Optimization of a modular continuous flow bioreactor system for acid mine drainage treatment using Plackett-Burman design

A novel modular continuous flow bioreactor system was designed to enhance the tolerance of bacteria to high concentration of heavy metal. This study evaluated the combined effect of high and low concentration levels of zinc, ferrous iron, copper, sulfate, and carbon source on the heavy metals and sulfate removal efficiencies. Statistically valid Plackett-Burman design (PBD) of experiments was employed to carry out this study. A maximum removal for each of zinc, copper, iron, and sulfate was 99.08%, 99.13%, 94.83%, and 58.89%, respectively. Analysis of variance (ANOVA) of zinc, copper, and sulfate reduction revealed that the effect due to zinc was highly significant (p < 0.05). To establish the roles of iron-oxidizing bacteria (IOB) and sulfate reducing bacteria (SRB) in their respective bioreactors, the characteristics of microbial communities in attached and suspended growth biomass in the bioreactors were analyzed by high-throughput sequencing during the steady operational process. Qualitative energy dispersive spectroscopy (EDS) analysis of the precipitates from sulfide precipitation was performed. The results revealed that the precipitates as sulfide zinc were confirmed by the EDS spectrum with strong peaks of zinc and sulfur.