Enhanced Microbial Oxidation-Neutralization Treatment of Acid Mine Drainage Rich in Ferrous Ions (Fe2+)

In this work, a method of enhanced packed-bed microbial oxidation-neutralization has been employed to treat Fe2+-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 Fe2+ to Fe3+. Results show that when the influent Fe2+ concentration is about 900 mg/L and the Fe2+ oxidation efficiency tends to 100%, the maximum oxidation rate of Fe2+ in the bio-ceramsite, bio-volcanic stone, and bio-activated carbon packed columns are 301 mg/(L center dot h), 234 mg/(L center dot h), and 139 mg/(L center dot h), respectively. Compared with the direct neutralization method, the enhanced microbial oxidation-neutralization method has several advantages. Firstly, it oxidizes Fe2+ to Fe3+, directly neutralizing the acid mine drainage at low pH and reducing the consumption of neutralizer. Secondly, more economical CaCO3 can be used as neutralizer. Thirdly, it produces precipitates with high solid content (5.50%), good settling performance (SV30 = 4%), and small volume, and the capillary suction time (CST) is 8.9 s, which is easy to dehydrate.