Flowing capacitive deionization system and method for selectively recovering carbon, nitrogen and phosphorus in alkaline fermentation liquor

Abstract

The invention provides a flowing capacitive deionization system and method for selectively recovering carbon, nitrogen and phosphorus in alkaline fermentation broth, and relates to the field of alkaline fermentation broth treatment.The flowing capacitive deionization system comprises a first collector plate, a first anion exchange membrane, a second anion exchange membrane, a cation exchange membrane and a second collector plate which are sequentially distributed in parallel from left to right; the area between the first collector plate and the second anion exchange membrane is an anode flow electrode chamber, the area between the cation exchange membrane and the second collector plate is a cathode flow electrode chamber, and the area between the second anion exchange membrane and the first anion exchange membrane is an acid liquid membrane chamber; through the innovative structure that the acid liquid membrane chamber is clamped by the two membranes, efficient selective separation and synchronous recycling of carbon, nitrogen and phosphorus in the sludge fermentation liquid are achieved for the first time, no chemical additive is added in the whole process, and an industrialized technical path is provided for solving the contradiction between carbon source shortage and nitrogen and phosphorus pollution of a sewage plant.

Description

Technical Field

[0001] This invention relates to the field of alkaline fermentation broth treatment technology, and in particular to a flow capacitor deionization system and method for the selective recovery of carbon, nitrogen and phosphorus from alkaline fermentation broth. Background Technology

[0002] Alkaline anaerobic fermentation technology for activated sludge has become a mainstream way for wastewater treatment plants to supplement carbon sources because it can convert sludge into volatile fatty acids (VFA). However, in addition to the target product VFA, the fermentation broth still contains more than 60% dissolved organic matter (DOM), ammonia nitrogen and phosphate. If it is directly reused, it will not only cause the COD of the effluent to exceed the standard, but also lead to the waste of nitrogen and phosphorus resources and potential secondary pollution. Therefore, how to recover VFA with high purity and recover nitrogen and phosphorus at the same time has become the core bottleneck of sludge resource utilization. For VFA separation, the existing technology mainly adopts the layered double hydroxide (LDH) selective adsorption method. This method uses Mg-Al-LDH material to adsorb VFA at a specific pH, and then recovers it by acidification and desorption. However, due to the insufficient selectivity of the material for acetic acid and propionic acid, the VFA recovery rate is only 65%-75%. At the same time, ammonia nitrogen and phosphate cannot be recovered simultaneously, and LDH regeneration requires strong acid washing, which brings the risk of secondary pollution. For nitrogen and phosphorus recovery, the magnesium salt precipitation method uses MgCl2 to form struvite precipitate, achieving simultaneous recovery of nitrogen and phosphorus. However, the precipitation process results in a 30%-40% loss of VFA due to the co-precipitation effect, and excess Mg... 2+ The introduction of [the substance] increases the ion load in the effluent, increases the cost of reagent input, and further weakens the economic efficiency of the process. Furthermore, flow electrode capacitive deionization (FCDI) technology utilizes an electric field to drive ion migration, which can enrich cations and anions, but it is less effective for anions of the same charge (VFA, PO4). 3- The lack of selectivity of DOM and the large molecular DOM easily clog the anion exchange membrane, with flux decay exceeding 50% within 24 hours, making it impossible to achieve directional separation of VFA and phosphorus, resulting in poor device stability. In summary, existing technologies have failed to achieve both highly selective separation of VFA and efficient recovery of nitrogen and phosphorus without the addition of chemicals. There is an urgent need to develop a new process that is highly integrated, selective, and environmentally friendly. Therefore, this invention proposes a flow capacitor deionization system and method for the selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth to solve the problems existing in the prior art. Summary of the Invention

[0003] To address the aforementioned problems, this invention proposes a flow capacitive deionization system and method for the selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth. This flow capacitive deionization system for the selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth achieves, for the first time, highly efficient selective separation and simultaneous resource recovery of carbon, nitrogen, and phosphorus in sludge fermentation broth through an innovative structure of a double-membrane-sandwiched acidic liquid membrane chamber. The entire process is carried out without the addition of chemical additives, providing an industrially feasible technical path for solving the contradiction between "carbon source shortage and nitrogen and phosphorus pollution" in wastewater treatment plants.

