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Abstract
Biological sulfate-reducing bacteria (SRB) may be effective in removing toxic lead and mercury ions (Pb(II) and Hg(II)) from wet flue gas desulfurization (FGD) wastewater through anaerobic sulfite reduction. To confirm this hypothesis, a sulfite-reducing up-flow anaerobic sludge blanket reactor was set up to treat FGD wastewater at metal loading rates of 9.2 g/m3-d Pb(II) and 2.6 g/m3-d Hg(II) for 50 days. The reactor removed 72.5 ± 7% of sulfite and greater than 99.5% of both Hg(II) and Pb(II). Most of the removed lead and mercury were deposited in the sludge as HgS and PbS. The contribution of cell adsorption and organic binding to Pb(II) and Hg(II) removal was 20.0 ± 0.1% and 1.8 ± 1.0%, respectively. The different bioavailable concentration levels of lead and mercury resulted in different levels of lethal toxicity. Cell viability analysis revealed that Hg(II) was less toxic than Pb(II) to the sludge microorganisms. In the batch tests, increasing the Hg(II) feeding concentration increased sulfite reduction rates. In conclusion, a sulfite-reducing reactor can efficiently remove sulfite, Pb(II) and Hg(II) from FGD wastewater.
Highlights
The limestone wet flue gas desulfurization (FGD) process is the most popular process for desulfurization in coal-burning power plants, especially in China[4]
The sulfite-reducing up-flow anaerobic sludge blanket (SrUASB) reactor was operated for 50 days continuously to treat FGD wastewater, using domestic wastewater as the carbon source
The influent of the system consisted of 529 ± 50 mg/L chemical oxygen demand (COD), 386 ± 15 mg/L SO32−-S, 32 mg/L NH4+-N, 2.3 mg/L Pb(II), and 570 μg/L Hg(II)
Summary
The limestone wet FGD process is the most popular process for desulfurization in coal-burning power plants, especially in China[4] This process generates large amounts of gypsum-containing waste and often causes blockages at facilities because of calcium sulfate deposits[8]. Acute toxicity, reported as lethal concentration 50 (LC50) values of MeHg, ranged from 24 μg/L to 54 μg/L19,20 For this reason, the treatment of mercury-contaminated wastewater by SRB is limited[21]. In a biological FGD wastewater treatment system, the effects of mercury and lead on the activity of SRB require investigation, especially the effects of the combined presence of both Pb(II) and Hg(II)
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