A two-step approach for arsenic removal by exploiting an autochthonous Delftia sp. BAs29 and neutralized red mud.

Groundwater arsenic contamination represents a global threat to human health. Among the proposed bioremediation applications, microbial transformation of arsenite (As (III)) seems to be the most favorable approach as it can be easily coupled with several adsorption techniques, without producing lethal by-products or demanding chemical addition. This study highlights the potential contribution of a highly efficient As (III) transforming bacteria Delftia sp. BAs29 followed by the adsorption of transformed arsenate (As (V)) using neutralized red mud under suitable treatment conditions. Diverse experimental conditions elucidated (inflow As (III) concentrations, flow rate) the rate and oxidation efficiency to mediate the process. Red mud is a waste by-product from the Bayer's process of the alumina industry, which when neutralized aids the removal of As (V). The neutralized red mud was characterized using X-ray diffraction (XRD) microanalysis, Scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) and Fourier-transform infrared spectroscopy (FTIR). Arsenate adsorption using neutralized red mud was also studied as a function of pH and time, adsorbent dosage, and initial As (V) concentration. The adsorption process was significantly affected by the solution pH, which on decreasing gradually increased the adsorption efficiency. The maximum monolayer capacity for adsorption of 274.1 mg/g As (V) was found at optimum conditions of pH 4.0 and a contact time of 30 min at a temperature of 30 °C, respectively. Furthermore, this process significantly contributed in fabricating a two-step bio-filter column for the removal of total arsenic from groundwater. Graphical abstract.