Municipal sewage treatment method and system integrating resource and energy recovery and sewage regeneration

Abstract

The invention relates to a municipal sewage treatment method and system integrating resource and energy recovery and sewage regeneration. The municipal sewage treatment method comprises the following steps: adding ferric chloride into raw water to be treated, mixing the raw water to be treated with the ferric chloride, and then performing coagulation and precipitation to obtain supernate and concentrated chemical sludge; performing denitrification on the supernate through a moving bed bio-membrane reactor, and further performing denitrification on effluent of the moving bed bio-membrane reactor through a vibrating membrane bioreactor to obtain reclaimed water; carrying out hydrolytic acidification on the concentrated chemical sludge to obtain hydrolytic acidification liquid; performing electrodialysis treatment on the hydrolytic acidification liquid to obtain fresh water and concentrated water rich in phosphate; and treating the fresh water through an anaerobic membrane bioreactor to generate methane and recovering the methane. The municipal sewage treatment method and system provided by the invention can synchronously and efficiently realize energy resource recovery and sewage regeneration.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment and resource utilization, and particularly relates to a municipal sewage treatment method and system for collecting resources, energy recovery and sewage regeneration. BACKGROUND

[0002] Under the background of the "double carbon" strategy, the sewage treatment industry is facing the urgent need for profound changes from simply pollutant reduction to "resourceization, energyization and low carbonization". There is a wealth of energy and resources in municipal sewage. However, the traditional municipal sewage treatment method (such as AAO-residual sludge anaerobic digestion) has the problems of high energy consumption and insufficient energy and resource recovery. On the one hand, in order to achieve biological denitrification and phosphorus removal, the organic matter in the sewage is removed as pollutants through aerobic biological treatment instead of being recovered as energy, resulting in the waste of potential energy; on the other hand, the long method line leads to insufficient recovery of phosphorus resources. Although the "carbon-nitrogen split treatment" strategy has been proposed to preferentially convert carbon sources into energy for recovery, and then to treat the remaining low-carbon-nitrogen ratio sewage based on anaerobic ammonia oxidation for autotrophic denitrification. However, this strategy has the problems of low methane yield, unstable denitrification effect of anaerobic ammonia oxidation, and ineffective recovery of phosphorus resources in the sewage. In the above background, in view of the current problems of high energy consumption, high carbon emission and low resource recovery in sewage treatment, it is urgent to break through the traditional sewage treatment method mode and build a new type of sewage treatment method that can simultaneously and efficiently achieve energy and resource recovery and sewage regeneration. SUMMARY

[0003] The purpose of the present application is to provide a new municipal sewage treatment method and system that can simultaneously and efficiently achieve energy and resource recovery and sewage regeneration.

[0004] Specifically, the present application is realized by the following technical solutions: The present application provides a municipal sewage treatment method, comprising: adding ferric chloride to raw water to be treated, mixing the raw water to be treated with the ferric chloride, and then performing coagulation and sedimentation to obtain supernatant and concentrated chemical sludge; making the supernatant pass through a moving bed biofilm reactor for denitrification, and making the effluent of the moving bed biofilm reactor pass through a vibrating membrane bioreactor for further denitrification to obtain regenerated water; hydrolyzing and acidifying the concentrated chemical sludge to obtain a hydrolysis and acidification liquid; electrodialysis treating the hydrolysis and acidification liquid to obtain fresh water and concentrated water rich in phosphate; making the fresh water pass through an anaerobic membrane bioreactor to produce methane and recover the methane.

[0005] Optionally, the concentration of the ferric chloride is 0.4-0.6 mmol / L.

[0006] Optionally, when the total COD concentration of the raw water is 200-300 mg / L, the concentration of the ferric chloride is 0.4 mmol / L; when the total COD concentration of the raw water is 300-400 mg / L, the concentration of the ferric chloride is 0.5 mmol / L; when the total COD concentration of the raw water is > 400 mg / L, the concentration of the ferric chloride is 0.6 mmol / L.

[0007] Optionally, 1-5% of the concentrated chemical sludge is refluxed for coagulation and sedimentation again.

[0008] Optionally, during the denitrification of the supernatant by the moving bed biofilm reactor, the mixed liquor in the moving bed biofilm reactor is intermittently aerated so that the dissolved oxygen concentration of the mixed liquor is < 0.1 mg / L and the oxidation-reduction potential (ORP) is <-50 mV.

