CN104593432B - The method that alkali improves maize straw anaerobic digestion methane production with salt combined pretreatment - Google Patents

Abstract

The method for improving the methane yield of anaerobic digestion of corn stalks through combined alkali and salt pretreatment belongs to the field of anaerobic fermentation of agricultural organic solid waste. After the corn stalks are crushed, potassium hydroxide and metal salts are used as pretreatment reagents to pretreat the corn stalks. The metal salts include ferrous chloride, cobalt chloride and nickel chloride; The total mass of water is six times the dry weight of corn stalks. After fully stirring, the sealing film is sealed; it is sealed and stored at room temperature for 3 days and then anaerobic fermentation is performed; the anaerobic fermentation process requires activated sludge, and the amount of activated sludge added is relative to 52g TS corn stalks are 12g TS, then add water to 80% of the total volume of the reaction device, fill with nitrogen, then seal with a rubber stopper, and fix the reactor in a shaker, the shaker temperature is constant at 35±2°C . The invention can shorten the anaerobic fermentation cycle, greatly increase the total gas production volume and total methane production volume, and significantly increase the dry matter removal rate.

Description

Alkali and salt combined pretreatment method to improve methane production in anaerobic digestion of corn stalks

technical field

The invention belongs to the field of anaerobic fermentation of agricultural organic solid waste. Specifically, it relates to a method for improving methane production in the anaerobic fermentation process of corn stalks by using alkaline compounds to pretreat corn stalks and adding metal salts.

Background technique

The annual output of crop straw in my country is huge, but the utilization rate of straw is not high. Most of the straw rots naturally or burns on the spot, resulting in a considerable amount of straw being abandoned and a great waste of resources. Therefore, the resource utilization of waste straw has always been a research hotspot, and the use of anaerobic digestion technology to convert straw into biogas with high calorific value has great development potential and utilization value.

The use of anaerobic digestion technology to treat corn stalks is a method that can effectively convert straws into clean energy and realize resource energy utilization. However, in the actual operation process, due to the complex structure of corn stalks, which are composed of cellulose, hemicellulose and cellulose, it is difficult to be degraded by anaerobic microorganisms, which leads to a long cycle of conventional anaerobic fermentation and digestion, and too little methane production. The output efficiency is poor, so the conventional anaerobic fermentation technology of straw has not been applied and developed on a large scale.

Studies have found that pretreatment of straw before anaerobic fermentation can greatly increase methane production. There are many kinds of straw pretreatment methods, the most commonly used is the chemical pretreatment method, and sodium hydroxide pretreatment is the most widely used chemical pretreatment method. Literature: Pang Yunzhi et al. Effect of temperature and chemical pretreatment on the gas production of anaerobic digestion of corn stalks, Bioprocessing, 2005, 3(1): 37-41. Sodium hydroxide pretreatment method was used to pretreat corn stalks , the pretreatment temperature was 35°C, and the pretreatment time with 4% sodium hydroxide was 30 days. Compared with the method without pretreatment, this method increases the cumulative gas production by 77%. Although the gas production volume during anaerobic digestion of corn stalks can be greatly increased, the methane content cannot be increased. In practical applications, excessive sodium hydroxide is usually added to ensure the expected treatment effect, which makes the pretreated material contain a large amount of lye, and the direct discharge of these lye will cause waste and cause serious environmental pollution.

Some metal salts are micronutrients necessary for the metabolism of anaerobic microorganisms and important components of anaerobic fermentation enzyme systems, which can promote the growth of anaerobic microorganisms, activate enzyme activities, and accelerate methane biosynthesis. In the process of anaerobic digestion, if the anaerobic microorganisms cannot take in an appropriate amount of micronutrients, it will lead to a decrease in metabolic activity, which in turn will affect the progress of the entire digestion process. Therefore, adding different metal salts at the beginning of anaerobic fermentation can effectively increase the activity of anaerobic microorganisms, thereby increasing the methane content.

