Let's talk about the conversion of organic nitrogen and ammonia nitrogen today. This is a very important part of sewage treatment, and understanding it is very beneficial for solving water quality problems.
First, let's talk about what organic nitrogen and ammonia nitrogen are. Organic nitrogen refers to nitrogen-containing substances that are bound to carbon elements, such as common proteins, amino acids, amides, and urea in daily life, all of which belong to organic nitrogen. They are widely present in various places, and there is the shadow of organic nitrogen in the domestic sewage we discharge and the wastewater generated by industrial production. Ammonia nitrogen refers to nitrogen that exists in the form of ammonia (NH3) or ammonium ions (NH ₄⁺). In natural water bodies such as rivers, lakes, and various treatment stages of sewage treatment plants, traces of ammonia nitrogen can be found.
Let's talk about how organic nitrogen is converted into ammonia nitrogen, which is called ammonification. The process of ammonification is mainly accomplished by microorganisms, such as ammonifying bacteria and fungi, which are the main force of ammonification. The entire ammonification process can be divided into two steps. The first step is to degrade complex nitrogen-containing organic compounds such as proteins and nucleic acids into simpler nitrogen-containing compounds such as peptides, amino acids, and amino sugars under the action of various enzymes secreted by microorganisms. For example, proteins are broken down into individual amino acids under the action of proteases. In the second step, these simple nitrogen-containing compounds undergo deamination and transform into ammonia (NH3). In this step, amino acids remove their amino groups, which turn into ammonia, while also producing other substances such as organic acids, alcohols, and so on. Moreover, ammonification can occur in both aerobic and anaerobic environments. Ammoniation reactions can occur in anaerobic tanks of sewage treatment plants and sewage pipelines. Take the sewage pipeline network as an example. When sewage flows through the pipeline, the organic nitrogen is slowly decomposed by microorganisms and converted into ammonia nitrogen. Therefore, sometimes you may find that the concentration of ammonia nitrogen increases as the sewage stays in the pipeline network for a long time.
What is the use of converting organic nitrogen into ammonia nitrogen? It's very useful! From the perspective of sewage treatment, ammonia nitrogen is more easily removed by subsequent treatment processes than organic nitrogen. By ammonification, complex organic nitrogen is transformed into relatively simple ammonia nitrogen, which is equivalent to starting a good start for subsequent treatment work. For example, in the activated sludge treatment process of sewage treatment plants, microorganisms can use ammonia nitrogen as a nitrogen source to synthesize the substances needed for their own growth, and further convert ammonia nitrogen into other harmless substances, thereby achieving the goal of purifying sewage. If organic nitrogen is not first converted into ammonia nitrogen and directly enters the subsequent treatment process, it will be much more troublesome and the treatment effect will be greatly reduced. Moreover, ammonification is also an important link in the nitrogen cycle in natural ecosystems. The organic nitrogen in animal and plant residues is converted into ammonia nitrogen through ammonification, which can then be absorbed and utilized by plants to re-enter life activities, ensuring the cycling and balance of nitrogen elements in the ecosystem. If there is no ammonification, the nitrogen element in animal and plant residues cannot be reused, and the ecosystem will be in chaos.
However, the process of converting organic nitrogen into ammonia nitrogen is also influenced by many factors. Temperature is a key factor. Generally speaking, the suitable temperature for microbial ammonification is between 25 ℃ and 35 ℃. If the temperature is too low, the activity of microorganisms will decrease and the rate of ammonification reaction will also slow down. Just like in winter, the ammonification effect of sewage treatment plants may not be as good as in summer. If the temperature is too high and exceeds the range that microorganisms can withstand, microorganisms may become inactive, and ammonification cannot proceed normally. The pH value is also important. Most microorganisms involved in ammonification prefer to live in neutral to weakly alkaline environments, with pH values between 7-8. If the environment is too acidic or alkaline, the growth and metabolism of microorganisms will be affected, and the conversion efficiency of ammonia nitrogen will naturally not be high. In addition, the balance of nutrients cannot be ignored. When microorganisms undergo ammonification, in addition to organic nitrogen as a nitrogen source, they also require other nutrients such as carbon and phosphorus sources. If there is insufficient carbon source in the sewage, microorganisms will not have enough energy to carry out ammonification reaction, and the conversion of ammonia nitrogen will also be limited. For example, in some industrial wastewater, the organic nitrogen content is quite high, but the carbon source is scarce. In this case, additional carbon sources such as methanol and glucose need to be added to ensure the smooth progress of ammonification.
Understanding the conversion of organic nitrogen and ammonia nitrogen is of great significance for wastewater treatment and environmental protection. In sewage treatment plants, staff can optimize treatment processes based on this conversion principle, improve sewage treatment efficiency, make discharged water cleaner, and reduce environmental pollution. In our daily lives, we can also contribute to the protection of water resources by properly discharging sewage and reducing the production of nitrogen-containing pollutants.
