An electrochemical system and method for recovering nutrients from biogas slurry using biogas residue carbon

Abstract

The present application relates to a kind of electrochemical system for recycling nutrients of biogas slurry by biogas residue carbon, comprising: the first reaction chamber and the second reaction chamber for placing reaction liquid, the second reaction chamber is interconnected with the first reaction chamber and the junction is equipped with cation exchange membrane;Biogas residue carbon electrode containing ash phosphorus is set in the first reaction chamber or the second reaction chamber, and biogas residue carbon electrode is connected with the anode or cathode of power supply by wire;Titanium alloy electrode is set in the first reaction chamber or the second reaction chamber, and titanium alloy electrode is connected with the anode or cathode of power supply by wire;Magnesium alloy electrode is set in the first reaction chamber or the second reaction chamber, and biogas residue carbon electrode is connected with the anode or cathode of power supply by wire;By releasing phosphorus in biogas residue carbon electrode to reaction liquid, then by reverse electrode, MAP precipitation reaction is carried out, and the recycling of nutrients of biogas slurry is realized.The present application also relates to a kind of method for recycling nutrients of biogas slurry by biogas residue carbon.Belongs to the technical field of recycling nutrients in breeding waste.

Description

Technical Field

[0001] This invention relates to the field of nutrient recovery technology from livestock waste, specifically to an electrochemical system and method for recovering nutrients from biogas slurry using biogas residue char. Background Technology

[0002] The livestock and poultry farming industry is expanding rapidly, leading to a surge in wastewater discharge. With the structural reform of rural livestock farming, large-scale farms are increasingly located in rural areas or suburbs, occupying significant land areas and often adjacent to farmland. Therefore, if the resulting manure is not properly treated, it can severely damage arable land. Livestock and poultry manure contains abundant nitrogen and phosphorus, essential elements for living organisms. Phosphorus, a non-renewable resource, may face depletion in the coming decades. Therefore, efficiently recovering nitrogen and phosphorus from livestock and poultry farm wastewater and reducing farm waste is crucial for lowering treatment costs and for environmental protection and the utilization of biological resources.

[0003] Currently, technologies for nitrogen and phosphorus recovery from biogas slurry include ion exchange, biological methods, and chemical precipitation. Chemical precipitation is the most common method, involving the addition of chemicals to the solution to precipitate elements and thus recover phosphorus. However, the addition of chemical reagents can easily cause pollution, and the reaction is complex, difficult to control, and highly susceptible to interference, making it difficult to obtain a pure product. MAP (Magnesium Ammonium Phosphate) crystallization, also known as struvite crystallization, is a technology for recovering N (nitrogen) and P (phosphorus) elements from various wastewaters, and can efficiently recover ammonia nitrogen and phosphate from biogas slurry. However, the struvite crystallization process is easily affected by solution pH, initial nitrogen and phosphorus concentrations, and the molar ratio of nitrogen to phosphorus. Traditional MAP processes achieve struvite precipitation by adding phosphorus-containing chemical agents and alkaline compounds to the biogas slurry, resulting in slow growth of magnesium ammonium phosphate crystals, small crystal grains, low efficiency, and low purity of the obtained precipitate. Summary of the Invention

[0004] In view of the technical problems existing in the prior art, the purpose of this invention is to provide an electrochemical system for recovering nutrients from biogas slurry using biogas residue char. This electrochemical system achieves efficient precipitation of struvite, thereby recovering phosphorus from biogas slurry.

[0005] Another objective of this invention is to provide a method for recovering nutrients from biogas slurry using biogas residue char, thereby solving the problem of low efficiency in nitrogen and phosphorus recovery from biogas slurry using existing methods.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An electrochemical system for recovering nutrients from biogas slurry using biogas residue char includes:

[0008] The first reaction chamber is used to hold the reaction solution;

[0009] The second reaction chamber is used to hold the reaction solution. The second reaction chamber is connected to the first reaction chamber. A cation exchange membrane is provided at the connection between the second reaction chamber and the first reaction chamber.