In view of the problems in the above pretreatment process, it is urgent to find a new pretreatment method to obtain a higher methane content and effectively reduce the impact of the pretreatment process on the environment. The invention adopts combined pretreatment technology of potassium hydroxide with certain parameters and different metal salts to increase the gas production and methane content of anaerobic digestion of corn stalks and reduce environmental pollution. The invention has mild operating conditions, low requirements on the pressure resistance and corrosion resistance of the reactor, can improve the biodegradability of corn stalks, significantly increase the effect of anaerobic digestion biogas production, and effectively reduce the impact of the pretreatment process on the environment.

Contents of the invention

The object of the present invention is to provide a method for increasing methane production in the anaerobic digestion process of pretreated straw by changing the amount of metal salt added.

The method for improving the methane yield of anaerobic digestion of corn stalks through combined alkali and salt pretreatment is characterized in that the steps are as follows:

After the corn stalks are crushed, potassium hydroxide and metal salts are used as pretreatment reagents to pretreat the corn stalks. The metal salts include ferrous chloride FeCl ₂ 4H ₂ O, cobalt chloride CoCl ₂ 6H ₂ O and chloride Nickel NiCl ₂ 6H ₂ O; Potassium hydroxide 2% of the dry weight of corn stalks, ferrous chloride FeCl ₂ 4H ₂ O 1%-15% of the dry weight of corn stalks, cobalt chloride CoCl ₂ The amount of 6H ₂ O added is 0.05%-1% of the dry weight of corn stalks, the amount of nickel chloride NiCl ₂ 6H ₂ O added is 0.05%-1% of the dry weight of corn stalks, and finally water is added to make it compatible with the dry weight of corn stalks. The total mass of water contained is six times the dry weight of corn stalks. After fully stirring with a glass rod, the sealing film is sealed; it is sealed and stored at room temperature for 3 days and then anaerobic fermentation is performed; the anaerobic fermentation process requires activated sludge, and activated sludge is added The amount is 12g TS relative to 52g TS corn stalks, then add water to 80% of the total volume of the reaction device, fill with nitrogen, then seal with a rubber stopper, and fix the reactor in a shaker, the shaker temperature is constant at 35 ± between 2°C.

Compared with the prior art, the present invention has the following beneficial effects:

1) The anaerobic fermentation cycle is significantly shortened. Combined pretreatment of corn stover with alkali and salt addition at room temperature can shorten the anaerobic fermentation period. For potassium hydroxide+salt pretreatment group, compared with potassium hydroxide pretreatment group and untreated group, T ₉₀ was shortened to 6-9d, respectively. If the results are applied to actual engineering, the investment cost can be greatly reduced.

2) The total gas production volume and total methane production volume have been greatly increased. By increasing the amount of different salts added in the potassium hydroxide pretreatment process, the total gas production volume and total methane production volume can be effectively increased, and the gas production performance of anaerobic fermentation can be improved, so that corn stalks can be better converted into clean energy. Compared with potassium hydroxide pretreated corn stover, the total methane production volume per unit TS of potassium hydroxide+salt pretreatment group increased by 24%-42%; compared with non-pretreated corn stover, it increased by 39%-101%.

3) The dry matter removal rate is significantly improved. By increasing the amount of different salts added in the pretreatment process of potassium hydroxide, the removal rate of dry matter can be effectively improved, so as to reduce the treatment of corn stalks. Compared with the potassium hydroxide pretreatment group, the removal rate of TS in the potassium hydroxide + salt pretreatment group increased by 5.47%-21.88%, and the removal rate of lignocellulose could increase by 1.23%-13.38%; compared with the untreated group, hydrogen The unit TS and VS removal rate of potassium oxide+salt pretreatment group can be increased by 35.39%-56.16%; lignocellulose removal rate can be increased by 22.60%-37.31%.

Description of drawings

Total gas production volume and total methane production volume figure in Fig. 1 embodiment 1;

Total gas production volume and total methane production volume figure in Fig. 2 embodiment 2;

Total gas production volume and total methane production volume figure in Fig. 3 embodiment 3.

Detailed ways

Concrete steps of the present invention are as follows:

1) In all the following tests, the total volume of the anaerobic fermentation reaction device is 1L, and the reaction volume is 0.8L, and 52g TS of corn stalks crushed to below 20 mesh is added, and the alkali pretreatment reagent used in the present invention is potassium hydroxide, salt The pretreatment reagents are ferrous chloride, cobalt chloride and nickel chloride. The amount of seed sludge added was 12g TS.

