Modelling of arsenate retention from aqueous solutions by living coryneform double-mutant bacteria

Abstract

Environmental contextIndustrial development has favoured the release of toxic elements to the environment and monitoring and assessment their environmental impact are key points. An important aspect of understanding these concerns is to evaluate how toxic substances interact with microorganisms, which has critical implications in the environment. Current studies show that heavy metals have the potential to affect bacterial viability, although a great deal remains to be understood concerning metal speciation using engineered bacterial cells. AbstractModelling of the arsenate (AsV) retention from aqueous solutions by a living, genetically modified coryneform bacterium (Corynebacterium glutamicum ArsC1–C2) was evaluated. The bacterium used was a double mutant strain unable to reduce arsenate to arsenite. Batch experiments were carried out to study the effects of high initial AsV concentrations, retention times and temperatures on the retention process. Arsenate retention kinetics was modelled using pseudo-second-order and Elovich models. Both models provided high coefficients of determination, but better applicability of the Elovich model was confirmed using the Z function. A useful generalised predictive equation, allowing evaluation of the simultaneous effects of time and the initial AsV concentration on the retention process, was proposed. The retention equilibrium for a wide concentration range of arsenate showed a mechanistic process underlying chemical-nature retention with the experimental data strongly consistent with the Langmuir isotherm. Thermodynamic studies defined the negative free energy changes and demonstrated the spontaneity of the retention process. Positive values for both enthalpy and entropy were indicative of endothermic retention and a high affinity for AsV by the bacteria. The high maximum retained quantity, 2.0 mg AsV g–1 bacteria, confirmed the bacterium’s high affinity for this arsenic species.