CN110779947A - Method for evaluating anaerobic digestion performance of lignocellulose raw material by pretreatment intensity - Google Patents
Method for evaluating anaerobic digestion performance of lignocellulose raw material by pretreatment intensity Download PDFInfo
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Abstract
A method for evaluating the anaerobic digestion performance of a lignocellulose raw material by using pretreatment strength belongs to the field of anaerobic digestion of organic solid wastes. The method comprises the following steps: adding a reagent into a lignocellulose raw material, carrying out hydrothermal pretreatment under the conditions of certain temperature and time, and measuring the pH value of the pretreated raw material; calculating the hydrothermal pretreatment intensity under different conditions; inoculating sludge, adding water to a constant volume, and performing anaerobic fermentation; the hydrothermal intensity is fitted to the methane production for use in the process of assessing methane potential. By implementing the invention, the following advantages can be achieved: (1) the provided hydrothermal strength evaluation method reduces complicated mathematical model calculation and fitting; (2) the experimental workload and the required time can be greatly reduced, and the anaerobic digestion time (30-60d) can be saved. (3) Simple operation and low cost, and can save the time for testing COD and the cost for treating and disposing waste liquid. (4) Simple operation, energy consumption saving, rapidness and environmental protection.
Description
Technical Field
The invention belongs to the field of organic solid waste treatment and recycling-anaerobic digestion, and particularly relates to a method for evaluating the performance of anaerobic digestion methane production of a hydrothermal pretreated lignocellulose raw material by utilizing pretreatment strength.
Background
Lignocellulosic biomass is a vast carbon resource on earth and is considered to be the most promising alternative to petroleum. However, the complex structure of lignocellulosic feedstocks prevents the contact of cellulase with lignocellulose, resulting in difficult degradation of lignocellulose. Therefore, in order to improve the methane production capacity of the lignocellulose raw material, various pretreatment means are developed by many scholars to destroy the spatial structure of the lignocellulose so that the lignocellulose is more easily contacted with microorganisms and enzymes, thereby providing the methane production performance. Since anaerobic digestion is a complex microbial digestion process, there is no particularly rapid and efficient way to obtain methanogenic potential directly through the pretreatment properties. At present, all pretreatment conditions require 30-60 days of anaerobic digestion, and the biogas production or the accumulation of the methane production is monitored every day to obtain the biogas production potential. This method is time consuming and also labor, material and financial resources. Therefore, if the parameter range of the optimal gas production can be preliminarily determined through the pretreatment parameters, the workload and the time can be greatly reduced.
Because anaerobic digestion raw materials are wide in source, different types of raw materials are different in physical and chemical properties, and different pretreatment methods are different, the methane production characteristics of different raw materials are different under different conditions, and therefore, a universal and simple method for calculating the methane production amount of different raw materials does not exist. The theoretical gas production rate is calculated by a formula after the determination of C, H, O, N in the existing method, and the theoretical gas production rate calculated by simple element composition is far from the actual gas production rate due to different influences of various pretreatment conditions and pretreatment reagents, so that the gas production potentials of different raw materials under different pretreatment conditions cannot be judged. For the kitchen waste and the waste water which have high water content, good fluidity and rich protein, a method for predicting gas production potential by using the kitchen waste as the raw material and fitting a Gompertz model and a first-order kinetic model is proposed [ Mingzhao star, CN107145725A ], on the premise that different pretreatment conditions need to be done once to obtain corresponding correction coefficients, and therefore, the workload is not reduced. In wastewater anaerobic digestion methanogenesis production, COD is often used to rapidly predict the methanogenesis potential, whereas in lignocellulosic anaerobic digestion methanogenesis research, its methanogenesis potential is often obtained By Methanogenesis Potential (BMP) experiments or Buswell's formula. Silva et al used pig manure and sludge as raw materials, estimated the potential for methane production by anaerobic digestion through early parameters, but the minimum required time still reaches 5-15 days [ Silva et al. Biochemical transmutative (BMP) tests: Reducing test time by early analysis parameter estimation [ J ]. Watermanage, 2017,71:19-24 ]
For lignocellulose raw materials, the method reported by the current literature has high operation difficulty, large pretreatment parameter range and difficult application of the method for evaluating the methanogenesis potential in the traditional sense. Therefore, no effective prediction method exists at present. At present, the hydrothermal pretreatment is a good pretreatment method, different raw materials are put into hot water with different temperatures for soaking or cooking, and pressurization or no pressurization and various chemical reagents can be added or not added. However, the pretreatment time, temperature, water content, whether chemical reagents are added and different raw materials have great influence on the pretreatment effect, and at present, no consistent conclusion exists, and each pretreatment method needs 30-60 days of anaerobic digestion to obtain the gas production potential. Therefore, aiming at the existing problems, the invention provides a method for evaluating the performance of anaerobic digestion and methane production of the hydrothermal pretreated lignocellulose raw material by utilizing pretreatment strength, which is used for quickly determining the better range of anaerobic digestion and methane production so as to achieve the aim of quickly screening pretreatment conditions.
