A wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with an MBBR

Abstract

This invention belongs to the field of wastewater treatment technology, specifically involving a wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR, comprising: (1) collecting wastewater, placing it in an equalization tank, adjusting the water quality and quantity fluctuations, and then effluent; (2) subjecting the effluent from step (1) to physical adsorption and biological ammonia removal, and then effluent; (3) sending the effluent from step (2) to an anaerobic digestion tank for treatment, and effluent from the supernatant; (4) sending the supernatant effluent from step (3) to a biological selection tank for treatment, and obtaining mixed liquor effluent; (5) sending the mixed liquor effluent from step (4) to an anoxic tank for denitrification treatment, and obtaining denitrified mixed liquor; (6) sending the denitrified mixed liquor from step (5) to an aerobic tank, and obtaining nitrified mixed liquor; (7) sending the nitrified mixed liquor from step (6) to a sedimentation tank, separating and then effluent from the supernatant, thus completing the wastewater treatment. The process of this invention does not require an external carbon source, has high denitrification efficiency, low operating costs, and meets emission standards.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with MBBR. Background Technology

[0002] By the end of 2023, there were over 6,000 highway service areas nationwide. These service areas play a vital role in ensuring daily travel and transportation safety; however, the wastewater generated by them cannot be ignored. Highway service area wastewater mainly consists of urine, toilet flushing water, feces, and some catering wastewater. Compared to general urban domestic sewage, it is characterized by large fluctuations in water volume, high shock loads, high organic nitrogen concentrations, and low influent carbon-to-nitrogen ratios.

[0003] Currently, traditional processes such as SBR, AO, MBR, and biological contact oxidation are mainly used to treat wastewater from highway service areas. However, due to factors such as lack of carbon sources and high shock loads, the treatment effect is generally poor. In addition to the above-mentioned traditional processes, new processes such as short-cut nitrification-denitrification, anaerobic ammonium oxidation, and constructed wetlands have also shown excellent shock resistance in the treatment of wastewater from highway service areas. However, the application of new processes requires higher technical personnel and operation and maintenance capabilities, and there are difficulties in long-term operation.

[0004] In the prior art: Patent document CN113860633A discloses an integrated wastewater 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 uses MBR to improve nitrogen removal efficiency. However, the use of biofilm increases operating costs and has limited treatment capacity when dealing with influent with low carbon-to-nitrogen ratios. Patent document CN119080246A discloses a wastewater treatment device and method for highway service areas based on the AOA-MBBR process. This method performs complete nitrification and denitrification treatment on wastewater from highway service areas, with a relatively long hydraulic retention time, and the shock load can still be further improved.

[0005] In summary, there is an urgent need to explore a wastewater treatment process for highway service areas that has good treatment effect, high nitrogen removal efficiency, strong resistance to shock loads, low operating costs, and meets the Class A standard requirements of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002). Summary of the Invention

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

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

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

[0009] (1) Equalization tank: Collect wastewater, put it into the equalization tank, and discharge the water after the fluctuation of water quality and quantity is stabilized;

[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. After passing through the anaerobic digester, the supernatant is discharged.

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

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

[0014] (6) Aerobic treatment: The denitrification mixture in step (5) is sent to an aerobic tank for nitrification treatment to obtain a nitrification mixture;

[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, thus completing the wastewater treatment.

[0016] For stable operation of the process, preferably, in step (1) of the present invention, the wastewater entering the equalization 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 ensure that the red mud-based molecular sieve has a good deammoniation effect, and at the same time 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 includes the following steps:

[0018] (1) Mix red mud and HCl solution with a concentration of 3-8 mol / L at a liquid-solid ratio of 2-6:1 mL / g, and acid leach for 1-3 h at room temperature. After acid leaching, wash and filter, and dry the filter to constant weight to obtain acid-leached red mud base.

