Regulation and control system for anaerobic digestion and magnetic biochar preparation method thereof

Abstract

The invention discloses a regulation and control system for anaerobic digestion and a magnetic charcoal preparation method thereof, which effectively achieve the purposes of increasing methane yield and reducing system energy consumption, and comprises: an anaerobic fermentation unit, which is provided with an aeration device and a heat exchanger; the micro-nano bubble generation unit is connected with the aeration device through a pipeline and comprises a switchable gas source for providing at least one of H2, N2 and CO2; the bubble generation assembly adopts a composite structure of a microporous membrane and a Venturi tube; the magnetic charcoal adding unit is connected with the anaerobic fermentation unit through a sealing pipeline and comprises a storage tank and a screw feeder; the intelligent control unit comprises a sensor array and an executing mechanism, the structure is novel, the conception is ingenious, operation is easy and convenient, the effects of accurately controlling the particle size of bubbles and maintaining the interface potential are effectively achieved, and the effect of intelligently switching gas components and the charcoal adding amount is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sludge treatment, and relates to a regulation system for anaerobic digestion and a preparation method of magnetic biochar thereof. BACKGROUND

[0002] Sludge anaerobic digestion is the mainstream technology for sludge resource utilization in wastewater treatment plants, which can convert organic matter into methane (CH4) and realize energy recovery. However, traditional anaerobic digestion has problems such as slow hydrolysis rate, low and unstable methane yield, and long reaction period, which are mainly limited by:

[0003] (1) Dense sludge structure: Microorganisms have difficulty in breaking through the physical barrier of cell wall / extracellular polymeric substance (EPS), resulting in insufficient release of organic matter and low hydrolysis efficiency.

[0004] (2) Mass transfer limitation: Insufficient contact between substrate and microorganisms, especially for hydrophobic organic matter.

[0005] (3) Low electron transfer efficiency: Slow rate of traditional interspecies hydrogen / formic acid transfer (IHT / IFT), and easy inhibition by VFAs / NH4+.

[0006] (4) Redox imbalance: Local micro-oxygen or H2 accumulation will inhibit methanogens (such as Methanosaeta).

[0007] In recent years, research has focused on the magnetic biochar (ZVI-BC) system, and ZVI corrosion produces Fe 2+ / Fe 3+ (like corrosion reaction: Fe 0 → Fe 2+ + 2e - (provide electrons), Fe 2+ + 2H + → Fe 3+ + H2↑ (maintain low ORP)). Form a conductive network with BC, provide electrons, adjust redox potential, and promote direct interspecies electron transfer (DIET). BC as a conductive medium accelerates DIET and adsorbs inhibitors (such as NH4+, H2S). At the same time, BC adsorbs active free radicals (such as ·OH) generated by MNBs to avoid their inhibition on microorganisms. However, ZVI is prone to passivation, H2 utilization rate is low, and the electron transfer capacity of BC is limited, and the mass transfer efficiency of static system is low, so it is necessary to introduce dynamic regulation means.

[0008] Micro-nano bubbles (MNBs) are widely used in the field of environment due to their high specific surface area, long residence time, and interface effect (such as free radical generation), but their dual role in anaerobic digestion (destroying sludge structure vs. regulating redox) has not been clearly defined, and there is a lack of research on intelligent synergistic mechanism with ZVI-BC.

[0009] Based on the application of the above micro-nano bubbles, a regulation system for anaerobic digestion and a preparation method of magnetic biochar are needed to integrate micro-nano bubble technology and improve methane yield. SUMMARY

[0010] To solve the above problems, the present application provides a regulation system for anaerobic digestion and a preparation method of magnetic biochar.

[0011] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0012] A regulation system for anaerobic digestion, comprising:

[0013] An anaerobic fermentation unit provided with an aeration device and a heat exchanger;

[0014] A micro-nano bubble generating unit connected to the aeration device through a pipeline, comprising:

[0015] A switchable gas source providing at least one of H2, N2 and CO2;

[0016] A bubble generating assembly adopting a composite structure of a microporous membrane and a Venturi tube;

[0017] A magnetic biochar dosing unit connected to the anaerobic fermentation unit through a sealed pipeline, comprising a storage tank and a screw feeder;

[0018] An intelligent control unit comprising a sensor array and an actuator;

[0019] The sensor array monitors the oxidation-reduction potential, pH, volatile fatty acids and methane production in real time;

[0020] The actuator dynamically adjusts the type of gas source, gas flow and magnetic biochar dosage.

