CN104593434A - Method for producing biogas by mixing and fermenting attapulgite, crop straw and excrement - Google Patents

Abstract

The invention discloses a method for producing biogas by fermenting attapulgite with crop straw and feces. The crop straw is crushed and pretreated with 4% to 6% NaOH by mass percentage for 5 to 7 days, and then the attapulgite and the pretreated The three raw materials of crop straw and manure are mixed and put into the digestion device for inoculation and fermentation; during this period, the initial carbon-nitrogen ratio is adjusted between 20 and 30:1; the amount of inoculum added is 10% to 20% of the dry weight of the fermentation material; the initial pH of the fermentation The value is adjusted to 6.5-7.5; the anaerobic fermentation reaction temperature is 25-35°C, biogas is generated in 1-2 days, and the fermentation period is 30-40 days. The present invention improves the efficiency of biogas and methane production by fermenting crop stalks and feces as raw materials by adding exogenous attapulgite, changes the embarrassing situation in vast rural areas where crop stalks are used as the main raw material for fermentation, resulting in generally low gas production, and improves the efficiency of agricultural production. Added value of waste crop straw.

Description

Method for producing biogas by fermenting attapulgite mixed crop straw and manure

technical field

The invention belongs to the technical field of resources and environment, and in particular relates to a method for producing biogas by fermenting attapulgite mixed with crop straw and manure.

Background technique

my country has a large amount of renewable straw resources, and the annual output can reach more than 700 million tons. At present, with the development of my country's agriculture and the improvement of farmers' living standards, the use of straw in rural areas is becoming less and less, and most of them are still treated by burning and returning to the field. Pollution also has adverse effects on some road and air traffic. Efficient use of straw and other cellulosic waste, turning waste into treasure has become a good thing for the country and the people.

At present, there are mainly the following ways to utilize agricultural and forestry waste lignocellulose such as straws: ① The lignocellulose is crushed and returned directly to the field, but because the lignocellulose itself is difficult to degrade and the process brings some additional costs to farmers and other factors It also leads to great resistance to the promotion of such measures, and the actual application area is small; ② Compressing straw into solid particles, as an efficient and clean solid fuel, has been used in many applications, but there are still problems such as limited application places and not wide use; ③ Establish a biomass power plant to burn waste lignocellulose to generate electricity. At present, there are some biomass power plants in many provinces and cities across the country, many of which are running well, but there are still problems such as power generation losses and relying on state subsidies; ④ Vehicle fuel ethanol The production of lignocellulose is the most meaningful use of lignocellulose. After large-scale production and promotion, it can alleviate China's dependence on petroleum and fossil energy, and play a positive role in the stability of national energy and food security. However, due to high costs, etc. The reason is that the current industrialization progress is still relatively slow. ⑤ The establishment of biogas digesters to ferment straw into biogas for farmers to burn and provide lighting is currently popular in some places, but there are still disadvantages such as difficult utilization of dry straw and low conversion efficiency.

