(a) Describe the sedimentation theory (Type I, II, IIl, and IV settling) and where they are applied in water/wastewater treatment. (10分)

7. To improve the nitrogen removal eficiency, an anoxic and aerobic (AO) process is proposed in a secondary municipal wastewater treatment plant. Please draw a schematic diagram and describe all the process, role of microorganisms, and mechanisms for nitrogen removal.(10分)