Method for promoting anaerobic digestion of municipal sludge by magnetic field driven magnetic biochar

Abstract

The present application relates to a kind of magnetic field driven magnetic biochar promotes the method for anaerobic digestion of municipal sludge, belong to sludge resource technology field.The present application is in anaerobic reactor with municipal sludge as substrate, magnetic biochar is added, while electric field is applied around anaerobic reactor to carry out anaerobic digestion methane production.By changing the applied voltage of electric field and other conditions, magnetic biochar is mixed uniformly in the reactor without precipitation.This can more effectively play the role of magnetic biochar conductivity, promote municipal sludge methane production fermentation.The method of the present application can not only reduce the great harm caused by municipal sludge, but also turn waste into treasure, carry out resource rational utilization, and has significant practical significance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sludge resource utilization, in particular to a method for promoting anaerobic digestion of municipal sludge by magnetic field driven magnetic biochar. BACKGROUND

[0002] With the continuous expansion of industrialization process and urbanization trend in China, the amount of urban sewage is increasing day by day, and a large amount of sludge will be derived after the harmless treatment of sewage. With the continuous advancement of sewage treatment technology, the sewage treatment rate and sludge production are increasing day by day, and the sewage sludge production can reach 7t per ten thousand people. According to the estimation, the annual output of urban sludge in China will break through 600 million tons by 2020. Due to the excessive heavy metal elements, large amount of bacteria breeding, microbial community enrichment and many kinds of toxic substances in urban sludge, if the urban sludge is not properly treated, it is easy to cause soil and water pollution, seriously endangering the ecological environment and human health. Moreover, the urban sludge has high water content and poor mechanical properties, which is easy to cause environmental secondary pollution. Although the urban sludge treatment technology has made great and stable development, due to its high cost and unsatisfactory effect, the safe disposal and utilization of urban sludge have become the current environmental problems that are concerned. However, the urban sludge also contains a large amount of organic matter, carbon, nitrogen, phosphorus and potassium, which can be treated and utilized by professional means, and can be used as a renewable resource that can be comprehensively utilized, which can not only reduce the great harm caused by urban sludge, but also turn waste into treasure and utilize resources reasonably, which has significant practical significance. Anaerobic digestion is one of the best sludge treatment technologies, and it can also produce energy such as methane during the treatment of sludge. However, due to the difficult-to-break microbial cells, complex flocculent structure and difficult-to-degrade organic matter, the organic solid degradation rate and anaerobic digestion rate are still at a low level. Biological carbon is a solid material obtained by high-temperature decomposition of biomass (wood, straw, etc.) carbonization, which mainly contains C, H, O, N, S and other elements. Compared with other conductive materials, biological carbon has the advantages of low cost, large specific surface area, strong adsorption performance and rich functional groups, and is widely used in production and life, such as heavy metal adsorption, wastewater decolorization, soil remediation, etc. In recent years, with the discovery of microbial extracellular respiration, biological carbon as a good conductor has attracted much attention for its role in enhancing microbial extracellular electron transfer. However, research shows that the addition of biological carbon, especially nano-biological carbon, is easy to agglomerate and precipitate to the bottom of the reactor. Nano-Fe3O4 has been widely studied and applied in the field of solid waste treatment due to its small particle size, high conductivity, superparamagnetism, high specific surface area, easy surface modification and biocompatibility. In anaerobic system, nano-Fe3O4 as a conductor material has strong conductivity and can improve the efficiency of electron transfer. In addition, nano-Fe3O4 may also strengthen the processes of organic matter removal and anaerobic methanation through dissimilatory iron reduction. Nano-Fe3O4 particles are loaded and dispersed into the pores and surface of the porous carrier to avoid agglomeration. Moreover, Fe3O4 is compounded with carbon materials with good conductivity to generate magnetic biological carbon, which can effectively improve the conductivity of the material and improve its electrochemical performance. SUMMARY

[0003] To solve the above technical problems, the application provides a method for promoting anaerobic digestion of municipal sludge by magnetic field driven magnetic biochar.

[0004] The application is achieved by the following technical solutions:

[0005] The first object of the application is to provide a method for promoting anaerobic digestion of municipal sludge by magnetic field driven magnetic biochar, which comprises the following steps:

[0006] In the anaerobic reactor, municipal sludge is used as a substrate, and digestion sludge is inoculated and magnetic biochar is added, and an electric field is applied around the anaerobic reactor for anaerobic digestion and methane production.

[0007] In an embodiment of the application, the concentration of the magnetic biochar in the anaerobic reactor is 0.5g / L-2.5g / L, preferably 2.0g / L.

[0008] In an embodiment of the application, the strength of the electric field is 0.6V-2.4V, preferably 1.8V.

[0009] In an embodiment of the application, the conditions for anaerobic digestion are as follows: the temperature for anaerobic digestion is 40℃-45℃; and the pH value for anaerobic digestion is 10-12.