The most fundamental reason for the slow promotion of crop straw biogas is the effectiveness and reliability of some key technologies: ① The effect of pretreatment technology is not ideal, and it is difficult to effectively destroy lignin that is difficult to degrade without producing any inhibitors. The dense structure cross-linked with hemicellulose and cellulose makes it impossible to further convert lignocellulose into soluble small molecular monosaccharides, and thus cannot efficiently perform anaerobic fermentation to produce biogas. At present, the commonly used pretreatment methods mainly include physical methods, chemical methods, biological methods and other pretreatment methods, and many scholars at home and abroad have shown that alkali pretreatment of straw has the advantages of short processing time and good gas production effect; Single fermentation raw material, the effect of biogas production is not ideal. Although crop straw is rich in C and H compounds such as cellulose and hemicellulose, it is a suitable raw material for biogas fermentation, but because it is difficult to decompose and discharge, and the C/N ratio is large, the volatile fatty acids (VFA) produced during fermentation ) will inhibit the activity of methane bacteria and other defects. For a long time, few straws have been used as fermentation raw materials, and rural biogas has always been dominated by human and animal manure. Human and animal manure contains more organic nitrogen, and the decomposition product NH ₄ ⁺ -N of organic nitrogen has a strong buffer capacity, which can weaken the pH drop caused by volatile organic acids (VFA). Therefore, human and animal manure and crop straw Mixed anaerobic fermentation to produce biogas has been widely used. ③ The main factors affecting the anaerobic fermentation process are not well controlled. At present, many studies focus on the main factors affecting the anaerobic fermentation process, such as pH, temperature and carbon-nitrogen ratio. In addition, toxic substances in the fermentation system such as heavy metals, phenols, various fungicides, S2- ^, etc. will also have a certain impact on the final gas production. Because some adsorbents can gather microorganisms and increase the density of microorganisms, at the same time, they can absorb harmful substances in the fermentation feed liquid and maintain a favorable environment for the growth of microorganisms, so that microorganisms can better degrade organic matter, accelerate the consumption of volatile acids, and increase production. Therefore, in order to solve this problem, these negative effects are generally eliminated by adding exogenous adsorbents to increase production.

Attapulgite (referred to as attapulgite) is a magnesium-rich silicate clay mineral, which is needle-like crystallized, with a unique three-dimensional spatial structure and a large specific surface area. Natural attapulgite has high adsorption activity and low cost. Its price is only 1/5-1/10 of activated carbon, and it is rich in resources. It has been proven that Xuyi County, Huai'an City, Jiangsu Province has a reserve of 272 million tons, accounting for Nearly 50% of the world's total reserves of attapulgite are high-quality mineral deposits in the world. As a good adsorbent, attapulgite has been widely used in the field of wastewater treatment.

Contents of the invention

The purpose of the present invention is to provide a method for producing biogas by fermenting attapulgite with mixed crop straw and feces in view of the low value-added utilization of lignocellulose such as existing crop straws, especially in view of the current low efficiency of lignocellulose per unit biogas production. The method is to increase the efficiency of fermenting crop straw and manure to produce biogas and methane by adding exogenous attapulgite. The method is simple in process and can effectively increase the added value of crop straw as agricultural waste.

Technical solution of the present invention is that this biogas production method comprises the following specific steps:

(1) Crop straw crushing;

(2) Pretreating the crushed crop stalks obtained in step (1) with 4% to 6% NaOH by mass;

(3) Add attapulgite and feces to the pretreated crop straw obtained in step (2), and adjust the ratio between the three, so that the initial carbon-nitrogen ratio of the mixed material is between 20 and 30:1;

(4) Put the mixed material obtained in step (3) into the digestion device and stir evenly, inoculate to obtain the fermented material, and the amount of the inoculum added is 10-20% of the dry weight of the mixed material;

(5) Adjust the initial pH value in the digestion unit between 6.5 and 7.5;

(6) Seal the digestion device and connect the gas storage device for fermentation to produce gas. The reaction temperature is 25-35°C, biogas is generated in 1-2 days, and the fermentation cycle is 30-40 days.

Wherein, the crop stalk refers to one of rice, wheat and corn stalks; the manure refers to one of human manure, pig manure and cow manure.

Wherein, the crushing of the crop straws in the step (1) is to manually or mechanically cut the harvested crop straws into small pieces of 3-5 cm; or crush them to 20-50 meshes with a straw kneading grinder.

Among them, the pretreatment process of step (2) is to adjust the moisture content of the crushed crop straw to 20% to 30% by mass with deionized water, and then immerse it in NaOH solution with a mass concentration of 4% to 6%, and mix it evenly. Seal it and put it in a constant temperature biochemical incubator at 25°C to react for 5-7 days.

Among them, the digestion device described in step (4) is a single-phase or solid-liquid two-phase anaerobic reactor; the inoculum is biogas slurry from old biogas digesters, anaerobic digestion sludge from urban domestic sewage treatment plants, and farm sludge One of.

