Published: CABEQ 18 (4) (2004) 423–428
Paper type: Original Scientific Paper

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Kinetics and Effects of Hydraulic Residence Time and Biomass Concentration on Removal of Organic Pollutants in a Continuous Unsteady State Activated Sludge Process

M. C. Márquez, C. Costa and M. Jul

Activated sludge processes are generally affected by the variation of influent flow leading to a modification in biomass concentration and COD removal efficiency. This unsteady state situation can be mathematically explained by a Monod–type kinetics transformed using γSo / γX (influent substrate to reactor biomass ratio) as a control parameter. The kinetic equation has been applied to experimental data obtained in an activated sludge lab plant (5.5 L) using synthetic wastewater (γCOD = 2200 ± 300 mg L–1). Organic load has been modified by increasing gradually influent flow in order to attain different hydraulic residence times (t = 10 to 45 h), leading to optimum values of biomass concentration (γX = 450 to 3200 mg L–1) for maximum COD removal. The application of this type of kinetics that explains experimental results on substrate utilization rate under unsteady state conditions is discussed.

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wastewater treatment, activated sludge, unsteady state, γSo / γX ratio