6. Explain the difference between the suspended growth and attached growth biological processes. Which one you prefer to use in a secondary wastewater treatment? Why? (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)