[0021] Preferably, in the bubble generating assembly:

[0022] The throat of the Venturi tube is connected to the microporous membrane assembly;

[0023] The gas is pre-dispersed through the microporous membrane and then enters the throat of the Venturi tube, where it is sheared and broken into micro-nano bubbles of 50-500 nm in the converging section.

[0024] Preferably, the sealed pipeline of the magnetic biochar dosing unit is fully protected by nitrogen, maintaining an oxygen content of <0.1%.

[0025] A regulation method for anaerobic digestion applied to the above regulation system for anaerobic digestion, comprising the following steps:

[0026] Phase determination: according to the changes of redox potential, volatile fatty acids and gas production parameters in the anaerobic digestion process, the reaction process is divided into hydrolysis period, acid production period and methane production period;

[0027] Dynamic intervention:

[0028] In the hydrolysis period, micro-nano bubbles with N2 volume ratio ≥95% are introduced;

[0029] In the acid production period, micro-nano bubbles with H2 volume ratio ≥95% are introduced;

[0030] In the methane production period, micro-nano bubbles are stopped and magnetic biochar is added.

[0031] Preferably, the logic of the phase determination includes:

[0032] Hydrolysis period: when the redox potential is lower than the first threshold value and the volatile fatty acid is lower than the second threshold value;

[0033] Acid production period: when the volatile fatty acid is higher than the third threshold value or the pH is lower than the fourth threshold value;

[0034] Methane production period: when the methane production is higher than the fifth threshold value and the H2 concentration is lower than the sixth threshold value.

[0035] Preferably, the first threshold value is -200mV to -300mV, the third threshold value is 1000-2000mg / L, and the sixth threshold value is 800-1200ppm.

[0036] Preferably, it also includes abnormal regulation:

[0037] When the redox potential is greater than -200mV, H2 micro-nano bubbles are started;

[0038] When the volatile fatty acid is greater than 2000mg / L, micro-nano bubbles with CO2 volume ratio ≥90% are introduced into the reactor.

[0039] A preparation method of magnetic biochar, comprising:

[0040] Step S1, reacting the iron-containing raw material with a reducing agent under an inert atmosphere to generate a complex containing zero-valent iron;

[0041] Step S2, anaerobic solid-liquid separation and cleaning of the reaction product;

[0042] Step S3, shaping treatment of the separated solid under low temperature conditions to maintain the porous structure;

[0043] Step S4, crushing, grading and packaging of the shaped solid in an anaerobic environment.

[0044] Preferably, the low temperature condition is -30℃ to -70℃, and the setting treatment time is 48-96 hours.

[0045] Preferably, the particle size after grading in step S4 is ≤150 μm, and the grading product is packaged in a gas-tight container and stored in an oxygen-free environment with residual O2 <0.1%.

[0046] Compared with the prior art, the present application has the following beneficial effects:

[0047] 1. The present application achieves the effects of precisely controlling the bubble particle size and maintaining the appropriate interfacial potential by the switchable gas source technology of the micro-nano bubble generating unit, improves the sludge disintegration rate, and at the same time inhibits the thickness of the oxidation layer on the surface of the magnetic biochar, and weakens the passivation problem of traditional zero-valent iron.

[0048] 2. The present application achieves the effects of intelligent switching of gas components (N2 / H2 / CO2) and biochar dosage according to the three stages (hydrolysis / acid production / methane production) of anaerobic digestion by the sensor array of the intelligent control unit, improves the methane production rate, and reduces the system energy consumption. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 It is a schematic diagram of the overall connection of the regulation system in the present application. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0051] The drawings in the embodiments of the present application will be described below. Figure 1 The specific embodiments of the present application will be further described in detail.