[0019] (2) After mixing acid-leached red mud with NaOH or Ca(OH)2 and polyvinyl alcohol in a mass ratio of 1:1-3:0.03-0.05, add 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, mix evenly, and calcine at 600-700℃ for 60-150 min to obtain alkali-soluble red mud;

[0020] (3) After the red mud is alkali-dissolved and cooled to room temperature, the Si / Al molar ratio is adjusted to 5-15:1 with Na2SiO3•9H2O. 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 temperature of 80-160℃ for 8-16h. The red mud-based molecular sieve obtained after the reaction is completed is separated, washed and dried. After drying, it is compacted into columnar particles with a diameter of 1-2cm and a length of 2-5cm using a mold. The columnar particles are fixed inside the container by filling the bed to obtain the red mud-based molecular sieve fixed bed. The columnar particles are red mud-based molecular sieve particle packing. In the wastewater treatment process, after the effluent is discharged in step (1), water is passed from bottom to top. During the process of water flowing through the red mud-based molecular sieve fixed bed, the particle packing undergoes physical adsorption, and the microbial film on the surface of the particle packing undergoes biological deammoniation.

[0021] In the preparation of columnar particles, silicon carbide whiskers, acting as high-strength fibrous fillers, are uniformly dispersed in the acid leaching system during calcination. During calcination, they form a three-dimensional network structure with zeolite and red mud, effectively inhibiting cracking or fragmentation of the acid-leached red mud matrix due to shrinkage stress during calcination. This reduces microcrack initiation by bridging particle gaps, improving yield, and ensuring the structural integrity of the acid-leached red mud matrix during high-temperature calcination, preventing material collapse and deformation. Furthermore, the porous nature of zeolite guides the directional growth of molecular sieve crystals, increasing the specific surface area and pore connectivity of the columnar particles, which is beneficial for improving adsorption performance. Stone provides hard support points, forming a "rigid-flexible" composite reinforcement system together with silicon carbide whiskers. The silicon carbide whiskers absorb dynamic impact energy. Meanwhile, polyvinyl alcohol decomposes during calcination, releasing gases (mainly CO2 and H2O), leaving interconnected channels in situ. This significantly increases the specific surface area and porosity of the red mud-based molecular sieve particle packing, facilitating wastewater flow and contact with active sites, and promoting microbial attachment and biofilm formation. Simultaneously, the hydroxyl groups on its molecular chains can form hydrogen bonds with inorganic components, reducing the surface tension of the silicon carbide whiskers, enhancing the organic-inorganic interface bonding strength, and reducing the risk of interlayer delamination. In this method of preparing columnar particles, their thermal shock resistance, wear resistance, crack resistance, and lifespan are all effectively improved.

[0022] The red mud-based molecular sieve fixed bed described in this invention utilizes red mud (a waste generated during aluminum processing) as a raw material, resulting in low cost.

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

[0024] To ensure good anaerobic digestion, preferably, the temperature in the anaerobic digester of step (3) of this invention is controlled at 37±2℃, 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] To flexibly respond to shock loads and ensure stable system operation, preferably, the biological selection tank in step (4) of this invention is equipped with aeration and stirring. When the C / N mass concentration ratio of the influent to the regulating tank in step (1) is ≤5, aeration is carried out, and the DO in the water is controlled at 2.0-3.5mg / L during aeration. When the C / N mass concentration ratio of the supernatant effluent is >5, aeration is stopped and stirring is carried out, and the DO in the water is controlled below 0.5mg / L.

[0026] To ensure good denitrification and full fluidization of the suspended carrier, preferably, the anoxic tank in step (5) of the present invention is equipped with a stirrer, the DO in the water is controlled below 0.5 mg / L, and the COD concentration is 100-200 mg / L.

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

[0028] To increase the diversity of microorganisms in the treatment system and improve the denitrification efficiency, preferably, MBBR suspended packing is placed inside the biological selection tank in step (4), the anoxic tank in step (5), and the aerobic tank in step (6) of the present invention. The filling volume is 20-40%. The MBBR suspended packing is in the form of a combined packing. The outer shell of the combined packing is a hollow sphere made of PP material. The hollow sphere is filled with polyurethane particles. The polyurethane filling volume is 80-90% of the internal volume of the hollow sphere.