[0010] A biogas residue carbon electrode containing ash and phosphorus is set in the first reaction chamber or the second reaction chamber, and the biogas residue carbon electrode is connected to the anode or cathode of the power supply through a wire.

[0011] A titanium alloy electrode is disposed in the first reaction chamber or the second reaction chamber, and the titanium alloy electrode is connected to the anode or cathode of the power supply via a wire.

[0012] Magnesium alloy electrodes are installed in the first or second reaction chamber, and biogas residue carbon electrodes are connected to the anode or cathode of the power supply via wires.

[0013] When the biogas residue carbon electrode is placed in the first reaction chamber, the titanium alloy electrode or magnesium alloy electrode is placed in the second reaction chamber; when the biogas residue carbon electrode is placed in the second reaction chamber, the titanium alloy electrode or magnesium alloy electrode is placed in the first reaction chamber.

[0014] The electrochemical system has a phosphorus release stage and a struvite precipitation stage. When the electrochemical system is in the phosphorus release stage, the biogas residue carbon electrode is connected to the anode via a wire, and the titanium alloy electrode is connected to the cathode via a wire. When the electrochemical system is in the struvite precipitation stage, the biogas residue carbon electrode is connected to the cathode via a wire, and the magnesium alloy electrode is connected to the anode via a wire.

[0015] As a preferred embodiment, the electrochemical system further includes a first platinum electrode clip, which is disposed in the first reaction chamber and is used to hold a biogas residue carbon electrode, titanium alloy electrode, or magnesium alloy electrode disposed in the first reaction chamber; the first platinum electrode clip is connected to a power source via a wire.

[0016] As a preferred embodiment, the electrochemical system further includes a second platinum electrode clip, which is disposed in the second reaction chamber and is used to hold a biogas residue carbon electrode, titanium alloy electrode, or magnesium alloy electrode disposed in the second reaction chamber; the second platinum electrode clip is connected to a power source via a wire.

[0017] As a preferred embodiment, the cation exchange membrane is fixed to the connection between the second reaction chamber and the first reaction chamber using a ball mill clamp.

[0018] A method for recovering nutrients from biogas slurry using biogas residue char, the method being implemented via an electrochemical system; the method includes the following steps:

[0019] S1: Preparation of biogas residue carbon electrode containing phosphorus ash;

[0020] S2: Preparation of reaction solution, which is formed by mixing biogas slurry and pure water in a 1:1 ratio;

[0021] S3: Add sodium chloride to the reaction solution;

[0022] S4: The reaction solution after adding sodium chloride is placed in the first and second reaction chambers of the electrochemical system. A biogas residue carbon electrode is installed in the first reaction chamber and connected to the anode of the power supply. The biogas residue carbon electrode undergoes an electrochemical reaction with the reaction solution in the first reaction chamber. A titanium alloy electrode plate is installed in the second reaction chamber and connected to the cathode of the power supply. The titanium alloy electrode plate undergoes an electrochemical reaction with the reaction solution in the second reaction chamber.

[0023] S5: After the first time period of step S4, replace the titanium alloy electrode in the second reaction chamber with a magnesium alloy electrode, connect the magnesium alloy electrode to the anode of the power supply and turn on the power, connect the biogas residue carbon electrode to the cathode of the power supply and turn on the power, and start the MAP precipitation reaction.

[0024] S6: After the MAP precipitation reaction, the reaction liquid in the first reaction chamber is filtered to obtain the struvite precipitate.

[0025] As a preferred method, in step S1, the method for preparing the biogas residue carbon electrode containing ash and phosphorus is as follows: the dried biogas residue is placed into a dry crucible, the crucible is wrapped with aluminum foil, and N2 is introduced into the atmosphere furnace. Under oxygen-free conditions, the temperature is raised to 750°C for pyrolysis. After the reaction is completed, the residue is placed in a desiccator and cooled to room temperature to obtain the biogas residue carbon electrode containing ash and phosphorus.

[0026] As a preferred option, in step S5, the first time period is 12 hours.