2) The amount of alkali and salt added. The amount of potassium hydroxide added is 2% of the dry weight of corn stalks, while the amount of ferrous chloride (FeCl ₂ 4H ₂ O) added is 1%-15% of the dry weight of corn stalks, cobalt chloride (CoCl ₂ 6H ₂ O) The addition amount is 0.05%-1% of the dry weight of corn stalks, and the addition amount of nickel chloride (NiCl ₂ ·6H ₂ O) is 0.05%-1% of the dry weight of corn stalks.

3) Specific implementation method: the present invention selects corn stalks that have been naturally air-dried and has no mildew, and crushes them to 20 meshes with a pulverizer, weighs a certain amount of corn stalks with a crucible, puts them in an oven at 105° C., and measures the corn stalks after 12 hours. Straw TS. Use a blue cap bottle (1L) as an anaerobic reaction vessel with a reaction volume of 0.8L. According to the corn stalk load of 65g TS/L, first weigh 52g TS corn stalks, and then use potassium hydroxide and metal salts as pretreatment reagents to treat the corn stalks. The straw is pretreated, the amount of potassium hydroxide is 2% of the dry weight of the corn straw, the ferrous chloride (FeCl ₂ ·4H ₂ O) is 1%-15% of the dry weight of the corn straw, and the cobalt chloride (CoCl ₂ · 6H ₂ O) was added in an amount of 0.05%-1% of the dry weight of corn stalks, and nickel chloride (NiCl ₂ 6H ₂ O) was added in an amount of 0.05%-1% of the dry weight of corn stalks, and finally 308.68mL of water was added to make it The total mass of the water (3.32mL) contained in the corn stalks is six times (312mL) of the dry weight of the corn stalks, fully stirred with a glass rod, and then sealed with a parafilm. Sealed and stored at room temperature for 3 days.

4) Anaerobic fermentation. The anaerobic fermentation process needs inoculum (activated sludge). The amount of activated sludge in the present invention is 12gTS (relative to 52g TS corn stalks). The activated sludge comes from a sewage treatment plant and contains a large amount of anaerobic microbial flora. The activated sludge The mud needs to settle for more than a week. First add 12g TS activated sludge to the pretreated corn stalks, then add tap water to 80% of the total volume of the reaction device, fill with nitrogen, then seal with a rubber stopper, and fix the reactor in a shaker, the shaker temperature Constantly between 35±2°C, shake to measure the total solid content TS and total volatile solid VS of the corn stalks and anaerobic inoculated sludge, use the drainage method to measure the daily gas production, measure the daily methane volume fraction, and calculate the daily methane production volume. T ₉₀ is a characteristic parameter of the length of the anaerobic fermentation cycle, and generally refers to the time to reach 90% of the total gas production. All data were used to evaluate the effect of potassium hydroxide pretreatment.

Example 1

Use a blue cap bottle (1L) as an anaerobic reaction vessel with a reaction volume of 0.8L. According to the corn stalk load of 65g TS/L, first weigh three parts of corn stalks crushed to below 20 mesh, each with a mass of 52g (calculated as TS ), add 2% potassium hydroxide of the dry weight of corn stalks, and simultaneously add metal salt salt solution (ferrous chloride (FeCl ₂ .4H ₂ O) is 1% of the dry weight of corn stalks, cobalt chloride (CoCl ₂ . 6H ₂ O) addition amount is 0.05% of corn stalk dry weight, nickel chloride (NiCl ₂ 6H ₂ O) addition amount is 0.05% of corn stalk dry weight), then add 308.68 milliliters of water to make it and corn stalk Water (3.32 ml) was six times the dry weight of corn stalks, mixed evenly, sealed in a blue cap bottle, and pretreated at room temperature for 3 days. Add 12g of TS anaerobic sludge to the pretreated corn stalks, and at the same time add tap water to 80% of the reactor volume. The control group was corn stover pretreated with 2% KOH and corn stover without pretreatment. Put the reactor filled with nitrogen gas and sealed after adding the materials into a shaker at 35°C, and shake. The daily gas production during the anaerobic fermentation process was recorded by the drainage gas collection method, and the volume fraction of methane was measured at the same time, the total gas production volume and total methane production volume were calculated, and then T ₉₀ was calculated. TS and lignocellulose removal rate were measured at the end of anaerobic fermentation.