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

[0030] The wastewater treatment process of the present invention requires biofilm startup before entering the normal operation stage. The specific steps are as follows: In step (1), when the COD / TN mass concentration ratio of the wastewater entering the equalization tank is >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 >5. When the effluent is discharged in step (7), the COD mass concentration is <50mg / L, the ammonia nitrogen mass concentration is <5mg / L, and the surface of the MBBR suspended packing is covered with a microbial film, it can be determined that the biofilm startup is completed. The carbon source includes glucose, sodium acetate, etc. After the biofilm startup is completed, no additional carbon source is required in the normal operation stage.

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

[0032] 1. The process of this invention can treat wastewater, especially wastewater generated in highway service areas, without the need for additional reagents or repeated replacement of biofilm packing, which greatly reduces the costs of reagent transportation, management and use.

[0033] 2. The red mud-based molecular sieve fixed bed used in the process of this invention uses inexpensive and readily available raw materials, and the preparation process is simple, realizing the resource utilization of solid waste. The prepared red mud-based molecular sieve fixed bed, due to its huge specific surface area, physically adsorbs ammonia nitrogen in the influent, while the microorganisms attached to the surface of the red mud-based molecular sieve bio-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 processes.

[0034] 3. The process of this invention has a short sludge acclimatization time and system start-up time. It can be freely switched between low load and high load conditions, operates stably, produces less sludge, and does not require an external carbon source.

[0035] 4. The wastewater treatment process based on red mud-based molecular sieve fixed bed coupled with MBBR provided by this invention has achieved good treatment results, especially in highway service areas, under two extreme operating modes: water volume and water quality shock load during holidays and low load during non-holiday periods. Moreover, 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 red mud-based molecular sieve fixed bed coupled with MBBR provided by this invention is particularly effective in treating wastewater from highway service areas. It exhibits good treatment results, high denitrification efficiency, no need for additional carbon source addition, strong resistance to shock loads, and low operating costs, and has promising application prospects. Attached Figure Description

[0037] Figure 1This is a process flow diagram of the present invention. Detailed Implementation

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1: Startup Phase

[0040] A wastewater treatment process based on a red mud-based molecular sieve fixed bed coupled with a molecular bioreactor (MBBR) requires biofilm formation start-up before entering the normal operation phase, including the following steps:

[0041] (1) Equalization tank: Collect wastewater and put it into the equalization tank to regulate the fluctuation of water quality and quantity (the existence of the equalization tank is to cope with the surge of water volume / sudden change in water quality, so that the influent flow and water quality at the back end are relatively stable) before effluent. The wastewater has a pH value of 6.5-7.5, a COD concentration of 200-500 mg / L, an ammonia nitrogen concentration of 50-150 mg / L, a total nitrogen concentration of 50-150 mg / L, and a total phosphorus concentration of 3-10 mg / L. When the COD / TN mass concentration ratio is detected to be ≤5, external carbon source glucose is added artificially to adjust the COD / TN concentration ratio to >5 in order 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 and biological deammoniation before being discharged;

[0043] (3) Anaerobic treatment: The effluent from step (2) is sent to an anaerobic digester for treatment. After passing through the anaerobic digester, the supernatant is discharged. The anaerobic digester is a folded plate anaerobic digester with double compartments. The double compartments are an inlet compartment and an outlet compartment that are 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℃, 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 the mixed liquor effluent is obtained after passing through the biological selection tank; the biological selection tank is intermittently aerated and stirred, with continuous aeration time of 4 hours and aeration and stirring stopped for 6 hours, and the operation is alternated. During the stirring period, DO is controlled below 0.5 mg / L, the purpose of which is to enrich different types of microbial communities in the biological selection tank.