[0004] To achieve the objectives of this invention, the following technical solution is provided: a flow capacitor deionization system for the selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth, comprising, from left to right, a first current collector, a first anion exchange membrane, a second anion exchange membrane, a cation exchange membrane, and a second current collector, arranged in parallel. The region between the first current collector and the second anion exchange membrane is the anode flow electrode chamber, and the region between the cation exchange membrane and the second current collector is the cathode flow electrode chamber. The region between the second anion exchange membrane and the first anion exchange membrane is an acidic liquid membrane chamber, the region between the first anion exchange membrane and the cation exchange membrane is a solution chamber, and the flowing electrode liquid in the anode flowing electrode chamber and the cathode flowing electrode chamber is activated carbon slurry. The inlet of the solution chamber is connected to an alkaline fermentation broth storage chamber. The anode flow electrode chamber is connected to an anode electrode liquid storage chamber via a circulation pump. The cathode flow electrode chamber is connected to a cathode electrode liquid storage chamber via a circulation pump. The acidic liquid membrane chamber is connected to an acidic solution storage chamber via a circulation pump.

[0005] A further improvement is that the first anion exchange membrane allows anions with a molecular weight less than 1 kDa to pass through and retains dissolved organic matter with a molecular weight greater than 1 kDa, while the second anion exchange membrane allows negatively charged ions to pass through.

[0006] A further improvement is that the acidic solution in the acidic solution storage chamber maintains the pH environment in the acidic liquid membrane chamber between 2 and 4.7.

[0007] A further improvement is that the first current collector is connected to the positive terminal of the power supply, the second current collector is connected to the negative terminal of the power supply, and the acidic liquid membrane chamber is made of an acrylic plate.

[0008] A further improvement is that the anode electrode liquid storage chamber is connected to a phosphorus recovery tank, the cathode electrode liquid storage chamber is connected to an ammonia nitrogen recovery tank, and the outlet of the acidic liquid membrane chamber is connected to a VFA concentration tank.

[0009] A further improvement is that the flowing electrode solution is prepared by mixing carbon black powder, activated carbon, and deionized water.

[0010] The method for selectively recovering flowing carbon, nitrogen, and phosphorus from alkaline fermentation broth using the above-mentioned capacitor deionization system includes the following steps: S1. Pump alkaline fermentation broth into the solution chamber; S2. Start the circulation pump to form circulation loops between the anolyte flow electrode chamber and the anolyte liquid storage chamber, between the cathode flow electrode chamber and the cathode liquid storage chamber, and between the acidic liquid film chamber and the acidic solution storage chamber. S3. Turn on the power to allow the first and second current collectors to operate under applied voltage. S4. After a certain period of time, recover the VFA-rich concentrate from the acidic solution storage chamber, recover the phosphorus-containing concentrate from the anode electrode solution storage chamber, and recover the ammonia nitrogen concentrate from the cathode electrode solution storage chamber.

[0011] A further improvement is made in step S1, where the alkaline fermentation broth is introduced using either a single-pass or circulating water intake method until the VFA concentrate, phosphorus concentrate, and ammonia nitrogen concentrate reach a predetermined concentration. Specifically, the single-pass water intake involves the alkaline fermentation broth being pumped from the alkaline fermentation broth storage chamber into the solution chamber via a circulating pump, followed by a single deionization and discharge. Specifically, the circulating water intake involves the alkaline fermentation broth being pumped from the alkaline fermentation broth storage chamber into the solution chamber via a circulating pump, followed by deionization, and then returning to the alkaline fermentation broth storage chamber for recirculation into the solution chamber for further processing.

[0012] A further improvement is that in step S4, the VFA concentrate is recovered as a carbon source and used in the biological treatment tank of the sewage treatment plant, while nitrogen and phosphorus are further recovered and reused as resources.

[0013] The beneficial effects of this invention are as follows: Through the innovative structure of the double-membrane clamping acidic liquid membrane chamber, this invention achieves for the first time the efficient and selective separation and simultaneous resource utilization of carbon, nitrogen and phosphorus in sludge fermentation liquid, without the addition of any chemical additives throughout the process, providing an industrializable technical path for solving the contradiction between "carbon source shortage and nitrogen and phosphorus pollution" in sewage treatment plants. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of the present invention.

