2020 Volume 56 Issue 4 Pages 79-90
Both the stepwise advanced treatment method (experimental system) for reducing the biochemical oxygen demand, total nitrogen, and total phosphorus in secondary treated water and standard activated sludge method (control system) were compared for 14 months. Performance was evaluated by Student’s t-test. The results revealed that the water quality items in the experimental system met the target water quality standard for stepwise advanced treatment and were significantly reduced compared to those in the control system.
Next, the removal efficiency of hygienically relevant microbes (total coliform, Escherichia coli, fecal streptococci, and enterococcus form) was compared. The concentrations of these microbes and removal ratio in the experimental system were significantly reduced and improved compared to in the control system, respectively. Particularly, the concentration of total coliform bacteria met the effluent standards (≤3,000 colony-forming units/mL) before disinfection treatment. The results of Pearson product moment correlation analysis and hierarchical variable cluster analysis indicated that the removal ratio of hygienically relevant microbes in the secondary treatment process were highly correlated with mixed liquor suspended solids, aerobic-solids retention time, dissolved oxygen, sludge age, air-to-flow ratio, and activated sludge biota. These results clarify the operating factors that increase the hygienically relevant microbe removal ratio in the stepwise advanced treatment method.
