With global warming and environmental deterioration, limiting and reducing greenhouse gas emissions is the only way, and methane is one of the main "greenhouse gases". At present, landfill is also a place that releases a lot of greenhouse gas-methane. If left unchecked, it will increase the total amount of greenhouse gases in the earth's atmosphere, and secondly, it will emit odor, pollute the local environment and affect human health.
The development and utilization of turning a landfill into an artificial biogas mine that I put forward is to transform and utilize the biogas "dry fermentation" technology, also called "anaerobic solid fermentation" technology, from the perspective of "turning harm into benefit and turning waste into treasure", which not only reduces the uncontrolled emission of harmful gases, but also produces quite good economic and environmental benefits.
I have been engaged in biogas promotion for many years, and I am familiar with the generation and utilization of biogas. Biogas technology is called "anaerobic fermentation or anaerobic digestion" internationally, which can be roughly divided into two categories: liquid fermentation and solid fermentation. Liquid fermentation technology is widely used, such as "trinity", "quaternity" and "hydraulic integrated biogas digester" commonly used in rural areas at present, that is, liquid fermentation method.
The solid fermentation method is rarely used, and we generally don't know much about it. In fact, landfill is a practical example of biogas solid fermentation. After the landfill is closed for a period of time, a large amount of biogas will be produced. You can insert a hole with a pole (it must pass through the closed layer), and you can feel a lot of biogas. (When doing this experiment, it is better to burn biogas in the sun in light blue, which is not easy to see clearly.
I think it is of great significance to use the solid dry fermentation technology of biogas to "green transform" the current landfill. First, turn it into an "artificial biogas mine" to generate a large amount of biogas and use it. Secondly, after the biogas utilization, the organic garbage which has been fully fermented and sterilized by anaerobic bacteria (at this time, the organic garbage has also been highly decomposed, generally called biogas residue) will be cultivated on a large scale (planting mushrooms). Finally, after the edible fungi are fully produced, they will be put into agriculture or other planting industries as organic fertilizers to improve soil fertility. At the same time, this landfill can be emptied for the next round of landfill treatment, and the land area can be recovered without expanding the land occupation.
Changing the traditional way of landfill without utilization should be of great significance to "solve pollution, turn waste into treasure, save land, increase benefits, and be beneficial to environmental protection".
Start from the pilot, accumulate experience, and then carry out carpet promotion. In the future, all domestic garbage, whether it is solid garbage in large, medium and small cities or rural areas, will enter a virtuous cycle of energy, use these "green energy" on a large scale, reduce the use of traditional "fossil energy", and gradually be replaced by biological and green energy, which will fundamentally protect the earth's atmospheric environment and produce a large number at the same time.
According to relevant data, petroleum energy may reach the peak of production in the middle of the 20th century, and then it will gradually dry up. It is estimated that the peak time of output will be around 2030, and the prospect of coal is not optimistic, that is, around 200 years. Other products such as natural gas and combustible ice-methane hydrate can be used for about 200-300 years, and there is no commercial report yet.
More importantly, due to the serious pollution of burning oil and coal to the atmosphere and environment, this energy fuel cannot be used in large quantities for a long time. Therefore, it is of great significance to vigorously develop green new energy sources that have no or little pollution to the environment and can be recycled for a long time. I think the development of domestic waste energy is of great strategic significance and should be explored and tested as soon as possible.
Based on some information I have, this paper attempts to demonstrate and analyze the possibility, expected benefits and methods of "turning landfill into artificial biogas mine" from several aspects.
First, the energy analysis of domestic organic waste.
The main component or major component of domestic waste is organic matter (including food waste, vegetable waste, excrement, etc.). After a period of time, these organic substances will be decomposed by a large number of anaerobic bacteria, and a large number of gases will be produced by natural fermentation, including methane, carbon dioxide and a small amount of nitrogen, oxygen, hydrogen and hydrogen sulfide. Collecting these gases, treating them and using them will get a lot of combustible gases and a lot of residual substances (we
Urban domestic waste comes from the daily life of thousands of households, and it is endless and never exhausted. Its total amount is very large. For example, a family of three can produce about one ton of garbage every year. If this ton of domestic waste is fully fermented, the research shows that the amount of biogas produced is about 300 cubic meters, and each cubic meter of biogas can generate one and a half electricity, which means that each ton of domestic waste can actually generate electricity.