[0015] The components are: 1. First collector plate; 2. Anode flow electrode chamber; 3. Second anion exchange membrane; 4. Acidic liquid membrane chamber; 5. First anion exchange membrane; 6. Solution chamber; 7. Cation exchange membrane; 8. Cathode flow electrode chamber; 9. Second collector plate; 10. Alkaline fermentation broth storage chamber; 11. Anode electrode liquid storage chamber; 12. Acidic solution storage chamber; 13. Cathode electrode liquid storage chamber. Detailed Implementation

[0016] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0017] according to Figure 1 As shown in the figure, this embodiment proposes a flow capacitor deionization system for the selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth. It includes, from left to right, a first current collector 1, a second anion exchange membrane 3, a first anion exchange membrane 5, a cation exchange membrane 7, and a second current collector 9, arranged in parallel. The region between the first current collector 1 and the second anion exchange membrane 3 is the anode flow electrode chamber 2, and the region between the cation exchange membrane 7 and the second current collector 9 is the cathode flow electrode chamber 8. The region between the second anion exchange membrane 3 and the first anion exchange membrane 5 is the acidic liquid membrane chamber 4, the region between the first anion exchange membrane 5 and the cation exchange membrane 7 is the solution chamber 6, and the flowing electrode liquid in the anode flowing electrode chamber 2 and the cathode flowing electrode chamber 8 is activated carbon slurry. The inlet of the solution chamber 6 is connected to the alkaline fermentation broth storage chamber 10. The anode flow electrode chamber 2 is connected to the anode electrode liquid storage chamber 11 via a circulation pump. The cathode flow electrode chamber 8 is connected to the cathode electrode liquid storage chamber 13 via a circulation pump. The acidic liquid membrane chamber 4 is connected to the acidic solution storage chamber 12 via a circulation pump.

[0018] The first anion exchange membrane 5 allows anions with a molecular weight less than 1 kDa to pass through and retains dissolved organic matter with a molecular weight greater than 1 kDa, while the second anion exchange membrane 3 allows negatively charged ions to pass through.

[0019] The acidic solution in the acidic solution storage chamber 12 maintains the pH environment in the acidic liquid film chamber 4 between 2 and 4.7.

[0020] The first current collector 1 is connected to the positive terminal of the power supply, the second current collector 9 is connected to the negative terminal of the power supply, and the acidic liquid membrane chamber 4 is made of an acrylic plate.

[0021] The anode electrode liquid storage chamber 11 is connected to the phosphorus recovery tank, the cathode electrode liquid storage chamber 13 is connected to the ammonia nitrogen recovery tank, and the outlet of the acidic liquid membrane chamber 4 is connected to the VFA concentration tank.

[0022] The flowing electrode solution is prepared by mixing carbon black powder, activated carbon, and deionized water.

[0023] The method for selectively recovering flowing carbon, nitrogen, and phosphorus from alkaline fermentation broth using the above-mentioned capacitor deionization system includes the following steps: S1. Pump alkaline fermentation broth into solution chamber 6; S2. Start the circulation pump to form a circulation loop between the anode flow electrode chamber 2 and the anode electrode liquid storage chamber 11, between the cathode flow electrode chamber 8 and the cathode electrode liquid storage chamber 13, and between the acidic liquid film chamber 4 and the acidic solution storage chamber 12. S3. Turn on the power so that the first current collector 1 and the second current collector 9 operate under the applied voltage condition; S4. After a certain period of time, recover the VFA-rich concentrate from the acidic solution storage chamber 12, recover the phosphorus-containing concentrate from the anode electrode liquid storage chamber 11, and recover the ammonia nitrogen concentrate from the cathode electrode liquid storage chamber 13.

[0024] In step S1, the alkaline fermentation broth is fed into the solution chamber via a circulating water intake method until the VFA concentrate, phosphorus concentrate, and ammonia nitrogen concentrate reach the predetermined concentration. Specifically, the circulating water intake method involves the alkaline fermentation broth being pumped from the alkaline fermentation broth storage chamber into the solution chamber 6 via a circulating pump. After deionization, the broth is then returned to the alkaline fermentation broth storage chamber and circulated back into the solution chamber 6 for further processing.

[0025] In step S4, the VFA concentrate is recovered as a carbon source and used in the biological treatment tank of the wastewater treatment plant, while nitrogen and phosphorus are further recovered and reused as resources.

