A method for cultivating and controlling membrane pollution of MPBR algal-bacterial granular sludge of urban sewage

Abstract

This invention discloses a method for enhancing the cultivation of algae and microorganism granular sludge and controlling membrane fouling in an MPBR (Multi-Mechanical Bioreactor) for urban wastewater, comprising the following steps: Step S1, inoculating flocculent activated sludge and microalgae into a continuous flow membrane photobioreactor; Step S2, preparing simulated wastewater as the influent to the reactor; Step S3, preliminary cultivation stage: operating the continuous flow membrane photobioreactor, controlling the sludge retention time to 20 days and the hydraulic retention time to 3 days, using an intermittent effluent mode to obtain initially cultivated algae and microorganism granular sludge, at which point the membrane fouling rate is relatively high; Step S4, performance enhancement stage: continuing to operate the continuous flow membrane photobioreactor, controlling the sludge retention time to 20 days, adjusting the hydraulic retention time to 2 days, maintaining the intermittent effluent mode to obtain performance-enhanced algae and microorganism granular sludge, at which point the membrane fouling rate is lower than in the preliminary cultivation stage; Step S5, performance optimization stage: continuing to operate the continuous flow membrane photobioreactor, controlling the sludge retention time to 20 days, adjusting the hydraulic retention time to 1.5 days, maintaining the intermittent effluent mode to obtain algae and microorganism granular sludge in optimal condition, at which point the membrane fouling rate is reduced to the lowest level. This application represents the first successful implementation of a stepwise rapid cultivation of algae and bacteria granular sludge in a continuous flow MPBR, while simultaneously achieving effective control of membrane fouling. This application is applicable to mainstream wastewater treatment scenarios in municipal wastewater treatment plants and has great potential for widespread adoption.

Description

Technical Field

[0001] This invention relates to the field of urban wastewater treatment technology, and in particular to a method for enhancing the cultivation of MPBR algae and bacteria granular sludge and controlling membrane fouling in urban wastewater. Background Technology

[0002] While the traditional activated sludge process is widely used, it suffers from several inherent drawbacks: First, aerobic aeration consumes a large amount of energy, accounting for 50% to 70% of the total energy consumption of wastewater treatment plants; second, it produces a large amount of excess sludge, resulting in high treatment and disposal costs; third, it releases large amounts of greenhouse gases (such as CO2, N2O, and CH4) during operation, with approximately 0.5 to 0.8 kg of CO2 equivalent emitted for every ton of domestic wastewater treated; fourth, to achieve nitrogen and phosphorus removal, it typically requires multiple reaction zones, including anaerobic, anoxic, and aerobic zones, making the process complex and difficult to control. These problems severely restrict the sustainable development of traditional processes.

[0003] In recent years, algae-bacterial granular sludge technology has received widespread attention as an emerging wastewater treatment technology. This technology combines microalgae with activated sludge, utilizing the photosynthesis of microalgae to generate oxygen for the metabolism of aerobic bacteria. The CO2 produced by bacterial metabolism is then absorbed and utilized by the microalgae, forming an efficient endogenous gas exchange cycle. This symbiotic system has the following outstanding advantages: (1) no external aeration is required or the aeration volume is greatly reduced, saving energy; (2) organic matter oxidation, nitrification, denitrification, and phosphorus absorption can be achieved simultaneously in a single-stage reactor; (3) the photosynthesis of microalgae can fix CO2, achieving carbon emission reduction; (4) the granular sludge has a dense structure, excellent settling performance, and good solid-liquid separation effect; (5) it can produce biomass rich in lipids, with resource recovery potential.

[0004] However, most existing algae-bacterial granular sludge technologies are based on batch photobioreactors (PSBR), which are not suitable for the continuous flow treatment mode commonly used in urban wastewater treatment plants in my country. In addition, under continuous flow conditions, the formation cycle of algae-bacterial granular sludge is relatively long, and the granular structure is loose and easily disintegrates, resulting in severe membrane fouling during membrane separation, which limits its engineering application.

