Wastewater treatment process based on coupling of red-mud-based molecular sieve fixed bed and MBBR (moving bed biofilm reactor)

Abstract

The invention belongs to the technical field of sewage and wastewater treatment, and particularly relates to a wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled MBBR (moving bed biofilm reactor), which comprises the following steps: (1) collecting wastewater, putting the wastewater into an adjusting tank, adjusting the water quality and water quantity to fluctuate, and discharging water; (2) carrying out physical adsorption deamination and biological deamination on the effluent in the step (1), and then discharging the effluent; (3) feeding effluent in the step (2) into an anaerobic digester for treatment, and discharging supernate; (4) feeding the supernatant effluent in the step (3) into a biological selection tank for treatment to obtain mixed liquor effluent; (5) feeding the effluent of the mixed solution in the step (4) into an anoxic tank for denitrification treatment to obtain a denitrified mixed solution; (6) feeding the denitrifying mixed solution in the step (5) into an aerobic tank to obtain a nitrifying mixed solution; and (7) feeding the nitrified mixed solution in the step (6) into a sedimentation tank, separating, and discharging supernate, thereby finishing wastewater treatment. The process does not need an external carbon source, is high in denitrification efficiency and low in operation cost, and meets the emission standard.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage and wastewater treatment, and in particular relates to a wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR. Background Art

[0002] By the end of 2023, there will be over 6,000 highway service areas nationwide. While service areas are crucial for ensuring daily travel and transportation safety, the wastewater they generate cannot be ignored. Highway service area wastewater primarily consists of urine, toilet flushing water, feces, and some restaurant wastewater. Compared to typical urban domestic sewage, it exhibits significant fluctuations in flow, high shock loads, elevated organic nitrogen concentrations, and a low influent carbon-nitrogen ratio.

[0003] Currently, traditional processes such as SBR, AO, MBR, and biological contact oxidation are primarily used to treat wastewater from highway service areas. However, due to factors such as a lack of carbon sources and high shock loads, treatment results are generally poor. In addition to these traditional processes, newer technologies such as short-cut nitrification and denitrification, anaerobic ammonium oxidation, and constructed wetlands have also demonstrated excellent shock resistance in highway service area wastewater treatment. However, these new processes require high technical expertise and operational maintenance, posing challenges in their long-term operation.

[0004] In the prior art: Patent document CN113860633A discloses an integrated sewage treatment device and method for highway service areas, which adds an iron-carbon-based composite biological carrier to provide a carbon source for denitrification, and adopts MBR to improve the denitrification efficiency. However, the use of biofilm increases operating costs and has limited treatment capacity when dealing with low carbon-nitrogen ratio influent; Patent document CN119080246A discloses a highway service area wastewater treatment device and method based on the AOOA-MBBR process. This method completely nitrifies and denitrifies the highway service area wastewater, has a relatively long hydraulic retention time, and the shock load can still be further increased.

[0005] In summary, there is an urgent need to explore a highway service area wastewater treatment process with good treatment effect, high denitrification efficiency, strong resistance to shock loads, low operating costs and in compliance with the Level A standard requirements of the "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (GB18918-2002). Summary of the Invention

[0006] The present invention aims to solve the above technical problems and provide a wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR, which does not require an external carbon source, has high denitrification efficiency, low operating costs, and meets emission standards.

[0007] The technical solution of the present invention is:

[0008] A wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR comprises the following steps:

[0009] (1) Regulating tank: collect wastewater and put it into regulating tank to adjust the water quality and quantity fluctuations and then discharge the water;

[0010] (2) Red mud-based molecular sieve fixed bed treatment: the effluent from step (1) is passed from bottom to top through the red mud-based molecular sieve fixed bed and then discharged;

[0011] (3) Anaerobic treatment: the effluent from step (2) is sent to an anaerobic digester for treatment, and the supernatant is discharged after the anaerobic digester;

[0012] (4) Biological selection treatment: the supernatant effluent from step (3) is sent to the biological selection tank for treatment, and a mixed liquid effluent is obtained after the biological selection tank;

[0013] (5) Anoxic treatment: the effluent from the mixed solution in step (4) is sent to an anoxic tank for denitrification treatment to obtain a denitrified mixed solution;

[0014] (6) Aerobic treatment: sending the denitrification mixed solution in step (5) into an aerobic tank for nitrification treatment to obtain a nitrification mixed solution;

[0015] (7) Sedimentation treatment: The nitrification mixture in step (6) is sent to the sedimentation tank for separation of mud and water. After separation, the supernatant is discharged, and the wastewater treatment is completed.

[0016] For stable operation of the process, preferably, in step (1) of the present invention, the wastewater entering the regulating tank has a COD concentration of 200-500 mg / L, an ammonia nitrogen concentration of 30-100 mg / L, a total nitrogen concentration of 50-150 mg / L, a total phosphorus concentration of 3-10 mg / L, and a pH value of 6-8.