[0027] As a preferred option, the MAP precipitation reaction time in step S5 is 5 hours.

[0028] As a preferred embodiment, in step S5, the reaction solution is stirred using a magnetic stirrer while the MAP precipitation reaction is being carried out.

[0029] As a preferred option, in step S3, the concentration of sodium chloride is 3 g / L.

[0030] Invention Principle: The method of this invention consists of two parts: electrochemical acid leaching of biogas residue carbon electrode for phosphorus release and electrochemical MAP treatment for nitrogen and phosphorus recovery from biogas slurry. Biogas residue from livestock and poultry farms is carbonized and enriched with phosphorus to prepare a biogas residue carbon electrode containing phosphorus in ash. Then, the biogas residue carbon electrode undergoes an electrochemical process for acid leaching and functionalization pretreatment, releasing phosphorus from the biogas residue carbon as a phosphorus source and magnesium from the magnesium alloy electrode as a magnesium source. Finally, nitrogen and phosphorus nutrients from the biogas slurry and biogas residue are recovered through an electrochemical magnesium ammonium phosphate chemical precipitation method. To reduce external input, biogas residue waste from livestock and poultry farms is directly used as the phosphorus source, accelerating the efficient conversion of livestock and poultry farm resources, improving nitrogen and phosphorus recovery efficiency, reducing costs, and achieving the harmlessness, resource utilization, and high-value utilization of biogas slurry and biogas residue. This provides an economically feasible and innovative method for the practical application of magnesium ammonium phosphate chemical precipitation in the nutrient recovery of livestock and poultry farm waste.

[0031] Electrochemistry involves two electrodes, anode and cathode. As the electrochemical reaction proceeds, the pH at the anode decreases, while the pH at the cathode increases.

[0032] The formation of struvite requires the following conditions: ① phosphorus source (biogas residue char) ② magnesium source (magnesium alloy sheet) ③ ammonia nitrogen (biogas slurry itself) ④ pH ≥ 8 (provided by electrochemical cathode).

[0033] Initially, the biogas residue char electrode was connected to the anode. At this point, the pH of the biogas residue char electrode decreased, promoting the release of phosphorus from the biogas residue char. Subsequently, the electrode was reversed; the biogas residue char electrode remained stationary, only the wire position was changed. At this point, the biogas residue char reaction zone became the cathode, and the original cathode area became the anode, with the titanium alloy electrode plate replaced by a magnesium alloy electrode plate. The dissolved magnesium source and ammonia nitrogen from the reaction then pass through the cation exchange membrane into the current cathode, while the pH of the cathode electrochemical reaction increases. At this point, all four requirements for struvite precipitation in the biogas residue char reaction zone are met.

[0034] In this invention, the phosphorus source and magnesium source are Mg, which is provided in the reaction (Formulas 1-3) of struvite. 2+ and PO4 3- The content, thereby increasing the NH4 content. + The recycling effect generates more struvite (magnesium ammonium phosphate);

[0035] Mg 2+ + NH4 + +PO4 3- +6H2O→MgNH4PO4·6H2O↓, Equation (1);

[0036] Mg 2+ + NH4 + +HPO4 2- +6H₂O→MgNH₄PO₄·6H₂O↓ +H + Equation (2);

[0037] Mg 2+ + NH4 + +H2PO4 - +6H2O→MgNH4 PO4·6H20↓ +2H + Equation (3);

[0038] This invention addresses the issue that during anaerobic fermentation, most phosphorus precipitates in the biogas residue. Biogas residue from livestock farms is phosphorus-rich waste, containing 2-5% (w / w) phosphorus. Simultaneously, biogas residue is rich in carbon, making it an ideal material for preparing biochar electrodes. Therefore, after carbonization, the phosphorus-rich nature of the biogas residue can be utilized as a phosphorus source, not only reducing phosphorus source costs but also enabling the treatment of biogas slurry from livestock farm waste, realizing the in-situ treatment concept of "using waste to treat waste." For the magnesium source, inexpensive and readily available magnesium alloys are a good choice. The pH change characteristic of the electrochemical process is utilized to perform acid leaching functionalization pretreatment on the biogas residue carbon electrode to extract the phosphorus source and the reaction environment for struvite crystallization. Therefore, using the biogas residue carbon electrode as a phosphorus source in the electrochemical MAP reaction of nitrogen and phosphorus in biogas slurry achieves chemical precipitation to recover nitrogen and phosphorus nutrients from the biogas slurry and biogas residue.