[0026] Working principle of the flow capacitor deionization system: After applying a certain voltage to the first current collector 1 and the second current collector 9 at both ends of the flow capacitor deionization system, the flow electrodes in the anode flow electrode chamber 2 and the cathode flow electrode chamber 8, through direct or indirect contact with the first current collector 1 and the second current collector 9, become positively and negatively charged, respectively. When the alkaline fermentation broth enters the solution chamber 6, under the action of the electric field, ammonium ions in the solution migrate through the cation exchange membrane 7 to the cathode flow electrode chamber 8. At the same time, due to the migration of different organic anion components in the electric field... Due to the different migration rates, the molecular sieving effect of the first anion exchange membrane 5 allows smaller molecular weight VFA and phosphate ions to pass through, while larger DOM molecules are retained. Only VFA and phosphate ions in the solution migrate through the first anion exchange membrane 5 to the acidic liquid membrane chamber 4. Then, these anions are protonated in the acidic liquid membrane chamber 4 (pH < 4.8). VFA will be acidified into uncharged molecules, while phosphate ions continue to retain their negative charge and continue to be affected by the electric field to migrate through the second anion exchange membrane 3 to the anolyte flow electrode chamber 2. After the operation is completed, phosphorus, nitrogen and VFA in the alkaline fermentation broth are enriched in the anode electrode liquid storage chamber 11, the cathode electrode liquid storage chamber 13 and the acidic solution storage chamber 12, respectively, realizing the selective separation of carbon, nitrogen and phosphorus in the alkaline fermentation broth. When phosphorus / nitrogen are enriched to a certain extent in the anode electrode liquid storage chamber 11 and the cathode electrode liquid storage chamber 13, the flowing electrode liquid is separated into solid and liquid by vacuum filtration or microfiltration. After the solid conductive agent is separated, a high-purity phosphorus / nitrogen-rich clear solution is obtained. The recovered solution is mixed with the solid conductive material generated after the solid-liquid separation of the electrode liquid and can be reused as a flowing electrode liquid.

[0027] During the experiment, the flow electrode solution was prepared by mixing carbon black powder (model: BP2000, CABOT, USA) and activated carbon (model: YEC-8B) at a mass ratio of 1:9, and then mixing with 18.2 MΩ deionized water. Before each experiment, the pH of the anolyte flow electrode was adjusted to 2 with 0.5M HCl. After the prepared flow electrode solution was placed in deionized water and ultrasonically treated for 1 h, it was stirred with a magnetic stirrer (model: Chijiu 85-1A) for 24 hours before use. During the experiment, three circulation pumps (model: Longer Pump YZ1515x) were used to pump in the flow electrode solution and alkaline fermentation broth, respectively. The operation mode was single-pass. The alkaline fermentation broth was pumped unidirectionally into solution chamber 6, then flowed out through anodic and cathodic flow electrode chambers 2 and 8. The flow rate and hydraulic residence time (HRT) were controlled by adjusting the speed of the circulating pump. Anodic or cathodic flow electrode chamber 8 operated in isolated closed-loop (ICC) mode, ensuring that the anodic and cathodic flow electrodes were pumped in at the same rate (15 mL / min). During the experiment, the carbon content was 5.0 wt%, the initial pH of the influent solution was 4.5, the flow rate and HRT were 10.9 min, and the current density was 13.3 A / m. 2 ; After the experiment, 79% of P and 68% of NH4 were removed from the alkaline fermentation broth. + -N, 84.33 mg / L of P was recovered at the anode, and 361.43 mg / L of NH4 was recovered at the cathode. + -N, and VFA at 4.7 g COD / L can be recovered in an acidic solution storage chamber.

[0028] Experimental verification shows that the flow capacitive deionization system for selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth effectively recovers VFA in the acidic liquid membrane chamber 4, enriches phosphorus in the anode electrode liquid storage chamber 11, and enriches ammonia nitrogen in the cathode electrode liquid storage chamber 13 when treating sludge alkaline fermentation broth. The recovered VFA is reused as a high-quality carbon source in the wastewater treatment plant, reducing the cost of purchased carbon sources, and nitrogen and phosphorus will be further recycled and utilized as resources.

[0029] This invention, through its innovative structure of a double-membrane-clamped acidic liquid membrane chamber 4, achieves for the first time highly efficient and selective separation and simultaneous resource utilization of carbon, nitrogen, and phosphorus in sludge fermentation broth, without the addition of any chemical additives throughout the entire process. This provides an industrially viable technical path for resolving the contradiction between "carbon source shortage and nitrogen and phosphorus pollution" in wastewater treatment plants.

