Biocalcification-Based Stabilization of Cadmium-Enriched Phytoremediation Biomass Using Advenella sp. AV1

The concentrated heavy metal in plant biomass, following successful phytoremediation of contaminated soil, needs to be disposed of sustainably. In this study, Bidens pilosa biomass harvested after phytoremediation of cadmium-contaminated soil was incinerated to ash and was further stabilized through a biocalcification process using a novel ureolytic strain Advenella sp. AV1. The changes in pH, ammonium ion (NH₄⁺) concentration, and residual calcium ions (Ca²⁺) were measured for 3 days in biocalcification experiments. The increase in pH (from 7.8 to 9.6), NH₄⁺ ions, and concomitant reduction in soluble Ca²⁺ in microbial “treatment” set containing B. pilosa biomass ash suggest the production of calcium carbonate (CaCO₃), which was further confirmed through Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy-energy dispersion X-ray analysis. Sequential extraction of bio-calcified ash revealed a decrease in easily available cadmium (Cd) fractions, while an increase in more stable oxide and organic matter bound fractions in comparison to that from non-calcified biomass ash. The results suggest a reduced risk of heavy metals leaching following the biocalcification of phytoremediated biomass ash.