title: Optimization of metal sulphide precipitation in fluidized-bed treatment of acidic wastewater.
abstract: Sulphate-reducing biofilm and suspension processes were studied for treatment of synthetic wastewater containing sulphate, zinc and iron. With lactate supplemented wastewater with 170-230mg/l Zn and 58mg/l Fe, the following precipitation rates were obtained: 250 and 350mg/l d for Zn in fluidized-bed (FBR) and upflow anaerobic sludge blanket reactors, respectively, and 80mg/l d for Fe in both reactors with hydraulic retention time of 16h. The effluent Zn and Fe concentrations remained at less than 0.1 mg/l. The alkalinity produced in lactate oxidation increased the initial pH of 2.5-3, resulting in effluent pH of 7.5-8.5. The highest sulphate reduction rate was over 2000 mg/l d. In terms of sulphate reduction, hydrogen sulphide production and effluent alkalinity, the start-up of the FBR with the 10% fluidization rate was superior to the FBRs with 20-30% fluidization rates. With increased loading rates, high recycling rate became an advantage. After process failure caused by intentional overloading, the sulphate reduction partially recovered within 2 weeks. Metal precipitates in the reactors were predominantly FeS2, ZnS and FeS. The metal mass balance was as follows: 73-86% of Zn and Fe accumulated into the reactors and water level adjustors, 14-23% of the metals were washed out as precipitates and 0.05-0.15% remained as soluble metals. Biomass yield in the sulphate-reducing processes was 0.039-0.054g dry biomass (VS or VSS) per g of lactate oxidized or 0.035-0.074g dry biomass per g of sulphate reduced. The results of this work demonstrate that the lactate supplemented sulphate-reducing processes precipitated the metals as sulphides and neutralized the acidity of the synthetic wastewater.
authors.affiliation: Institute of Environmental Engineering and Biotechnology, Tampere University of Technology, P.O. Box 541, FIN-33101 Tampere, Finland.
authors.forename: A H
authors.initials: AH
authors.lastname: Kaksonen
authors.forename: M L
authors.initials: ML
authors.lastname: Riekkola-Vanhanen
authors.forename: J A
authors.initials: JA
authors.lastname: Puhakka
mesh_terms: D018441:Biofilms; D011232:Chemical Precipitation; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D013440:Sulfides / Q000737:chemistry*; D016999:Sulfur-Reducing Bacteria / Q000502:physiology; D014865:Waste Disposal, Fluid; D019287:Zinc Sulfate / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D013440:Sulfides; C024823:ferric sulfate; D019287:Zinc Sulfate