Biological treatment of heavy metals contaminated waters

The precipitation of metals with biologically produced H2S by Sulphate Reducing Bacteria (SRB) in Permeable Reactive Barriers (PRB) has been proposed as a technology for the treatment of heavy metals contaminated waters. The aim of the work was the comparison between a selected reactive mixture containing organic matter for SRB and other electron donors, such as ethanol, glucose and polysaccharides. The different substrates were compared by testing their ability in sustaining SRB activities. Batch tests were conducted for the screening of solid mixtures for SRB growth. A continuously operating fixed-bed column was filled with the selected mixture (6% leaves, 9% compost, 3% zero valent iron, 30% silica sand, 30% perlite, 22% limestone) and inoculated by SRB. Column was regularly fed with a solution containing heavy metals and sulphates. At steady state 50±10% sulphate abatement was reached and metals were totally removed. Batch tests with ethanol showed the ability of SRB to grow on this substrate efficiently. Experimentation using ethanol was performed using two different column reactors filled with perlite, one inoculated by SRB and the other used as blank. Both columns were regularly fed with a solution containing sulphate and ethanol. Sulphate abatements of the inoculated column were 70±10% against 10±5% of the blank column. Preliminary batch tests with polysaccharides showed the ability of bacteria to grow on these substrates.