China produces hundreds of millions of tons of domestic garbage every year. If all the fermented gas is converted into electric energy, it is equivalent to the total power generation of several Gezhouba power plants.
The urban population of Lanzhou is 2.47 million. According to the method described above, each person's domestic garbage can produce 100 cubic meter of biogas every year, so if all the domestic organic garbage in Lanzhou is converted into biogas, there will be 247 million cubic meters, which can generate 370.5 million kWh of electricity.
Calculated from the calorific value of biogas (5000-5700 kcal/m3), it is equivalent to 247 million kg of ordinary coal, and the calorific value of ordinary coal is also 5000 kcal/kg, which is equivalent to the calorific value of biogas 1 m3, that is, the conversion standard coal coefficient is equivalent.
Note: the conversion coefficient of standard coal refers to the ratio of the actual calorific value of an energy source to the calorific value of standard fuel. The standard fuels commonly used in the world are: oil equivalent, electric equivalent, thermal mechanical equivalent and coal equivalent. China adopts coal equivalent, that is, the calorific value per kilogram of standard coal is 29.3076 megajoules (7000 kcal). Divide the calorific value of various energy sources by 29.3076 MJ (7000 kcal), and convert the calorific value of various energy sources into the calorific value of standard coal for calculation, such as the calorific value of ordinary coal we use every day.
Calories/kg, equivalent to 1 m3 of biogas calorific value.
Therefore, through the above analysis and calculation, we can know that there is huge available energy in the landfill.
Second, the change of organic domestic waste in anaerobic environment
Description and introduction of methane production by anaerobic conversion;
When the food residue of domestic garbage and all urban organic garbage include leaves, sewage sludge, sludge from sewage treatment plants, solid excrement from dry toilets, etc. They are all buried underground, and the process of "anaerobic fermentation" will occur when oxygen is isolated. Here is a brief description of this process:
In nature, green plants synthesize carbohydrates through photosynthesis, mainly forming sugar, starch, cellulose and so on. Cellulose has the largest amount of synthesis and storage, and is a substance that is difficult to be decomposed by microorganisms on the earth. Under aerobic conditions, cellulose can be oxidized and decomposed by some microorganisms, eventually producing CO2 and H2O. At present, Trichoderma viride is known to be the microorganism with the strongest ability to decompose cellulose.
(C6H 10O5)n+nO2→nCO2+nH2O
Under anaerobic conditions, cellulose is fermented by anaerobic microorganisms, and finally CH4 is produced.
Methane is mainly formed in swamps, paddy fields, sewers, river and lake sludge and rumen of ruminants. Rumen of ruminants has good conditions for methane production, so rumen is called a natural and efficient continuous fermentor for methane production.
1. Microbial process of methane formation: from anaerobic fermentation of organic matter to methane formation.
This is a very complicated process, which can not be completed by a single bacterium. Many bacteria participated in this joint action.
Result.
(1) binding is formed from organic matter to methane, which is formed by combining many bacteria.
Result. Methanobacteria play a role in the final stage of synthesis. It uses the generations provided by accompanying bacteria.
Products H2 and carbon dioxide are used to synthesize methane. The whole process can be divided into the following stages:
The above stages are not completely separated, there is no obvious boundary, and they are not carried out in isolation, but
Closely linked and crossed with each other.
(2) In the process of biogas fermentation, H2 is transferred between species, producing acid bacteria and associated bacteria.
Fermented organic matter produces H2, which is used by methanogens to reduce CO2 and synthesize CH4.
Associated bacteria and methanogens formed a * * * relationship during fermentation. S- strain decomposes ethanol to produce H2, which inhibits it from further decomposing ethanol, while Mohs strain can use H2 to remove the inhibition for S- strain. Two people live together for common interests, and it is impossible to live alone.
(3) Methanoacetic acid produced by acetic acid is the main organic matter in anaerobic fermentation.
Metabolites are also important intermediates for methane production.
The experiment shows that acetic acid produced by organic matter fermentation and decomposition forms methane, accounting for about 72% of the total methane production, and methane formed by other products accounts for about 28%. The process of producing methane from acetic acid is also very complicated. Tracer atom test with 14C shows that there are two ways for acetic acid to form methane:
① Methane is formed by methyl group of acetic acid.
