Method for controlling membrane fouling of anaerobic membrane bioreactor by jointly adding biosurfactant and filler

Abstract

The application discloses a method for controlling membrane pollution of an anaerobic membrane bioreactor by jointly adding biological surfactant and filler, which is used for treating municipal sewage by the anaerobic membrane bioreactor (AnMBR), biological surfactant and filler are added into the AnMBR, and a membrane assembly and a mechanical stirring device are arranged. The membrane pollution control process is that a certain concentration of biological surfactant and a certain volume ratio of filler are jointly added into the reactor. In the AnMBR reactor, the biological surfactant is added to promote the dissolution of viscous substances and insoluble substances in the sludge mixed liquid, the dissolved organic molecules are wrapped by micelles formed by the surfactant, and the contact of organic pollutants with the membrane surface is reduced. Further, the filler is added, which is beneficial to the adhesion of sludge flocs in the suspension and the adsorption of the biological surfactant solubilization, and the concentration of sludge flocs and organic matters in the mixed liquid is reduced, so that the membrane pollution of the AnMBR is effectively slowed down under the premise of ensuring the operation efficiency of the reactor.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method for controlling membrane fouling in anaerobic membrane bioreactors by combining the addition of biosurfactants and packing materials. Background Technology

[0002] Anaerobic membrane bioreactors (AnMBRs) are a novel wastewater treatment process that combines anaerobic biological treatment with membrane separation technology. They offer advantages such as high treatment efficiency, low sludge production, and biogas production as a clean energy source. However, membrane fouling increases the operating costs of AnMBRs, becoming a bottleneck limiting their widespread application.

[0003] Currently, membrane fouling in AnMBRs is mainly controlled through methods such as modifying membrane materials, improving mixed liquor properties, and altering reactor operating conditions. Among these, improving mixed liquor properties is a crucial means of mitigating membrane fouling. Most studies have focused on reducing the content of polysaccharides, proteins, humic substances, and other materials in the mixed liquor by adding coagulants, flocculants, packing materials, quorum sensing quenching enzymes, and quorum sensing inhibitors to the reactor, thereby mitigating membrane fouling.

[0004] In recent years, studies have explored adding surfactants to membrane bioreactors (MBRs) to mitigate membrane fouling by influencing the properties of the mixed liquor through their solubilizing, emulsifying, surface tension-reducing, and hydrophilic / hydrophobic properties. However, traditional synthetic surfactants exhibit significant toxicity to microorganisms; for example, sodium dodecyl sulfate (SDS), Triton X-100, and tetradecyltrimethylammonium bromide may have adverse effects on sludge mixed liquor. Biosurfactants, on the other hand, possess advantages such as non-toxicity, biodegradability, temperature and high salt tolerance, wide pH range adaptability, and environmental friendliness, making their application in controlling membrane fouling in MBRs a research hotspot. Currently, there are patent reports on research into using biosurfactants to control membrane fouling. For example, a method for preparing sophorolipids via fermentation and its application in reverse osmosis membrane agents (CN114807271B) involves adding sophorolipids to the feed water. Analysis shows that sophorolipids significantly inhibit organic matter (bovine serum albumin) and metal salts (including calcium ions) in the feed water during reverse osmosis membrane filtration. Through bridging, it stabilizes the organic matter and metal salts in the water, preventing their deposition on the reverse osmosis membrane and effectively preventing fouling. Another example is the application of rhamnolipin as a biological cleaning agent (CN102399644A), which uses rhamnolipin as a cleaning agent to clean fouled filter membranes. The former intercepts organic matter in simulated wastewater, while the latter cleans fouled membranes. Both methods involve relatively simple environmental components and conditions when using biosurfactants. They do not examine the impact of biosurfactants on membrane fouling control in complex membrane bioreactor systems with coexisting pollutants and microorganisms, nor do they delve into how biosurfactants intercept organic matter in solution and prevent contact between the membrane and the biosurfactant.