[0009] Optionally, during the hydrolysis acidification of the concentrated chemical sludge, a potential of +0.6-1.2 V is applied to promote the release of phosphorus.

[0010] Optionally, in the electrodialysis treatment, a voltage of 0.8-1.2 V is applied to each pair of membranes of the electrodialysis device.

[0011] Optionally, the anaerobic membrane bioreactor is filled with conductive carriers and is provided with conductive electrodes, and a voltage of 0.3-0.6 V is applied to the conductive electrodes.

[0012] Optionally, the conductive carriers are carbon felt, carbon cloth or carbon brush, and the filling rate of the conductive carriers is 20-30%.

[0013] In one aspect, the present application provides a municipal wastewater treatment system, comprising: a coagulation and concentration tank 10, a moving bed biofilm reactor 20, a vibrating membrane bioreactor 30, a hydrolysis acidification tank 40, an electrodialysis device 50, and an anaerobic membrane bioreactor 60; the coagulation and concentration tank 10 is connected to the moving bed biofilm reactor 20 by a pipeline; the moving bed biofilm reactor 20 is connected to the vibrating membrane bioreactor 30 by a pipeline; the coagulation and concentration tank 10 is connected to the hydrolysis acidification tank 40 by a pipeline; the hydrolysis acidification tank 40 is connected to the electrodialysis device 50 by a pipeline; and the electrodialysis device 50 is connected to the anaerobic membrane bioreactor 60 by a pipeline.

[0014] The municipal wastewater treatment method and system provided by the present specification can simultaneously and efficiently realize energy resource recovery and wastewater regeneration. BRIEF DESCRIPTION OF DRAWINGS

[0015] The accompanying drawings, which are included to provide a further understanding of the present description and constitute a part of the present description, illustrate the preferred embodiments of the present description and serve to explain the present description together with the specification. In the drawings: Figure 1 The structural schematic diagram of the municipal sewage treatment system provided in the present description is shown. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical scheme and advantages of the present description clearer, the technical scheme of the present description will be described in detail below in connection with the specific embodiments of the present description and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present description, but not all the embodiments. Based on the embodiments in the present description, all the other embodiments obtained by those skilled in the art without any creative work under the premise that the present description falls within the scope of protection of the present description.

[0017] The technical scheme provided by each embodiment of the present description will be described in detail below in connection with the drawings.

[0018] The present application aims to provide a new municipal sewage treatment method and system which can realize energy resource recovery and sewage regeneration synchronously and efficiently.

[0019] The operation process of the municipal sewage treatment method provided in the present description comprises the following steps: Chlorinated iron is added to the raw water to be treated, the raw water to be treated is mixed with the chlorinated iron, and then coagulation and sedimentation are performed to obtain supernatant and concentrated chemical sludge; The supernatant is subjected to denitrification by a moving bed biofilm reactor (MBBR), and the effluent of the MBBR is further subjected to denitrification by a vibrating membrane bioreactor (VMBR) to obtain regenerated water; The concentrated chemical sludge is subjected to hydrolysis acidification to obtain a hydrolysis acidification liquid; The hydrolysis acidification liquid is subjected to electrodialysis treatment to obtain fresh water and concentrated water rich in phosphate; The fresh water is subjected to AnMBR treatment to produce methane, and the methane is recovered.

[0020] As Figure 1As shown, the municipal wastewater treatment system provided by the present disclosure comprises: a coagulation concentration tank 10, a moving bed biofilm reactor 20 (MBBR), a vibrating membrane bio-reactor 30 (VMBR), a hydrolysis acidification tank 40, an electrodialysis device 50, and an anaerobic membrane bioreactor 60 (AnMBR); the coagulation concentration tank 10 is connected to the moving bed biofilm reactor 20 through a pipeline; the moving bed biofilm reactor 20 is connected to the vibrating membrane bio-reactor 30 through a pipeline; the coagulation concentration tank 10 is connected to the hydrolysis acidification tank 40 through a pipeline; the hydrolysis acidification tank 40 is connected to the electrodialysis device 50 through a pipeline; and the electrodialysis device 50 is connected to the anaerobic membrane bioreactor 60 through a pipeline.

