Application of autochthonous extremophilic Bacillus xiamenensis in remediation of groundwater- A sorption-based metal cleaning approach

Abstract

Surface water and groundwater used for drinking and agricultural purposes are contaminated due to anthropogenic and geogenic activities. Escalated metal concentrations, xenobiotic pollutants, competitive ions, and reusability issues are main hindrances towards decontamination of water. Moreover, the expensive purification technology brings obstacles to the underdeveloped community from availing clean water. In this context, the present work offers a sustainable cost-effective approach by providing an effective and sustainable sorption-based purification method by novel polyextremophilic bacteria Bacillus xiamenensis ISIGRM16 isolated from metal-rich industrial waste, red mud. Batch adsorption study revealed that the bacterium can remove Cd2+(>99%), Ni2+(>85%), and Cr6+(>40%) from aqueous solution. The optimum parametric conditions for the removal of Cd2+ and Ni2+ were observed at a temperature of 30 °C and a pH of 6, while for Cr6+ removal, the optimal conditions were a temperature of 45 °C and a pH of 2. The adsorption process of Cd2+ was best explained by Freundlich isotherm (R2 ≥ 0.95), revealing multilayer adsorption. Ni2+ and Cr6+ followed the Langmuir isotherm, indicated adsorption onto the monolayer surface. The interaction mechanism was determined to be following 2nd order kinetics, with both exothermic (Cd2+, Ni2+) and endothermic (Cr6+) characteristics. The maximum adsorption capacities were found to be 31.42, 29.30, and 15.21 mg g−1 for Cd2+, Ni2+, and Cr6+ respectively. In the ternary system, the adsorption capacity followed the order Ni2+ > Cd2+ > Cr6+, as confirmed by both their relative adsorption capacity and from analysis visual MINTEQ. Microscopic and spectroscopic analyses revealed, altered cell morphology, metal deposition on the bacterial cell surface, and the involvement of hydroxyl, carboxyl, and amide groups in the elimination of Cd2+, Ni2+, and Cr6+. Further the sequential adsorption-desorption study confirmed a significantly preserved removal efficacy (p < 0.05), indicating the advantageous use of the bacterium as a biosorbent.