Bioassessment of heavy metal toxicity and enhancement of heavy metal removal by sulfate-reducing bacteria in the presence of zero valent iron.

A simple and valid toxicity evaluation of Zn(2+), Mn(2+) and Cr(6+) on sulfate-reducing bacteria (SRB) and heavy metal removal were investigated using the SRB system and SRB+Fe(0) system. The heavy metal toxicity coefficient (β) and the heavy metal concentration resulting in 50% inhibition of sulfate reduction (I) from a modeling process were proposed to evaluate the heavy metal toxicity and nonlinear regression was applied to search for evaluation indices β and I. The heavy metal toxicity order was Cr(6+) > Mn(2+) > Zn(2+). Compared with the SRB system, the SRB+Fe(0) system exhibited a better capability for sulfate reduction and heavy metal removal. The heavy metal removal was above 99% in the SRB+Fe(0) system, except for Mn(2+). The energy-dispersive spectroscopy (EDS) analysis showed that the precipitates were removed primarily as sulfide for Zn(2+) and hydroxide for Mn(2+) and Cr(6+).The method of evaluating the heavy metal toxicity on SRB was of great significance to understand the fundamentals of the heavy metal toxicity and inhibition effects on the microorganism and regulate the process of microbial sulfate reduction.