Humic acid capacitor for exciting microbial electrical metabolism and application of humic acid capacitor in anaerobic digestion

Abstract

The invention discloses a humic acid capacitor for stimulating microbial electrical metabolism and application of the humic acid capacitor in anaerobic digestion, and belongs to the field of biological metabolism and transformation application. The electron storage capacity of humic acid is improved through micro-current catalysis, so that the humic acid becomes a biological capacitor capable of promoting microbial electrical metabolism. The biological capacitor can be used for adjusting unbalanced metabolism between acid-producing bacteria and methanogens in the sludge anaerobic digestion process, the electron utilization rate in a biological metabolism and conversion system is improved, and the methane production performance of sludge anaerobic digestion is greatly improved; the humic acid capacitor can increase the daily methane yield in the sludge anaerobic digestion process by 80-100%. According to the method, the biological capacitor with excellent performance can be obtained only by applying the micro current, and the method is green, environment-friendly, low in cost and high in efficiency, is a new method and idea for improving the anaerobic digestion performance of the sludge, can be popularized to the fields of development and utilization of new energy such as other biological metabolism and conversion and solar energy, and has huge application value.

Description

Technical Field

[0001] The invention relates to a humic acid capacitor for stimulating microbial electrical metabolism and a method for applying the capacitor to anaerobic digestion of sludge, and belongs to the field of biological metabolism and conversion application. Background Art

[0002] Municipal sludge is rich in organic matter, heavy metals, pathogenic microorganisms and other components. If it is directly piled up without proper treatment, it may cause serious pollution to the surrounding surface water, groundwater and soil environment. The use of anaerobic digestion technology can achieve sludge reduction, harmlessness and resource utilization, which can not only solve the problem of sludge pollution, but also bring economic benefits. In the process of anaerobic digestion of sludge, acidogenic bacteria and methanogenic bacteria are in a symbiotic relationship. Unbalanced electron metabolism will cause the system to be unbalanced, which will lead to problems such as hydrolysis acidification and low methanogenesis efficiency in anaerobic digestion of sludge. Among them, the unbalanced metabolism between acidogenic bacteria and methanogenic bacteria is the key factor affecting the efficiency of anaerobic digestion.

[0003] In anaerobic digestion of sludge under high-load conditions, methanogens often cannot consume the excess electrons and hydrogen ions produced by the oxidation of organic matter in a timely manner, resulting in the accumulation of H2 in the system. + The Gibbs free energy of reduction to H2 will become positive, thus preventing the spontaneous conversion of organic matter in the hydrolytic acidification stage. Therefore, the hydrolytic acidification process at the front end may be inhibited. Although the addition of electron shuttles can improve the efficiency of electron transfer between microorganisms, the problem of metabolic imbalance between acidogens and methanogens remains unsolved.

[0004] Therefore, it is necessary to develop a new method to solve this problem. Summary of the invention

[0005] The problem to be solved by the present invention is the unbalanced metabolism of acidogenic bacteria and methanogenic bacteria, low organic matter conversion rate and poor methanogenic performance during the anaerobic digestion of municipal sludge. The present invention drives humic acid through electric potential to make it a biocapacitor with good electron storage capacity, thereby improving the methanogenic performance of the sludge anaerobic digestion system.

[0006] The first aspect of the present invention is to provide a method for preparing a humic acid capacitor for stimulating microbial electrical metabolism, comprising the following steps:

[0007] S11. dissolving humic acid in an alkaline water sample, and then adjusting the pH to prepare a humic acid concentrate;

[0008] S12. Inject the humic acid concentrate into a micro-current electrolytic cell with positive and negative electrodes, fill it with inert gas to lower the redox potential of the reactor, stop ventilation, seal the reactor, start stirring under anaerobic conditions, and apply external voltage to electrocatalyze humic acid to form a humic acid capacitor.

[0009] Humic acid is rich in quinone, hydroquinone and other electron-carrying groups, which have the ability to accept / release electrons. When the number of electron-carrying groups Q1 in the quinone side chain of humic acid reaches a certain level, humic acid can have 1-10 mmol e - / g's ability to accept electrons plays a good role in electron storage.

[0010] Furthermore, the humic acid used in step S11 comes from a natural environment with strong reducing properties, such as sludge and soil.

[0011] Humic acid is abundant in municipal sludge, accounting for about 6% to 20% of organic matter (based on VSS), but it is mainly distributed in the solid phase of sludge. With the widespread application of thermal hydrolysis technology, a large amount of humic acid organic matter is released into the liquid phase. Soluble humic acid becomes the main component of residual organic matter in sludge digestion liquid.