[0005] Zhang et al.'s research (Separation and Purification Technology, 2023, 326, 124855) combined the addition of rhamnolipin and magnetic powder in an aerobic membrane bioreactor, finding that rhamnolipin could mitigate membrane fouling to some extent by reducing the viscosity of the mixed liquor. However, this study did not fully utilize the changes in sludge mixed liquor characteristics caused by the addition of biosurfactants to further combine with other technologies to control membrane fouling. Furthermore, the method of combining biosurfactants with packing materials to control membrane fouling in anaerobic membrane bioreactors has not yet been reported. Summary of the Invention

[0006] To address the aforementioned technical problems in existing technologies, the present invention aims to provide a method for controlling membrane fouling in anaerobic membrane bioreactors (AnMBRs) by jointly adding biosurfactants and packing materials, thereby further mitigating AnMBR membrane fouling and promoting the widespread application of AnMBRs in municipal wastewater treatment. This invention controls AnMBR membrane fouling by jointly adding a certain concentration of sophorolipid (SL) and a certain volume fraction of polyurethane foam bio-packing material (PUS) to the AnMBR. Sophorolipid is a nonionic biosurfactant whose solubilizing effect promotes the dissolution of viscous and insoluble substances in the sludge mixture. The dissolved organic molecules are encapsulated by micelles formed by the surfactant, thereby reducing the contact between proteins, polysaccharides, and other organic matter and the membrane surface. Furthermore, the addition of packing materials facilitates the adhesion of sludge flocs in the sludge mixture, and the polyurethane foam packing material, containing carboxyl, hydroxyl, and amino groups, also facilitates the adsorption of dissolved organic matter, ultimately reducing the concentration of suspended particles and organic matter in the mixture and mitigating membrane fouling. The combined addition of both can reduce the concentration of suspended particles and organic pollutants such as proteins and polysaccharides in the mixed liquor, thereby mitigating membrane fouling while ensuring the quality of the effluent and achieving stable operation of the AnMBR reactor.

[0007] The technical solution adopted in this invention is as follows:

[0008] A method for controlling membrane fouling in an anaerobic membrane bioreactor by combining the addition of biosurfactants and fillers is characterized in that: an anaerobic membrane bioreactor (AnMBR) is used to treat municipal wastewater. The AnMBR is equipped with a membrane module and a mechanical stirring device. The AnMBR contains an aqueous suspension of anaerobic sludge. The membrane module is suspended in the aqueous suspension. The outlet of the membrane module is connected to an effluent pump through a pipeline. A pressure gauge is installed on the pipeline between the outlet of the membrane module and the effluent pump. The gas outlet of the AnMBR is connected to a gas collection bag.

[0009] When treating municipal wastewater, the aqueous suspension in the AnMBR is continuously stirred, and biosurfactants and packing materials are added to the AnMBR. The combined effect of biosurfactants and packing materials reduces membrane fouling, and methane gas generated during wastewater treatment is collected.

[0010] Furthermore, the membrane module of the anaerobic membrane bioreactor is a submerged flat sheet membrane with a pore size of 0.1±0.05μm and made of polyvinylidene fluoride (PVDF), which is installed in the middle position inside the anaerobic membrane bioreactor AnMBR.

[0011] Furthermore, AnMBR operates in a continuous flow mode. When the transmembrane pressure difference TMP of the membrane module reaches a set value, the membrane module is disassembled for chemical cleaning, and then the cleaned membrane module is reinstalled to continue the operation.

[0012] Furthermore, when the transmembrane pressure difference (TMP) of the membrane module reaches 25 kPa, the membrane module is cleaned. The specific cleaning method is to soak it in a sodium hypochlorite solution with a mass fraction of 0.2-0.5% for at least 12 hours, then rinse it with clean water and continue to use the membrane module.

[0013] Furthermore, the biosurfactant is a glycolipid biosurfactant called sophorolipid, which has a high interfacial potential and a strong affinity for organic matter, with an effective content of 50±5% and a pH range of 6-7.

[0014] Furthermore, the filler is a polyurethane foam bio-filler. Polyurethane foam (PUS), as an organic bio-filler, contains OH, NH, COOH, and other groups. It has strong hydrophilicity, a large specific surface area, a porosity of 95±3%, and a density of 15±2 kg / m³. 3 The polyurethane sponge biofiller is cubic in shape, with a diameter of 1-5 cm, preferably 2-3 cm.