[0005] While some studies have attempted to cultivate aerobic granular sludge (AGS) in continuous flow reactors, research on algae-bacterial symbiotic systems is limited, and there is a lack of control strategies to accelerate cultivation. Hydraulic retention time (HRT), a key parameter for reactor design and operation, has an unclear mechanism of influence on the algae-bacterial granulation process. How to rapidly and stably cultivate high-performance algae-bacterial granular sludge under continuous flow conditions and effectively control membrane fouling is a pressing technical challenge in this field. Summary of the Invention

[0006] The main objective of this invention is to provide a method for enhancing the cultivation of algae and bacteria granular sludge and controlling membrane fouling in MPBR (Multi-Phase Integrated Circuit) systems for urban wastewater treatment, in order to solve the technical problems in the prior art, such as the difficulty in forming algae and bacteria granular sludge, poor particle stability, and severe membrane fouling in continuous flow urban wastewater treatment systems.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for enhancing the cultivation of algae-bacterial granular sludge and controlling membrane fouling in urban wastewater MPBR (Multi-Mechanical Bioreactor) systems, specifically comprising the following steps:

[0009] Step S1: Inoculate flocculent activated sludge and microalgae into a continuous flow membrane photobioreactor;

[0010] Step S2: Configure simulated wastewater as the influent to the reactor;

[0011] Step S3, Preliminary Cultivation Stage: The continuous flow membrane photobioreactor is operated, the sludge retention time is controlled at 20 days, the hydraulic retention time is controlled at 3 days, and the intermittent effluent mode is adopted to obtain the preliminarily cultivated algae and bacteria granular sludge. At this time, the membrane fouling rate is relatively high.

[0012] Step S4, Performance Enhancement Stage: Continue to operate the continuous flow membrane photobioreactor, control the sludge retention time to 20 days, adjust the hydraulic retention time to 2 days, maintain the intermittent effluent mode, and obtain performance-enhanced algae and bacteria granular sludge. At this time, the membrane fouling rate is lower than that in the initial cultivation stage.

[0013] Step S5, Performance Optimization Stage: Continue operating the continuous flow membrane photobioreactor, control the sludge retention time to 20 days, adjust the hydraulic retention time to 1.5 days, maintain the intermittent effluent mode, and obtain algae and bacteria granular sludge in optimal condition. At this time, the membrane fouling rate is reduced to the minimum.

[0014] In a preferred embodiment of the present invention, the continuous flow membrane photobioreactor in step S1 is provided with an inner cylinder and an outer cylinder, and a ceramic membrane assembly is fixedly installed inside the inner cylinder.

[0015] In a preferred embodiment of the present invention, the ceramic membrane module has a pore size of 0.1 μm and an effective area of ​​0.04 m². 2 .

[0016] In a preferred embodiment of the present invention, the inner cylinder has an inner diameter of 10cm, the outer cylinder has an inner diameter of 22cm, and the upper edge of the outer cylinder is higher than the upper edge of the inner cylinder.

[0017] In a preferred embodiment of the present invention, a level gauge, a pH sensor, an aeration disc, and a DO sensor are installed inside the continuous flow membrane photobioreactor. The aeration disc is located at the bottom of the outer cylinder, and a row of lights is fixedly installed on the outer side wall of the outer cylinder.

[0018] In a preferred embodiment of the present invention, a water inlet pump is fixedly connected to the top of the outer cylinder, and a water inlet tank is fixedly connected to the end of the water inlet pump away from the outer cylinder.

[0019] In a preferred embodiment of the present invention, an aeration pump is connected below the aeration disc, and a gas flow meter is provided between the aeration disc and the aeration pump.

[0020] In a preferred embodiment of the present invention, a water pump is connected to the top of the ceramic membrane assembly, and a water tank is connected to the end of the water pump away from the ceramic membrane assembly. A pressure gauge is provided between the ceramic membrane assembly and the water pump.

[0021] In a preferred embodiment of the present invention, the continuous flow membrane photobioreactor further includes an online monitoring and control device, which is connected to the inlet pump, the exhaust lamp, the level gauge, the pressure gauge, the DO sensor, the pH sensor, the outlet pump, and the aeration pump, respectively, and monitors the parameters of the continuous flow membrane photobioreactor.

[0022] In a preferred embodiment of the present invention, the online monitoring and control device further includes a computer control system connected to the online monitoring and control device, which controls the parameters of the online monitoring and control device by controlling the online monitoring and control device.

[0023] In a preferred embodiment of the present invention, the illuminance of the array of lights is 5000 lux.

[0024] In a preferred embodiment of the present invention, the aeration intensity of the aeration disc is 43.50 L / h.

[0025] In a preferred embodiment of the present invention, the ceramic membrane module is prepared using alumina.

[0026] In a preferred embodiment of the present invention, the simulated wastewater in step S2 uses sodium acetate as a carbon source, ammonium chloride as a nitrogen source, potassium dihydrogen phosphate as a phosphorus source, sodium bicarbonate as a pH adjuster, and adds MgSO4·7H2O, CaCl2·2H2O and trace elements required for microbial growth.