[0017] In order to make the red mud-based molecular sieve have a good deamination effect and to improve the high temperature resistance and crack resistance of the red mud-based molecular sieve fixed bed, the preparation method of the red mud-based molecular sieve fixed bed in step (2) of the present invention comprises the following steps:

[0018] (1) Red mud and HCl solution with a concentration of 3-8 mol / L were mixed at a liquid-to-solid ratio of 2-6:1 mL / g, and acid-leached at room temperature for 1-3 h. After acid-leaching, the mixture was washed and filtered, and the filtrate was dried to a constant weight to obtain an acid-leached red mud base;

[0019] (2) After acid-leached red mud is mixed with NaOH or Ca(OH)2 and polyvinyl alcohol in a mass ratio of 1:1-3:0.03-0.05, 1-3 wt% zeolite based on acid-leached red mud and 0.3-0.5 wt% silicon carbide whiskers based on acid-leached red mud are added, the mixture is evenly mixed, and the mixture is calcined at 600-700 °C for 60-150 min to obtain alkali-soluble red mud;

[0020] (3) After the alkali-soluble red mud is cooled to room temperature, the Si / Al molar ratio is adjusted to 5-15:1 with Na2SiO3•9H2O, and then water is added to adjust the liquid-solid ratio to 7.5-15:1 mL / g. The hydrothermal method is used to carry out the homogenization reaction at a hydrothermal temperature of 80-160°C for 8-16 hours. The red mud-based molecular sieve obtained after the reaction is separated, washed and dried. After drying, it is compacted into columnar particles with a diameter of 1-2 cm and a length of 2-5 cm using a mold. The columnar particles are fixed inside the container in the form of a bed filling, thus obtaining a red mud-based molecular sieve fixed bed. The columnar particles are red mud-based molecular sieve particle fillers. After the water is discharged from step (1) in the wastewater treatment process, water is passed from bottom to top. During the process of water flowing through the red mud-based molecular sieve fixed bed, the particle fillers are physically adsorbed, and the microbial film on the surface of the particle fillers undergoes biological deammoniation.

[0021] When preparing columnar particles, during the calcination process, silicon carbide whiskers are used as high-strength fibrous fillers and are evenly dispersed in the acid leaching system. During the calcination process, they form a three-dimensional network structure with zeolite and red mud, effectively inhibiting the cracking or fragmentation of the acid-leached red mud base due to shrinkage stress during the calcination process, reducing the initiation of microcracks by bridging the gaps between particles, and improving the yield rate. At the same time, it ensures that the acid-leached red mud base maintains structural integrity during high-temperature calcination to prevent material collapse and deformation. At the same time, the porous characteristics of zeolite itself can guide the directional growth of molecular sieve crystals, increase the specific surface area and pore connectivity of the columnar particles, and are beneficial to the improvement of adsorption performance. The red mud-based molecular sieve particles are made of quartz and quartz. ...

[0022] The red mud-based molecular sieve fixed bed of the present invention utilizes red mud (waste material generated during aluminum processing) as a solid waste as raw material, and has low cost.

[0023] In order to convert the organic ammonia in the influent into ammonia nitrogen, preferably, the anaerobic digester in step (3) of the present invention is a folded plate anaerobic tank, and the folded plate anaerobic tank adopts a double compartment, and the double compartment is an influent compartment and an effluent compartment adjacent to each other, and the volume ratio of the influent compartment to the effluent compartment is 1:3-5.

[0024] In order to achieve a good anaerobic digestion effect, preferably, the temperature in the anaerobic digester of step (3) of the present invention is controlled to be 37±2°C, the pH value is 6.5-7.5, the hydraulic retention time is 12-48h, the sludge concentration is 4000-7000mg / L, and the volatile acid concentration is less than 5mg / L.

[0025] In order to flexibly deal with shock loads and ensure stable operation of the system, preferably, aeration and stirring are provided in the biological selection tank in step (4) of the present invention. When the C / N mass concentration ratio of the influent of the regulating tank in step (1) is ≤5, aeration is performed, and the DO in the water is controlled at 2.0-3.5 mg / L during aeration. When the C / N mass concentration ratio of the supernatant effluent is greater than 5, aeration is stopped and stirring is performed, and the DO in the water is controlled at below 0.5 mg / L.

[0026] In order to ensure a good denitrification effect and sufficient fluidization of the suspended carrier, preferably, the anoxic tank in step (5) of the present invention is stirred, the DO in the water is controlled below 0.5 mg / L, and the COD concentration is 100-200 mg / L.

[0027] To ensure a good nitrification effect, preferably, the DO concentration in the aerobic pool water in step (6) of the present invention is controlled at 2.0-3.5 mg / L.

[0028] In order to increase the diversity of microorganisms in the treatment system and improve the denitrification efficiency, preferably, MBBR suspended fillers are placed inside the biological selection tank treatment in step (4), the anoxic tank in step (5), and the aerobic tank in step (6) of the present invention, and the filling volume is 20-40%. The MBBR suspended filler adopts a composite filler form, and the shell of the composite filler is a hollow ball made of PP material, and the interior of the hollow ball is filled with polyurethane particles, and the polyurethane filling volume is 80-90% of the internal volume of the hollow ball.

[0029] The water outlet of the regulating tank of the present invention is provided with a bypass pipeline to the water inlet of the anaerobic tank; the water outlet of the aerobic tank is provided with a nitrification liquid return pipeline to the water inlet of the anoxic tank; the bottom of the sedimentation tank is provided with a sludge return pipeline to the water inlet of the biological selection tank, and the bottom of the sedimentation tank is provided with sludge return to replenish the sludge carried away by the front-end water flow.