The total gas production volume and total methane production volume are shown in Figure 1.

As can be seen from Figure 1, the total gas production volume of the potassium hydroxide+metal salt pretreatment group is significantly higher than that of the potassium hydroxide pretreatment group and the untreated group, which can be increased by 15.85% and 29.64%; the total methane production volume is also significantly higher than Potassium hydroxide pretreatment group and untreated group, can increase 28.84% and 47.39%.

The _T90 experimental results are shown in Table 1:

Table 1

Potassium hydroxide + metal salt pretreatment Potassium hydroxide pretreatment unprocessed T ₉₀ /d 35 38 42

The T ₉₀ of the potassium hydroxide + metal salt pretreatment group was 35d, which was 3d and 7d earlier than the T ₉₀ of the potassium hydroxide pretreatment group and the non-pretreatment group.

Select the shortest T ₉₀ , and calculate the methane production volume per unit TS and unit VS within this period of time under different treatment conditions. The results are shown in Table 2:

Table 2

Potassium hydroxide + metal salt pretreatment Potassium hydroxide pretreatment unprocessed Unit TS methane production volume/mL 179 139 124 Unit VS Methanogenic Volume/mL 199 155 138

It can be seen from Table 2 that the unit TS and unit VS methanogenic volume of the potassium hydroxide + metal salt pretreatment group are greatly improved compared with the potassium hydroxide pretreatment and untreated groups. Compared with the potassium hydroxide pretreatment group, the unit TS and VS methanogenic volume of the potassium hydroxide + metal salt pretreatment group can be increased by about 28%; compared with the potassium hydroxide pretreatment group and the untreated group, the potassium hydroxide +Methanogenic volume per unit TS and VS of the metal salt pretreatment group can be increased by about 44%.

The unit TS removal rate, VS removal rate and lignocellulose removal rate are shown in Table 3:

table 3

Potassium hydroxide + metal salt pretreatment Potassium hydroxide pretreatment unprocessed TS removal rate/% 50.1 45.7 35.6 Lignocellulose removal rate/% 59.4 56.8 46.9

It can be seen from Table 3 that the unit TS removal rate and lignocellulose removal rate of the potassium hydroxide + metal salt pretreatment group are greatly improved compared with the potassium hydroxide pretreatment phase and the untreated group. Compared with the potassium hydroxide pretreatment group, the unit TS removal rate of the potassium hydroxide + metal salt pretreatment group can be increased by 9.63% and 4.93%, and the lignocellulose removal rate can be increased by 4.58%; The unit TS of the potassium + metal salt pretreatment group can be increased by 40.73% and 30.09%, and the lignocellulose removal rate can be increased by 26.65%.

Example 2

Use a blue cap bottle (1L) as an anaerobic reaction vessel with a reaction volume of 0.8L. According to the corn stalk load of 65g TS/L, first weigh three parts of corn stalks crushed to below 20 mesh, each with a mass of 52g (calculated as TS ), add 2% potassium hydroxide of the dry weight of corn stalks, and simultaneously add metal salt salt solution (ferrous chloride (FeCl ₂ .4H ₂ O) is 7.5% of the dry weight of corn stalks, cobalt chloride (CoCl ₂ . 6H ₂ O) was added in an amount of 0.5% of the dry weight of corn stalks, and nickel chloride (NiCl ₂ 6H ₂ O) was added in an amount of 0.5% of the dry weight of corn stalks), and then 308.68 milliliters of water was added to make it mix with the corn stalks Water (3.32 ml) was six times the dry weight of corn stalks, mixed evenly, sealed in a blue cap bottle, and pretreated at room temperature for 3 days. Add 12g of TS anaerobic sludge to the pretreated corn stalks, and at the same time add tap water to 80% of the reactor volume. The control group was corn stover pretreated with 2% KOH and corn stover without pretreatment. Put the reactor filled with nitrogen gas and sealed after adding the materials into a shaker at 35°C, and shake. The daily gas production during the anaerobic fermentation process was recorded by the drainage gas collection method, and the volume fraction of methane was measured at the same time, the total gas production volume and total methane production volume were calculated, and then T ₉₀ was calculated. TS and lignocellulose removal rate were measured at the end of anaerobic fermentation.

