Effects of temperature and pH on the biokinetic properties of thiocyanate biodegradation under autotrophic conditions

Abstract

The simultaneous effects of temperature and pH on the biokinetic properties of thiocyanate biodegradation under mixed-culture, autotrophic conditions were investigated using response surface analysis (RSA) combined with biokinetic modeling. A partial cubic model, based on substrate inhibition biokinetics, was constructed for each kinetic coefficient in Andrew model (i.e., maximum specific growth rate (μ(m)), saturation coefficient (K(S)), and substrate inhibition coefficient (K(SI))). Each model proved statistically reliable to approximate the responses of the kinetic coefficients to temperature and pH changes (r(2) > 0.8, p < 0.05). The response surface plots demonstrated that the biokinetic coefficients change with respect to temperature and pH significantly and in different ways. The model response surfaces were substantially different to each other, indicating distinct correlations between the independent (temperature and pH) and dependent (model response) variables in the models. Based on the estimated response surface models, temperature was shown to have significant effects on all biokinetic coefficients tested. A dominant influence of temperature on μ(m) response was observed while the interdependence of temperature and pH was apparent in the K(S) and K(SI) models. Specific growth rate (μ) versus substrate (i.e., thiocyanate) concentration plots simulating using the obtained response surface models confirmed the significant effects of temperature and pH on the microbial growth rate and therefore on the thiocyanate degradation rate. Overall, the response surface models able to describe the biokinetic effects of temperature and pH on thiocyanate biodegradation within the explored region (20-30 °C and pH 6.0-9.0) were successfully constructed and validated, providing fundamental information for better process control in thiocyanate treatment.