A device for selectively separating organic acids from anaerobic digestion liquid on-line

Abstract

The present invention provides an online selective separation device for organic acid from anaerobic digestion liquid, which is connected to an anaerobic reactor in which digestion liquid is placed, and comprises: a box body, a cathode and an anode arranged at both ends of the box body, and multiple groups of bipolar membranes and anion exchange membranes alternately stacked between the cathode and the anode, wherein the multiple groups of bipolar membranes and anion exchange membranes divide the box body into multiple compartments, namely, a cathode chamber, an anode chamber, and multiple alkali chambers and multiple acid chambers arranged between the cathode chamber and the anode chamber, the alkali chamber and the anaerobic reactor are connected by a pipeline to form a loop, and a microfilter for microfiltering the digestion liquid is arranged on the pipeline of the digestion liquid in the anaerobic reactor entering the alkali chamber, and a membrane contactor is embedded in the acid chamber. The present invention greatly saves energy consumption and improves the stability and efficiency of anaerobic digestion.

Description

Technical Field

[0001] The invention belongs to the field of anaerobic digestion, and in particular relates to a device for online selective separation of organic acid from anaerobic digestion liquid. Background Art

[0002] After the implementation of garbage classification, a large amount of biodegradable wet garbage (or kitchen waste, perishable garbage) needs to be effectively treated and utilized as a resource. The mainstream treatment method is to use anaerobic digestion technology to reduce the amount of biomass waste while recovering the energy in it in the form of methane. However, the main problems currently faced by anaerobic digestion are: the instability of the methanogenesis stage, the low effective utilization rate and utilization value of methane, and the inconvenience of methane transportation and storage; methanogenic archaea are extremely sensitive to changes in environmental conditions. When environmental conditions fluctuate, it is easy to cause the accumulation of organic acids, especially volatile fatty acids (Volatile Fatty Acids, VFAs), which will further inhibit the activity of methanogens. In severe cases, it may cause the reactor to fail or even need to be restarted.

[0003] On the one hand, separating VFAs and lactic acid from the methanogenic reactor where acid accumulation occurs will effectively improve the stability of the system. On the other hand, VFAs and lactic acid are widely used in the fields of food, chemical industry, medicine, etc., and have a higher market value than methane. VFAs and lactic acid can be efficiently produced by blocking the methanogenic process. In addition, these short-chain VFAs can be extended to medium-chain fatty acids (MCCAs) through microbial carbon chain extension. MCCAs have higher energy density and wider application. At present, the industrial production of the above-mentioned organic acids still depends on petrochemicals. The main obstacle to biological production is the lack of low-cost technology to separate them from anaerobic digestion liquid. Solving the problem of separation from anaerobic digestion liquid, using microorganisms to produce the above-mentioned products through biomass waste will have extremely high environmental benefits and competitiveness.

[0004] At present, the mainstream methods are solvent extraction and distillation, and hydrophobic organic extractants have high selectivity for organic acids. [Chinese invention patent, method and device for extracting organic acids from mixed salts separated from fermentation broth, publication number: CN112479868 A] A hydrophobic organic solvent is used to extract organic acids from mixed salts separated from fermentation broth, and the device includes a connected acid treatment unit, an extraction unit and a distillation unit; [Chinese invention patent, a method for extracting organic acids from fermentation broth, publication number: CN 106748734 A] An ester-containing compound or an alkylamine compound is used as an extractant to extract organic acids from low-pH fermentation broth. On the one hand, the solvent extraction method lacks an effective method for stripping and separating organic acids from the extract, and distillation requires very high energy consumption; on the other hand, the above method cannot be used online, and the direct contact between the extractant and the fermentation broth will be toxic to microorganisms. In addition, a low pH (1.5-3.5) is required to keep the organic acids in the fermentation broth in molecular form before the organic acids can be selectively extracted.