[0030] The wastewater treatment process of the present invention needs to be started up before entering the conventional operation stage, and the specific steps are: in the step (1), in the step (1), when the COD / TN mass concentration ratio of the wastewater entering the regulating tank is greater than 5, no nitrogen source is added; if the COD / TN mass concentration ratio is ≤5, a carbon source is added until the COD / TN mass concentration ratio is greater than 5; when the water discharged from step (7) is less than 50 mg / L, the ammonia nitrogen mass concentration is less than 5 mg / L, and the surface of the MBBR suspended filler is covered with a microbial film, it can be determined that the biofilm start-up is completed, and the carbon source includes glucose, sodium acetate, etc.; after the biofilm start-up is completed, no additional carbon source needs to be added in the conventional operation stage.

[0031] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0032] 1. The process of the present invention is used to treat wastewater, especially wastewater generated in highway service areas, without the need for additional reagents to be added and repeated replacement of biofilm fillers, which greatly reduces the cost of reagent transportation, management and use.

[0033] 2. The red mud-based molecular sieve fixed bed used in the process of the present invention uses cheap and easily available raw materials, has a simple preparation process, and realizes the resource utilization of solid waste. The prepared red mud-based molecular sieve fixed bed, due to its huge specific surface area, physically adsorbs the ammonia nitrogen in the influent, while the microorganisms attached and growing on the surface biologically desorb the ammonia nitrogen fixed on the surface of the red mud-based molecular sieve. Different types of microorganisms can also perform anaerobic digestion to remove some organic matter, further improving the impact resistance of subsequent process flows.

[0034] 3. The process of the present invention shortens the sludge acclimation time and system startup time, can switch freely between low load and high load states, operates stably, produces less sludge, and does not require an external carbon source.

[0035] 4. The present invention provides a wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR, which can achieve good treatment effects in both extreme operating modes of holiday water volume and water quality shock load and low load during non-holiday periods, especially in highway service areas. In addition, this method does not require an external carbon source, has high denitrification efficiency, low operating costs, and meets emission standards.

[0036] In summary, the wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR provided by the present invention has good treatment effect, high denitrification efficiency, no need for additional carbon source addition, strong resistance to shock load, and low operating costs when treating wastewater from highway service areas, especially when treating wastewater from highway service areas. It has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0038] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0039] Example 1: Startup phase

[0040] A wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR requires biofilm startup before entering the regular operation phase, including the following steps:

[0041] (1) Regulating tank: collect wastewater and put it into the regulating tank to regulate the water quality and quantity fluctuations to be stable (the regulating tank is set up to deal with the surge in water volume / sudden change in water quality, so that the back-end water flow and water quality are relatively stable) and then discharge the water. The pH value of the wastewater is 6.5-7.5, the COD concentration is 200-500 mg / L, the ammonia nitrogen concentration is 50-150 mg / L, the total nitrogen concentration is 50-150 mg / L, and the total phosphorus concentration is 3-10 mg / L. When the COD / TN mass concentration ratio is detected to be ≤5, external carbon source glucose is artificially added to adjust the COD / TN concentration ratio to >5 to maintain the optimal growth state of microorganisms;

[0042] (2) Red mud-based molecular sieve fixed bed treatment: The effluent from step (1) is passed from bottom to top through a red mud-based molecular sieve fixed bed for physical adsorption deamination and biological deamination, and then the effluent is discharged;

[0043] (3) Anaerobic treatment: the effluent from step (2) is sent to an anaerobic digester for treatment. After the anaerobic digester, the supernatant is discharged. The anaerobic digester is a folding plate anaerobic tank. The folding plate anaerobic tank adopts a double compartment. The double compartment is an inlet compartment and an outlet compartment adjacent to each other. The volume ratio of the inlet compartment to the outlet compartment is 1:3. The temperature in the anaerobic digester is controlled at 37±2°C, the pH is 6.5, the hydraulic retention time is 12h, the sludge concentration is 4000-7000mg / L, and the volatile acid concentration is less than 5mg / L.

[0044] (4) Biological selection treatment: the supernatant effluent from step (3) is sent to the biological selection tank for treatment, and a mixed effluent is obtained after the biological selection tank; the biological selection tank is aerated and stirred intermittently, with a continuous aeration time of 4 hours and aeration and stirring stopped for 6 hours, and the operation is alternated. During the stirring period, the DO is controlled below 0.5 mg / L, and the purpose is to enrich different types of microbial communities in the biological selection tank;

[0045] (5) Anoxic treatment: the effluent from the mixed solution in step (4) is sent to an anoxic tank for denitrification treatment to obtain a denitrified mixed solution;

[0046] (6) Aerobic treatment: the denitrification mixture in step (5) is sent to an aerobic tank for nitrification treatment to obtain a nitrification mixture; the DO concentration in the aerobic tank is controlled at 2.0 mg / L;

[0047] (7) Sedimentation treatment: The nitrification mixture in step (6) is sent to the sedimentation tank for separation. After separation, the supernatant is discharged. When the COD concentration of the supernatant is less than 50 mg / L, the ammonia nitrogen concentration is less than 5 mg / L, and the surface of the MBBR suspended filler is covered with a microbial film, the biofilm formation is completed (the process lasts for 12 days).

[0048] The method for preparing the red mud-based molecular sieve fixed bed in the above step (2) comprises the following steps:

[0049] (1) Red mud and 5 mol / L HCl solution were mixed at a liquid-to-solid ratio of 3:1 mL / g and acid-leached for 1.5 h at room temperature. After acid leaching, the mixture was washed and filtered, and the filtrate was dried in an oven at 105 °C to constant weight to obtain an acid-leached red mud base.