[0012] In some embodiments of the present invention, the humic acid reducing property is ≤100 mV.

[0013] Further, in step S11, the pH of the alkaline water sample is ≥ 11.0, and the pH is adjusted to 6.0-8.0;

[0014] In some embodiments of the present invention, in step S11, the dissolution process of humic acid is: first dissolving humic acid powder in alkaline water sample (pH>11.0), and then adjusting the humic acid solution to neutral (pH=7.0).

[0015] In some embodiments of the present invention, in step S11, the concentration of the humic acid concentrate is ≤50 g / L. The lower the concentration of humic acid, the better the activity effect, but the lower the electricity utilization efficiency.

[0016] In some embodiments of the present invention, in step S12, the redox potential of the electrolytic cell is controlled at -200 to -600 mV.

[0017] Potential drive can change the structural characteristics of humic acid, expose more quinone groups, and increase the electron storage capacity of humic acid. Humic acid capacitors accept and store electrons produced by electrodes and acid-producing microorganisms, and release them to the methanogenic process under appropriate conditions to promote the metabolism of methanogens. Humic acid has good stability in the anaerobic digestion process, so its pseudocapacitive characteristics play a stable role, promote the metabolism of microorganisms in the anaerobic digestion of sludge, and improve the methanogenic performance and treatment efficiency of anaerobic digestion of sludge.

[0018] In some embodiments of the present invention, in step S12, the power-on time is 1-48 hours. Preferably, the power-on time is 24.0 hours.

[0019] In some embodiments of the present invention, in step S12, the temperature is 20-50°C;

[0020] In some embodiments of the present invention, in step S12, the current is controlled to be 0.5-5.0 mA.

[0021] In a preferred embodiment, in step S12, the redox potential of the electrolytic cell is controlled at -200 to -600 mV, the pH value is 6.0-8.0, and the stirring speed is ≥50 rpm.

[0022] The second aspect of the present invention is to provide a humic acid capacitor prepared by the method, wherein the specific capacitance of the humic acid capacitor is 10-100 μF / g.

[0023] In some embodiments of the present invention, the specific capacitance of the humic acid capacitor is 60-85 μF / g.

[0024] The third aspect of the present invention is to provide a humic acid capacitor prepared by the method, comprising the following steps:

[0025] S21. Mixing an appropriate amount of humic acid capacitor with organic waste and adding inoculated sludge to construct an anaerobic digestion reaction system;

[0026] S22. Introduce positive and negative electrodes into the anaerobic digestion system of step S21, and charge the humic acid capacitor material in the reactor at a certain frequency. After the humic acid capacitor material obtains electrons, it slowly releases the electrons and transfers them to the microorganisms. The humic acid capacitor material that loses electrons regains electrons in the next charging cycle and continues to participate in the microbial electrical metabolism.

[0027] In some embodiments of the present invention, in step S21, the humic acid concentration needs to be ≤1.5 g / L; preferably, the humic acid concentration is 0.4-0.8 g / L.

[0028] In some embodiments of the present invention, in step S22, the charging voltage of the anaerobic digestion system is ≤1.2V; preferably, the charging voltage of the anaerobic digestion system is 0.5-0.7V.

[0029] Furthermore, the organic waste includes organic solid waste and organic wastewater.

[0030] In some embodiments of the present invention, in step S22, the charging frequency is ≥ 2.0 h / d.

[0031] In some preferred embodiments, in step S22, the charging frequency is ≥ 4.0 h / d.

[0032] The present invention also provides the application of the above method in the field of biological metabolism and transformation such as organic solid waste and organic wastewater treatment.

[0033] Beneficial effects achieved by the present invention:

[0034] (1) The present invention provides a humic acid capacitor that stimulates microbial electrical metabolism, which has excellent electrical properties, a specific capacitance of up to 80.7 μF / g, and excellent cycle performance;

[0035] (2) The humic acid capacitor provided by the present invention uses electric potential to drive humic acid as a biocapacitor to promote microbial electrical metabolism, improve the electron utilization rate and transfer efficiency between acid-producing bacteria and methanogens during anaerobic digestion, and enhance the anaerobic digestion methanogen performance;