[0005] Membrane-based selective separation technology has the advantages of environmental protection and low cost. For example, using a microporous hydrophobic breathable membrane and using NaOH or KOH solution as the absorption liquid on the other side can extract highly volatile VFAs, but fatty acids with carbon atoms > 4 are often less volatile and the separation effect is not ideal, such as: [Aydin, S., Yesil, H., Tugtas, AE2018. Recovery of mixed volatile fatty acids from anaerobically fermented organic wastes by vapor permeation membrane contactors. Bioresour. Technol., 250, 548-555]; using an organic extraction solvent with high affinity for high-carbon fatty acids (such as mineral oil + 3% trioctylphosphine oxide) combined with a membrane can avoid the contact toxicity of the extractant to microorganisms and achieve selective extraction of C6-C8 fatty acids, such as: [Ge, S., Usack, JG, Spirito, CM, Angenent, LT2015. Long-term n-caproic acid production from yeast-fermentation beer in an anaerobic bioreactor with continuous product extraction.Environ Sci Technol,49(13),8012-8021】. However, the microporous membrane separation method can only allow molecular organic acids to cross the membrane. The pK aBoth are around 4.8, and the pK of lactic acid a Even as low as 3.8, so it is mostly used in a batch mode by adding acid to the digestate. Online use requires the digestate to maintain a very low pH (<5.5), and too low pH will reduce microbial activity and lead to a decrease in production rate.

[0006] The pH of the digestive fluid that is conducive to the acid production of microorganisms is neutral or weakly acidic. Under such conditions, the above organic acids mainly exist in ionic form. Therefore, electrodialysis is an effective way to separate ionic organic acid salts. However, the disadvantage is that other inorganic ions (such as Cl - ,CO3 2- etc.) will cross the ion exchange membrane together, resulting in low product purity and great difficulty in further separation of the mixed salt solution, such as: [Jones, RJ, Massanet-Nicolau, J., Guwy, A., Premier, GC, Dinsdale, RM, Reilly, M. 2015. Removal and recovery of inhibitory volatile fatty acids from mixed acid fermentations by conventional electrodialysis. Bioresource Technology, 189, 279-284].

[0007] Therefore, it is necessary to design a device that can solve the above problems. Summary of the invention

[0008] The present invention is made to solve the above-mentioned problem, and its purpose is to provide a device for online selective separation of organic acid from anaerobic digestion liquid.

[0009] The present invention provides an online selective separation device for organic acid from anaerobic digestion liquid, which is connected to an anaerobic reactor in which digestion liquid is placed, and has the following characteristics: a box body, a cathode and an anode arranged at both ends of the box body, and a plurality of groups of bipolar membranes and anion exchange membranes alternately stacked between the cathode and the anode, wherein the plurality of groups of bipolar membranes and anion exchange membranes divide the inside of the box body into a plurality of compartments, namely a cathode chamber, an anode chamber, and a plurality of alkali chambers and a plurality of acid chambers arranged between the cathode chamber and the anode chamber, and the alkali chamber and the acid chamber are arranged at intervals, the alkali chamber and the anaerobic reactor are connected by a pipeline to form a loop, and a microfilter for microfiltering the digestion liquid is arranged on the pipeline from the digestion liquid in the anaerobic reactor to the alkali chamber, and a membrane contactor is embedded in the acid chamber.

[0010] In the device for online selective separation of organic acids from anaerobic digestion liquid provided by the present invention, it can also have the following characteristics: wherein, the membrane contactor adopts a microporous hydrophobic membrane, the microporous hydrophobic membrane adopts a tubular fiber membrane or a hollow fiber membrane, and the material used for the microporous hydrophobic membrane is any one of polytetrafluoroethylene, polypropylene or polyvinylidene fluoride.

[0011] The device for selectively separating organic acids from anaerobic digestion liquid on-line provided by the present invention may also have the following characteristics: wherein the pore size of the microporous hydrophobic membrane is 0.1 μm to 1 μm, and the effective contact area is 0.05 m 2 .

[0012] The device for online selective separation of organic acids from anaerobic digestion liquid provided by the present invention may also have the following characteristics: wherein the membrane contactor is used to place a solution, the pH value of the solution is greater than or equal to 9 and less than or equal to 12, and the flow rate of the solution is 5 L / h.

[0013] The device for selectively separating organic acids from anaerobic digestion liquid on-line provided by the present invention may also have the following characteristics: wherein the effective area of ​​the anion exchange membrane and the bipolar membrane are both 150 cm 2 , the membrane surface flow rate is 2cm / s~4cm / s.

