CN112430631A

CN112430631A - Application of alkali-treated biogas residue in methane production

Info

Publication number: CN112430631A
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: 2021-03-02
Anticipated expiration: 2040-12-23
Also published as: CN112430631B

Abstract

The invention discloses an application of alkali-treated 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 first anaerobic fermentation on straws and then carrying out alkali treatment on the straw biogas residue after the anaerobic fermentation; the invention adopts straws and alkali-treated biogas residues as substrates, and produces methane through anaerobic fermentation. The biogas residue obtained after the straw is subjected to anaerobic fermentation has considerable methane production potential. According to the invention, the 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 residue in methane production

Technical Field

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

Background

China is a traditional big country for agricultural production and can produce a large amount of crop straws every year. At present, most of China's common treatment modes for crop straws are as follows: crushing and returning to fields, papermaking, livestock feed, in-situ incineration and the like, wherein incineration is still the main treatment mode. A large amount of straws are randomly stacked or are incinerated in the open air, so that resource waste is caused, and the environment can be seriously polluted by particles and nitrogen oxides generated by combustion, so that extreme weather phenomena such as haze, acid rain and the like are caused. Therefore, the reduction, harmless and resource treatment of agricultural wastes is one of the important requirements in the field of environmental protection in China and is also a key link for the construction of agricultural circular economy in China.

The biogas residue is residue and waste liquid left after the 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 more complex components, and not only comprises floating slag (namely, residue which becomes light after fermentation, non-degreased straws and the like) on the surface, but also comprises mud-like substances precipitated at the bottom of the biogas digester; the liquid part is the liquid in the middle part of the methane tank. The biogas residue contains rich nutrient components and active substances, is a high-quality organic fertilizer, can be widely used in agriculture, and reduces the use of chemical fertilizers and pesticides. In developed countries, the biogas residues are basically stored for a long time and then applied to fields as fertilizers, but in China, due to the fact that the population is large, the land for absorbing the biogas residues is far less than the demand, if unreasonable treatment is carried out, organic matters, nitrogen, phosphorus, pathogenic microorganisms and the like in the biogas residues enter the environment, secondary pollution to the environment and resource waste can be caused, so that the 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 residues has important significance for the sustainable development of the biogas engineering.

Disclosure of Invention

In order to solve the problems, the biogas residues obtained by anaerobic fermentation of the straws are discovered to have considerable methane production potential by analyzing the components of the straw biogas residues. But the structure is complex and difficult to be degraded anaerobically due to the high content of lignocellulose. Researches show that the alkali treatment can break hydrogen bonds between cellulose and hemicellulose and ester bonds between the hemicellulose and lignin by sodium hydroxide, ammonia water and the like, change the structure of lignocellulose and improve the anaerobic efficiency of the lignocellulose. In view of the above, the invention adopts a thermal-alkaline post-treatment mode to treat the straw biogas residues after anaerobic fermentation, and then further carries out anaerobic digestion to improve the overall biogas production potential of the straws.

The first purpose of the invention is to provide the application of the alkali-treated biogas residue in methane production, and the preparation method of the alkali-treated biogas residue is that the straws are firstly subjected to anaerobic fermentation for the first time, and then the straw biogas residue after the anaerobic fermentation is subjected to alkali treatment.

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

In one embodiment of the present invention, the alkali treatment temperature is 100-.

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

(1) anaerobic fermentation: putting the straws into an anaerobic fermentation tank for anaerobic fermentation; controlling the temperature of the anaerobic fermentation tank at 35-45 ℃, and continuously stirring at a stirring speed of 10-15 r.min^-1Fermenting for 150-;

(2) alkali treatment: and (2) carrying out alkali treatment on the straw biogas residue obtained in the step (1), wherein the adding amount of alkali is 20-80mg/g, and treating for 0.5-2h at the temperature of 100-.

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

In one embodiment of the invention, the VS ratio of the straw to 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) first anaerobic fermentation: putting the straws into an anaerobic fermentation tank for anaerobic fermentation; controlling the temperature of the anaerobic fermentation tank at 35-45 ℃, and fermenting for 150-200d to obtain straw biogas residues;

(2) alkali treatment: performing alkali treatment on the straw biogas residue obtained in the step (1), wherein the adding amount of alkali is 20-80mg/g, and treating for 0.5-2h at the temperature of 100-;

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

The third purpose of the invention is to provide a device for producing biogas, which comprises an anaerobic generator and an alkali treatment tank; the discharge hole of the anaerobic generator is connected with the feed inlet of the alkali treatment tank, the biogas residue generated by the anaerobic reactor is guided into the alkali treatment tank for alkali treatment, the discharge hole of the alkali treatment tank is connected with the feed inlet of the anaerobic generator through a reflux pump, and the alkali-treated biogas residue is refluxed to the anaerobic generator to promote anaerobic fermentation.