[0039] In summary, the present invention has the following advantages:

[0040] 1. The system and method of the present invention provide a large amount of phosphorus source for MAP by acid leaching of biogas residue carbon electrode through electrochemical process, and combine it with MAP reaction to recover nitrogen and phosphorus nutrients in biogas slurry, thereby improving nitrogen and phosphorus recovery efficiency and being able to recover 99% of phosphorus and 97% of nitrogen in biogas slurry.

[0041] 2. The system and method of the present invention utilize an electrochemical process instead of a compound reagent as a leaching agent, which not only promotes the dissolution of Mg2+ and phosphorus, but also inhibits the influence of the compound reagent on struvite formation.

[0042] 3. This invention is the first to propose using an electrochemical process to extract phosphorus from biogas residue as a MAP phosphorus source, which not only reduces the cost of phosphorus source, but also utilizes phosphorus-rich biogas residue char generated within livestock and poultry farms to treat nitrogen-rich biogas slurry, realizing the in-situ treatment concept of "treating waste with waste", while also forming struvite precipitate. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of an electrochemical system in the phosphorus release phase.

[0044] Figure 2 This is a schematic diagram of an electrochemical system in the struvite precipitation stage.

[0045] Figure 3a This is a schematic diagram of the carbon electrode of biogas residue before the electrochemical reaction.

[0046] Figure 3b This is a schematic diagram of the SEM image of the biogas residue carbon electrode after the electrochemical reaction.

[0047] Figure 4a The graph shows the effect of different current magnitudes on NH3-N recovery.

[0048] Figure 4b The graph shows the effect of different sodium chloride concentrations on NH3-N recovery.

[0049] Figure 4c This is a graph showing the effect of different current magnitudes on pH.

[0050] Figure 4d For different current magnitudes of PO4 3- A graph showing the change in -P content.

[0051] Figure 4e PO4 after reversing the electrode 3- -P content variation curve.

[0052] Figure 5a This is a schematic diagram of an SEM image of the recovered product containing struvite.

[0053] Figure 5b The image shows the EDX spectrum of the recovered product containing struvite, where the horizontal axis represents the X-ray energy and the vertical axis represents the number of X-ray photons.

[0054] Figure 6 The XRD pattern of the recovered product containing struvite is shown, where the horizontal axis represents twice the incident angle of the X-rays, and the vertical axis represents the intensity after diffraction.

[0055] The components include: a first reaction chamber 1, a second reaction chamber 2, a first platinum sheet electrode clamp 3, a second platinum sheet electrode clamp 4, a biogas residue carbon electrode 5, a titanium alloy electrode 6, a magnesium alloy electrode 7, a ball mill clamp 8, a cation exchange membrane 9, an electrochemical system I, and a DC power supply II. Detailed Implementation

[0056] The present invention will now be described in further detail with reference to specific embodiments.

[0057] This embodiment provides a method for recovering nutrients from biogas slurry using biogas residue char. It recovers nitrogen and phosphorus from biogas slurry from livestock and poultry farms under laboratory conditions. These farms can be chicken farms, duck farms, pig farms, etc. For example, this embodiment uses biogas slurry from a duck farm. The method is implemented through an electrochemical system, such as... Figure 1-2 As shown, the electrochemical system includes:

[0058] First reaction chamber 1, used to hold the reaction solution;

[0059] The second reaction chamber 2 is used to hold the reaction solution. The second reaction chamber is connected to the first reaction chamber. A cation exchange membrane is provided at the connection between the second reaction chamber and the first reaction chamber. The amount of reaction solution in the first reaction chamber and the second reaction chamber is the same. The first reaction chamber and the second reaction chamber are glass containers with an open top. The side wall at the bottom of the glass container has a horizontally extending connecting channel. The two connecting channels of the first reaction chamber and the second reaction chamber are connected to each other. The cation exchange membrane is located at the connection between the two connecting channels.

