Method for evaluating the degree of membrane fouling and clogging of dtro for landfill leachate treatment

Abstract

The application provides an evaluation method for DTRO membrane blockage and pollution degree for landfill leachate treatment, and belongs to the technical field of landfill leachate treatment. i The evaluation method adopts a normalized membrane water permeability reduction ratio (R i ) of the DTRO membrane as an evaluation index for the membrane blockage and pollution degree, divides three pollution degrees, can remove the influence of factors such as temperature and sludge concentration on the membrane water permeability change, objectively and directly evaluates the membrane water permeability, further judges the membrane blockage and pollution degree, provides a basis for the DTRO membrane cleaning and maintenance scheme making and optimization, is favorable for scientifically and rationally determining the membrane cleaning and maintenance period, improves the membrane operation efficiency, and prolongs the service life of the membrane. Meanwhile, the method also sets the rapid increase of the normalized membrane water permeability reduction ratio of the DTRO membrane as a characteristic index for the serious blockage and irreversible pollution of the membrane, realizes the rapid evaluation of the current state of the membrane in an effective, accurate and rapid manner.

Description

Technical Field

[0001] This invention belongs to the field of landfill leachate treatment technology, and relates to a method for assessing the degree of DTRO membrane clogging and fouling in landfill leachate treatment. Background Technology

[0002] Landfill leachate is characterized by its complex composition, high pollutant concentration, and significant variations in water quality and quantity, classifying it as high-salinity, high-CODcr wastewater. To meet discharge requirements, combined processes such as "pretreatment + biological treatment + advanced treatment," "biological treatment + advanced treatment," or "pretreatment + advanced treatment" are typically employed. According to the "Explanatory Notes on the Draft of the <Standards for Pollution Control of Municipal Solid Waste Landfills>", my country has 557 leachate treatment facilities constructed after July 1, 2008, with a total treatment capacity of 40,888 t / d. Among these, 268 facilities utilize DTRO membrane (RO) technology, with a treatment capacity of 22,661 t / d. RO is the core technology for advanced leachate treatment, effectively retaining small-molecule organic matter and inorganic salts to ensure leachate meets discharge standards. Compared to spiral wound reverse osmosis, disc tube reverse osmosis (DTRO membrane) has wider channels, shorter flow paths, and can generate high-speed turbulent flow, making it more suitable for landfill leachate treatment.

[0003] DTRO membrane applications face a series of problems, including long-term membrane clogging and fouling, leading to reduced water production and high cleaning and maintenance costs. Substances causing DTRO membrane clogging and fouling include small-molecule organic matter, inorganic salts, and microorganisms. These substances adhere to, deposit, and cross-link on the membrane surface or within the pores, reducing pore size, causing clogging and fouling, and further exacerbating concentration polarization, resulting in a significant decrease in membrane water production and filtration performance.

[0004] Membrane cleaning and maintenance is a crucial aspect of DTRO membrane process operation, encompassing both physical and chemical cleaning. Currently, DTRO membrane cleaning and maintenance plans for seawater desalination are primarily determined by process technicians based on guidance from membrane product manufacturers, considering the quality and quantity of the raw seawater influent and the membrane permeate flow rate. This lack of objective assessment methods for membrane fouling and discoloration levels hinders the precise formulation and optimization of cleaning and maintenance plans, resulting in either excessively high or low cleaning frequency and ineffective cleaning. Therefore, establishing a method for assessing DTRO membrane fouling and discoloration levels to predict and evaluate these conditions, and subsequently providing precise guidance for membrane cleaning and maintenance, is of great significance for improving the efficiency of landfill leachate DTRO membrane treatment and ensuring permeate quality. Summary of the Invention

[0005] This invention provides a method for assessing the degree of DTRO membrane clogging and fouling in landfill leachate treatment. This method uses the percentage decrease in normalized membrane permeability R of the DTRO membrane. iAs an assessment indicator of membrane fouling and pollution levels, it can objectively and directly evaluate the membrane's permeability, thereby determining the degree of membrane fouling and pollution. This helps to scientifically and rationally determine the membrane cleaning and maintenance cycle, improve membrane operating efficiency, and extend membrane lifespan.