Disclosure of Invention
The method is provided for solving the problems that the evaluation workload of the anaerobic digestion methane production performance of different hydrothermal pretreated lignocellulose raw materials is large and difficult to realize. The invention aims to provide an index for evaluating the effect of generating methane by anaerobic digestion of lignocellulose subjected to hydrothermal pretreatment, quickly determine the pretreatment range of better methane generation, and greatly reduce the operation workload of a subsequent anaerobic digestion link.
The method is provided for solving the problems that the evaluation workload of the anaerobic digestion methane production performance of different hydrothermal pretreated lignocellulose raw materials is large and difficult to realize. The invention aims to provide an index for evaluating the effect of generating methane by anaerobic digestion of lignocellulose subjected to hydrothermal pretreatment, quickly determine the pretreatment range of better methane generation, and greatly reduce the operation workload of a subsequent anaerobic digestion link.
The invention specifically comprises the following contents:
(1) hydrothermal pretreatment condition determination
In the hydrothermal pretreatment process, pretreatment temperature and pretreatment time are important factors that affect the hydrothermal pretreatment process. The pretreatment temperature range of the invention is 50-200 ℃, and the pretreatment time range is 5min-3 d. The water content of the pretreated material is adjusted to 70-90% by using tap water.
The pretreatment method comprises the following steps:
a. weighing crushed lignocellulose raw materials (including corn straw, cow dung and rice hull lignocellulose raw materials) in a fixed container, adding a chemical reagent, and adjusting the water content of the raw materials by using tap water;
b. and transferring the mixed materials into a container, uniformly stirring the materials by using a glass rod, and then placing the materials into a reactor to perform heating pretreatment for different times under different temperature conditions.
c. And (4) taking out the material after the pretreatment is finished, and measuring the pH value of the lignocellulose raw material.
(2) Hydrothermal Strength calculation
Calculating integral factor R under the pretreatment temperature and time conditions according to the pretreatment temperature and the pretreatment time
0Wherein a is a starting time and b is an ending time;
then, according to the formula (1) and by combining the change of the acid-base property of the lignocellulose before and after pretreatment, the influence of an acid reagent is shown by the concentration of H & lt + & gt after pretreatment, and an acidification factor R is calculated
0' deriving formula (2):
R＇
0＝R
0·[H
+]formula (2)
Substituting the formula (2) into the formula (1), taking logarithm at both sides to obtain the formula (3),
log(R＇
0)＝logR
0-pH formula (3)
The pretreatment intensity factor R is deduced by correcting on the basis of the formula (3) and quickly and uniformly comparing the hydrothermal pretreatment effect after adding the acid-base reagent
0”：
Wherein T is hydrothermal pretreatment time (min), T is hydrothermal pretreatment temperature (DEG C), and pH is the pH value after pretreatment.
Anaerobic digestion for methane production
Mixing the pretreated material with the inoculum, adding water to a constant volume to reach the effective volume of the fermentation tank, sealing, and placing in a constant-temperature water bath water tank for mesophilic anaerobic digestion. The biogas yield was recorded daily by a water drainage and gas collection method. And measuring the methane content in the methane by a gas chromatograph.
Evaluation of anaerobic digestion methanogenesis performance by hydrothermal pretreatment strength
The evaluation index logR in the formula (4) is adopted
0And calculating the hydrothermal pretreatment strength, and carrying out anaerobic digestion on the pretreated material to obtain the methane yield. The hydrothermal pretreatment intensity and the anaerobic digestion methane production performance are fitted, and the optimal hydrothermal pretreatment intensity range of the raw materials is obtained according to the fitting result and is shown in figure 1. Provides a basis for predicting the potential of methane for different pretreatment conditions.
