Method for improving anaerobic gas production performance of corn straws through combined pretreatment of heat-activated persulfate and phosphoric acid
Technical Field
The invention relates to an anaerobic digestion technology for carrying out oxidation pretreatment on straws in advance, in particular to a technology for improving the anaerobic digestion performance of the straws by the combined oxidation pretreatment of heat-activated persulfate and phosphoric acid.
Background
The biomass straw is always the most abundant renewable resource on the earth, and the high-efficiency utilization of the biomass straw is always a global research hotspot. It is estimated that global photosynthesis produces plant biomass of up to 1100 hundred million tons per year, with lignocellulosic feedstocks accounting for 60% to 80%. China is a big agricultural country, the amount of straws generated in each year is about 8 hundred million tons on average, and only 50 percent of straws are effectively utilized. The anaerobic digestion technology can solve the increasingly severe resource and environmental problems in China, and provides an effective way for the resource utilization of straws.
The content of lignocellulose in the straws is relatively high, and the degradation and digestion capacity of the anaerobic microorganisms on the lignocellulose is relatively weak, so that the straws are slowly hydrolyzed, and the subsequent acidification and gasification processes are influenced; in addition, the fermented biogas residues contain high-content lignin, so that the lignin cannot be reasonably utilized, and resource waste is caused. Therefore, the reasonable pretreatment of the straws is very important. At present, the pretreatment methods for lignocellulose raw materials mainly comprise crushing and grinding, acid pretreatment, alkali pretreatment, oxidation pretreatment and the like. The mechanical treatment method can improve the utilization rate of the straw raw material, and has the advantages of low cost and convenient use, but does not separate lignin and hemicellulose which cause obstruction to the microbial degradability from fibers, so the degradation speed and the fermentation rate are not high. Compared with other pretreatment means, the temperature and pressure in the acid method and alkali method pretreatment processes are slightly low, the pretreatment can be carried out at room temperature, but the requirement on the corrosion resistance of equipment is high, a large amount of waste acid and waste alkali solution remained after the reaction is easy to cause secondary pollution to the environment, the reaction time is long, and usually more than three days are needed. The oxidant can degrade lignin and hemicellulose in the raw material and effectively remove the lignin in the raw material, and the common oxidant mainly comprises H2O2、O2And O3. The literature: travaini R, oxygen M D M, Coca M, et al, organic base catalysis prediction, effect on enzymatic differentiation and inhibition composition]Bioresource technology,2013,133(4): 332-. In the literature, the bagasse can be pretreated by adopting ozone to improve the digestibility of the lignocellulose material, but in the treatment process, the ozone consumption is extremely high, so that the cost is increased. The literature: experimental study of pretreatment of corn stover with soda and Hydrogen peroxide [ J]Renewable energy, 2011,29(1): 19-22. The alkali and hydrogen peroxide pretreatment in the literature can effectively degrade lignin and hemicellulose in the corn straws, but the optimal pretreatment time needs 72 hours, the optimal solid-to-liquid ratio is 1:20, the pretreatment time is relatively long, and the solid-to-liquid ratio is relatively high.
The persulfate advanced oxidation technology is a method for generating SO by activating persulfate4 -And OH to degrade organic matters in water. So far, no report related to the anaerobic digestion methane production technology for pretreating straws by using heat activated sodium persulfate combined with phosphoric acid exists, and compared with other pretreatment methods, the method has the advantages of short pretreatment time, low solid-to-liquid ratio, simple equipment, convenience in operation and the like.
Disclosure of Invention
In order to further solve the problem of lignin degradation, the invention aims to provide a novel pretreatment method which can effectively improve the pretreatment effect of the corn straws, shorten the pretreatment time and improve the gas production performance of the corn straws, and SO generated by thermally activating persulfate4 -Degrading lignin together with OH, destroying the stereoscopic grid structure of the straw, and simultaneously combining the degradation effect of phosphoric acid on cellulose and hemicellulose to obtain the raw material beneficial to subsequent anaerobic fermentation.
The specific method of the invention is as follows:
A. and (3) the corn straws which are crushed to be less than 20 meshes and are naturally dried without mildewing are packaged into plastic package bags. Preparing a sodium persulfate solution, adjusting the pH value of the sodium persulfate solution to 4-7 by using phosphoric acid, pouring the sodium persulfate solution into a container, uniformly mixing the sodium persulfate solution with the straws, sealing the container, and then placing the container at 50 ℃ for constant-temperature pretreatment for 12-48 hours.
The adding amount of sodium persulfate in the sodium persulfate solution is 0.5-1.0% of the dry weight of the straws, and the ratio of the mass of the straws to the amount of water added in the solution is 1: 10-1: 12.
B. B, adding the straws pretreated in the step A and the inoculum into an anaerobic digestion reactor, adding tap water to 80-90% of the total volume of the reactor to form anaerobic reaction liquid, and sealing the reactor to keep the materials in the reactor at the temperature of 35-37 ℃ for anaerobic reaction; adjusting the pH value of the system to be 6.9-8.0, and the preferable range is 7.0-7.5; finally, discharging the biogas slurry and the biogas residues. The anaerobic reaction time is determined according to the fact that the accumulated gas production accounts for 80-90% of the total gas production, and the anaerobic reaction time of the method is 25-40 days.