[0006] To achieve the above objectives, the present invention provides a method for assessing the degree of DTRO membrane clogging and fouling in landfill leachate treatment, comprising the following steps: Calculate the temperature normalization factor A for water permeability of DTRO membrane, the normalization factor B for total dissolved solids, and the normalization factor E for chemical oxygen demand; Calculate the actual permeability L of the current DTRO membrane. i The normalized membrane permeability L of the current DTRO membrane was calculated using the temperature normalization coefficient A, the total dissolved solids normalization coefficient B, and the chemical oxygen demand normalization coefficient E. in =L i ×[1+(T i -20)×A] -1 ×[1+(C i -25000)×B] -1 ×[1+(E i -1000)×E] -1 ; Calculate the standard permeability L of the standard DTRO membrane under normalized conditions within a certain period. 0a ; Calculate the normalized membrane permeability L of the current DTRO membrane. in Normalized permeability L of a standard DTRO membrane over a certain period 0a The decrease in the ratio R i ; Through R i The range of values ​​is used to evaluate the degree of DTRO membrane clogging and fouling.

[0007] Preferably, the temperature normalization coefficient A of the DTRO membrane permeability is calculated using the following method: The total dissolved solids (TDS) and chemical oxygen demand (COD) of the DTRO membrane feed water were controlled at 25,000 mg / L and 1,000 mg / L, respectively. An average of 5-8 temperature conditions were taken within the temperature range of 5-30℃ to test the membrane flux (J) of the DTRO membrane at different temperatures. i and transmembrane pressure difference ΔP i Calculate the actual membrane permeability L i =J i / ΔP i ; With L i For the dependent variable, (T) i Using -20) as the independent variable, a linear fit is performed to obtain the approximate linear fit formula L. i =L0+L0×(Ti -20)×A, and then calculate the temperature normalization coefficient A of the DTRO membrane permeability in °C. -1 Among them, T i The temperature value collected by the online instrument is represented in °C; L0 is the normalized water permeability of the DTRO membrane, in L·m. -2 ·h -1 ·kPa -1 .

[0008] Preferably, the normalized coefficient B of the DTRO membrane's water permeability and total dissolved solids is calculated using the following method: The DTRO membrane influent temperature was controlled at 20℃ and the chemical oxygen demand (COD) at 1000 mg / L. An average of 5-8 dissolved solids (TSD) conditions were taken within the TSD range of 20000-30000 mg / L to test the DTRO membrane flux J under different TSD conditions. i and transmembrane pressure difference ΔP i Calculate the actual membrane permeability L i ; With L i For the dependent variable, (C) i Using -25000 as the independent variable, a linear fit was performed to obtain the approximate linear fit formula L. i =L0+L0×(C i -25000)×B, and then calculate the normalized coefficient B of DTRO membrane permeability and total dissolved solids, in L / mg; Among them, C i L0 represents the total dissolved solids value collected by the online instrument, in mg / L; L0 is the normalized permeability of the DTRO membrane, in L·m -2 ·h -1 ·kPa -1 .

[0009] Preferably, the normalization coefficient E of chemical oxygen demand is calculated by the following method: The DTRO membrane influent temperature was controlled at 20℃ and the total dissolved solids (TOS) at 25000 mg / L. Five to eight COD conditions were averaged within the range of 500-2000 mg / L to test the DTRO membrane flux J under different COD levels. i and transmembrane pressure difference ΔP i Calculate the actual membrane permeability L i ; With L i For the dependent variable, (E) i Using -1000 as the independent variable, a linear fit is performed to obtain the approximate linear fit formula L. i =L0+L0×(E i-1000)×E, and then calculate the normalization coefficient E of DTRO membrane permeability chemical oxygen demand, in units of L / mg; Among them, E i L0 represents the chemical oxygen demand (COD) value collected by online instruments, in mg / L; L0 is the normalized water permeability of the DTRO membrane, in L·m. -2 ·h -1 ·kPa -1 .

[0010] As a preferred option, the standard water permeability L of the DTRO membrane under normalized conditions within a certain period is... 0a Specifically, it is the average value of the DTRO normalized membrane permeability L0 after each restorative chemical cleaning in a certain period; The specified period is 2-3 months.

