Bacterial removal of mercury from sewage

Mercury-resistant bacteria, which are able to reduce mercuric ion (Hg(2+)) to metallic mercury (Hg(0)), were examined for their ability to remove mercury from waste-water aerobically. Growth studies in artificial medium indicated that mercury increases the lag phase, but does not effect the growth rate of these bacteria. Further studies demonstrated that growth was minimal during a phase of rapid mercury removal, after which growth resumed. Small but significant amounts of carbohydrates are required for the mercuric ion reduction. Prolonged periods of bacterial growth under nonsterile conditions was accomplished without the loss of the mercuric reducing ability of the culture. A continuous culture of the resistant organism was maintained on raw sewage for two weeks, during which time relatively high concentrations of mercury (70 mg/L) were removed from the sewage at a rate of 2.5 mg/L h and at efficiencies exceeding 98%.