When we talk about sewage treatment, agricultural fertilization, or environmental protection topics, we often hear the words "organic nitrogen" and "ammonia nitrogen". Many people may wonder, what is the relationship between these two? How is organic nitrogen gradually converted into ammonia nitrogen? Today, let's use plain language to explain the process of conversion, and then talk about the commonly used conversion techniques in practice, to ensure that you can hear it clearly. First, clarify: What is organic nitrogen? What is ammonia nitrogen? Before talking about transformation, we need to first identify these two 'protagonists' clearly. The nitrogen element around us is quite mischievous, always appearing in various "vests". Organic nitrogen is one of the "vests", which usually hides in organic matter, such as the protein we eat, nitrogen-containing compounds in plant straw, and various organic compounds in sewage, all of which contain a lot of organic nitrogen. What is ammonia nitrogen? Ammonia nitrogen is actually another "vest" of nitrogen exchange, mainly existing in the form of ammonia gas (NH3) or ammonium ions (NH ₄⁺). It is very common in water, for example, the water in our fish tank at home will smell after a long time, and there may be ammonia nitrogen in it; The nitrogen fertilizer applied in farmland is washed into rivers by water, which also increases the amount of ammonia nitrogen in the water. The process of converting organic nitrogen into ammonia nitrogen, simply put, is the process of nitrogen element changing from "organic nitrogen vest" to "ammonia nitrogen vest". This process often occurs in nature and our industrial processes, and we call it "ammonification". The 'magic' in nature: how does organic nitrogen turn into ammonia nitrogen on its own? You may not know that in nature, there is no need for us to worry about the conversion of organic nitrogen into ammonia nitrogen. There is a group of "little experts" silently working, they are microorganisms. Microorganisms are everywhere around us, such as bacteria, fungi, and other invisible creatures that love to "eat" organic matter. When they 'digest' organic matter containing organic nitrogen, just like how we break down protein into amino acids when we eat it, microorganisms break down the complex structures in organic nitrogen. For example, proteins are first broken down into amino acids, which are then further "broken down", and the nitrogen element inside will slowly turn into ammonia (NH3). If it is in water, ammonia can easily react with water to form ammonium ions (NH ₄⁺), which turns organic nitrogen into ammonia nitrogen. This process can be seen everywhere in nature: in autumn, fallen leaves fall to the ground and are decomposed by microorganisms, and the organic nitrogen inside will turn into ammonia nitrogen and return to the soil; Animal feces emit a foul odor during composting, which is actually due to the work of microorganisms that convert organic nitrogen in the feces into ammonia nitrogen, resulting in an ammonia odor. And this process can be carried out without the need for oxygen. Whether in aerobic soil or anaerobic sewage sludge, microorganisms can work, isn't it very powerful? How can we 'accelerate' this transformation process in industry and daily life? In daily life and industry, we often need to treat wastewater containing organic nitrogen, such as urban domestic wastewater, livestock wastewater, and wastewater from food processing plants. If the organic nitrogen in these waters is not treated and discharged directly, it will pollute the environment. Therefore, we need to find ways to quickly convert organic nitrogen into ammonia nitrogen for subsequent treatment.
1. Aerobic biological treatment process: allowing microorganisms to "breathe big" to work. Aerobic biological treatment is to allow microorganisms to "breathe freely" in an oxygen-containing environment, rapidly decompose organic matter, and convert organic nitrogen into ammonia nitrogen. The commonly used activated sludge process is a typical aerobic process. In the aeration tank of the sewage treatment plant, the workers will blow a large amount of air into the water through pipelines to fill the water with oxygen. At this point, oxygen loving microorganisms (such as aerobic bacteria) will become "active" and crazily "eat" organic matter in sewage, gradually decomposing organic nitrogen into ammonia nitrogen. This process is very fast because when there is sufficient oxygen, microorganisms multiply quickly and work efficiently. Moreover, the sludge in the aeration tank is like a "microbial warehouse", containing a large number of microorganisms that can continuously treat organic nitrogen in wastewater. However, this process requires oxygen consumption and specialized aeration equipment, which is suitable for treating domestic or industrial wastewater with low organic nitrogen concentration.
