What are the advantages and disadvantages of AAO and AO processes? (Part 1)
Written by: Jasmine
Contact email: Kate@aquasust.com
1. Comparative analysis of AAO and AO removal performance
1.1 AAO, AO process: COD removal performance comparison
1.2 AAO, AO process: comparison of denitrification performance
1.3 AAO, AO process: comparison of phosphorus removal performance
1.4 AAO and AO process: comparison and summary of removal performance
2. Influence of temperature on nitrogen and phosphorus removal by AAO and AO
2.1 Influence of temperature on COD removal by two processes
2.2 The effect of temperature on the denitrification of the two processes
2.3 The effect of temperature on phosphorus removal by two processes
3. Effects of Influent C/N Ratio on Nitrogen and Phosphorus Removal by AAO and AO
3.1 Influence of influent C/N ratio on COD removal in two processes
3.2 Influence of influent C/N ratio on denitrification of two processes
3.3 Influence of influent C/N ratio on phosphorus removal by two processes
4. Effects of Influent C/P Ratio on Nitrogen and Phosphorus Removal by AAO and AO
4.1 Influence of influent C/P ratio on COD removal in two processes
4.2 Influence of influent C/P ratio on denitrification of two processes
4.3 Influence of influent C/P ratio on phosphorus removal by two processes
Written by: Jasmine
Contact email: Kate@aquasust.com
At present, most of the nitrogen and phosphorus removal technologies used in sewage treatment plants all over the world are biological methods, such as AO process, AAO process, oxidation ditch process, AB process, SBR process, etc...
These processes do not sound advanced, and they look quite simple, but it takes a lot of work to really understand their respective advantages and disadvantages and compare which ones are good and which are bad.
To this end, I read a lot of literature, but after a study, I found that most of the comparative analysis of peers focused on AAO, SBR, and oxidation ditch processes, and few people compared AO and AAO processes.
Therefore, in order to explore the characteristics of AO and AAO, thoroughly understand their respective removal rates of COD, NH3-N, TN, and TP in sewage, as well as temperature, influent C/N ratio, and influent C/P ratio. Regarding the impact of nitrogen and phosphorus removal by process, I visited Director Wang of Xinling Sewage Treatment Plant. Director Wang directly took out the monthly averages of the influent and effluent indicators of Xinling Sewage Treatment Plant in 2019 (AO process) and 2021 (AAO process), and gave me the following comparative analysis.
Written by: Jasmine
Contact email: Kate@aquasust.com
1. Comparative analysis of AAO and AO removal performance
1.1 AAO, AO process: COD removal performance comparison
The ability of the wastewater treatment process to remove organic matter is one of the main indicators to characterize the efficiency of the process. The size of COD directly reflects the amount of organic matter in the wastewater.
The DPS data processing system was used to test the significance of differences in the COD concentration and COD removal rate of the influent and effluent of the two processes. The results showed that there was no significant difference in COD in the influent of the two processes, but there were significant differences in the COD and removal rate of the effluent. The removal is significantly better than the AO process.
The reason is that in the AO process, the denitrification reaction in the anoxic section can consume a part of the organic matter in the sewage, but most of the organic matter is removed by aerobic degradation, while the hydraulic retention time of the aerobic section of the AO process in the first phase of Xinling Sewage Plant Project Short, the volume of the aeration tank is small, and the amount of aeration is not enough, resulting in poor removal of organic matter.
In the AAO process, most of the organic matter is converted into PHB by phosphorus accumulating bacteria in the anaerobic section and stored in the cells, and part of the organic matter is removed by denitrification in the anoxic section. When the wastewater enters the aerobic section, the COD concentration is basically close to the discharge standard. , will be further degraded in the aerobic stage.
Studies have shown that the COD removal rate of the anaerobic section of the AAO process can reach more than 80%, while the removal rate of the anoxic section is lower than 10% on average.
Written by: Jasmine
Contact email: Kate@aquasust.com
1.2 AAO, AO process: comparison of denitrification performance
In recent years, with the increasing degree of eutrophication of environmental water quality and the continuous improvement of sewage discharge standards, finding an effective denitrification process has become one of the important issues in the design of current sewage treatment plants. Both the AAO process and the AO process have the function of biological denitrification, and the denitrification principle of the two processes is the same, and both are denitrification and denitrification.
Through the significant difference experiment on the TN concentration and TN removal rate in the influent and effluent of the two processes, the results show that there is no significant difference in the influent TN of the two processes, but the effluent TN and removal rate are significantly different, and the AAO process can remove TN significantly better than AO process.
In the denitrification and denitrification process, nitrate nitrogen is the main substance in the total nitrogen in the effluent, and the removal rate of nitrate nitrogen in the anoxic section can be higher than 90%. Some studies have pointed out that controlling the nitrate concentration of the effluent in the anoxic zone to 1 mg/L to 2 mg/L can maximize the removal rate of TN and make full use of COD to improve the denitrification capacity of the anoxic zone. The mixed liquid in the aerobic zone contains a large amount of nitrate nitrogen, which is returned to the anoxic zone through the internal circulation, and the denitrification reaction is carried out in the anoxic zone.
The HRT in the anoxic section of the AO process in Xinling Wastewater Treatment Plant is too short, only 1.8h, which is less than 3.46h in the AAO process, and the internal reflux ratio is 50% to 100%, which is less than 150% to 250% of the AAO process, resulting in denitrification. Not as functional as AAO. Moreover, the denitrification effect of the AO process is not as stable as that of the AAO process, and is greatly affected by external factors (temperature, C/N ratio, etc.).
Written by: Jasmine
Contact email: Kate@aquasust.com
1.3 AAO, AO process: comparison of phosphorus removal performance
Excessive phosphorus content in water will also lead to the proliferation of microorganisms, the vigorous growth of plankton, and the emergence of eutrophication. The emergence of denitrification phosphorus removal technology is a breakthrough to the traditional biological phosphorus removal theory, which can not only solve the contradictions existing in the traditional process, but also help to realize the sustainable treatment of sewage.
Through the significant difference experiment on the TP concentration and TP removal rate of the influent and effluent of the two processes, the results show that there is no significant difference in the influent TP of the two processes, but the effluent TP and removal rate are significantly different, and the AAO process can remove TP significantly better than AO process.
The reason is that there is no anaerobic phosphorus release section in the AO process of the first-phase project of Xinling WWTP, and in the process of biological phosphorus removal, the phosphorus accumulating bacteria can only fully release phosphorus in the anaerobic section to ensure that the anaerobic section and aerobic This process has a good phosphorus absorption effect, and the removal of phosphorus by this process is only through the assimilation of microorganisms.
The phosphorus removal of AAO process is mainly completed by phosphorus accumulating bacteria. Generally speaking, the amount of phosphorus taken up by phosphorus accumulating bacteria in the anoxic and aerobic periods is more than that released in the anaerobic period. Studies have shown that the ratio of the average phosphorus absorption to the average phosphorus release in the AAO process is 1.28, and the phosphorus absorption in the anoxic stage is higher than that in the aerobic stage.
Written by: Jasmine
Contact email: Kate@aquasust.com
1.4 AAO and AO process: comparison and summary of removal performance
In summary, the AAO process for the removal of organic matter, nitrogen and phosphorus is significantly better than the AO process, especially for phosphorus removal. Since the AO process has no anaerobic stage, only a small part of phosphorus can be removed through the assimilation of microorganisms. If phosphorus removal is required, do not choose this process or increase chemical phosphorus removal.
Written by: Jasmine
Contact email: Kate@aquasust.com