[0011] As a preferred method, the normalized membrane permeability L0 of the DTRO membrane is calculated using the following method: With a DTRO membrane influent temperature of 20℃, total dissolved solids of 25000 mg / L, and chemical oxygen demand of 1000 mg / L as normalization conditions, the normalized membrane permeability of the DTRO membrane was measured to be L0=J0 / ΔP0.

[0012] Wherein, J0 and ΔP0 represent the membrane flux and transmembrane pressure difference measured after each restorative chemical cleaning, respectively, and only the average normalized membrane permeability after each cleaning can represent the performance of the DTRO membrane before fouling and clogging.

[0013] As a preferred option, the current DTRO membrane normalized membrane permeability reduction ratio R i The calculation formula is as follows: R i =(L 0a -L in ) / L 0a ×100%.

[0014] As a preferred option, through R i The range of values ​​used to evaluate the degree of DTRO membrane clogging and fouling is as follows: When R i ≤10% indicates mild clogging and contamination of the DTRO membrane; When 10% <R i ≤20% indicates moderate clogging and fouling of the DTRO membrane; When R i >20% indicates severe clogging and fouling of the DTRO membrane.

[0015] As a preferred option, in the case of R i Before evaluating the degree of DTRO membrane clogging and fouling, the range of values ​​also includes a step of determining whether the membrane has been broken or damaged.

[0016] As a preferred method, the specific steps for determining whether the membrane has broken or been damaged are as follows: When the DTRO membrane flux J i >J max Or transmembrane pressure difference ΔP i <ΔP min At that time, it can be determined that the membrane has broken or been damaged.

[0017] Preferably, when the DTRO membrane has broken or been damaged, the membrane fibers should be repaired promptly; when the DTRO membrane is in a state of mild clogging and fouling, it should be backwashed and air-washed regularly; when the DTRO membrane is in a state of mild clogging and fouling, it should be maintained with chemical cleaning; when the DTRO membrane is in a state of severe clogging and fouling, it should be restored with chemical cleaning; when the percentage of DTRO membrane normalized permeability decreases rapidly over a period of time (R... i When the / t value increases sharply, the membrane may become severely clogged and irreversibly fouled. The cleaning program (including cleaning time, type of agent, concentration, etc.) should be adjusted and optimized.

[0018] Of course, as a further optimization, the normalized membrane permeability of the DTRO membrane can be rapidly increased by increasing R. i Ri / t serves as a characteristic indicator of severe membrane clogging and irreversible fouling. Specifically, by comparing the current Ri / t of the DTRO membrane with the Ri / t of the DTRO membrane in historical data, if a sharp increase in the current Ri / t is found, it indicates that the cleaned DTRO membrane is rapidly fouled and clogged, resulting in irreversible fouling.

[0019] Compared with the prior art, the advantages and positive effects of the present invention are as follows: 1. The method for assessing the clogging and fouling degree of DTRO membranes specifically for landfill leachate treatment provided by this invention uses the DTRO membrane normalized permeability reduction ratio (R0). i As an assessment indicator of membrane fouling and fouling, the boundary conditions are divided into three levels of fouling. This can eliminate the influence of factors such as temperature and sludge concentration on membrane permeability changes, objectively and directly assess membrane permeability performance, and thus determine the degree of membrane fouling and fouling. This provides a basis for the formulation and optimization of DTRO membrane cleaning and maintenance programs, which is conducive to scientifically and rationally determining the membrane cleaning and maintenance cycle, improving membrane operating efficiency, and extending membrane service life.

[0020] 2. The evaluation method provided by this invention sets the rapid increase of the normalized membrane permeability of DTRO membrane as a characteristic indicator of severe membrane blockage and irreversible fouling, thereby achieving an effective, accurate and rapid assessment of the current state of the membrane. Attached Figure Description

[0021] Figure 1Photograph of the disc tube type DTRO membrane element provided in Embodiment 1 of the present invention. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 A landfill leachate treatment project has a capacity of 1000 cubic meters per day and adopts a two-stage nitrification-denitrification + MBR (membrane bioreactor) + DTRO membrane process. The DTRO membrane functional layer is made of aromatic polyamide, with a pore size of 0.1 nm. It is a disc-tube type DTRO membrane, and the designed membrane flux is 5-12 L·m³. -2 ·h -1 The transmembrane pressure difference is 50-150 kPa.

