The treatment of industrial wastes containing both toxic and nontoxic organic compounds is often accomplished by biological processes. Despite its success in many instances, the complex nature of the effects of toxic substances on process performance and kinetics is not well understood. This study was conducted to examine the behavior of an aerated submerged fixed-film (ASFF) biological system receiving a mixture of toxic (phenol) and nontoxic (sucrose) bisubstrate and evaluate its kinetic parameters. Laboratory experiments were carried out using a 50-litre ASFF reactor composed of four equal compartments.

Heterogeneous biomass acclimated to a bisubstrate (phenol/sucrose) system demonstrated the preference of microorganisms to utilize sucrose with a slower concomitant utilization of phenol. However, the removal in a bisubstrate system is slightly higher than that in a single substrate system which may be attributed to the extra biomass accumulated from the utilization of the other substrate. A steady-state approach to process kinetics indicates that substrate removal in the first compartment follows the Monod model for both sucrose and phenol where no mhibition (Haldane rate expression) appears over the studied range of phenol concentrations up to 800 mg/l. Meanwhile, substrate removal in the second through fourth compartments is better described by a variable order model which is likely to be a function of the hydraulic loading.

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