[0014] The device for online selective separation of organic acids from anaerobic digestion liquid provided by the present invention may also have the following characteristics: wherein the working voltage of the cathode and the anode is 2V to 12V, and the circulation flow rate of the digestion liquid is 40L / h to 100L / h.

[0015] Functions and Effects of the Invention

[0016] The device for selectively separating organic acids from anaerobic digestion liquid online of the present invention utilizes the natural low pH condition formed by the acid chamber, does not need to add additional inorganic acid to the digestion liquid for acidification operation, can be directly coupled to the anaerobic reactor for in-situ and online separation of organic acids without interfering with microbial activity; uses potential difference as the driving force for separation of ionic organic acids, and subsequently uses a membrane contactor to utilize the concentration difference of organic acids for spontaneous diffusion to separate organic acids from mixed salts. Compared with the process requiring distillation, the energy consumption of the entire device is extremely low; avoids the use of a large amount of organic extraction solvents, avoids the toxicity of organic extraction solvents to microorganisms and possible secondary pollution; the device is widely applicable to scenarios, modular combination operation, and can select different stack numbers and membrane contactor types according to the treatment object to highly selectively separate organic acids within a specific carbon atom number range; the OH generated by the alkali chamber - It is recycled back to the reactor together with the digestion liquid and can be used to adjust the pH drop in the reactor caused by acid production, reducing the use of additional chemicals.

[0017] Furthermore, the device for online selective separation of organic acids from anaerobic digestion liquid of the present invention is a bipolar membrane electrodialysis stack unit assembly, which can alternately form acid chambers without acidifying the digestion liquid through the reasonable arrangement of electrodes, anion exchange membranes and bipolar membranes. The ionic organic acid that crosses the anion exchange membrane is converted into a molecular form in the acid chamber and is separated from other ions in combination with an embedded hydrophobic microporous membrane contactor.

[0018] In summary, the present invention can be connected to an anaerobic reactor to achieve online application without adjusting the pH of the digestate, while avoiding the use of a large amount of extractants and distillation, which can greatly save energy consumption; it has a wide range of applicable scenarios and can be used to solve the acid inhibition problem of methanogenic reactors and the product separation problem of acidogenic and carbon chain extension reactors, thereby improving the stability and efficiency of anaerobic digestion. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the device for online selective separation of organic acids from anaerobic digestion liquid of the present invention. DETAILED DESCRIPTION

[0020] In order to make the technical means and effects achieved by the present invention easier to understand, the present invention is described in detail below in conjunction with embodiments and drawings.

[0021] Figure 1 It is a schematic diagram of the device for online selective separation of organic acids from anaerobic digestion liquid of the present invention.

[0022] like Figure 1 As shown, the present invention provides a device for online selective separation of organic acids from anaerobic digestion liquid, which is actually an electrodialysis module, which is connected to an anaerobic reactor 6 in which the digestion liquid is placed, and is used for selectively separating short-chain and medium-chain fatty acids, including acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid and lactic acid, and comprises: a box body 1, a cathode 2 and an anode 3 arranged at both ends of the box body 1, and a bipolar membrane 4 and an anion exchange membrane 5 alternately stacked between the cathode 2 and the anode 3.

[0023] In the present invention, the anaerobic reactor 6 includes an acid-inhibited methanogenic reactor, an acidogenic reactor and a carbon chain extension reactor. The combination of the anaerobic reactor 6 and the microfilter 7 can also be directly realized by a membrane bioreactor. The preferred pore size of the microfilter is 5 μm.

[0024] In the present invention, multiple groups of bipolar membranes 4 and anion exchange membranes 5 divide the interior of the box body 1 into multiple compartments, namely a cathode chamber 8, an anode chamber 9, and multiple alkali chambers 10 and multiple acid chambers 11 spaced between the cathode chamber 8 and the anode chamber 9. In addition, the alkali chamber 10 is connected to the anaerobic reactor 6 through a pipeline to form a loop, and a microfilter 7 for microfiltering the digestive liquid in the anaerobic reactor 6 is provided on the pipeline for the digestive liquid in the anaerobic reactor 6 to enter the alkali chamber, and a membrane contactor 12 is embedded in the acid chamber 11.

[0025] Furthermore, the OH generated in the alkali chamber 10 - The digestate is circulated back to the anaerobic reactor and can be used to adjust the pH value of the anaerobic reactor 6 and alleviate the pH drop caused by acid production.

