METAL REMOVAL BY SULFATE-REDUCING BACTERIA FROM NATURAL AND CONSTRUCTED WETLANDS

The use of wetlands is a promising technology to treat acid mine drain age, yet there is little understanding of the fundamental biological p rocesses in involved. They are considered to centre on the complex ana erobic ecology within sediments and involve the removal of metals by s ulphate-reducing bacteria (SRB). These bacteria generate hydrogen sulp hide and cause precipitation of metals from solution as the insoluble metal sulphide. Sulphate-reducing bacteria have been isolated from nat ural and constructed wetlands receiving acid mine drainage. Sulphide p roduction by isolates and removal of the metals iron, manganese and zi nc were measured, as well as utilization of a range of carbon sources. Marked ecological differences between the wetlands were reflected in population composition of SRB enrichments, and these consortia display ed significant differences in sulphide generation and rates of metal r emoval from solution. Rates of metal removal did not correlate with su lphide generation in all cultures, suggesting the involvement of other biological mechanisms of metal removal. Differences in substrate util ization have highlighted the need for further investigation of carbon from and potential carbon sources within constructed wetlands.