What is biological nitrogen removal process?

Biological nitrogen removal is simply to give you a reactor in ammoniation stage and remove organic matter by the way; In the nitrification stage, you will be given another reactor, which only converts the ammonia nitrogen produced by the last reaction tank into nitrate nitrogen; After that, it is time to remove nitrogen. Ok, let's have another reactor and continue to change nitrate nitrogen in the last tank into nitrogen. I don't know if you have found any problems. Both the ammoniation process in the first reactor and the nitrification process in the second reactor require oxygen. So the predecessors had a brainwave and merged into one. As a result, the following two-stage biological nitrogen removal process appeared. This improvement can save a lot of capital construction costs.