Dolloff F. Bishop

STUDIES ON BIOSORPTION OF ZINC(II) AND COPPER(II) ON DESULFOVIBRIO DESULFURICANS

Abstract The objectives of these studies are to determine the equilibrium concentration and kinetics of metal sorption on sulfate-reducing bacteria (SRB) isolates. Adsorption establishes the net reversible cellular metal uptake and is related to SRB metal toxicity and the effects of environmental factors. Results from biosorption equilibria and kinetics of copper(II) and zinc(II) ions on Desulfovibrio desulfuricans and the effects of adsorption of these metals on SRB are discussed. Adsorption studies were conducted using stationary phase cells with equilibrium uptake at 24 h and pHs in the range of 4–7. Equilibrium adsorption in milligram of metal/g dry cell for copper(II) of 2.03 (pH 4.0) and 16.7 (pH 5.0) and zinc(II) of 6.40 (pH 5.5), 13.8 (pH 6.0), 39.2 (pH 6.2) and 49.6 (pH 6.6) was measured experimentally. Negligible biosorption of copper and zinc was found below pH 4.0, with metal sorption increasing within a limited range of pH mainly due to the neutral and/or deprotonated state of binding ligands on cell walls. Competition of metal ions during biosorption was investigated by conducting sorption experiments with Zn(II) using potassium phosphate buffer (KP) and deionized/distilled water. Zn(II) sorption capacity was lower in KP buffer than deionized water due to competition from potassium ions. Scanning Electron Microscope micrographs indicated that metal biosorption on SRB may be related to the production of extracellular polymeric substance (e.g., polysaccharide).

Treatment of acid mine drainage: I. Equilibrium biosorption of zinc and copper on non-viable activated sludge

Biosorption is potentially attractive technology for treatment of acid mine drainage for separation/recovery of metal ions and mitigation of their toxicity to sulfate reducing bacteria. This study describes the equilibrium biosorption of Zn(II) and Cu(II) by nonviable activated sludge in a packed column adsorber. The Zn(II) uptake capacity of unconditioned sludge (not subjected to processing other than drying) was found to decrease in repeated adsorption–desorption cycles, declining by a factor greater than 20 from cycle 1 to cycle 6. Equilibrium uptake of metals by dried sludge conditioned by exposure to deionized water at a pH corresponding to that of the feed solution showed a strong pH dependence and was modeled using the Langmuir adsorption isotherm. Equilibrium metal uptakes from solutions containing single metal ion were 2.5 mg g(dry biomass)−1 and 3.4 mg g(dry biomass)−1 for Zn(II), and 1.9 mg g(dry biomass)−1 and 5.9 mg g(dry biomass)−1 for Cu(II) at pH 3.0 and 3.8, respectively. Equilibrium uptakes from binary mixtures were 30% lower than single component solution uptakes for both metals, indicating some competition between the two metals. No hysteresis was detected between adsorption and desorption equilibria. Anion concentration and pH measurements indicated that simultaneous sorption of metal cation and sulfate anion was probably occurring at pH 3.0, while proton exchange predominated at pH 3.8. Results of the study point to the usefulness of non-viable activated sludge as a biosorbent for recovery/separation of metal ions from acid mine drainages.

Biodegradation of toluene in a membrane biofilter

A membrane biofilter is used to biodegrade toluene in the gas phase. Active microorganisms are immobilized on the outside of a hollow fiber membrane cartridge and air containing toluene as the contaminant is passed through the membrane fibers. A porous polysulfone membrane containing water in the pore is used through which both toluene and oxygen are diffused to the biofilm attached to the outside surface. High conversion of toluene (84%) is achieved with a 16 second gas-phase residence time, based on total internal volume of the hollow fibers. A mathematical model is then developed to estimate toluene removal efficiencies at higher air flow rates.

Treatment of trichloroethylene (TCE) in a membrane biofilter.

This article reports on the biodegradation of trichloroethylene (TCE) in a hollow‐fiber membrane biofilter. Air contaminated with TCE was passed through microporous hollow fibers while an oxygen‐free nutrient solution was recirculated through the shell side of the membrane module. The biomass was attached to the outside surface of the microporous hollow fibers by initially supplying toluene in the gas phase that flows through the fibers. While studies on TCE biodegradation were conducted, there was no toluene present in the gas phase. At 20‐ppmv inlet concentration of TCE and 36‐s gas‐phase residence time, based on total internal volume of the hollow fibers, 30% removal efficiency of TCE was attained. At higher air flow rates or lower gas‐phase residence times, lower removal efficiencies were observed. During TCE degradation, the pH of the liquid phase on the shell side of the membrane module decreased due to release of chloride ions. A mathematical model was developed to describe the synchronous aerobic/anaerobic biodegradation of TCE.

Genotoxic properties of municipal wastewaters in Ohio

Wastewaters from six municipal wastewater treatment plants in Ohio were tested at different stages of treatment for mutagenicity in the Ames/Salmonella assay. The chlorinated secondary effluents were also evaluated for induction of sister chromatid exchanges in Chinese hamster ovary cells. Direct-acting microbial mutagenicity was observed for extracts of the effluents from all six plants for both an initial and a repeat sampling series. In some cases, the mutagenicity was greatly enhanced by S9 metabolic activation (MA). In general, the specific mutagenicity of the extracts increased following activated sludge treatment. Chlorination resulted in substantial increases in mutagenic activity for some of the Wastewaters but had no effect on others. SCE inducing activity was detected in five out of six extracts for the first sample series, and for two out of five extracts for the second sample series. There was no obvious correlation in the ability of the extracts from the chlorinated secondary effluents to induce SCE in CHO cells and to induce mutations in Salmonella.