Bacteria-algae symbiotic system, denitrification equipment and nitrogenous wastewater treatment method

Abstract

The invention relates to the technical field of water treatment, in particular to an algal-bacterial symbiotic system, denitrification equipment and a nitrogenous wastewater treatment method. The magnetic nitrogen-doped biochar material is coupled with the algal-bacterial symbiotic system, algal-bacterial symbiotic system equipment under the spontaneous low-dissolution condition is innovatively provided, the magnetic biochar provides more reaction sites for microorganisms and algae, and directional regulation and control of a nitrogen metabolic pathway and improvement of electron transfer efficiency under the low-dissolved-oxygen condition are achieved. And the high specific surface area and the excellent pore structure provide stable conditions for self-generation of a low dissolved oxygen environment. According to the technology and the equipment, while the denitrification rate of the wastewater is increased, the aeration cost can be saved, additional carbon sources are not needed, secondary utilization of organic matters in the wastewater is achieved, algae in the treated wastewater is separated, resource recycling is achieved, and the technology and the equipment have wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and in particular to a bacteria-algae symbiotic system, denitrification equipment and a method for treating nitrogen-containing wastewater. Background Art

[0002] The bacterial-algal symbiotic system is a wastewater treatment technology that combines bacteria and algae. By decomposing macromolecular organic matter through microorganisms, the algae can directly utilize a carbon source. The CO2 produced in this process also feeds the algae for photosynthesis. Therefore, using a bacterial-algal symbiotic system to treat wastewater effectively utilizes the organic matter in the wastewater.

[0003] Traditional algae-bacteria symbiotic systems often experience high levels of dissolved oxygen (DO) due to the high photosynthesis of algae, inhibiting denitrification. Furthermore, traditional technologies often rely on a complete nitrification-denitrification process, resulting in lengthy processes and low denitrification efficiency. Furthermore, traditional algae-bacteria symbiotic systems often require additional aeration during the denitrification phase to reduce DO, resulting in high energy consumption. Summary of the Invention

[0004] In view of this, the present invention aims to provide a bacterial-algal symbiotic system, denitrification equipment, and a method for treating nitrogen-containing wastewater. The bacterial-algal symbiotic system provided by the present invention has the advantages of high denitrification efficiency, can achieve short-range nitrification and denitrification, does not require additional aeration, spontaneously forms a low dissolved oxygen environment, and has low operating costs.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a bacteria-algae symbiotic system, comprising activated sludge, Chlorella vulgaris acclimated with nitrogen-containing wastewater, and magnetic nitrogen-doped biochar;

[0007] The activated sludge is domesticated activated sludge; the microorganisms in the activated sludge include short-range nitrifying bacteria and denitrifying bacteria;

[0008] The mass ratio of the activated sludge, the Chlorella acclimated with nitrogen-containing wastewater and the magnetic nitrogen-doped biochar is (2-4):0.01:(1-5);

[0009] The magnetic nitrogen-doped biochar includes porous carbon and N and magnetic Fe species doped in the porous carbon.

[0010] Preferably, the mass content of the C element in the magnetic nitrogen-doped biochar is 60-75%, the mass content of the N element is 1-5%, the mass content of the Fe element is 5-15%, and the mass content of the O element is 15-20%; the specific surface area of ​​the magnetic nitrogen-doped biochar is 500-600m 2 / g.

[0011] The present invention provides the application of the bacteria-algae symbiotic system described in the above scheme in treating nitrogen-containing wastewater.

[0012] The present invention provides a denitrification device, comprising a bacteria-algae symbiotic reactor 3 and an automatic detection-control device; the bacteria-algae symbiotic reactor 3 is constructed with the bacteria-algae symbiotic system described in the above scheme;

[0013] The automatic detection and control device includes a water inlet control switch 301, a dissolved oxygen sensor 302, a CO2 detector 303, a pH sensor, a temperature sensor, an online water quality detector 305, a motor 306, a central control unit 307, a pH metering pump, a COD supplementary pump, a heating plate 309, a stirring paddle 310, a lighting unit 311, a water outlet control switch 312 and a mud discharge control switch 313;

[0014] The dissolved oxygen sensor 302, CO2 detector 303, redox potential detector, pH sensor, temperature sensor and detection head of the online water quality detector 305 are placed in the bacteria-algae symbiotic reactor 3; the heating plate 309 is located at the bottom of the bacteria-algae symbiotic reactor 3; the lighting unit 311 is installed on the outer wall of the bacteria-algae symbiotic reactor 3;

[0015] The stirring paddle 310 is located in the bacteria-algae symbiotic reactor 3 and is controlled by a motor 306;

[0016] The pH metering pump is used to add a pH regulator to the bacteria-algae symbiotic reactor 3 ; the COD supplementary pump is used to supplement a carbon source to the bacteria-algae symbiotic reactor 3 .

[0017] Preferably, it also includes an algae separator 4 and an algae collector 43; the water inlet of the algae separator 4 is connected to the water outlet of the bacteria-algae symbiotic reactor 3, and the algae outlet of the algae separator 4 is connected to the inlet of the algae collector 43; an ultrasonic module 41 is arranged inside the algae separator 4, and an external magnetic field 42 is arranged outside.

[0018] Preferably, it further comprises a filtering device 1 and a sedimentation tank 2; the water outlet of the filtering device 1 is connected to the water inlet of the sedimentation tank 2, and the water outlet of the sedimentation tank 2 is connected to the water inlet of the bacteria-algae symbiotic reactor 3.

[0019] The present invention provides a method for treating nitrogen-containing wastewater, which uses the denitrification equipment described in the above scheme to treat nitrogen-containing wastewater, comprising the following steps:

[0020] The nitrogen-containing wastewater is passed into the bacteria-algae symbiotic reactor 3 for short-term nitrification and denitrification. The light-dark ratio in the bacteria-algae symbiotic reactor 3 is adjusted to 1:0.2~1 and the CO2 compensation point is 30~60μL / L through the automatic detection-control device, so that the ratio of the net photosynthetic rate of algae to the microbial respiration rate under light conditions is 0.5~1, and a low dissolved oxygen environment is spontaneously formed. The low dissolved oxygen environment refers to a dissolved oxygen content of 0.4~1.2mg / L.

[0021] Preferably, the following measures are taken to control the spontaneous formation of a dissolved oxygen environment in the bacteria-algae symbiotic reactor 3:

[0022] Under the illumination conditions, an automatic detection and control device is used for coordinated control. When the CO2 compensation point drops to 5-28 μL / L, the COD supplement pump is started to supplement 5-10 mg / L of carbon source on the basis of the original carbon source to promote microbial respiration. When the CO2 compensation point rises to 60-65 μL / L, the illumination unit 311 is used to increase the light intensity by 5-20% on the basis of the original light intensity to promote the photosynthesis of Chlorella vulgaris.

[0023] Under light conditions, oxygen is produced to carry out short-term nitrification reaction. When the water quality online detector monitors NO2 - -N, NO3 - When the -N concentration meets the nitrite nitrogen accumulation rate of 75-85%, stop the light and avoid the light; under the light-avoiding condition, the aerobic-anaerobic short-range denitrification reaction is carried out. When monitoring NO2 - -N concentration is 2-5 mg / L, start the illumination unit 311, and adjust the illumination intensity to 1500-5000 lux;

[0024] Under illumination conditions, the dissolved oxygen is regulated by an automatic detection-control device. When the dissolved oxygen rises to 1.2-1.25 mg / L, the illumination unit 311 is controlled to reduce the illumination intensity by 5-15%. When the dissolved oxygen drops to 0.35-0.4 mg / L, the illumination unit 311 is controlled to increase the illumination intensity by 10-15%.

