Synergistic cadmium immobilization in agricultural soil via tea waste-amended microbial carbonate precipitation using...

This study evaluates the synergistic use of tea-waste (TW) amendments and microbially induced carbonate precipitation (MICP) for cadmium (Cd) immobilization in agricultural soils (microcosms). Lysinibacillus fusiformis and a dual-strain consortium with Sporosarcina pasteurii were tested across TW loadings of 5-25 % (w/w) at Cd spikes of 10 and 20 mg/kg. The 20 % TW amendment delivered the strongest performance, with Cd immobilization efficiencies of 67.7 % and 71.4 % for the 10 and 20 mg/kg soils, respectively. Sequential extraction showed a 340.7 % increase in the carbonate-bound Cd fraction alongside marked declines in exchangeable Cd. Mechanistically, improvements arose from (i) enhanced urease activity and carbonate precipitation and (ii) TW-mediated complexation by oxygenated functional groups. Mineralogical and spectroscopic data (XRD/FTIR/TGA) support formation of CaCO₃ and Cd-bearing carbonates, while SEM-EDS provided elemental co-localization (Ca-C-O with Cd) at carbonate-like microdomains. The consortium outperformed single strains by ≈15-20 %, consistent with niche complementarity and facilitation, and TW increased available N/P/K by up to 235 %/205 %/215 %, with pH stabilized near neutrality to mildly alkaline. Under our conditions, 20 % TW + consortium represents an effective baseline recipe for Cd immobilization; future work should refine dose-efficient delivery tailored to soil type for field translation. We outline optimization paths for different soil types and field deployment considerations.