Removal of sulfate and heavy metals by sulfate reducing bacteria in short-term bench scale upflow anaerobic packed bed reactor runs

Mildly acidic metal (Cu, Zn, Ni, Fe, Al and Mg), arsenic and sulfate contaminated waters were treated, over a 14 day period at 25°C, in a bench-scale upflow anaerobic packed bed reactor filled with silica sand and employing a mixed population of sulfatereducing bacteria (SRB). The activity of SRB increased the water pH from ~4.5 to 7.0, and enhanced the removal of sulfate and metals in comparison to controls not inoculated with SRB. Addition of organic substrate and sulfate at loading rates of 7.43 and 3.71 kg d^-1 m^-3, respectively, resulted in >82% reduction in sulfate concentration. The reactor removed more than 97.5% of the initial concentrations of Cu, Zn and Ni, while only >77.5% and >82% of As and Fe were removed, respectively. In contrast, Mg and Al levels remained unchanged during the whole treatment process. The removal patterns for Cu, Zn, Ni and Fe reflected the trend in their solubility for their respective metal sulfides, while As removal appeared to coincide with decreasing Cu, Zn, Ni and Fe concentrations, which suggests adsorption or concomitant precipitation with the other metal sulfides.