Kinetic Study and Modeling of Aerobic Biological Oxidation of Organic Wastewater

Abstract

The complex organic wastewater from agrochemical industry consists of a large number of solids and dissolved compounds. For the design and scale-up of any activated sludge reactor, it is desirable to know the kinetics of oxidation, which strongly depends upon the nature of wastewater and the microorganism. In the present work, the kinetics of aerobic biological oxidation of an agrochemical plant waste is investigated, having initial COD of 800-1200 mg/L. Experiments are performed at five different dissolved oxygen (DO) levels; viz. (i) 1.5 to 2.5 mg/L, (ii) 2.5 to 3.5 mg/L, (iii) 3.5 to 4.5 mg/L, (iv) 4.5 to 5.5 mg/L, and (v) 5.5 to 6.5 mg/L. For each DO level five mixed liquor suspended solids (MLSS) are studied in the range of 6000-20000 mg/L. The maximum percentage reduction of COD is 74.1%, 74.8%, 89.9%, 73.3% and 89.6% at different DO levels of 1.5-2.5 mg/L, 2.5 to 3.5 mg/L, 3.5 to 4.5 mg/L, 4.5 to 5.5 mg/L, and 5.5 to 6.5 mg/L and MLSS concentrations from 6000 to 20000 mg/L, respectively. An attempt is made to propose the kinetics of substrate utilization that does not actively support growth of organism. A kinetic model is proposed to understand the effect of DO and MLSS concentration.