Wherein, the acid for adjusting the initial pH of the fermentation system in step (5) is H ₂ SO ₄ with a mass concentration of 10%.

Wherein, at the end of the fermentation in step (6), when the daily gas production of the fermentation device is lower than 30% of the average daily gas production, the reaction ends, and a new round of fermentation is carried out by feeding again.

Advantage of the present invention and beneficial effect are:

1. In view of the high adsorption activity of natural attapulgite, add a certain amount of exogenous attapulgite appropriately, and use straw and feces as mixed raw materials for anaerobic fermentation to overcome the harmful effects of heavy metals and phenols in the fermentation feed liquid. Substances inhibit the activity of methane bacteria to reduce the defect of biogas production, further increase biogas production and methane content, provide a new idea for the mixed anaerobic fermentation production biogas technology system, and further enrich the fermentation raw materials and exogenous additives for biogas production , changed the embarrassing situation that the vast rural areas mainly use livestock and poultry manure as fermentation raw materials, and also made the agricultural residues be rationally utilized as resources, reducing the secondary pollution caused by straw burning, and finally formed the added attapulgite There have been no reports at home and abroad on the research content of improving the biogas yield and methane content of fermentation with straw and human and animal manure as mixed raw materials.

2. In order to overcome the defect that harmful substances in the fermentation feed liquid inhibit the activity of methane bacteria and thus reduce the biogas production, a certain amount of attapulgite is added to improve the conversion efficiency of biogas production using straw and manure as fermentation raw materials. The operation process is simple. Equipment requirements are low, management is convenient, and the environment is friendly.

3. By adding attapulgite, the crop straw can be used efficiently, effectively reducing the threats to the ecological environment, agriculture, animal husbandry and fishery, residents' health and transportation caused by incineration and random discarding due to its difficulty in utilization, so as to achieve its Take control and "turn harm into benefit".

4. By adding attapulgite and using crop straw as raw material to ferment and efficiently produce biogas, it effectively solves the problem of insufficient raw materials for anaerobic fermentation in rural areas, increases rural biogas energy, and produces a large amount of high-quality organic fertilizer biogas residue and Biogas slurry can solve the problem of soil compaction caused by excessive application of chemical fertilizers and shortage of organic fertilizers in rural areas, and promote the efficient resource utilization of straw to a certain extent.

5. By adding attapulgite, the present invention efficiently realizes resource utilization, reduction and harmless utilization of crop stalks, and has good environmental and economic benefits. According to data, the annual output of crop straw in China can reach more than 700 million tons. Calculated according to the actual usability rate of 80%, take 560 million tons, and calculate the moisture content as 40%, the annual crop straw biomass resources harvested in the country will reach 3.36 100 million tons (dry matter); according to the research, the gas production potential of attapulgite mixed crop straw dry matter and manure anaerobic fermentation can be increased by 0.04-0.06m ³ /kg, and an additional 13.44-20.16 billion cubic meters of biogas can be obtained every year, equivalent to 158 to 2.36 million tons of standard coal; taking rural areas as an example, a 4m ³ biogas digester can process more than 2,500kg of crop straw annually, and produce about 90m ^{3 of} biogas, which can provide 4 months of living energy for a family of 3 to 5, saving The burning cost is about 240 yuan. At the same time, the annual output of biogas fertilizer is more than 80kg; in addition, due to the increase of methane content, the quality of biogas combustion is also directly improved.

Description of drawings

Fig. 1 is the variation curve of cumulative gas production and methane content between the implementation group and the control group in Example 1.

Fig. 2 is the change curve of cumulative gas production and methane content between the implementation group and the control group in Example 2.

Fig. 3 is the change curve of cumulative gas production and methane content between the implementation group and the control group in Example 3.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with specific examples, and these examples should not be construed as limitations on the technical solutions.

