Treatment Of Metal-containing Wastewater Research Articles

Sulfidogenic fluidized-bed treatment of metal-containing wastewater at 8 and [formula omitted] temperatures is limited by acetate oxidation

Acetate utilization in sulfidogenic fluidized-bed reactors (FBRs) was investigated for the treatment of iron containing wastewater at low ( 8 ∘ C ) and high ( 65 ∘ C ) temperatures. The FBRs operated at low and high temperatures were inoculated with cultures of sulfate-reducing bacteria (SRB) originally enriched from arctic and hot mining environments, respectively. Acetate was not utilized as a carbon and electron source for SRB at 8 ∘ C . With ethanol, hydrogen sulfide was produced from ethanol to acetate oxidation, which precipitated the iron. Then, several attempts were made to obtain acetate oxidation at 8 ∘ C . Inoculation of two different low temperature enrichments and operating the FBR for a long period of time (321 days) did not result in enrichment of acetate oxidizing SRB. Due to the absence of acetate oxidation at 8 ∘ C , external alkalinity addition was required to keep the pH neutral. At 65 ∘ C , average acetate and sulfate removals were 52 ± 12 % and 24 ± 8 % at 670 mg/L d acetate and 1500 mg/L d sulfate loadings, respectively. The produced alkalinity from acetate oxidation increased the pH from 6.4 to around 7.5 and electron flow to sulfate reduction averaged 65%. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA genes showed quite stable SRB community at 8 ∘ C , whereas, at 65 ∘ C SRB community was dynamic. In the FBRs, Desulfomicrobium apsheronum and Desulfosporosinus sp. at 8 ∘ C and Desulfotomaculum sp. at 65 ∘ C were detected.

Toxic effects of dissolved heavy metals on Desulfovibrio vulgaris and Desulfovibrio sp. strains

Biological treatment of metal-containing wastewaters with sulphate-reducing bacteria (SRB) is an attractive technique for the bioremediation of this kind of medium. In order to design a suitable engineering process to address this environmental problem, it is crucial to understand the inhibitory effect of dissolved heavy metals on these bacteria. Batch studies were carried out to evaluate the toxic effects of several heavy metal ions [Cr(III), Cu(II), Mn(II), Ni(II) and Zn(II)] on two cultures of SRB ( Desulfovibrio vulgaris and Desulfovibrio sp.). The experimental data indicate that SRB show different responses to each metal. At the highest metal concentration tolerated for each metal, the precipitation levels for D. vulgaris were as follows: 24.7%-15 ppm Cr(III), 45%-4 ppm Cu(II), 60%-10 ppm Mn(II), 96%-8.5 ppm Ni(II) and 9%-20 ppm Zn(II). The corresponding values for Desulfovibrio sp. were: 25.5%-15 ppm Cr(III), 71%-4 ppm Cu(II), 66.2%-10 ppm Mn(II), 96.1%-8.5 ppm Ni(II) and 93%-20 ppm Zn(II). Results obtained in batch studies will be taken into account for the subsequent design of a sulphate-reducing bioreactor to reduce levels of heavy metals present in different types of contaminated media.

Treatment of metal-containing wastewaters with a novel extractive membrane reactor using sulfate-reducing bacteria

This work reports a novel system for the treatment of acidic metal-containing wastewaters, the Extractive Membrane Bioreactor–Sulfate-Reducing Bacteria (EMB-SRB) system. In this system, hydrogen sulfide is produced in the bioreactor by the sulfate-reducing bacteria, transfers through a dense phase membrane, and precipitates metal ions in the wastewater. The non-porous membrane prevents the SRB from having direct contact with the toxic metals, extremes of pH, or high salinity in the wastewater. Silicone rubber, which is permeable to H2S but virtually impermeable to ionic species in the system, was used as a membrane. The rate of mass transfer of H2S across the membrane was studied and found to be well described by a resistances-in-series model. kov values vary in the range 5 × 10−6 –10 × 10−6 ms−1 1 depending on the membrane thickness. A continuous EMB–SRB system was operated and more than 90% (w/v) of the Zn2+ present in a wastewater was removed. A film of metal precipitate was found to build up on the inside (wastewater) side of the membrane, and became the dominant resistance contributing to the overall mass transfer coefficient during operation. © 2001 Society of Chemical Industry