[0026] In the present invention, the bipolar membranes 4 and the anion exchange membranes 5 are alternately stacked, and the number of stacks can be adjusted according to the amount of digestion liquid to be processed and actual work needs, thereby obtaining different numbers of alkali chambers and acid chambers to meet the needs.

[0027] Furthermore, the effective area of ​​the anion exchange membrane 5 and the bipolar membrane 4 is 150 cm 2 , the membrane surface flow rate is 2cm / s~4cm / s, and the compartment spacing is 5cm.

[0028] In addition, the membrane contactor 12 is used to separate molecular organic acids, using a microporous hydrophobic membrane, a breathable microporous membrane for separating volatile fatty acids, and a microporous membrane filled with an extractant for separating non-volatile organic acids. In addition, the microporous hydrophobic membrane uses a tubular fiber membrane or a hollow fiber membrane, and the material used for the microporous hydrophobic membrane is any one of polytetrafluoroethylene, polypropylene or polyvinylidene fluoride, etc. The pore size of the microporous hydrophobic membrane is 0.1μm to 1μm, preferably 0.1μm to 0.5μm, and the effective contact area is 0.05m 2 The pH value of the solution placed in the membrane contactor 12 is greater than or equal to 9 and less than or equal to 12. When the pH drops below 9, 2M solution is added thereto to restore the pH value to 12, and the flow rate of the solution is 5L / h. The solution placed in the membrane contactor 12 is preferably a NaOH solution or a KOH solution.

[0029] Furthermore, the preparation method of the microporous membrane filled with an organic extractant is as follows: immersing the microporous membrane in an organic extractant, treating it with ultrasound (25kHz~30kHz, 240W) for 15min~30min to allow the extractant to fully fill the micropores, and then removing it and absorbing the organic solvent remaining on the surface. The extractant used to fill the microporous membrane includes: conventional oxygen-containing extractants, such as esters and ethers; organic phosphorus extractants, such as trioctylphosphine oxide and tributyl phosphate; aliphatic amine extractants, such as trioctylamine and dodecylamine.

[0030] In addition, the breathable microporous membrane has high permeability to highly volatile short-chain fatty acids, and the microporous membrane filled with extractant has higher selectivity for fatty acids above C4. They can be selected according to needs, such as selecting a breathable membrane in an organic acid production reactor and selecting an extractant-filled membrane in a carbon chain extension reactor.

[0031] In the present invention, the anode 3 is preferably a titanium ruthenium electrode, the cathode 2 is preferably a stainless steel electrode, the circulation flow rate of the digestion liquid and the acid chamber solution is 40L / h to 100L / h, and the preferred circulation flow rate is 60L / h to 80L / h, and the initial solution of the acid chamber is 0.01M HCl and 0.01M NaCl. In addition, the anode chamber 9 and the cathode chamber 8 are both 5% Na2SO4 solution, the working voltage of the cathode 2 and the anode 3 is 2V to 12V, and the preferred working voltage for the actual digestion liquid is ≥10V.

[0032] Furthermore, the device of the present invention works at room temperature of 10-38°C. When the performance of the membrane is significantly reduced, the alkaline chamber 10 is first cleaned with a 0.2M NaOH solution to wash away most of the organic membrane contamination, and then the alkaline chamber 10 is cleaned with a 0.2M HCl solution to wash away the alkali metal precipitation on the surface of the bipolar membrane 4.

[0033] The working process of the device for online selective separation of organic acids from anaerobic digestion liquid of the present invention specifically includes the following steps:

[0034] Step 1, the alkali chamber 10 is directly connected to the anaerobic reactor 6, the digestate flows through the alkali chamber 10 after microfiltration, and finally circulates back to the anaerobic reactor 6;

[0035] Step 2, under the action of the electric field, the anions (organic acid radicals and other inorganic anions) in the digestion liquid flowing through the alkali chamber 10 are transferred across the anion exchange membrane 5 to the corresponding acid chamber 11;

[0036] Step 3: The bipolar membrane 4 releases H into the acid chamber under the action of the electric field. + , without additional pH adjustment, a pH<3 environment can be formed and maintained in the acid chamber 11, and the ionic organic acid that crosses the anion exchange membrane 5 is converted into a molecular organic acid here;

[0037] In step 4, the acid chamber 11 is embedded with a hydrophobic microporous membrane contactor 12, and one side of the membrane is in contact with the acid chamber solution, and the other side circulates the NaOH solution. The transmembrane pH gradient causes the organic acid molecules to continuously diffuse and transfer from the acid chamber 11 to the absorption liquid, thereby separating them from other anionic impurities.

