The effect of hydraulic residence time and initial COD concentration on color and COD removal performance of the anaerobic–aerobic SBR system

An anaerobic–aerobic sequencing batch reactor, SBR, was operated with a textile dyestuff (Remazol Rot RR) containing synthetic wastewater at different anaerobic–aerobic residence times (θHanaerobic = 2–19 h) and initial COD concentrations (COD0 = 400–1800 mg l−1). The total reaction time was kept constant at 23 h in all experiments. A dyestuff biodegrading facultative anaerobic bacterial consortium called PDW was used as the dominant bacterial culture. The environmental conditions were adjusted to T = 28 °C and pH 7. The experimental results indicated that anaerobic and aerobic residence times in SBR systems significantly affected the system's performance. Color was mainly removed under anaerobic conditions and it was almost completed within 4–6 h of the anaerobic residence time with about 90% decolorization efficiency for an initial dyestuff concentration of 60 mg l−1. The initial COD concentration did not significantly affect the system and COD0 = 500 mg l−1 was determined as sufficient to obtain over 90% of the color, more than 85% COD removal efficiency in SBR. Higher concentrations did not improve color removal but decreased the COD removal performance of the system.