The percentage sign "%" involved in the present invention, if not specified, refers to the mass percentage; but the percentage of the solution, unless otherwise specified, refers to the number of grams of solute contained in 100 mL of the solution; the percentage between liquids, Refers to the ratio of capacity at 20°C.

Embodiment 1: produce biogas according to the following steps

(1) Rice straw crushing: the harvested rice straw is manually cut into small pieces of 3 to 5 cm;

(2) Weigh 94.6g (dry weight 80g) of the rice straw obtained in step (1) and put it into a 2L fermenter, adjust its water content to 20% with deionized water, then immerse it in 4% NaOH solution, mix well , sealed and placed in a 25°C constant temperature biochemical incubator to react for 5 days;

(3) Add attapulgite 93.3g (dry weight 80g) and cow dung 136.3g (dry weight 80g) to the pretreated crop straw obtained in step (2), and mix evenly. At this time, the initial carbon-nitrogen ratio of the mixed material is About 20:1;

(4) Inoculate 135g of biogas slurry from an old biogas digester with a water content of 92.8% into the fermenter. At this time, the amount of the inoculum added is 10% of the dry weight of the mixed material; pH adjusted to 6.5;

(5) Seal the fermenter and connect the gas storage device for fermentation to produce gas. The reaction temperature is 25±1°C, biogas will be generated within 24 hours, and the reaction will be carried out for 30 days.

The change curve of cumulative gas production and methane content is shown in Figure 1. The daily gas production decreased significantly, and the next round of feeding and inoculation was completed after one round of reaction was completed.

In order to facilitate the explanation of the promotion effect of adding attapulgite on the mixed fermentation of rice straw and cow dung to produce biogas, a group of control cases (that is, without adding attapulgite) were also made, and the implementation steps were the same as above.

Embodiment 2: produce biogas according to the following steps

(1) Wheat straw crushing: the harvested wheat straw is mechanically cut into small pieces of 3 to 5 cm;

(2) Weigh 100.7g (dry weight 80g) of the wheat straw obtained in step (1) and put it into a 2L fermenter, adjust its water content to 25% with deionized water, then immerse it in 5% NaOH solution, mix well , sealed and placed in a 25°C constant temperature biochemical incubator to react for 6 days;

(3) Add attapulgite 81.7g (dry weight 70g) and pig manure 119.3g (dry weight 70g) to the pretreated crop straw obtained in step (2), and mix evenly. At this time, the initial carbon-nitrogen ratio of the mixed material is about 25:1;

(4) Inoculate 198g of anaerobic digested sludge from an urban sewage treatment plant with a moisture content of 95.2% into the fermenter. At this time, the amount of the inoculum added is 15% of the dry weight of the mixed material; Adjust the initial pH value to 7.0;

(5) Seal the fermenter and connect the gas storage device for fermentation to produce gas. The reaction temperature is 30±1°C, biogas will be generated within 24 hours, and the reaction will be carried out for 35 days.

The change curve of cumulative gas production and methane content is shown in Figure 2. The daily gas production dropped significantly, and the next round of feeding and inoculation was completed after one round of reaction was completed.

In order to facilitate the explanation of the promotion effect of adding attapulgite on the mixed fermentation of wheat straw and pig manure to produce biogas, a set of control cases (that is, without adding attapulgite) were also made, and the implementation steps were the same as above.

Embodiment 3: produce biogas according to the following steps

(1) Corn stalk crushing: the harvested corn stalks are crushed to 20-50 mesh through a straw kneading grinder;

(2) Weigh 102.6g (dry weight 80g) of corn stalks obtained in step (1) and put them into a 2L fermenter, adjust the water content to 30% with deionized water, then immerse in 6% NaOH solution, and mix well , sealed and placed in a 25°C constant temperature biochemical incubator to react for 7 days;

(3) Add attapulgite 70.0g (dry weight 60g) and human manure 102.2g (dry weight 60g) to the pretreated crop straw obtained in step (2), and mix evenly. At this time, the initial carbon-nitrogen ratio of the mixed material is About 30:1;

(4) Inoculate 269g of slaughterhouse sludge with a moisture content of 93.1% into the fermenter. At this time, the amount of the inoculum added is 20% of the dry weight of the mixture; add water to 2L, and then adjust the initial pH value in the fermenter to 7.5;

(5) Seal the fermenter and connect the gas storage device for fermentation to produce gas. The reaction temperature is 35±1°C, biogas will be generated within 24 hours, and the reaction will last for 40 days.