[0015] Furthermore, the effective concentration of the biosurfactant sophorolipid added to the aqueous suspension in the AnMBR is 20-100 mg / L, and the amount of packing added is 4-10% of the effective volume of the reactor. The 4-10% amount of packing added refers to the percentage of the total volume of the added packing to the volume of the aqueous suspension in the AnMBR during the actual operation of the reactor.

[0016] Furthermore, the packing material of the anaerobic membrane bioreactor is uniformly arranged inside it, and the stirring speed is controlled at 400-500 rpm.

[0017] Furthermore, the AnMBR operates using continuous membrane filtration, with a membrane flux of 6–10 LMH and a hydraulic retention time (HRT) of 24–48 h. The average operating temperature is 25–28 °C, and the sludge concentration is 6–8 g / L.

[0018] Furthermore, the COD value of the municipal wastewater is 400±20mg / L, and the COD value of the treated clean water continuously discharged through the membrane module is 20±5mg / L.

[0019] Compared with the prior art, the beneficial effects achieved by this application are:

[0020] (1) The present invention uses the biosurfactant sophorolipid to control membrane fouling. It has a solubilizing effect, which promotes the dissolution of viscous and insoluble substances in the sludge mixture. The solubilized organic molecules are encapsulated in micelles formed by the surfactant, thereby reducing the contact between organic matter such as proteins and polysaccharides and the membrane surface, thus effectively mitigating membrane fouling.

[0021] (2) The addition of biosurfactants has no significant negative impact on microbial activity and can ensure stable effluent quality of AnMBR. In addition, the solubilization process of adding surfactants is conducive to promoting the anaerobic process, providing more substrates (such as soluble proteins and short-chain fatty acids) for methanogens, thereby increasing the yield of anaerobic methanogenesis.

[0022] (3) In addition to providing a carrier for biofilm formation and reducing the concentration of suspended solids in sludge, the added polyurethane packing mainly adsorbs excessively high concentrations of dissolved organic matter generated during the solubilization process of sophorolipid addition, especially organic matter with a particle size distribution of 1-5 μm that is closely related to membrane fouling. Furthermore, the polyurethane sponge packing contains carboxyl, hydroxyl, and amino groups on its surface. The addition of sophorolipid can encapsulate the hydrophobic organic matter that has been solubilized and form hydrophilic micelles. These micelles can adhere to the packing surface through chemical bonds, thereby further reducing the organic matter in the mixed liquor. Attached Figure Description

[0023] Figure 1 Figure showing the effect of different dosages of sophorolipids on membrane fouling in anaerobic membrane bioreactors;

[0024] Figure 2 Figure showing the effect of combined addition of sophorolipid and packing material on membrane fouling in anaerobic membrane bioreactors;

[0025] Figure 3 a and Figure 3 Figure b shows the effect of combined addition of sophorolipids and packing material on the proportion and concentration of organic matter (proteins, polysaccharides) in the mixed liquor of the anaerobic membrane bioreactor;

[0026] Figure 4 Figure showing the effect of combined addition of sophorolipid and packing material on COD removal rate of anaerobic membrane bioreactor;

[0027] Figure 5 The figure shows the effect of combined addition of sophorolipid and packing material on methane gas production in an anaerobic membrane bioreactor. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0029] In Embodiment 1 of the present invention, the following operating conditions are adopted:

[0030] The influent was designed to simulate municipal wastewater, and its formulation was: beef extract 28 mg / L, C6H 12The concentrations of the following nutrients are: O6280 mg / L, peptone 82 mg / L, NH4Cl 153.6 mg / L, NaHCO3 725 mg / L, KH2PO4 20 mg / L. The trace element formula is: FeSO4·7H2O 2.5 mg / L, CaCl2 0.44 mg / L, MgCl2·6H2O 0.19 mg / L, Na2MoO4·2H2O 0.19 mg / L, CoCl2·6H2O 0.13 mg / L, MnCl2·4H2O 0.06 mg / L, ZnCl2 0.06 mg / L, H3BO3 0.06 mg / L, CuSO4 0.06 mg / L, NiCl2·6H2O 0.04 mg / L. The COD is maintained at around 400 mg / L.