[0021] The coagulation concentration tank 10 mainly comprises a raw water pump, a dosing system 102, a pipeline mixer 101, a coagulation tank 103, and an inclined tube sedimentation tank 104. The raw water pump pumps municipal wastewater into the pipeline mixer as raw water to be treated at a set flow rate. The dosing system comprises a dosing barrel and a diaphragm pump. The dosing barrel is configured with a high-concentration (5-10%) ferric chloride solution, and the diaphragm pump pumps the ferric chloride into the pipeline mixer to mix with the raw water at a set flow rate. The pipeline mixer is a common type on the market, which is used to quickly mix the ferric chloride and the raw water, and then enters the coagulation tank. The coagulation tank comprises a central water inlet pipe, a stirring device, and a peripheral overflow port. The pipeline mixer is connected to the central water inlet pipe, and the quickly mixed water flows through the central water inlet pipe into the bottom of the coagulation tank. The flocculation formed by the bridging of ferric chloride and organic matter rises with the water flow, and enters the inclined tube sedimentation tank from the overflow port. The inclined tube sedimentation tank comprises a water inlet, a water outlet, an inclined tube, a sludge discharge port, a peripheral overflow weir, and a bottom sludge hopper. The mixed liquid from the coagulation tank overflow enters from the bottom of the sedimentation tank. After separation by the inclined tube sedimentation tank, the flocculation settles into the bottom sludge hopper to accumulate and form concentrated chemical sludge rich in carbon, phosphorus, and iron. The concentrated chemical sludge is pumped from the sludge discharge port to the hydrolysis acidification tank by a sludge pump. The supernatant flows out from the periphery of the tank along the peripheral overflow weir, and is conveyed to the MBBR tank by a water inlet pump.

[0022] The MBBR 20 mainly comprises an MBBR tank, suspended carriers, a stirring motor, a water system and an air system. The MBBR tank is provided with a water inlet and a water outlet. The water inlet is arranged at the bottom of the tank, and the water outlet is arranged at the top of the tank. The MBBR tank contains suspended fillers, which are common types on the market (for example, K3 fillers), and the filling rate is 30-50%. The MBBR tank also contains suspended sludge, and the sludge concentration is 4000-5000 mg / L. The main function is anoxic or anaerobic biology, and the main functional microorganism is iron-trophic denitrifying bacteria (for example, anaerobic iron ammonia oxidizing bacteria), which can utilize the Fe(III) accumulated in the water inlet and the MBBR tank to realize ammonia oxidation. The stirring motor is arranged at the center of the tank to stir the carriers and the mixed liquid. The water system is connected with the water inlet and the water outlet of the MBBR tank, and comprises a water inlet pipe, a water outlet pipe, a backflow pipe and valves and instruments. The backflow pipe is connected with the VMBR backflow port and the MBBR water inlet, and backflow is realized through a backflow pump, which is beneficial to the intensification of sludge and water mixing and sludge circulation. The air system comprises a fan, an air inlet pipe, a microporous aeration disc and valves and instruments. The air inlet pipe is provided with a gas flow meter and an electromagnetic valve. The fan is connected with the microporous aeration disc through the air inlet pipe, and is used for providing oxygen for the MBBR tank. The aeration flow rate is such that the dissolved oxygen (DO) concentration of the MBBR mixed liquid is less than 0.1 mg / L, and the oxidation-reduction potential (ORP) of the MBBR mixed liquid is less than -50 mV.

[0023] The VMBR 30 mainly comprises a VMBR tank, a membrane assembly, a water system, an air system and a liquid level system. The VMBR tank is used for realizing further oxidation and removal of ammonia in the MBBR effluent and sludge retention. The water inlet is arranged at the middle of the tank to receive the effluent from the MBBR. The backflow port is arranged at the bottom of the tank and connected with the MBBR backflow pipe for sludge backflow. The liquid level system is installed in the tank to control the start of the VMBR water production pump. The perforated pipe is installed at the bottom of the tank for aeration and oxygen supply and VMBR membrane fouling control. In order to ensure sufficient aerobic ammonia oxidation effect, the aeration amount needs to make the DO concentration of the VMBR mixed liquid be within 2-5 mg / L.