[0050] (2) After acid-leached red mud was mixed with Ca(OH)2 and polyvinyl alcohol in a mass ratio of 1:3:0.04, 2 wt% zeolite based on acid-leached red mud and 0.4 wt% silicon carbide whiskers (particle size ≤ 50 μm) based on acid-leached red mud were added, ultrasonically dispersed and mixed uniformly, and calcined at 600 °C for 120 min to obtain alkali-soluble red mud;

[0051] (3) After the alkali-soluble red mud is cooled to room temperature, the Si / Al molar ratio is adjusted to 5:1 with Na2SiO3•9H2O, and then water is added to adjust the liquid-solid ratio to 15:1 mL / g. The hydrothermal method is used for homogenization reaction at a hydrothermal temperature of 120°C for 8 hours. The red mud-based molecular sieve obtained after the reaction is separated, washed and dried to constant weight. After drying, it is compacted into columnar particles with a diameter of 1 cm and a length of 2 cm using a mold. The columnar particles are fixed inside the container in the form of a bed filling, thus obtaining a red mud-based molecular sieve fixed bed. The volume filling rate of the columnar particles in the container is 30%. The columnar particles are red mud-based molecular sieve particle fillers. After the water is discharged from step (1) in the wastewater treatment process, water is passed from bottom to top. During the process of water flowing through the red mud-based molecular sieve fixed bed, the particle fillers are physically adsorbed, and the microbial film on the surface of the particle fillers undergoes biological deammoniation.

[0052] Suspended fillers are placed inside the biological selection tank treatment in step (4), the anoxic tank in step (5), and the aerobic tank in step (6), and the filling volume is 30%. The suspended fillers are in the form of combined fillers, and the shell of the combined fillers is a hollow ball made of PP material. The interior of the hollow ball is filled with polyurethane particles, and the polyurethane filling volume is 85% of the internal volume of the hollow ball.

[0053] During the biofilm formation start-up phase, the test results of four groups of inlet and outlet water were collected on the 3rd, 6th, 9th and 12th days, as shown in Table 1.

[0054] Table 1 Water effluent test results at each stage of Example 1

[0055]

[0056] It can be seen that after adjustment with the addition of external carbon source, the nutrients in the system are sufficient and the microorganisms are fully enriched; after the biofilm is started, the system effluent can meet the Level A standard requirements of the "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (GB18918-2002).

[0057] Example 2: Normal operation stage

[0058] A wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR, after the biofilm formation is started, includes the following steps:

[0059] (1) Regulating tank: collect wastewater and put it into the regulating tank to regulate the water quality and quantity fluctuations (the regulating tank is set up to deal with the surge in water volume / sudden change in water quality, so that the back-end water flow and water quality are relatively stable). The wastewater has a pH value of 6.5-7.5, a COD concentration of 200-500 mg / L, an ammonia nitrogen concentration of 30-100 mg / L, a total nitrogen concentration of 100-200 mg / L, and a total phosphorus concentration of 3-10 mg / L.

[0060] (2) Red mud-based molecular sieve fixed bed treatment: The effluent from step (1) is passed from bottom to top through a red mud-based molecular sieve fixed bed for physical adsorption deamination and biological deamination, and then the effluent is discharged;

[0061] (3) Anaerobic treatment: the effluent from step (2) is sent to an anaerobic digester for treatment. After the anaerobic digester, the supernatant is discharged. The anaerobic digester is a folded plate anaerobic tank. The folded plate anaerobic tank adopts a double compartment. The double compartment is an inlet compartment and an outlet compartment adjacent to each other. The volume ratio of the inlet compartment to the outlet compartment is 1:3. The temperature in the anaerobic digester is controlled at 37±2°C, the pH is 7.5, the hydraulic retention time is 48h, the sludge concentration is controlled at 4000-7000mg / L, and the volatile acid concentration is less than 5mg / L.

[0062] (4) Biological selection treatment: the supernatant effluent from step (3) is sent to the biological selection tank for treatment, and a mixed effluent is obtained after the biological selection tank; the biological selection tank is intermittently aerated and stirred, with an interval of 4 hours, and aeration and stirring are stopped for 6 hours, and the operation is alternated. During the stirring period, DO is controlled below 0.5 mg / L, and the purpose is to enrich different types of microbial communities in the biological selection tank;

[0063] (5) Anoxic treatment: the effluent from the mixed solution in step (4) is sent to an anoxic tank for denitrification treatment to obtain a denitrified mixed solution;

[0064] (6) Aerobic treatment: the denitrification mixture in step (5) is sent to an aerobic tank for nitrification treatment to obtain a nitrification mixture; the DO concentration in the aerobic tank is controlled at 3.5 mg / L;

[0065] (7) Sedimentation treatment: The nitrification mixture in step (6) was sent to the sedimentation tank for separation of mud and water. After separation, the supernatant was discharged, and the wastewater treatment was completed. Three sets of inlet and outlet water data were collected during the process. The specific test results are shown in Table 2.