[0031] The anaerobic membrane bioreactor adopts a rectangular cavity with a bottom side length of 120mm × 120mm and a height of 210mm, with a total volume of approximately 3000mL. The membrane module is a flat-sheet membrane module made of polyvinylidene fluoride (PVDF) with a pore size of 0.1μm and an effective filtration area of ​​98cm². 2 The total volume of liquid and anaerobic sludge in the reactor was controlled at approximately 2.5 L, the sludge concentration was maintained at approximately 6 g / L, the HRT of the wastewater in the reactor was 43 h, the operating temperature was 25.0 ± 3.7 °C, the membrane flux was 6 L M H, and the TMP changes were observed during the reactor operation period.

[0032] In this invention, the glycolipid biosurfactant sophorolipid (Shandong Yousuo Chemical Technology Co., Ltd.) has an effective content of 50% and a pH range of 6-7. Sophorolipid is a microbial secondary metabolite produced by Candida albicans using sugars and vegetable oils as carbon sources through a fermentation process under certain conditions. The concentration of sophorolipid added during the experiment is its effective concentration. In the AnMBR process for treating municipal wastewater of this invention, sophorolipid is added directly to the reactor at the required concentration during the initial stage of operation, without needing to be added to the influent.

[0033] In this embodiment of the invention, the polyurethane sponge biological packing material was purchased from Henan Saiyue Environmental Protection Equipment Co., Ltd., and the material is polyurethane. The polyurethane sponge biological packing material added in the experiment has a cubic structure with a size of 3×3×3cm. During the experiment, multiple 3×3×3cm cubic packing materials were added according to the required amount of packing material. The 6% packing material addition amount refers to the percentage of the total volume of the added packing material to the volume of the water suspension in the AnMBR reactor during actual operation.

[0034] Example 1:

[0035] In this embodiment 1, an anaerobic membrane bioreactor was used, and multiple concentration gradients were set up to select the most suitable amount of sophorolipid added. Five groups were set up: "no sophorolipid added", "sophorolipid added at a concentration of 0.024 g / L", "sophorolipid added at a concentration of 0.05 g / L", "sophorolipid added at a concentration of 0.1 g / L", and "sophorolipid added at a concentration of 0.2 g / L". The optimal concentration of sophorolipid added was selected.

[0036] Reference Figure 1 It can be seen that when a low concentration of sophorolipid was added (0.05 g / L), the TMP growth trend was the slowest, with a cycle of 7.5 days to reach 25 kPa, which was 2.5 days longer than the control group (5 days). However, high concentrations (0.1 g / L, 0.2 g / L) exacerbated membrane fouling, with a faster TMP growth rate than the control group. This may be because the high concentration of surfactant caused excessive dissolution of soluble microbial products, increasing the concentration of organic pollutants such as proteins and polysaccharides in the sludge mixture, thus leading to more severe membrane fouling.

[0037] Therefore, the present invention provides a method for controlling membrane fouling in anaerobic membrane bioreactors by jointly adding biosurfactants and fillers, wherein the concentration of biosurfactants is controlled at 0.05 g / L.

[0038] Example 2:

[0039] The anaerobic membrane bioreactor in Example 2 is the same as that in Example 1, except that it is set with four conditions: "blank", "addition of polyurethane sponge packing with a volume fraction of 6%", "addition of sophorolipid with a concentration of 0.05 g / L", and "addition of polyurethane sponge packing with a volume fraction of 6% + addition of sophorolipid with a concentration of 0.05 g / L".

[0040] The membrane fouling of AnMBR under four conditions is summarized in the following table. Figure 2 middle. Figure 2 During multiple cycle operations, when the TMP reaches 25 kPa, the membrane module is removed and chemically rinsed by soaking in a 0.3% sodium hypochlorite solution for 12 hours, followed by thorough rinsing with clean water. The cleaned membrane module is then used for the next cycle. Figure 2 The results showed that the membrane fouling cycles for the control group (AnMBR), the AnMBR with polyurethane sponge filler alone, the AnMBR with sophorolipid alone, and the AnMBR with both sophorolipid and polyurethane sponge filler combined to reach a TMP of 25 kPa were approximately 5 days, 8 days, 7 days, and 10 days, respectively. This indicates that the addition of surfactants and fillers alone can effectively mitigate membrane fouling, while the combined addition of surfactants and fillers has the best effect on membrane fouling control, extending the membrane fouling cycle by twice that of the control group.

