Mechanisms and Kinetics of COD Removal and Simultaneous Oxygen Consumption in a Rotating Biological Contactor Biofilm

Abstract

A study on aerobic biofilm COD removal and simultaneous respiration is made using a Wazu respirationmeter unit. In a closed recirculating system completely submerged RBC biofilm samples have been examined in short-term batch experiments, using the corresponding waste water or dissolved acetate. The removal of dissolved organic substrate and the respiration were found to answer the ½-order/0-order kinetic model, whereas the removal of suspended solids COD (CODs) showed 1-order kinetics. Under conditions usually met in practice the 0-order rates for dissolved COD(CODd) removal and respiration were 30–40 gm−2d−1 and 10–16 gm−2d−1, respectively; in absence of organic substrate a certain background respiration was observed (3.5–9.0 gm−2d−1). As a result of the 1-order kinetics over a wide concentration range, extremely high CODs removal rates were observed even exceeding 300 gm−2d−1. The difference between the maximum respiration and the CODs removal rates is attributed to physical biofilm adsorption processes. Biofilm COD removal kinetics for waste water containing both CODs and CODd are discussed, illustrating that the kinetic order of the combined process and the reaction constant strongly depends on the CODs/CODd ratio. Conclusion is that a RBC biofilm loaded with a CODs/CODd mixture oxidizes some dissolved organic matter and acts as a catalyst in the coagulation and flocculation of fine suspended solids.