Abstract
Controlling of solids retention time (SRT) in the activated sludge process is critical for ensuring effective wastewater treatment. Because of the disadvantages of conventional control methods, the hydraulic method of controlling SRT was improved in this study and applied into the step-feed biological nitrogen removal process. After the application of the hydraulic control method, conventional SRT changed from 17.67 to 19.08 days and hydraulic SRT was constant at a desired 20 days. Hydraulic control of SRT simplified process control, and produced good effluent quality where the total nitrogen removal efficiency with four stages ascended from 72.6 to 85%. Variations of hydraulic SRT under different influent wastewater strength and flow rates were investigated, and the results showed that a relative constant SRT value could be maintained easily. The feasibilities of applying the hydraulic method of controlling SRT in step-feed biological nitrogen removal process with different operational modes, including different stage numbers processes, different influent flow rate distributions, and volumes in each stage and different volume ratios of the anoxic zone to the aerobic in each stage, were verified and the results were satisfactory. Under constant SRT the total nitrogen removal efficiency of the step-feeding process with three, four, and five stages was 80, 85, and 95%, respectively.
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