KINETICS AND MODELING OF AUTOTROPHIC THIOCYANATE BIODEGRADATION

The biokinetic parameters for autotrophic systems are difficult to obt ain and are often mistakenly determined because the size of the autotr ophic population in mixed (i.e., heterotrophic and autotrophic) cultur es cannot be accurately estimated. This article presents a systematic approach, combining bioenergetic calculations and experimental data, t o obtain values of the biokinetic parameters pertinent to the aerobic, autotrophic biodegradation of thiocyanate. Nonlinear regression techn iques were employed using both initial thiocyanate utilization rate da ta and single thiocyanate depletion curves. Both types of data were ne cessary to overcome the problems arising from the linear nature of the substrate depletion curves and the high correlation of the biokinetic model parameters inherent in nonlinear regression analysis. The aerob ic biodegradation of thiocyanate followed a substrate inhibition patte rn that was successfully described by the Haldane-Andrews model. Altho ugh regression analysis did not yield unique biokinetic parameter esti mates, the following parameter value ranges were obtained: maximum spe cific substrate utilization rate (k), 0.26 to 0.44 mg SCN-/mg biomass. h; half-saturation coefficient (K-s), 2.3 to 7.1 mg SCN-/L; and inhibi tion coefficient (K-i), 28 to 109 mg SCN-/L. Based on the estimated bi okinetic parameter values, a design and operation diagram was construc ted that depicts the steady-state thiocyanate concentration as a funct ion of solids retention time for a completely mixed, continuous-flow r eactor. (C) 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 1-11, 1 999.