[0052] A regulation system for anaerobic digestion, as shown in Figure 1 in order to achieve the purpose of increasing the methane production rate, comprising:

[0053] An anaerobic fermentation unit, comprising a cylindrical fermentation tank (volume 4-50 m 3 ), which is internally provided with:

[0054] A heat exchanger: 304 stainless steel coil, connected to a constant temperature water bath system, maintaining the reaction temperature at 35±0.5℃;

[0055] An aeration device: titanium alloy microporous aeration disc (pore size 50 μm), installed at the bottom of the tank, connected to pipeline L1 through DN50 flange;

[0056] The micro-nano bubble generating unit is connected with the aeration device through a pipeline L1 and comprises:

[0057] Switching gas source: including H2 / N2 / CO2 high-pressure tank (purity ≥ 99.95%), equipped with electromagnetic valve group to realize automatic switching of gas;

[0058] Bubble generating assembly (core innovative structure):

[0059] Venturi tube: 316L stainless steel material, throat diameter 5mm, contraction angle 15°;

[0060] Microporous membrane assembly: polytetrafluoroethylene membrane (pore size 0.1μm), directly connected with the throat of the Venturi tube through a reducing joint;

[0061] Zeta potential regulation module: built-in platinum electrode pair, -1.0V bias is applied, the bubble interface potential is maintained at ≤-30mV, and the Malvern particle size instrument is used for real-time monitoring during the period;

[0062] It should be noted that when the gas passes through the microporous membrane, it will be pre-dispersed, and then pass through the throat of the Venturi tube, and under the shearing action of high-speed airflow (flow rate ≥ 15m / s), 50-500nm bubbles are generated.

[0063] Magnetic biochar dosing unit, connected with the anaerobic fermentation unit through a sealed pipeline, comprising a storage tank and a screw feeder, wherein the storage tank has a volume of 100L and stores magnetic biochar (zero-valent iron ZVI loading amount 12wt%), the screw feeder is used for outputting the magnetic biochar, and the magnetic biochar is obtained by the following magnetic biochar preparation method;

[0064] The storage tank is connected with a sealed pipeline L2 supported by a double-layer 316L stainless steel pipe, the interlayer is filled with high-purity nitrogen (mass fraction greater than or equal to 99.99%), and an oxygen sensor is arranged in the sealed pipeline L2 for real-time monitoring and maintaining O2<0.1% in the pipeline (exceeding the standard will automatically trigger nitrogen flushing);

[0065] Intelligent control unit, including a sensor array and an actuator;

[0066] The sensor array monitors the oxidation-reduction potential (ORP), the pH value, the volatile fatty acid (VFAs) and the methane (CH4) production in real time;

[0067] Specifically, the sensor array comprises:

[0068] ORP electrode, placed 1.5m below the liquid surface, with a measurement range of -500-500mV and a detection accuracy of ±5mV;

[0069] Raman H2 probe, arranged in the biogas output pipe, with a measurement range of 0-5000ppm and a detection accuracy of ±50ppm;

[0070] CH4 flow meter, set at the end of the pipeline, range 0-100L / h, detection accuracy ±2%.

[0071] The actuator dynamically adjusts the type of gas source, gas flow and magnetic biochar dosage;

[0072] The actuator specifically comprises:

[0073] The gas source solenoid valve group has a response time of <0.1s;

[0074] The frequency of the feeder frequency converter is adjustable in the range of 0-50Hz;

[0075] The flow rate of the Venturi centrifugal pump is adjustable in the range of 0.1-1.0m 3 / h.

[0076] In the bubble generating assembly:

[0077] The throat of the Venturi tube is connected to the microporous membrane assembly;

[0078] After being pre-dispersed by the microporous membrane, the gas enters the Venturi tube throat, and is sheared and broken into 50-500nm micro-nano bubbles in the contraction section; the micro-nano bubble generator is provided with a Zeta potential regulation module to maintain the bubble interface potential ≤-30mV;

[0079] The sealed pipeline of the magnetic biochar dosing unit is protected by nitrogen throughout, and the oxygen content is maintained at <0.1%.

[0080] In addition, the present application provides a regulation method for anaerobic digestion, which is applied to the above-mentioned regulation system for anaerobic digestion, and comprises the following steps:

[0081] Phase determination: according to the changes of oxidation-reduction potential (ORP), volatile fatty acids (VFAs) and gas production parameters in the anaerobic digestion process, the reaction process is divided into hydrolysis period, acid production period and methane production period;

[0082] Dynamic intervention:

[0083] In the hydrolysis period, that is, when the oxidation-reduction potential (ORP) is lower than the first threshold value and the volatile fatty acid (VFAs) is lower than the second threshold value, micro-nano bubbles with N2 volume ratio ≥95% are introduced, specifically N2-MNBs (volume ratio ≥95%), the bubble particle size is controlled to be 50-200nm (Venturi tube flow rate 15m / s), the first threshold value is-200mV to-300mV, and the second threshold value is 500mg / L (which is the critical point of SCOD release rate);