[0038] <Example 1>

[0039] In this embodiment, volatile fatty acids were extracted from a simulated solution prepared in the laboratory. For volatile small molecule fatty acids, a polytetrafluoroethylene breathable membrane was selected as the microporous membrane; the simulated VFAs solution prepared in the laboratory was 2L in total, containing: 1000mg / L acetic acid, 1000mg / L propionic acid, 1000mg / L butyric acid, 1000mg / L valeric acid, and 3000mg / L NaCl. 2M NaOH and 2M HCl were used to adjust the pH to 7.0. Since the prepared simulated solution did not contain suspended solids (SS), a microfilter was not used, and it was directly circulated in the electrodialysis module of the experimental device through a magnetic pump. The electrodialysis module used two sets of membrane stacks, such as Figure 1 As shown, the circulation flow rate is set to 40L / h, the acid chamber 11 circulates at the same circulation flow rate, and the NaOH in the microporous membrane contactor 12 circulates at a flow rate of 5L / h through a peristaltic pump. After each passage and the electrodialysis chamber are filled with liquid and fully circulated, the DC power supply is turned on and a voltage of 6V is applied. After the current drops below 0.1A, the voltage is slightly increased.

[0040] After 2 h of DC electric field application, the fatty acids in the simulated solution dropped to less than 5% of the initial concentration, among which the concentration of acetic acid dropped the fastest, with a transfer rate of 97% at 60 min and 99% at 2 h. The organic acid radicals transferred to the acid chamber 11 reacted with the H generated by the electrolysis of water by the bipolar membrane 4. + Combined into molecular organic acids, since the solution inside the membrane contactor 12 always maintains 12≥pH≥9, the organic acids across the microporous membrane are immediately absorbed and converted into ionic form again, so there is a continuous concentration gradient on both sides of the membrane contactor 12 to maintain the transmembrane transfer of organic acids. After 2 hours of power-on, the concentrations of organic acids in the NaOH solution inside the membrane contactor 12 are: acetic acid 430mg / L, propionic acid 372mg / L, butyric acid 401mg / L, valeric acid 364mg / L, indicating that the extraction speed through the membrane contactor 12 is slow, and some organic acids still remain in the acid chamber 11.

[0041] The low voltage of 2 V was maintained to prevent the reverse diffusion of organic acid radicals through the anion exchange membrane 5, and the NaOH absorption solution and the acid chamber solution were continuously circulated. After another 2 hours, the final recovery rates of the organic acids were: acetic acid 78%, propionic acid 65%, butyric acid 72%, and valeric acid 73%.

[0042] The following is a method for separating organic acids from anaerobic digestion liquid online using the device of this embodiment, and the specific steps are as follows:

[0043] Step 1, connecting the device of Example 1 to an anaerobic acid production reactor, the anaerobic acid production reactor (hereinafter referred to as the reactor) has an effective working volume of 3L, uses food waste collected from the cafeteria as feed, has an organic load of 23g COD / L / d, a hydraulic retention time of 2d, an initial reactor pH of 6.84, and does not control the pH of the anaerobic acid production reactor initially. When the pH of the anaerobic acid production reactor naturally drops to 5.5 (about the 7th day, the acetic acid concentration reaches 1173mg / L, the propionic acid concentration reaches 3866mg / L, the butyric acid concentration reaches 4600mg / L, and the content of other acids is relatively low), the device is turned on to simultaneously perform separation of organic acids and pH control.

