The effect of acidic pH and presence of metals as parameters in establishing a sulfidogenic process in anaerobic reactor

ABSTRACT

The successful use of anaerobic reactors for bioremediation of acid mine drainage has been shown in systems with neutral pH. However, the choice of an efficient and suitable process for such wastewater must consider the capability of operating at acidic pH and in the presence of metals. This work studies the performance of an anaerobic batch reactor, under conditions of varying initial pH for its efficiencies in sulfate removal and metal precipitation from synthetic acid mine drainage. The chemical oxygen demand/sulfate (COD/SO₄²⁻) ratio used was 1.00, with ethanol chosen as the only energy and carbon source. The initial pH of the synthetic drainage was progressively set from 7.0 to 4.0 to make it as close as possible to that of real acid mine drainage. Metals were also added starting with iron, zinc, and finally copper. The effectiveness of sulfate and COD removal from the synthetic acid mine drainage increased as the initial pH was reduced. The sulfate removal increased from 38.5 ± 3.7% to 52.2 ± 3%, while the removal of organic matter started at 91.7 ± 2.4% and ended at 99 ± 1%. These results indicate that the sulfate reducing bacteria (SRB) community adapted to lower pH values. The metal removal observed was 88 ± 7% for iron, 98.0 ± 0.5% for zinc and 99 ± 1% for copper. At this stage, an increase in the sulfate removal was observed, which reaches up to 82.2 ± 5.8%. The kinetic parameters for sulfate removal were 0.22 ± 0.04 h⁻¹ with Fe, 0.26 ± 0.04 h⁻¹ with Fe and Zn and 0.44 ± 0.04 h⁻¹ with Fe, Zn, and Cu.

KEYWORDS:

• Acid mine drainage
• acidic pH
• anaerobic batch reactor
• kinetic parameters
• metal removal
• sulfate removal

Funding

The authors thank Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for providing research funds (Process 479184/2011-9 and 490210/2012-0).