[0084] In this process, the N2 bubble cavitation effect destroys the EPS structure, so that the SCOD is improved;

[0085] In the acid production period, when the volatile fatty acids (VFAs) are higher than the third threshold value or the pH is lower than the fourth threshold value, micro-nano bubbles with a volume fraction of H2≥95% are introduced, specifically, the gas is H2-MNBs (volume fraction≥95%), the bubble particle size is 100-300 nm, the third threshold value is 1000-2000 mg / L (preferably 1500 mg / L, VFAs conversion rate inflection point), and the fourth threshold value is pH=6.2 (lower limit of the optimum pH of acid-producing bacteria);

[0086] In this process, H2 dissolution promotes homoacetogenic metabolism, so that the conversion rate of VFAs to acetic acid is improved;

[0087] In the methane production period, when the methane (CH4) production is higher than the fifth threshold value and the H2 concentration is lower than the sixth threshold value, the introduction of micro-nano bubbles is stopped, and magnetic biochar is added, the fifth threshold value is 5 L / h (corresponding to the activity threshold value of methanogens), and the sixth threshold value is 800-1200 ppm (preferably 1000 ppm, to prevent H2 accumulation inhibition);

[0088] In addition, abnormal regulation is also included:

[0089] When the oxidation-reduction potential (ORP) is >-200 mV, corresponding to an abnormal increase in oxidation-reduction potential, H2 micro-nano bubbles are started;

[0090] When the volatile fatty acids (VFAs) are >2000 mg / L, i.e., the acidification risk is higher than the threshold value, micro-nano bubbles with a volume fraction of CO2≥90% are introduced into the reactor, specifically, the introduced gas is CO2-MNBs (volume fraction≥90%), and the bubble particle size is 200-400 nm. In this process, CO2 dissolution buffers pH (maintains 6.8-7.2), which can promote acetic acid synthesis.

[0091] A preparation method of magnetic biochar, comprising:

[0092] Step S1, reacting the iron-containing raw material with a reducing agent under an inert atmosphere to generate a complex containing zero-valent iron (ZVI);

[0093] Step S2, anaerobic solid-liquid separation and cleaning of the reaction product;

[0094] Step S3, shaping treatment of the separated solid under low temperature conditions to maintain the porous structure;

[0095] Step S4, crushing, grading and packaging of the shaped solid in an anaerobic environment.

[0096] Wherein, the low temperature condition is-30℃ to-70℃, and the shaping treatment time is 48-96 hours.

[0097] Wherein, the particle size of the classified particles in step S4 is ≤ 150 μm, and the classified particles are packaged in a gas-tight container in an anaerobic environment with residual O2 < 0.1% for storage.

[0098] Specifically, the sludge containing iron flocculants in the sewage treatment plant is placed in a glass container, deionized water is added and stirred to form a 85% slurry, and NaBH4 solution (molar ratio of Fe 3+ to NaBH4 is 1:3), and the mixture is stirred for 20 min under N2 protection, and then filtered under vacuum using a circulating water vacuum pump to achieve solid-liquid separation. The obtained mixture particles are placed in a vacuum freeze dryer for freeze-drying for 72 h, and then crushed and sieved (100 mesh) to obtain the magnetic biochar ZVI-BC. The magnetic biochar is sealed and stored under anaerobic conditions for standby use. The reaction principle is as follows:

[0099]

[0100] It should be noted that the preparation method of the magnetic biochar is applied to the above-mentioned one kind of regulation system for anaerobic digestion.

[0101] Sampling detection: On the 0th, 5th, 10th, 15th, 20th, 25th and 30th day, about 20.0 mL of the digestion solution was extracted using a peristaltic pump for analysis.

[0102] ① The digestion solution was centrifuged at 2000g for 10 minutes, and the liquid supernatant was filtered through a 0.45μm ultrafiltration membrane. The filtered liquid was used to measure volatile fatty acids VFA (determined using a gas chromatograph equipped with an organic acid analysis column and a hydrogen flame ionization detector), total solids TS (standard method) and volatile solids VS (standard method), and the hydrolysis capacity of WAS was determined accordingly.

[0103] ② Deoxyribonucleic acid (DNA) was extracted from the digestion solution. High-throughput sequencing technology was used to detect the abundance and types of microorganisms therein to determine the differences in microbial communities in different anaerobic bottles.

[0104] Biogas production and composition: biogas production - determined using a gas flow meter; methane concentration in biogas - determined using a biogas analyzer.