[0027] In a preferred embodiment of the present invention, the trace elements required for the growth of the microorganisms include FeSO4·7H2O, H3BO3, ZnSO4·7H2O, CuSO4·5H2O, MnCl2·4H2O, and Na2MoO4·2H2O.

[0028] In a preferred embodiment of the present invention, the simulated wastewater in step S2 has a COD concentration of 340-430 mg / L, a total nitrogen concentration of 41-45 mg / L, a total phosphorus concentration of 3.40-4.70 mg / L, a pH of 7-8, a MgSO4·7H2O concentration of 18-22 mg / L, and a CaCl2·2H2O concentration of 8-11 mg / L.

[0029] In a preferred embodiment of the present invention, the intermittent effluent mode of the continuous flow membrane photobioreactor in step S3 is set to produce water for 3 minutes and then stop for 2 minutes, and the transmembrane pressure difference is monitored by a pressure gauge.

[0030] Compared with the prior art, the present invention has the following outstanding advantages:

[0031] 1. This invention utilizes a continuous flow membrane photobioreactor composed of an inner and outer cylinder, forming an internal and external circulation structure to enhance the turbulence of the mixed liquid and promote particle collision and aggregation. The inner cylinder has an inner diameter of 10 cm, and the outer cylinder has an inner diameter of 22 cm. The upper edge of the outer cylinder is higher than the upper edge of the inner cylinder to ensure smooth internal and external circulation. A level gauge, pH sensor, and DO sensor are installed inside the device for real-time monitoring of the continuous flow membrane photobioreactor's operation. The light intensity is set to 5000 lux, provided by a row of lights surrounding the reactor. Aeration is provided by a bottom aeration disc at an aeration rate of 43.50 L / h, providing both hybrid power and a CO2 source for microalgal photosynthesis.

[0032] 2. This invention uses the simulated wastewater as the reactor influent. Sodium acetate is used as the carbon source, ammonium chloride as the nitrogen source, and potassium dihydrogen phosphate as the phosphorus source. Sodium bicarbonate is added as a pH adjuster to maintain the pH between 7 and 8. In addition, minerals and trace elements required for microbial growth are supplemented. The influent water quality simulates the moderate pollution load of typical urban sewage and is representative.

[0033] 3. This invention sets the sludge retention time (SRT) in the continuous flow membrane photobioreactor to a fixed 20 days. The reactor operates continuously for three SRT cycles, totaling 60 days. Within each SRT cycle (20 days), different hydraulic retention times (HRT) are set: HRT = 3 days from day 1 to 20, HRT = 2 days from day 21 to 40, and HRT = 1.5 days from day 41 to 60. The reduction of HRT is achieved by increasing the influent flow rate, resulting in a stepwise increase in the influent organic load, nitrogen load, and phosphorus load. In the first cycle with HRT = 3 days, i.e., days 0 to 20, the reactor starts up and initially forms algae-bacteria granular sludge. At this time, the particle size is small, with an average value of 123.99 μm. The structure is not yet stable, but it already has the rudimentary granular shape. In the second cycle (20-40 days) with an HRT of 2 days, increased hydraulic shear and substrate loading promoted rapid proliferation of microalgae and bacteria, leading to an increase in particle size to 285.50 μm, significantly improved particle strength, better settling performance, and a reduced membrane fouling rate. In the third cycle (40-60 days) with an HRT of 1.5 days, the particles further matured, reaching a particle size of 340 μm with an integrity factor exceeding 80%, achieving optimal pollutant removal efficiency while minimizing the membrane fouling rate.

[0034] 4. This invention reveals a novel mechanism by which IAA acts as a granulation signaling molecule, providing a theoretical and strategic basis for the targeted regulation of algal and bacterial granular sludge. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the process for enhancing the cultivation of algae and bacteria granular sludge and controlling membrane fouling in MPBR of urban sewage according to the present invention.

[0036] Figure 2 This is a schematic diagram of the continuous flow membrane photobioreactor in this invention;

[0037] Figure 3 These are stereomicroscopic images of the algal-bacterial granular sludge obtained after culturing the present invention on days 20, 40, and 60.

[0038] Figure 4 Images showing the removal effects at each reaction stage of the reaction system of this invention;

[0039] Figure 5 This is an image showing the change in IAA content in the reaction system of this invention.

[0040] Figure 6 Images showing changes in transmembrane pressure difference, membrane flux, and membrane permeability in the reaction system of this invention.