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

[0046] (6) Aerobic treatment: The denitrification mixture from step (5) is sent to an aerobic tank for nitrification treatment to obtain a nitrified 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 of mud and water. After separation, the supernatant is discharged. When the COD concentration of the supernatant is <50mg / L, the ammonia nitrogen concentration is less than 5mg / L, and the surface of the MBBR suspended packing is covered with microbial film, the biofilm initiation is completed (this process lasts for 12 days).

[0048] The preparation method of the red mud-based molecular sieve fixed bed in step (2) above includes the following steps:

[0049] (1) Red mud and 5 mol / L HCl solution were combined at a liquid-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. The filtered material was dried in an oven at 105 °C to constant weight to obtain acid-leached red mud base.

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

[0051] (3) After the red mud is dissolved in alkali and cooled to room temperature, the Si / Al molar ratio is adjusted to 5:1 with Na2SiO3•9H2O. 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 120℃ for 8 hours. The red mud-based molecular sieve obtained after the reaction is completed is separated, washed and dried to constant weight. After drying, it is compacted into columnar particles with a diameter of 1cm and a length of 2cm using a mold. The columnar particles are fixed inside the container by bed filling, thus obtaining the 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 packing. In the wastewater treatment process, after the effluent is discharged in step (1), water is passed from bottom to top. During the process of water flowing through the red mud-based molecular sieve fixed bed, the particle packing undergoes physical adsorption, and the microbial film on the surface of the particle packing undergoes biological deammoniation.

[0052] Suspended packing material is placed inside the biological selection tank in step (4), the anoxic tank in step (5), and the aerobic tank in step (6) above. The filling volume is 30% of the total volume. The suspended packing material is a combined packing material. The outer shell of the combined packing material is a hollow sphere made of PP material. The hollow sphere is filled with polyurethane particles. The polyurethane filling volume is 85% of the internal volume of the hollow sphere.

[0053] During the biofilm formation start-up phase, test results of four sets of influent and effluent were collected on days 3, 6, 9, and 12, as detailed in Table 1.

[0054] Table 1. Results of effluent tests at each stage of Example 1

[0055]

[0056] It can be seen that after the addition of an external carbon source, the system has sufficient nutrients and microorganisms are fully enriched; after the biofilm formation is started, the system effluent can meet the Class A standard requirements of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002).

[0057] Example 2: Routine Operation Phase

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

[0059] (1) Equalization tank: Collect wastewater and put it into the equalization tank to regulate the fluctuation of water quality and quantity (the existence of the equalization tank is to cope with the surge of water volume / sudden change in water quality, so that the influent flow and water quality at the back end are relatively stable) before effluent. 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 and biological deammoniation before being discharged;

[0061] (3) Anaerobic treatment: The effluent from step (2) is sent to an anaerobic digester for treatment. After passing through the anaerobic digester, the supernatant is discharged. The anaerobic digester is a folded plate anaerobic digester with double compartments. The double compartments are an inlet compartment and an outlet compartment that are 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℃, 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 the mixed liquor effluent is obtained after passing through the biological selection tank; the biological selection tank is intermittently aerated and stirred, with a time interval of 4 hours and a stop aeration and stirring for 6 hours, and the operation is alternated. During the stirring period, DO is controlled below 0.5 mg / L, the purpose of which is to enrich different types of microbial communities in the biological selection tank.

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

[0064] (6) Aerobic treatment: The denitrification mixture from step (5) is sent to an aerobic tank for nitrification treatment to obtain a nitrified 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) is sent to the sedimentation tank for separation of mud and water. After separation, the supernatant is discharged, thus completing the wastewater treatment. Three sets of influent and effluent data were collected during the process. The specific test results are shown in Table 2.

[0066] The preparation method of the aforementioned red mud-based molecular sieve fixed bed includes the following steps:

[0067] (1) Mix red mud and HCl solution with a concentration of 3 mol / L at a liquid-solid ratio of 2:1 mL / g, and acid leaching at room temperature for 3 h. After acid leaching, wash and filter, and dry the filter at room temperature to constant weight to obtain acid-leached red mud base.

