harmless treatment and resource utilization processes or methods for the nanofiltration concentrate produced by the leachate MBR+NF process basically contain a nanofiltration system independent of the leachate treatment MBR+NF process to ensure nanofiltration concentration. The tail water of the liquid harmless treatment and resource utilization process can reach the standard, and the nanofiltration system is basically the same as the nanofiltration unit in the leachate treatment MBR+NF process. Therefore, it can be considered to omit the nanofiltration system and directly use the leachate treatment process. To achieve this purpose by using a medium nanofiltration unit, the advanced treatment method of the leachate of the present invention is formed.

The specific technical improvements of the present invention are as follows: (1) The nanofiltration unit in the MBR+NF process is treated with leachate by tapping the potential. Generally, the nanofiltration unit has a certain margin in the design, and the receiving nanofiltration can be obtained by appropriately increasing the operating pressure. The tail water treatment capacity generated by the concentrate treatment and resource utilization process (generally not more than 20% of the leachate treatment scale). This not only saves the investment, land occupation and operation workload required for adding a nanofiltration system, but also the feed water quality of the nanofiltration unit changes very little, while if an independent nanofiltration system is added, its Compared with the feed water quality, the quality of the feed will be significantly worse. Therefore, the direct use of the nanofiltration unit can obtain better effluent water quality and ensure the discharge up to the standard. (2) High-efficiency separation of organic matter (humic acid) and inorganic salts in nanofiltration concentrate through two-stage ultrafiltration, obtaining humic acid-containing water-soluble fertilizer raw materials that meet the requirements of relevant standards, and forming good water quality (both organic matter and inorganic salt content are equal) Lower humic acid extraction process tail water, recycled back to the nanofiltration unit of the leachate treatment MBR+NF process, will not have a significant impact on its influent water quality. (3) In order to regulate the concentration of divalent ions in the feed of each membrane system in the process of extracting humic acid, to ensure that each membrane system can operate stably for a long time, a gypsum crystallization system is used to effectively reduce the concentration of calcium and sulfate ions and avoid the formation of high membranes The osmotic pressure on both sides causes the membrane flux to be too low to lose the engineering use value, or the calcium and sulfate ion concentrations in the membrane feed are too high to precipitate gypsum crystals on the membrane surface, thereby causing irreversible pollution to the membrane and even damage to the membrane.

The technical parameters of the new advanced treatment method for landfill leachate for extraction and utilization of humic acid from the coupled nanofiltration concentrate according to the present invention:

1. One-stage ultrafiltration system

Working pressure 0.6~2.5Mpa,

The concentration ratio is 4~12 times,

Molecular weight cut off 500~2500Da,

COD >20000mg/L;

2. Two-stage ultrafiltration system

Working pressure 0.5~2.0MPa,

The concentration ratio is 3~10 times,

Molecular weight cut off 1000~5000Da,

Humic acid ≥30g/L;

3. Calcium and sulfate ion gypsum crystallization system

The reaction temperature is 25~40℃,

The reaction pH is 1.8~3,

The reaction time is 4~6h;

4. Nanofiltration unit in leachate treatment system

Working pressure 0.5~1.5Mpa,

The concentration ratio is 8~20 times,

Molecular weight cut off 150~300Da,

COD >2500mg/L.

Example 1

The present invention is further described below by taking the advanced treatment of landfill leachate for extraction and utilization of humic acid from a coupled nanofiltration concentrate in a domestic landfill leachate treatment plant as an example.

The domestic waste leachate treatment plant treats the mixed leachate of the landfill and the incineration plant. The total amount of leachate water is 2,100 tons per day. The daily leachate produced by the sanitary landfill and the waste incineration power plant is 1,700 tons and 400 tons, respectively. ton, the two types of leachate are collected separately and mixed in a certain proportion in the equalization tank. The main leachate treatment system is MBR+NF process, and the effluent stably meets the discharge standard. The nanofiltration concentrate produced by the leachate treatment plant can be directly lifted by the pump into the primary ultrafiltration system. The molecular weight cutoff of the primary ultrafiltration membrane is 500~2500Da, the operating pressure difference is 0.8~1.5Mpa, and the concentration ratio is 4~ 7 times, the COD of the first-stage ultrafiltration retentate after membrane separation is 20000~30000mg/L, the conductivity is 15~25mS/cm, the humic acid concentration is about 13000~22000mg/L, and the color is black, reddish-brown; the first-stage ultrafiltration The permeate COD is 1000~1800mg/L, the conductivity is 12-23mS/cm, the color is light yellow, and it is returned to the MBR outlet pool of the leachate treatment system. The first-stage ultrafiltration retentate continues to be pumped into the second-stage ultrafiltration system. The molecular weight cut-off of the ultrafiltration membrane is 1000~5000Da, the operating pressure difference is 0.5~1.0Mpa, and the concentration ratio is 3~7 times. After the membrane separation, the second stage ultrafiltration The COD of the retentate reaches 65000~80000mg/L, the conductivity is 18~28mS/cm, the humic acid concentration is about 30000~45000mg/L, and the color is black, indicating that the humic acid content in the secondary ultrafiltration retentate has satisfied the humic acid content. The index requirements for humic acid for water-soluble fertilizer products can be used as raw materials for water-soluble fertilizers containing humic acid. The secondary ultrafiltration permeate is transparent and yellowish-brown, and flows into the gypsum crystallization system. The temperature is maintained at 25~40°C, and the pH of the reaction liquid is adjusted to 1.8~3, so that calcium and sulfate ions react for 4~6h; after the reaction, calcium The supernatant with greatly reduced sulfate ion concentration is further filtered and returned to the primary ultrafiltration system for re-separation and concentration. The first-stage ultrafiltration permeate obtained after being separated by the first-stage ultrafiltration system of the present invention is mixed with the MBR effluent of the leachate treatment system and then pumped into the nanofiltration unit of the leachate treatment system as a feed liquid for treatment together.

