Biotreatment and bioassessment of heavy metal removal by sulphate reducing bacteria in fixed bed reactors

In this work a batch-optimised mixture (w/w %: 6% leaves, 9% compost, 3% Fe(0), 30% silica sand, 30% perlite, 22% limestone) was investigated in a continuous fixed bed column reactor for the treatment of synthetic acid-mine drainage (AMD). A column reactor was inoculated with sulphate-reducing bacteria and fed with a solution containing sulphate and heavy metals (As(V), Cd, Cr(VI), Cu and Zn). At steady state, sulphate abatement was 50+/-10%, while metals were totally removed. A degradation rate constant (k) of 0.015+/-0.001h(-1) for sulphate removal was determined from column data by assuming a first order degradation rate. Reduction of AMD toxicity was assessed by using the nematode Caenorhabditis elegans as a test organism. A lethality assay was performed with the toxicants before and after the treatment, showing that only 5% of the animals were still alive after 48h in presence of the contaminants, while the percentage increased to 73% when the nematodes were exposed to the solution eluted from the column.