[0024] The hydrolysis acidification tank 40 mainly comprises a water inlet, a water outlet and a stirring device. The concentrated chemical sludge is subjected to hydrolysis, iron reduction and release of phosphate in an acidic environment in the hydrolysis acidification tank. The water inlet receives the concentrated chemical sludge from the front-end inclined tube sedimentation tank and the landfill leachate for co-digestion. After the concentrated chemical sludge and the landfill leachate are mixed, hydrolysis acidification is carried out in the lower part of the tank, and the supernatant flows into the electrodialysis for phosphorus separation and recovery. The submerged stirrer is installed at the bottom of the tank for mixing of the concentrated chemical sludge, the landfill leachate and the hydrolysis acidification bacteria.

[0025] The electrodialysis unit 50 mainly includes a security filter, an electrodialysis assembly (including a pair of anode and cathode chambers, multiple pairs of anion and cation exchange membranes, multiple pairs of dilute water chambers and concentrated water chambers), an adjustable power supply, concentrated water chambers, dilute water chambers and a diaphragm pump. The security filter is a common type on the market, configured with a hydrophilic filter core, with a filter pore size of 30-60 μm, and functions to remove particulate matter in the supernatant of the hydrolysis acidification tank to prevent the electrodialysis assembly from being blocked. The chamber liquid of the electrodialysis assembly is an acidic sodium sulfate solution, which is driven by the diaphragm pump to circulate in the anode and cathode chambers to provide the required electric field conditions (the adjustable power supply applies a voltage of 0.8-1.2 V to each pair of ion exchange membranes) while avoiding electrolytic water. The dilute water chamber receives the supernatant of the hydrolysis acidification tank, and the supernatant filtered by the security filter is pumped into the dilute chamber of the electrodialysis assembly by the diaphragm pump, and the phosphate therein migrates to the concentrated water chamber under the electric field formed by the adjustable power supply. Part of the treated dilute water is pumped into the AnMBR, and the other part is circulated back to the dilute water chamber. The concentrated chamber of the electrodialysis assembly uses the hydrolysis acidification liquid as the working liquid and receives the phosphate from the dilute water chamber. The diaphragm pump drives the circulation of the concentrated water in the concentrated water chamber, and finally obtains concentrated water rich in high-concentration phosphate, which can be used to form a phosphorus product in the subsequent process.

[0026] The AnMBR 60 mainly includes a water inlet, a membrane assembly, a water outlet, an air outlet, a water production pump and a vacuum circulation pump. The water inlet receives the dilute water outlet of the electrodialysis. The vacuum circulation pump sucks the headspace gas of the AnMBR, and then blows it out from the gas distribution pipe at the bottom of the membrane assembly, so that the biogas sweeps the surface of the membrane assembly to achieve membrane fouling control. The organic carbon in the dilute water chamber of the electrodialysis is converted into biogas in the AnMBR, which is collected through the air outlet and can be used to generate electricity to recover energy. The water produced by the membrane assembly is pumped into the water inlet pipeline of the MBBR by the water production pump, mixed with the supernatant of the inclined tube sedimentation tank, and then enters the MBBR for denitrification.

[0027] The municipal sewage treatment method provided in the specification adopts ferric chloride for chemical strengthening of the front end on the energy and resource recovery side; then, in view of the characteristics of low hydrolysis efficiency, insufficient phosphorus release and slow methanogenesis of the obtained high-solid chemical sludge, a combined hydrolysis-acidification-electrodialysis-anaerobic membrane bioreactor (AnMBR) is used as the core of energy and resource recovery. The hydrolysis-acidification section releases the solid-phase phosphorus in the chemical sludge to the liquid phase through hydrolysis of macromolecular organic matter and acid production. The electrodialysis realizes the recovery of phosphorus in the sewage by selectively enriching free phosphate to concentrated water. The AnMBR realizes the decoupling of sludge retention time and hydraulic retention time by virtue of membrane separation technology, thereby solving the problems of microbial loss, low system processing efficiency and unsatisfactory methanogenesis rate, and providing reliable energy output for the entire system. On the sewage regeneration side, multi-path coupled denitrification technology is constructed around low carbon-nitrogen ratio sewage. In view of the problems of unstable operation and difficult control of the anaerobic ammonia oxidation technology, an iron cycle denitrification system capable of self-driving and continuously maintaining high reaction activity is constructed by coupling the anaerobic iron-ammonia oxidation and ferrous chemical oxidation processes, thereby getting rid of the dependence on the anaerobic ammonia oxidation denitrification pathway. At the same time, the remaining iron ions after chemical strengthening of the front end are used as a supplement, avoiding the introduction of additional reagents; the intermittent aeration is used to realize the efficient recycling of iron, thereby greatly reducing the energy consumption demand of aeration, and providing a solid foundation for the sustainability and economy of the core method.

