The fifth day of the Lunar New Year, breaking the five-fold poverty: breaking away the poor spirit, bad luck, and methane? !

To rise from below;

Prosperity in the darkest places;

Even in seclusion, they share life and are connected with each other.

This is the feast of Tartarus,

The Sword of Blood Maple Forest

Note:

1. Tartarus: The abyss where the Titans were imprisoned after their defeat.

2. Blood Maple Forest: The place where Chi You’s head turned into after he died in battle.

Written by Li Qingchao (Shandong Normal University)

The fifth day of the first lunar month is one of the most important days of the Lunar New Year, and this day is commonly known as "breaking the fifth day". People clean up and set off firecrackers happily on this day (readers in prohibited areas should abide by the ban), in order to sweep out the God of Poverty, use firecrackers to drive away the five poor (poor in wisdom, poor in learning, poor in literature, poor in life, and poor in friendship), and welcome the God of Wealth, praying for a prosperous business and abundant wealth after the market opens. Children don't like to do housework and clean up, but they are good at setting off firecrackers, such as blowing up ice and snow, and blowing up cabbage (some students: I have blown up more exciting ones). Wow! Pay attention to safety when setting off fireworks and firecrackers, especially parents should give their children a good safety education. Today, let's talk about the mysterious power of "you explode it, and it explodes you".

If you collapse the sewer, the sewer will collapse you. Source: Internet

"I was so scared just looking at the GIF. If I were there, I would have been shocked right away." No, you should have stopped it right away! "Don't throw firecrackers into the sewer, kid. Otherwise, you might fall down and die in the fire! Your firecracker may not have such great power, but it does!"

It is——

Biogas

Most people know about biogas from the biogas digesters in textbooks. This "organized and disciplined" biogas that can be collected and used in a controlled manner can be used for cooking, lighting and power generation. Therefore, biogas is a secondary energy source and a renewable energy source. In addition to producing biogas, biogas digesters not only solve the pollution problems caused by the burning of waste such as human and animal feces and agricultural straw, but also produce biofertilizers with higher fertilizer efficiency, which is an important part of my country's ecological rural construction.

Figure 1: Structure and purpose of a biogas digester[1]

In fact, bubbles in a stinky ditch or farts from animals are likely to be methane. However, this "bulk" methane released into an open environment will dissipate immediately, so there is generally no need to worry about explosions. In a closed environment, methane is continuously produced and accumulated "in an organized and undisciplined" manner. When it reaches a certain amount and encounters an open flame, it becomes a bomb. When combustible materials (combustible gases, vapors or dust) are evenly mixed with air (or oxygen), they will explode only when they encounter a fire source within a certain concentration range. This concentration range is called the explosion limit. When 5% to 15% methane gas is mixed in the air, it will explode when it encounters a spark. The mass of 1 cubic meter of methane is about 0.657 kilograms, and the energy generated by the explosion is 36.5 megajoules, equivalent to 8.7 kilograms of TNT[2]. Be careful, naughty children, and don't mess with the sewers.

Is “unorganized and undisciplined” biogas harmless? On a small scale, biogas smells bad because, in addition to carbon dioxide and methane, it also contains toxic gases such as hydrogen sulfide. If you are in a low-lying, heavily polluted, or air-impeded confined space, you should be especially careful not to rush into such an environment. If someone has already fallen, rushing in to save them may still result in death. On a larger scale, the methane in biogas is a potent greenhouse gas. Urban landfills, animal husbandry, and other human activities will produce large amounts of methane, exacerbating global warming.

Figure 2. Methane is the simplest organic substance. Source: Wikipedia

Anaerobic microorganisms

The life of all things is nothing more than three kinds of circulation: matter, energy, and information. When life is dealing with various chemical substances, decomposing and synthesizing substances, it is often accompanied by the generation and storage of energy.

When green plants perform photosynthesis, they use the energy of sunlight to convert carbon dioxide and water into sugars, releasing oxygen, and storing energy in the sugars (photoautotrophy). When humans and animals break down sugars, they consume oxygen, produce carbon dioxide and water, and generate energy for their own use (chemoheterotrophy).

In these processes, water is split and oxygen is formed, or oxygen is consumed and water is generated. In essence, the focus is on the flow of electrons and hydrogen, and the accompanying consumption or generation of large amounts of energy.

But in places where there is no sunlight and no oxygen, life has another plan.

What to do if there is no sunlight as an energy source? Use the energy generated by the oxidation process of reducing inorganic substances as an energy source to reduce carbon dioxide to sugars (chemoautotrophy). For example, the energy released during the oxidation of ammonia to nitrite and nitrate can be stored by nitrifying bacteria.