[0041] In the diagram: 1. Inlet tank; 2. Inlet pump; 3. Light bar; 4. Inner cylinder; 5. Outer cylinder; 6. Level gauge; 7. Ceramic membrane module; 8. Pressure gauge; 9. DO sensor; 10. pH sensor; 11. Aeration disc; 12. Gas flow meter; 13. Aeration pump; 14. Outlet tank; 15. Outlet pump; 16. Online monitoring and control device; 17. Computer control system. Detailed Implementation

[0042] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0043] Example 1:

[0044] A method for enhancing the cultivation of algae and bacteria granular sludge and controlling membrane fouling in urban wastewater MPBR, such as Figures 1-6 As shown, the method specifically includes the following steps:

[0045] Step S1: Inoculate 0.4 g / L microalgae (mainly Chlorella) and 1.6 g / L (calculated as MLSS) flocculent activated sludge into a continuous flow membrane photobioreactor.

[0046] Among them, such as Figure 2 As shown, the continuous flow membrane photobioreactor has an effective volume of 13.88L and is equipped with an inner cylinder 4 and an outer cylinder 5. The inner cylinder 4 has an inner diameter of 10cm and a height of 32cm, while the upper cavity of the outer cylinder 5 has an inner diameter of 22cm and a height of 35cm. The inner cylinder 4 and the outer cylinder 5 form an internal and external circulation structure to improve the turbulence of the mixed liquid and promote particle collision and aggregation. The upper edge of the outer cylinder is 6cm higher than the upper edge of the inner cylinder to ensure smooth internal and external circulation.

[0047] The inner cylinder 4 is equipped with a set of alumina ceramic membrane modules 7 (membrane pore size 0.1µm, effective area 0.04m²). 2 The device is equipped with a level gauge, pH sensor, and DO sensor to control the liquid level and monitor pH and DO concentrations, and to monitor the operation status of the continuous flow membrane photobio in real time.

[0048] A row of lights 3 with a light intensity of 5000 lux is fixedly installed on the outer side wall of the outer cylinder 5. This light intensity is sufficient to meet the photosynthetic needs of microalgae without causing light inhibition. The measured chlorophyll a+b concentration is highest under this light intensity.

[0049] The aeration disc 11 is located at the bottom of the outer cylinder 5. Aeration is carried out through the aeration disc 11 with an aeration intensity of 43.5 L / h. This provides a hybrid power source for microalgae photosynthesis without excessively shearing particles.

[0050] like Figure 2As shown, an inlet pump 2 is fixedly connected to the top of the outer cylinder 5, and an inlet tank 1 is fixedly connected to the end of the inlet pump 2 away from the outer cylinder 5; an aeration pump 13 is connected to the bottom of the aeration disc 11, and a gas flow meter 12 is provided between the aeration disc 11 and the aeration pump 13; an outlet pump 15 is connected to the top of the ceramic membrane assembly 7, and an outlet tank 14 is connected to the end of the outlet pump 15 away from the ceramic membrane assembly 7; a pressure gauge 8 is provided between the ceramic membrane assembly 7 and the outlet pump 15.

[0051] like Figure 2 As shown, the continuous flow membrane photobioreactor also includes an online monitoring and control device 16, which is connected to the inlet pump 2, the light 3, the level gauge 6, the pressure gauge 8, the DO sensor 9, the pH sensor 10, the outlet pump 15, and the aeration pump 13, respectively. The online monitoring and control device 16 monitors the parameters of the continuous flow membrane photobioreactor.

[0052] like Figure 2 As shown, the online monitoring and control device 16 also includes a computer control system 17, which is connected to the online monitoring and control device 16 and controls the operating parameters of the entire equipment by controlling the online monitoring and control device 16.

[0053] Step S2: Configure simulated wastewater as the influent to the reactor;

[0054] Simulated wastewater was used as the reactor influent. Sodium acetate was used as the carbon source, ammonium chloride as the nitrogen source, potassium dihydrogen phosphate as the phosphorus source, and sodium bicarbonate as the pH adjuster. Simultaneously added were MgSO4·7H2O, CaCl2·2H2O, FeSO4·7H2O, H3BO3, ZnSO4·7H2O, CuSO4·5H2O, MnCl2·4H2O, and Na2MoO4·2H2O. The influent water quality was configured as follows: COD 340-430 mg / L, TN 41-45 mg / L, TP 3.40-4.70 mg / L, pH = 7.5±0.3, 20 mg / L MgSO4·7H2O, 10 mg / L CaCl2·2H2O, and 0.5 mL / L trace elements. This influent water quality simulates a moderate pollution load of typical urban wastewater and is representative.

