What are the advantages and disadvantages of AAO and AO processes? (Part 3)
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
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
For the AAO process, the COD removal rate remained basically stable regardless of the C/N ratio.
Some data show that most of the COD is synthesized into the intracellular storage PHA by phosphorus accumulating bacteria in the anaerobic zone. The average utilization rate is between 75% and 85%. About 10% of the COD enters the anoxic zone, and there is almost no remaining. The easily biodegradable organic matter enters the aerobic zone, so this process can fully utilize the carbon source of the influent water and is less affected by the impact of organic matter load.
The C/N ratio has a certain influence on the removal of COD in the AO process. According to the data of Xinling Wastewater Treatment Plant, when the C/N ratio is greater than 10, the COD removal rate decreases slightly with the increase of the C/N ratio, and the organic matter load has an impact on the system.
Written by: Jasmine
Contact email: Kate@aquasust.com
3.2 Influence of influent C/N ratio on denitrification of two processes
With the increase of C/N ratio in A/O process, the removal rate of TN decreases almost linearly, and the organic matter concentration has a serious impact on the production rate of nitrification process.
This is because nitrifying bacteria are autotrophic bacteria, and the concentration of organic matter is not the limiting factor for its growth. If the concentration of organic matter is too high, the heterotrophic bacteria with fast proliferation speed will multiply rapidly, and the oxygen in the water will be preferentially utilized. To the advantage, the activity was inhibited, which affected the nitrification reaction.
In the AAO process, experimental data show that when the influent C/N ratio increases from 5 to 9, the TN removal rate increases steadily. When the C/N ratio is 8.9, the TN removal rate is as high as 83.2%. When the N ratio increased from 9 to 14, the removal rate of TN did not increase but decreased.
When the C/N ratio increased to a certain value and the TN removal rate reached the highest, the TN removal rate decreased with the increase of the C/N ratio.
The main reason is the same as that of the AO process. The increase of the C/N ratio leads to less and less autotrophic bacteria in the system, the nitrification efficiency decreases, and the total nitrogen removal rate decreases. Some data show that the minimum theoretical C/N ratio for complete denitrification is 2.86 without the storage of internal carbon sources, but the actual required value is much larger than this number.
Written by: Jasmine
Contact email: Kate@aquasust.com
3.3 Influence of influent C/N ratio on phosphorus removal by two processes
The C/N ratio has a great influence on the phosphorus removal effect of the AAO process. The experimental data show that when the influent C/N ratio increases from 5 to 9, the TP removal rate gradually increases.
This is mainly because the influent carbon source is insufficient when the influent C/N ratio is low, and the return sludge contains a large amount of nitrate, which consumes a large amount of COD, resulting in insufficient phosphorus release in the anaerobic zone and a decrease in the system phosphorus removal rate.
When the influent C/N ratio increased from 9 to 14, the total phosphorus removal rate decreased, especially when the C/N ratio was greater than 11, the total phosphorus removal rate decreased almost linearly.
This is because at a relatively high organic load, the organic matter in the influent cannot be fully utilized by the phosphorus accumulating bacteria in the anaerobic section, and the remaining excess organic matter will promote the growth of polysaccharide bacteria, which will lead to the accumulation of activated sludge. The proportion of phosphorus bacteria decreased, which affected the phosphorus removal effect.
The influent C/N ratio has little effect on the phosphorus removal effect of the AO process, mainly because the phosphorus removal by the AO process is only through the assimilation of microorganisms, while the C/N ratio has little effect on the assimilation.
Written by: Jasmine
Contact email: Kate@aquasust.com