Short-process diaphragm sulfur autotrophic denitrification process

Abstract

The application discloses a short-process diaphragm sulfur autotrophic denitrification process, which comprises the following steps: after pretreatment, the wastewater containing nitrate nitrogen to be treated is introduced into a reactor; sulfur powder and sodium bicarbonate are added into the reactor to generate a sulfur autotrophic denitrification reaction; a membrane assembly is vibrated to generate a shearing force for controlling membrane pollution, enhancing water body turbulence, strengthening mass transfer and improving reaction efficiency; part of the effluent is used as backwashing water to backwash the membrane assembly; sludge and sulfur powder are enriched and internally circulated and backflowed to the water inlet end; and the treated effluent meeting the discharge standard is discharged. The application integrates the traditional pretreatment, sulfur autotrophic denitrification and membrane separation into one unit, has a simple process, occupies a small area and does not need an external carbon source. Meanwhile, the vibration membrane device is used to realize efficient membrane pollution control, and the sulfur powder is used as an electron donor to realize low-carbon and efficient denitrification.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, specifically to a short-process vibrating membrane autotrophic denitrification process. Background Technology

[0002] With increasing human activities, large amounts of nitrogenous pollutants are discharged into rivers, lakes, and seas, leading to a growing problem of eutrophication and severely impacting water body functions and ecological balance. Controlling point source nitrogen emissions is one of the key measures to curb eutrophication. Wastewater treatment plants, as important entities for nitrogen emission reduction, must strengthen their nitrogen removal processes to reduce nitrogen emissions. However, due to the low carbon-to-nitrogen ratio of municipal wastewater in my country, wastewater denitrification often faces the problem of insufficient carbon sources, requiring the addition of large amounts of artificial carbon sources. This not only significantly increases operating costs but also increases carbon emissions during wastewater treatment and poses a risk of secondary pollution from carbon source leakage. Therefore, the development of low-carbon / zero-carbon denitrification technologies has received increasing attention.

[0003] Sulfur autotrophic denitrification technology has recently received widespread research and attention, and is increasingly being applied in engineering projects for denitrification of municipal wastewater and industrial wastewater. Currently, most sulfur autotrophic denitrification processes utilize fixed packed beds, resulting in high initial investment costs and difficulties in controlling the operation. Furthermore, recent engineering practice and research have revealed that when the influent electron acceptor is insufficient, a sulfur disproportionation reaction occurs in the fixed bed, producing large amounts of hydrogen sulfide that are difficult to recover. To better promote the application of sulfur autotrophic denitrification technology, there is an urgent need to develop novel sulfur autotrophic bioreactors. In fluidized bed sulfur autotrophic reactors, due to the relatively uniform mixing of sulfur powder, sludge, and water, sulfur disproportionation only occurs when the influent nitrogen load is low. Some papers and patents have proposed using bottom aeration to address the hydrogen sulfide production problem in fluidized bed reactors. However, current fluidized bed sulfur autotrophic reactors generally have a high depth-to-width ratio in their design to ensure sufficient fluidization through pump circulation, leading to overlapping bottom aeration effects. Moreover, in conventional fluidized bed sulfur autotrophic reactors, nitrogen carries a large amount of floating sludge away from the reactor during denitrification, causing water quality deterioration and loss of functional microbial communities. Summary of the Invention

[0004] Objective: This invention addresses the problems of long process flows, large footprints, and high energy consumption in traditional wastewater treatment plants by proposing a short-process vibrating membrane autotrophic denitrification process. This process effectively retains functional bacteria and sulfur powder microcarriers, and enhances mass transfer through turbulent kinetic energy generated by the reciprocating motion of the membrane module, thereby improving the efficiency of sulfur autotrophic denitrification and achieving efficient autotrophic denitrification in a short process. Simultaneously, the small depth-to-width ratio of the tank allows for effective suppression of hydrogen sulfide production during sulfur disproportionation by incorporating bottom micro-aeration. This invention is of great significance for energy conservation, cost reduction, efficiency improvement, and efficient nitrogen control in wastewater treatment plants through a short-process approach.