[0024] Over a period of nearly 3 months, under conditions of 20℃, total dissolved solids of 25000 mg / L, and chemical oxygen demand of 1000 mg / L, the membrane flux (J0) and transmembrane pressure difference (ΔP0) of the DTRO membrane after chemically enhanced cleaning were tested. The RO membrane permeability L0 = J0 / ΔP0, and the standard RO membrane permeability L... 0a This represents the average value of L0 over a period of nearly 3 months. 0a =0.0825 L·m -2 ·h -1 ·kPa -1 .

[0025] Calculate the temperature normalization factor A for the water permeability of the DTRO membrane. Controlling the total dissolved solids and chemical oxygen demand in the DTRO membrane feed water to be consistent (select C) i =25000 mg / L, E i =1000mg / L), and the membrane flux J of the DTRO membrane was tested at 5-8 average temperature conditions (8℃, 12℃, 16℃, 20℃, 24℃) within the temperature range of 5-30℃. i and transmembrane pressure difference ΔP i Calculate the actual membrane permeability L i =J i / ΔP i ; With L i For the dependent variable, (T) i Using -20) as the independent variable, a linear fit is performed to obtain the approximate linear fit formula L. i =0.0825+0.0825×(Ti -20) × 0.0106, and then the temperature normalization coefficient of DTRO membrane permeability is calculated to be A = 0.0106℃. -1 .

[0026] Calculate the normalized coefficient B of water permeability and total dissolved solids of DTRO membrane. Control the DTRO membrane influent temperature and chemical oxygen demand to be consistent (select T). i =20 ℃, E i =1000 mg / L), and averaged 5-8 total dissolved solids conditions (21000 mg / L, 23000 mg / L, 25000 mg / L, 27000 mg / L, 29000 mg / L) within the range of 20000-30000 mg / L, to test the flux J of the DTRO membrane under different total dissolved solids. i and transmembrane pressure difference ΔP i Calculate the actual membrane permeability L i ; With L i For the dependent variable, (C) i Using -25000 as the independent variable, a linear fit was performed to obtain the approximate linear fit formula L. i =0.0825+0.0825×(C i -25000)×(-0.000032), and then the normalized coefficient of total dissolved solids permeability of DTRO membrane B=-0.000032 L / mg is calculated.

[0027] Calculate the normalized coefficient E of DTRO membrane chemical oxygen demand. Control the DTRO membrane feed water temperature and total dissolved solids to be consistent (select T). i =20 ℃, C i =25000 mg / L), and an average of 5-8 chemical oxygen demand (COD) conditions (600 mg / L, 900 mg / L, 1200 mg / L, 1500 mg / L, 1800 mg / L) were taken within the COD range of 500-2000 mg / L to test the flux J of the DTRO membrane under different COD conditions. i and transmembrane pressure difference ΔP i Calculate the actual membrane permeability L i ; With L i For the dependent variable, (E) i Using -1000 as the independent variable, a linear fit is performed to obtain the approximate linear fit formula L. i =0.0825+0.0825×(E i-1000)×(-0.00015), and then the normalization coefficient of chemical oxygen demand permeability of DTRO membrane is calculated to be E=-0.00015 L / mg.

[0028] Online collection of operating parameters The DTRO membrane inlet water temperature (T) is collected online using online monitoring equipment. i Total dissolved solids (C) i Chemical oxygen demand (E) i ) and membrane flux (J i ), transmembrane pressure difference (ΔP) i Operational data such as DTRO membrane feed water T i =15.2℃, C i =22700mg / L, E i =950 mg / L, J i =6.8 L·m -2 ·h -1 ΔP i =95 kPa.