[0036] (3) The preparation method of the humic acid capacitor provided by the present invention is simple in process; the electron storage capacity of humic acid is improved by microcurrent catalysis, making it a biocapacitor that can promote microbial electrical metabolism. After the electrochemical system electrocatalyzes humic acid, more high-density storage groups are exposed, which improves the storage capacity of humic acid and enhances the positive effect of humic acid on anaerobic microbial metabolism; the pseudocapacitive properties of humic acid can be directionally improved, making humic acid a biocapacitor that stimulates microbial electrical metabolism;

[0037] (4) The present invention also provides the application of humic acid capacitors in the anaerobic digestion and degradation of organic waste. The humic acid capacitors can significantly improve the anaerobic methane production performance during the anaerobic digestion process, and the average daily methane production of the system can be increased by 40%-100%. The present invention solves the problems of system instability and low organic matter conversion rate caused by the metabolic imbalance between acid-producing bacteria and methanogens during the anaerobic digestion of sludge, and provides a new solution for improving the methane production performance of anaerobic digestion of sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings:

[0039] Figure 1 The storage capacity (a) and quinone content (b) of humic acid after different charging times in Example 1;

[0040] Figure 2 Gas production performance of sludge anaerobic digestion system under different charging time of humic acid in Example 2;

[0041] Figure 3 The gas production performance of the sludge anaerobic digestion system under the humic acid capacitor charge and discharge cycle conditions in Example 3. DETAILED DESCRIPTION

[0042] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification. The experimental methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0043] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other different ways, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. The present invention is not limited to the specific embodiments disclosed below.

[0044] In the following embodiments,

[0045] (1) Humic acid capacitance cyclic voltammetry:

[0046] The test instrument is Chenhua CHI660E electrochemical workstation, a three-electrode system, including a glassy carbon working electrode, a platinum wire counter electrode and an Ag / AgCl reference electrode (Luton R0303, Shanghai). All potentials in the present invention are based on the saturated Ag / AgCl reference electrode. The measurement was carried out in the potential range of -0.8 to +0.8V (relative to Ag / AgCl) under anaerobic conditions, with a scanning rate of 10mV / s and a test temperature of 30°C. 30mg / L humic acid was dissolved in an electrolyte of 50mM phosphate buffer (pH=7.0), purged with N2 and saturated with the solution for 1 hour to eliminate oxygen. Considering that the properties of humus are affected by light, all tests were carried out in the dark.

[0047] (2) The methane content was determined by gas chromatography: the test instrument was a Fuli GC-9790Ⅱ high-efficiency gas chromatograph, the column box temperature was 100°C, the injection temperature was 150°C, and the methane peak time was 3.642 min;

[0048] The municipal sludge was dewatered sludge from Wuxi Shuofang Municipal Wastewater Treatment Plant. The electrochemical reactor uses a single-chamber reactor, the reactor anode is a carbon brush, the cathode is a nickel mesh, and the anode and cathode are connected to the external circuit using titanium wire. Two openings are set on the top of the reactor for sampling and gas collection.

[0049] Example 1 Preparation of Humic Acid Capacitor

[0050] First, take an appropriate amount of sludge humic acid and dissolve it in 1mol / L NaOH solution to obtain 10g / L humic acid alkaline concentrate. Then adjust the pH of the humic acid concentrate to 7 with 1mol / L HCl. Then inject the sludge humic acid concentrate (300mL) into a micro-current electrolyzer with anode and cathode electrodes, fill with nitrogen to reduce the redox potential of the reactor, stop nitrogen filling, seal the reactor, and ensure an anaerobic environment. In a constant temperature chamber at 37°C, stir with a magnetic stirrer, apply 2mA micro-current to charge the humic acid concentrate, and set the charging time to 0, 12, 24, 36, 48h.

[0051] The humic acid concentrate was taken out after being charged by the electrochemical system, and a certain amount of the concentrate was diluted to 30 mg / L with PBS solution. The capacitance of the humic acid after charging was measured using a three-electrode system. The results are as follows: Figure 1 As shown in (a), the capacitance of humic acid increases first and then decreases with the increase of charging time. The capacitance of humic acid charged for 24 hours can be increased by 30.1%. It can be seen that the appropriate charging time can enable humic acid to fully accept the oxidizing force / reducing force from the electrode, humic acid exposes more high-density electron-carrying groups, and the pseudocapacitive characteristics of humic acid are prominent.

[0052] For further verification, reduction-oxidation cycle treatment was used to qualitatively and quantitatively analyze the quinone groups in humic acid.