[0028] Example 1, municipal sewage treatment Ferric chloride is added to the raw water to be treated, the raw water to be treated is mixed with the ferric chloride, and then coagulation and sedimentation are performed to obtain supernatant and concentrated chemical sludge.

[0029] The wastewater after the primary sedimentation tank of the sewage plant is used as the influent of this method. The raw water and high-concentration (5%-10%) ferric chloride solution are mixed at a certain flow ratio (the flow ratio of raw water to high-concentration ferric chloride solution is (650-1000):1, corresponding to the ferric chloride dosage of 0.6-0.4 mmol / L. The mixing ratio of high-concentration ferric chloride solution to raw water is adjusted in time according to the influent COD concentration, when the total COD concentration is 200-300 mg / L, the ferric chloride concentration after mixing is 0.4 mmol / L; when the total COD concentration is 300-400 mg / L, the ferric chloride concentration after mixing is 0.5 mmol / L-raw water; when the total COD concentration is >400 mg / L, the ferric chloride concentration after mixing is 0.6 mmol / L) through a pipeline mixer for rapid and uniform mixing, and then enters the center inlet pipe of the coagulation tank, and forms flocculation alunite flowers through slow stirring in the tank. The suspended flocculation alunite flowers enter the bottom of the inclined tube sedimentation tank with the water flow from the overflow port, and are gravity precipitated to the sludge hopper at the bottom to form concentrated chemical sludge, which is then transported to the hydrolysis acidification tank by a sludge pump for hydrolysis acidification. The concentrated chemical sludge at the bottom of the inclined tube sedimentation tank can also be returned to the center inlet pipe of the coagulation tank by a peristaltic pump at a return ratio of 1-5%. By adding this return, the microbial flocs with high flocculation, adhesion and adsorption activity in the concentrated chemical sludge can be used to enhance the adsorption and capture of COD in the raw water, thereby reducing the dosage of ferric chloride and the resulting drug consumption and carbon emissions. The supernatant (low C / N ratio, containing <0.5 mg-P / L and <15 mg-Fe / L) produced after flocculation and precipitation is collected by the peripheral overflow weir and then transported to the MBBR by an influent pump for main stream denitrification.

[0030] The influent is municipal wastewater after coarse and fine screening. The total COD (tCOD) of the municipal wastewater raw water is 410.4±162.6 mg / L, of which the dissolved COD (sCOD) is about 93.7±23.1 mg / L; the total phosphorus (tP) is 8.0±1.6 mg / L, of which the dissolved phosphorus (sP) is about 3.0±0.7 mg / L. The ferric chloride dosage is 0.5 mmol / L-raw water. The hydraulic retention time of municipal wastewater in the coagulation tank is 60 minutes, and the retention time of concentrated chemical sludge in the inclined tube sedimentation zone is about 1.5 days. The concentration effect is shown in Table 1.

[0031] Table 1 By using chemical enhanced front-end concentration by adding ferric chloride, the redirection of various elements in the wastewater is achieved. The limited carbon and phosphorus are precisely shunted to the side stream of anaerobic digestion for methane production (energy recovery) and electrodialysis for phosphorus recovery (resource recovery), while creating stable low C / N ratio conditions for the main stream denitrification system, realizing the premise of efficient autotrophic denitrification. The municipal wastewater resource energy recovery and regeneration are organically coordinated.

[0032] The supernatant is subjected to denitrification by a moving bed biofilm reactor (MBBR), and the effluent of the MBBR is subjected to further denitrification by a vibrating membrane bio-reactor (VMBR) to obtain reclaimed water.

[0033] The supernatant with a low C / N ratio produced after precipitation is mixed with the effluent of the AnMBR and then enters from the water inlet at the bottom of the MBBR. Feammox bacteria oxidize ammonia nitrogen to nitrogen gas using Fe(III) as an electron acceptor, and Fe(III) is correspondingly reduced to Fe(II). In order to ensure the sustainable use of Fe(III) and thus achieve sustainable denitrification, the mixed liquor in the MBBR tank is intermittently aerated to re-chemically oxidize Fe(II) to Fe(III) using oxygen in the air. The MBBR needs to adjust the intermittent aeration frequency in a timely manner according to the ammonia nitrogen concentration of the influent, so as to ensure that Fe(III) can be timely reduced to Fe(II). The aeration adjustment required by the MBBR should make the dissolved oxygen (DO) concentration of the mixed liquor in the MBBR <0.1 mg / L, and the oxidation-reduction potential (ORP) of the mixed liquor in the MBBR <-50 mV.

