Ludmila G. Peeva

Ethanol utilization by sulfate-reducing bacteria : An experimental and modeling study

A mixed culture of sulfate-reducing bacteria containing the species Desulfovibrio desulfuricans was used to study sulfate-reduction stoichiometry and kinetics using ethanol as the carbon source. Growth yield was lower, and kinetics were slower, for ethanol compared to lactate. Ethanol was converted into acetate and no significant carbon dioxide production was observed. A mathematical model for growth of sulfate-reducing bacteria on ethanol was developed, and simulations of the growth experiments on ethanol were carried out using the model. The pH variation due to sulfate reduction, and hydrogen sulfide production and removal by nitrogen sparging, were examined. The modeling study is distinct from earlier models for systems using sulfate-reducing bacteria in that it considers growth on ethanol, and analyzes pH variations due to the product-formation reactions.

Microbial sulfate reduction in a liquid-solid fluidized bed reactor.

A liquid-solid fluidized bed reactor was used to carry out sulfate reduction with a mixed culture of sulfate reducing bacteria. The bacteria were immobilized on porous glass beads. Stable fluidized bed operation with these biofilm-coated beads was possible. The low specific gravity of the hydrated beads allowed operation at low liquid recirculation rates. H(2)S level in the reactor was controlled by N(2) sparging, which also served as the location for liquid feed and removal. Ethanol was used as the electron donor/carbon source for the bacteria. Sulfate reduction rates up to 6.33 g sulfate L(-1) day(-1) were attained in the reactor at a hydraulic retention time of 5.1 h. The effect of hydraulic retention time and biomass loading on the beads, on reactor performance, and efficiency were examined. The efficiency of sulfate reduction increases considerably as the hydraulic retention increases, until the bacteria became very strongly substrate-limited at 55h HRT. The effect of bead biomass loading on bed expansion at various liquid superficial velocities was studied. A model for the reactor was developed. Simulations of the continuous flow experiments indicate that the model can describe the system well, and thus could be used in the design/scale-up of such reactors. The model suggests that a significant increase in the sulfate reduction capacity of the system is possible by increasing the volume of the bed relative to the total liquid volume of the system.

Membrane Separation in Green Chemical Processing

Abstract: This paper describes ideas together with preliminary experimental results for applying solvent nanofiltration to liquid phase organic synthesis reactions. Membranes for organic solvent nanofiltration have only recently (during the 1990s) become available and, to date, have been applied primarily to food processing (vegetable oil processing, in particular) and refinery processes. Applications to organic synthesis, even at a laboratory feasibility level, are few. However, these membranes have great potential to improve the environmental performance of many liquid phase synthesis reactions by reducing the need for complex solvent handling operations. Examples that are shown to be feasible are solvent exchanges, where it is desired to swap a high molecular weight molecule from one solvent to another between separate stages in a complex synthesis, and recycle and reuse of homogeneous catalysts. In solvent exchanges, nanofiltration is shown to provide a fast and effective means of swapping from a high boiling point solvent to a solvent with a lower boiling point—this is a difficult operation by means of distillation. Solvent nanofiltration is shown to be able to separate two distinct types of homogeneous catalysts, phase transfer catalysts and organometallic catalysts, from their respective reaction products. In both cases the application of organic solvent nanofiltration allows several reuses of the same catalyst. Catalyst stability is shown to be an essential requirement for this technique to be effective. Finally, we present a discussion of scale‐up aspects including membrane flux and process economics.

Batchwise and Continuous Nanofiltration of POSS-Tagged Grubbs–Hoveyda-Type Olefin Metathesis Catalysts

New molecular-weight-enlarged metathesis catalysts, which bear polyhedral oligomeric silsesquioxane (POSS) tags, were synthesized and characterized. The catalysts can be recovered from the reaction mixture by using nanofiltration techniques and can be reused. It was found that the membranes Starmem 228 and PuraMem 280 successfully separate the catalyst from the post-reaction mixtures to below 3 ppm. The application of these POSS-tagged catalysts in a continuous metathesis reaction was also investigated.

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

Membrane enhanced peptide synthesis

This communication reports a new technology platform that advantageously combines organic solvent nanofiltration (a newly emerging technology capable of molecular separations in organic solvents) with solution phase peptide synthesis-Membrane Enhanced Peptide Synthesis (MEPS).

Separation of reaction product and palladium catalyst after a Heck coupling reaction by means of organic solvent nanofiltration.

Organic solvent nanofiltration (OSN) is a recently commercialized technology, which we have used to develop a method for the separation of a target product and the Pd catalyst from a Heck coupling postreaction mixture. The experimental setup included commercially available polyimide copolymer membranes with molecular weight cut-off (MWCO) values in the range of 150-300 Da, acetone as the solvent, and a working pressure (N(2)) of 3 MPa. The investigation of the membranes revealed that a membrane with a MWCO of 200 Da provided quantitative retention of the Pd catalyst and quantitative recovery of the target product by means of a cross-flow dia-nanofiltration procedure.

Stability and Performance of Xanthobacter autotrophicus GJ10 during 1,2-Dichloroethane Biodegradation

ABSTRACT A nucleic acid-based approach was used to investigate the dynamics of a microbial community dominated by Xanthobacter autotrophicus GJ10 in the degradation of synthetic wastewater containing 1,2-dichloroethane (DCE). This study was performed over a 140-day period in a nonsterile continuous stirred-tank bioreactor (CSTB) subjected to different operational regimens: nutrient-limiting conditions, baseline operation, and the introduction of glucose as a cosubstrate. The microbial community was analyzed by a combination of fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE). Under nutrient-limiting conditions, DCE degradation was restricted, but this did not affect the dominance of strain GJ10, determined by FISH to comprise 85% of the active population. During baseline operation, DCE degradation improved significantly to over 99.5% and then remained constant throughout the subsequent experimental period. DGGE profiles revealed a stable, complex community, while FISH indicated that strain GJ10 remained the dominant species. During the addition of glucose as a cosubstrate, DGGE profiles showed a proliferation of other species in the CSTB. The percentage of strain GJ10 dropped to 8% of the active population in just 5 days, although this did not affect the DCE biodegradation performance. The return to baseline conditions was accompanied by the reestablishment of strain GJ10 as the dominant species, suggesting that this system responds robustly to external perturbations, both at the functional biodegradation level and at the individual strain level.

Insights into the Transport of Toluene and Phenol Through Organic Solvent Nanofiltration Membranes

Overall mass transfer coefficients (OMTCs) during membrane solvent extraction (MSE) for a microfiltration membrane Accurel, an organic solvent nanofiltration (OSN) membrane MPF 50, and silicone rubber were investigated with a hydrophilic solute (phenol) and a hydrophobic solute (toluene) in a membrane solvent extractor. Decanol was used to extract phenol or toluene from water. In MSE of phenol from water, MPF 50 has an OMTC intermediate between Accurel and silicone rubber, and has a much higher breakthrough pressure than Accurel. For MPF 50, it was observed that the solute–membrane interaction makes a major contribution to the mass transport of hydrophobic compounds, such as toluene, through the membrane. This suggests that solution-diffusion type models may be more appropriate than pore-flow models for describing transport of solvents through these kinds of membranes.

One step synthesis of MOF–polymer composites

Two different approaches for the one step synthesis of metal organic framework – polymer composites are discussed. An emulsion templating approach allows simultaneous MOF crystallization and polymerization of the internal phase of the emulsion resulting in the formation of porous MOF–polyHIPE composites.