title: Effects of hydraulic retention time and sulfide toxicity on ethanol and acetate oxidation in sulfate-reducing metal-precipitating fluidized-bed reactor.
abstract: The effects of hydraulic retention time (HRT) and sulfide toxicity on ethanol and acetate utilization were studied in a sulfate-reducing fluidized-bed reactor (FBR) treating acidic metal-containing wastewater. The effects of HRT were determined with continuous flow FBR experiments. The percentage of ethanol oxidation was 99.9% even at a HRT of 6.5 h (loading of 2.6 g ethanol L(-1) d(-1)), while acetate accumulated in the FBR with HRTs below 12 h (loading of 1.4 g ethanol L(-1) d(-1)). Partial acetate utilization was accompanied by decreased concentrations of dissolved sulfide (DS) and alkalinity in the effluent, and eventually resulted in process failure when HRT was decreased to 6.1 h (loading of 2.7 g ethanol L(-1) d(-1)). Zinc and iron precipitation rates increased to over 600 mg L(-1) d(-1) and 300 mg L(-1) d(-1), respectively, with decreasing HRT. At HRT of 6.5 h, percent metal precipitation was over 99.9%, and effluent metal concentrations remained below 0.08 mg L(-1). Under these conditions, the alkalinity produced by substrate utilization increased the wastewater pH from 3 to 7.9-8.0. The percentage of electron flow from ethanol to sulfate reduction averaged 76 +/- 10% and was not affected by the HRT. The lowest HRT did not result in significant biomass washout from the FBR. The effect of sulfide toxicity on the sulfate-reducing culture was studied with batch kinetic experiments in the FBR. Noncompetitive inhibition model described well the sulfide inhibition of the sulfate-reducing culture. (DS) inhibition constants (K(i)) for ethanol and acetate oxidation were 248 mg S L(-1) and 356 mg S L(-1), respectively, and the corresponding K(i) values for H(2)S were 84 mg S L(-1) and 124 mg S L(-1). In conclusion, ethanol oxidation was more inhibited by sulfide toxicity than the acetate oxidation.
authors.affiliation: Institute of Environmental Engineering and Biotechnology, Tampere University of Technology, P.O. Box 541, FIN-33101 Tampere, Finland. anna.kaksonen@tut.fi
authors.forename: Anna H
authors.initials: AH
authors.lastname: Kaksonen
authors.forename: Peter D
authors.initials: PD
authors.lastname: Franzmann
authors.forename: Jaakko A
authors.initials: JA
authors.lastname: Puhakka
mesh_terms: D000085:Acetates / Q000378:metabolism*; D018533:Biomass; D019149:Bioreactors; D011232:Chemical Precipitation; D000431:Ethanol / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D013431:Sulfates / Q000378:metabolism*; D013440:Sulfides / Q000633:toxicity*; D016999:Sulfur-Reducing Bacteria / Q000254:growth & development / Q000378:metabolism; D013997:Time Factors; D014865:Waste Disposal, Fluid
chemical_list: D000085:Acetates; D013431:Sulfates; D013440:Sulfides; D000431:Ethanol