[0034] The remaining part of the ammonia nitrogen in the effluent of the MBBR enters the VMBR, is further oxidized and removed through aerobic oxidation, and finally realizes effective removal of nitrogen to meet the discharge requirements. In order to improve the energy utilization rate, the aeration frequency of the MBBR tank is a key operating parameter, which needs to be adjusted accordingly according to the ammonia nitrogen concentration of the influent. By coupling the VMBR, the total sludge concentration in the device can be increased to more than 7000 mg / L, ensuring a higher overall reaction rate.

[0035] The characteristics of the influent water quality are: ammonia nitrogen 40-100 mg / L, carbon-nitrogen ratio 1.0-1.8. The content of Fe 3+ in the mixed influent is 5-15 mg / L.

[0036] The hydraulic retention time ratio of the MBBR to the VMBR is about 20:4. For example, the hydraulic retention time of the MBBR tank is set to 20 h, and the hydraulic retention time of the VMBR tank is 4 h. The operating conditions of the MBBR are: aeration flow rate 1 m3 / h, aeration frequency adjusted as needed, sludge retention time >40 d, and total sludge concentration 5000-10000 mg / L. The denitrification effect is shown in Table 2.

[0037] Table 2 By employing multiple pathways, including anaerobic iron ammonia oxidation coupled with ferrous chemical oxidation, deep denitrification and Fe(III) regeneration of supernatant with low carbon-to-nitrogen ratio can be achieved. This allows for the full utilization of the remaining iron ions in the supernatant as electron donors to drive autotrophic denitrification, thereby reducing the addition of external carbon sources. Furthermore, adjusting the aeration frequency can improve energy utilization, thereby reducing Category 2 and Category 3 carbon emissions.

[0038] Concentrated chemical sludge is hydrolyzed and acidified to obtain hydrolyzed acidified liquid.

[0039] The high-solids-content concentrated chemical sludge generated in step S101 is pumped to a hydrolysis acidification tank and mixed with landfill leachate at a certain flow ratio (the flow ratio of high-solids-content concentrated chemical sludge to landfill leachate is 1-2:1 (calculated by tCOD)) in the lower part of the tank for hydrolysis acidification. Landfill leachate is characterized by high dissolved organic matter concentration (tCOD > 50000 mg / L, sCOD / tCOD > 80%) and low solids content (> 85%). Introducing landfill leachate for co-digestion can rapidly establish a hydrolysis acidification bacterial community within the system, causing the particulate COD in the concentrated chemical sludge to hydrolyze into soluble COD (sCOD), which is more conducive to subsequent methane production. At the same time, the low pH environment caused by the hydrolysis acidification process can release solid phosphorus in the concentrated chemical sludge into the liquid phase, which is beneficial for subsequent recovery. In addition, landfill leachate is a global environmental problem due to its significant environmental hazards. This method can treat it simultaneously and partially convert it into energy.

[0040] Furthermore, conductive electrodes can be introduced into the hydrolysis acidification tank. The electrode materials can be carbon felt, carbon cloth, or carbon brushes, and a voltage is applied to control the bioanolyte potential to 0.6-1.2V (relative to the standard electrode potential). Conductive carbon materials such as carbon felt, carbon cloth, or carbon brushes can serve as microbial carriers, enhancing the attachment, enrichment, and retention of functional microorganisms. Electro-acclimation can increase the relative and absolute abundance of electroactive bacteria on the bioanolyte, enhancing the dissimilar iron reduction process and promoting the conversion of Fe(III) to Fe(II), thereby obtaining Fe(II)-P compounds with better solubility. Electro-acclimation can also increase the absolute abundance and metabolic activity of non-electroactive bacteria on the bioanolyte, increasing the activity of hydrolytic enzymes and enhancing acidification, promoting the dissolution of solid-phase P. Introducing electrodes into the hydrolysis acidification tank with a relatively low voltage saves energy and avoids the adverse effects of excessively high potentials on the microorganisms in the hydrolysis acidification zone. By introducing electrodes and energizing the hydrolysis acidification tank to enhance phosphorus release, the amount of landfill leachate required to maintain the hydrolysis acidification effect can be reduced, thereby enhancing the system's resilience and stability.