[0025] Preferably, the operating conditions of the bacteria-algae symbiotic reactor 3 include: water inlet 3 to 5 minutes, stirring 700 to 1400 minutes, sedimentation 15 to 30 minutes, water outlet 3 to 5 minutes, hydraulic retention time of 12 to 24 hours, sludge age of 5 to 7 days, stirring speed of 50 to 150 r / min, light exposure during stirring for 2 to 4 hours, light avoidance for 0.5 to 2 hours, light intensity of 1500 to 3000 lux, temperature of 25 to 30°C, and pH value of 7.5 to 8.5.

[0026] Preferably, after the short-cut nitrification and denitrification is completed, the method further includes recovering the magnetic nitrogen-doped biochar and Chlorella in the effluent of the bacteria-algae symbiotic reactor 3 .

[0027] The present invention provides a bacteria-algae symbiotic system, which enhances the denitrification performance of the system by introducing magnetic nitrogen-doped biochar. Specifically, nitrogen atoms have a high electronegativity and can change the electronic structure of the carbon skeleton, thereby facilitating the formation of free radicals. The doped biochar can also participate in nitrification and denitrification as an electron donor, thereby improving catalytic performance and redox capacity. Iron doping can promote electron transfer in redox reactions, improve the generation efficiency of free radicals, and prolong their active life. Moreover, after nitrogen and iron are added to biochar, the specific surface area is increased and the pore structure is expanded on the basis of the original biochar, which has a positive synergistic effect and improves the degradation rate of organic matter and the nitrogen removal rate.

[0028] The present invention provides a denitrification device that makes systematic innovation and integrated optimization of the overall system structure and monitoring and control modules. Through the introduction of automation, the system is able to spontaneously form a low dissolved oxygen environment.

[0029] The present invention introduces an automatic detection and control device to achieve "measuring and adjusting at the same time, automatic closed-loop control", avoids manual intervention, and improves the stability of the reaction system.

[0030] Furthermore, the denitrification equipment provided by the present invention integrates a microalgae recovery module, which can separate algae in the treated wastewater to achieve directional recovery and recycling, and has broad application prospects.

[0031] The present invention provides a method for treating nitrogen-containing wastewater. By adjusting the light-dark ratio and the carbon dioxide compensation point, the system is placed in a spontaneous low dissolved oxygen state, and the microbial community in the reactor is directed to be domesticated and enriched, so that the system enters a short-range nitrification-denitrification process. Compared with complete nitrification-denitrification, short-range nitrification-denitrification has multiple advantages: such as energy saving and consumption reduction (low oxygen consumption, and a reduction of about 40% in the carbon source for denitrification); increased reaction rate (shortened hydraulic retention time, and a 1.5-fold increase in the denitrification rate); sludge reduction and enhanced stability; N2O emission reduction, avoiding NO3 - →NO2 - →Intermediate accumulation pathway for N2O, reducing greenhouse gas risks.

[0032] The treatment method provided by the present invention can shorten the reaction stage, improve the denitrification efficiency, and quickly denitrify nitrogen-containing wastewater such as agricultural non-point source pollution, domestic sewage, and industrial wastewater.

[0033] The present invention uses magnetic nitrogen-doped biochar, coupled with a bacterial-algal symbiotic system, to provide more reaction sites for microorganisms and algae, enabling directional regulation of nitrogen metabolic pathways and increased electron transfer efficiency under low dissolved oxygen conditions. The high specific surface area and excellent pore structure provide stable conditions for the spontaneous generation of a low dissolved oxygen environment. While increasing the denitrification rate of wastewater, the present invention does not require additional aeration, saving aeration costs. It also does not require the addition of an additional carbon source, enabling secondary utilization of organic matter in wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic structural diagram of the denitrification equipment in Example 1;

[0035] Figure 2 It is a schematic diagram of the structure of the bacteria-algae symbiotic reactor under low dissolved oxygen conditions;

[0036] Figure 3 This is a schematic diagram of the algae collection system;

[0037] Figure 4 The COD concentration of the effluent treated by the magnetic biochar-enhanced bacteria-algae symbiotic system;

[0038] Figure 5 The removal rate of NH4+-N from wastewater by magnetic biochar-enhanced bacterial-algal symbiotic system;

[0039] Figure 6 SEM images of different positions of magnetic nitrogen-doped biochar in Example 1;

[0040] Among them, 1-filtration device; 2-sedimentation tank; 21-water pipe; 22-water outlet controller; 3-bacteria-algae symbiotic reactor; 301-water inlet control switch; 302-dissolved oxygen sensor; 303-CO2 detector; 304-multi-parameter integrated online detector; 305-water quality online detector; 306-motor; 307-central control unit; 308-dual-zone regulating pump; 309-heating plate; 310-stirring paddle; 311-lighting unit; 312-water outlet control switch; 313-sludge discharge control switch; 4-algae separator; 41-ultrasonic module; 42-external magnetic field; 43-algae collector; 44-algae collector water outlet switch; 5-water storage tank. DETAILED DESCRIPTION

[0041] The invention provides a bacteria-algae symbiotic system, comprising activated sludge, Chlorella vulgaris acclimated with nitrogen-containing wastewater, and magnetic nitrogen-doped biochar.

[0042] The activated sludge is first described below.

[0043] In the present invention, the activated sludge is domesticated activated sludge; the microorganisms in the activated sludge include short-range nitrifying bacteria and denitrifying bacteria.

[0044] In the present invention, the acclimation of the activated sludge preferably includes: subjecting the activated sludge to aeration for 3 to 10 days, gradually increasing the volume load by intermittent aeration to adjust the sludge concentration (MLSS) to 1000 to 5000 mg / L, the sludge settling index (SVI) to 50 to 150 mL / g, and the sludge particle size to 50 to 300 μm;

[0045] The conditions of the intermittent aeration include: aeration for 10 to 30 seconds, pause for 10 to 30 seconds, a total aeration time (referring to aeration + pause) of 150 to 210 minutes, DO of 0.5 to 1.0 mg / L for enriching short-range nitrifying bacteria, passing N2 for 30 to 120 seconds after the end of aeration until DO reaches 0.1 to 0.3 mg / L, stopping, starting stirring, and stirring for 30 to 60 minutes for enriching denitrifying bacteria, so that the ammonia nitrogen removal rate is stabilized at 65 to 80% to complete the acclimation.

[0046] The aeration rate during the acclimation process is preferably controlled by a PID (proportional-integral-differential control algorithm) unit in coordination with a dissolved oxygen sensor, with an N2 flow rate of 0.5 to 2 L / min.

[0047] The present invention has no special requirements on the source of the activated sludge, and any anaerobic activated sludge known in the art can be used. In a specific embodiment, activated sludge from a sewage plant is used.

[0048] In a specific embodiment, the activated sludge exposure time can be 3, 5, 8 or 10 days; the MLSS can be 1000, 2000, 2500, 3000, 4000 or 5000 mg / L; and the SVI can be 50, 75, 100, 125 or 150 mL / g.

[0049] The aeration time can be 10, 20 or 30 seconds, the pause time can be 10, 20 or 30 seconds, and the total aeration time can be 150, 170, 190, 200 or 210 minutes.

[0050] The present invention adopts a novel intermittent aeration method, and by controlling the aeration conditions, inhibits nitrite oxidizing bacteria that react with nitrite as a substrate, thereby shortening the nitrification reaction. When the aeration is stopped, anaerobic conditions are quickly reached to allow denitrifying bacteria to reproduce, so that ammonia oxidizing bacteria and short-range denitrifying bacteria are quickly enriched in the same reactor, which is beneficial to the symbiosis of short-range nitrifying and denitrifying bacteria.