Determination of methane potential of lignocellulosic feedstock
By utilizing a relationship graph (figure 1) of hydrothermal pretreatment strength and methane yield under different pretreatment conditions, the performance of anaerobic digestion of the raw material for producing methane under different pretreatment conditions can be rapidly judged. Other people do not need to repeatedly do anaerobic digestion experiments, and can know the methane production potential range of the other people only by combining the pretreatment intensity calculated by the formula (4) with the pH value after pretreatment, the pretreatment time and the pretreatment temperature and looking up the fitting graphs (figure 1) of different raw materials. The workload of parameter screening is greatly reduced.
The method comprises the following specific steps:
(1) hydrothermal pretreatment
Weighing lignocellulose raw materials (corn straws, cow dung and rice husks) with required mass, calculating by using the raw material TS, adding a pretreatment chemical reagent, and adjusting the water content by using tap water; and adding the mixed materials into a glass container, uniformly stirring the materials by using a glass rod, and then placing the materials into a hydrothermal reactor for heating pretreatment. Pre-treating at 100 deg.c for 1-3 days; the pretreatment experiment at 100 deg.C or above is maintained for 5-30 min.
And (3) cooling by using water cooling and air cooling after the pretreatment is finished, taking out the materials after the cooling is finished, and detecting the pH, the reducing sugar and the VFAs properties of the pretreated raw materials and whether toxic and harmful substances exist.
(2) Calculating hydrothermal pretreatment intensity
And (4) calculating the hydrothermal pretreatment intensity under different pretreatment conditions by using the formula (4) and combining the time, the temperature and the pH value of the hydrothermal pretreatment.
(3) Anaerobic digestion
Mixing the pretreated material and the inoculum, adding water to a constant volume to reach the effective volume of a fermentation tank, sealing, and placing in a constant-temperature water bath water tank for anaerobic digestion, wherein the anaerobic digestion time is adjusted by different raw materials.
And recording the daily gas production and the daily methane production in the anaerobic digestion process. The methane yield was calculated.
(4) Fitting of hydrothermal pretreatment intensity and anaerobic digestion methanogenesis performance
Fitting the calculated pretreatment intensity and the anaerobic digestion methane yield, and finding the optimal hydrothermal pretreatment intensity range of the raw material through common software such as Excel, SPSS, Origin and the like in the fitting process through a trend relation line of the two, wherein economic and other benefits are comprehensively considered in the actual operation process.
(5) By utilizing the relationship graph of hydrothermal pretreatment strength and methane yield under different pretreatment conditions, the performance of anaerobic digestion methane production of raw materials under different pretreatment conditions can be rapidly judged. And other people do not need to repeatedly do anaerobic digestion experiments, and can know the methane production potential range of the artificial wetland only by combining the pretreatment intensity calculated by the formula (4) with the pH value after pretreatment, the pretreatment time and the pretreatment temperature and looking up a fitting graph.
Compared with the prior art, the invention has the following beneficial effects:
(1) compared with other methods for evaluating the methane production performance by anaerobic digestion, the hydrothermal strength evaluation method provided by the invention can judge the methane production performance by hydrothermal pretreatment and pH measurement, and combines the pretreatment time and temperature, so that complicated mathematical model calculation and fitting are reduced;
(2) the invention can greatly reduce the experimental workload and the time required by the experimental workload, and the time required by the invention is only the time required by measuring the pH value after pretreatment and calculating the pretreatment strength by using a formula. This saves anaerobic digestion time (30-60d) and allows determination of approximate ranges without subsequent anaerobic digestion.
(3) The method only needs to measure the pH value of the raw material after hydrothermal pretreatment (which can be finished by a pH meter for 1-2 s), and has the advantages of simple operation and low cost. In the production of methane by anaerobic digestion of wastewater, the commonly used method for quickly predicting the methanogenesis potential of COD has the advantages of complex reagent preparation, long consumed time, higher risk and more expensive waste liquid treatment and disposal cost, and the method can save the time required by COD test (only the COD test needs 3h to 1d, and the medicine preparation and sample preparation time needs 1 to 2d) and the waste liquid treatment and disposal cost (about 1200 yuan/kg).
(4) The method is simple to operate, energy-saving, rapid and environment-friendly.