The change curve of cumulative gas production and methane content is shown in Figure 1. The daily gas production decreased significantly, and the next round of feeding and inoculation was completed after one round of reaction was completed.

In order to facilitate the explanation of the promotion effect of adding attapulgite on the mixed fermentation of corn stalks and human manure to produce biogas, a set of control cases (that is, without adding attapulgite) were also made, and the implementation steps were the same as above.

It can be seen from Figures 1, 2, and 3 that compared with the control group, by adding a certain amount of attapulgite, the fermented biogas yield and methane content of crop straw and manure under different conditions and different ratios in the three implementation cases were significantly lower. There is a substantial improvement.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made. These improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (7)

1. attapulgite mixing crop material and manure fermentation produce the method for biogas, it is characterized in that this biogas production method comprises following concrete steps:

(1) crop material is pulverized;

(2) by the NaOH pre-treatment of the crop material after the pulverizing of step (1) gained by mass percent 4% ~ 6%;

(3) in the pretreated crop material of step (2) gained, add attapulgite and ight soil, the ratio between adjustment three, makes the initial carbon-nitrogen ratio of mixture between 20 ~ 30:1;

(4) being put into by step (3) gained mixture in slaking apparatus and to stir, inoculate to obtain fermentation material, the add-on of inoculum is 10% ~ 20% of mixture dry weight;

(5) to regulate in slaking apparatus initial pH value between 6.5 ~ 7.5;

(6) seal slaking apparatus, and carry out fermentation gas after connecting accumulator unit, temperature of reaction is 25 ~ 35 DEG C, within 1 ~ 2 day, produces biogas, fermentation period 30 ~ 40 days.

2. attapulgite mixing crop material according to claim 1 and manure fermentation produce the method for biogas, it is characterized in that: described crop material refers to the one in paddy rice, wheat and maize stalk; Ight soil refers to the one in human excrement, pig manure and cow dung.

3. attapulgite mixing crop material according to claim 1 and manure fermentation produce the method for biogas, it is characterized in that: it is the segment harvested crop material being cut into 3 ~ 5 cm by artificial or mechanical means that crop material described in step (1) is pulverized; Or be crushed to 20 ~ 50 orders with stalk rubbing pulverizer.

4. attapulgite mixing crop material according to claim 1 and manure fermentation produce the method for biogas, it is characterized in that: in step (2), preprocessing process first the water ratio deionized water of the crop material after pulverizing is adjusted to mass percent 20% ~ 30%, be immersed in the NaOH solution of mass concentration 4% ~ 6% again, mix, 25 DEG C of constant temperature biochemical cultivation case reactions 5 ~ 7 days are put in sealing.

5. attapulgite mixing crop material according to claim 1 and manure fermentation produce the method for biogas, it is characterized in that: described in step (4), slaking apparatus is single-phase or solid-liquid two-phase anaerobic reactor; Inoculum is the one in the natural pond liquid of old methane-generating pit, the anaerobically digested sludge of city domestic sewage treatment plant and plant's mud.

6. attapulgite mixing crop material according to claim 1 and manure fermentation produce the method for biogas, it is characterized in that: the acid of the initial pH of step (5) described adjustment fermentation system is mass concentration 10% H ₂sO ₄.

7. attapulgite mixing crop material according to claim 1 and manure fermentation produce the method for biogas, it is characterized in that: in the fermentation latter stage of step (6), when fermentation unit daily output tolerance lower than average daily output tolerance 30% time, reaction terminates, and again feeds intake and carries out new round fermentation.