Removal of mercury in fixed-bed continuous upflow reactors by mercury-resistant bacteria and effect of sodium chloride on their performance

Urgent need to reduce the amount of toxic mercury compounds in the wastewater of industries and subsequent reuse of metal ions, has led to an increasing interest in microbial bioremediation. Two Pseudomonas aeruginosa strains, namely, isolate CH07 and isolate Bro12, and a genetically engineered strain P. putida (KT 2442 mer::73) were used to study the kinetics of mercury removal from liquid M9 medium, considering the potential of the bacteria in volatilizing ionic mercury to its gaseous form. The P. aeruginosa strains were further used to remove toxic mercury from synthetic wastewater in fixed-bed, continuous upflow reactors and thereafter to recover the toxic metal from the reactor beds. We also studied the effect of sodium chloride on the kinetics of mercury removal by the isolate CH07 from marine sediment, as well as the other two non-marine bacteria. After a successful run of over a month, the bioreactors were able to retain the toxic metal, which resulted in a recovery of approximately 64% of the influent mercury. No major alteration in the retention capacity of the bioreactors occurred during drastic changes in concentration of inflowing metals or salt concentration.