[0051] In the present invention, the gradually increasing volume load preferably includes: the initial COD concentration of the influent is 50 mg / L, NH4 +The concentration is 10 mg / L, the TP concentration is 2.5 mg / L, and the concentration load is increased by 50% every 7 days. The final COD concentration is 150 mg / L, and the COD:N:P concentration ratio is 5:1:0.25.

[0052] The present invention has no special requirements for the composition of the influent during the acclimation process, and the acclimation influent well known in the art can be used. In the embodiment of the present invention, the carbon source of the acclimation influent is glucose, the nitrogen source is NH4Cl, the phosphorus source is KH2PO4, the initial influent trace elements are shown in Table 2, and the vitamins are shown in Table 3; the initial influent COD concentration is 50 mg / L, NH4 + The concentration is 10 mg / L, the TP concentration is 2.5 mg / L, and the concentration load is increased by 50% every 7 days. The final COD concentration is 150 mg / L, the COD:N:P concentration ratio is 5:1:0.25, the trace element concentration is 1 g / L, the vitamin concentration is 10 g / L, the pH value is 7.5, the temperature is 30°C, and before the water is injected into the system, nitrogen must be passed for 10 minutes to blow off the dissolved oxygen in the water.

[0053] The following is an explanation of Chlorella acclimated with nitrogen-containing wastewater.

[0054] In the present invention, the acclimation of the chlorella preferably includes: centrifuging the activated chlorella algae liquid to obtain a microalgae concentrate; mixing the microalgae concentrate with nitrogen-containing wastewater at a volume ratio of 1:80-110, a light-dark ratio of 1:1-1.5, a light intensity of 1500-3000 lux, a temperature of 25-30°C, an oscillation shaking frequency of 1-2 minutes / time, and an interval of 1-2 hours each time, the nitrogen-containing wastewater adopts a stepwise concentration increase, and the culture period is 8-10 days, wherein the nitrogen-containing wastewater includes NH4 + -N is 20~150mg / L, NO2 - -N is 5-30mg / L, TN is 25-180mg / L, and the algae concentration reaches 10 4 ~10 6 cells / mL acclimation culture is completed.

[0055] In the present invention, the step-by-step concentration increase preferably includes: initial NH4 + -N is 20mg / L, and when the TN removal rate is 80%, replace the influent water, NH4 + -N influent concentration increases to 60, 120, and 150 mg / L in sequence; initial NO2 - -N is 5mg / L, followed by NO2 - -N concentration increased successively to 10, 20, and 30 mg / L; the initial TN was 25 mg / L.

[0056] In the present invention, the centrifugal speed is preferably 1500-3500 r / min, and the time is preferably 10-15 min.

[0057] In the present invention, the activated Chlorella is preferably obtained by separation, purification and identification from nitrogen-containing wastewater and sludge, and has strong adaptability to pollution and strong resistance to shock loads and is a photoautotrophic Chlorella.

[0058] In the present invention, the separation and purification of photoautotrophic Chlorella preferably adopts a rapid dissolved oxygen dynamic control method, wherein the algal cells in the nitrogenous wastewater are filtered at 80-100 μm, centrifuged at 2000-3500 r / min for 10-15 minutes, the supernatant is discarded and placed in a culture medium, the initial inoculation chlorophyll A content is 0.5-2 μg / mL, and high DO (5-8 mg / L) and low DO (0.1-0.3 mg / L) are selected for alternating culture; the initial switching cycle is 10-12 hours, which is then gradually reduced to 3-4 hours, and the culture is continuously cultured for 20-25 days, and the rapidly growing single algal colony is picked.

[0059] The magnetic nitrogen-doped biochar is described below.

[0060] In the present invention, the magnetic nitrogen-doped biochar includes porous carbon and N and magnetic Fe species doped in the porous carbon.

[0061] In the present invention, the mass content of the C element in the magnetic nitrogen-doped biochar is preferably 70-80%, and in specific embodiments it can be 70%, 72%, 74%, 76%, 78% or 80%; the mass content of the N element is preferably 1-5%, and in specific embodiments it can be 1%, 2%, 3%, 4% or 5%; the mass content of the Fe element is preferably 5-15%, and in specific embodiments it can be 5%, 7%, 10%, 12% or 15%; the mass content of the O element is preferably 5-10%, and in specific embodiments it can be 5%, 6%, 7%, 8%, 9% or 10%; the specific surface area of ​​the magnetic nitrogen-doped biochar is preferably 500-600m 2 / g, in specific embodiments, it can be 500, 520, 530, 540, 550, 580 or 600 m 2 / g; the pore volume of the magnetic nitrogen-doped biochar is preferably 1.5 to 2.5 cm 3 / g.

[0062] In the present invention, the magnetic saturation intensity of the magnetic nitrogen-doped biochar is preferably 35 to 75 emu / g. Under a magnetic field intensity of 0.1 to 0.3 T, solid-liquid separation can be achieved within 10 to 30 seconds, with a recovery rate of 85 to 95%.

[0063] In the present invention, the preparation of the magnetic nitrogen-doped biochar preferably comprises the following steps:

[0064] The nitrogen-containing biomass, K2FeO4 and water are mixed and subjected to a hydrothermal reaction to obtain iron-nitrogen doped biomass;

[0065] The iron-containing nitrogen-doped biomass is pyrolyzed under a protective atmosphere to obtain the magnetic nitrogen-doped biochar.

[0066] The present invention mixes nitrogen-containing biomass, K2FeO4 and water, and performs a hydrothermal reaction to obtain iron-containing and nitrogen-doped biomass.

[0067] In the present invention, the mass ratio of C to N in the nitrogen-containing biomass is preferably 10-20:1, and in specific embodiments, it can be 10:1, 13:1, 15:1, or 20:1. The present invention preferably mixes a high-nitrogen feedstock (N content of 3-6 wt%) with a low-nitrogen feedstock (N content of 0.1-0.8 wt%) to obtain the desired nitrogen-containing biomass. In the present invention, the nitrogen-containing biomass can be nitrogen-containing agricultural and forestry waste.

[0068] In the present invention, the nitrogen-containing biomass is preferably pre-treated before the hydrothermal reaction. In the present invention, the pre-treatment preferably includes washing, drying, crushing and screening in sequence.

[0069] In the present invention, the mass ratio of the nitrogen-containing biomass to K2FeO4 is preferably 2:1 to 4, and in specific embodiments, it can be 2:1, 2:2, 2:3, or 2:4. The present invention utilizes magnetic Fe species generated by K2FeO4 to enhance the biochar's magnetic properties and high adsorption activity, while also activating the biochar to provide dual oxidation and adsorption functions.

[0070] In the present invention, the water is preferably ultrapure water, and the ratio of the nitrogen-containing biomass to water is preferably 20-30 g: 400-600 mL.

[0071] In the present invention, the temperature of the hydrothermal reaction is preferably 150-250° C., and in specific embodiments may be 150, 200 or 250° C.; the time of the hydrothermal reaction is preferably 6-12 h, and in specific embodiments may be 6, 8, 10 or 12 h.

[0072] During the hydrothermal reaction, under a high-temperature and high-pressure hydrothermal environment, macromolecular substances such as cellulose and lignin in the biomass undergo hydrolysis and dehydration reactions to generate a carbon skeleton and a small amount of aromatic carbon clusters. K2FeO4 (potassium ferrate) decomposes to obtain Fe(OH)3 and partially dehydrates to Fe2O3 or FeOOH at high temperatures, and coordinates with biomass groups (carboxyl, hydroxyl, amino) to form Fe-N, Fe-OC and other bonded structures. In addition, under hydrothermal conditions, the biomass releases NH3, amines or amide intermediates, which may form pyridinic nitrogen, graphitic nitrogen, and quaternary ammonium salt structures, which are initially combined with the carbon skeleton.

