Precipitation of Copper (II) in a Two-Stage Continuous Treatment System Using Sulfate Reducing Bacteria

Biologically driven precipitation of dissolved copper and other trace metals has been used to treat contaminated aqueous streams. However, high dissolved trace metal concentrations can lead to toxicity, and their bioremediation difficult. Furthermore sorption of trace metals onto biomass might result in large amounts of contaminated byproducts. The aim of this work was to develop and test a two-stage reactor to bypass the toxic effects on the bacteria and chemically precipitate copper without contaminating the bulk of the biomass. Hence, copper removal using a sulfate reducing bacteria culture was investigated in a two-stage continuous treatment system. The first reactor was a sand-filled biological reactor in which the sulfate is reduced, followed by a second reactor/clarifier where the chemical precipitation and sedimentation of a CuS phase occurs. The influent Cu²⁺ concentration was varied systematically between 15 and 600 mg/L, and the precipitation of Cu²⁺ metal as CuS was achieved in the second reactor, resulting in complete (within detection limits) Cu²⁺ removal. EDS analysis on the solid phase collected from the second reactor confirmed the presence of Cu and S in the precipitate. EDS analysis on the solid phase collected from the second reactor confirmed the presence of Cu and S in the precipitate, and a CuS phase with minimal biomass was obtained. This configuration avoids toxicity effects of heavy metals in the biological reactor, as well as the contamination of biomass with the trace metal. Furthermore, the biomass free CuS precipitates can be easily disposed or even used to recover the trace metal.