CN112430631B

CN112430631B - Application of alkali-treated biogas residues in methane production

Info

Publication number: CN112430631B
Application number: CN202011537849.4A
Authority: CN
Inventors: 黄振兴; 朱剑豪; 王涛; 廖家林; 阮文权
Original assignee: Jiangnan University
Current assignee: Jiangnan University
Priority date: 2020-12-23
Filing date: 2020-12-23
Publication date: 2023-06-13
Anticipated expiration: 2040-12-23
Also published as: CN112430631A

Abstract

The invention discloses an application of alkali treatment biogas residues in methane production, and belongs to the technical field of treatment and utilization of solid organic wastes. The preparation method of the alkali-treated biogas residue comprises the steps of firstly carrying out anaerobic fermentation on straws, and then carrying out alkali treatment on the straw biogas residue after anaerobic fermentation; the invention adopts straw and alkali treatment biogas residues as substrates, and methane is produced through anaerobic fermentation. Biogas residues obtained after anaerobic fermentation of straw have quite large methane production potential. According to the invention, straw biogas residues are subjected to hot alkali post-treatment, so that the biogas yield is improved by 33% and the methane yield is improved by 35% under high organic load.

Description

Application of alkali-treated biogas residues in methane production

Technical Field

The invention relates to an application of alkali treatment biogas residues in methane production, and belongs to the technical field of treatment and utilization of solid organic wastes.

Background

China is a traditional agricultural production country, and a large amount of crop straws are produced each year. At present, the common disposal modes of crop straws in most areas of China are as follows: crushing and returning to the field, papermaking, livestock feed, in-situ incineration and the like, wherein the incineration is still the main treatment mode. A large amount of straws are randomly stacked or burned in the open air, so that not only is the resource wasted, but also particulate matters and nitrogen oxides generated by combustion can seriously pollute the environment, and extreme weather phenomena such as haze, acid rain and the like are caused. Therefore, the reduction, harmless and recycling treatment of the agricultural wastes is one of the important demands in the field of environmental protection in China, and is also a key link of the construction of agricultural recycling economy in China.

Biogas residues are residues and waste liquid which are remained after organic waste is subjected to anaerobic fermentation to produce biogas. The biogas digester consists of a solid part and a liquid part, wherein the solid part has complex components, and not only comprises floating slag on the surface (namely, residues which are light after fermentation, and non-defatted straws and the like), but also comprises mud-like substances deposited at the bottom of the biogas digester; the liquid part is the liquid in the middle part of the methane tank. As the biogas residue contains rich nutrient components and active substances, the biogas residue is a high-quality organic fertilizer, can be widely used in agriculture, and reduces the use of chemical fertilizers and pesticides. In developed countries, biogas residues are basically stored for a long time and then are applied to the field as fertilizer, but in China, because of the population, the land for absorbing the biogas residues is far less than the demand, if organic matters, nitrogen, phosphorus, pathogenic microorganisms and the like in the biogas residues enter the environment through unreasonable treatment, secondary pollution and resource waste of the environment can be caused, so that reasonable treatment of the biogas residues limits the development of biogas engineering in China to a great extent, and the resource utilization of the biogas engineering has important significance for the future sustainable development of the biogas engineering.

Disclosure of Invention

In order to solve the problems, through analyzing the composition of the straw biogas residue, we find that the biogas residue obtained after the straw is subjected to anaerobic fermentation has quite large methane production potential. However, due to its high lignocellulose content, the structure is complex and difficult to be degraded anaerobically. It was found that alkali treatment breaks the hydrogen bond between cellulose and hemicellulose and the ester bond between hemicellulose and lignin by sodium hydroxide, ammonia water or the like, and changes the structure of lignocellulose, thereby improving the anaerobic efficiency. In view of the above, the invention adopts a heat-alkali post-treatment mode to treat straw biogas residues after anaerobic fermentation, and then further carries out anaerobic digestion so as to improve the overall biogas production potential of the straw.

The first object of the invention is to provide an application of alkali treatment biogas residue in methane production, wherein the alkali treatment biogas residue is prepared by performing first anaerobic fermentation on straws and then performing alkali treatment on the straw biogas residue after anaerobic fermentation.

In one embodiment of the invention, the alkali in the alkali treatment is sodium hydroxide, and the adding amount of the sodium hydroxide is 20-80mg/g straw.

In one embodiment of the invention, the alkali is preferably added in an amount of 60mg/g straw.

In one embodiment of the invention, the alkaline treatment temperature is 100-140℃and the treatment time is 0.5-2h.