[0073] After the hydrothermal reaction is completed, the present invention preferably further comprises cooling, washing and drying the reaction product to obtain iron-nitrogen doped biomass.

[0074] After obtaining the iron-containing nitrogen-doped biomass, the present invention pyrolyzes the iron-containing nitrogen-doped biomass under a protective atmosphere to obtain the magnetic nitrogen-doped biochar.

[0075] In the present invention, the pyrolysis temperature is preferably 550-750°C, and in specific embodiments, it can be 550, 600, 650, 700, or 750°C; the heating rate is preferably 5-10°C / min; the pyrolysis time is preferably 1-3 hours, and in specific embodiments, it can be 1, 2, or 3 hours. In the present invention, the protective atmosphere is preferably a nitrogen atmosphere, and the nitrogen protective flow rate is preferably 35-50 mL / min.

[0076] In the process of pyrolysis, the biomass decomposes and forms a pore structure. The chemical changes in the pyrolysis process mainly include: reduction and conversion of Fe species (precursors such as Fe(OH)3, FeOOH, and Fe2O3 in the hydrothermal product are reduced to Fe3O4, Fe 0 or Fe-Nx active sites); the formation of nitrogen-doped structures; and the aromatization and graphitization of the carbon skeleton.

[0077] In addition, during the pyrolysis process, iron can combine with functional groups such as carboxyl, carbonyl, and hydroxyl in the carbon skeleton to form an iron-carbon complex, thereby improving the persistence of free radicals in the short-range nitrification-denitrification process.

[0078] In the present invention, the mass ratio of the activated sludge, the Chlorella acclimated with nitrogen-containing wastewater and the magnetic nitrogen-doped biochar is (2-4):0.01:(1-5), preferably 3:0.01:(1-5); in specific embodiments, it can be 3:0.01:1.5, 3:0.01:2, 3:0.01:3, 3:0.01:4 or 3:0.01:5.

[0079] The present invention has no special requirements for the construction method of the bacteria-algae symbiotic system. The components can be directly added into the reactor for mixing, or added into the reactor after mixing.

[0080] The present invention provides the application of the bacteria-algae symbiotic system described in the above scheme in treating nitrogen-containing wastewater.

[0081] This method optimizes the short-range nitrification and denitrification process by coupling magnetic nitrogen-doped biochar with its excellent electron transport capacity, strong redox properties, and high specific surface area adsorption capacity, increasing the reaction rate and denitrification efficiency. Furthermore, magnetic nitrogen-doped biochar, due to its magnetic properties, also has the advantage of being easily recyclable.

[0082] The present invention provides a denitrification device, comprising a bacteria-algae symbiotic reactor 3 and an automatic detection-control device; the bacteria-algae symbiotic reactor 3 is constructed with the bacteria-algae symbiotic system described in the above scheme;

[0083] like Figure 2 As shown, the automatic detection and control device includes a water inlet control switch 301, a dissolved oxygen sensor 302, a CO2 detector 303, a pH sensor, a temperature sensor, an online water quality detector 305, a motor 306, a central control unit 307, a pH metering pump, a COD supplementary pump, a heating plate 309, a stirring paddle 310, a lighting unit 311, a water outlet control switch 312 and a mud discharge control switch 313;

[0084] The dissolved oxygen sensor 302, CO2 detector 303, redox potential detector, pH sensor, temperature sensor and detection head of the online water quality detector 305 are placed in the bacteria-algae symbiotic reactor 3; the heating plate 309 is located at the bottom of the bacteria-algae symbiotic reactor 3; the lighting unit 311 is installed on the outer wall of the bacteria-algae symbiotic reactor 3;

[0085] The stirring paddle 310 is located in the bacteria-algae symbiotic reactor 3 and is controlled by a motor 306;

[0086] The pH metering pump is used to add a pH regulator to the bacteria-algae symbiotic reactor 3 ; the COD supplementary pump is used to supplement a carbon source to the bacteria-algae symbiotic reactor 3 .

[0087] As an embodiment of the present invention, the pH sensor and the temperature sensor can be integrated into one body. In the embodiment of the present invention, a multi-parameter integrated online detector 304 is specifically used. The multi-parameter integrated online detector 304 has both pH value detection and temperature detection functions.

[0088] As an embodiment of the present invention, the pH metering pump and the COD supplementary pump can be integrated into one body. In the embodiment of the present invention, a dual-zone regulating pump 308 is specifically used.

[0089] In the present invention, the water inlet control switch 301 is used to control the water inlet of the bacteria-algae symbiosis reactor 3, and the water inlet of the bacteria-algae symbiosis reactor 3 is preferably located at the upper part of the side wall of the reactor; the water outlet control switch 312 is used to control the water outlet of the bacteria-algae symbiosis reactor 3, and the water outlet is located at a height position of 1 / 3 to 1 / 2 of the reactor; the mud discharge control switch 313 is used to control the mud discharge of the bacteria-algae symbiosis reactor 3, and the mud discharge port is located near the bottom of the side wall of the bacteria-algae symbiosis reactor 3.

[0090] In the present invention, the central control unit 307 uses a programmable logic controller (PLC) to control each sensor.

[0091] In the present invention, the central control unit 307 is capable of setting a threshold for DO; the dissolved oxygen sensor 302 transmits the DO signal to the central control unit 307 in real time. When the DO is detected to exceed the threshold, the central control unit 307 triggers the illumination unit 311 to reduce or increase the illumination, thereby making the DO threshold range 0.4 to 1.2 mg / L.

[0092] In the present invention, the temperature sensor transmits the temperature signal to the central control unit 307 in real time. When the temperature in the reactor is <25°C, the central control unit 307 triggers the heating plate 309 to heat up. When the temperature is >32°C, the central control unit 307 reduces the power of the heating plate 309. When the temperature is ≥35°C, the central control unit 307 stops heating and triggers the alarm system.

[0093] In the present invention, the pH sensor transmits the pH signal to the central control unit 307 in real time. When the pH value in the detection reactor is lower than the threshold, the central control unit 307 triggers the pH metering pump to add an alkaline reagent; when the pH value in the detection reactor is higher than the threshold, the central control unit 307 triggers the pH metering pump to add an acidic reagent.

[0094] In the present invention, the water quality online detector 305 is used to detect the NO2 - -N concentration index, NO2 - When the -N concentration is 100-150 mg / L, the central control unit 307 turns on the sludge discharge control switch 313. The system automatically discharges 10-20% of the sludge and then turns off the switch, shortening the sludge age to optimize the short-range nitrification and denitrification process.

[0095] In the present invention, the CO2 detector 303 is used to detect the CO2 concentration in the reactor and feed back the CO2 compensation point information to the central control unit 307 in real time. When the CO2 compensation point is lower than the threshold, the central control unit 307 triggers the COD supplementary pump to supplement the carbon source; when the CO2 compensation point is higher than the threshold, the central control unit 307 triggers the illumination unit 311 to increase the illumination intensity.

[0096] like Figure 1 As shown, the denitrification equipment provided by the present invention also includes a filtering device 1 and a sedimentation tank 2; the water outlet of the filtering device 1 is connected to the water inlet of the sedimentation tank 2, and the water outlet of the sedimentation tank 2 is connected to the water inlet of the bacteria-algae symbiotic reactor 3.

[0097] In the present invention, the filtering device 1 uses two screens, a coarse screen and a medium screen, to remove floating objects and suspended solids in sewage.

[0098] In the present invention, the filtering device 1 and the sedimentation tank 2 are connected via a water pipe 21 .

[0099] In the present invention, the sedimentation tank 2 is used to separate sludge with finer particles.

