Stimulation of microbial sulphate reduction in a constructed wetland: microbiological and geochemical analysis

Microbial sulphate reduction was stimulated successfully in enclosures installed in a constructed wetland. When sucrose (2.4 mM) and NH4Cl (600 μM) were added to water in the test enclosures, the indigenous microbial community was able to remove over 90% of the sulphate, present as a contaminant from nearby mining activity at a concentration of 384 mg l−1 (4 mM), over 50 days. Over 90% of the sucrose was also removed. Sulphate was not reduced in control enclosures containing no added sucrose or NH4Cl. Fermentation of sucrose by obligate anaerobes including Clostridium sp. and Bacteriodes sp. preceded sulphate reduction in the test enclosures. Sulphate reduction was biphasic, with maximum rates noted between 2–5 and 23–27 days after the addition of the growth substrates. Relatively unbiased 16S rDNA analysis suggested that nitrogen-fixing bacteria were important constituents of the microbial community in the test enclosures at day 23, suggesting that soluble nitrogen was limiting in the amended test enclosures during the experiment.