[0005] The technical solution adopted in this invention is a short-process vibrating membrane autotrophic denitrification process, comprising the following steps:

[0006] S1. The vibrating membrane autotrophic denitrification process described above uses a vibrating membrane autotrophic bioreactor comprising a tank, a vibrating membrane device, a backwash water circulation device, a sludge circulation device, a sulfur powder dosing system, an alkalinity dosing system, a micro-aeration emergency system, and an automatic control system; the tank comprises a sludge hopper, an inlet, a sludge internal return outlet, a sulfur powder dosing outlet, and an alkalinity dosing outlet; the vibrating membrane device comprises a permeate pump, a permeate solenoid valve, a reciprocating pump, and a hollow fiber membrane module; the backwash water circulation device comprises a backwash water pump and a backwash water storage tank;

[0007] S2. Nitrate-containing wastewater flows into the inlet in the middle of the tank. Sodium bicarbonate solution is added simultaneously by the alkalinity addition system to make the alkalinity (calculated as CaCO3) of the wastewater in the tank ≥ 7.5:1.0 with a denitrification equivalent of ≥ 7.5:1.0 and the pH value controlled between 6.5 and 8.0.

[0008] S3. When the influent reaches the set high level: When the water level is 30-60cm above the membrane module, the automatic control system controls the permeate pump to start, and 10%-30% of the effluent preferentially enters the backwash water storage tank for storage. The backwash water storage tank is equipped with an overflow pipe, and excess effluent flows into the effluent main pipe through the overflow pipe; When the membrane tank level drops to the set low level: When the water level is 0-20cm below the membrane module, the automatic control system controls the permeate pump to shut down.

[0009] S4. After sulfur powder is made into a sulfur powder slurry, it is added to the tank through the sulfur powder dosing system. The sulfur powder settling direction is considered to be laminar flow. According to Stokes' equation, the original sulfur powder has the fastest settling velocity. After settling at a rate of 4.5 to 30.0 mm / s for 1.0 to 7.5 minutes, it enters the bottom sedimentation zone, 0.5 to 1.0 m from the bottom. After staying in the sedimentation zone for 1.0 to 3.0 hours, a biofilm forms. The sulfur powder microcarrier enriched with sulfur autotrophic denitrification bacteria such as denitrifying sulfur bacteria is returned to the inlet end through the sludge circulation device. After continuous sulfur autotrophic denitrification reaction, the sulfur powder particle size decreases and the settling velocity slows down. The mature sulfur powder microcarrier can continue to function in the tank.

[0010] S5. When the ORP of the tank is below -300mV or the hydrogen sulfide concentration above the tank is above 0.5mg / L, activate the micro-aeration emergency system as an emergency measure to control the DO concentration in the tank at 0.2-0.5mg / L and the ORP above -300mV.

[0011] Furthermore, the water inlet is supplied by a pump or by gravity flow, with a water retention time of 1.5 to 3.0 hours and a sludge concentration of 3000 to 5000 mg / L in the pool, which increases with the depth of the pool.

[0012] Furthermore, the hollow fiber membrane module is sized similarly to the tank body, and the reciprocating motion direction of the membrane module maintains a 20-40 cm edge distance from the edge of the tank body. The hollow fiber membrane module uses PVDF or PTFE membranes with a pore size of 0.05-0.22 μm, an operating vibration frequency of 20-60 times / minute, an amplitude of 1.0-5.0 cm, and a permeate flux of 10-20 L / (m³). 2 ·h).

[0013] Furthermore, the membrane module of the vibrating membrane device is set to a vibration frequency of 40 times / minute, an amplitude of 2.0 cm, and a permeate flux of 15 L / (m²). 2 •h) can effectively alleviate membrane fouling, reduce operating energy consumption, and reduce the risk of membrane fiber breakage due to excessive stretching.

[0014] Furthermore, the backwashing water circulation device has a backwashing frequency of 1 to 4 times / day and a backwashing water volume of 20 to 40 L / (m³). 2 ·h).

[0015] Furthermore, the sludge circulation device has its inlet located at the bottom of the sludge hopper and its outlet located at the top of the tank. The sludge is discharged horizontally and fully mixed with the incoming water to prevent short-circuiting. The sludge circulation device operates intermittently at a frequency of 1 to 3 hours per cycle, and the volume of circulated sludge is equal to the volume of the sludge hopper.