[0010] In an embodiment of the application, the magnetic biochar is prepared by the following method:

[0011] The biomass is crushed and sieved, and calcined to obtain biochar particles. The obtained biochar particles are sequentially subjected to alkali washing, acid washing and alcohol washing to remove ash and grease, and then are ground and sieved to obtain biochar carriers with a particle size of 0.35mm-0.65mm.

[0012] Under the protection of inert gas, the obtained biochar carriers are mixed and stirred with an iron source, and then citric acid and a crosslinking agent are added. After complete dissolution, heating is performed, the pH is adjusted to alkaline, and the reaction is continued to obtain the magnetic biochar.

[0013] The crosslinking agent is selected from ethylenediamine and / or glutaraldehyde.

[0014] In an embodiment of the present application, the biomass is selected from one or more of rice straw, wheat straw and corn straw.

[0015] In an embodiment of the present application, the calcination condition is 550-650 DEG C for 1-2 h.

[0016] In an embodiment of the present application, the iron source is selected from one or more of ferric chloride hexahydrate and / or ferrous sulfate heptahydrate, FeCl2.4H2O and iron acetylacetonate.

[0017] In an embodiment of the present application, the mass ratio of the biochar carrier to the iron source is 1:1-1:2.

[0018] In an embodiment of the present application, the heating temperature is 60-80 DEG C; and the alkaline pH value is 9-10.

[0019] The present application relates to a kind of urban sludge anaerobic treatment method, using unique coprecipitation method to synthesize magnetic biochar with straw as raw material, when the concentration of added magnetic biochar is 2g / L, the optimal voltage intensity is 1.8V, the cumulative methane production is 550mL.

[0020] The above technical scheme of the present application has the following advantages compared with the prior art:

[0021] 1、The present application provides a kind of magnetic field driven magnetic biochar promotes urban sludge anaerobic digestion method, and magnetic biochar preparation is simple, raw material is relatively cheap.

[0022] 2、The addition of citric acid in the present application can enhance the dispersibility, stability and biocompatibility of nano-magnetic particles, solve the problems of traditional coprecipitation method prepared nano-magnetic particles, such as serious agglomeration, large particle size, wide particle size distribution and poor crystallinity.

[0023] 3、The present application adds electric field outside anaerobic fermentation reactor, which can prevent biochar from precipitating and is beneficial to the uniform distribution of magnetic biochar in fermentation reactor. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to make the content of the present application more easily understood, the present application will be further described in detail below according to specific embodiments of the present application and in conjunction with the drawings, wherein

[0025] Figure 1 is the reactor device in the embodiment of the present application;

[0026] Figure 2 is the cumulative methane production of different magnetic biochar concentrations added in the embodiment 2 of the present application;

[0027] Figure 3is the cumulative methane production under different voltages in Example 3 of the present application;

[0028] Figure 4 is the influence of different voltage intensities applied inside on the methane production in the comparative example of the present application. DETAILED DESCRIPTION

[0029] The present application will be further described below in conjunction with the drawings and specific examples, so that those skilled in the art can better understand the present application and implement it, but the examples are not limiting to the present application.

[0030] Example 1

[0031] The present embodiment provides a method for anaerobic treatment of municipal sludge, Figure 1 The reactor device), specifically comprising the following steps:

[0032] (1) The biomass (straw) is broken into 1.5 mm or less by a crusher, sieved, and the obtained powder is filled in a crucible to fullness, and the lid is tightly covered to create an oxygen-limited environment. Then the crucible filled with biomass (straw) is placed in a muffle furnace and calcined at a temperature of 580℃ for 70 min, with a heating rate of 12℃ / min, to produce biochar particles. The produced biochar particles are sequentially subjected to alkali washing (1.25 mol / L sodium hydroxide), acid washing (1.25 mol / L hydrochloric acid), and ethanol cleaning to remove ash and grease in the biochar, and then ground and sieved to obtain biochar carriers.

[0033] (2) 20 mL of ultrapure water is taken in a three-necked flask, and nitrogen gas is introduced at room temperature for 20 min while stirring to exhaust the air in the flask. 0.32 g of biochar carrier, 0.32 g of ferric chloride hexahydrate, and 0.15 g of ferrous sulfate heptahydrate are weighed into the flask for stirring, and then 0.6 g of citric acid and 6 mL of ethylenediamine are added. After stirring until complete dissolution, the stirring mixture is heated to 70℃ in a water bath, and then cooled to 30℃ by stirring. 3M NaOH solution is added dropwise to raise the pH to 9-10, so that the iron oxide precipitate is formed. The stirring reaction is continued in a 30℃ water bath for 1.5 h, and the whole experiment is carried out under nitrogen protection. After the reaction is completed, the stirring is cooled for 15 h, and then separated by a magnet. Finally, the magnetic biochar is washed with distilled water and alcohol.

[0034] (3) The magnetic biochar obtained in step (2) is added to the anaerobic reactor at a concentration of 2.0 g / L. At the same time, an electric field is applied around the anaerobic reactor, and the electric field intensity is controlled at 1.8V. By adjusting the voltage, the distribution of magnetic biochar in the reactor is controlled, so as to increase the electron transfer rate of the system and improve the methane production.