In one embodiment of the invention, the preparation method of the alkali treatment biogas residue comprises the following steps:

(1) Anaerobic fermentation: putting the straw into an anaerobic fermentation tank for anaerobic fermentation; the temperature of the anaerobic fermentation tank is controlled at 35-45 ℃ and is continuously stirred, and the stirring speed is maintained at 10-15 r.min ^-1 Fermenting for 150-200d to obtain straw biogas residues;

(2) Alkali treatment: alkali treatment is carried out on the straw biogas residue obtained in the step (1), the adding amount of alkali is 20-80mg/g straw biogas residue, and the treatment is carried out for 0.5-2h at the temperature of 100-140 ℃ to obtain alkali treatment biogas residue.

The second object of the invention is to provide a method for producing methane by anaerobic fermentation by adopting straw and alkali treated biogas residues as substrates; the preparation method of the alkali-treated biogas residue comprises the steps of carrying out first anaerobic fermentation on straws, and then carrying out alkali treatment on the straw biogas residue after anaerobic fermentation.

In one embodiment of the invention, the VS ratio of the straw and the alkali treated biogas residue is 1: (1-5).

In one embodiment of the present invention, preferably, the VS ratio of the straw and the alkali treated biogas residue is 1: (1.5-5).

In one embodiment of the invention, the method comprises the steps of:

(1) Anaerobic fermentation for the first time: putting the straw into an anaerobic fermentation tank for anaerobic fermentation; controlling the temperature of the anaerobic fermentation tank at 35-45 ℃ and fermenting for 150-200 days to obtain straw biogas residues;

(2) Alkali treatment: alkali treatment is carried out on the straw biogas residue obtained in the step (1), the adding amount of alkali is 20-80mg/g straw biogas residue, and the treatment is carried out for 0.5-2h at the temperature of 100-140 ℃ to obtain alkali treatment biogas residue;

(3) And (3) carrying out anaerobic fermentation for the second time: adding the alkali-treated biogas residues and the straws obtained in the step (2) into an anaerobic fermentation tank for anaerobic fermentation, controlling the temperature of the anaerobic fermentation tank to be 35-45 ℃, and collecting methane generated in the anaerobic fermentation tank.

A third object of the present invention is to provide an apparatus for producing biogas, the apparatus comprising an anaerobic generator and an alkali treatment tank; the discharging port of the anaerobic generator is connected with the feeding port of the alkali treatment tank, biogas residues generated by the anaerobic reactor are led into the alkali treatment tank for alkali treatment, the discharging port of the alkali treatment tank is connected with the feeding port of the anaerobic generator through a reflux pump, and the biogas residues subjected to alkali treatment are refluxed to the anaerobic generator to promote anaerobic fermentation.

In one embodiment of the invention, the anaerobic generator and the alkali treatment tank are both provided with heating means.

The invention has the beneficial effects that:

the invention opens up a new resource way for the treatment and disposal of the straw. The anaerobic digestion of straw to produce biogas is an important way for recycling and reducing organic waste. The hydrolysis stage of anaerobic digestion can degrade macromolecular organic matters with complex structures into soluble micromolecular matters, so that straws are effectively degraded, and methane is further produced by methanogenic microorganisms. According to the invention, straw biogas residues are subjected to hot alkali post-treatment, so that the biogas yield is improved by 33% and the methane yield is improved by 35% under high organic load.

Drawings

Fig. 1 is a process flow diagram.

FIG. 2 shows biogas yield and methane yield at different organic loads during the operation in example 1.

FIG. 3 shows TS, cellulose, hemicellulose, and lignin degradation rates at various stages in example 1.

FIG. 4 is a horizontal anaerobic reactor.

Fig. 5 shows the anaerobic digestion of straw and biogas residue to produce methane under the conditions of different mixing ratios in example 2.

FIG. 6 is a comparison of biogas yield and methane yield of straw and post-treatment biogas residue mixed fermentation and straw single fermentation in example 2.

Detailed Description

The following description of the preferred embodiments of the present invention is provided for better illustration of the invention, and should not be construed as limiting the invention.