[0055] The continuous flow membrane photobioreactor was operated. It was run in an intermittent effluent mode, producing water for 3 minutes followed by a 2-minute pause. Transmembrane pressure differential (TMP) was monitored periodically using pressure gauge 8. The sustained filtration time (SRT) was set to 20 days, and the reactor was continuously operated for three SRT cycles (60 days) during the reaction: the initial culture stage, the performance enhancement stage, and the performance optimization stage. The hydraulic filtration time (HRT) was progressively shortened in each cycle by increasing the influent flow rate, resulting in a corresponding stepwise increase in the influent organic load, nitrogen load, and phosphorus load.

[0056] Step S3, Preliminary Cultivation Stage: The continuous flow membrane photobioreactor is operated, the sludge retention time is controlled at 20 days, the hydraulic retention time is controlled at 3 days, and the intermittent effluent mode is adopted to obtain the preliminarily cultivated algae and bacteria granular sludge; at this time, the particle size is small, with an average value of about 123.99 μm, and the structure is still unstable, but it has already formed a granular prototype.

[0057] HRT is set to 3 days, corresponding to a flux of 8.03 L (m³). 2 The influent loading rates for COD, TN, and TP were 131.50 kg COD / (m³) and 131.50 kg TN / (m³) respectively. 3 ∙d), 14.38 kgN / (m 3 ∙d), 1.39kgP / (m 3 ∙d). The experiment ran for 20 days.

[0058] During the experimental operation phase, the physicochemical and biochemical indicators of the algae-bacterial granular sludge were measured.

[0059] The measured data are as follows:

[0060] After 20 days of operation, the average particle size measured by the laser particle size analyzer was 123.99µm.

[0061] The SVI5 / SVI will stabilize within the next ten days. 30 The ratio is 1.21, indicating that the particles still contain some flocculent material (a ratio close to 1 indicates good settling properties).

[0062] After stirring at 400 rpm for 5 minutes, the proportion of remaining particles and the integrity factor (IC) were 57.30%.

[0063] This indicates that the particles have been initially formed, but their structural stability still needs to be improved.

[0064] At this point, the average IAA concentration was 0.66 μg / L;

[0065] The average MLSS was 2.04g;

[0066] The average concentration of chlorophyll a+b was 23.80 mg / L;

[0067] The biomass yield was 102 mg / (L·d), indicating that the algal biomass was initially established and the growth rate was low.

[0068] The average SOUR was 44.81 mg-O2 / (g-MLSS·h), the average SOPR was 11.73 mg-O2 / (g-MLSS·h), and the average EPS concentration was 110.48 mg / gMLSS, reflecting that the metabolic activity of algae and bacteria is still at a low level.

[0069] In terms of pollutant removal performance, the COD removal rate was 92.73%, TN removal rate was 53.87%, and the average TP removal rate was 77.85%. Meanwhile, the membrane fouling rate was 0.82 L / (m²). 2 ·h 2 ·kPa).

[0070] The results showed that after 20 days of operation, algal and bacterial granular sludge had been initially formed in the reactor, but the particle size was small and the particle strength was low. The efficiency of pollutant removal, especially denitrification, needed to be improved, and the membrane fouling rate was high.

[0071] Step S4, Performance Enhancement Stage: Continue operating the continuous flow membrane photobioreactor, control the sludge retention time to 20 days, adjust the hydraulic retention time to 2 days, maintain the intermittent effluent mode, and obtain performance-enhanced algae and bacteria granular sludge; the hydraulic shear force is enhanced, the substrate load is increased, promoting the rapid proliferation of microalgae and bacteria, the particle size increases to 285.50 μm, the particle strength is significantly improved, and the settling performance is improved.

[0072] Based on Example 1, starting from day 21, the HRT was adjusted to 2 days, and the influent flow rate was increased accordingly, with the flux increasing to 12.05 L / (m³). 2 •h). With the influent water quality remaining constant, the COD load increased to approximately 182.8 kg / (m³). 3 ·d), TN load 21.3 kg / (m 3 ·d), TP load 1.98 kg / (m 3 ·d). Continue running for 20 days (days 21-40).

[0073] After 20 days of operation, the physicochemical and biochemical indicators of the algae-bacterial granular sludge were measured.

[0074] The measurement results are as follows:

[0075] The measured data are as follows:

[0076] After 20 days of operation, the average particle size measured by the laser particle size analyzer was 285.50µm.

[0077] The SVI5 / SVI will stabilize within the next ten days. 30The ratio is 1.10, which is closer to 1, indicating that the floc content is decreasing;

[0078] After stirring at 400 rpm for 5 minutes, the proportion of remaining particles and the integrity factor (IC) were 71.59%.