[0066] The above-mentioned method for preparing the red mud-based molecular sieve fixed bed comprises the following steps:

[0067] (1) Red mud and 3 mol / L HCl solution were mixed at a liquid-to-solid ratio of 2:1 mL / g, and acid-leached at room temperature for 3 h. After acid-leaching, the mixture was washed and filtered, and the filtrate was dried at room temperature to a constant weight to obtain an acid-leached red mud base;

[0068] (2) After acid-leached red mud was mixed with NaOH and polyvinyl alcohol in a mass ratio of 1:1:0.03, 1 wt% zeolite based on acid-leached red mud and 0.3 wt% silicon carbide whiskers (particle size ≤ 50 μm) based on acid-leached red mud were added, ultrasonically dispersed and mixed uniformly, and calcined at 700 °C for 60 min to obtain alkali-soluble red mud;

[0069] (3) After the alkali-soluble red mud is cooled to room temperature, the Si / Al molar ratio is adjusted to 5:1 with Na2SiO3•9H2O, and then water is added to adjust the liquid-solid ratio to 7.5:1 mL / g. The hydrothermal method is used for homogenization reaction at a hydrothermal temperature of 80°C for 16 h. The red mud-based molecular sieve obtained after the reaction is separated, washed and dried to constant weight. After drying, it is compacted into columnar particles with a diameter of 2 cm and a length of 5 cm using a mold. The columnar particles are fixed inside the container in the form of bed filling, thus obtaining a red mud-based molecular sieve fixed bed. The volume filling rate of the columnar particles in the container is 30%. The columnar particles are red mud-based molecular sieve particle fillers. After the water is discharged from step (1) in the wastewater treatment process, water is passed from bottom to top. During the process of water flowing through the red mud-based molecular sieve fixed bed, the particle fillers undergo physical adsorption, and the microbial film on the surface of the particle fillers undergoes biological deammoniation.

[0070] MBBR suspended fillers are placed inside the above-mentioned biological selection tank treatment, the anoxic tank of step (5), and the aerobic tank of step (6), and the filling volume is 40%. The MBBR suspended fillers are in the form of composite fillers, and the shell of the composite filler is a hollow ball made of PP material. The interior of the hollow ball is filled with polyurethane particles, and the polyurethane filling volume is 90% of the internal volume of the hollow ball.

[0071] Table 2 Water outlet test results at each stage during normal operation of Example 2

[0072]

[0073] It can be seen that after the biofilm is started, during normal operation, without the need for an external carbon source, the system effluent can meet the Level A standard requirements of the "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (GB18918-2002).

[0074] Example 3: Low-load treatment effect of the present invention

[0075] A wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR comprises the following steps:

[0076] The difference from Example 2 is:

[0077] The influent of the regulating tank in step (1) is in a loaded influent state (influent 200-300 mg / L, TN 30-50 mg / L), and aeration and stirring are provided in the biological selection tank in step (4). During the influent process, aeration is performed when the C / N mass concentration ratio of the influent of the regulating tank in step (1) is detected to be ≤5, and the DO in the water is controlled at 2.0-3.5 mg / L during the aeration period; when the C / N mass concentration ratio of the influent of the regulating tank in step (1) is detected to be >5, aeration is stopped and stirring is performed, and the DO in the water is controlled to be below 0.5 mg / L;

[0078] The remaining step parameters are the same as in Example 2.

[0079] Among them, three groups of water quality data of inlet and outlet water under low-load inlet conditions were recorded, as shown in Table 3.

[0080] Table 3 Low load water inlet and outlet test results of Example 3

[0081]

[0082] It can be seen that after the biofilm is started, in the normal stable operation stage, the low load, that is, the influent COD is 200-300 mg / L, TN30-50 mg / L, and the effluent is significantly lower than the Level A standard of the "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (GB18918-2002). No additional carbon source is required during the operation, and the operation effect is good.

[0083] Example 4: High-load treatment effect of the present invention

[0084] The difference from Example 2 is:

[0085] The influent of the regulating tank in step (1) is in a high-load influent state (COD of the influent of the regulating tank is 200-300 mg / L, TN>50 mg / L), and aeration and stirring are provided in the biological selection tank in step (4). During the influent process, aeration is performed when the C / N mass concentration ratio of the influent of the regulating tank in step (1) is detected to be ≤5, and DO in the water is controlled at 2.0-3.5 mg / L during the aeration period; aeration is stopped and stirring is performed when the C / N mass concentration ratio of the influent of the regulating tank in step (1) is detected to be >5, and DO in the water is controlled at below 0.5 mg / L;

[0086] The remaining step parameters are the same as in Example 2.

[0087] Among them, three groups of water quality data of inlet and outlet water under high-load water inlet conditions were recorded, as shown in Table 4.

[0088] Table 4 Example 4 High load water inlet and outlet test results

[0089]

[0090] It can be seen that in the stable operation stage, the high load, that is, the COD is 200-300 mg / L, TN>50 mg / L, and the effluent is significantly lower than the Level A standard of the "Pollutant Discharge Standard for Urban Wastewater Treatment Plants" (GB18918-2002). No additional carbon source is required during the operation process, and it has a good anti-shock load effect.