The raw material load of the straw in the anaerobic reaction liquid is 50-90 gTS/L, and the inoculum load is 15-45 gVS/L.
The inoculum is anaerobic digestion liquid containing methane bacteria, such as anaerobic digestion liquid of a methane tank or anaerobic sludge of a sewage treatment plant, and the like, and a precipitate is taken after standing.
And (3) determining parameters such as the degradation rate of the straws before and after pretreatment, the anaerobic daily gas production rate, the methane content, the total solid content TS and the total volatile solid VS of feeding and discharging materials before and after the anaerobic treatment, the pH value and the like, and evaluating the pretreatment effect and the anaerobic gas production performance of the thermally activated sodium persulfate.
Compared with the prior art, the invention has the following beneficial effects:
1) so far, no report is found about the methane production technology by anaerobic digestion of straws pretreated by combination of heat activated sodium persulfate and phosphoric acid. The biogas slurry and residue generated after anaerobic digestion can be used for producing phosphate fertilizer.
2) Due to the combined action of sulfate radicals and hydroxyl radicals generated by thermal activation of sodium persulfate, the pretreatment time of the straws is shortened to 12-48 h, and compared with the test of Zhongxifang et al, the optimal pretreatment time of the alkali and hydrogen peroxide combined pretreatment is 72h, the pretreatment time is shortened by 24-60 h, and the pretreatment time is shortened by 33.33-83.33%. Compared with the ozone pretreatment method of Travaini R and the like, the method has simple operation and relatively less equipment investment.
3) After the pretreatment of the thermally activated sodium persulfate for 12-48 hours, the structure of lignocellulose in the straw is effectively destroyed, and the degradation rate of the corn straw can reach 20-23%.
4) In the pretreatment process of 16h, the structure of lignocellulose in the straw is effectively destroyed and the chemical components of the lignocellulose are changed through the oxidation of thermally activated sodium persulfate. Compared with the corn straw which is not pretreated, the gas yield of the pretreated corn straw unit TS (dry weight of the straw) is 12.58-22.86% higher than that of the corn straw which is not pretreated, and the accumulated methane yield is improved by 13.70-31.47%.
5) When the accumulated gas production of the corn straws pretreated by the combination of the thermally activated sodium persulfate and the phosphoric acid reaches 80 percent of the total gas productionIs T80For 21-26 days, T90The cumulative gas production of the corn straws which are not pretreated reaches T within 26-31 days80The required time is 17 days, T90It was 22 days. The anaerobic digestion time is prolonged by 4-9 days, and the straw is subjected to pretreatment so that more degradable substances are released.
Drawings
FIG. 1 is a graph of the rate of degradation over time during a heat activated sodium persulfate pretreatment;
FIG. 2 daily gas production graphs for the experimental formulation and comparative example in example 1
FIG. 3 daily gas production graph of the experimental formulation and the comparative example in example 2
FIG. 4 daily gas production graph of the experimental formulation and the comparative example in example 3
Detailed Description
The fermentation raw materials used in the following experiments were corn stalks crushed to below 20 mesh by a crusher, the effective volume of the anaerobic fermentation reactor was 0.4L, and the corn stalk addition load was 50 gTS/L. The addition amount of the inoculated sludge was 15 gVS/L.
Example 1
Weighing 3 parts of corn straws in a plastic package bag, wherein each part of the corn straws is 21.39g (calculated by 50g TS/L), respectively adding sodium persulfate accounting for 0.5 percent of the dry weight of the corn straws into 200g of water (equivalent to 10 times of the dry weight of the corn straws), adjusting the pH of the solution to 5 by using phosphoric acid, uniformly mixing the solution and the straws, sealing the plastic package bag, and sealing and storing for 16 hours at 50 ℃. Meanwhile, the corn stalks which are not pretreated are used as a reference.
The pretreated raw material and 126.85g (calculated as 15 gVS/L) of inoculum sludge are mixed and added into an anaerobic digestion reaction device, and water is added to the effective volume of the reactor to be 0.4L. The reactor was sealed and subjected to anaerobic reaction at 37 ℃ for 40 days, and the daily gas production and methane content were measured every day, and the results are shown in FIG. 2. After the experiment, the cumulative gas production (i.e. total gas production), unit TS gas production and VS gas production were calculated, and the gas production analysis results are shown in table 1.
TABLE 1 Effect of pretreatment on anaerobic digestion gas production
As can be seen from FIG. 2 and Table 1, the total gas yield of the straw pretreated by the thermal activation of 0.5% sodium persulfate is increased by 22.04% compared with that of the non-pretreated straw. The unit TS gas production is improved by 22.04 percent compared with that of the non-pretreated gas production, and the accumulated methane production is improved by 31.47 percent compared with that of the non-pretreated gas production.