[0105] The conclusions after detection are as follows:

[0106] Key time comparison table:

[0107]

[0108]

[0109] Key index comparison:

[0110]

[0111]

[0112] Key functional flora content comparison:

[0113]

[0114] The application has novel structure, ingenious concept, simple and convenient operation, effectively achieves the effects of precisely controlling bubble particle size and maintaining interface potential, realizes the effects of intelligently switching gas components and biochar dosage, and achieves the purposes of increasing methane yield and reducing system energy consumption.

[0115] Although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art can modify the technical solutions recorded in the foregoing embodiments or equivalently replace part of the technical features, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A regulatory system for anaerobic digestion, characterized by: Comprising: an anaerobic fermentation unit provided with an aeration device and a heat exchanger; a micro-nano bubble generating unit connected to the aeration device through a pipeline, comprising: a switchable gas source providing at least one of H2, N2, and CO2; a bubble generating assembly adopting a composite structure of a micro-porous membrane and a Venturi tube; a magnetic biochar dosing unit connected to the anaerobic fermentation unit through a sealed pipeline, comprising a storage tank and a screw feeder; an intelligent control unit comprising a sensor array and an actuator; the sensor array monitors the oxidation-reduction potential, pH, volatile fatty acids, and methane production in real time; the actuator dynamically adjusts the type of gas source, gas flow, and magnetic biochar dosage.

2. A regulatory system for anaerobic digestion according to claim 1, characterized in that: In the bubble generating assembly: the throat of the Venturi tube is connected to the micro-porous membrane assembly; after pre-dispersion through the micro-porous membrane, the gas enters the throat of the Venturi tube and is sheared and broken into micro-nano bubbles of 50-500 nm in size in the contraction section.

3. A regulatory system for anaerobic digestion according to claim 2, wherein: The sealed pipeline of the magnetic biochar dosing unit is protected by nitrogen throughout, maintaining an oxygen content of <0.1%.

4. A method for regulating anaerobic digestion, applied to a system for regulating anaerobic digestion according to any one of claims 1 to 3, characterized in that: Comprising the following steps: Phase determination: based on the changes in oxidation-reduction potential, volatile fatty acids, and gas production parameters during anaerobic digestion, the reaction process is divided into hydrolysis, acid production, and methane production stages; Dynamic intervention: During the hydrolysis stage, micro-nano bubbles with a N2 volume fraction of ≥95% are introduced; During the acid production stage, micro-nano bubbles with a H2 volume fraction of ≥95% are introduced; During the methane production stage, micro-nano bubbles are stopped, and magnetic biochar is added.

5. A method for regulating anaerobic digestion according to claim 4, characterized in that: The logic of the phase determination includes: Hydrolysis stage: when the oxidation-reduction potential is below the first threshold value and the volatile fatty acid is below the second threshold value; Acid production stage: when the volatile fatty acid is above the third threshold value or the pH is below the fourth threshold value; Methane production stage: when the methane production is above the fifth threshold value and the H2 concentration is below the sixth threshold value.

6. A method for regulating anaerobic digestion according to claim 5, characterized in that: The first threshold value is -200 mV to -300 mV, the third threshold value is 1000-2000 mg / L, and the sixth threshold value is 800-1200 ppm.

7. The method for regulating anaerobic digestion according to claim 4, wherein: Also includes abnormal regulation: When the oxidation-reduction potential is >-200 mV, start H2 micro-nano bubbles; When the volatile fatty acid is >2000 mg / L, introduce CO2 micro-nano bubbles with a volume fraction of ≥90% into the reactor.

8. A method of producing magnetic biochar, characterized by: Comprising: Step S1, reacting iron-containing raw materials with a reducing agent under an inert atmosphere to form a complex containing zero-valent iron; Step S2, performing anaerobic solid-liquid separation and cleaning of the reaction product; Step S3, shaping the separated solid under low-temperature conditions to maintain the porous structure; Step S4, crushing, grading, and packaging the shaped solid in an anaerobic environment.

9. A method of producing magnetic biochar according to claim 8, characterised in that: The low-temperature condition is -30℃ to -70℃, and the shaping treatment time is 48-96 hours.

10. The method of claim 8, wherein the magnetic biochar is prepared by: The particle size after grading in step S4 is ≤150 μm, and the packaging is performed in an anaerobic environment with residual O2 <0.1% in a gas-tight container.

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