Enhanced Microbial Oxidation–Neutralization Treatment of Acid Mine Drainage Rich in Ferrous Ions (Fe(2+))

In this work, a method of enhanced packed-bed microbial oxidation–neutralization has been employed to treat Fe(2+)-rich acid mine drainage. The method features the use of a large number of immobile Acidithiobacillus ferrooxidans (A. ferrooxidans) in a bioreactor to promote the oxidation of Fe(2+) to Fe(3+). Results show that when the influent Fe(2+) concentration is about 900 mg/L and the Fe(2+) oxidation efficiency tends to 100%, the maximum oxidation rate of Fe(2+) in the bio-ceramsite, bio-volcanic stone, and bio-activated carbon packed columns are 301 mg/(L·h), 234 mg/(L·h), and 139 mg/(L·h), respectively. Compared with the direct neutralization method, the enhanced microbial oxidation–neutralization method has several advantages. Firstly, it oxidizes Fe(2+) to Fe(3+), directly neutralizing the acid mine drainage at low pH and reducing the consumption of neutralizer. Secondly, more economical CaCO(3) can be used as neutralizer. Thirdly, it produces precipitates with high solid content (5.50%), good settling performance (SV(30) = 4%), and small volume, and the capillary suction time (CST) is 8.9 s, which is easy to dehydrate.