[0100] In the present invention, the sedimentation tank 2 is provided with a water inlet controller ( Figure 1 The sedimentation tank 2 includes a tank body and a tank cover. The present invention does not make any special requirements on the shape of the sedimentation tank 2, and it can be a rectangular parallelepiped or a cylinder.

[0101] like Figure 1 As shown, the denitrification equipment provided by the present invention also includes an algae separator 4 and an algae collector 43; the water inlet of the algae separator 4 is connected to the water outlet of the bacteria-algae symbiotic reactor 3, and the algae outlet of the algae separator 4 is connected to the inlet of the algae collector 43; an ultrasonic module 41 is provided inside the algae separator 4, and an external magnetic field 42 is provided outside. In an embodiment of the present invention, the ultrasonic module 41 is fixed to the bottom of the algae separator 4 through a sealing flange and a threaded interface to ensure that the ultrasonic wave can directly act on the liquid medium. The power cord used must be well waterproofed and an external constant power regulator must be connected to control the frequency and time. In a specific embodiment, a probe-type ultrasonic processor is used as the ultrasonic module 41 with a power of 60W.

[0102] In the present invention, the external magnetic field 42 can be provided by an electromagnet. As an embodiment of the present invention, an iron core type DC electromagnet is used with a suction force of 30N. The electromagnet is placed on the outer wall of the algae separator 4 and installed on the lower part or side wall near the algae outlet to ensure that the magnetic particles can settle downstream and be quickly adsorbed. A U-shaped holder and a stainless steel bracket are used for fixing to ensure that there is no shaking. The present invention uses a low-voltage DC regulated power supply to connect with the electromagnet. In the present invention, the ultrasonic module 41 is used to promote the full contact between the magnetic nitrogen-doped biochar and the algae in the algae separator 4, so that the magnetic nitrogen-doped biochar adsorbs Chlorella; when the external magnetic field 42 is turned on, it will quickly adsorb the magnetic particles (magnetic particles formed by magnetic nitrogen-doped biochar and Chlorella). When the external magnetic field 42 is turned off, it will flow downstream into the algae collector 43, thereby achieving rapid separation of algae-containing magnetic particles.

[0103] The denitrification equipment provided by the present invention further comprises a water storage tank 5. The water outlet of the algae separator 4 is connected to the water storage tank 5 via a pipeline, and an algae separator water outlet switch 44 is provided on the pipeline.

[0104] The present invention provides a method for treating nitrogen-containing wastewater, which uses the denitrification equipment described in the above scheme to treat nitrogen-containing wastewater, comprising the following steps:

[0105] The nitrogen-containing wastewater is passed into the bacteria-algae symbiotic reactor 3 for short-term nitrification and denitrification. The light-dark ratio in the bacteria-algae symbiotic reactor 3 is adjusted to 1:0.2~1 and the CO2 compensation point is 30~60μL / L through the automatic detection-control device, so that the ratio of the net photosynthetic rate of algae to the microbial respiration rate under light conditions is 0.5~1, and a low dissolved oxygen environment is spontaneously formed. The low dissolved oxygen environment refers to a dissolved oxygen content of 0.4~1.2mg / L.

[0106] The present invention has no special requirements on the source of the nitrogen-containing wastewater. Any nitrogen-containing wastewater known in the art can be used, such as farmland drainage (NH4 + -N concentration 5 ~ 20mg / L, TP concentration 0.5 ~ 10mg / L, COD concentration 500 ~ 2000mg / L), high ammonia nitrogen wastewater (NH4 + -N concentration 50 ~ 500mg / L, TP concentration 0.5 ~ 5mg / L, COD concentration 50 ~ 200mg / L) and industrial nitrogen-containing organic wastewater (NH4 + -N concentration 10 ~ 200 mg / L, TP concentration 0.1 ~ 5 mg / L, COD concentration 1000 ~ 100000 mg / L).

[0107] In the present invention, the nitrogen-containing wastewater is preferably filtered and precipitated first, and then introduced into the bacteria-algae symbiotic reactor 3 .

[0108] In the present invention, the light-to-dark ratio can be specifically 1:0.2, 1:0.33, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1, and is most preferably 1:0.33.

[0109] The dissolved oxygen in the low dissolved oxygen environment fluctuates within the range of 0.4 to 1.2 mg / L.

[0110] The present invention preferably adopts the following measures to control the spontaneous formation of a dissolved oxygen environment in the bacteria-algae symbiotic reactor 3:

[0111] Under the illumination conditions, an automatic detection and control device is used for coordinated control. When the CO2 compensation point drops to 5-28 μL / L, the COD supplement pump is started to supplement 5-10 mg / L of carbon source on the basis of the original carbon source to promote microbial respiration. When the CO2 compensation point rises to 60-65 μL / L, the illumination unit 311 is used to increase the light intensity by 5-20% on the basis of the original light intensity to promote the photosynthesis of Chlorella vulgaris.

[0112] Under the light condition, oxygen is produced to carry out short-range nitrification reaction. When the water quality online detector 305 monitors NO2 - -N, NO3 -When the -N concentration meets the nitrite nitrogen accumulation rate of 75-85%, stop the light and avoid the light; under the light-avoiding condition, the aerobic-anaerobic short-range denitrification reaction is carried out. When monitoring NO2 - -N concentration is 2 to 5 mg / L, start the illumination unit 311, and adjust the illumination intensity to 1500 to 5000 lux; wherein, the nitrite nitrogen accumulation rate NAR (%) = [NO2 - -N] / ([NO2 - -N]+[NO3 - -N])×100%;

[0113] Under illumination conditions, the dissolved oxygen is regulated by an automatic detection-control device. When the dissolved oxygen rises to 1.2-1.25 mg / L, the illumination unit 311 is controlled to reduce the illumination intensity by 5-15%. When the dissolved oxygen drops to 0.35-0.4 mg / L, the illumination unit 311 is controlled to increase the illumination intensity by 10-15%.

[0114] The present invention adjusts the light-dark ratio and CO2 compensation point so that the system is in a reaction process of alternating oxygen production and consumption, and a low dissolved oxygen environment is spontaneously formed. Under light conditions, algae use carbon dioxide to photosynthesize oxygen, and low-speed stirring is performed in the reactor, so that the oxygen in the water is continuously exchanged into the lower layer of activated sludge, forming a low dissolved oxygen environment. At this stage, due to the low dissolved oxygen conditions, ammonia oxidizing bacteria are enriched in large quantities and the reproduction of nitrite oxidizing bacteria is inhibited, which can convert NH4 + -N is converted into NO2- for short-term nitrification. Under dark conditions, algae and microorganisms respire together, significantly reducing the oxygen content in the reactor. Denitrifying bacteria then utilize NO2- for short-term denitrification under anoxic or anaerobic conditions. Short-term nitrification and denitrification not only improves denitrification efficiency but also reduces aeration costs and the carbon source required for unnecessary reactions. The magnetic biochar obtained through pyrolysis has a superior specific surface area and pore structure, providing more reaction sites for the entire system and facilitating the symbiotic growth of bacteria and algae.

[0115] In the present invention, the operating conditions of the bacteria-algae symbiotic reactor 3 preferably include: water inlet 3 to 5 minutes, stirring 700 to 1400 minutes, sedimentation 15 to 30 minutes (avoid light during sedimentation), water outlet 3 to 5 minutes, hydraulic retention time of 12 to 24 hours, sludge age of 5 to 7 days, stirring speed of 50 to 150 r / min, light exposure during stirring for 2 to 4 hours, avoid light for 0.5 to 2 hours, light intensity of 1500 to 3000 lux, temperature of 25 to 30°C, and pH value of 7.5 to 8.5.

[0116] In a specific embodiment, the stirring time can be 700, 800, 900, 1000, 1100, 1200, 1300 or 1400 min, the precipitation time can be 15, 20, 25 or 30 min, and the light intensity can be 1500, 2000, 2500 or 3000 lux.