[0030] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A flow capacitor deionization system for selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth, comprising, from left to right, a first current collector (1), a first anion exchange membrane (5), a second anion exchange membrane (3), a cation exchange membrane (7), and a second current collector (9), wherein the region between the first current collector (1) and the second anion exchange membrane (3) is an anode flow electrode chamber (2), and the region between the cation exchange membrane (7) and the second current collector (9) is a cathode flow electrode chamber (8), characterized in that: The region between the second anion exchange membrane (3) and the first anion exchange membrane (5) is an acidic liquid membrane chamber (4), the region between the first anion exchange membrane (5) and the cation exchange membrane (7) is a solution chamber (6), and the flowing electrode liquid in the anode flowing electrode chamber (2) and the cathode flowing electrode chamber (8) is activated carbon slurry; The inlet of the solution chamber (6) is connected to the alkaline fermentation broth storage chamber (10), the anode flow electrode chamber (2) is connected to the anode electrode liquid storage chamber (11) via a circulation pump, the cathode flow electrode chamber (8) is connected to the cathode electrode liquid storage chamber (13) via a circulation pump, and the acidic liquid membrane chamber (4) is connected to the acidic solution storage chamber (12) via a circulation pump.

2. The flow capacitor deionization system for selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth according to claim 1, characterized in that: The first anion exchange membrane (5) allows anions with a molecular weight less than 1 kDa to pass through and retains dissolved organic matter with a molecular weight greater than 1 kDa. The second anion exchange membrane (3) allows negatively charged ions to pass through.

3. The flow capacitor deionization system for selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth according to claim 1, characterized in that: The acidic solution in the acidic solution storage chamber (12) maintains the pH environment in the acidic liquid film chamber (4) between 2 and 4.

7.

4. A flow capacitor deionization system for selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth according to claim 1, characterized in that: The first current collector (1) is connected to the positive terminal of the power supply, the second current collector (9) is connected to the negative terminal of the power supply, and the acidic liquid membrane chamber (4) is made of an acrylic plate.

5. A flow capacitor deionization system for selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth according to claim 1, characterized in that: The anode electrode liquid storage chamber (11) is connected to the phosphorus recovery tank, the cathode electrode liquid storage chamber (13) is connected to the ammonia nitrogen recovery tank, and the outlet of the acidic liquid membrane chamber (4) is connected to the VFA concentration tank.

6. A flow capacitor deionization system for selective recovery of carbon, nitrogen, and phosphorus from alkaline fermentation broth according to claim 1, characterized in that: The flowing electrode solution is prepared by mixing carbon black powder, activated carbon, and deionized water.

7. A method for selectively recovering flowing carbon, nitrogen, and phosphorus from alkaline fermentation broth using a capacitor deionization system according to claims 1-6, characterized in that: Includes the following steps; S1. Pump alkaline fermentation broth into solution chamber (6); S2. Start the circulation pump to form a circulation loop between the anode flow electrode chamber (2) and the anode electrode liquid storage chamber (11), between the cathode flow electrode chamber (8) and the cathode electrode liquid storage chamber (13), and between the acidic liquid film chamber (4) and the acidic solution storage chamber (12); S3. Turn on the power so that the first current collector (1) and the second current collector (9) operate under the applied voltage condition; S4. After a certain period of time, recover the VFA-rich concentrate from the acidic solution storage chamber (12), recover the phosphorus-containing concentrate from the anode electrode liquid storage chamber (11), and recover the ammonia nitrogen concentrate from the cathode electrode liquid storage chamber (13).

8. The method for selective recovery of flowing carbon, nitrogen, and phosphorus from alkaline fermentation broth according to claim 7, characterized in that: In step S1, the alkaline fermentation broth is introduced in a single-pass or circulating manner until the VFA concentrate, phosphorus concentrate, and ammonia nitrogen concentrate reach the predetermined concentration. Specifically, the single-pass water intake means that the alkaline fermentation broth is pumped from the alkaline fermentation broth storage chamber into the solution chamber (6) by a circulating pump and discharged after a single deionization. Specifically, the circulating water intake means that the alkaline fermentation broth is pumped from the alkaline fermentation broth storage chamber into the solution chamber (6) by a circulating pump, and after deionization, it returns to the alkaline fermentation broth storage chamber and is circulated back into the solution chamber (6) for further processing.

9. The method for selective recovery of flowing carbon, nitrogen, and phosphorus from alkaline fermentation broth according to claim 7, characterized in that: In step S4, the VFA concentrate is recovered as a carbon source and used in the biological treatment tank of the wastewater treatment plant, while nitrogen and phosphorus are further recovered and reused as resources.

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