[0041] During the mid-stage of AnMBR operation (TMP = 15 kPa), 50 mL of sludge mixture was taken from the reactor sampling port and centrifuged at 2000 rpm for 5 min. The mixture was then sequentially passed through filter membranes with different pore sizes (10, 5, 1, and 0.45 μm). The filtrates obtained from each pore size were collected, and the concentrations of proteins and polysaccharides filtered through these membranes were tested. The results are shown in [Figure number missing]. Figure 3 (b). According to Figure 3 (b) Results were used to calculate the percentage of protein content with different particle sizes in the sludge mixed liquor relative to the total protein content, and the percentage of polysaccharide content with different particle sizes in the sludge mixed liquor relative to the total polysaccharide content. The comparison results of the percentages of protein or polysaccharide content at different particle sizes are summarized in [the table / section]. Figure 3 (a). From Figure 3 (b) As shown in the figure, in the experimental group with sophorolipids added alone, the concentration of proteins and polysaccharides in the mixed solution increased due to the solubilizing effect of sophorolipids, especially in the 1–5 μm particle size distribution. This is likely because large organic molecules are solubilized into relatively small 1–5 μm organic molecules by biosurfactants. In the experimental group with the combined addition of sophorolipids and polyurethane sponge filler, the concentration of organic matter in the 1–5 μm size was significantly reduced compared to the group with sophorolipids added alone. This indicates that the addition of the filler is beneficial for adsorbing the solubilized products of biosurfactants. The combined addition of both effectively controlled the concentration of sludge particles and organic matter in the mixed solution, thereby mitigating membrane fouling.

[0042] COD of AnMBR effluent under four conditions as follows Figure 4 , Figure 4 The data in each bar chart represent the effluent COD measured on the third day of reactor operation when the TMP did not reach 25 kPa. The results show that the effluent COD of the blank AnMBR group was 17 mg / L, the effluent COD of the group with polyurethane sponge packing alone was 18 mg / L, the effluent COD of the group with sophorolipids alone was 22 mg / L, and the effluent COD of the group with both polyurethane sponge packing and sophorolipids was 20 mg / L. The COD removal rate of all four reactors was above 90%. This indicates that sophorolipids, polyurethane sponge packing, and their combined addition had no significant effect on the COD removal of AnMBR.

[0043] The methane production of AnMBR under four conditions is as follows: Figure 5 Under all four conditions, the AnMBR reactor recorded methane data collected during one operating cycle from the start to the end of the experiment. Figure 5The vertical axis represents the ratio of total methane gas volume to effluent COD removal rate within a cycle, indicating the amount of methane produced by microorganisms for every 1g of COD removed. The calculation process is: total gas volume for one cycle * methane content percentage / [(influent COD concentration for that cycle - effluent COD concentration) * influent volume for that cycle]. Results showed that methane production was higher in the control group when polyurethane sponge packing alone, when sophorolipids were added alone, and when polyurethane sponge packing and sophorolipids were added in combination, increasing by 1.6, 2.2, and 2.5 times, respectively. This may be because the packing material facilitates the enrichment of methanogenic bacteria, while the solubilization effect of sophorolipids promotes the production of more substrates (soluble proteins and short-chain fatty acids) required by methanogenic bacteria.

[0044] Therefore, the present invention provides a method for controlling membrane fouling in an anaerobic membrane bioreactor by jointly adding biosurfactants and packing materials, which is expected to effectively alleviate membrane fouling and contribute to anaerobic methanogenesis. The present invention combines the addition of biosurfactants and packing materials in an AnMBR. The biosurfactant, sophorolipid, promotes the dissolution of viscous and insoluble substances in the sludge mixture (mainly extracellular polymers present inside or on the surface of activated sludge flocs, proteins adhering to the filter membrane surface, etc.), preventing the accelerated formation of the filter cake layer due to the presence of these viscous and insoluble substances. The dissolved organic molecules are encapsulated by micelles formed by the surfactant, thereby reducing the contact between proteins, polysaccharides, and other organic matter and the membrane surface. The added polyurethane sponge packing material facilitates the adhesion of sludge flocs in the sludge mixture and the adsorption of dissolved organic matter, ultimately reducing the concentration of suspended particles and organic matter in the mixture. This mitigates membrane fouling while ensuring effluent quality, achieving stable operation of the AnMBR reactor.