Put the reactor filled with nitrogen gas and sealed after adding the materials into a shaker at 35°C, and shake. The daily gas production during the anaerobic fermentation process was recorded by the drainage gas collection method, and the volume fraction of methane was measured at the same time, the total gas production volume and total methane production volume were calculated, and then T ₉₀ was calculated. TS and lignocellulose removal rate were measured at the end of anaerobic fermentation.

The total gas production and total methane production are shown in Figure 2.

It can be seen from Figure 2 that the total gas production volume of the potassium hydroxide + metal salt pretreatment group is significantly higher than that of the potassium hydroxide pretreatment group and the untreated group, which can be increased by 27.91% and 43.13%; the potassium hydroxide + metal salt pretreatment group The total methane production volume of KOH pretreatment group and untreated group was significantly higher, which can be increased by 41.77% and 62.18%.

The _T90 experimental results are shown in Table 4 below:

Table 4

Potassium hydroxide + metal salt pretreatment Potassium hydroxide pretreatment unprocessed T ₉₀ /d 33 38 42

The T ₉₀ of the potassium hydroxide + metal salt pretreatment group was 33d, which was 5d and 9d earlier than the T ₉₀ of the potassium hydroxide pretreatment group and the non-pretreatment group.

Select the shortest T ₉₀ , and calculate the methane production volume per unit TS and unit VS within this period of time under different treatment conditions. The results are shown in Table 5:

table 5

Potassium hydroxide + metal salt pretreatment Potassium hydroxide pretreatment unprocessed Unit TS methane production/mL 198 139 124 Unit VS methane production/mL 220 155 138

It can be seen from Table 5 that the unit TS and unit VS methanogenic volume of the potassium hydroxide + metal salt pretreatment group are greatly improved compared with the potassium hydroxide pretreatment and untreated groups. Compared with the potassium hydroxide pretreatment group, the unit TS and VS methanogenic volume of the potassium hydroxide + metal salt pretreatment group can be increased by about 42%; compared with the potassium hydroxide pretreatment group and the untreated group, the potassium hydroxide +The unit TS and VS methanogenic volume of the metal salt pretreatment group can be increased by about 59%.

The unit TS removal rate, VS removal rate and lignocellulose removal rate are shown in Table 6:

Table 6

Potassium hydroxide + metal salt pretreatment Potassium hydroxide pretreatment unprocessed TS removal rate/% 55.7 45.7 35.6 Lignocellulose removal rate/% 64.4 56.8 46.9

It can be seen from Table 6 that the unit TS removal rate and lignocellulose removal rate of the potassium hydroxide + metal salt pretreatment group are greatly improved compared with the potassium hydroxide pretreatment and untreated groups. Compared with the potassium hydroxide pretreatment group, the unit TS removal rate of the potassium hydroxide + metal salt pretreatment group can be increased by 21.88% and 20.26%, and the lignocellulose removal rate can be increased by 13.38%; compared with the untreated group, hydrogen The unit TS removal rate of potassium oxide + metal salt pretreatment group can be increased by 56.16% and 49.09%, and the lignocellulose removal rate can be increased by 37.31%.

Example 3:

Use a blue cap bottle (1L) as an anaerobic reaction vessel with a reaction volume of 0.8L. According to the corn stalk load of 65g TS/L, first weigh three parts of corn stalks crushed to below 20 mesh, each with a mass of 52g (calculated as TS ), add 2% potassium hydroxide of the dry weight of corn stalks, and simultaneously add metal salt salt solution (ferrous chloride (FeCl ₂ .4H ₂ O) is 15% of the dry weight of corn stalks, cobalt chloride (CoCl ₂ . 6H ₂ O) was added in an amount of 1% of the dry weight of corn stalks, and the amount of nickel chloride (NiCl ₂ 6H ₂ O) was added in 1% of the dry weight of corn stalks), and then 308.68 milliliters of water was added to make it mix with the corn stalks Water (3.32 ml) was six times the dry weight of corn stalks, mixed evenly, sealed in a blue cap bottle, and pretreated at room temperature for 3 days. Add 12g of TS anaerobic sludge to the pretreated corn stalks, and at the same time add tap water to 80% of the reactor volume. The control group was corn stover pretreated with 2% KOH and corn stover without pretreatment. Put the reactor filled with nitrogen gas and sealed after adding the materials into a shaker at 35°C, and shake. The daily gas production during the anaerobic fermentation process was recorded by the drainage gas collection method, and the volume fraction of methane was measured at the same time, the total gas production volume and total methane production volume were calculated, and then T ₉₀ was calculated. TS and lignocellulose removal rate were measured at the end of anaerobic fermentation.