[0060] The biogas residue carbon electrode 5 containing ash and phosphorus is set in the first reaction chamber or the second reaction chamber. The biogas residue carbon electrode is connected to the anode or cathode of the power supply through a wire. The biogas residue carbon electrode can be set in either the first reaction chamber or the second reaction chamber, but the connection of the anode or cathode of the power supply needs to be adjusted according to different reaction stages.

[0061] The titanium alloy electrode 6 is disposed in the first reaction chamber or the second reaction chamber, and the titanium alloy electrode is connected to the anode or cathode of the power supply through a wire.

[0062] Magnesium alloy electrode 7 is set in the first reaction chamber or the second reaction chamber, and biogas residue carbon electrode is connected to the anode or cathode of the power supply through a wire.

[0063] When the biogas residue carbon electrode is placed in the first reaction chamber, the titanium alloy electrode or magnesium alloy electrode is placed in the second reaction chamber; when the biogas residue carbon electrode is placed in the second reaction chamber, the titanium alloy electrode or magnesium alloy electrode is placed in the first reaction chamber.

[0064] The electrochemical system has a phosphorus release stage and a struvite precipitation stage. During the phosphorus release stage, the biogas residue carbon electrode is connected to the anode via a wire, and the titanium alloy electrode is connected to the cathode via a wire. During the struvite precipitation stage, the biogas residue carbon electrode is connected to the cathode via a wire, and the magnesium alloy electrode is connected to the anode via a wire. During the phosphorus release stage, the magnesium alloy electrode is not needed; simply connect the biogas residue carbon electrode and the titanium alloy electrode to the anode and cathode of the power supply, respectively. The biogas residue carbon electrode undergoes acid leaching functionalization pretreatment using an electrochemical process to release phosphorus from the biogas residue carbon as a phosphorus source. During the struvite precipitation stage, the titanium alloy electrode is not needed; it is removed and replaced with a magnesium alloy electrode. The biogas residue carbon electrode is switched from being connected to the anode to being connected to the cathode of the power supply, and the magnesium alloy electrode is connected to the anode of the power supply, releasing magnesium from the magnesium alloy as a magnesium source.

[0065] The electrochemical system also includes a first platinum electrode clip 3, which is disposed in the first reaction chamber. The first platinum electrode clip is used to hold the biogas residue carbon electrode, titanium alloy electrode, or magnesium alloy electrode disposed in the first reaction chamber. The first platinum electrode clip is connected to a power source via a wire. By providing the first platinum electrode clip, it is convenient to hold the biogas residue carbon electrode in the first reaction chamber, and it is also convenient to replace the biogas residue carbon electrode.

[0066] The electrochemical system also includes a second platinum electrode clip 4, which is disposed in the second reaction chamber. The second platinum electrode clip is used to hold the biogas residue carbon electrode, titanium alloy electrode, or magnesium alloy electrode disposed in the second reaction chamber. The second platinum electrode clip is connected to a power source via a wire. The second platinum electrode clip facilitates the holding of the titanium alloy electrode or magnesium alloy electrode in the second reaction chamber and also facilitates the replacement of the titanium alloy electrode or magnesium alloy electrode.

[0067] The cation exchange membrane 9 is fixed to the connection between the second reaction chamber and the first reaction chamber using a ball-ground clamp 8. The ball-ground clamp secures the cation exchange membrane between the second and first reaction chambers to prevent leakage of the reaction solution.

[0068] The electrochemical system also includes a pH meter (not shown in the figure), which is used to detect the pH value of the reaction solution in the second reaction chamber and the first reaction chamber in real time.