[0068] (2) After mixing acid-leached red mud 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 ≤50μm) based on acid-leached red mud are added, ultrasonically dispersed and mixed evenly, and calcined at 700℃ for 60 min to obtain alkali-soluble red mud.

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

[0070] MBBR suspended packing material was placed inside the biological selection tank, the anoxic tank in step (5), and the aerobic tank in step (6) mentioned above. The filling volume was 40%. The MBBR suspended packing material was a combined packing material. The outer shell of the combined packing material was a hollow sphere made of PP material. The hollow sphere was filled with polyurethane particles. The polyurethane filling volume was 90% of the internal volume of the hollow sphere.

[0071] Table 2. Water effluent test results at each stage of normal operation in Example 2

[0072]

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

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

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

[0076] The difference from Example 2 is as follows:

[0077] In step (1), the water entering the equalization tank is under load (influent 200-300 mg / L, TN 30-50 mg / L). In step (4), the biological selection tank is equipped with aeration and stirring. During the water intake process, when the C / N mass concentration ratio of the water entering the equalization tank in step (1) is detected to be ≤5, aeration is carried out, 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 water entering the equalization tank in step (1) is detected to be >5, aeration is stopped and stirring is carried out, and the DO in the water is controlled below 0.5 mg / L.

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

[0079] Among them, three sets of water quality data for influent and effluent under low load conditions were recorded, as detailed in Table 3.

[0080] Table 3 Results of Low-Load Inlet and Outlet Water Tests in Example 3

[0081]

[0082] It can be seen that after the biofilm is started, during the stable operation phase, at low loads, i.e., when the influent COD is 200-300 mg / L and TN is 30-50 mg / L, the effluent is significantly lower than the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002). No additional carbon source needs to be added during operation, and it has good operating performance.

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

[0084] The difference from Example 2 is as follows:

[0085] In step (1), the water entering the equalization tank is in a high-load water entering state (the COD of the water entering the equalization tank is 200-300 mg / L, and TN is >50 mg / L). In step (4), the biological selection tank is equipped with aeration and stirring. During the water entering process, when the C / N mass concentration ratio of the water entering the equalization tank in step (1) is detected to be ≤5, aeration is carried out. During the aeration period, the DO in the water is controlled at 2.0-3.5 mg / L. When the C / N mass concentration ratio of the water entering the equalization tank in step (1) is detected to be >5, aeration is stopped and stirring is carried out. The DO in the water is controlled below 0.5 mg / L.

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

[0087] Among them, three sets of water quality data for influent and effluent under high-load influent conditions were recorded, as detailed in Table 4.

[0088] Table 4 Results of High-Load Inlet and Outlet Water Test in Example 4

[0089]

[0090] Therefore, it can be seen that during the stable operation phase, the high load means that the COD is 200-300 mg / L and the TN is >50 mg / L. The effluent is significantly lower than the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002). No additional carbon source needs to be added during the operation, and it has a good resistance to shock loads.

[0091] Example 5

[0092] The difference from Example 2 lies in the preparation method of the red mud-based molecular sieve fixed bed. Specifically, the preparation method of the red mud-based molecular sieve fixed bed is as follows:

[0093] (1) Mix red mud and HCl solution with a concentration of 8 mol / L at a liquid-solid ratio of 6:1 mL / g. Mix evenly and acid leaching at room temperature for 3 h. After acid leaching, wash and filter. Dry the filter material at room temperature to constant weight to obtain acid-leached red mud base.