T80、T90The results are shown in Table 2. As can be seen from Table 2, the time T is the time taken for the cumulative gas production of the straws pretreated by the thermal activation of 0.5 percent sodium persulfate for 16 hours to reach 80 percent of the total gas production8022 days, the time T is the cumulative gas production rate which reaches 90 percent of the total gas production rate90The cumulative gas production of the corn straws which are not pretreated reaches T within 27 days80The required time is 17 days, T90The anaerobic digestion time is prolonged to 22 days, which shows that the straws can release more degradable substances through the pretreatment of the thermally activated sodium persulfate, and the gas production is greatly improved.
TABLE 2 Effect of pretreatment on anaerobic digestion time
Example 2
Weighing 3 parts of corn straws in a plastic package bag, wherein each part of the corn straws is 21.39g (calculated by 50g TS/L), respectively adding sodium persulfate accounting for 0.5 percent of the dry weight of the corn straws into 240g of water (equivalent to 12 times of the dry weight of the corn straws), adjusting the pH of the solution to 4 by using phosphoric acid, uniformly mixing the solution and the straws, sealing the plastic package bag, and sealing and storing for 48 hours at 50 ℃. Meanwhile, the corn stalks which are not pretreated are used as a reference.
The pretreated raw material and 126.85g (calculated as 15 gVS/L) of inoculum sludge are mixed and added into an anaerobic digestion reaction device, and water is added to the effective volume of the reactor to be 0.4L. The reactor was sealed and subjected to anaerobic reaction at 37 ℃ for 40 days, and the daily gas production and methane content were measured every day, and the results are shown in FIG. 2. After the experiment, the cumulative gas production (i.e. total gas production), unit TS gas production and VS gas production were calculated, and the gas production analysis results are shown in table 3.
TABLE 3 Effect of pretreatment on anaerobic digestion gas production
As can be seen from FIG. 3 and Table 3, the total gas yield of the straw pretreated with 0.5% sodium persulfate through thermal activation for 48 hours is increased by 22.86% compared with that of the non-pretreated straw. The unit TS gas production is improved by 22.86 percent compared with that of the non-pretreated gas production, and the accumulated methane production is improved by 26.04 percent compared with that of the non-pretreated gas production.
T80、T90The results are shown in Table 4. As can be seen from Table 4, the time T is the cumulative gas production of the straw pretreated by thermally activating 0.5% sodium persulfate until the cumulative gas production reaches 80% of the total gas production80The time taken for the cumulative gas production to reach 90% of the total gas production is T of 26 days90The cumulative gas production of the corn straws which are not pretreated reaches T within 31 days80The required time is 21 days, T90The anaerobic digestion time is prolonged for 31 days, which shows that the straws can release more degradable substances through the pretreatment of the thermally activated sodium persulfate, and the gas production is greatly improved.
TABLE 4 Effect of pretreatment on anaerobic digestion time
Example 3
Weighing 3 parts of corn straws in a plastic package bag, wherein each part of the corn straws is 21.39g (calculated by 50g TS/L), respectively adding sodium persulfate accounting for 1.0 percent of the dry weight of the corn straws into 200g of water (equivalent to 10 times of the dry weight of the corn straws), adjusting the pH of the solution to 7 by using phosphoric acid, uniformly mixing the solution and the straws, sealing the plastic package bag, and sealing and storing for 16 hours at the temperature of 60 ℃. Meanwhile, the corn stalks which are not pretreated are used as a reference.
The pretreated raw material and 126.85g (calculated as 15 gVS/L) of inoculum sludge are mixed and added into an anaerobic digestion reaction device, and water is added to the effective volume of the reactor to be 0.4L. The reactor was sealed and subjected to anaerobic reaction at 37 ℃ for 40 days, and the daily gas production and methane content were measured every day, and the results are shown in FIG. 4. After the experiment, the cumulative gas production (i.e., total gas production), unit TS gas production and VS gas production were calculated, and the gas production analysis results are shown in table 5.
As can be seen from FIG. 4 and Table 5, the total gas yield of the straw pretreated with 2.0% sodium persulfate through thermal activation was increased by 12.58% as compared with that of the non-pretreated straw. The unit TS gas production is improved by 12.58 percent compared with that of the non-pretreated gas production, and the accumulated methane production is improved by 13.70 percent compared with that of the non-pretreated gas production.
TABLE 5 Effect of pretreatment on anaerobic digestion gas production
T80、T90The results are shown in Table 6. As can be seen from Table 6, the time T taken for the cumulative gas production of the straws pretreated for 16 hours by thermally activating 1.0 percent of sodium persulfate to reach 80 percent of the total gas production80The time taken for the cumulative gas production to reach 90% of the total gas production is T for 21 days90The cumulative gas production of the corn straws which are not pretreated reaches T within 26 days80The required time is 20 days, T90The anaerobic digestion time is prolonged by 25 days, and the gas production rate is improved.
TABLE 6 Effect of pretreatment on anaerobic digestion time