In one embodiment of the invention, the anaerobic generator and the alkaline 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 the straws to produce the biogas is an important way for the resource utilization and reduction of organic wastes. The hydrolysis stage of anaerobic digestion can degrade macromolecular organic matters with complex structures into soluble micromolecular substances, so that straws are effectively degraded, and methane is further generated by methanogenic microorganisms. According to the invention, the 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 the biogas yield and methane yield at different organic loadings during operation in example 1.

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

FIG. 4 is a horizontal anaerobic reactor.

FIG. 5 shows the methane production by anaerobic digestion of straw and biogas residue in different mixing ratios in example 2.

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

Detailed Description

The following description of the preferred embodiments of the present invention is provided for the purpose of better illustrating the invention and is not intended to limit the invention thereto.

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 → thermal alkali post-treatment of straw biogas residue

Step one, first anaerobic digestion:

the experiment was carried out in a horizontal anaerobic reactor for a total of 180 days. 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 the stirring rate maintained at 10 r.min^-1。

Step two, treating straw biogas residues after thermokalization:

adding 100g of straw biogas residue into a 500mL conical flask, wherein the adding amount of NaOH is respectively 0, 20, 40, 60 and 80mg ·g^-1(based on the addition amount of NaOH of SS per unit mass), 100g of deionized water is added at the same time, the mixture is fully stirred, and the mixture is treated for 1 hour in an autoclave at the temperature of 121 ℃. A part of the post-treated straw biogas residues is used for measuring the change of organic components such as cellulose and the like, and a part of the post-treated straw biogas residues is used for a methane generation potential experiment.

Analyzing the components of raw materials and inoculum, wherein the straws and biogas residues mainly comprise cellulose, hemicellulose and lignin.

TABLE 2 feedstock and inoculum Properties

a: based on wet weight; b: on a dry weight basis; NA: not testing; + -: a standard deviation; the number of repetitions n is 3.

(1) First anaerobic digestion of biogas production and lignocellulosic changes

The horizontal anaerobic digestion reactor for straws runs for 6 stages (H1-H6) in total, and corresponding parameters are shown in a table 3. The biogas and methane yields for each stage are shown in fig. 2, for a total run time of 180 d. The average biogas production rate at each stage state is 458, 444, 458, 449, 450, and

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

the methane content in the H1-H6 stages is about 55%.

TABLE 3 operating parameters of the various stages

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 stages H1-H6 are shown in FIG. 3, and the cellulose degradation rates in six stages H1, H2, H3, H4, H5 and H6 are 69.4%, 72.6%, 70.9%, 71.6%, 72.3% and 55.1% respectively; the degradation rates of hemicellulose are respectively 88.2%, 90.6%, 95.2%, 94.6%, 95.2% and 60.3%; the 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 alkaline heat post-treatment of biogas residues

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

TABLE 4 dosage of sodium hydroxide for degradation rate of lignocellulose in biogas residue at different dosage of alkali

Example 2: application of alkali-treated biogas residue in methane production

A method for producing methane by using straws and 60 mg-g in example 1^-1The 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) BMP mixed fermentation:

a serum bottle with the volume of 500mL is used as a digestion bottle, and the effective working volume is 300 mL. Get 60 meridians before the start of the experimentmg/L sodium hydroxide post-treated biogas residue 1.67g_vs、2.31g_vs、3.75g_vs、5g_vsLoading into different serum bottles with 3 mol. L^-1Adjusting pH to about 7.5 with HCl, and adding 8.33g of straw respectively_vs、7.69g_vs、6.25g_vs、5g_vsThe dry matter mass (in VS) ratio is 2:10, 3:10, 6:10 and 10:10, and 10g of the dry matter mass is taken out_vsStraw and 10g_vsThe post-treated biogas residues are put into different serum bottles, 200g of inoculated sludge is added and fully mixed. And continuously introducing nitrogen into the bottle for 3min to keep an anaerobic state, controlling the anaerobic digestion temperature to be 39 +/-1 ℃, and carrying out co-fermentation to produce gas for 40 d.

(2) Mixed fermentation of a horizontal anaerobic reactor:

the reaction is carried out in a horizontal anaerobic reactor (figure 4), the volume of the reactor is 200L, and the effective volume is 190L. In this experiment, the reactor temperature was controlled at 39. + -. 1 ℃ and continuous stirring was carried out at a stirring rate of 10 r.min-1. The organic load of the straws is increased by the anaerobic reactor every 30 days, the anaerobic reactor is divided into six operation stages (H1-H6), and corresponding parameters are shown in a table 5. During the reactor run, the total solids content of the system was maintained at 15% to 18%, feeding was done at fixed times per day, with samples taken every 2 days before feeding. The substrate is a mixture of straw and 60mg/g sodium hydroxide post-treated biogas residue, and the ratio is recorded as 10 by VS: 3.