[0044] Step 2, using a jet pump to circulate the digestate from the anaerobic acid production reactor through the microfilter 7 at a cross-flow rate of 40L / h, the filtrate flow rate is about 1L / h, and the filtrate is sent to the circulation of the electrodialysis module by a peristaltic pump. The magnetic pump provides internal circulation at a circulation flow rate of 60L / h, and the volume of the circulating part is maintained at 2L. The acid chamber liquid and the pole chamber liquid circulate internally at the same flow rate; the initial voltage is 15V, and after maintaining the above conditions for stable operation for 12h, the pH of the reactor slowly recovers to 7.0. At this time, the acetic acid concentration in the anaerobic acid production reactor drops to 3240mg / L, the propionic acid concentration drops to 1935mg / L, and the butyric acid concentration drops to 2288mg / L. Through balance, the recovery rate of organic acids finally recovered in the NaOH absorption solution is: acetic acid 62%, propionic acid 48%, butyric acid 48%.

[0045] Step 3, the opening of the device can effectively adjust the pH in the reactor. In order to efficiently produce acid and recover it, the pH of the reactor is maintained at 6.5-7.0. After the above device has been running for 12 hours, the pH is adjusted to the target range, and the connection with the reactor can be disconnected to clean the membrane assembly. The alkaline chamber liquid and the acid chamber liquid are replaced with a cleaning solution and circulated at a flow rate of 80L / h. The cleaning solution is: first use 0.2M NaOH solution to clean the alkaline chamber 10 to wash away most of the organic membrane contamination, and then use 0.2M HCl solution to clean the alkaline chamber 10 to wash away the alkali metal precipitation on the surface of the bipolar membrane 4.

[0046] Step 4, when the pH of the reactor drops below 6.5 again, connect the cleaned device and start it, and repeat step 2 of this embodiment. When the pH is restored, repeat step 3 to achieve online organic acid separation and pH control.

[0047] <Example 2>

[0048] The experimental apparatus and settings of this embodiment are the same as those of Example 1, except that the microporous membrane contactor is replaced with a microporous membrane contactor filled with the extractant trioctylamine, and the following are additionally added to the simulated solution: caproic acid 1000 mg / L, lactic acid 1000 mg / L, and other operating conditions are consistent with those of Example 1. The final recovery rates of various organic acids are: acetic acid 39%, propionic acid 76%, butyric acid 85%, valeric acid 89%, caproic acid 91%, and lactic acid 42%.

[0049] <Example 3>

[0050] The experimental device of this embodiment is the same as that of embodiment 1, except that VFAs are extracted from actual anaerobic digestion liquid. The actual digestion liquid is taken from an anaerobic digestion tank in the acid production stage using food waste as raw material, with a pH of 7.35, and the pH is no longer adjusted separately. The VFAs and concentrations contained therein are: acetic acid 12667 mg / L, propionic acid 7335 mg / L, butyric acid 4025 mg / L, valeric acid 481 mg / L, and caproic acid 58 mg / L. The fermentation liquid has a high content of C2-C4 fatty acids and a low content of fatty acids >C4. The microporous membrane is a microporous breathable membrane consistent with that in embodiment 1.

[0051] The digestate was first filtered through a 5 μm microfiltration membrane to remove SS, and the filtrate was Figure 1 The alkali chamber 10 of the electrodialysis module is circulated in the manner shown, and the circulation flow rate is set to 80L / h, with a stronger surface flow rate for flushing to reduce possible scaling effects. The acid chamber 11 circulates at the same circulation flow rate. The NaOH circulation flow rate in the membrane contactor 12 is consistent with that in Example 1. After each passage and the electrodialysis chamber are filled with liquid and fully circulated, the DC power supply is turned on and a voltage of 8V is applied. When the current drops below 0.2A, the voltage is increased to 12V. After 2h, more than 90% of the acetic acid, and more than 80% of the propionic acid, butyric acid and valeric acid are transferred across the anion exchange membrane 5 to the acid chamber 11. A low voltage of 2V is maintained to prevent reverse diffusion, and the NaOH absorption liquid and the acid chamber solution continue to circulate.

[0052] After another 2 hours, the final recovery rates of the organic acids were: acetic acid 71%, propionic acid 57%, butyric acid 61%, and valeric acid 69%.

[0053] Functions and Effects of the Embodiments

[0054] It can be seen from Examples 1 to 3 that when the device of the present invention is connected to an anaerobic reactor, after a certain period of reaction, the final recovery rate of organic acid is high and the effect is good.

