Excessive ammonia nitrogen levels in the Cass process
Thread Content
I would like some advice: Regarding the Cass process for treating municipal wastewater, the inflow volume is 12,000 m3/day, with a COD level of 150. There are 4 reaction tanks; the DO level is between 2 and 3, while the SV30 value is around 25. The sludge has good settling properties, and the COD level in the effluent remains within the specified limits, around 30. However, the ammonia nitrogen level stays high, ranging from 12 to 15. The pH of the influent water is low, between 6 and 7. I am considering adding sodium carbonate to increase the alkalinity and provide an inorganic carbon source. I would appreciate suggestions from experts regarding the dosage and timing of addition, or any other better measures that could be taken
If the pH is low, the aeration method can be adjusted
It is recommended to test the ammonia nitrogen, nitrate nitrogen, and total nitrogen in the inlet and outlet water in order to determine which stage of the denitrification process is experiencing problems.
When the pH is below 7, the nitrification reaction is inhibited and comes to a halt. Based on what you’ve described, if the pH of the effluent can be kept above 7, ammonia nitrogen levels will decrease significantly, and it’s even possible for them to drop to 0; therefore, alkalinity should be replenished as soon as possible. Base selection: Sodium carbonate can also be used; sodium hydroxide is an option as well. Personally, I think using sodium hydroxide is better ； Location of addition: It can be at the biochemical influent inlet, or it can be added to the aerobic tank at the end of the drainage process (this method is recommended for raising the pH value initially); make sure to add it evenly ； Dosage method: A metering pump can be chosen, or dosing by gravity can also be used.
If the goal is to cultivate nitrifying bacteria by adding alkalinity and a carbon source, it is recommended to use sodium carbonate. Adding sodium hydroxide can only adjust the pH. This is my personal opinion for reference only.
The pH of the incoming water is low, resulting in insufficient alkalinity; without enough alkalinity, ammonia levels cannot be reduced. Adding sodium carbonate or caustic soda will work, with the choice depending mainly on local prices.
At low pH, the nitrification process is certainly inhibited; insufficient alkalinity also hinders nitrification. Therefore, it is recommended to measure the alkalinity level. If the alkalinity is sufficient, adding sodium hydroxide alone will suffice. If the alkalinity is not enough, then a mixture of sodium hydroxide and soda ash should be used. It is necessary to carefully measure the specific parameters.