[0117] During operation, when the pH sensor detects that the pH value in the bacteria-algae symbiotic reactor 3 is between 7 and 7.5, the pH metering pump adds an alkaline reagent; when the pH value is between 8.5 and 9, the pH metering pump adds an acidic reagent.

[0118] During operation, the temperature sensor transmits the temperature signal to the central control unit 307 in real time. When the temperature in the reactor is <25°C, the central control unit 307 triggers the heating plate 309 to increase the temperature. When the temperature is >32°C, the central control unit 307 reduces the power of the heating plate 309. When the temperature is ≥35°C, the central control unit 307 stops heating and triggers the alarm system.

[0119] During operation, the water quality online detector 305 detects water NO2 - -N indicator, NO2 - When the -N concentration is 100-150 mg / L, the central control unit 307 turns on the sludge discharge control switch 313. The system automatically discharges 10-20% of the sludge and then turns off the switch, shortening the sludge age to optimize the short-range nitrification and denitrification process.

[0120] In the present invention, during the operation, the free ammonia (FA) concentration in the bacteria-algae symbiotic reactor 3 is preferably 5 to 45 mg / L, and the COD:N mass ratio is preferably 1:0.1 to 0.5.

[0121] After the short-range nitrification and denitrification is completed, the effluent from the bacteria-algae symbiotic reactor 3 enters the algae collector 4. The present invention preferably recovers the magnetic nitrogen-doped biochar and Chlorella in the effluent from the bacteria-algae symbiotic reactor 3.

[0122] The present invention preferably adjusts the pH value of the wastewater in the algae separator 4 to 9-10, adds 3-5g / L of magnetic nitrogen-doped biochar, activates the ultrasonic module 41 for rapid adsorption for 5-10 minutes at a frequency of 20-40kHz, and then applies an external magnetic field 42. After observing the aggregation of magnetic particles formed by the magnetic nitrogen-doped biochar and Chlorella, the external magnetic field 42 is turned off. Specifically, after the effluent from the bacteria-algae symbiotic reactor 3 flows into the algae separator 4, the ultrasonic module 41 is activated to allow the magnetic nitrogen-doped biochar to fully adsorb the algae particles. The external magnetic field 42 is then powered on to form a strong magnetic field on the wall of the algae separator 4. After the magnetic particles aggregate and settle, the magnetic field is turned off.

[0123] Traditional bacteria-algae symbiotic systems often lead to high DO due to high algae photosynthesis, which inhibits denitrification; DO is difficult to control. The present invention constructs a spontaneous low-DO environment, and through microecological regulation, respiration exceeding photosynthesis rate, and CO2 compensation point adjustment, a low-oxygen environment without aeration is achieved.

[0124] The bacteria-algae symbiotic system, denitrification equipment and nitrogen-containing wastewater treatment method provided by the present invention are described in detail below with reference to the embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0125] The Chlorella used in the following examples and comparative examples is a photoautotrophic Chlorella obtained by separation, purification, and identification from nitrogen-containing wastewater and sludge, and has strong adaptability to pollution and strong resistance to shock loads.

[0126] The identification process is as follows:

[0127] Through the control experiment, BG11 was used as the basic culture medium and cultured under the conditions of constant temperature of 30℃, light intensity of 500lux, 12h light / 12h dark. The initial inoculation concentration OD 680 0.2 (Note: OD 680 It is called light absorption value, which is the optical density at a wavelength of 680nm). A is the control group without any pollutants added, and it is only cultured in the culture medium; B is the chronic pollution group, with initial NH4 + -N concentration is 0, and 100 mg / L NH4 is added every 2 days + -N solution until the concentration reaches 600mg / L; C is the initial addition of 600mg / L NH4 in the shock group + -N solution; D is the recovery group. After 24 hours of shock treatment, the algae solution was transferred to fresh non-contaminated culture medium to observe the recovery. During the experiment, OD was measured at 0h, 24h, 3rd day and 7th day. 680 , cell viability, and ROS accumulation. Although group B was slightly affected by high NH4 + -N concentration effect (24h OD 680 Decline), but Chlorella can still + -N gradually increased to 600 mg / L and maintained activity and continued to grow; OD 680 Close to the control group, the cell viability was maintained at about 89%. 680 The activity dropped slightly to 72%, but the cells did not disintegrate, indicating that the short-term 600mg / LNH4 + -N shock was not fatal. Chlorella began to recover after 3 days. OD 680The OD value reached 0.81, and the activity recovered to 85%. After being transferred to clean culture medium, the recovery group (D) quickly resumed growth on the third day, and the OD value returned to almost normal (0.95) on the seventh day, with ROS levels close to the control. These experimental results fully demonstrate that Chlorella can maintain a good growth state under high-concentration ammonia nitrogen stress, and has excellent shock resistance and recovery capabilities, showing significant anti-fouling and anti-load properties, suitable for resource-based treatment systems for ammonia nitrogen wastewater.

[0128] Example 1 and Comparative Examples 1-2

[0129] 1) Activated sludge from a sewage treatment plant was anaerobicly acclimated and aerated for 10 days. Intermittent aeration and a stepwise concentration ramp were used to gradually increase the volumetric load to 2500 mg / L, the sludge settling index (SVI) to 75 mL / g, and the sludge particle size to 180 μm. The operating conditions included: 30 seconds of aeration followed by a 30-second pause, for a total aeration time of 210 minutes. A DO of 0.5-1.0 mg / L was used to enrich short-range nitrifying bacteria. At the end of aeration, nitrogen was introduced for 80 seconds until the DO reached 0.1-0.3 mg / L, and then agitation was initiated for 60 minutes to enrich denitrifying bacteria. Acclimation was completed by stabilizing the ammonia nitrogen removal efficiency at 75%. The aeration rate was controlled using a PID unit in conjunction with a dissolved oxygen sensor, with an nitrogen flow rate of 1.2 L / min.

[0130] The composition of the influent during the acclimation process was as follows: the carbon source was glucose, the nitrogen source was NH4Cl, and the phosphorus source was KH2PO4. The initial influent trace elements are shown in Table 2, and the vitamins are shown in Table 3. The initial influent COD concentration was 50 mg / L, NH4 + The concentration is 10 mg / L, the TP concentration is 2.5 mg / L, and the concentration load is increased by 50% every 7 days. The final COD concentration = 150 mg / L, COD:N:P concentration ratio = 5:1:0.25, trace elements = 1 g / L, vitamins = 10 g / L, pH value = 7.5, temperature 30°C, and before the water is injected into the system, nitrogen must be passed for 10 minutes to blow off the dissolved oxygen in the water.

[0131] 2) The activated Chlorella algae liquid was centrifuged at 3000r / min for 10min to obtain a microalgae concentrate. The microalgae concentrate was mixed with nitrogenous wastewater at a volume ratio of 1:100, a light-dark ratio of 3:1, a light intensity of 2000lux, a temperature of 30℃, and an oscillation frequency of 2min / time, with an interval of 2h each time. The nitrogenous wastewater was gradually increased in concentration, with the initial NH4 + -N is 20mg / L, and when the TN removal rate is 80%, replace the influent water, NH4 + -N influent concentration increases to 60, 120, and 150 mg / L in sequence; initial NO2 --N is 5mg / L, followed by NO2 - -N concentration increases to 10, 30, and 30 mg / L in sequence; the initial TN is 25 mg / L, and the nitrogen-containing wastewater concentration includes NH4 + -N is 20~150mg / L, NO2 - -N is 5~30mg / L, TN is 25~180mg / L, and algae concentration is 10 4 ~10 6 cells / mL culture is complete.

