Improving the transfer of dissolved oxygen in a biological Fe2+ oxidation process using a venturi jet as an intensive aeration system

Abstract

The low bio-production of Fe³⁺ as a leaching agent is one of the main limitations to implementing industrial bio-processes at feasibility conditions. The main limitation of the bio-oxidation process of Fe²⁺ is the low oxygen transfer to the aqueous phase because of the low oxygen solubility. This study assesses the effectiveness of the venturi jet as an innovative and intensive aeration device for overcoming the oxygen limitation in a continuous ferrous oxidation process in a fixed-bed reactor with immobilized acidithiobacillus ferrooxidans, in contrast to the conventional diffuser aeration device. Firstly, the influence of the airflow and the influence of the medium concentration were determined for the following parameters for both aeration devices; Volumetric mass transfer coefficient (k_La), Standard Oxygen Transfer Rate (SOTR), Standard Aeration Efficiency (SAE), and Standard Oxygen Transfer Efficiency (SOTE). Then, both aeration devices were compared in a continuous bio-oxidation process in an up-flow packed bio-reactor (UFPB). The system performance was assessed by monitoring temperature, pH, oxidation-reduction potential, and dissolved oxygen concentration for 69 days. Findings displayed that when aerating with the diffuser, the ferrous oxidation rate was restricted by the low dissolved oxygen availability, being about 1 ppm (1 mg L⁻¹). Under these oxygen-limiting conditions, the maximum ferrous (Fe²⁺) oxidation rate was 9.09 g L⁻¹ h⁻¹. However, when aerating with the venturi jet, the dissolved oxygen concentration increased up to 2.70 mg L⁻¹, achieving a maximum of 29.11 g L⁻¹ h⁻¹. So, this study has demonstrated that the change in the aeration device has resulted in an improvement in the process, achieving a 3.5-fold increase in the oxidation rate. Furthermore, the venturi jet offered additional advantages over the diffuser, such as requiring less power to deliver the same amount of air, being unaffected by jarosite precipitates, and not requiring a supply of compressed air.