[0091] Example 5

[0092] The difference from Example 2 is that the preparation method of the red mud-based molecular sieve fixed bed is different. The preparation method of the red mud-based molecular sieve fixed bed is specifically as follows:

[0093] (1) Red mud and 8 mol / L HCl solution were mixed at a liquid-to-solid ratio of 6:1 mL / g, mixed evenly, and acid-leached at room temperature for 3 h. After acid leaching, the mixture was washed and filtered, and the filtrate was dried at room temperature to a constant weight to obtain an acid-leached red mud base;

[0094] (2) After acid-leached red mud was mixed with Ca(OH)2 and polyvinyl alcohol in a mass ratio of 1:3:0.05, 3 wt% zeolite based on acid-leached red mud and 0.5 wt% silicon carbide whiskers (particle size ≤ 50 μm) based on acid-leached red mud were added, the mixture was uniformly dispersed by ultrasonic dispersion, and the mixture was calcined at 650 °C for 100 min to obtain alkali-soluble red mud.

[0095] (3) After the alkali-soluble red mud is cooled to room temperature, the Si / Al molar ratio is adjusted to 10:1 with Na2SiO3•9H2O, and then water is added to adjust the liquid-solid ratio to 12.5:1 mL / g. A hydrothermal method is used to carry out a homogenous reaction at a hydrothermal temperature of 120°C for 15 hours. The red mud-based molecular sieve obtained after the reaction is separated, washed and dried. After drying, it is compacted into columnar particles with a diameter of 1-2 cm and a length of 2-5 cm using a mold, thereby obtaining the red mud-based molecular sieve fixed bed with a filling rate of 30%. The columnar particles are red mud-based molecular sieve particle fillers. After the water is discharged from step (1) in the wastewater treatment process, water is passed from bottom to top. During the process of water flowing through the red mud-based molecular sieve fixed bed, the particle fillers undergo physical adsorption, and the microbial film on the surface of the particle fillers undergoes biological deammoniation.

[0096] The remaining steps and parameters are the same as in Example 2.

[0097] Example 6

[0098] The difference from Example 5 is:

[0099] The influent of the regulating tank in step (1) is in a loaded influent state (influent 200-300 mg / L, TN 30-50 mg / L). In step (4), aeration and stirring are provided in the biological selection tank. During the influent process, aeration is performed when the C / N mass concentration ratio of the influent of the regulating tank in step (1) is detected to be ≤5, and the DO in the water is controlled at 2.0-3.5 mg / L during the aeration period. When the C / N mass concentration ratio of the influent of the regulating tank in step (1) is detected to be >5, aeration is stopped and stirring is performed, and the DO in the water is controlled at below 0.5 mg / L. The parameters of the remaining steps are the same as those in Example 5. The test results of the influent and effluent under low load are shown in Table 5.

[0100] Table 5 Low load water inlet and outlet test results of Example 6

[0101]

[0102] Example 7

[0103] The difference from Example 5 is:

[0104] In step (1), the regulating tank inlet water is in a high-load inlet state (COD of the regulating tank inlet water is 200-300 mg / L, TN>50 mg / L), and in step (4), aeration and stirring are provided in the biological selection tank. During the water inlet process, aeration is performed when the C / N mass concentration ratio of the regulating tank inlet water in step (1) is detected to be ≤5, and the DO in the water is controlled at 2.0-3.5 mg / L during the aeration period; when the C / N mass concentration ratio of the regulating tank inlet water in step (1) is detected to be >5, aeration is stopped and stirring is performed, and the DO in the water is controlled at below 0.5 mg / L. The parameters of the remaining steps are the same as those in Example 5. The test results of the inlet and outlet water under high load are shown in Table 6.

[0105] Table 6 Results of low / high load water inlet and outlet tests of Example 7

[0106]

[0107] It can be seen from the effluent data in Tables 5 and 6 that when the preparation parameters of the red mud-based molecular sieve are changed within the scope of this claim, the effluents at low and high loads both meet the effluent standards.

[0108] Comparative Example 1

[0109] The difference from Example 2 is that: the red mud molecular sieve fixed bed treatment in step (2) is not performed during the biofilm formation startup and conventional operation stages, wherein the conventional stage step (3) is a biological selection treatment: the supernatant effluent in step (3) is sent to the biological selection tank for treatment, and a mixed liquid effluent is obtained after the biological selection tank; the two states of the biological selection tank at low load and high load water inflow are monitored:

[0110] When the water is fed into the regulating tank in step (1), the water is fed into the regulating tank in a loaded state (water feed 200-300 mg / L, TN 30-50 mg / L). In step (4), aeration and stirring are provided in the biological selection tank. During the water feeding process, aeration is performed when the C / N mass concentration ratio of the water fed into the regulating tank in step (1) is detected to be ≤5, and the DO in the water is controlled at 2.0-3.5 mg / L during the aeration period. When the C / N mass concentration ratio of the water fed into the regulating tank in step (1) is detected to be >5, aeration is stopped and stirring is performed, and the DO in the water is controlled at below 0.5 mg / L. The remaining steps and parameters are the same as those in Example 2.

[0111] When the water is influent at a high load: the water in the regulating tank in step (1) is in a high load water inflow state (the COD of the water in the regulating tank is 200-300 mg / L, and TN is greater than 50 mg / L), and aeration and stirring are provided in the biological selection tank in step (4). During the water inflow process, aeration is performed when the C / N mass concentration ratio of the water in the regulating tank in step (1) is detected to be ≤5, and the DO in the water is controlled at 2.0-3.5 mg / L during the aeration period; when the C / N mass concentration ratio of the water in the regulating tank in step (1) is detected to be greater than 5, aeration is stopped and stirring is performed, and the DO in the water is controlled to be below 0.5 mg / L; the remaining steps and parameters are the same as those in Example 2.