Table 1 test items and methods

Example 1: preparation method of alkali-treated biogas residues

A preparation method of alkali-treated biogas residues comprises the following specific operation steps:

straw-first anaerobic digestion-hot alkali post-treatment of straw biogas residue

Step one, first anaerobic digestion:

the experiment was performed in a horizontal anaerobic reactor, running for 180d in total. The reactor volume was 200L and the effective volume was 190L. In this experiment, the reactor temperature was controlled at 39.+ -. 1 ℃ and continuous stirring was carried out with stirring rate maintained at 10 r.min ^-1 。

Step two, heat alkali post-treatment of straw biogas residues:

100g of straw biogas residues are added into a 500mL conical flask, and the addition amounts of NaOH are respectively 0, 20, 40, 60 and 80 mg.g ^-1 (based on the NaOH addition amount per unit mass of SS), 100g of deionized water was added at the same time with sufficient stirring, and the mixture was treated in an autoclave at 121℃for 1 hour. Part of the straw biogas residues after post-treatment is used for measuring the change of organic components such as cellulose and the like, and the other part is used for a methane generation potential experiment.

The analysis raw materials and the inoculant composition are composed of straw and biogas residues, wherein the straw and the biogas residues mainly comprise cellulose, hemicellulose and lignin.

TABLE 2 Properties of raw materials and inoculum

a: based on wet weight; b: on a dry weight basis; NA: not measured; and (3) the following steps: standard deviation; the repetition number n=3.

(1) Biogas yield and lignocellulose change in first anaerobic digestion

The straw horizontal anaerobic digestion reactor is operated for 6 stages (H1-H6), and the corresponding parameters are shown in Table 3. Biogas yield and methane yield per stage are shown in fig. 2 for a total run time of 180d. Average biogas yields at each stage are 458, 444, 458, 449, 450, and

the corresponding methane yields were 237, 236, 251, 246, 250, and

the methane content at stages H1-H6 was about 55%.

Table 3 operating parameters for each stage

Straw lignocellulose consists of cellulose, hemicellulose and lignin, but the degradation laws of these components are not consistent during anaerobic digestion. The degradation rates of the components in the stages H1 to H6 are shown in FIG. 3, and the degradation rates of cellulose in the six stages H1, H2, H3, H4, H5 and H6 are 69.4%, 72.6%, 70.9%, 71.6%, 72.3% and 55.1% respectively; hemicellulose degradation rates are 88.2%, 90.6%, 95.2%, 94.6%, 95.2%, and 60.3%, respectively; lignin degradation rates were 12.9%, 13.8%, 15.3%, 16.5%, 15.7% and 14.7%, respectively.

(2) Change of degradation condition of lignocellulose after alkali thermal post-treatment of biogas residue

In the experiment, the influence of NaOH post-treatment with different concentrations on the degradation rate of lignocellulose in straw biogas residues is reflected in Table 4, the degradation rate of lignin reaches the maximum value of 35.21% after the 60mg g-1NaOH post-treatment, the degradation rate of cellulose is 9.21%, the degradation rate of hemicellulose is 40.31%, and the higher the concentration of NaOH is, the stronger the removal effect on lignocellulose in straw is. Lignin is a complex macromolecular phenolic polymer which is difficult to be utilized by microorganisms, and by adopting a NaOH post-treatment mode, covalent structures formed by the lignin and hemicellulose are destroyed, and the wrapped cellulose is released, so that the anaerobic microorganisms are more fully contacted with the cellulose, and the methane conversion of straw is promoted.

TABLE 4 sodium hydroxide addition amounts of biogas residue lignocellulose degradation rate under different alkali addition amounts

Example 2: application of alkali treatment biogas residues in methane production

A method for producing methane, which comprises the steps of using straw and 60 mg.g in example 1 ^-1 The biogas residue obtained under the condition is used as a substrate, and methane is produced through anaerobic fermentation, and the method comprises the following steps:

(1) Mixing and fermenting BMP:

serum bottles with a volume of 500mL were used as digestion bottles with an effective working volume of 300mL. 1.67g of biogas residues subjected to 60mg/L sodium hydroxide post-treatment are taken before the experiment starts _vs 、2.31g _vs 、3.75g _vs 、5g _vs Filling into different serum bottles with 3 mol.L ^-1 HCl is regulated to pH 7.5, and 8.33g of straw is respectively added _vs 、7.69g _vs 、6.25g _vs 、5g _vs The dry matter mass (expressed as VS) ratio was 2:10, 3:10, 6:10, 10:10, respectively 10g was taken _vs Straw and 10g _vs The post-treatment biogas residues are filled into different serum bottles, and 200g of inoculation sludge is added for full mixing. Nitrogen is continuously introduced into the bottle for 3min to keep anaerobic state, the anaerobic digestion temperature is controlled at 39+/-1 ℃, and the co-fermentation gas production is carried out for 40d.