The total gas production and total methane production are shown in Figure 3.

It can be seen from Figure 3 that the total gas production volume of the potassium hydroxide + metal salt pretreatment group is significantly higher than that of the potassium hydroxide pretreatment group and the untreated group, which can be increased by 7.86% and 20.69%; the potassium hydroxide + metal salt pretreatment group The total methane production volume of KOH pretreatment group and untreated group can be increased by 23.29% and 41.04%.

The _T90 experimental results are shown in Table 7 below:

Table 7

Potassium hydroxide + metal salt pretreatment Potassium hydroxide pretreatment unprocessed T ₉₀ /d 36 38 42

The T ₉₀ of the potassium hydroxide + metal salt pretreatment group was 36d, which was 2d and 6d earlier than the T ₉₀ of the potassium hydroxide pretreatment group and the non-pretreatment group.

Select the shortest T ₉₀ , and calculate the methane production volume per unit TS and unit VS within this period of time under different treatment conditions. The results are shown in Table 8:

Table 8

It can be seen from Table 8 that the unit TS and unit VS methanogenic volume of the potassium hydroxide + metal salt pretreatment group are greatly improved compared with the potassium hydroxide pretreatment and untreated groups. Compared with the potassium hydroxide pretreatment group, the unit TS and VS methanogenic volume of the potassium hydroxide + metal salt pretreatment group can be increased by about 24%; compared with the potassium hydroxide pretreatment group and the untreated group, the potassium hydroxide +Methanogenic volume per unit TS and VS of the metal salt pretreatment group can be increased by about 39%.

The unit TS removal rate and lignocellulose removal rate are shown in Table 9:

Table 9

It can be seen from Table 9 that the unit TS removal rate and lignocellulose removal rate of the potassium hydroxide + metal salt pretreatment group are greatly improved compared with the potassium hydroxide pretreatment and untreated groups. Compared with the potassium hydroxide pretreatment group, the unit TS removal rate of the potassium hydroxide + metal salt pretreatment group can be increased by 5.47% and 1.82%, and the lignocellulose removal rate can be increased by 1.23%; compared with the untreated group, hydrogen The unit TS removal rate of potassium oxide + metal salt pretreatment group can be increased by 35.39% and 26.24%, and the lignocellulose removal rate can be increased by 22.60%.

Claims (1)

1. the method that alkali improves maize straw anaerobic digestion methane production with salt combined pretreatment, it is characterised in that：Step is as follows：

Maize straw is pre-processed as pretreating reagent using potassium hydroxide and metallic salt using after corn straw smashing, Metal salt includes frerrous chloride FeCl₂·4H₂O, cobalt chloride CoCl₂·6H₂O and nickel chloride NiCl₂·6H₂O；Potassium hydroxide adds Dosage is the 2% of maize straw dry weight, frerrous chloride FeCl₂·4H₂O be maize straw dry weight 1%-15%, cobalt chloride CoCl₂·6H₂O additions are the 0.05%-1%, nickel chloride NiCl of maize straw dry weight₂·6H₂O additions are maize straw The 0.05%-1% of dry weight, finally add water and be allowed to and the gross mass of water contained in maize straw is maize straw dry weight six Times, after being sufficiently stirred, sealed membrane sealing；Anaerobic fermentation after being sealed under room temperature condition 3 days；Anaerobic fermentation process needs activity Sludge, activated sludge addition are 12gTS relative to 52g TS maize straws, add water to reaction unit cumulative volume 80%, be filled with nitrogen, then with rubber stopper seal, and reactor be fixed in shaking table, shaking table temperature it is constant 35 ± 2 DEG C it Between.