② Acetic acid is converted into CO2 and H2 to form methane.
2. Ecological relationship between microorganisms in biogas fermentation.
Biogas fermentation is an extremely complex biochemical process, including various metabolic pathways completed by different types of microorganisms. These microorganisms and their metabolism are not carried out alone in an isolated environment, but interact in a mixed environment. The interaction between them includes the interaction between methanogens and methanogens; Interaction between methanogens and interaction between methanogens.
In the process of biogas fermentation, methanogenic bacteria and methanogenic bacteria depend on each other, creating and maintaining good environmental conditions for each other's life activities, but they are mutually restricted and always in a state of balance in the fermentation process. The main relationship between them is shown in the following aspects:
① Methanogenic bacteria provide substrates for the growth and methane production of methanogenic bacteria.
Non-methanogenic bacteria can anaerobically decompose various complex organic substances, such as carbohydrates, fats and protein, and generate H2, CO2, NH3, VFA, methanol, propionic acid and butyric acid. Propionic acid and butyric acid can also be decomposed into H2, CO2 and acetic acid by hydrogen bacteria and acetic acid bacteria, which provide methanogens with carbon precursors, electron donors, hydrogen donors and nitrogen sources for synthesizing cytoplasm and forming methane, so that methanogens can finally use these substances.
② Non-methanogenic bacteria create suitable redox potential conditions for methanogenic bacteria.
In the early stage of biogas fermentation, air is brought into the fermentation device during the feeding process, and dissolved oxygen is also present in the liquid raw materials, which is obviously harmful to methanogens. The removal of oxygen depends on the oxidation ability of methane-producing bacteria to use oxygen. Therefore, the redox potential decreases. In the fermentation device, various anaerobic microorganisms, such as cellulose decomposing bacteria, sulfate reducing bacteria, nitrate reducing bacteria, ammonia-producing bacteria, acetic acid-producing bacteria, etc. , have different adaptability to redox potential. Through the orderly and alternating growth activities of these bacteria, the redox potential in the fermentation broth is continuously reduced, and the suitable redox potential conditions are gradually created for the growth of methanogens, so that methanogens can grow well.
③ Non-methanogenic bacteria remove harmful substances for methanogenic bacteria.
When industrial wastewater or waste is used as fermentation raw materials, the raw materials may contain phenols, cyanide, benzoic acid, long-chain fatty acids and some heavy metal ions. These substances are toxic to methanogens, but many methanogens can crack benzene rings, some bacteria can also use cyanide as carbon source and energy source, and some bacteria can decompose long-chain fatty acids to produce acetic acid. These effects not only reduce the toxicity to methanogens, but also provide nutrients for methanogens. In addition, hydrogen sulfide, a metabolite of some methanogenic bacteria, can react with some heavy metal ions to generate insoluble metal sulfides, thus removing the toxic effects of some heavy metal ions.
H2S+Cu2+→CuS↓+2H+
H2S+pH2+→PbS↓+2H+
The concentration of H2S should not be too high. When H2S is greater than 150× 10-6, it is also toxic to methanogens.
④ Methanogenic bacteria released the feedback inhibition on the biochemical reaction of methanogenic bacteria.
Fermentation products of methanogenic bacteria can inhibit the continuous hydrogen production of hydrogen-producing bacteria, and acid accumulation can inhibit the continuous acid production of acid-producing bacteria. When the concentration of acetic acid in anaerobic digester exceeds 3× 10-3, acidification will occur, which will lead to the failure of anaerobic digestion and biogas fermentation. In order to maintain good anaerobic digestion effect, the concentration of acetic acid is about 0.3× 10-3. In the normal biogas fermentation engineering system, methanogens can continuously use hydrogen, acetic acid and CO2 generated by methanogens to synthesize methane, and will not generate the accumulation of hydrogen and acid, thus removing the feedback inhibition of methanogens, enabling methanogens to continue their normal life and providing carbon precursors for methanogens to synthesize methane.
⑤ Both methanogenic bacteria and methanogenic bacteria * * * keep proper pH value in the environment.
The amount of organic acid, CO2 and CO2 can be partially dissolved in water to form carbonic acid, which obviously reduces the pH value in the fermentation broth. But there is another kind of methanogenic bacteria called ammonifying bacteria, which can rapidly decompose protein to produce ammonia, and ammonia can neutralize some acids and continue normal fermentation until the raw materials are completely decomposed.