[0045] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for controlling membrane fouling in an anaerobic membrane bioreactor by jointly adding biosurfactants and packing materials, characterized in that: An anaerobic membrane bioreactor (AnMBR) is used to treat municipal wastewater. The AnMBR is equipped with a membrane module and a mechanical stirring device. The AnMBR contains an aqueous suspension of anaerobic sludge, and the membrane module is suspended in the aqueous suspension. The outlet of the membrane module is connected to an effluent pump through a pipeline. A pressure gauge is installed on the pipeline between the outlet of the membrane module and the effluent pump. The gas outlet of the AnMBR is connected to a gas collection bag. When treating municipal wastewater, the aqueous suspension in the AnMBR is continuously stirred, and biosurfactants and packing materials are added to the AnMBR. The combined effect of biosurfactants and packing materials reduces membrane fouling, and methane gas generated during wastewater treatment is collected. The biosurfactant is a glycolipid biosurfactant, sophorolipid, with an effective content of 50±5% and a pH range of 6-7; the effective concentration of the biosurfactant sophorolipid added to the aqueous suspension in AnMBR is 20~50 mg / L. The filler material is a polyurethane sponge biological filler, which has strong hydrophilicity, large specific surface area, porosity of 95±3%, and density of 15±2 kg / m³. 3 The polyurethane sponge bio-filler is cubic in shape, with a diameter of 1-5 cm. The amount of filler added is 4-10% of the effective volume of the reactor. The 4-10% filler addition refers to the percentage of the total volume of the filler added relative to the volume of the water suspension in the AnMBR during actual operation of the reactor.

2. The method for controlling membrane fouling in an anaerobic membrane bioreactor by jointly adding biosurfactants and fillers as described in claim 1, characterized in that: AnMBR operates in a continuous flow mode. When the transmembrane pressure difference (TMP) of the membrane module reaches a set value, the membrane module is disassembled for chemical cleaning, and then the cleaned membrane module is reinstalled to continue the cycle.

3. The method for controlling membrane fouling in an anaerobic membrane bioreactor by jointly adding biosurfactants and fillers as described in claim 2, characterized in that: When the transmembrane pressure difference (TMP) of the membrane module reaches 25 kPa, the membrane module is chemically flushed by soaking it in a sodium hypochlorite solution with a mass fraction of 0.2-0.5% for at least 12 hours, followed by rinsing it thoroughly with clean water before continuing to use the membrane module.

4. The method for controlling membrane fouling in an anaerobic membrane bioreactor by jointly adding biosurfactants and packing materials according to claim 1, characterized in that: The polyurethane sponge biofiller is cubic in shape, with a diameter of 2-3 cm.

5. The method for controlling membrane fouling in an anaerobic membrane bioreactor by jointly adding biosurfactants and packing materials according to claim 1, characterized in that: The membrane module of the anaerobic membrane bioreactor is a submerged flat sheet membrane with a pore size of 0.1±0.05μm and made of PVDF, which is installed in the middle of the anaerobic membrane bioreactor AnMBR.

6. The method for controlling membrane fouling in an anaerobic membrane bioreactor by jointly adding biosurfactants and packing materials according to claim 1, characterized in that: The packing material of the anaerobic membrane bioreactor is uniformly arranged inside it, and the stirring speed is controlled at 400~500 rpm; the anaerobic membrane bioreactor is operated at a flux of 6~10 LMH and a sludge concentration of 6~8 g / L.

7. The method for controlling membrane fouling in an anaerobic membrane bioreactor by jointly adding biosurfactants and packing materials according to claim 1, characterized in that: The COD value of the municipal wastewater is 400±20 mg / L, and the COD value of the treated water continuously discharged through the membrane module is 20±5 mg / L.

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