[0112] The test results of water inlet and outlet under different operating loads of Comparative Example 1 are shown in Table 7.

[0113] Table 7 Comparative Example 1 low / high load water inlet and outlet test results

[0114]

[0115] As can be seen from the effluent data in the table above, in Comparative Example 1, without a red mud-based molecular sieve bed, the effluent failed to meet the effluent standards at both low and high loads. This is because the red mud-based molecular sieve in the fixed bed of the present invention has a large specific surface area and rich pore structure, which can adsorb some organic matter and ammonia nitrogen, improving the system's resistance to shock loads and ensuring that the effluent meets the standards.

[0116] Comparative Example 2

[0117] The difference from Example 2 is that: no MBBR suspended filler is added in the biofilm startup and normal operation stages (4), (5), and (6), that is, pure activated sludge is used). In the normal stage, step (3) is biological selection treatment: the supernatant effluent in step (3) is sent to the biological selection tank for treatment, and a mixed liquid effluent is obtained after the biological selection tank; the two states of the biological selection tank at low load and high load water inflow are monitored:

[0118] When the water is fed into the regulating tank in step (1), the water is fed into the regulating tank in a loaded state (water feed 200-300 mg / L, TN 30-50 mg / L). In step (4), aeration and stirring are provided in the biological selection tank. During the water feeding process, aeration is performed when the C / N mass concentration ratio of the water fed into the regulating tank in step (1) is detected to be ≤5, and the DO in the water is controlled at 2.0-3.5 mg / L during the aeration period. When the C / N mass concentration ratio of the water fed into the regulating tank in step (1) is detected to be >5, aeration is stopped and stirring is performed, and the DO in the water is controlled at below 0.5 mg / L. The remaining steps and parameters are the same as those in Example 2.

[0119] When the water is influent at a high load: the water in the regulating tank in step (1) is in a high load water inflow state (the COD of the water in the regulating tank is 200-300 mg / L, and TN is greater than 50 mg / L), and aeration and stirring are provided in the biological selection tank in step (4). During the water inflow process, aeration is performed when the C / N mass concentration ratio of the water in the regulating tank in step (1) is detected to be ≤5, and the DO in the water is controlled at 2.0-3.5 mg / L during the aeration period; when the C / N mass concentration ratio of the water in the regulating tank in step (1) is detected to be greater than 5, aeration is stopped and stirring is performed, and the DO in the water is controlled to be below 0.5 mg / L; the remaining steps and parameters are the same as those in Example 2.

[0120] The test results of water inlet and outlet under different operating loads of Comparative Example 1 are shown in Table 8.

[0121] Table 8 Comparative Example 2 low / high load water inlet and outlet test results

[0122]

[0123] As shown in the effluent data above, in Comparative Example 2, without suspended fillers, the effluent at both low and high loads only met the Class B requirements of the Pollutant Discharge Standard for Municipal Wastewater Treatment Plants (GB18918-2002). The microorganisms carried on the surface of the suspended fillers not only increased the species richness within the system but also enhanced its organic matter removal and denitrification capabilities.

[0124] The compressive strength and thermal shock stability of the columnar particles obtained in the preparation method of the red mud-based molecular sieve fixed bed were tested. The thermal shock stability test conditions were: alternate heating to 600°C and then water cooling until visible cracks appeared, which was the failure criterion. The test groups were set up as follows:

[0125] (1) Example 1: Columnar particles prepared by the method for preparing a red mud-based molecular sieve fixed bed in Example 1.

[0126] (2) Comparative Example 3: The preparation method of the columnar particles is as follows:

[0127] 1) Red mud and 5 mol / L HCl solution were mixed at a liquid-to-solid ratio of 3:1 mL / g, and acid-leached at room temperature for 1.5 h. After acid leaching, the mixture was washed and filtered, and the filtrate was oven-dried at 105°C to constant weight to obtain an acid-leached red mud base;

[0128] 2) Acid-leached red mud and Ca(OH)2 were mixed in a mass ratio of 1:3 and calcined at 600°C for 120 min to obtain alkali-soluble red mud;

[0129] 3) After the alkali-soluble red mud is cooled to room temperature, the Si / Al molar ratio is adjusted to 5:1 with Na2SiO3•9H2O, and then water is added to adjust the liquid-solid ratio to 15:1 mL / g. The homogenization reaction is carried out by hydrothermal method at a hydrothermal temperature of 120°C for 8 h. The red mud-based molecular sieve obtained after the reaction is separated, washed and dried to constant weight. After drying, it is compacted into columnar particles with a diameter of 1 cm and a length of 2 cm using a mold.

[0130] (3) Comparative Example 4: The difference from Example 1 is that the comparative example 4 does not contain silicon carbide whiskers.

[0131] (4) Comparative Example 5: The difference from Example 1 is that it does not contain zeolite.

[0132] The test results are shown in Table 9.

[0133] Table 9 Performance of columnar particles in different groups

[0134]

[0135] As can be seen from Table 9, the method of the present invention can improve the crack resistance and thermal shock stability of the columnar particle filler used in the red mud-based molecular sieve fixed bed, extend the service life of the red mud-based molecular sieve fixed bed, and reduce the replacement frequency.

