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·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 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.