(2) Mixing fermentation in a horizontal anaerobic reactor:

the reaction was carried out in a horizontal anaerobic reactor (FIG. 4) having a reactor volume of 200L and an effective volume of 190L. In this experiment, the reactor temperature was controlled at 39.+ -. 1 ℃ and continuous stirring was carried out with stirring rate maintained at 10 r.min-1. The anaerobic reactor increases the organic load of the straw every 30d, and is divided into six operation stages (H1-H6), and the corresponding parameters are shown in Table 5. During the operation of the reactor, the total solids content of the system was maintained at 15% to 18% and fed at a fixed time per day, with samples taken every 2d before feeding. The substrate is a biogas residue mixture of straw and 60mg/g sodium hydroxide after-treatment, and the ratio of VS is 10:3.

table 5 operating parameters for each stage

(1) Mixing ratio affects the methane production performance of anaerobic fermentation:

cumulative methane production is one of the important indicators characterizing the gas production performance of the substrate. The treated biogas residues and straws are used for BMP experiments in the experiment, and the co-fermentation gas production is carried out for 40d. As shown in table 6, the cumulative methane yield was 3:10 group >2:10 group >6:10 group > straw group >10:10 group > post-treatment biogas residue group. When the biogas residues and the straws are mixed in a ratio of 3:10, the highest accumulated methane yield is 2238.2mL, and the unit methane yield reaches 223.8 mL.g-1 VS, which is 1.15 times and 1.65 times that of the straw group and the post-treatment biogas residue group respectively. Daily methane production as shown in figure 5, each group reached a peak in methane production at 1d, and readily available components of the substrate were rapidly degraded by the microorganism. Then the gas yield gradually decreases until the fermentation is finished. In conclusion, the biodegradability of the straw and the biogas residues is affected by different mixing ratios, the influence of the ratios is larger, and the anaerobic digestion performance of an experimental group with the mixing ratio of 3:10 is optimal.

(2) Straw and biogas residue mixed fermentation gas production rule of horizontal anaerobic reactor:

the mixture ratio of the post-treatment biogas residues and the straws is 3:10 and is used as a substrate, the gas production performance in the anaerobic digestion process is shown in table 7 and fig. 6, and the average volume biogas yield of each stage of mixed substrate fermentation H1-H6 is 0.63, 0.84, 1.19, 1.4, 2.09 and 2.66L (L.d) ^-1 Compared with single fermentation of straw, the method improves the fermentation rate by 0.04, 0.07, 0.1, 0.13, 0.15 and 0.66L (L.d) ^-1 The method comprises the steps of carrying out a first treatment on the surface of the Average volumetric methane yield ratios of 0.33, 0.45, 0.64, 0.8, 1.14 and 1.5L (L.d) ^-1 Compared with single fermentation of straw, the method improves the fermentation efficiency by 0.02 and 0.04. 0.05, 0.06 and 0.39L (L. D) ^-1 . The result shows that especially under high load, the mixed fermentation of the post-treatment biogas residues and the straw can effectively improve the gas production efficiency.

TABLE 6 anaerobic digestion of straw and biogas residue to methane conditions under different mixing ratios

Table 7 comparison of biogas yield and methane yield of straw and post-treatment biogas residue mixed fermentation and straw single fermentation in horizontal reactor

Example 3: device for producing biogas

An apparatus for producing biogas, the apparatus comprising an anaerobic generator (see fig. 4) and an alkali treatment tank; the discharging port of the anaerobic generator is connected with the feeding port of the alkali treatment tank, biogas residues generated by the anaerobic reactor are led into the alkali treatment tank for alkali treatment, the discharging port of the alkali treatment tank is connected with the feeding port of the anaerobic generator through a reflux pump, and the biogas residues subjected to alkali treatment are refluxed to the anaerobic generator to promote anaerobic fermentation; the anaerobic generator is also provided with a gas collecting port for collecting methane; the anaerobic generator and the alkali treatment tank are both provided with heating devices.

While the invention has been described with reference to the preferred embodiments, it is not limited thereto, and various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method of producing methane, the method comprising the steps of:

(2) Alkali treatment: alkali treatment is carried out on the straw biogas residue obtained in the step (1), the adding amount of alkali is 60mg/g straw biogas residue, and the treatment is carried out for 0.5-2h at the temperature of 100-140 ℃ to obtain alkali treatment biogas residue; the alkali in the alkali treatment is sodium hydroxide;

(3) And (3) carrying out anaerobic fermentation for the second time: adding the alkali-treated biogas residues and the straws obtained in the step (2) into an anaerobic fermentation tank for anaerobic fermentation, controlling the temperature of the anaerobic fermentation tank to be 35-45 ℃, and collecting methane generated in the anaerobic fermentation tank; the VS ratio of the biogas residues and the straws treated by alkali is 3:10.