[0132] 3)① Using nitrogen-containing agricultural and forestry waste as raw materials, high-nitrogen raw materials (N = 6wt%) and low-nitrogen raw materials (N = 0.5wt%) are taken and mixed according to the overall C:N element mass ratio of 13:1 after mixing. They are washed, dried, crushed and sieved in sequence. 25g of pre-treated biomass powder and 500mL of ultrapure water are taken, and the biomass:K2FeO4 mass ratio is 2:1 and added into the hydrothermal reactor. The reaction conditions are: temperature 200℃, reaction 6h, and then cooling, washing and drying are carried out respectively to obtain iron-nitrogen doped biomass.

[0133] ② The iron-nitrogen-doped biomass was pyrolyzed in a tubular furnace under the following pyrolysis conditions: temperature 750°C, heating rate 10°C / min, nitrogen protection flow rate 35 mL / min, and pyrolysis for 2 h to obtain magnetic nitrogen-doped biochar.

[0134] ③ The magnetic biochar material after pyrolysis was analyzed by SEM scanning electron microscopy. Figure 6 It can be seen that the biochar surface is loaded with magnetism and has rich pores. Table 1 shows that the magnetic biochar material has a high specific surface area and pore structure, with a specific surface area of ​​537.87 m 2 / g, total pore volume greater than 2cm 3 / g; the C element content is about 71%, the Fe element content is about 10%, the N element content is about 4%, and the O element content is about 15%.

[0135] 4)① Centrifuge the acclimated sludge at 3500r / min for 10min and add Figure 2 In the reactor shown, the total sludge volume to influent volume ratio is 1:10, and the sludge concentration after addition to the influent is 500 mg / L.

[0136] ② The domesticated Chlorella liquid was centrifuged at 3000r / min for 10min, and then a small amount of farmland drainage water was added and transferred to the above reactor. According to the water inflow, the Chlorella cell content after transfer was 4.5×10 6 cell / mL This group of devices was named R1 (Comparative Example 1).

[0137] ③ Take another reactor, and add activated sludge and Chlorella in the same manner as in the above two steps (i.e., step 4) ① and ②), and additionally add the prepared magnetic nitrogen-doped biochar at 2 g / L (here, each liter is the mixed volume after the influent is introduced) into the above reactor, with a mass ratio of sludge: algae: magnetic nitrogen-doped biochar = 3:0.01:1.5 to fully mix it with the sludge. This set of devices is named R2 (Example 1).

[0138] ④ Take another reactor and add only the activated sludge in the above proportion, and additionally add the prepared magnetic biochar at 2 g / L into the above reactor to fully mix it with the sludge. This group of devices is named R3 (Comparative Example 2).

[0139] ⑤During the operation of R1, R2 and R3 reactors, except for the different ways of adding sludge, microalgae and magnetic carbon, all other control conditions remained consistent to ensure the comparability of the experiments and the reliability of the data.

[0140] 5) The pH value inside the system is detected by a pH sensor, and the pH metering pump is controlled by the central control unit 307 to adjust the pH value within the range of 7.5 to 8.5.

[0141] 6) The operating conditions of the magnetic biochar enhanced algae-bacteria symbiosis system are as follows: fully mixed flow with low-speed stirring, water inlet for 5 min, stirring for 1400 min, sedimentation for 30 min, water outlet for 5 min, hydraulic retention time of 12 h, sludge age of 7 d, stirring speed of 150 r / min, light exposure for 3 h during stirring, dark avoidance for 1 h, light intensity of 2000 lux, temperature of 30 °C, and DO regulated at 0.4-1.2 mg / L.

[0142] 7) The temperature sensor transmits the temperature signal to the central control unit 307 in real time. When the temperature in the reactor is less than 25°C, the central control unit 307 triggers the heating plate 309 to increase the temperature. When the temperature is greater than 32°C, the central control unit 307 reduces the power of the heating plate 309. When the temperature is greater than or equal to 35°C, heating is stopped and the alarm system is triggered.

[0143] Under light conditions, oxygen is produced to carry out short-term nitrification reaction. When the water quality online detector 305 monitors NO2 - -N, NO3 - When the -N concentration meets the nitrite nitrogen accumulation rate of 75-85%, stop the light and avoid the light; under the light-avoiding condition, the aerobic-anaerobic short-range denitrification reaction is carried out. When monitoring NO2 - The -N concentration is 2 mg / L, the illumination unit 311 is started, and the initial illumination intensity is 2000 lux.

[0144] Under light conditions, the central control unit 307 sets a threshold for DO. When DO rises to 1.2-1.25 mg / L, the illumination unit 311 is controlled to reduce the light intensity by 5-15%. When DO drops to 0.35-0.4 mg / L, the illumination unit 311 is controlled to increase the light intensity by 10-15%. The DO threshold range is 0.4-1.2 mg / L.

[0145] Under the light conditions, each sensor coordinates with the central control unit 307 for control. When the CO2 compensation point is 15 μL / L, the COD supplement pump is started to supplement 10 mg / L of carbon source on the original basis to promote microbial respiration. When the CO2 compensation point rises to 60-65 μL / L, the light unit 311 increases the light intensity by 10% to promote photosynthesis of Chlorella vulgaris.

[0146] 8) Detect NO2 in water through water quality online detector 305 - Indicator, NO2 - When the -N concentration is 100-150 mg / L, the central control unit 307 turns on the sludge discharge control switch 313. The system automatically discharges 10-20% of the sludge and then turns off the switch, shortening the sludge age to optimize the short-range nitrification and denitrification process. After sludge discharge, the algae cell content in the reactor is monitored and algae are added until the concentration before sludge discharge is restored to 4.5×10 6 cell / mL. Due to the high magnetic properties of magnetic biochar, the magnetic carbon content of the discharged sludge is recovered and weighed and added to the reactor.

[0147] 9) For the first 10 days of the reactor, the simulated influent FA was 5 mg / L and NH4 + -N is 30mg / L, COD:N:P concentration = 5:1:0.15, used to stabilize the initial microbial state of the reactor, 10 to 20 days to adjust the influent FA to 10mg / L, NH4 + -N is 60mg / L and other conditions remain unchanged, detect NH4 + The -N removal rate was 83%, and the nitrite conversion rate was >80%, indicating that ammonia-oxidizing bacteria were dominant and nitrite-oxidizing bacteria were suppressed, which was conducive to short-range nitrification. The wastewater to be treated was then directly introduced.

[0148] 10) The farmland water was introduced into the reactor and the water was replaced according to HRT. The sampling period was 20 days before operation and every two days thereafter to detect NO2 in the water. - -N, NO3 - -N、NH4 + -N, COD, TP concentrations.

[0149] 11) The microalgae-containing water treated by the bacteria-algae symbiosis device was passed into an algae separator, the pH was adjusted to 9.5, 4 g / L of magnetic nitrogen-doped biochar was added, the ultrasonic module was turned on for rapid adsorption, and the magnetic field was turned on. After the magnetic particles aggregated and settled, the magnetic field was turned off and the algae were recycled.

[0150] 12) The magnetic biochar used in the bacteria-algae symbiosis device and algae collection device can be reused after high-intensity ultrasonic cleaning. After five ultrasonic cleanings and recycling, the algae recovery efficiency reached 85%.

[0151] After the system has been running stably for 60 days, Figure 4 and Figure 5 As shown in the data, NH4 of R1 and R2 + The -N removal rates were 80% and 92%, respectively, and the effluent COD concentrations were 167 mg / L and 98 mg / L, respectively. The results showed that the treatment effect of R2 was significantly better than that of R1. The addition of nitrogen-doped magnetic carbon effectively promoted microbial electron transfer, enhanced the utilization of electron donors by denitrifying bacteria, and increased the degradation rate of organic matter.