[0016] Furthermore, the sulfur powder dosing system and alkalinity dosing system include a dosing pump and a water distribution tank. The water distribution tank is equipped with a stirring device. The uniformly mixed sulfur powder slurry and sodium bicarbonate solution are added into the tank. The sulfur powder is selected with a particle size of 200-500μm. The sulfur powder is added every 3-5 days at a concentration of 2-5 times the nitrate nitrogen concentration of the influent. When the alkalinity of the influent (calculated as CaCO3) is lower than 7.5 times the denitrification equivalent, sodium bicarbonate is continuously added at a dosage of 2-5 times the nitrate nitrogen concentration of the influent.

[0017] This invention's backwash water circulation device uses a portion of the treated effluent as backwash water for the backwash membrane assembly. A sludge circulation device returns the sludge and sulfur powder accumulated at the bottom of the reactor to the inlet. A micro-aeration emergency system provides micro-aeration to the reactor, preventing anaerobic fermentation and sulfur disproportionation. A sulfur powder dosing system adds micron-sized sulfur powder to the reactor as an electron donor for denitrification and provides enrichment microcarriers for functional microorganisms. An alkalinity dosing system replenishes alkalinity to the reactor. This invention's reactor utilizes the characteristics of sulfur-autotrophic microorganisms to achieve autotrophic denitrification under low dissolved oxygen conditions, thereby saving carbon source addition, significantly reducing energy consumption, and lowering carbon emissions. Simultaneously, it enriches functional bacterial communities, ensuring stable effluent quality.

[0018] This invention introduces a pretreated wastewater containing nitrate nitrogen into a reactor. Sulfur powder and sodium bicarbonate are added to the reactor to induce an autotrophic denitrification reaction. A vibrating membrane device is activated to generate shear force to control membrane fouling, while simultaneously enhancing water turbulence, mass transfer, and reaction efficiency. Part of the effluent is used as backwash water to backwash the membrane assembly. Bottom sludge and sulfur powder are recycled back to the inlet via internal circulation. The treated effluent that meets discharge standards is then discharged.

[0019] The beneficial effects of this invention:

[0020] (1) A vibrating membrane bioreactor is used to achieve mud-water separation, retaining sulfur powder microcarriers and autotrophic functional bacteria, with high membrane flux and stable operation;

[0021] (2) By utilizing the sedimentation distribution of sludge and sulfur powder in the membrane tank, a sludge concentration gradient is constructed to accelerate sludge maturation and alleviate membrane fouling in the middle and upper membrane modules.

[0022] (3) The internal circulation pump operates intermittently to improve denitrification efficiency and significantly reduce operating energy consumption;

[0023] (4) Short hydraulic retention time, high denitrification load, single sludge system construction and no need for sludge discharge, low sludge yield coefficient;

[0024] (5) Modular design, suitable for widespread application. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process system of the present invention.

[0026] Figure 2 This is a schematic diagram of the structure of a vibrating membrane sulfur autotrophic bioreactor.

[0027] Figure 3 It is a vibrating membrane sulfur autotrophic bioreactor for NO3 - The effect of removing -N is shown in the image. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 As shown, a short-process vibrating membrane autotrophic denitrification process includes the following steps:

[0030] S1. The vibrating membrane autotrophic denitrification process described above uses a vibrating membrane autotrophic bioreactor comprising a tank body 1, a vibrating membrane device 2, a backwash water circulation device 3, a sludge circulation device 4, a sulfur powder dosing system 5, an alkalinity dosing system 6, a micro-aeration emergency system 7, and an automatic control system; the tank body includes a sludge hopper, an inlet, an internal sludge return outlet, a sulfur powder dosing outlet, and an alkalinity dosing outlet; the vibrating membrane device includes a permeate pump, a permeate solenoid valve, a reciprocating pump, and a hollow fiber membrane module; the backwash water circulation device includes a backwash water pump and a backwash water storage tank, such as... Figure 2 As shown;

[0031] S2. Nitrate-containing wastewater flows into the inlet in the middle of the tank. Sodium bicarbonate solution is added simultaneously by the alkalinity addition system to make the alkalinity (calculated as CaCO3) of the wastewater in the tank ≥ 7.5:1.0 with a denitrification equivalent of ≥ 7.5:1.0 and the pH value controlled between 6.5 and 8.0.

[0032] S3. When the influent reaches the set high level: When the water level is more than 50cm above the membrane module, the automatic control system controls the permeate pump to start, and 10% of the effluent enters the backwash water storage tank first. The backwash water storage tank is equipped with an overflow pipe, and excess effluent enters the effluent main pipe through the overflow pipe; When the water level drops to the set low level: When the water level is less than 15cm above the membrane module, the automatic control system controls the permeate pump to shut down.

