Effect of rice husk biochar as a carrier for Sporosarcina pasteurii in zinc removal through MICP process

Microbially induced calcite precipitation (MICP) has emerged as a promising technique for heavy metal immobilization; however, its effectiveness can be compromised by bacterial survival and distribution in contaminated soils. This study evaluates the potential of rice husk biochar as a carrier for Sporosarcina pasteurii to enhance MICP-mediated Zn immobilization. After spiking the soil with 500 mg kg⁻¹ Zn (as ZnCl ₂ .2H ₂ O), five treatments were applied: SP (inoculation of bacteria at approximately 10 ⁸ cells mL ^− 1 , 1% v/w), B (application of rice husk biochar at 1% w/w), BSP (approximately 10 ⁸ cells mL ^− 1 + biochar), IBSP (immobilized bacteria on biochar), and C (control, soil without any treatments). Soil properties, including pH, electrical conductivity (EC), organic carbon (OC) content, microbial basal respiration, microbial biomass carbon, urease activity, and Zn concentrations in soluble-exchangeable and carbonate fractions, were measured over 28 days. The IBSP treatment showed the highest Zn immobilization, reducing the soil Zn soluble-exchangeable fraction by 93.1% compared to the C. By the end of the incubation period, the soil Zn carbonate fraction increased by 56.5% in the IBSP treatment, while the BSP and SP treatments exhibited increases of 52.2% and 41.9%, respectively. Additionally, significant increases in pH, EC, and microbial activity were observed in the IBSP treatment relative to the other treatments. Therefore, applying rice husk biochar as a carrier for S . pasteurii improves soil biological properties and significantly enhances Zn immobilization via the MICP process, suggesting its potential as a cost-effective and sustainable approach for remediating Zn-contaminated soils.