TABLE 5 operating parameters for the various stages

(1) The mixing proportion has influence on the methane production performance of anaerobic fermentation:

the accumulated methane yield is one of the important indexes for representing the gas production performance of the substrate. In the experiment, the treated biogas residues and straws are used for a BMP experiment, and the co-fermentation is performed to produce gas for 40 days. As shown in Table 6, the accumulated methane yield was 3:10, 2:10, 6:10, straw, 10:10 and the post-treatment biogas residue. 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 of that of the straw group and the post-treatment biogas residue group respectively. The daily methane yield is shown in figure 5, the daily methane yield of each group reaches the peak of gas production at the 1 st day, and easily utilized components in the substrate are quickly degraded by microorganisms. Then the gas production is gradually reduced until the fermentation is finished. In conclusion, different mixing ratios affect the biodegradability of the straws and the biogas residues, the mixing ratios are greatly affected, and the experimental group with the mixing ratio of 3:10 has the best anaerobic digestion performance.

(2) The mixed fermentation gas production rule of the straw and the biogas residue of the horizontal anaerobic reactor is as follows:

the mixing ratio of the post-treated biogas residues and the straws is 3:10 as a substrate, the gas production performance in the anaerobic digestion process is shown in Table 7 and figure 6, and the average volumetric biogas yields in the stages of the mixed substrate fermentation H1-H6 are 0.63, 0.84, 1.19, 1.4, 2.09 and 2.66L (L.d)^-1Compared with straw single fermentation, the yield is improved by 0.04, 0.07, 0.1, 0.13, 0.15 and 0.66L (L.d)^-1(ii) a Average volumetric methane production ratio of 0.33, 0.45, 0.64, 0.8, 1.14 and 1.5L (L.d)^-1Compared with straw single fermentation, the yield is improved by 0.02, 0.04, 0.05, 0.06 and 0.39L (L.d)^-1. The result shows that the mixed fermentation of the post-treated biogas residues and the straws can effectively improve the gas production efficiency especially under high load.

TABLE 6 methane production by anaerobic digestion of straw and biogas residue at different mixing ratios

TABLE 7 comparison of biogas and methane yields for mixed fermentation of straw and post-treatment biogas residue and single straw fermentation in horizontal reactors

Example 3: device for producing methane

An apparatus for producing biogas, said apparatus comprising an anaerobic generator (see fig. 4) and an alkaline treatment tank; a discharge hole of the anaerobic generator is connected with a feed hole of the alkali treatment tank, biogas residues generated by the anaerobic reactor are guided into the alkali treatment tank for alkali treatment, a discharge hole of the alkali treatment tank is connected with the feed hole of the anaerobic generator through a reflux pump, and the alkali-treated biogas residues 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.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that 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. The application of the alkali-treated biogas residue in methane production is characterized in that the preparation method of the alkali-treated biogas residue is that the straws are subjected to anaerobic fermentation, and then the anaerobic-fermented straw biogas residue is subjected to alkali treatment to obtain the alkali-treated biogas residue.

2. The use according to claim 1, wherein the alkali in the alkali treatment is sodium hydroxide, potassium hydroxide, calcium hydroxide or ammonia water.

3. The use according to claim 1 or 2, wherein the amount of alkali added is 20-80mg/g straw biogas residue.

4. Use according to any one of claims 1 to 3, characterized in that the alkali treatment temperature is 100 ℃ and 140 ℃ and the treatment time is 0.5 to 2 h.

5. The use according to any one of claims 1 to 4, wherein the process for the preparation of alkali-treated biogas residue comprises the steps of:

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

6. A method for producing methane is characterized in that straws and alkali-treated biogas residues are used as substrates, and methane is produced through anaerobic fermentation; the preparation method of the alkali-treated biogas residue comprises the steps of firstly carrying out first anaerobic fermentation on straws and then carrying out alkali treatment on the straw biogas residue after the anaerobic fermentation.

7. The method of claim 6, wherein the straw and alkali treated biogas residue have a VS ratio of 1: (1-5).

8. Method according to claim 6 or 7, characterized in that it comprises the following steps:

9. A device for producing biogas is characterized by comprising an anaerobic generator and an alkali treatment tank; the discharge hole of the anaerobic generator is connected with the feed inlet of the alkali treatment tank, the biogas residue generated by the anaerobic reactor is guided into the alkali treatment tank for alkali treatment, the discharge hole of the alkali treatment tank is connected with the feed inlet of the anaerobic generator through a reflux pump, and the alkali-treated biogas residue is refluxed to the anaerobic generator to promote anaerobic fermentation.

10. The biogas production apparatus of claim 9, wherein the anaerobic generator and the alkaline treatment tank are provided with heating means.