Arsenic removal in a sulfidogenic fixed-bed column bioreactor

Area of Science:

• Environmental Science
• Environmental Engineering
• Biotechnology

Background:

• Acidic wastewater often contains toxic heavy metals like arsenic.
• Arsenic contamination poses significant risks to ecosystems and human health.
• Bioremediation offers a sustainable approach for removing arsenic from industrial effluents.

Purpose of the Study:

• To investigate the bioremoval of arsenate (As(5+)) from synthetic acidic wastewater.
• To evaluate the impact of ferrous iron (Fe(2+)) and chemical oxygen demand (COD) on arsenic removal efficiency.
• To identify the mechanisms of arsenic precipitation mediated by sulfate-reducing bacteria (SRB).

Main Methods:

• Utilized an anaerobic up-flow fixed bed column bioreactor fed with ethanol.
• Varied concentrations of arsenate, ferrous iron, and chemical oxygen demand.
• Analyzed precipitate composition using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS).

Main Results:

• Arsenic removal was minimal (8%) without iron supplementation.
• Adding 100 mg/L Fe(2+) increased removal to 63%; 200 mg/L Fe(2+) improved it to 85%.
• Optimizing COD and maintaining 200 mg/L Fe(2+) and 20 mg/L As(5+) achieved 96% arsenic removal.

Conclusions:

• Ferrous iron addition is crucial for efficient arsenic bioremoval.
• Optimized substrate (ethanol) and iron concentrations maximize arsenic removal by SRB.
• Arsenic removal occurs primarily through the precipitation of arsenic sulfides and co-precipitation with iron sulfides.