[0079] This indicates a significant improvement in particle strength;

[0080] At this point, the average IAA concentration was 0.87 μg / L;

[0081] The average MLSS was 2.50g;

[0082] The average concentration of chlorophyll a+b was 40.34 mg / L;

[0083] The bioyield was 125 mg / (L·d);

[0084] The average SOUR was 52.77 mg-O2 / (g-MLSS·h), the average SOPR was 12.78 mg-O2 / (g-MLSS·h), and the average EPS concentration was 121.49 mg / gMLSS (of which protein was 70.2 mg / gMLSS and polysaccharides were 51.29 mg / gMLSS), reflecting enhanced metabolic activity of microalgae and bacteria.

[0085] In terms of pollutant removal performance, the COD removal rate was 95.63%, TN removal rate was 62.60%, and the average TP removal rate was 80.77%. Meanwhile, the membrane fouling rate was 0.80 L / (m²). 2 ·h 2 ·kPa).

[0086] The results showed that when the HRT was shortened to 2 days, the influent load increased, the metabolic activity of microalgae and bacteria was enhanced, the particle size increased, the structural stability was significantly improved, the pollutant removal performance was improved, and the membrane fouling rate decreased.

[0087] Step S5, Performance Optimization Stage: Continue operating the continuous flow membrane photobioreactor, control the sludge retention time to 20 days, adjust the hydraulic retention time to 1.5 days, maintain the intermittent effluent mode, and obtain algae and bacteria granular sludge in optimal condition; the granules are further matured, the particle size reaches 340μm, the integrity coefficient exceeds 80%, the pollutant removal efficiency reaches the optimal level, and the membrane fouling rate is reduced to the minimum.

[0088] Based on Example 2, the HRT was adjusted to 1.5 days starting from day 41, with a flux of 16.06 L / (m³). 2 COD load rose to 235.2 kg / (m³) (·h). 3 ·d), TN load 26.5 kg / (m 3 ·d), TP load 2.51 kg / (m3 ·d). Continue running for 20 days (days 41-60).

[0089] After 20 days of operation, the physicochemical and biochemical indicators of the algae-bacterial granular sludge were measured.

[0090] The measurement results are as follows:

[0091] After 20 days of operation, the average particle size measured by the laser particle size analyzer was 345.84µm.

[0092] The SVI5 / SVI will stabilize within the next ten days. 30 The ratio is 1.06, which is very close to 1, indicating excellent particle settling performance;

[0093] After stirring at 400 rpm for 5 minutes, the proportion of remaining particles and the integrity factor (IC) were 83.55%.

[0094] This indicates that the particle strength has achieved high strength;

[0095] At this time, the average IAA concentration was 1.01 μg / L. Previous studies have shown that IAA can promote microbial aggregation, regulate extracellular polymer secretion and enhance particle structure stability. The increase in IAA level indirectly promotes the formation and stability of algal granular sludge. In this invention, the IAA level and particle performance indicators show good consistency.

[0096] The average MLSS was 3.16g;

[0097] The average concentration of chlorophyll a+b was 60.40 mg / L;

[0098] The bioyield was 158 mg / (L·d);

[0099] The average SOUR (Solubility O2) was 59.97 mg-O2 / (g-MLSS·h), the average SOPR (Solubility O2 Permeability) was 13.91 mg-O2 / (g-MLSS·h), and the average EPS (Expanded Polysaccharide) concentration was 144.49 mg / gMLSS (including 85.1 mg / gMLSS of protein and 59.39 mg / gMLSS of polysaccharides), reflecting further enhanced metabolic activity of microalgae and bacteria. In terms of pollutant removal performance, COD was 97.55%, TN was 70.35%, and the average TP removal rate was 93.28%. Meanwhile, the membrane fouling rate was 0.79 L / (m³). 2 ·h 2 ·kPa).

[0100] Combining the three embodiments and Figures 2-5It can be concluded that as the HRT is shortened from 3 days to 1.5 days, the various performance indicators of algae and bacteria granular sludge are continuously optimized. The IAA concentration is significantly positively correlated with particle strength and particle size. The effluent quality is improved from close to Class B to a stable Class A standard. The membrane fouling rate is reduced by about 3.7%, which is the minimum value.

[0101] The technical principle of this invention is as follows:

[0102] First, the hydraulic shear time (HRT) is shortened in a stepwise manner during the initial cultivation stage, performance enhancement stage, and performance optimization stage. Shorter HRT means increased influent flow rate, resulting in enhanced upward flow velocity and turbulence within the reactor. Moderate hydraulic shear force promotes collision and adhesion between microbial cells, accelerating the granulation process. However, excessive shear force can damage the particle structure. This invention uses a stepwise, rather than abrupt, shortening of HRT, allowing the microbial community to gradually adapt to the enhanced hydraulic conditions, thus avoiding particle disintegration while continuously promoting particle densification.