At this time, we will find that the original domestic garbage and organic garbage have fundamentally changed their properties, from the state of being toxic and harmful and having a large number of infectious bacteria to the state of being non-toxic and harmless, and all kinds of infectious bacteria have been completely eliminated, that is, we have achieved the above-mentioned anaerobic bacteria environmental protection treatment effect. In the process of treatment, we can first obtain a large number of "inexhaustible" "green energy-biogas"
Third, the comprehensive utilization of garbage biogas.
1, biogas power generation:
Biogas power generation is the most preferred way of energy utilization, because the whole system is relatively simple, the technical difficulty is not high, it is a very mature technology, and there is no high-voltage equipment, and the cost is the lowest. In fact, in ordinary diesel generator sets, biogas is introduced into the intake pipe of diesel engine, where biogas and air are premixed, and then when the mixed gas is compressed to make the diesel engine work, the diesel injected into the cylinder will be ignited. When the diesel engine is running, it can be clearly seen that the fuel consumption will be greatly reduced, while the power output will remain unchanged. This is the so-called "biogas and diesel mixed combustion mode", which is realized on a diesel engine. The highest fuel saving rate of mixed combustion is about 50-85%. According to foreign reports, the fuel saving rate reaches 90%. If the biogas supply is insufficient, diesel will automatically adjust and increase the proportion of diesel, which is relatively stable, thus greatly saving diesel.
If the generated electricity is incorporated into the large power grid, huge economic benefits can be obtained by selling electricity, at least to offset their own electricity expenses, that is, "realizing the reversal of electricity meters" in the practical sense.
If biogas is used as the gas fuel of gasoline engine and no other fuel is used, it is a "pure combustion" mode. Pure combustion can achieve the fuel saving rate of 100%, that is, only biogas can be used, but the combustion calorific value (mass) of biogas is very high, otherwise it will not work stably.
Either way, when using biogas, 30-55% of carbon dioxide contained in biogas should be removed, otherwise the diesel oil will overheat due to the delayed ignition point, the exhaust pipe of diesel engine will burn red, and the exhaust valve will burn out, which will make it unable to work normally.
Because the content of carbon dioxide in biogas is unstable in pure combustion and the total gas calorific value is low, the gasoline engine can not run normally and smoothly. Therefore, in the process of biogas power generation, this "redundant" carbon dioxide that cannot participate in combustion must be removed. I have a patent for a biogas storage tank that can remove carbon dioxide. Please contact me directly for more details.
2, biogas compressed natural gas way:
After removing carbon dioxide, biogas is pure methane. The gas extracted from oil mines is methane produced by anaerobic bacteria for millions of years. General natural gas refers to methane mined from underground, which is the same as methane produced in garbage. These pure methane are compressed by a high-pressure compressor into special steel cylinders (the pressure is about 200 kg/cm2), which can be used as fuel for automobiles. Most of our buses and taxis in Lanzhou are here.
3. Biogas liquefied natural gas:
In the process of biogas compression to 162kg/cm2, cryogenic cooling is adopted. When the temperature reaches-160℃, methane will become liquid, which is LNG mode. This model greatly reduces the volume of methane. When this high-pressure and low-temperature liquid changes back to gas, its volume can be increased by 600 times, and at the same time it will absorb a lot of heat. This fuel can be used as various fuels.
4, biogas preservation:
Biogas can also be used to keep food fresh, such as grains, vegetables and fruits, with good results.
5. Replace and reduce the energy consumption of "burning garbage":
In the aspect of garbage disposal, there is a method to generate electricity by burning combustible garbage, but the preheating, heating and insulation of the incinerator must use traditional energy, and biogas can be used as the fuel for incineration, replacing or greatly reducing the consumption of other traditional fuels.
Fourthly, the comprehensive utilization of biogas residue.
When the combustible gas in the "artificial biogas mine" we introduced is exhausted and the garbage raw materials are fully fermented, these residues are called biogas residues, which are rich in various nitrogen, phosphorus, potassium and trace elements, and are the best raw materials for cultivating edible fungi. In the process of anaerobic fermentation, various aerobic bacteria and toxic and harmful bacteria in raw materials are decomposed and destroyed. At this time, if edible fungi strains are planted on these biogas residues, a large number of edible fungi will grow. Years of experiments have proved that 1 kg biogas residue can produce 1 kg Pleurotus ostreatus or Pleurotus ostreatus, and the cultivation of Lentinus edodes, Volvariella volvacea and Lentinus edodes has also achieved great success.