[0069] The specific steps of the recycling operation process in this embodiment are as follows:

[0070] 1. Dry biogas residue from duck farms is prepared by drying it in an oven at 105℃ for 12 hours. After drying, the dry biogas residue is ground through a 200-mesh sieve. A small amount of the sieved dry biogas residue is weighed and mixed with agar resin in a 5:1 ratio to form a sheet. The sheet is placed in a 2*3cm square drying crucible, wrapped with aluminum foil, and then placed in an atmosphere furnace. N2 is introduced at a rate of 8-8.5L / h, and the temperature is raised to 750℃ for 1 hour under anaerobic conditions at a rate of 10-15℃ / min to obtain a biogas residue carbon electrode containing phosphorus ash. After the reaction is complete, the electrode is removed and cooled to room temperature in a desiccator. The biogas residue carbon electrode is then sealed and stored in a plastic bag. By directly extracting and processing the biogas slurry from duck farms, electrode sheets are prepared to replace the commonly used electrochemical metal electrodes. This eliminates the need for transportation to other locations for processing, reducing costs and solving the disposal problems of phosphorus-rich biogas residue and nitrogen-rich biogas slurry from pig farms. This provides an innovative process for the resource utilization of manure from large-scale livestock and poultry farms.

[0071] 2. A 1:1 mixture of collected biogas slurry and pure water was used as the reaction solution for the electrochemical reaction. A certain amount of sodium chloride was added to the reaction solution to enhance its conductivity; the concentration of liquid sodium chloride was 3 g / L. The reaction solution was evenly placed in the first and second reaction chambers. A 2*3 cm biogas residue carbon electrode and a titanium alloy electrode were fixed using electrode clamps (first platinum electrode clamp and second platinum electrode clamp) and placed in the first and second reaction chambers respectively. The first platinum electrode clamp was connected to the anode of the DC power supply, and the second platinum electrode clamp was connected to the cathode of the DC power supply. The reaction was then carried out at a constant current of 0.2 A for 12 hours, and stirred for 12 hours using a magnetic stirrer at 120 r / min. The purpose here is to use an electrochemical process to perform acid leaching functionalization pretreatment on the biogas residue carbon electrode to release phosphorus from the biogas residue carbon as a phosphorus source.

[0072] 3. Using the above reaction solution as the phosphorus source for the MAP reaction, a magnesium alloy electrode was added to induce MAP precipitation. The purpose here is to utilize an electrochemical process to electrolytically release magnesium from the magnesium alloy electrode as a magnesium source. Specifically, a 2*3cm titanium alloy electrode was replaced with a magnesium alloy electrode. Without changing the electrode position, the DC power supply was switched, and the reaction was carried out at a constant current of 0.2A for 5 hours. The mixture was then stirred with a magnetic stirrer at 120 rpm for 5 hours to induce MAP precipitation. Immediately after the reaction, 20 μL of HCl (6 mol / L) was added to the water sample to stop the reaction, reduce ammonia volatilization, and prevent the MAP precipitation reaction from continuing and affecting the numerical measurements. The solution was filtered through a 0.45 μm filter membrane, and various indicators in the filtrate were measured to obtain the struvite precipitate. The reaction solution was stirred with a magnetic stirrer during the MAP precipitation reaction to ensure a more complete reaction.

[0073] The physicochemical parameters of the biogas slurry, biogas residue, and biogas residue char are shown in Table 1-2. When operated in the above manner, under the optimal leaching conditions of current magnitude and sodium chloride concentration in the reaction solution, and under the optimal MAP process conditions, 99% of the phosphorus in the biogas slurry can be recovered, and the nutrient recovery effect is very obvious. Most of the nitrogen and phosphorus are recovered by the biogas residue char electrode through electrochemical action, while the recovery is enhanced by the synergistic effect of the functional group bonding of biogas residue char, and finally struvite precipitate is formed.

[0074] Table 1. Quality of biogas slurry from the duck farm

[0075]

[0076] Note: The values ​​shown in the table are the mean ± standard error. The mean is obtained by averaging n samples. In this example, n = 3.

[0077] Table 2 Basic physicochemical parameters of the experimental biogas residue

[0078]

[0079] Note: The values ​​shown in the table are the mean ± standard error. The mean is obtained by averaging n samples. In this example, n = 3.