Drawings
FIG. 1 is a plot of hydrothermal intensity as a function of methane yield
FIG. 2 is a fitting graph of hydrothermal intensity of corn stalks and methane yield
FIG. 3 shows fitting graph of rice hull hydrothermal intensity and methane yield
FIG. 4 is a graph of the water heat intensity of cow dung and the methane yield
FIG. 5 is a fitting graph of hydrothermal intensity of wheat straw and biogas yield
Detailed Description
(1) Hydrothermal pretreatment
Weighing lignocellulose raw materials (corn straws, cow dung, rice hulls and the like in the embodiment of the invention), adding 2% ammonia water or 2% KOH (potassium hydroxide) of the dry weight of the raw materials according to the mass of the raw materials TS, and adjusting the water content of the raw materials TS to 80%; and adding the mixed materials into a glass container, uniformly stirring the materials by using a glass rod, and then placing the materials into a hydrothermal reactor for heating pretreatment. Pre-treating at 100 deg.c for 1-3 days; the pretreatment experiment at 100 deg.C or above is maintained for 5-30 min.
And (3) cooling by using water cooling and air cooling after the pretreatment is finished, taking out the materials after the cooling is finished, and detecting the properties of pH, reducing sugar, VFAs and the like and the existence of toxic and harmful substances after the pretreatment of the raw materials.
(2) Calculating hydrothermal pretreatment intensity
Using formula (4)
And calculating the hydrothermal pretreatment intensity under different pretreatment conditions by combining the time, the temperature and the pH value of the hydrothermal pretreatment.
(3) Anaerobic digestion
Mixing the pretreated material and the inoculum in a 500mL blue-cap bottle, adding water to a constant volume of 400mL, sealing, and performing medium-temperature anaerobic digestion in a constant-temperature water bath water tank with the temperature of 35 +/-1 ℃ for 50 days.
And (4) recording the daily gas production in the anaerobic digestion process by a drainage method, and measuring the percentage content of the daily methane. The methane yield was calculated.
(4) Fitting of hydrothermal pretreatment intensity and anaerobic digestion methanogenesis performance
Fitting the calculated pretreatment intensity with the anaerobic digestion methane yield, and finding the optimal hydrothermal pretreatment intensity range of the raw material through common software such as Excel, SPSS, Origin and the like by the fitting process through a trend relation line of the two.
(5) By utilizing the relationship graph of hydrothermal pretreatment strength and methane yield under different pretreatment conditions, the performance of anaerobic digestion methane production of raw materials under different pretreatment conditions can be rapidly judged. And other people do not need to repeatedly do anaerobic digestion experiments, and can know the methane production potential range of the artificial wetland only by combining the pretreatment intensity calculated by the formula (4) with the pH value after pretreatment, the pretreatment time and the pretreatment temperature and looking up a fitting graph.
Example 1
(1) Hydrothermal pretreatment
Weighing 20g of corn straw, calculating by using raw material TS, and dividing pretreatment experiments into two groupsOne group is independently subjected to hydrothermal pretreatment, and the other group is simultaneously added with NH with the weight of 2 percent of the dry weight of the corn straws
3·H
2O; adding ammonia water with the dry weight of 2% of the corn straw into the ammonia water heating pretreatment group, and adjusting the water content to 80%; tap water was added to the single hydrothermal group to adjust the water content to 80%. Adding the raw materials, water and the like into a glass container, uniformly stirring by using a glass rod, and then placing into a hydrothermal reactor for heating pretreatment. The pretreatment conditions set for the pretreatment of the corn straws are as follows: the pretreatment time at 50 ℃ is 1d, 2d and 3d, the pretreatment time at 70 ℃ is 1d and 2d, the pretreatment time at 90 ℃ is 2h and 4h, the pretreatment time at 100 ℃ is 5min, 10min, 20min and 30min, the pretreatment time at 150 ℃ is 5min, 10min and 20min, and the pretreatment time at 200 ℃ is 5min and 10 min. Set 3 sets of parallels for each pretreatment condition.
And (3) cooling by using water cooling and air cooling after the pretreatment is finished, taking out the corn straws after the cooling is finished, and detecting the properties of pH, reducing sugar, VFAs and the like and the existence of toxic and harmful substances after the pretreatment of the raw materials.
(2) Calculating hydrothermal pretreatment intensity
With the use of the formula (4),
and calculating the hydrothermal pretreatment intensity under different pretreatment conditions by combining the time, the temperature and the pH value of the hydrothermal pretreatment. The hydrothermal treatment strength is shown in Table 1.