Judging from the current market economy, its economic benefit is to provide a large number of raw materials for the cultivation of edible fungi. The most common is to grow mushrooms with cottonseed hulls, and the market price is 0.5-0.8 yuan RMB per kilogram. Because the total output of cottonseed hull is limited, it is necessary to solve the problem of a large number of raw materials in order to vigorously develop edible fungi and greatly increase the total output. The most economical aspect of this "artificial biogas mine" is to use biogas residue after biogas production as a huge raw material for cultivating and producing edible fungi.
What is more valuable is that it can reduce the land area occupied by traditional landfills, which is of great significance in China and should be vigorously promoted.
Verb (abbreviation of verb) gives some suggestions on the application of this project.
1, development and utilization of existing landfill:
If the existing landfill is well covered, it will generally produce a lot of biogas. We can drill gas wells with different depths on it by drilling wells and pumping water, and pump the biogas out and store it in the biogas digester for use. According to the mechanism of biogas production, artificial injection of untreated domestic sewage can promote the full decomposition of organic matter in raw materials to produce more biogas, which can produce a certain vacuum when pumping, and the vacuum state can improve the gas production. My work "Biogas Vacuum Fermentation" (February 2006 15) obtained the patent certificate; Patent number: ZL20042008652 1.5) is based on many years of biogas research experience, which can greatly improve the patented technology of biogas. Interested parties can contact me.
2. Design of new landfill:
There is no standard for the new landfill, but at least there should be a bottom layer to prevent leakage and a pipeline system to discharge leaked liquid, because biogas fermentation will produce a part of liquid, called leachate, which is biogas slurry, which is rich in methanogenic bacteria and can be poured back and forth into the landfill to speed up the fermentation process. The method of laying plastic impervious layer in Yuanmingyuan is a good one. In addition, it is necessary to make an oxygen isolation cover that is easy to cover and take out the raw materials after biogas production, and of course, there must be a special management department to manage it.
3. Pretreatment of raw materials:
Because this landfill method can produce huge economic benefits, more expensive equipment can be used for fine processing of raw materials, such as removing plastics, metals and other parts of garbage that do not participate in fermentation.
In the past, there were automatic sorting and processing equipment at home and abroad for garbage utilization. However, due to the lack of any late-stage and large economic output, these expensive equipment can not be used only when dealing with garbage. We can use it boldly when we change our thinking and turn the traditional landfill into an "artificial biogas mine" with great economic benefits.
When using these advanced equipment, we can not only produce more ideal biogas raw materials, but also have the side effect of recycling useful substances. At the same time, we can sort out many recyclable materials, such as metal, plastic, glass, paper and so on. , which solves the problem of garbage classification. In addition, according to the best formula in biogas production (the ratio of nitrogen to carbon is 25-30: 1), a large number of crops or plant straws should be added to maximize it.
4. Artificial biogas mine industrial model chain:
(1) Biogas power generation: use biogas (carbon dioxide must be removed) to start the generator set to generate electricity, and then integrate it into the large power grid.
(2) After being compressed, biogas is put into high-pressure steel cylinders for automobiles (of course, carbon dioxide removal treatment is required) to replace part of gasoline.
(3) Scientifically explore other utilization occasions of biogas to generate greater economic and social benefits.
(4) With regard to the utilization of biogas residue, a large-scale edible fungus production company can be established to cultivate a variety of edible fungi, such as common Pleurotus ostreatus, Pleurotus ostreatus, Lentinus edodes, straw mushroom, auricularia auricula and even Ganoderma lucidum, etc., and the used raw materials will be further processed and utilized as organic fertilizers for improving low-and medium-yield fields, and put into rural areas to improve farmland, reduce the use of chemical fertilizers and improve the quality of agricultural products. It can also be sold to mushroom growers as raw materials.
(5) A large number of laborers can be arranged at the same time when the landfill is turned into an "artificial biogas mine", which is also an effective means to solve the employment problem and will generate a large number of jobs in large-scale development.