Treatment of metal-contaminated water and vertical distribution of metal precipitates in an upflow anaerobic bioreactor

A lab-scale upflow anaerobic bioreactor filled with granular sludge and cow manure was operated for 140 days to determine the mechanism of metal removal and the vertical distribution of metal precipitates. Heavy metal ions were removed in the order of Cu2+, Cd2+, ZnZ(2+), Fe2+ and Mn2+ with respect to the height in the reactor. The solid phase analysis showed that the heavy metals were mostly precipitated in the form of metal sulfides by sulfate reduction. The contents of metal precipitates in the reactor were as follows: (i) Cd and Zn were highest in the bottom, (ii) Fe was highest at the low-middle layer, and (iii) Mn was increased with the height in the reactor. The vertical distribution of metal sulfides in the reactor was directly related to the solubility product (Ksp). Results obtained in this study suggest a feasibility of the application to separate precipitation of metal ions and recovery of valuable metals from metal-containing wastewater.