Iron bioremediation by utilizing biochar-bacterial composites

Iron (Fe) contamination in groundwater is a gradual yet significant concern driven by industrial, urban, and agricultural activities, resulting in undesirable organoleptic effects in drinking water. Surface immobilization of bacterial strains onto biochar offers a promising strategy for enhancing adsorption-based remediation.

This study investigates the adsorption behaviour of Fe(II) ions using a bacterial-biochar immobilized adsorbent derived from rice husk and Bacillus subtilis, isolated from iron-rich soil samples near handpumps located in Haridwar, Uttarakhand, India. The goal was to evaluate the impact on the adsorption capacity for Fe (II) through various sorption and kinetic models, along with material modified properties.

Rice husk biochar was immobilized with Bacillus subtilis and characterized using SEM, BET surface area analysis, and FTIR spectroscopy. Batch adsorption experiments were conducted across Fe(II) concentrations of 10-40 mg/L. Three Sorption kinetics were modeled for fitting the data and similarly three Isotherm behaviors were assessed, supported by regression analyses.

The bacterial-biochar immobilized adsorbent achieved 79.3% Fe(II) removal, outperforming pristine biochar. BET surface areas of 67.76 and 91.84 m²/g correlated with enhanced adsorption. The FTIR revealed functional groups (alkene: C-H stretching, alcohol: O-H bending, conjugated alkenes: C = C stretching) and metal carbonate structures, provided an insight of active bio sorption sites. A decline in adsorption at higher concentrations, indicated optimal performance at 10-15 mg/L concentration of Fe (II) ions. Kinetic (pseudo-first-order and Weber-Morris intraparticle diffusion) and isotherm (Freundlich and Redlich-Peterson) models validated the presence of heterogeneous adsorption sites.

Surface immobilization of Bacillus subtilis onto rice husk biochar significantly enhances Fe(II) adsorption. These findings highlight the potential of bacterial-biochar immobilized adsorbent as a basis for valorization of the green biotechnology usage in groundwater remediation applications.