[0080] Figures 3a-3b The images shown are SEM images of the biogas residue carbon electrode before and after the electrochemical reaction in the examples. (a) is the SEM image of the biogas residue carbon electrode before the electrochemical reaction, and (b) is the SEM image of the biogas residue carbon electrode after the electrochemical reaction. Figure 3a As can be seen from the above, there is no obvious pore distribution on the surface of the biogas residue carbon electrode before the reaction. Figure 3b As can be seen, the biogas residue carbon electrode after the electrochemical reaction is loose and porous, indicating that the surface of the biogas residue carbon electrode provides electrochemical reaction sites to promote the reaction. Figure 4 shows the effects of current magnitude, sodium chloride concentration in the reaction solution, pH change, and phosphorus content in the reaction solution on the nitrogen and phosphorus recovery efficiency in the example. Among them, ( Figure 4a The effect of different current magnitudes on the NH3-N recovery efficiency is shown in the figure. Figure 4b The effect of different sodium chloride concentrations on the recovery efficiency of NH3-N is shown in the figure. Figure 4c The effect of different current magnitudes on pH changes, Figure 4d ) for different current magnitudes on PO4 3- The effect of changes in -P content, Figure 4e ) is PO4 after reversal electrode 3- The change in -P content, and the reversal electrode, refers to the biogas residue char electrode switching from being the anode connected to the power source to the cathode connected to the power source. From Figure 4a As shown in -e, under the optimal operating conditions of a current of 0.2A, a sodium chloride concentration of 3g / L, and a reaction time of 12h, the PO4 in the filtrate within the first reaction chamber containing the biogas residue carbon electrode after the reaction is [data missing]. 3- With a phosphorus content of 300 mg / L, after reversing the electrode and reacting for 5 hours under the optimal MAP process conditions, 99% of the phosphorus in the biogas slurry can be recovered, and the nutrient recovery effect is very obvious. Figures 5a-5b The images show SEM and EDX spectra of the recovered product containing struvite in the examples. From... Figure 5a As can be seen from the sample, the precipitate contains mainly oblique square crystal structures with few fine amorphous crystal particles attached to the surface. This structure is a typical struvite crystal structure, indicating that the final precipitate of the biogas slurry nitrogen and phosphorus recovery process using the electrochemical process and biogas residue carbon electrode in this embodiment contains struvite crystals. Figure 6 The image shows the XRD pattern of the recovered product containing struvite in the example. Figure 6 As can be seen from the data, the main mineral phase is struvite, indicating that the precipitate crystals produced by the nitrogen and phosphorus treatment of the recovered biogas slurry are mainly composed of magnesium ammonium phosphate (MAP).

[0081] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An electrochemical system for recovering nutrients from biogas slurry using biogas residue carbon, characterized by, It comprises: A first reaction chamber for placing reaction liquid; A second reaction chamber for placing reaction liquid, the second reaction chamber is in communication with the first reaction chamber, and a cation exchange membrane is arranged at the connection between the second reaction chamber and the first reaction chamber; A biogas residue carbon electrode containing ash phosphorus is arranged in the first reaction chamber or the second reaction chamber, and the biogas residue carbon electrode is connected with the anode or the cathode of the power supply through a wire; the method for preparing the biogas residue carbon electrode containing ash phosphorus comprises the following steps: drying biogas residue is loaded into a drying crucible, the crucible is wrapped with aluminum foil, and the wrapped crucible is placed in an atmosphere furnace and supplied with N2; under the condition of no oxygen, the temperature is raised to 750 DEG C for pyrolysis; after the reaction is completed, the biogas residue carbon electrode containing ash phosphorus is cooled to room temperature in a dryer, and the biogas residue carbon electrode containing ash phosphorus is obtained; A titanium alloy electrode is arranged in the first reaction chamber or the second reaction chamber, and the titanium alloy electrode is connected with the anode or the cathode of the power supply through a wire; A magnesium alloy electrode is arranged in the first reaction chamber or the second reaction chamber, and the biogas residue carbon electrode is connected with the anode or the cathode of the power supply through a wire; When the biogas residue carbon electrode is arranged in the first reaction chamber, the titanium alloy electrode or the magnesium alloy electrode is arranged in the second reaction chamber; when the biogas residue carbon electrode is arranged in the second reaction chamber, the titanium alloy electrode or the magnesium alloy electrode is arranged in the first reaction chamber; The electrochemical system has a phosphorus release stage and a struvite precipitation stage; when the electrochemical system is in the phosphorus release stage, the biogas residue carbon electrode is connected with the anode through a wire, and the titanium alloy electrode is connected with the cathode through a wire; when the electrochemical system is in the struvite precipitation stage, the biogas residue carbon electrode is connected with the cathode through a wire, and the magnesium alloy electrode is connected with the anode through a wire.

