Evaluation of low-cost calcium sources for microbially induced calcite precipitation (MICP): Implications for sustainable bio-cementation

• Economical Ca sources significantly enhance MICP bio-cementation • Calci-Carb and industrial waste tripled CaCO₃ yield • Varied calcium sources altered CaCO₃ crystal morphology • XRD confirmed stable calcite as the predominant polymorph • Study offers cost savings, waste valorization, lower carbon footprint Microbially induced calcite precipitation (MICP) is a sustainable bio-cementation technique that employs ureolytic bacteria to generate calcium carbonate, thereby enhancing the mechanical performance of granular media. However, the reliance on high purity chemical-grade calcium sources, such as CaCl 2 , increases production costs and restricts large scale adoption. This study aimed to assess the feasibility of using three specific and low-cost calcium inputs—Calci Bor agricultural fertilizer, Calci Carb agricultural fertilizer, and a calcium-rich liquid effluent from a petrochemical facility—as substitutes for reagent grade CaCl 2 in the MICP. Experiments were conducted with Sporosarcina pasteurii under standardized incubation (OD 600 ≈ 1.0; 37 ° C; 16 h). Gravimetric analyses showed that Calci Carb and petrochemical effluent achieved 610–690 mg CaCO 3 /100 mL, representing a 2.3–2.5-fold increase over the CaCl 2 control (280–300 mg). In contrast, Calci Bor produced negligible precipitation, likely due to boric acid toxicity and limited Ca 2+ bioavailability. Microscopic analysis revealed distinct morphologies: dense spherical grains (CaCl 2 ), irregular fragmented crystals (Calci Carb), and fine powdery particles (effluent). X-ray diffraction confirmed calcite (> 95 wt%) as the dominant phase, with minor quartz detected in the effluent-derived product. The results demonstrated that one of the agricultural fertilizers and the studied industrial effluent can serve as effective calcium sources for MICP. These alternatives are economically viable and low-carbon, offering a more sustainable bio-cementation approach. Moreover, they contribute to waste valorization by utilizing industrial by-products. By reducing dependency on high-purity chemical reagents, they align with the growing need for sustainable and cost-effective solutions in ground improvement engineering.