Enhancement of the conversion of toluene by Pseudomonas putida F-1 using organic cosolvents.

Pseudomonas putida F-1 (ATCC700007) was used as a model organism in stirred tank reactors to study conversion enhancement of poorly soluble substrates by organic cosolvents. After a literature study, silicone oil was used as a solvent system to enhance the mass transfer rate. To study the benefits of the organic solvent addition, batch experiments were conducted in two side-by-side fermentation vessels (experimental and control) at three different levels of silicone oil (10, 30, and 50%). Results showed that the presence of silicone oil resulted in a 100% increase in the toluene mass transfer compared to the control. Experiments in continuous stirred-tank reactors showed that improved conversion could be obtained at higher agitation rates.

Influence of high biomass concentrations on alkane solubilities.

Alkane solubilities were measured experimentally for high-density biomass. The resulting Henry's law constants for propane were found to decrease significantly for both dense yeast suspensions and an actual propane-degrading biofilm consortium. At the biomass densities of a typical biofilm, propane solubility was about an order of magnitude greater than that in pure water. For example, a dense biofilm had a propane Henry's law constant of 0.09+/-0.04 atm m(3) mol(-1) compared to 0.6+/-0.1 atm m(3) mol(-1) measured in pure water. The results were modeled with mixing rules and compared with octanol-water mixtures. Hydrogels (agar) and salts decreased the alkane solubility. By considering a theoretical solubility of propane in dry biomass, estimates were made of intrinsic Henry's law constants for propane in pure yeast and biomass, which were 13+/-2 and 5+/-2 atm kg biomass mol(-1) for yeast and biofilm consortium, respectively.

In situ global method for measurement of oxygen demand and mass transfer.

Two aerobic microorganisms, Saccharomycopsis lipolytica and Brevibacterium lactofermentum, have been used in a study of mass transfer and oxygen uptake from a global perspective, using a closed gas system. Oxygen concentrations in the gas and liquid were followed using oxygen electrodes; the results allowed for easy calculation of in situ oxygen transport. The cell yields on oxygen for S. lipolytica and B. lactofermentum were 1.01 and 1.53 g/g, respectively. The mass transfer coefficient was estimated as 10/h at 500 rpm for both fermentations. The advantages with this method are noticeable, since the use of model systems may be avoided, and the in situ measurements of oxygen demand assure reliable data for scale-up.

Microbial removal of alkanes from dilute gaseous waste streams: kinetics and mass transfer considerations.

Treatment of dilute gaseous hydrocarbon waste streams remains a current need for many industries, particularly as increasingly stringent environmental regulations and oversight force emission reduction. Biofiltration systems hold promise for providing low-cost alternatives to more traditional, energy-intensive treatment methods such as incineration and adsorption. Elucidation of engineering principles governing the behavior of such systems, including mass transfer limitations, will broaden their applicability. Our processes exploit a microbial consortium to treat a mixture of 0.5% n-pentane and 0.5% isobutane in air. Since hydrocarbon gases are sparingly soluble in water, good mixing and high surface area between the gas and liquid phases are essential for biodegradation to be effective. One liquid-continuous columnar bioreactor was operated for more than 30 months with continued degradation of n-pentane and isobutane as sole carbon and energy sources. The maximum degradation rate observed in this gas-recycle system was 2 g of volatile organic compounds (VOC)/(m3.h). A trickle-bed bioreactor was operated continuously for over 24 months to provide a higher surface area (using a structured packing) with increased rates. Degradation rates consistently achieved were approximately 50 g of VOC/(m3.h) via single pass in this gas-continuous columnar system. Effective mass transfer coefficients comparable to literature values were also measured for this reactor; these values were substantially higher than those found in the gas-recycle reactor. Control of biomass levels was implemented by limiting the level of available nitrogen in the recirculating aqueous media, enabling long-term stability of reactor performance.

Experimental data analysis : an algorithm for determining rates and smoothing data.

Reaction rate determination from experimental data is generally an essential part of evaluating enzyme or microorganism growth kinetics and the effects on them. Commonly used methods include forward, centered, or backward finite difference equations using two or more data points. Another commonly applied method for determining rates is least-square regression techniques, and when the sought function is unknown, polynomials are often applied to represent the data. The cubic spline functions presented in this article represent a versatile method of evaluating rates. The advantage in using this method is that experimental error may be largely accounted for by the incorporation of a smoothing step of the experimental data without force-fitting of the data. It also works well when data are unevenly spaced (often the case for experiments running over long periods of time). The functions are easily manipulated, and the algorithm can be written concisely for computer programming. The development of spline functions to determine derivatives as well as integrals is presented.

Reductive microbial dechlorination of indigenous polychlorinated biphenyls in soil using a sediment-free inoculum.

In laboratory experiments, unagitated soil slurry bioreactors inoculated with micro-organisms extracted from polychlorinated biphenyl-contaminated (PCBs) sediments from the Hudson River were used to anaerobically dechlorinate PCBs. The onset of dechlorination activity was accelerated by the addition of certain organic acids (pyruvate and maleate) and single congeners (2,3,6-trichlorobiphenyl). Dechlorination was observed under several working conditions after 19 weeks of incubation with PCB-contaminated soil and nutrient solution. Best results showed a drop in average chlorine content from 4.3 to 3.6 chlorines per biphenyl due to a loss of m-chlorines. Soil used for these experiments was obtained from a PCB-contaminated (weathered Aroclor 1248) site at an electric power substation. Dechlorination was observed with no sediment particles or other matrix being added.

Sequential anaerobic-aerobic biodegradation of PCBs in soil slurry microcosms.

Many industrial locations have identified the need for treatment of polychlorinated biphenyl (PCB) wastes and remediation of PCB-contaminated sites. Biodegradation of PCBs is a potentially effective technology for treatment of PCB-contaminated soils and sludges; however, a practicable remediation technology has not yet been demonstrated. In laboratory experiments, soil slurry microcosms inoculated with microorganisms extracted from PCB-contaminated Hudson River sediments have been used for anaerobic dechlorination of weathered Aroclor 1248 in contaminated soil with a low organic carbon content. Anaerobic incubation was then followed by exposure to air, addition of biphenyl, and inoculation with Pseudomonas sp. LB400, an aerobic PCB degrader. The sequential anaerobic-aerobic treatment constituted an improvement compared to anaerobic or aerobic treatment alone by reducing the total amount of PCBs remaining and decreasing the tendency for end products to accumulate in humans. A 70% reduction of PCBs was observed during sequential treatment with products containing fewer chlorines and having a shorter half-life in humans than the original PCBs. The aerobic treatment alone was also quite effective as a stand-alone treatment reducing the PCBs by 67%. The results represent a case in which anaerobic river sediment organisms have been successfully transferred to a matrix free of river or lake sediments.

Performance of trickle-bed bioreactors for converting synthesis gas to methane.

Carbon monoxide, H2, and CO2 in synthesis gas can be converted to CH4 by employing a triculture of Rhodospirillum rubrum, Methanosarcina barkeri, and Methanobacterium formicicum. Trickle-bed reactors have been found to be effective for this conversion because of their high mass-transfer coefficients. This paper compares results obtained for the conversion of synthesis gas to CH4 in 5-cm- and 16.5-cm-diameter trickle-bed reactors. Mass-transfer and scale-up parameters are defined, and light requirements for R. rubrum are considered in bioreactor design.