[0033] S4. After sulfur powder is made into a sulfur powder slurry, it is added to the tank through the sulfur powder dosing system. The sulfur powder settling direction is considered to be laminar flow. According to Stokes' equation, the original sulfur powder has the fastest settling velocity. After settling at a rate of 4.5 to 30.0 mm / s for 1.0 to 7.5 minutes, it enters the bottom sedimentation zone, 0.5 to 1.0 m from the bottom. After staying in the sedimentation zone for 1.0 to 3.0 hours, a biofilm forms. The sulfur powder microcarrier enriched with sulfur autotrophic denitrification bacteria such as denitrifying sulfur bacteria is returned to the inlet end through the sludge circulation device. After continuous sulfur autotrophic denitrification reaction, the sulfur powder particle size decreases and the settling velocity slows down. The mature sulfur powder microcarrier can continue to function in the tank.

[0034] S5. When the ORP of the tank is below -300mV or the hydrogen sulfide concentration above the tank is above 0.5mg / L, activate the micro-aeration emergency system as an emergency measure to control the DO concentration in the tank at 0.2-0.5mg / L and the ORP above -300mV.

[0035] The reactor tank has dimensions of 1.7m in length, 1.3m in width, and an effective depth of 2.5m. The sludge hopper is 0.7m deep, and the effective reactor volume is 3.8m³. 3 .

[0036] The membrane module uses a PVDF hollow fiber membrane, and the membrane module area is 150m². 2 Membrane pore size 0.1 μm, vibration frequency 40 times / min, amplitude 2.5 cm, permeate flux 15 L / (m²)2 The total residence time in the reactor is 1.8 hours. Backwashing is performed twice daily. The sludge circulation system is set to circulate every 2 hours, operating for 10 minutes each time, returning 0.74 m³ of the bottom sulfur powder-sludge mixture. 3 The sludge concentration in the tank is controlled at around 5000 mg / L MLVSS. Sulfur powder with a particle size of 400 μm is added every 3 days. The sulfur powder dosing system is based on a mass ratio of sulfur powder:nitrate nitrogen of 2.5:1.0. Since the influent alkalinity is sufficient, no additional sodium bicarbonate alkalinity supplementation is required during operation in this embodiment.

[0037] The operational performance of the short-process vibrating membrane autotrophic denitrification process of this invention:

[0038] This embodiment applies a vibrating membrane sulfur autotrophic bioreactor to a treatment capacity of 50m³. 3 / d of municipal wastewater. This wastewater is the effluent from the aerobic tank, with a temperature of approximately 20℃, a pH of approximately 7.6, a COD concentration of approximately 50mg / L, and NO3... - -N concentration is approximately 20 mg / L.

[0039] For the first 50 days of reactor operation, the internal circulation of sulfur powder is shut off, and stirring is achieved solely through the reciprocating motion of the membrane module. During this period, the device is unlikely to effectively remove nitrogen (e.g., Figure 3 As shown in the image, most of the sulfur powder settles at the bottom of the pool, and NO3 is emitted from the effluent after the internal circulation is started. - -N concentration decreased significantly, and ultimately, even with a relatively short residence time of 1.8 hours, the NO3 concentration in the reactor effluent decreased. - -N concentration <0.5mg / L, TN removal rate >97.5%. Without replenishing alkalinity, the effluent pH value remained above 6.5, and no significant membrane fouling issues were observed in the unit without chemical cleaning.