[0029] The above describes the acquisition of DTRO membrane flux J. i and transmembrane pressure difference ΔP i Afterwards, a rapid membrane integrity test can be performed to determine whether any breakage or damage has occurred. The criterion for judgment is the DTRO membrane flux (J). i >J max Or transmembrane pressure difference ΔP i <ΔP min Based on the actual situation, namely the DTRO membrane flux J... i <12 L·m -2 ·h -1 And the transmembrane pressure difference ΔP i With a pressure >50 kPa, the membrane integrity is good, and further assessment of clogging and fouling levels can proceed.

[0030] Calculate the normalized membrane permeability L of the current DTRO membrane. in T i =15.2℃, C i =22700 mg / L, E i =950 mg / L, J i =6.8 L·m -2 ·h -1 ΔP i Substituting 95 kPa into the DTRO membrane normalized permeability formula, the result is as follows: L i ×[1+(T i -20)×A] -1 ×[1+(C i-25000)×B] -1 ×[1+(E i -1000)×E] -1 = (6.8 / 95) × [1 + (15.2 - 20) × 0.0106] -1 ×[1+(22700-30000)×(-0.000032)] -1 ×[1+(950-1000)×-0.00015] -1 =0.0697 L·m -2 ·h -1 ·kPa -1 .

[0031] Calculate the percentage decrease in normalized water permeability of the current DTRO membrane. R i =(L 0a -L in ) / L 0a ×100%=(0.0825-0.0697) / 0.0825×100%=15.48%.

[0032] Combined with the DTRO membrane clogging and fouling assessment criteria (the criteria are as follows: when R... i ≤10% indicates mild clogging and fouling of the DTRO membrane; when 10% <R i ≤20% indicates moderate DTRO membrane clogging and fouling; when R i >20% indicates severe clogging and fouling of the DTRO membrane; the proportion of decreased normalized membrane permeability of the DTRO membrane increases rapidly (R0). i When the / t value increases sharply (indicating severe clogging and fouling), it can be concluded that the DTRO membrane provided in Example 1 is currently in a state of moderate clogging and fouling, and should be maintained with chemical cleaning in a timely manner. Combined with... Figure 1 The photographs of the DTRO membrane element and membrane sheet shown indicate that the feed water and membrane surface of the membrane element are covered with a certain amount of dark brown contaminants.

[0033] As can be seen from the above, the DTRO membrane clogging and fouling assessment method and corresponding evaluation criteria provided in this application can objectively and directly assess the membrane's permeability, accurately determine the current degree of DTRO membrane clogging and fouling, and help to scientifically and rationally determine the membrane cleaning and maintenance cycle, improve membrane operating efficiency, and extend membrane service life. Figure 1 This provides corresponding evidence, demonstrating that the method is indeed objective, accurate, and efficient.

