AN INTERNAL SEDIMENTATION BIOREACTOR FOR LABORATORY-SCALE REMOVAL OF TOXIC METALS FROM SOIL LEACHATES USING BIOGENIC SULFIDE PRECIPITATION

An internal-sedimentation bioreactor was employed to provide biomass f eedback and process intensification in a laboratory-scale sulphide-bio precipitation system for toxic metals (Cd, Cr, Cu, Mn, Ni, Zn) present in acid leachates from metal-contaminated soil. Biomass feedback was improved by addition of a cationic polymer flocculant and the activity of the sulphate-reducing bacterial culture was increased by the addit ion of cornsteep in addition to the ethanol used as carbon/energy subs trate. A mass-balance was carried out for carbon and sulphur in the sy stem. Sulphate reduction in the reactor was able to remove acidity at moderate sulphate concentrations up to 50 mM although it was insuffici ent at the highest levels tested, When presented with a simulated toxi c metal-containing leachate, the reactor was able to precipitate metal s efficiently under all of the conditions of sulphate concentration an d pH tested, producing an effluent with metal concentrations suitable for environmental discharge.