TABLE 1 Table of pH and pretreatment intensity after hydrothermal pretreatment of corn stalks
Where HM denotes hydrothermal pretreatment; HMA means hydrothermal simultaneous addition of ammonia;
(3) anaerobic digestion
Transferring the pretreated corn straws into a 500mL blue-covered bottle, adding 8g of inoculum (calculated by TS), adding water to a constant volume of 400mL of the effective volume of the fermentation tank, sealing and placing the fermentation tank into a constant-temperature water bath water tank at 35 +/-1 ℃ for medium-temperature anaerobic digestion, wherein the anaerobic digestion time is 50 days.
And (4) recording the daily gas production in the anaerobic digestion process by a drainage method, and measuring the percentage of the daily methane production by a gas chromatograph. The methane yield was calculated.
The methane yields at each pretreatment condition are shown in table 2:
TABLE 2 table of anaerobic digestion methane yield of corn
Where HM denotes hydrothermal pretreatment; HMA means hydrothermal simultaneous addition of ammonia;
(4) fitting of hydrothermal pretreatment intensity and anaerobic digestion methanogenesis performance
Fitting the pretreatment intensity calculated in the table 1 with the anaerobic digestion methane yield in the table 2, and finding the optimal hydrothermal pretreatment intensity range of the corn straws through common software Excel in the fitting process according to a trend relation line of the pretreatment intensity and the anaerobic digestion methane yield.
(5) By utilizing the relationship graph of hydrothermal pretreatment strength and methane yield under different pretreatment conditions, the performance of anaerobic digestion methane production of corn straws under different pretreatment conditions can be rapidly judged. And other people do not need to repeatedly do anaerobic digestion experiments, and can know the methane production potential range of the artificial wetland only by combining the pretreatment intensity calculated by the formula (4) with the pH value after pretreatment, the pretreatment time and the pretreatment temperature and looking up a fitting graph. Fitting a graph of the hydrothermal strength of the attached corn straws and the methane yield. As shown in figure 2, the corn straw methane yield has better performance when the pretreatment intensity is about 2.5, the methane yield can be improved by 40.11 percent at most,
in the subsequent screening work of hydrothermal pretreatment parameters of the corn straws, the hydrothermal pretreatment intensity is calculated according to the pretreatment time, the pretreatment temperature and the pretreated pH value, and then the approximate range of the anaerobic digestion methane yield can be quickly predicted by referring to a fitting graph (figure 2).
Example 2
(1) Hydrothermal pretreatment
Weighing 20g of rice hulls, calculating by using raw material TS, and performing pretreatment experiments in two groups, wherein one group is subjected to independent hydrothermal pretreatment, and the other group is subjected to independent hydrothermal pretreatmentSimultaneously adding NH with the dry weight of 2 percent of the corn straw
3·H
2O; adding ammonia water with the dry weight of 2% of the rice hull into the ammonia water heating pretreatment group, and adjusting the water content to 80%; tap water was added to the single hydrothermal group to adjust the water content to 80%. Adding the raw materials, water and the like into a glass container, uniformly stirring by using a glass rod, and then placing into a hydrothermal reactor for heating pretreatment. The rice hull pretreatment set pretreatment conditions are as follows: the pretreatment time at 50 ℃ is 1d, the pretreatment time at 3d, the pretreatment time at 70 ℃ is 1d, the pretreatment time at 3d, the pretreatment time at 90 ℃ is 2h, 4h, the pretreatment time at 100 ℃ is 5min, the pretreatment time is 30min, the pretreatment time at 150 ℃ is 5min, the pretreatment time at 10min, and the pretreatment time at 200 ℃ is 5min, 10 min. Set 3 sets of parallels for each pretreatment condition.
And (3) cooling by using water cooling and air cooling after the pretreatment is finished, taking out the rice hulls after the cooling is finished, and detecting the properties of the pretreated rice hulls, such as pH, reducing sugar, VFAs and the like and the existence of toxic and harmful substances.
(2) Calculating hydrothermal pretreatment intensity
With the use of the formula (4),
and calculating the hydrothermal pretreatment intensity under different pretreatment conditions by combining the time, the temperature and the pH value of the hydrothermal pretreatment. The hydrothermal treatment strength is shown in Table 3.