Claims

1. A method for assessing the degree of DTRO membrane clogging and fouling in landfill leachate treatment, characterized in that, Includes the following steps: Calculate the temperature normalization factor A for water permeability of DTRO membrane, the normalization factor B for total dissolved solids, and the normalization factor E for chemical oxygen demand; Calculate the actual permeability L of the current DTRO membrane. i The normalized membrane permeability L of the current DTRO membrane was calculated using the temperature normalization coefficient A, the total dissolved solids normalization coefficient B, and the chemical oxygen demand normalization coefficient E. in =L i ×[1+(T i -20)×A] -1 ×[1+(C i -25000)×B] -1 ×[1+(E i -1000)×E] -1 ; Calculate the standard permeability L of the standard DTRO membrane under normalized conditions within a certain period. 0a ; Calculate the normalized membrane permeability L of the current DTRO membrane. in Normalized permeability L of a standard DTRO membrane over a certain period 0a The decrease in the ratio R i ; Through R i The range of values ​​is used to evaluate the degree of DTRO membrane clogging and fouling; The temperature normalization coefficient A of the DTRO membrane permeability was calculated using the following method: The total dissolved solids (TDS) and chemical oxygen demand (COD) of the DTRO membrane feed water were controlled at 25000 mg / L and 1000 mg / L, respectively. An average of 5-8 temperature conditions were taken within the temperature range of 5-30℃ to test the membrane flux (J) of the DTRO membrane at different temperatures. i and transmembrane pressure difference ΔP i Calculate the actual membrane permeability L i =J i / ΔP i ; With L i For the dependent variable, (T) i Using -20) as the independent variable, a linear fit is performed to obtain the approximate linear fit formula L. i =L0+L0×(T i -20)×A, and then calculate the temperature normalization coefficient A of the DTRO membrane permeability in °C. -1 Among them, T i The temperature value collected by the online instrument is represented in °C; L0 is the normalized water permeability of the DTRO membrane, in L·m. -2 ·h -1 ·kPa -1 ; The normalized coefficient B of the DTRO membrane's water permeability and total dissolved solids was calculated using the following method: The DTRO membrane influent temperature was controlled at 20℃ and the chemical oxygen demand (COD) at 1000 mg / L. An average of 5-8 dissolved solids (TSD) conditions were taken within the TSD range of 20000-30000 mg / L to test the DTRO membrane flux J under different TSD conditions. i and transmembrane pressure difference ΔP i Calculate the actual membrane permeability L i ; With L i For the dependent variable, (C) i Using -25000 as the independent variable, a linear fit was performed to obtain the approximate linear fit formula L. i =L0+L0×(C i -25000)×B, and then calculate the normalized coefficient B of DTRO membrane permeability and total dissolved solids, in L / mg; Among them, C i L0 represents the total dissolved solids value collected by the online instrument, in mg / L; L0 is the normalized permeability of the DTRO membrane, in L·m -2 ·h -1 ·kPa -1 ; The normalization coefficient E for chemical oxygen demand was calculated using the following method: The DTRO membrane influent temperature was controlled at 20℃ and the total dissolved solids (TOS) at 25000 mg / L. Five to eight COD conditions were averaged within the range of 500-2000 mg / L to test the DTRO membrane flux J under different COD levels. i and transmembrane pressure difference ΔP i Calculate the actual membrane permeability L i ; With L i For the dependent variable, (E) i Using -1000 as the independent variable, a linear fit is performed to obtain the approximate linear fit formula L. i =L0+L0×(E i -1000)×E, and then calculate the normalization coefficient E of DTRO membrane permeability chemical oxygen demand, in units of L / mg; Among them, E i L0 represents the chemical oxygen demand (COD) value collected by online instruments, in mg / L; L0 is the normalized water permeability of the DTRO membrane, in L·m. -2 ·h -1 ·kPa -1 ; Standard water permeability L of DTRO membrane under normalized conditions within a certain period 0a Specifically, it is the average value of the DTRO normalized membrane permeability L0 after each restorative chemical cleaning in a certain period; The specified period is 2-3 months; The normalized permeability L0 of the DTRO membrane was calculated using the following method: With a DTRO membrane feed water temperature of 20℃, total dissolved solids of 25000 mg / L, and chemical oxygen demand of 1000 mg / L as normalization conditions, the normalized membrane permeability of the DTRO membrane was measured to be L0=J0 / ΔP0, where J0 and ΔP0 represent the membrane flux and transmembrane pressure difference measured after each restorative chemical cleaning, respectively.

2. The evaluation method according to claim 1, characterized in that, DTRO membrane normalized membrane water permeability decrease ratio R i The calculation formula is as follows: R i =(L 0a -L in ) / L 0a ×100%。 3. The evaluation method according to claim 2, characterized in that, Through R i The range of values ​​used to evaluate the degree of DTRO membrane clogging and fouling is as follows: When R i ≤10% indicates mild clogging and contamination of the DTRO membrane; When 10% <R i ≤20% indicates moderate clogging and fouling of the DTRO membrane; When R i >20% indicates severe clogging and fouling of the DTRO membrane.

4. The evaluation method according to claim 3, characterized in that, In passing R i Before evaluating the degree of DTRO membrane clogging and fouling, the range of values ​​also includes a step of determining whether the membrane has been broken or damaged.

5. The evaluation method according to claim 4, characterized in that, The specific steps to determine whether the membrane has broken or been damaged are as follows: When the DTRO membrane flux J i <12L·m -2 ·h -1 And the transmembrane pressure difference ΔP i >50kPa indicates good membrane integrity.

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