[0053] The humic acid concentrates of each group after charging in Example 1 were diluted to 0.5 g / L, and then the 0.5 g / L humic acid solution was placed in three serum bottles. The pH was adjusted to 6.5, 8 and 8, respectively, and then Pd-C, Pd-C and Pd catalysts were added respectively. After being exposed to hydrogen for 30 minutes, the mixture was placed in a constant temperature shaker for reaction for 24 hours. 500 μL of the sample was taken and filtered through a 0.22 μm filter membrane to determine the number of electron transfers of the reduced sample. Then the catalyst in the remaining sample was removed, the air was exposed for 30 minutes, and 500 μL of the sample was taken to determine the number of electron transfers of the oxidized sample. Then the remaining sample was exposed to nitrogen for 30 minutes at 40°C and the catalyst was added again to prepare for the next reduction-oxidation cycle. The reduction-oxidation cycle was carried out three times in total. The measurement of the number of electron transfers of humic acid was carried out in an anaerobic glove box. 100 μL of the humic acid sample and 100 μL of potassium ferrocyanide solution were mixed and reacted for 30 minutes, and the Fe(Ⅱ) concentration was determined by the Ferrozine method. The number of electrons transferred from the humic acid sample to Fe(III) was calculated according to the Fe(II) concentration, and the difference between the number of electrons transferred from the reduced sample and the oxidized sample was defined as the sample ECC. The humic acid ECC obtained under different experimental conditions was named ECC pH＝6.5 / Pd-C 、ECC pH-8 / Pd-C and ECC pH＝8 / PdThe contents of Q1, Q2 and NQ in humic acid quinone groups were calculated using the following formula. Figure 1 As shown in (b), the content of the electron-carrying group Q1 on the quinone side chain of humic acid increases first and then decreases with the increase of charging time. The content of the Q1 group in the humic acid charged for 12-48 hours increases significantly to 69.3-80.7 μF / g, and the increase after charging for 24 hours reaches 30.2%.

[0054]

[0055] in:

[0056] ECC pH＝6.5 / Pd-C =ECC-R pH＝6.5 / Pd-C -ECC-O pH＝6.5 / Pd-C

[0057] ECC pH＝8 / Pd =ECC-R pH＝8 / Pd -ECC-O pH＝8 / Pd

[0058] ECC pH＝8 / Pd-C =ECC-R pH＝8 / Pd-C -ECC-O pH＝8 / Pd-C

[0059] Example 2

[0060] First, the residual sludge is adjusted to a moisture content of 90%, and thermally hydrolyzed at a temperature of 100°C for 30 minutes to release the organic matter in the sludge into the liquid phase. The solid phase residue in the thermal hydrolysis product is removed by solid-liquid separation to obtain a sludge hydrolyzate; due to the low hydrolysis temperature, the humic acid concentration of the sludge hydrolyzate is negligible. The humic acid capacitor electrocatalyzed by the electrochemical system in Example 1 is added to the sludge hydrolyzate, and inoculated sludge is added to construct an anaerobic digestion reaction system, and a semi-continuous anaerobic digestion methane production experiment is carried out. The working volume of the reactor is 300mL, the inoculation ratio is 10%, the pH of the reaction system is 7.0±1.0, and the organic load is 2.5kg / L · d -1 , the feeding frequency is 1 day / time.

[0061] The experimental results are as follows Figure 2 As shown, the average daily methane production during the experimental period of adding humic acid capacitors charged for 24 hours can reach 150.9mL, which is 105.0% higher than that of the blank control group.

[0062] Example 3

[0063] First, the residual sludge is adjusted to a moisture content of 90%, and thermally hydrolyzed at a temperature of 100°C for 30 minutes to release the organic matter in the sludge into the liquid phase. The solid phase residue in the thermal hydrolysis product is removed by solid-liquid separation to obtain a sludge hydrolyzate; due to the low hydrolysis temperature, the concentration of humic acid in the sludge hydrolyzate can be ignored. The humic acid capacitor charged for 24 hours in Example 1 is added to the sludge hydrolyzate, and inoculated sludge is added to construct an anaerobic digestion system, and a semi-continuous anaerobic digestion experiment is carried out. The working volume of the reactor is 300mL, the inoculation ratio is 10%, the pH of the reaction system is 7.0±0.1, and the organic load is set to 2.5kg / L in the blank control stage. · d -1 The feeding frequency is 1 time per day. After entering the charging and discharging stage of the humic acid capacitor, no more feeding and discharging is done. A certain mass of hydrolyzate is added to the system every day to supplement the organic substrate consumed by gas production, and the reactor is charged at a certain frequency.