TABLE 3 PH and pretreatment intensity meter after hydrothermal pretreatment of rice hulls
Where HM denotes hydrothermal pretreatment; HMA means hydrothermal simultaneous addition of ammonia;
(3) anaerobic digestion
Transferring the pretreated rice hulls into a 500mL blue-covered bottle, adding 8g of inoculum (calculated by TS), adding water to fix the volume to 400mL of the effective volume of a fermentation tank, sealing and placing the fermentation tank into a constant-temperature water bath water tank at 35 +/-1 ℃ for medium-temperature anaerobic digestion, wherein the anaerobic digestion time is 50 days.
And (4) recording the daily gas production in the anaerobic digestion process by a drainage method, and measuring the percentage of the daily methane production by a gas chromatograph. The methane yield was calculated.
The methane yields at each pretreatment condition are shown in table 4:
TABLE 4 anaerobic digestion methane productivity table of rice husk
Where HM denotes hydrothermal pretreatment; HMA means hydrothermal simultaneous addition of ammonia;
(4) fitting of hydrothermal pretreatment intensity and anaerobic digestion methanogenesis performance
Fitting the pretreatment intensity calculated in the table 3 with the anaerobic digestion methane yield in the table 4, and finding the optimal hydrothermal pretreatment intensity range of the rice hulls through a common software Excel in the fitting process according to a trend relation line of the pretreatment intensity and the anaerobic digestion methane yield.
(5) By utilizing the relationship graph of hydrothermal pretreatment strength and methane yield under different pretreatment conditions, the performance of anaerobic digestion methane production of rice hulls under different pretreatment conditions can be rapidly judged. And other people do not need to repeatedly do anaerobic digestion experiments, and can know the methane production potential range of the artificial wetland only by combining the pretreatment intensity calculated by the formula (4) with the pH value after pretreatment, the pretreatment time and the pretreatment temperature and looking up a fitting graph. Fitting graph of rice hull attached hydrothermal strength and methane yield. As shown in figure 3, the yield of the anaerobic digestion methane of the rice hulls is better within the range of pretreatment intensity of 2.45-2.75, and the yield of the methane can be improved by 47.60 percent
In the following rice hull hydrothermal pretreatment parameter screening work, the hydrothermal pretreatment intensity is calculated through pretreatment time, temperature and the pH value after pretreatment, and then the approximate range of the anaerobic digestion methane yield can be quickly predicted by referring to a fitting graph (figure 3).
Example 3
(1) Hydrothermal pretreatment
Weighing 20g of cow dung, calculating by using the raw material TS, wherein the pretreatment experiment is independent hydrothermal pretreatment, and adding tap water into the cow dung to adjust the water content to 80%. Adding the raw materials, water and the like into a glass container, uniformly stirring by using a glass rod, and then placing into a hydrothermal reactor for heating pretreatment. The pretreatment conditions set for the pretreatment of the cattle manure are as follows: the pretreatment time at 50 ℃ is 1d, the pretreatment time at 3d, the pretreatment time at 70 ℃ is 1d, the pretreatment time at 3d, the pretreatment time at 90 ℃ is 2h, 4h, the pretreatment time at 100 ℃ is 5min, the pretreatment time is 30min, the pretreatment time at 150 ℃ is 5min, the pretreatment time at 10min, and the pretreatment time at 200 ℃ is 5min, 10 min. Set 3 sets of parallels for each pretreatment condition.
And after the pretreatment is finished, cooling by using water cooling and air cooling, taking out the cow dung after the cooling is finished, and detecting the properties of the pretreated cow dung such as pH, reducing sugar, VFAs and the like and the existence of toxic and harmful substances.
(2) Calculating hydrothermal pretreatment intensity
With the use of the formula (4),
and calculating the hydrothermal pretreatment intensity under different pretreatment conditions by combining the time, the temperature and the pH value of the hydrothermal pretreatment. The hydrothermal treatment strength is shown in Table 5.
TABLE 5 Table of pH and pretreatment intensity after hydrothermal pretreatment of cow dung
Where HM denotes hydrothermal pretreatment
(3) Anaerobic digestion
Transferring the pretreated cow dung into a 500mL blue-covered bottle, adding 8g of inoculum (calculated by TS), adding water to a constant volume of 400mL of the effective volume of the fermentation tank, sealing and placing the fermentation tank into a constant-temperature water bath water tank at 35 +/-1 ℃ for medium-temperature anaerobic digestion, wherein the anaerobic digestion time is 50 days.