What if there is no oxygen to accept hydrogen ions or electrons? Then the electrons or hydrogen ions are converted into hydrogen gas and released directly (hydrogen-producing bacteria), or they are given to oxidants (such as methanogens or sulfate-reducing bacteria that produce hydrogen sulfide). This biological oxidation process that uses exogenous inorganic oxides or organic matter as hydrogen and electron acceptors is called anaerobic respiration. Organisms that do not need oxygen to grow are called anaerobic organisms.

Tips

Today, the Earth's atmosphere is rich in oxygen. In fact, the early Earth was an anaerobic environment lacking oxygen. Anaerobic bacteria dominated the Earth and spent a happy billion years. Until the emergence of cyanobacteria, the oxygen content of the Earth's atmosphere gradually increased. Most anaerobic organisms regard oxygen as poisonous gas, and like Titan, they can only live in the mud and the abyss.

Figure: The Earth is 4.6 billion years old, and anaerobic organisms dominated it for about a billion years.[3]

Biogas fermentation

In an environment containing a large amount of organic matter, aerobic bacteria initially multiply in large numbers, and the aerobic respiration process consumes all the oxygen, creating an environment suitable for the growth of anaerobic microorganisms. The main bacteria that produce methane are methanogens. Methanogens are a type of archaea that can produce methane in an anaerobic environment. They exist in wetlands, the intestines of ruminants, the intestines of humans, and seafloor sediments, and they also play an indispensable role in sewage treatment. More than fifty species of methanogens have been identified [4].

Figure 4: Methanogens. a, Scanning electron micrograph of Methanobrevibacter smithii; b, TEM pseudo-color image of Methanococcoides burtonii[5]

Methanogens use hydrogen as an inorganic reductant and as an energy source, transferring hydrogen to exogenous inorganic oxide carbon dioxide, and use the energy released in this process as an energy source for anabolism. Therefore, methanogens are a type of chemoautotrophic microorganism.

When microorganisms degrade and utilize glucose, they do not completely oxidize it, and eventually produce acetic acid (and formic acid), hydrogen, and carbon dioxide, releasing 216 or 209 kcal of energy per mole [6]. The energy produced by this process is much less than that of aerobic respiration.

The nutrients required by acid-producing and hydrogen-producing bacteria rely on a class of microorganisms that can hydrolyze macromolecular nutrients and perform preliminary fermentation. For example, bacteria such as Clostridium and Bacteroides degrade macromolecular organic matter such as carbohydrates and proteins into small molecular organic compounds such as glucose and amino acids. Clostridium, Bacteroides and other bacteria (such as lactic acid bacteria and Propionibacterium) then further degrade the hydrolysis products into small molecular alcohols and organic acids[7].

From this, we can see that the methane fermentation process is very complex, and methanogens alone are not enough: it requires multiple bacterial groups to work together in a microbial ecological way to complete it. This ecosystem includes five major groups: fermentative bacteria, hydrogen-producing acetogenic bacteria, hydrogen-consuming acetogenic bacteria, hydrogen-consuming methanogens, and acetogenic methanogens.

The first three species cannot produce methane, but they can hydrolyze or preliminarily ferment nutrients to provide raw materials for methanogens. The latter two can use hydrogen, acetic acid and other substances produced by other bacteria to produce methane. They support and restrict each other and jointly complete the biogas fermentation process.

Figure 5: Biogas fermentation requires the cooperation of multiple microbial groups[8]

In the process of anaerobic fermentation of organic matter, not all hydrogen or reducing power is accepted by carbon dioxide. If sulfur oxides or sulfate ions accept hydrogen, they will gradually be reduced to toxic hydrogen sulfide gas. In the process of decay of human or animal corpses rich in phosphorus, the reducing power is accepted by phosphates, and the phosphorus element is gradually reduced to phosphine. Phosphine is very easy to self-ignite, producing a blue-green jumping flame, which is the legendary "ghost fire".

Figure 6: In sulfate-reducing bacteria, sulfate acts as an inorganic electron acceptor and is gradually reduced to hydrogen sulfide. Source: Wikipedia

Conclusion

"I am afraid of ghosts but they have never hurt me." I am not afraid of sewers, but they may cause real harm. What we should really fear is not ghosts and gods, but "respect science and fear ignorance." Ignorant people are like naughty children.

Don’t throw cigarette butts around. Source: Internet

Watching this on Chinese New Year is too exciting. Drink a cup of yogurt to calm your nerves. Yogurt is also a product of anaerobic fermentation.

References

[1] https://www.sohu.com/a/122710853_545662

[2] http://china.cnr.cn/xwwgf/20210210/t20210210_525412787.shtml

[3] https://slideplayer.com/slide/5758625/

[4] https://en.wikipedia.org/wiki/Methanogen

[5] Prescotts Microbiology 11th Edition by Joanne Willey, Kathleen

[6] https://en.wikipedia.org/wiki/Fermentative_hydrogen_production

[7] https://baike.baidu.com/item/%E6%B2%BC%E6%B0%94/

[8] Xin Mingxiu et al. Microbiology (4th edition)

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