[0152] After the system has been running stably for 60 days, Figure 4 and Figure 5 As shown in the data, NH4 of R2 and R3 + -N removal rates were 92% and 70% respectively, and the effluent COD concentrations were 98mg / L and 277mg / L respectively. The results showed that the treatment effect of R2 was significantly better than that of R3. The addition of algae formed a low dissolved oxygen environment, promoted the short-term nitrification and denitrification stage, and accelerated the NO2 - -N reduction rate, increasing NH4 + -N and organic matter removal rates.

[0153] Table 1 Specific surface area and pore volume of magnetic biochar

[0154]

[0155]

[0156] Table 2 Trace element composition and content

[0157]

[0158] Table 3 Vitamin composition and content

[0159] Nutrient name Chemical formula <![CDATA[Concentration (g·L -1 )]]> zinc chloride <![CDATA[ZnCl2]]> 0.07 Copper chloride dihydrate <![CDATA[CuCl2·2H2O]]> 0.015 Sodium molybdate dihydrate <![CDATA[Na2MoO4·2H2O]]> 0.025 Ferrous chloride tetrahydrate <![CDATA[FeCl2·4H2O]]> 1.5 Manganese chloride tetrahydrate <![CDATA[MnCl2·4H2O]]> 0.01 Cobalt chloride hexahydrate <![CDATA[CoCl2·6H2O]]> 0.12 Nickel chloride hexahydrate <![CDATA[NiCl2·6H2O]]> 0.025

[0160] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A bacteria-algae symbiotic system, characterized in that: It includes activated sludge, Chlorella vulgaris acclimated with nitrogenous wastewater, and magnetic nitrogen-doped biochar; The activated sludge is domesticated activated sludge; the microorganisms in the activated sludge include short-range nitrifying bacteria and denitrifying bacteria; The mass ratio of the activated sludge, the Chlorella acclimated with nitrogen-containing wastewater and the magnetic nitrogen-doped biochar is (2-4):0.01:(1-5); The magnetic nitrogen-doped biochar includes porous carbon and N and magnetic Fe species doped in the porous carbon.

2. The bacteria-algae symbiotic system according to claim 1, characterized in that: The mass content of the C element in the magnetic nitrogen-doped biochar is 60-75%, the mass content of the N element is 1-5%, the mass content of the Fe element is 5-15%, and the mass content of the O element is 15-20%. The specific surface area of ​​the magnetic nitrogen-doped biochar is 500-600m 2 / g.

3. Use of the bacteria-algae symbiotic system according to any one of claims 1 to 2 in treating nitrogen-containing wastewater.

4. A denitrification device, characterized in that: It comprises a bacteria-algae symbiotic reactor (3) and an automatic detection-control device; the bacteria-algae symbiotic reactor (3) is constructed with the bacteria-algae symbiotic system according to any one of claims 1 to 2; The automatic detection and control device comprises a water inlet control switch (301), a dissolved oxygen sensor (302), a CO2 detector (303), a pH sensor, a temperature sensor, an online water quality detector (305), a motor (306), a central control unit (307), a pH metering pump, a COD supplementary pump, a heating plate (309), a stirring paddle (310), an illumination unit (311), a water outlet control switch (312), and a mud discharge control switch (313); The detection heads of the dissolved oxygen sensor (302), CO2 detector (303), redox potential detector, pH value sensor, temperature sensor and water quality online detector (305) are placed in the bacteria-algae symbiotic reactor (3); the heating plate (309) is located at the bottom of the bacteria-algae symbiotic reactor (3); and the illumination unit (311) is installed on the outer wall of the bacteria-algae symbiotic reactor (3); The stirring paddle (310) is located in the bacteria-algae symbiotic reactor (3), and the stirring paddle (310) is controlled by a motor (306); The pH metering pump is used to add a pH regulator to the bacteria-algae symbiotic reactor (3); and the COD supplementing pump is used to supplement a carbon source to the bacteria-algae symbiotic reactor (3).

5. The denitrification equipment according to claim 4, characterized in that It also includes an algae separator (4) and an algae collector (43); the water inlet of the algae separator (4) is connected to the water outlet of the bacteria-algae symbiotic reactor (3), and the algae outlet of the algae separator (4) is connected to the inlet of the algae collector (43); an ultrasonic module (41) is provided inside the algae separator (4), and an external magnetic field (42) is provided outside the algae separator (4).

6. The denitrification equipment according to claim 4 or 5, characterized in that: It also includes a filtering device (1) and a sedimentation tank (2); the water outlet of the filtering device (1) is connected to the water inlet of the sedimentation tank (2), and the water outlet of the sedimentation tank (2) is connected to the water inlet of the bacteria-algae symbiotic reactor (3).

7. A method for treating nitrogen-containing wastewater, characterized in that: The method of treating nitrogen-containing wastewater using the denitrification equipment according to any one of claims 4 to 6 comprises the following steps: The nitrogen-containing wastewater is introduced into the bacteria-algae symbiotic reactor (3) for short-range nitrification and denitrification. The light-dark ratio in the bacteria-algae symbiotic reactor (3) is adjusted to 1:0.2-1 by an automatic detection-control device, and the CO2 compensation point is adjusted to 30-60 μL / L, so that the ratio of the net photosynthetic rate of algae to the respiration rate of microorganisms under light conditions is 0.5-1, and a low dissolved oxygen environment is spontaneously formed, wherein the low dissolved oxygen environment refers to a dissolved oxygen content of 0.4-1.2 mg / L.

8. The processing method according to claim 7, characterized in that: The following measures are taken to control the spontaneous formation of dissolved oxygen environment in the bacteria-algae symbiotic reactor (3): Under the illumination condition, an automatic detection-control device is used for coordinated control. When the CO2 compensation point drops to 5-28 μL / L, a COD supplement pump is started to supplement 5-10 mg / L of carbon source on the basis of the original carbon source to promote microbial respiration. When the CO2 compensation point rises to 60-65 μL / L, the illumination unit (311) is used to increase the light intensity by 5-20% on the basis of the original light to promote the photosynthesis of Chlorella vulgaris. Under light conditions, oxygen is produced to carry out short-term nitrification reaction. When the water quality online detector monitors NO2 - -N, NO3 - When the -N concentration meets the nitrite nitrogen accumulation rate of 75-85%, stop the light and avoid the light; under the light-avoiding condition, the aerobic-anaerobic short-range denitrification reaction is carried out. When monitoring NO2 - -N concentration is 2 to 5 mg / L, the illumination unit (311) is started, and the illumination intensity is adjusted to 1500 to 5000 lux; Under illumination conditions, the dissolved oxygen is regulated by an automatic detection-regulation device, and when the dissolved oxygen rises to 1.2 to 1.25 mg / L, the illumination unit (311) is controlled to reduce the illumination intensity by 5 to 15%; When the dissolved oxygen drops to 0.35-0.4 mg / L, the illumination unit (311) is controlled to increase the illumination intensity by 10-15%.

9. The processing method according to claim 7 or 8, characterized in that: The operating conditions of the bacteria-algae symbiotic reactor (3) include: water inlet 3-5 minutes, stirring 700-1400 minutes, sedimentation 15-30 minutes, water outlet 3-5 minutes, hydraulic retention time 12-24 hours, sludge age 5-7 days, stirring speed 50-150 r / min, light exposure during stirring for 2-4 hours, light avoidance for 0.5-2 hours, light intensity 1500-3000 lux, temperature 25-30°C, and pH value 7.5-8.

5.

10. The processing method according to claim 7 or 8, characterized in that: After the short-range nitrification and denitrification is completed, the method further comprises recovering the magnetic nitrogen-doped biochar and Chlorella in the effluent of the bacteria-algae symbiotic reactor (3).

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