Impact assessment of major operating factors on internal tracking behavior in a phase-separated ditch

The purpose of this study was to evaluate the performance of a bench-scale phase separation ditch system and assess the impact of major operating factors. This assessment also focused on the conversion reactions of nitrogen and phosphorus compounds across consecutive phases within an operational cycle. Phase separation could be achieved by scheduling flow and aeration patterns, and was easily confirmed through observations of the dissolved oxygen (DO) profile and oxidation–reduction potential (ORP) change. As the hydraulic retention time (HRT) became longer, phosphorus (P) release was reduced due to decreased organic loading during the cycle, and the period of P uptake was not related to the quantity of released phosphate. The amount of released phosphate at a shorter solids retention time (SRT) of 20 d was also higher than that at a longer SRT of 30 d. When separate sewer wastewater was used, unlike combined sewer wastewater with low strength, dramatic reaction profiles along consecutive phases were observed, even at a longer HRT of 12 h. When the anoxic–anaerobic phase length was prolonged from 1.5 to 3 h, P release was well maintained during the anaerobic phase, and sufficient P uptake occurred during the aerobic phases.