[0094] (2) After mixing acid-leached red mud with Ca(OH)2 and polyvinyl alcohol in a mass ratio of 1:3:0.05, 3wt% zeolite based on acid-leached red mud and 0.5wt% silicon carbide whiskers (particle size ≤50μm) based on acid-leached red mud are added, ultrasonically dispersed and mixed evenly, and calcined at 650℃ for 100min to obtain alkali-soluble red mud;

[0095] (3) After the red mud is dissolved in alkali and cooled to room temperature, the Si / Al molar ratio is adjusted to 10:1 with Na2SiO3•9H2O. Then, water is added to adjust the liquid-solid ratio to 12.5:1 mL / g. The homogenization reaction is carried out by hydrothermal method at 120℃ for 15 hours. The red mud-based molecular sieve obtained after the reaction is completed 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 red mud-based molecular sieve fixed bed is obtained with a filling rate of 30%. The columnar particles are red mud-based molecular sieve particle packing. In the wastewater treatment process, after the effluent is discharged in step (1), water is passed from bottom to top. During the process of water flowing through the red mud-based molecular sieve fixed bed, the particle packing undergoes physical adsorption, and the microbial film on the surface of the particle packing 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 as follows:

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

[0100] Table 5 Results of Low-Load Inlet and Outlet Water Tests in Example 6

[0101]

[0102] Example 7

[0103] The difference from Example 5 is as follows:

[0104] In step (1), the influent to the equalization tank is in a high-load influent state (COD of the influent to the equalization tank is 200-300 mg / L, TN > 50 mg / L). In step (4), the biological selection tank is equipped with aeration and stirring. During the influent process, when the C / N mass concentration ratio of the influent to the equalization tank in step (1) is detected to be ≤ 5, aeration is carried out, 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 influent to the equalization tank in step (1) is detected to be > 5, aeration is stopped and stirring is carried out, and the DO in the water is controlled below 0.5 mg / L; the parameters of the remaining steps are the same as in Example 5. The test results of the influent and effluent under high load are shown in Table 6.

[0105] Table 6 Results of Low / High Load Inlet / Outlet Water Tests in Example 7

[0106]

[0107] As can be seen from the effluent data in Tables 5 and 6, under the condition of changing the preparation parameters of red mud-based molecular sieves within the scope of this claim, the effluent under both low and high loads meets 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 present in either the biofilm start-up or normal operation stages. In the normal stage, step (3) is biological selection treatment: the supernatant effluent from step (3) is sent to the biological selection tank for treatment, and the mixed liquor effluent is obtained after passing through the biological selection tank; the two states of the biological selection tank under low load and high load influent are monitored:

[0110] When the water is fed at low load: the water fed into the equalization tank in step (1) is in the load water feeding state (water 200-300mg / L, TN 30-50mg / L). The biological selection tank in step (4) is equipped with aeration and stirring. During the water feeding process, when the C / N mass concentration ratio of the water fed into the equalization tank in step (1) is detected to be ≤5, aeration is carried out. During the aeration period, the DO in the water is controlled at 2.0-3.5mg / L. When the C / N mass concentration ratio of the water fed into the equalization tank in step (1) is detected to be >5, aeration is stopped and stirring is carried out. The DO in the water is controlled below 0.5mg / L. The remaining steps and parameters are the same as in Example 2.

[0111] When the water is fed under high load: the water fed into the equalization tank in step (1) is in a high load state (the COD of the water fed into the equalization tank is 200-300 mg / L, and TN is >50 mg / L). In step (4), the biological selection tank is equipped with aeration and stirring. During the water feeding process, when the C / N mass concentration ratio of the water fed into the equalization tank in step (1) is ≤5, aeration is carried out. During the aeration period, the DO in the water is controlled at 2.0-3.5 mg / L. When the C / N mass concentration ratio of the water fed into the equalization tank in step (1) is >5, aeration is stopped and stirring is carried out. The DO in the water is controlled below 0.5 mg / L. The remaining steps and parameters are the same as in Example 2.

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

[0113] Table 7 Comparative Example 1: Low / High Load Inlet and Outlet Water 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 under both low and high loads. This is because the red mud-based molecular sieve in the fixed bed of the red mud molecular sieve in this invention has a large specific surface area and abundant 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 MBBR suspended packing is not added in steps (4), (5), and (6) of the biofilm initiation and normal operation stages (i.e., pure activated sludge is used). In the normal stage step (3), biological selection treatment is carried out by sending the supernatant effluent from step (3) into the biological selection tank for treatment. After passing through the biological selection tank, mixed liquor effluent is obtained. The two states of the biological selection tank under low load and high load influent are monitored.