2. Anaerobic biological treatment process: In the "anaerobic workshop", some wastewater with particularly high concentrations of organic matter, such as manure from breeding farms and wastewater from distilleries, is silently transformed. At this time, it is not cost-effective to use aerobic processes because too much oxygen is required. At this point, we will use anaerobic biological treatment technology to allow microorganisms to work in an oxygen free environment. Anaerobic processes are generally carried out in closed reactors, such as common UASB reactors (upflow anaerobic sludge beds) and anaerobic digestion tanks. In these reactors, without oxygen, specialized "anaerobic" microorganisms will come into play. Their process of decomposing organic matter is slightly more complex than aerobic microorganisms, which involves several steps to "break down" the organic matter. Organic nitrogen is slowly converted into ammonia nitrogen during this process. You may ask, doesn't anaerobic treatment produce methane? That's right, but while producing methane, ammonification is also quietly taking place. Moreover, anaerobic processes are particularly energy-efficient as they do not require aeration and can generate methane as an energy source, making them ideal for treating high concentration organic wastewater. For example, after anaerobic treatment, the manure from a livestock farm not only converts organic nitrogen into ammonia nitrogen, but also collects biogas for cooking and power generation, killing two birds with one stone.
3. Hydrolysis and acidification process: First, "break down" organic matter, and then convert ammonia nitrogen. Sometimes the structure of organic matter in sewage is very complex, and it is difficult for microorganisms to "eat" it. At this time, it is necessary to first "simplify" them. Hydrolysis and acidification process is for this purpose. The microorganisms in the hydrolysis acidification tank will first "shred" complex organic matter (such as proteins and cellulose) into simple small molecule organic matter (such as amino acids and glucose). In this "shredding" process, organic nitrogen will also be decomposed, with a portion directly converted into ammonia nitrogen, and the remaining nitrogen elements in small molecule organic matter will be further converted into ammonia nitrogen by other microorganisms. This process is generally used as a "pretreatment" step in wastewater treatment, allowing difficult to treat organic nitrogen to "loosen its muscles and bones" first, making it easier for subsequent aerobic or anaerobic processes to treat more efficiently. It is particularly suitable for treating industrial wastewater containing a large amount of complex organic matter, such as printing and dyeing wastewater and paper making wastewater.
4. Composting and biogas engineering: The "little masters" of ammonification in agriculture not only need to convert organic nitrogen into wastewater treatment, but also frequently use this principle in agriculture. For example, when composting, we pile straw and feces together, add some water to keep them moist, and then cover them with plastic sheeting. The microorganisms inside will proliferate in an aerobic and slightly humid environment, decomposing organic matter and turning organic nitrogen into ammonia nitrogen, which will remain in the compost. The fertilizer piled up in this way is rich in ammonia nitrogen, which can be absorbed by plants in the field and used as nitrogen fertilizer. Biogas engineering is similar to composting, but it involves anaerobic treatment in a closed biogas digester. Feces and straw are decomposed by anaerobic microorganisms in the pond, producing biogas. At the same time, organic nitrogen is converted into ammonia nitrogen, and the remaining biogas slurry and residue are also good fertilizers. The ammonia nitrogen inside can be used by crops, which is both environmentally friendly and energy-saving.
Why convert organic nitrogen into ammonia nitrogen? Is this conversion important? Some people may ask, what is the purpose behind putting so much effort into converting organic nitrogen into ammonia nitrogen? In fact, this conversion process is particularly important in both environmental protection and agriculture. From an environmental perspective, if organic nitrogen is directly discharged into water, it will be slowly decomposed by microorganisms in the water, which will consume oxygen in the water and cause fish and shrimp to die due to hypoxia. Moreover, organic nitrogen may decompose into nitrate in the end, and excessive nitrate entering groundwater may cause illness if consumed. And by first converting organic nitrogen into ammonia nitrogen, we can use subsequent processes (such as nitrification and denitrification) to further process ammonia nitrogen into nitrogen and discharge it into the air, reducing environmental pollution. From an agricultural perspective, plants cannot directly absorb organic nitrogen and must wait for it to turn into ammonia nitrogen or other inorganic nitrogen before they can "eat" it. So the ammonification process in composting and biogas engineering is actually to turn "ineffective nitrogen" into "effective nitrogen", making fertilizers more nutritious and crops grow better. Finally, to summarize: the conversion of organic nitrogen to ammonia nitrogen relies on microorganisms. Ultimately, the core of the conversion of organic nitrogen to ammonia nitrogen is the work of microorganisms. Whether it is the decomposition of fallen leaves in nature or the aeration tanks in sewage treatment plants, microorganisms release nitrogen elements from organic nitrogen when decomposing organic matter, turning them into ammonia or ammonium ions. And the various processes invented by humans are essentially creating a more comfortable "working environment" for microorganisms to complete this transformation process more efficiently. After understanding this process, do you think the nitrogen cycle around you is quite wonderful? From invisible microorganisms to massive sewage treatment plants, it turns out that the goal is to turn nitrogen into a valuable resource, protecting the environment and serving our daily lives. Next time you hear the words' ammonia nitrogen 'and' organic nitrogen ', you will be able to easily explain their relationship!
