[Weekly Topic] -008- The impact of carbon-nitrogen ratio on the operation of activated sludge process
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This post was last edited by Gorō’s Eight Trigrams Staff on 2015-7-8 at 10:21. As we all know, the recommended carbon-to-nitrogen ratio in the activated sludge process is 100:5. However, in practice, it is quite difficult to maintain this ratio; it tends to fluctuate either too high or too low. So here comes the question: 1. At what range of carbon-to-nitrogen ratios does a high or low ratio start to have an impact on the operation of the activated sludge process? 2. Considering the carbon-nitrogen ratio, at what level does the ammonia nitrogen content begin to affect the operation of activated sludge, and what is the limit value?
An excessively high carbon-to-nitrogen ratio can affect the proper functioning of activated sludge; the normal growth and reproduction of microorganisms are inhibited due to a lack of carbon sources, resulting in incomplete degradation of organic matter and a decrease in removal efficiency, which in turn affects the quality of the effluent to meet regulatory standards； An excessively high carbon-to-nitrogen ratio can lead to excessive growth of Ballotrynia, a decrease in sludge concentration, and the proliferation of filaments ； It is generally believed that a carbon-to-nitrogen ratio within the range of 150:5 does not have a significant impact on the operation of activated sludge.
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This post was last edited by zhaolijun on 2015-7-9 at 10:17. An ammonia nitrogen level exceeding 100 ppm can have an inhibitory effect on biochemical processes. As for the carbon-to-nitrogen ratio, I believe that carbon sources provide energy for microorganisms, while nitrogen sources are essential elements for synthesizing the cytoplasmic matrix. If there is an excess of nitrogen sources and a shortage of carbon sources, it will result in excessive total nitrogen levels in the effluent
A high or low carbon-to-nitrogen ratio is not a major issue, but a ratio below 10:1 is problematic; during denitrification for nitrogen removal, insufficient carbon sources may hinder the progress of this process.
This post was last edited by Gorō’s Eight Trigrams Staff on 2015-7-9 at 15:59. In terms of technical analysis, an ammonia nitrogen level above 100 ppm has an inhibitory effect on biochemical processes. As for the carbon-to-nitrogen ratio, I believe that the carbon source provides energy for microorganisms, while the nitrogen source is an essential element for synthesizing the cytoplasmic matrix. If there is an excess of nitrogen source and a shortage of carbon source, it will result in excessive total nitrogen levels in the effluent.
Generally, an ammonia nitrogen level of 150 mg/L in the influent of biological units is safe and will not have a significant impact on the activated sludge.
In a wastewater treatment plant with an effluent standard of Class B-1, the C:N ratio is not a problem. It’s mainly the C:P ratio. Currently, the COD level of the wastewater entering the treatment plants is extremely low; sometimes it even meets the standards, which means that the total phosphorus level becomes quite high, in my opinion.
Carbon is an important component of microorganisms； Nitrogen is an essential element for proteins and nucleic acids in microbial cells. If a 100:5 ratio cannot be achieved, the missing element should be added in order to adjust the nutritional balance of the microorganisms.
A sudden significant increase in ammonia nitrogen can create a shock load. The concentration of ammonia nitrogen in the influent water depends on the biomass present in the biological treatment tank, as well as on the BOD content of the influent water. A ratio of 20:1 is a theoretical value; in my opinion, the upper limit should not exceed 30:1, while the lower limit should not be below 3:1. A ratio above 30:1 indicates a shortage of nitrogen sources, whereas a ratio below 3:1 indicates a shortage of carbon sources – both conditions can affect the growth of active microorganisms