2. The electrochemical system for recovering nutrients from biogas slurry according to claim 1, wherein: It also comprises a first platinum sheet electrode clamp, which is arranged in the first reaction chamber and is used for clamping the biogas residue carbon electrode, the titanium alloy electrode or the magnesium alloy electrode arranged in the first reaction chamber; the first platinum sheet electrode clamp is connected with the power supply through a wire and is electrified.

3. The electrochemical system for recovering nutrients from biogas slurry according to claim 1, wherein: It also comprises a second platinum sheet electrode clamp, which is arranged in the second reaction chamber and is used for clamping the biogas residue carbon electrode, the titanium alloy electrode or the magnesium alloy electrode arranged in the second reaction chamber; the second platinum sheet electrode clamp is connected with the power supply through a wire and is electrified.

4. The electrochemical system for recovering nutrients from biogas slurry according to claim 1, wherein: The cation exchange membrane is fixed at the connection between the second reaction chamber and the first reaction chamber through a ball mill mouth clamp.

5. A method for recovering nutrients from biogas slurry using biogas residue charcoal, characterized by, The method is implemented by the electrochemical system according to any one of claims 1-4; the method comprises the following steps: S1: preparing a biogas residue carbon electrode containing ash phosphorus; S2: preparing reaction liquid, which is formed by mixing biogas liquid and pure water at a ratio of 1:1; S3: adding sodium chloride to the reaction liquid; S4: placing the reaction liquid after adding sodium chloride in the first reaction chamber and the second reaction chamber of the electrochemical system, clamping the biogas residue carbon electrode in the first reaction chamber, connecting the biogas residue carbon electrode with the anode of the power supply and electrifying, and performing electrochemical reaction between the biogas residue carbon electrode and the reaction liquid in the first reaction chamber; clamping the titanium alloy electrode sheet in the second reaction chamber, connecting the titanium alloy electrode sheet with the cathode of the power supply and electrifying, and performing electrochemical reaction between the titanium alloy electrode sheet and the reaction liquid in the second reaction chamber; S5: After the first time period of step S4, replace the titanium alloy electrode in the second reaction chamber with a magnesium alloy electrode, connect the magnesium alloy electrode to the anode of the power supply and turn on the power, connect the biogas residue carbon electrode to the cathode of the power supply and turn on the power, and start the MAP precipitation reaction. S6: After the MAP precipitation reaction, the reaction liquid in the first reaction chamber is filtered to obtain the struvite precipitate.

6. A method of recovering nutrients from biogas slurry using biogas residue carbon according to claim 5, characterized in that: In step S5, the first time period is 12 hours.

7. A method of recovering nutrients from biogas slurry using biogas residue carbon according to claim 5, characterized in that: In step S5, the MAP precipitation reaction takes 5 hours.

8. A method of recovering nutrients from biogas slurry using biogas residue carbon according to claim 5, characterized in that: In step S5, the reaction solution is stirred using a magnetic stirrer while the MAP precipitation reaction is taking place.

9. A method for recovering nutrients from biogas slurry using biogas residue carbon according to claim 5, characterized in that: In step S3, the concentration of sodium chloride is 3 g / L.

Images