Long term performance of an AMD treatment bioreactor using chemolithoautotrophic sulfate reduction and ferrous iron precipitation under in situ groundwater conditions

Chemolithoautotrophic sulfate reduction (CSR) was tested to treat natural acid mine drainage influenced groundwaters. The long term behavior was studied for more than 3 years under groundwater conditions (10 °C, autochthonous sulfate reducing bacteria (SRB)) without biomass replenishment in a 190 L bench scale reactor. The process produces water with alkalinity >10 mM. pH can be controlled by p(CO2) for all expectable water qualities. SRB were immobilized using an expanded clay bed. After 1.3 years of operation, a constant biomass content and sulfate reduction rate of 0.25 – 0.30 mmol SO 4 ( L h ) - 1 were established. The sulfate reduction rate was limited by biomass content. Most of the electrons were used for sulfate reduction (98%). The hydrogen turn over in competing processes like methanogenesis and homoacetogenesis was successfully suppressed by adjusting the sulfate concentration to be >2 mM in the runoff.