Figure 1. Schematic diagram of process (1. raw wastewater tank; 2. pre-anoxic zone; 3. anaerobic zone; 4. anoxic zone; 5. aerobic zone; 6. settler; 7. air pump; 8. mixer; 9. internal recycle; 10. external recycle; 11. influent; 12. pump; 13. airflow meter; 14. DO and ORT meter)

From

Optimization of Retention Time of Microbial Community Structure of Activated Sludge Process

M P. Shah

American Journal of Water Resources. 2014, 2(6), 149-158 doi:10.12691/ajwr-2-6-3