[0118] When the water is fed at low load: the water fed into the equalization tank in step (1) is in the load water feeding state (water 200-300mg / L, TN 30-50mg / L). The biological selection tank in step (4) is equipped with aeration and stirring. During the water feeding process, when the C / N mass concentration ratio of the water fed into the equalization tank in step (1) is detected to be ≤5, aeration is carried out. During the aeration period, the DO in the water is controlled at 2.0-3.5mg / L. When the C / N mass concentration ratio of the water fed into the equalization tank in step (1) is detected to be >5, aeration is stopped and stirring is carried out. The DO in the water is controlled below 0.5mg / L. The remaining steps and parameters are the same as in Example 2.

[0119] When the water is fed under high load: the water fed into the equalization tank in step (1) is in a high load state (the COD of the water fed into the equalization tank is 200-300 mg / L, and TN is >50 mg / L). In step (4), the biological selection tank is equipped with aeration and stirring. During the water feeding process, when the C / N mass concentration ratio of the water fed into the equalization tank in step (1) is ≤5, aeration is carried out. During the aeration period, the DO in the water is controlled at 2.0-3.5 mg / L. When the C / N mass concentration ratio of the water fed into the equalization tank in step (1) is >5, aeration is stopped and stirring is carried out. The DO in the water is controlled below 0.5 mg / L. The remaining steps and parameters are the same as in Example 2.

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

[0121] Table 8 Comparative Example 2: Low / High Load Inlet and Outlet Water Test Results

[0122]

[0123] As can be seen from the effluent data in the table above, in Comparative Example 2, without suspended media, the effluent under low and high load conditions only meets the Class B standard requirements of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002). The microorganisms loaded on the surface of the suspended media enhance the species richness within the system, while simultaneously improving the system's organic matter removal and denitrification capabilities.

[0124] In the preparation method of red mud-based molecular sieve fixed beds, the columnar particles obtained were tested for compressive strength and thermal shock stability. The thermal shock stability test conditions were: alternating heating to 600℃ followed by water cooling until visible cracks appeared, which was used as the failure criterion. The test groups were set up as follows:

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

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

[0127] 1) Mix red mud and 5 mol / L HCl solution at a liquid-solid ratio of 3:1 mL / g, and acid leach for 1.5 h at room temperature. After acid leaching, wash and filter, and dry the filter material in an oven at 105 ℃ to constant weight to obtain acid-leached red mud base.

[0128] 2) After mixing acid-leached red mud and Ca(OH)2 at a mass ratio of 1:3, the mixture is calcined at 600℃ for 120 min to obtain alkali-soluble red mud;

[0129] 3) After the red mud dissolved in alkali is cooled to room temperature, the Si / Al molar ratio is adjusted to 5:1 with Na2SiO3•9H2O. 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 120℃ for 8 hours. The red mud-based molecular sieve obtained after the reaction is completed 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 it 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 shown in Table 9, the method of the present invention can improve the crack resistance and thermal shock stability of the columnar particle packing used in red mud-based molecular sieve fixed beds, extend the service life of red mud-based molecular sieve fixed beds, and reduce the replacement frequency.