[0103] Secondly, the HRT time for the initial culture stage, performance enhancement stage, and performance optimization stage has been shortened from 3 days to 1.5 days. The higher matrix concentration induces microorganisms to secrete more extracellular polymers (EPS). EPS, as a "bio-glue", can tightly bind cells and microalgae together to form a stable three-dimensional structure.

[0104] Then, this invention discovers for the first time that the concentration of indoleacetic acid (IAA) in the reactor gradually increases with shortening of the HRT and increase in the load. IAA is an important plant hormone-like microbial signaling molecule that can promote cell division, elongation, and aggregation. Increased IAA levels not only promote the synergistic growth of microalgae and bacteria but also upregulate the expression of EPS synthesis-related genes, thereby enhancing the structural stability of the particles. IAA concentration is significantly positively correlated with particle size and integrity coefficient (R2>0.95), indicating that it is a key biochemical factor driving particle formation.

[0105] Finally, this invention reveals that the membrane fouling rate is closely related to the properties of the mixed liquor. When the HRT (Heat Retention Time) is long and particles are not fully formed, fine flocs and free microorganisms easily deposit on the membrane surface, causing pore blockage and filter cake fouling. As the HRT shortens, the particle size increases, and settling performance improves. Suspended solids in the mixed liquor are more easily separated from the membrane module by gravity settling, and the filter cake layer on the membrane surface becomes loose and easily washed away. Simultaneously, optimizing the protein / polysaccharide ratio in EPS (Expanded Polysaccharide) also reduces the tendency for membrane fouling, achieving synergistic control of membrane fouling.

[0106] Comparative Example 1:

[0107] The initial HRT was set directly to 1.5 days, with other conditions remaining unchanged. The results showed that pollutant removal was poor during the first 10 days of reactor operation, followed by severe membrane fouling, with TMP rapidly rising above 50 kPa, forcing the reactor to shut down on the 15th day. This comparison demonstrates that directly using a short HRT leads to excessive hydraulic load shocks, preventing microorganisms from adapting and causing system collapse. In contrast, a stepped reduction in HRT provides a gradual adaptation process for the microbial community, which is crucial for the successful cultivation of algal-bacterial granular sludge.

[0108] Comparing Experimental Example 1 with Comparative Example 1, it can be seen that HRT=3 days is the initial value, ensuring a low upflow velocity and substrate load, which is conducive to microbial attachment and initial particle formation. HRT=1.5 days is the final value, corresponding to higher hydraulic shear force and load, which is the optimal point for promoting particle maturation and improving treatment efficiency.

[0109] The method provided by this invention can be applied to the upgrading and renovation of existing urban wastewater treatment plants. By introducing flocculent microalgae into the existing aerobic tank, adding membrane modules and light sources, and optimizing the HRT (Heat Retention Technology) operation strategy, algae-bacterial granular sludge can be cultivated within 60 days, achieving a transition from traditional activated sludge to algae-bacterial granular sludge. This method requires no additional land, has low construction costs, reduces operating energy consumption by 20%–30%, and simultaneously achieves carbon emission reduction and resource recovery. The algae-bacterial biomass can be used as raw material for fertilizer or biofuel. Therefore, this invention has significant economic and environmental benefits.

[0110] It should be noted that the sensors, control systems, and online monitoring and control devices in this invention all adopt conventional technical solutions in the field and can be adapted to suit actual application scenarios. This method can achieve automated parameter optimization through a software platform and can also be adapted to portable terminals for on-site auxiliary design, possessing strong flexibility and practicality. All embodiments in this application are described in a related manner, and the same or similar parts between the embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments.

Claims

1. A method for enhancing municipal wastewater MPBR algal-bacterial granular sludge cultivation and membrane fouling control, characterized in that, Includes the following steps: Step S1: Inoculate flocculent activated sludge and microalgae into a continuous flow membrane photobioreactor; Step S2: Configure simulated wastewater as the influent to the reactor; Step S3, Preliminary Cultivation Stage: The continuous flow membrane photobioreactor is operated, the sludge retention time is controlled at 20 days, the hydraulic retention time is controlled at 3 days, and the intermittent effluent mode is adopted to obtain the preliminarily cultivated algae and bacteria granular sludge. At this time, the membrane fouling rate is relatively high. Step S4, Performance Enhancement Stage: Continue to operate the continuous flow membrane photobioreactor, control the sludge retention time to 20 days, adjust the hydraulic retention time to 2 days, maintain the intermittent effluent mode, and obtain performance-enhanced algae and bacteria granular sludge. At this time, the membrane fouling rate is lower than that in the initial cultivation stage. Step S5, Performance Optimization Stage: Continue operating the continuous flow membrane photobioreactor, control the sludge retention time to 20 days, adjust the hydraulic retention time to 1.5 days, maintain the intermittent effluent mode, and obtain algae and bacteria granular sludge in optimal condition. At this time, the membrane fouling rate is reduced to the minimum.