[0064] After testing, it was found that Figure 3 As shown, the humic acid capacitor charged for 24 hours can undergo multiple charge and discharge cycles. After 2 cycles, the daily methane production of the anaerobic digestion system containing the humic acid capacitor can still reach 177.6 mL, which is 101.4% higher than that of the blank control group.

[0065] The humic acid capacitor provided by the present invention can promote microbial electrical metabolism, regulate the metabolic balance between acid-producing bacteria and methanogens, and improve the anaerobic digestion performance of sludge. The preparation method is simple. After the electrochemical system electrocatalyzes humic acid, more high-density electricity storage groups are exposed, which improves the electricity storage capacity of humic acid and enhances the positive effect of humic acid on anaerobic microbial metabolism. The humic acid capacitor improves the electron utilization rate and transfer efficiency between acid-producing bacteria and methanogens during anaerobic digestion, enhances the anaerobic digestion methane production performance, and the average daily methane production of the system can be increased by 40%-100%; it solves the problems of system instability and low organic matter conversion rate caused by the metabolic imbalance between acid-producing bacteria and methanogens during anaerobic digestion of sludge, and provides a new solution for improving the methane production performance of anaerobic digestion of sludge.

[0066] The technical solution of the present invention only requires the application of a microcurrent to obtain a bio-capacitor with superior performance. It is green, environmentally friendly, low-cost, and highly efficient. It is a new method and idea for improving the anaerobic digestion performance of sludge, and can be extended to other biological metabolism and transformation, as well as new energy development and utilization fields such as solar energy, and has great application value.

[0067] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the present invention.

Claims

1. A method for preparing a humic acid capacitor for stimulating microbial electrical metabolism, characterized in that: The following steps are involved: S11. dissolving humic acid in an alkaline water sample, and then adjusting the pH to prepare a humic acid concentrate; S12. Inject the humic acid concentrate into a micro-current electrolytic cell with positive and negative electrodes, fill it with inert gas to lower the redox potential of the reactor, stop ventilation, seal the reactor, start stirring under anaerobic conditions, and apply external voltage to electrocatalyze humic acid to form a humic acid capacitor.

2. The method for preparing a humic acid capacitor for stimulating microbial electrical metabolism according to claim 1, characterized in that: In step S11, the humic acid reducing property is ≤100mV; And / or, in step S11, the pH of the alkaline water sample is ≥ 11.0, and the pH is adjusted to 6.0-8.0; And / or, in step S11, the concentration of the humic acid concentrate is ≤50 g / L.

3. The method for preparing a humic acid capacitor for stimulating microbial electrical metabolism according to claim 1, characterized in that: In step S12, the redox potential of the electrolytic cell is controlled at -200 to -600 mV.

4. The method for preparing a humic acid capacitor for stimulating microbial electrical metabolism according to claim 1, characterized in that: In step S12, the power-on time is 1-48 hours.

5. The method for preparing a humic acid capacitor for stimulating microbial electrical metabolism according to claim 1, characterized in that: In step S12, the temperature is 20-50°C; And / or, in step S12, the current is controlled at 0.5-5.0 mA.

6. The humic acid capacitor prepared by the method according to any one of claims 1 to 5, characterized in that: The specific capacitance of the humic acid capacitor is 10-100 μF / g.

7. The use of the humic acid capacitor according to claim 6 or the humic acid capacitor obtained by the method according to any one of claims 1 to 5 in anaerobic digestion and degradation of organic waste, characterized in that: The following steps are involved: S21. Mixing an appropriate amount of humic acid capacitor with organic waste and adding inoculated sludge to construct an anaerobic digestion reaction system; S22. Introduce positive and negative electrodes into the anaerobic digestion system of step S21, and charge the humic acid capacitor material in the reactor at a certain frequency. After the humic acid capacitor material obtains electrons, it slowly releases the electrons and transfers them to the microorganisms. The humic acid capacitor material that loses electrons regains electrons in the next charging cycle and continues to participate in the microbial electrical metabolism.

8. The use according to claim 7, characterized in that: In step S21, the humic acid concentration needs to be ≤1.5 g / L; And / or, in step S22, the charging voltage of the anaerobic digestion system is ≤1.2V.

9. The use according to claim 8, characterized in that: In step S21, the humic acid concentration is 0.4-0.8 g / L; And / or, in step S22, the charging voltage of the anaerobic digestion system is 0.5-0.7V.

10. The use according to claim 7, characterized in that: The organic waste includes organic solid waste and organic wastewater; And / or, in step S22, the charging frequency is ≥ 2.0 h / d.

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