Carboxylic acid reduction and sulfate-reducing bacteria stabilization combined remediation of Cr (VI)-contaminated soil

For controlling heavy metal pollution, the utilization of carboxylic acids (CAs) combined with sulfate-reducing bacteria (SRB) for continuous and stable remediation of Cr (VI)-contaminated soil was comprehensively investigated. At pH 3, citrate and lactate had photocatalysis characteristics that enabled them to reduce high Cr (VI) concentrations. The reduction efficiencies of citrate and lactate were 99.16–100% and 80.78–87.00%, respectively. In the 40 mg L−1 Cr (VI) treatment, the total Cr adsorption rate of soil was 61.39–68.31%; as the pH increased, the Cr species adsorption capacity of the soil decreased. Following the addition of exogenous 100 mg L−1 Cr (VI), the Cr (VI) content of re-contaminated soil was reduced to 16.2734 ± 0.9505 mg L−1 or 15.8618 mg kg−1 by adding citrate or lactate. Then, using SRB via culture by mulching, addition of citrate or lactate markedly reduced the toxicity of Cr (VI). The respective citrate or lactate treatments had sulfur concentrations of sulfide from deep soil (high-sulfide layer) of 70.54 ± 17.59 and 98.85 ± 13.84 mg kg−1, respectively, and released Cr (VI) concentrations of 0.22 ± 0.25 and 3.64 ± 3.32 mg kg−1, respectively, due to oxidation upon air exposure. We used a two-stage remediation strategy for these treatments: First, CAs were used for photocatalytic reduction to reduce Cr (VI); next, CAs were utilized as carbon sources by SRB, which further reduced Cr (VI) and stabilized Cr species. In addition, citrate was more conducive than lactate to maintaining the stability of the soil microbial community. The results show that this method has potential in the remediation of Cr (VI)-contaminated soil. •CAs combined with SRB was investigated for remediation of Cr (VI)-contaminated soil.•A two-stage remediation strategy was developed.•At pH 3, citrate and lactate were able to reduce high Cr (VI) concentrations.•Citrate was most conducive in maintaining the soil microbial community stability.•The method has potential applications in Cr (VI)-contaminated soil remediation.