Remediation of heavy metal-contaminated estuarine sediments by strengthening microbial in-situ mineralization

Abstract

The production of in-situ iron-sulfide minerals through sulfate reduction is commonly used to immobilize heavy metals in sediments and waste residues from abandoned non-ferrous mines. Ensuring a consistent supply of organic carbon sources, such as small molecular organic acids, under optimal reduction conditions, is essential for effective biomineralization. In this study, we developed a technique to enhance the biomineralization (iron-sulfide minerals) capacity of native sulfate-reducing bacteria to immobilize heavy metals, using the facultative anaerobic fermentation bacterium Bacillus coagulans to bind to waste olivine, providing small molecular organic acids required by sulfate-reducing bacteria while providing more reduction conditions for remediation systems.Our results showed that, compared with the control group (Control) and the group added with medium (Cul), the groups added with Bacillus coagulans (Cul + Bio) and the combination of Bacillus coagulans and olivine (Cul + Bio + Oli), significantly increased the overlying water pH value, pH remained above 8 in the final stage of remediation, and decreased the redox potential and sulfate concentration, ORP remained −80 mV, SO42− concentration below 600 mg/L at the end of remediation. The addition of Bacillus coagulans and olivine helped stabilize heavy metals Cu, Pb, Zn, and Cd by reducing their release into the liquid phase. Cd and Pb were found to be in more stable forms within the solid phase. In the Cul + Bio and Cul + Bio + Oli groups, sulfur primarily existed as more reductive FeS, accounting for 55% and 75% of the sulfur speciations, respectively. Desulfuromonadia, Desulfuromonas, Desulfofustis, and Geothermobacter have been identified in the Cul + Bio + Oli experimental group in high abundance and are capable of dissimilatory sulfate reduction. The combined application of microorganisms and waste olivine offers an effective strategy for remediating in-situ heavy metal-contaminated soils/sediments, thereby establishing a theoretical and practical foundation for employing microbial mineralization in the in-situ remediation of heavy metals in sediment.