And (4) recording the daily gas production in the anaerobic digestion process by a drainage method, and measuring the percentage of the daily methane production by a gas chromatograph. The methane yield was calculated.
The methane yields at each pretreatment condition are shown in table 4:
TABLE 6 methane productivity monitor for cow dung anaerobic digestion
Where HM denotes hydrothermal pretreatment;
(4) fitting of hydrothermal pretreatment intensity and anaerobic digestion methanogenesis performance
Fitting the pretreatment intensity calculated in the table 5 with the anaerobic digestion methane yield in the table 6, and finding the optimal hydrothermal pretreatment intensity range of the cow dung through common software Excel in the fitting process according to the trend relation line of the two.
(5) By utilizing the relationship graph of hydrothermal pretreatment strength and methane yield under different pretreatment conditions, the performance of methane production by cow dung anaerobic digestion under different pretreatment conditions can be rapidly judged. And other people do not need to repeatedly do anaerobic digestion experiments, and can know the methane production potential range of the artificial wetland only by combining the pretreatment intensity calculated by the formula (4) with the pH value after pretreatment, the pretreatment time and the pretreatment temperature and looking up a fitting graph. And (3) fitting a graph of the hydrothermal strength of the cow dung and the methane yield. As shown in figure 4, after the cow dung is pretreated by the water heat, the methane production performance is better when the pretreatment intensity is about 3.5, and the methane yield can be improved by 14.90-21.00%.
In the subsequent cow dung hydrothermal pretreatment parameter screening work, the hydrothermal pretreatment intensity is calculated according to the pretreatment time, the pretreatment temperature and the pretreated pH value, and then the approximate range of the anaerobic digestion methane yield can be quickly predicted by referring to a fitting graph (figure 4).
Example 4
(1) Hydrothermal pretreatment
Weighing 40g of wheat straws (calculated by raw material TS), carrying out a pretreatment experiment in two groups, wherein one group is subjected to hydrothermal pretreatment independently, and the other group is added with KOH with the weight of 2% of the dry weight of the wheat straws; adding a KOH solution with the dry weight of 2 percent of the wheat straws into the K hydrothermal pretreatment group, and then adjusting the water content of the mixture; tap water was added to the single hydrothermal group to adjust the water content. Adding the raw materials, water and the like into a glass container, uniformly stirring by using a glass rod, and then placing into a hydrothermal reactor for heating pretreatment. The pretreatment conditions set for straw pretreatment are as follows: the pretreatment time at 50 ℃ was 1d, and the water content of the pretreatment was set to 70%, 80%, and 90%. Set 3 sets of parallels for each pretreatment condition.
And (3) cooling by using water cooling and air cooling after the pretreatment is finished, taking out the wheat straws after the cooling is finished, and detecting the properties of the pretreated wheat straws, such as pH, reducing sugar, VFAs and the like and the existence of toxic and harmful substances.
(2) Calculating hydrothermal pretreatment intensity
Using formula (4)
And calculating the hydrothermal pretreatment intensity under different pretreatment conditions by combining the time, the temperature and the pH value of the hydrothermal pretreatment. The hydrothermal treatment strength is shown in Table 7.
TABLE 7 PH and pretreatment intensity table after hydrothermal pretreatment of straws
Where HM denotes hydrothermal pretreatment and HMK denotes hydrothermal pretreatment by adding KOH
(3) Anaerobic digestion
And (3) transferring the pretreated straws into a 1000mL blue-covered bottle, adding 16g of inoculum (calculated by TS), adding water to a constant volume of 800mL of the effective volume of the fermentation tank, sealing and placing the fermentation tank into a constant-temperature water bath water tank at 35 +/-1 ℃ for medium-temperature anaerobic digestion, wherein the anaerobic digestion time is 50 days.
And (4) recording the daily gas production in the anaerobic digestion process by a drainage method, and measuring the percentage of the daily methane production by a gas chromatograph. And calculating the methane yield.
The biogas yield under each pretreatment condition is shown in table 8:
TABLE 8 methane yield table for anaerobic digestion of straw
Where HM denotes hydrothermal pretreatment; HMK shows hydrothermal pretreatment by adding KOH
(4) Fitting of hydrothermal pretreatment intensity and performance of anaerobic digestion methane production
Fitting the pretreatment intensity calculated in the table 7 with the anaerobic digestion biogas yield in the table 8, and finding the optimal hydrothermal pretreatment intensity range of the straw through Excel fitting according to the trend relation line of the two.