[0136] The above description is a detailed description of the preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR, characterized in that: The normal operation phase includes the following steps: (1) Regulating tank: collect wastewater and put it into regulating tank to adjust the water quality and quantity fluctuations and then discharge the water; (2) Red mud-based molecular sieve fixed bed treatment: the effluent from step (1) is passed from bottom to top through the red mud-based molecular sieve fixed bed and then discharged; (3) Anaerobic treatment: the effluent from step (2) is sent to an anaerobic digester for treatment, and the supernatant is discharged after the anaerobic digester; (4) Biological selection treatment: the supernatant effluent from step (3) is sent to the biological selection tank for treatment, and a mixed liquid effluent is obtained after the biological selection tank; (5) Anoxic treatment: the effluent from the mixed solution in step (4) is sent to an anoxic tank for denitrification treatment to obtain a denitrified mixed solution; (6) Aerobic treatment: sending the denitrification mixed solution in step (5) into an aerobic tank for nitrification treatment to obtain a nitrification mixed solution; (7) Sedimentation treatment: The nitrification mixture in step (6) is sent to the sedimentation tank for separation of mud and water. After separation, the supernatant is discharged, and the wastewater treatment is completed.

2. The wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR according to claim 1, characterized in that: In step (1), the wastewater entering the regulating tank has a COD concentration of 200-500 mg / L, an ammonia nitrogen concentration of 30-100 mg / L, a total nitrogen concentration of 50-150 mg / L, a total phosphorus concentration of 3-10 mg / L, and a pH value of 6-8.

3. The wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR according to claim 1, characterized in that: The method for preparing the red mud-based molecular sieve fixed bed in step (2) comprises the following steps: (1) Red mud and HCl solution with a concentration of 3-8 mol / L were mixed at a liquid-to-solid ratio of 2-6:1 mL / g, and acid-leached at room temperature for 1-3 h. After acid-leaching, the mixture was washed and filtered, and the filtrate was dried to a constant weight to obtain an acid-leached red mud base; (2) After acid-leached red mud is mixed with NaOH or Ca(OH)2 and polyvinyl alcohol in a mass ratio of 1:1-3:0.03-0.05, 1-3 wt% zeolite based on acid-leached red mud and 0.3-0.5 wt% silicon carbide whiskers based on acid-leached red mud are added, the mixture is evenly mixed, and the mixture is calcined at 600-700 °C for 60-150 min to obtain alkali-soluble red mud; (3) After the alkali-soluble red mud is cooled to room temperature, the Si / Al molar ratio is adjusted to 5-15:1 with Na2SiO3•9H2O, and then water is added to adjust the liquid-solid ratio to 7.5-15:1 mL / g. The homogenization reaction is carried out by hydrothermal method at a hydrothermal temperature of 80-160°C for 8-16 hours. The red mud-based molecular sieve obtained after the reaction is separated, washed and dried. After drying, it is compacted into columnar particles with a diameter of 1-2 cm and a length of 2-5 cm using a mold. The columnar particles are fixed inside the container in the form of bed filling to obtain a fixed bed of red mud-based molecular sieve.

4. The wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR according to claim 1, characterized in that: The anaerobic digester in step (3) is a folded plate anaerobic tank, which adopts a double compartment. The double compartment is an inlet compartment and an outlet compartment adjacent to each other, and the volume ratio of the inlet compartment to the outlet compartment is 1:3-5.

5. The wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR according to claim 1, characterized in that: The temperature in the anaerobic digester of step (3) is controlled to be 37±2°C, the pH value is 6.5-7.5, the hydraulic retention time is 12-48h, the sludge concentration is 4000-7000mg / L, and the volatile acid concentration is less than 5mg / L.

6. The wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR according to claim 1, characterized in that: In the step (4), aeration and stirring are provided in the biological selection tank. When the C / N mass concentration ratio of the influent of the regulating tank in step (1) is less than or equal to 5, aeration is performed, and the DO in the water is controlled at 2.0-3.5 mg / L during aeration. When the C / N mass concentration ratio of the effluent supernatant is greater than 5, aeration is stopped and stirring is performed, and the DO in the water is controlled at less than 0.5 mg / L.

7. The wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR according to claim 1, characterized in that: In step (5), the anoxic tank is stirred and the DO in the water is controlled below 0.5 mg / L.

8. The wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR according to claim 1, characterized in that: The DO concentration in the aerobic pool water in step (6) is controlled at 2.0-3.5 mg / L.

9. The wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR according to claim 1, characterized in that: MBBR suspended fillers are placed inside the biological selection tank treatment in step (4), the anoxic tank in step (5), and the aerobic tank in step (6), and the filling volume is 20-40%. The MBBR suspended fillers are in the form of combined fillers, and the shell of the combined fillers is a hollow ball made of PP material, and the interior of the hollow ball is filled with polyurethane particles, and the polyurethane filling volume is 80-90% of the internal volume of the hollow ball.

10. The wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR according to any one of claims 1 to 9, characterized in that: Before entering the normal operation stage, biofilm startup is required. The specific steps are as follows: in step (1), when the COD / TN mass concentration ratio of the wastewater entering the regulating tank is greater than 5, no nitrogen source is added. If the COD / TN mass concentration ratio is ≤5, a carbon source is added until the COD / TN mass concentration ratio is greater than 5; when the effluent in step (7) is effluent, the COD mass concentration is less than 50 mg / L, the ammonia nitrogen mass concentration is less than 5 mg / L, and the surface of the MBBR suspended filler is covered with a microbial film, it can be determined that biofilm startup is completed.

Images