Kinetic Modeling of Downflow Hanging Sponge (DHS) System Treating Synthetic Domestic Wastewater

Abstract

A downflow hanging sponge (DHS) unit was established for treating synthetic domestic wastewater (SDW) for over 100 days of continuous feed. The DHS system was operated at a chemical oxygen demand (COD) concentration of 531.62 ± 93.6 mg/L, and different hydraulic retention times (HRTs) = 6.0–2.0 h to determine the system kinetics. The substrate removal kinetics of the DHS reactor was calculated using modified Stover–Kincannon, Monod, Grau’s second-order and first-order models. The Monod model has the following decay coefficient (Kd), yield coefficient (Y), and maximum specific growth rate of bacteria (μmax) that were, respectively, 0.0025 1/d, 0.1337 gVSS/gCOD, and 0.0364 1/d. Maximum substrate utilization rate (Umax) and saturation value constant (KB) for the modified Stover–Kincannon model were determined to be, respectively, 15.46 and 14.45 g/L/d. While the kinetic coefficient for the second-order model ranged was 0.516–0.641 1/d versus 27.627 1/d for the first-order model, the constants of the Grau second-order model (a and b) were estimated as 0.0366 and 0.9215. The Grau second-order and modified Stover–Kincannon models showed an R2 value of 0.995, making them the most convenient for the experimental results. The results indicated that these models could be used to predict the DHS reactor behavior at different scales.

Keywords

• long-term continuous feed
• operating condition
• sewage
• sponge-based technology
• Monod
• Grau second-order model