[0040] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A short-process vibrating membrane autotrophic denitrification process for sulfur, characterized in that, Includes the following steps: S1. The vibrating membrane autotrophic denitrification process described above uses a vibrating membrane autotrophic bioreactor comprising a tank, a vibrating membrane device, a backwash water circulation device, a sludge circulation device, a sulfur powder dosing system, an alkalinity dosing system, a micro-aeration emergency system, and an automatic control system; the tank comprises a sludge hopper, an inlet, a sludge internal return outlet, a sulfur powder dosing outlet, and an alkalinity dosing outlet; the vibrating membrane device comprises a permeate pump, a permeate solenoid valve, a reciprocating pump, and a hollow fiber membrane module; the backwash water circulation device comprises a backwash water pump and a backwash water storage tank; S2. Nitrate-containing wastewater flows into the inlet in the middle of the tank, and sodium bicarbonate solution is added simultaneously by the alkalinity addition system to make the alkalinity of the wastewater in the tank: nitrogen equivalent ≥ 7.5: 1.0, and the pH value controlled between 6.5 and 8.0; S3. When the influent reaches the set high level: When the water level is 30-60cm above the hollow fiber membrane module, the automatic control system controls the permeate pump to start and run continuously. 10%-30% of the effluent is preferentially stored in the backwash water tank. The backwash water tank is equipped with an overflow pipe, and excess effluent flows into the effluent main pipe through the overflow pipe. When the water level drops to the set low level: When the water level is 0-20cm below the membrane module, the automatic control system controls the permeate pump to shut off. S4. After sulfur powder is made into a sulfur powder slurry, it is added to the tank through the sulfur powder dosing system. The sulfur powder settling direction is considered to be laminar flow. According to Stokes' equation, the original sulfur powder has the fastest settling velocity. After settling at a rate of 4.5 to 30.0 mm / s for 1.0 to 7.5 minutes, it enters the bottom sedimentation zone, 0.5 to 1.0 m from the bottom. After staying in the sedimentation zone for 1.0 to 3.0 hours, a biofilm forms. The sulfur powder microcarrier enriched with sulfur autotrophic denitrification bacteria such as denitrifying sulfur bacteria is returned to the inlet end through the sludge circulation device. After continuous sulfur autotrophic denitrification reaction, the sulfur powder particle size decreases and the settling velocity slows down. The mature sulfur powder microcarrier can continue to function in the tank. S5. When the ORP of the tank is below -300mV or the hydrogen sulfide concentration above the tank is above 0.5mg / L, activate the micro-aeration emergency system as an emergency measure to control the DO concentration in the tank at 0.2-0.5mg / L and the ORP above -300mV.

2. The short-process vibrating membrane autotrophic denitrification process according to claim 1, characterized in that, The inlet is supplied with water by pump or gravity flow, with a water retention time of 1.5 to 3.0 hours and a sludge concentration of 3000 to 5000 mg / L, which increases with the depth of the pool.

3. The short-process vibrating membrane autotrophic denitrification process according to claim 2, characterized in that, The hollow fiber membrane module of the vibrating membrane device is similar in size to the tank body. The reciprocating motion direction of the membrane module must maintain a 20-40 cm edge distance from the tank body edge. The hollow fiber membrane module uses PVDF or PTFE membranes with a pore size of 0.05-0.22 μm. During operation, the vibration frequency is 20-60 times / minute, the amplitude is 1.0-5.0 cm, and the permeate flux is 10-20 L / (m³). 2 ·h).

4. The short-process vibrating membrane autotrophic denitrification process according to claim 3, characterized in that, The vibration frequency of the vibrating diaphragm device is set to 40 times / minute, with an amplitude of 2.0 cm and a water production flux of 15 L / (m²). 2 ·h).

5. The short-process vibrating membrane autotrophic denitrification process according to claim 4, characterized in that, The backwash water circulation device has a backwash frequency of 1 to 4 times / day and a backwash water volume of 20 to 40 L / (m³). 2 ·h).

6. The short-process vibrating membrane autotrophic denitrification process according to claim 5, characterized in that, The sludge circulation device has its inlet located at the bottom of the sludge hopper and its outlet located at the top of the tank. The sludge is discharged horizontally and fully mixed with the incoming water to prevent short-circuiting. The sludge circulation device operates intermittently at a frequency of 1 to 3 hours per cycle, and the volume of circulated sludge is equal to the volume of the sludge hopper.

7. The short-process vibrating membrane autotrophic denitrification process according to claim 6, characterized in that, The sulfur powder dosing system and alkalinity dosing system include a dosing pump and a water distribution tank. The water distribution tank is equipped with a stirring device. The uniformly mixed sulfur powder slurry and sodium bicarbonate solution are added into the tank. The sulfur powder is selected with a particle size of 200-500μm. The sulfur powder is added every 3-5 days at a concentration of 2-5 times the nitrate nitrogen concentration of the influent. When the alkalinity of the influent is lower than 7.5 times the denitrification equivalent, sodium bicarbonate is continuously added at a dosage of 2-5 times the nitrate nitrogen concentration of the influent.

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