2. The enhanced municipal wastewater MPBR algal-bacterial granular sludge cultivation method according to claim 1, characterized by, In step S1, the continuous flow membrane photobioreactor is provided with an inner cylinder (4) and an outer cylinder (5). A ceramic membrane assembly (7) is fixedly installed inside the inner cylinder (4). The upper edge of the outer cylinder (5) is higher than the upper edge of the inner cylinder (4).

3. The enhanced municipal wastewater MPBR algal-bacterial granular sludge cultivation method according to claim 2, characterized by, The continuous flow membrane photobioreactor is equipped with a level gauge (6), a pH sensor (10), an aeration disc (11) and a DO sensor (9). The aeration disc (11) is located at the bottom of the outer cylinder (5), and a row of lights (3) is fixedly installed on the outer side wall of the outer cylinder (5).

4. The enhanced method for MPBR algae and bacteria granular sludge cultivation in urban wastewater according to claim 3, characterized in that, A water inlet pump (2) is fixedly connected to the top of the outer cylinder (5), and a water inlet tank (1) is fixedly connected to the end of the water inlet pump (2) away from the outer cylinder (5); an aeration pump (13) is connected to the bottom of the aeration disc (11), and a gas flow meter (12) is provided between the aeration disc (11) and the aeration pump (13); a water outlet pump (15) is connected to the top of the ceramic membrane assembly (7), and a water outlet tank (14) is connected to the end of the water outlet pump (15) away from the ceramic membrane assembly (7), and a pressure gauge (8) is provided between the ceramic membrane assembly (7) and the water outlet pump (15).

5. The enhanced method for MPBR algae and bacteria granular sludge cultivation in urban wastewater according to claim 4, characterized in that, The continuous flow membrane photobioreactor also includes an online monitoring and control device (16), which is connected to the inlet pump (2), the lamp array (3), the level gauge (6), the pressure gauge (8), the DO sensor (9), the pH sensor (10), the outlet pump (15), and the aeration pump (13), respectively. The online monitoring and control device (16) monitors the parameters of the continuous flow membrane photobioreactor.

6. The enhanced method for cultivating MPBR algae-bacterial granular sludge in urban wastewater according to claim 5, characterized in that, The online monitoring and control device (16) also includes a computer control system (17), which is connected to the online monitoring and control device (16) and controls the operating parameters of the entire equipment by controlling the online monitoring and control device (16).

7. The enhanced method for MPBR algae and bacteria granular sludge cultivation in urban wastewater according to claim 1, characterized in that, In step S2, the simulated wastewater uses sodium acetate as a carbon source, ammonium chloride as a nitrogen source, potassium dihydrogen phosphate as a phosphorus source, sodium bicarbonate as a pH adjuster, and adds MgSO4·7H2O, CaCl2·2H2O, and trace elements required for microbial growth.

8. The enhanced method for cultivating MPBR algae-bacteria granular sludge in urban wastewater according to claim 7, characterized in that, The trace elements required for the growth of the microorganisms include FeSO4·7H2O, H3BO3, ZnSO4·7H2O, CuSO4·5H2O, MnCl2·4H2O, and Na2MoO4·2H2O.

9. The enhanced method for MPBR algae and bacteria granular sludge cultivation in urban wastewater according to claim 8, characterized in that, In step S2, the simulated wastewater has a COD concentration of 340-430 mg / L, a total nitrogen concentration of 41-45 mg / L, a total phosphorus concentration of 3.40-4.70 mg / L, a pH of 7-8, a MgSO4·7H2O concentration of 18-22 mg / L, and a CaCl2·2H2O concentration of 8-11 mg / L.

10. The enhanced method for cultivating MPBR algae-bacteria granular sludge in urban wastewater according to claim 4, characterized in that, In steps S3-S5, the intermittent effluent mode of the continuous flow membrane photobioreactor is set to produce water for 3 minutes and stop for 2 minutes, and the transmembrane pressure difference is monitored by pressure gauge (8).

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