[0041] The water quality characteristics of the concentrated chemical sludge were tCOD 19047.6 ± 5709.2 mg / L and tP 508.1 ± 149.6 mg / L. The water quality characteristics of the landfill leachate were tCOD 76946.0 ± 1311.0 mg / L and tP 500.4 ± 34.9 mg / L. The hydraulic retention time was 4.6 days. The results of the hydrolysis acidification are shown in Table 3.

[0042] Table 3 By using the hydrolysis acidification treatment of concentrated chemical sludge with electrically enhanced, the release of phosphorus can be enhanced with low energy consumption, while the amount of co-digestion substrate added is saved, the competition of other dissolved components in the hydrolysis acidification liquid with phosphate in electrodialysis is reduced, and the efficiency of recovering phosphorus from the concentrated water of electrodialysis is improved.

[0043] The hydrolysis acidification liquid is treated by electrodialysis to obtain fresh water and concentrated water rich in phosphate.

[0044] The phosphorus-rich hydrolysis acidification liquid is pumped into the fresh water chamber of the electrodialysis, and the phosphate in it is further enriched in the concentrated water chamber under the action of the electric field after circulating to the fresh water chamber, so that concentrated water with higher phosphorus concentration is obtained, so as to reach the required phosphate concentration of traditional phosphorus recovery methods such as precipitation method, so as to recover phosphorus elements. The phosphorus element concentration in the fresh water chamber effluent can be reduced to below 5 mg / L, and the phosphorus element concentration in the concentrated water chamber effluent can be increased to about 500 mg / L, with a recovery rate of more than 95%.

[0045] The hydrolysis acidification liquid is taken as the treatment object, and the electrodialysis assembly composed of 80 pairs of cation and anion exchange membranes is taken as the treatment unit. A constant voltage of 80 V is applied to the positive and negative electrodes. The residence time of the hydrolysis acidification liquid in the assembly is about 8.7 min, and the cross-flow speed is about 18.7 cm / s. The results of electrodialysis are shown in Table 4.

[0046] Table 4 The fresh water is subjected to AnMBR treatment to produce methane and recover methane.

[0047] The fresh water is pumped into the AnMBR to undergo further hydrolysis acidification, acetic acidification, organic matter mineralization and methane production. The AnMBR membrane effluent is mixed with the supernatant of the inclined tube sedimentation tank and then enters the MBBR tank for deep denitrification.

[0048] To strengthen the anaerobic methane production, conductive carriers such as granular activated carbon (GAC) can be added to the AnMBR tank. The filling ratio of the conductive carrier is 20-30% of the capacity of the AnMBR tank. The conductive carrier not only serves as a microbial carrier to enrich methanogenic bacteria, but also promotes the direct interspecies electron transfer (DIET) process between syntrophic bacteria and methanogenic bacteria, changes the methanogenesis from indirect hydrogen mediation to direct electron transfer, accelerates the degradation of volatile fatty acids (VFAs), effectively maintains the activity of methanogenic archaea, and alleviates the risk of acid inhibition.

[0049] Conductive electrodes can also be introduced into the AnMBR. The electrode material can be conductive carbon material such as carbon felt, carbon cloth or carbon brush. The conductive electrode can serve as a microbial carrier to enrich functional bacteria. The anode enriches hydrolytic acidification bacteria, which can further pull organic matter into small molecules, promote the hydrolysis and acidification of soluble COD, and is conducive to acetate-type methanogenesis. At the same time, the electrons generated by the degradation of organic matter can be transferred to the cathode through an external circuit. The cathode enriches methanogenic bacteria, which can use the electrons transferred through the external circuit for hydrogen-type methanogenesis. The comprehensive effect is to accelerate the mineralization of organic matter and the conversion to methane, and to comprehensively improve the methanogenic efficiency and impact load capacity of the system. The voltage applied by the conductive electrode is very small, ranging from 0.3 to 0.6 V. Not only does it require low energy consumption, but it also avoids the risk of high current caused by applying higher voltage due to the high iron content of concentrated chemical sludge, which can adversely affect the microorganisms in the anaerobic zone.

