Effects of metal additions on sulfate reduction activity in wastewaters

Abstract Sulfate reducing bacteria (SRB) convert sulfate to sulfide resulting in the odor and corrosion prohlems in sewers. Evaluation of metal toxicity on SRB was conducted in three phase: screening tests in test tubes, batch tests of wastewater with enriched SRB culture, and serum bottle tests with raw wastewater. The inhibitory metal concentrations towards SRB in test tubes were relatively high, and the inhibitory order was: Cu > Cd > Ni > Zn > Cr > Pb. The addition of metal mixture exhibited a synergistic toxic effect. In the batch tests, the dissolved metal concentrations were found to be much lower than those added; thus, the dissolved metal concentrations per se might not be responsible for inhibiting sulfate reduction. Inhibition of sulfate reduction was observed at relatively high metal dosages: 20 mg/L Cd, 20 mg/L Cu, 25 mg/L Zn. 20 mg/L Ni, 60 mg/L Cr(III), 75 mg/L Pb, and 10 mg/L metal mixture. Similar pattern was also observed in the serum bottle tests. Key Words: Sulfate reductionsulfate reducing bacteriametal toxicity