(5) By utilizing the relationship graph of the hydrothermal pretreatment strength and the methane yield under different pretreatment conditions, the performance of methane production by anaerobic digestion of methane under different pretreatment conditions can be quickly judged. And other people do not need to repeatedly do anaerobic digestion experiments, and can know the methane production potential range of the artificial wetland only by combining the pretreatment intensity calculated by the formula (4) with the pH value after pretreatment, the pretreatment time and the pretreatment temperature and looking up a fitting graph. Fitting graph of straw hydrothermal strength and biogas yield. As shown in figure 5, after the straws are pretreated by hydrothermal treatment, the gas production performance is better when the pretreatment strength is about 2.5-3.5, and the biogas yield can be improved by 28.98% -31.25%.
In the subsequent screening work of the straw hydrothermal pretreatment parameters, the hydrothermal pretreatment intensity is calculated according to the pretreatment time, the pretreatment temperature and the pretreated pH value, and then the approximate range of the anaerobic digestion biogas yield can be quickly predicted by referring to a fitting graph (figure 5).
Claims (1)
1. The method for evaluating the anaerobic digestion performance of the lignocellulose raw material by using the pretreatment intensity is characterized by comprising the following steps of:
(1) hydrothermal pretreatment
a. Weighing the crushed lignocellulose raw material into a fixed container, adding a chemical reagent, and adjusting the water content of the lignocellulose raw material to 70-90% by using tap water;
b. transferring the mixed materials into a container, uniformly stirring the materials by using a glass rod, and then placing the materials into a reactor to perform heating pretreatment for different times under different temperature conditions; the pretreatment temperature range is 50-200 ℃, and the pretreatment time range is 5min-3 d;
c. taking out the material after the pretreatment is finished, and measuring the pH value of the lignocellulose raw material;
(2) hydrothermal Strength calculation
Calculating integral factor R under the pretreatment temperature and time conditions according to the pretreatment temperature and the pretreatment time
0Wherein a is a starting time and b is an ending time;
then, the pretreatment H is used in accordance with the formula (1) in combination with the change of the acid-base property of the lignocellulose before and after the pretreatment
+The concentration of the acid reagent indicates the influence of the acid reagent, and the acidification factor R is calculated
0' deriving formula (2):
R＇
0＝R
0·[H
+]formula (2)
Substituting the formula (2) into the formula (1), taking logarithm at both sides to obtain the formula (3),
log(R＇
0)＝logR
0-pH formula (3)
The pretreatment intensity factor R is deduced by correcting on the basis of the formula (3) and uniformly comparing the hydrothermal pretreatment effects after adding the chemical reagent
0”：
Wherein T is hydrothermal pretreatment time (min), T is hydrothermal pretreatment temperature (DEG C), and pH is the pH value after pretreatment;
(3) anaerobic digestion for methane production
Mixing the pretreated material with the inoculum, adding water to a constant volume to reach the effective volume of a fermentation tank, sealing, and placing in a constant-temperature water bath water tank for mesophilic anaerobic digestion; recording the methane output by a drainage and gas collection method every day; measuring the methane content in the biogas by a gas chromatograph;
(4) evaluation of anaerobic digestion methanogenesis performance by hydrothermal pretreatment strength
The evaluation index logR in the formula (4) is adopted
0Calculating the strength of hydrothermal pretreatment and carrying out the pretreatment on the materialAnaerobic digestion to obtain methane yield; fitting the hydrothermal pretreatment intensity and the anaerobic digestion methane production performance, and obtaining a fitting graph of the relationship between the hydrothermal intensity of the raw materials and the methane yield according to the fitting result;
(5) determination of methane potential of lignocellulosic feedstock
Judging the performance of anaerobic digestion methane production of the lignocellulose raw material under different pretreatment conditions by utilizing a relationship graph of hydrothermal pretreatment strength and methane yield under different pretreatment conditions; and (3) calculating the pretreatment intensity by combining the pH value after pretreatment and the pretreatment time and temperature according to a formula (4), and looking up a fitting graph of the relationship between the hydrothermal intensity and the methane yield of different raw materials to obtain the methane production potential range.
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