[0035] Example 2

[0036] The embodiment provides effects of different concentrations of magnetic biochar on methane production, and specific steps are as follows:

[0037] Magnetic biochar with concentrations of 0, 0.5 g / L, 1 g / L, 1.5 g / L, 2 g / L and 2.5 g / L is respectively added into an anaerobic digestion reactor containing municipal sludge to produce methane through anaerobic digestion. Cumulative methane production amounts of the magnetic biochar with different concentrations are as shown in Figure 2 Figure 2 It can be seen that, as the addition amount of the magnetic biochar increases, the cumulative methane production amount gradually increases, and when the addition amount reaches 2 g / L, the cumulative methane production amount reaches 200 mL, and when the concentration of the magnetic biochar is further increased, the cumulative methane production amount decreases. This is because high concentration of the magnetic biochar can cause osmotic and oxidative stress of microbial cell walls, and cause toxicity to microorganisms in the system.

[0038] Example 3

[0039] The embodiment provides effects of different voltage intensities on methane production, and specific steps are as follows:

[0040] Magnetic biochar with a concentration of 2 g / L is added into an anaerobic digestion reactor containing municipal sludge, and effects of different voltage intensities on methane production are studied in the range of 0-2.4 V, and results are as shown in Figure 3 Figure 3 It can be seen that, when the optimal voltage intensity is 1.8 V, the cumulative methane production amount is 550 mL. When the voltage intensity exceeds 1.8 V to reach 2.4 V, the cumulative methane production amount decreases to 420 mL. This is because further increasing the voltage is easy to cause effects on anaerobic microorganisms in the granular sludge or even death, and therefore the methane production decreases.

[0041] Comparative Example

[0042] The comparative example provides effects of different voltage intensities applied in the reactor on methane production. The scheme of the comparative example is similar to that of Example 3, and the only difference is that different constant voltages (50 mV, 100 mV, 150 mV, 200 mV) are applied in the anaerobic reactor, and a non-electricity group is set as a control group for experiment.

[0043] ​​The results showed that the cumulative methane production was the highest at 100 mV, which was 268.90 mL, and the cumulative methane production increased by 23.5% compared with the control group without electricity, which was 205 mL. However, when the voltage was continuously increased to 150 mV and 200 mV, the methane production decreased, because the application of 100 mV voltage could improve the relative abundance of acetate-type methanogens, promote the degradation efficiency of substrate acetic acid, and thus improve the methanogenesis efficiency. However, further increasing the voltage would easily affect the anaerobic microorganisms in the granular sludge and even cause death, thus the methane production decreased.

[0044] Obviously, the above examples are only examples for clearly illustrating, not limiting the embodiments. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, all the embodiments are not required to be exhausted, and the obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for promoting anaerobic digestion of municipal sludge by magnetic field driven magnetic biochar, characterized in that, The method comprises the following steps: Methane is produced by anaerobic digestion in an anaerobic reactor, using municipal sludge as a substrate, inoculating digestion sludge, adding magnetic biochar, and applying an electric field around the anaerobic reactor; wherein the TS of the digestion sludge is 62.5 g / L-68.3 g / L, the VS is 33.8 g / L-37.6 g / L, and the VS / TS is 54%-55%; The pH value of the anaerobic digestion is 10-12; the intensity of the electric field is 0.6 V-2.4 V; the electric field can prevent the magnetic biochar from precipitating and is conducive to the uniform distribution of the magnetic biochar in the anaerobic reactor; The magnetic biochar is prepared by the following method: The biomass is crushed, sieved, calcined, and then the obtained biochar particles are sequentially subjected to alkali washing, acid washing, and alcohol washing to remove ash and grease, and then are ground and sieved to obtain a biochar carrier; Under the protection of inert gas, the obtained biochar carrier is mixed and stirred with an iron source, then citric acid and a crosslinking agent are added, and after complete dissolution, heating is performed, the pH is adjusted to alkaline, and the reaction is continued to obtain the magnetic biochar; The heating temperature is 60℃-80℃; the alkaline pH value is 9-10.

2. The method of claim 1, wherein, In the anaerobic reactor, the concentration of the magnetic biochar is 0.5 g / L-2.5 g / L.

3. The method of claim 1, wherein, The conditions of the anaerobic digestion are as follows: the temperature of the anaerobic digestion is 40℃-45℃.

4. The method of claim 1, wherein, The biomass is selected from one or more of rice straw, wheat straw, and corn straw.

5. The method of claim 1, wherein, The calcination conditions are as follows: calcination at 550-650℃ for 1 h-2 h.

6. The method of claim 1, wherein, The iron source is selected from one or more of ferric chloride hexahydrate, ferrous sulfate heptahydrate, FeCl2·4H2O, and acetylacetone iron.

7. The method of claim 1, wherein, The mass ratio of the biochar carrier to the iron source is 1:1-1:2.

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