A novel biological sulfur reduction process for mercury-contaminated wastewater treatment

Abstract The sulfidogenic process driven by sulfate-reducing bacteria (SRB) is not suitable for mercury-contaminated wastewater treatment due to the highly toxic methyl-mercury (MeHg) produced by SRB. In our previous study, we observed in short-term batch tests that sulfur-reducing bacteria (S 0 RB) could remove mercury ions without MeHg production. Thus, the aim of this study is to develop a biological sulfur reduction process driven by S 0 RB for mercury-contaminated wastewater, and investigate its long-term performance on mercury removal and MeHg accumulation. Receiving mercury-contaminated wastewater containing 0–50 mg Hg(II)/L for 326 days, S 0 RB in the sulfur-reducing bioreactor showed high tolerance with mercury toxicity, and removed 99.4% ± 1.4% of the influent Hg(II) by biogenic sulfide. MeHg was always found to be undetectable in the bioreactor, even though the sulfidogenic bacteria were exposed to high levels of Hg(II) in long-term trials. The result of qPCR analysis further revealed that the mercury-methylation functional gene (hgcA) concentration in the bioreactor sludge was found to be extremely lower than in the SRB-enriched sludge, Geobacter sulfurreducens PCA and Desulfomicrobium baculatum DSM 4028, implying that there was no or few mercury methylators in the bioreactor. In short, the biological sulfur reduction process using S 0 RB can efficiently treat mercury-contaminated wastewater, with high Hg(II) removal efficiency and no MeHg accumulation.