Among them, compared with the traditional leachate treatment MBR+NF process, the operating parameters of the nanofiltration unit in the treatment method of the present invention have changed, and the volume concentration ratio of the nanofiltration unit in the traditional process is generally 5~6 times. 15 times, the operating pressure is increased from 0.3~0.6MPa to 0.5~0.9MPa, the COD of the nanofiltration concentrate is also increased from 1000~3000mg/L to 2500~6000mg/L, and the color is brownish yellow; but the nanofiltration unit is treated by leachate The water quality of the feed liquid after mixing the system MBR effluent and the first-stage ultrafiltration permeate does not change much. For example, the COD only increases by about 10~30% to ensure that the nanofiltration effluent (permeate) can meet the standard.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (5)

1. a novel landfill leachate advanced treatment method of coupling nanofiltration concentrated solution humic acid extraction and utilization, is characterized in that: may further comprise the steps: 1) The filtrate MBR effluent is pumped into the nanofiltration unit to obtain the nanofiltration permeate and the nanofiltration concentrate; the obtained nanofiltration permeate is discharged up to the standard; the generated nanofiltration concentrate is pumped into the primary ultrafiltration system, After membrane separation, a first-grade ultrafiltration retentate and a first-grade ultrafiltration permeate are obtained; 2) The primary ultrafiltration retentate obtained in step 1) is pumped into the secondary ultrafiltration system, and the secondary ultrafiltration retentate and the secondary ultrafiltration permeate are obtained after membrane separation; the secondary ultrafiltration retentate is used as Raw materials for water-soluble fertilizers containing humic acid; 3) The secondary ultrafiltration permeate obtained in step 2) is pumped into the gypsum crystallization system, and the supernatant and the sediment are obtained after crystallization precipitation and mud-water separation; the supernatant is circulated back into the primary ultrafiltration system for re-processing. Separation and concentration; dewatering and disposal of the sediment and the excess sludge produced by MBR treatment; 4) The first-stage ultrafiltration permeate obtained in step 1) is recycled back into the leachate treatment nanofiltration unit, and treated together with the leachate MBR effluent. 2. The novel advanced treatment method of landfill leachate for extraction and utilization of humic acid from a coupled nanofiltration concentrate according to claim 1, characterized in that: the operating pressure of the nanofiltration unit in step 1) is 0.5-1.5MPa, and the concentration ratio is 0.5-1.5MPa. It is 8~20 times, and the molecular weight cut-off of the nanofiltration membrane used is 150~300Da. 3. The novel advanced treatment method of landfill leachate for extraction and utilization of humic acid from a coupled nanofiltration concentrate according to claim 1, characterized in that: the operating pressure of the first-stage ultrafiltration system in step 1) is 0.6-2.5MPa, The concentration ratio is 4~12 times, and the molecular weight cut-off of the ultrafiltration membrane used is 500~2500Da. 4. The novel advanced treatment method of landfill leachate for extraction and utilization of humic acid from coupled nanofiltration concentrate according to claim 1, characterized in that: in step 2) the operating pressure of the secondary ultrafiltration system is 0.5-2.0 MPa, and the concentrated The multiple is 3~10 times, and the molecular weight cut-off of the ultrafiltration membrane used is 1000~5000Da. 5. The novel advanced treatment method of landfill leachate for extraction and utilization of humic acid from coupled nanofiltration concentrate according to claim 1, characterized in that: the reaction temperature of the crystallization precipitation in step 3) is 25-40°C, and the reaction feed liquid The pH is 1.8~3, and the reaction time is 4~6h.