[0136] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of 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 an MBBR, characterized in that, The routine operation phase includes the following steps: (1) Equalization tank: Collect wastewater, put it into the equalization tank, and discharge the water after the fluctuation of water quality and quantity is stabilized; (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. After passing through the anaerobic digester, the supernatant is discharged. (4) Biological selection treatment: The supernatant effluent from step (3) is sent to the biological selection tank for treatment, and the mixed liquor effluent is obtained after the biological selection tank; (5) Anoxic treatment: The effluent from the mixed liquor in step (4) is sent to the anoxic tank for denitrification treatment to obtain a denitrified mixed liquor; (6) Aerobic treatment: The denitrification mixture in step (5) is sent to an aerobic tank for nitrification treatment to obtain a nitrification mixture; (7) Sedimentation treatment: The nitrification mixture in step (6) is sent to a sedimentation tank for mud-water separation. After separation, the supernatant is discharged, thus completing the wastewater treatment. The preparation method of the red mud-based molecular sieve fixed bed in step (2) includes the following steps: 1) Mix red mud with HCl solution with a concentration of 3-8 mol / L at a liquid-solid ratio of 2-6:1 mL / g, and acid leach for 1-3 hours at room temperature. After acid leaching, wash and filter, and dry the filter material to constant weight to obtain acid-leached red mud base. 2) After mixing acid-leached red mud base with NaOH or Ca(OH)2 and polyvinyl alcohol in a mass ratio of 1:1-3:0.03-0.05, add 1-3 wt% zeolite and 0.3-0.5 wt% silicon carbide whiskers to the acid-leached red mud base, mix evenly, and calcine at 600-700℃ for 60-150 min to obtain alkali-soluble red mud; 3) After the red mud is dissolved in alkali and cooled to room temperature, the Si / Al molar ratio is adjusted to 5-15:1 with Na2SiO3•9H2O. 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 temperature of 80-160℃ for 8-16h. The red mud-based molecular sieve obtained after the reaction is completed is separated, washed and dried. After drying, it is compacted into columnar particles with a diameter of 1-2cm and a length of 2-5cm using a mold. The columnar particles are fixed inside the container by filling the bed to obtain the red mud-based molecular sieve fixed bed. MBBR suspended packing material is placed inside the biological selection tank in step (4), the anoxic tank in step (5), and the aerobic tank in step (6). The filling volume is 20-40%. The MBBR suspended packing material is a combined packing material. The outer shell of the combined packing material is a hollow sphere made of PP material. The hollow sphere is filled with polyurethane particles. The polyurethane filling volume is 80-90% of the internal volume of the hollow sphere.

2. The wastewater treatment process based on red mud-based molecular sieve fixed bed coupled MBBR as described in claim 1, characterized in that: In step (1), the wastewater entering the equalization 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 red mud-based molecular sieve fixed bed coupled with MBBR as described in claim 1, characterized in that: The anaerobic digester in step (3) is a folded plate anaerobic digester. The folded plate anaerobic digester has two compartments, which are adjacent inlet compartment and outlet compartment. The volume ratio of the inlet compartment to the outlet compartment is 1:3-5.

4. The wastewater treatment process based on red mud-based molecular sieve fixed bed coupled MBBR as described in claim 1, characterized in that: The temperature in the anaerobic digester of step (3) is controlled at 37±2℃, 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.

5. The wastewater treatment process based on red mud-based molecular sieve fixed bed coupled with MBBR as described in claim 1, characterized in that: In step (4), the biological selection tank is equipped with aeration and stirring. When the C / N mass concentration ratio of the influent to the conditioning tank in step (1) is ≤5, aeration is carried out, and the DO in the water is controlled at 2.0-3.5mg / L during aeration. When the C / N mass concentration ratio of the influent to the conditioning tank in step (1) is >5, aeration is stopped and stirring is carried out, and the DO in the water is controlled below 0.5mg / L.

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

7. The wastewater treatment process based on red mud-based molecular sieve fixed bed coupled with MBBR as described in 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.

8. The wastewater treatment process based on red mud-based molecular sieve fixed bed coupled MBBR as described in any one of claims 1-7, characterized in that: Before entering the normal operation stage, biofilm startup needs to be carried out. The specific steps are as follows: In step (1), when the COD / TN mass concentration ratio of the wastewater entering the equalization tank is >5, no carbon source is added. When the COD / TN mass concentration ratio is ≤5, carbon source is added until the COD / TN mass concentration ratio is >5. When the effluent from step (7) is discharged, if the COD mass concentration is <50mg / L, the ammonia nitrogen mass concentration is <5mg / L, and the surface of the MBBR suspended packing is covered with a microbial film, it can be determined that biofilm startup has been completed.

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