[0055] The device for selectively separating organic acids from anaerobic digestion liquid online of the present invention utilizes the natural low pH condition formed by the acid chamber, does not need to add additional inorganic acid to the digestion liquid for acidification operation, can be directly coupled to the anaerobic reactor for in-situ and online separation of organic acids without interfering with microbial activity; uses potential difference as the driving force for separation of ionic organic acids, and subsequently uses a membrane contactor to utilize the concentration difference of organic acids for spontaneous diffusion to separate organic acids from mixed salts. Compared with the process requiring distillation, the energy consumption of the entire device is extremely low; avoids the use of a large amount of organic extraction solvents, avoids the toxicity of organic extraction solvents to microorganisms and possible secondary pollution; the device is widely applicable to scenarios, modular combination operation, and can select different stack numbers and membrane contactor types according to the treatment object to highly selectively separate organic acids within a specific carbon atom number range; the OH generated by the alkali chamber - It is recycled back to the reactor together with the digestion liquid and can be used to adjust the pH drop in the reactor caused by acid production, reducing the use of additional chemicals.

[0056] Furthermore, the device for online selective separation of organic acids from anaerobic digestion liquid of the present invention is a bipolar membrane electrodialysis stack unit assembly, which can alternately form acid chambers without acidifying the digestion liquid through the reasonable arrangement of electrodes, anion exchange membranes and bipolar membranes. The ionic organic acid that crosses the anion exchange membrane is converted into a molecular form in the acid chamber and is separated from other ions in combination with an embedded hydrophobic microporous membrane contactor.

[0057] In summary, the present invention can be connected to an anaerobic reactor to achieve online application without adjusting the pH of the digestate, while avoiding the use of a large amount of extractants and distillation, which can greatly save energy consumption; it has a wide range of applicable scenarios and can be used to solve the acid inhibition problem of methanogenic reactors and the product separation problem of acidogenic and carbon chain extension reactors, thereby improving the stability and efficiency of anaerobic digestion.

[0058] The above-mentioned embodiments are preferred examples of the present invention and are not intended to limit the protection scope of the present invention.

Claims

1. A device for selectively separating organic acids from anaerobic digestion liquid online, connected to an anaerobic reactor containing digestion liquid, characterized in that: include: A box body, a cathode and an anode disposed at both ends of the box body, and a plurality of groups of bipolar membranes and anion exchange membranes alternately stacked between the cathode and the anode. The plurality of groups of bipolar membranes and anion exchange membranes divide the interior of the box into a plurality of compartments, namely, a cathode chamber, an anode chamber, and a plurality of alkali chambers and a plurality of acid chambers spaced between the cathode chamber and the anode chamber. The alkali chamber and the anaerobic reactor are connected by a pipeline to form a loop, and a microfilter for microfiltering the digestive liquid is arranged on the pipeline where the digestive liquid in the anaerobic reactor enters the alkali chamber. A membrane contactor is embedded in the acid chamber. The membrane contactor adopts a microporous hydrophobic membrane. The microporous hydrophobic membrane adopts a tubular fiber membrane or a hollow fiber membrane. The material of the microporous hydrophobic membrane is any one of polytetrafluoroethylene, polypropylene or polyvinylidene fluoride. The membrane contactor is soaked and filled with an extractant, trioctylamine.

2. The device for online selective separation of organic acids from anaerobic digestion liquid according to claim 1, characterized in that: in, The pore size of the microporous hydrophobic membrane is 0.1 μm to 1 μm, and the effective contact area is 0.05 m 2 .

3. The device for online selective separation of organic acids from anaerobic digestion liquid according to claim 1, characterized in that: in, The membrane contactor is used to place a solution, the pH value of the solution is greater than or equal to 9 and less than or equal to 12, and the flow rate of the solution is 5 L / h.

4. The device for online selective separation of organic acids from anaerobic digestion liquid according to claim 1, characterized in that: in, The effective area of ​​the anion exchange membrane and the bipolar membrane is 150 cm 2 , the membrane surface flow rate is 2cm / s~4cm / s.

5. The device for online selective separation of organic acids from anaerobic digestion liquid according to claim 1, characterized in that: in, The working voltage of the cathode and the anode is 2V to 12V, and the circulation flow rate of the digestive liquid is 40L / h to 100L / h.

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