[0050] The fresh water obtained after electrodialysis is taken as the treatment object, and the AnMBR with conductive carrier of granular activated carbon for enhanced production is taken as the treatment unit. The organic load (OLR) of the AnMBR is 1.2 kg-COD / m 3 / d, and the HRT is 10 d.

[0051] After the start-up is completed, the methane production gradually increases and is affected by the environmental temperature. When the temperature is 15-20℃, the methane conversion rate is 0.14-0.175 L (standard conditions) / g-COD influent (i.e. the COD equivalent of the generated methane accounts for 40%-50% of the influent COD); when the temperature is 25-30℃, the methane conversion rate reaches 0.210-0.245 L (standard conditions) / g-COD influent (i.e. the COD equivalent of the generated methane accounts for 60%-70% of the influent COD).

[0052] The AnMBR with conductive carrier / electrical enhancement can be used to treat the fresh water after electrodialysis. The interspecies electron transfer / anode and cathode enrichment of different functional microorganisms can accelerate the mineralization of organic matter and the conversion to methane, comprehensively improve the methanogenic efficiency and impact load capacity of the system, and ultimately achieve efficient energy recovery of municipal wastewater.

[0053] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, should be covered within the protection scope of the present application.

Claims

1. A method for municipal sewage treatment, comprising: adding ferric chloride to raw water to be treated, mixing the raw water to be treated with the ferric chloride, and then coagulating and precipitating to obtain supernatant and concentrated chemical sludge; subjecting the supernatant to denitrification in a moving bed biofilm reactor, and further subjecting effluent from the moving bed biofilm reactor to denitrification in a vibrating membrane bioreactor to obtain regenerated water; subjecting the concentrated chemical sludge to hydrolysis acidification to obtain a hydrolysis acidification liquid; subjecting the hydrolysis acidification liquid to electrodialysis treatment to obtain fresh water and concentrated water rich in phosphate; and subjecting the fresh water to anaerobic membrane bioreactor treatment to produce and recover methane.

2. The method of claim 1, wherein, The concentration of the ferric chloride is 0.6-0.4 mmol / L.

3. The method of claim 2, wherein, When the total COD concentration of the raw water is 200-300 mg / L, the concentration of the ferric chloride is 0.4 mmol / L; when the total COD concentration of the raw water is 300-400 mg / L, the concentration of the ferric chloride is 0.5 mmol / L; and when the total COD concentration of the raw water is >400 mg / L, the concentration of the ferric chloride is 0.6 mmol / L.

4. The method of claim 1, wherein, 1-5% of the concentrated chemical sludge is recirculated for coagulation and precipitation again.

5. The method of claim 1, wherein, During the denitrification of the supernatant in the moving bed biofilm reactor, the mixed liquor in the moving bed biofilm reactor is intermittently aerated so that the dissolved oxygen concentration of the mixed liquor is <0.1 mg / L and the oxidation-reduction potential (ORP) is <-50 mV.

6. The method of claim 1, wherein, During the hydrolysis acidification of the concentrated chemical sludge, a potential of +0.6-1.2 V is applied to promote the release of phosphorus.

7. The method of claim 1, wherein, In the electrodialysis treatment, a voltage of 0.8-1.2 V is applied to each pair of membranes of an electrodialysis device.

8. The method of claim 1, wherein, The anaerobic membrane bioreactor is filled with a conductive carrier and is provided with a conductive electrode, and a voltage of 0.3-0.6 V is applied to the conductive electrode.

9. The method of claim 8, wherein, The conductive carrier is carbon felt, carbon cloth or carbon brush, and the filling rate of the conductive carrier is 20-30%.

10. A municipal sewage treatment system comprising: A coagulation and concentration tank (10), a moving bed biofilm reactor (20), a vibrating membrane bioreactor (30), a hydrolysis acidification tank (40), an electrodialysis device (50), and an anaerobic membrane bioreactor (60); the coagulation and concentration tank (10) is connected to the moving bed biofilm reactor (20) by a pipeline; the moving bed biofilm reactor (20) is connected to the vibrating membrane bioreactor (30) by a pipeline; the coagulation and concentration tank (10) is connected to the hydrolysis acidification tank (40) by a pipeline; the hydrolysis acidification tank (40) is connected to the electrodialysis device (50) by a pipeline; and the electrodialysis device (50) is connected to the anaerobic membrane bioreactor (60) by a pipeline.

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