John W. Barton

Influence of high biomass concentrations on Alkane solubilities

Alkane solubilities were measured experimentally for high‐density biomass. The resulting Henrys 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 Henrys law constant of 0.09 ± 0.04 atm m3 mol−1 compared to 0.6 ± 0.1 atm m3 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 Henrys 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.

Reductive Microbial Dechlorination of Indigenous Polychlorinated Biphenyls in Soil Using a Sediment-Free Inoculum

In laboratory experiments, unagitated soil slurry bioreactors inoculated with microorganisms 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.

Nomenclature and Methodology for Classification of Nontraditional Biocatalysis

Recent nontraditional biocatalytic techniques, particularly those which have involved introduction of enzymes into organic liquid phases, have revolutionized the way we think about biocatalysis. Within the past decade, a variety of research programs and open literature publications have arisen investigating nonaqueous enzyme activities and the potential for using such processes commercially. However, because of the wide variety of reaction and reactor types possible, as well as vague and easily misinterpreted terminology, it is often difficult to ascertain which reaction configurations are being studied and how these may be contrasted with similar research. We propose a systematic nomenclature and vocabulary such that reaction types can be quickly classified and compared with other nontraditional systems. The approach we have taken to distinguish between systems is primarily dependent upon the phase in which each of the critical reaction components (biocatalyst, reactant(s), and product(s) ) is present. Possible resident phases include aqueous (A), organic (O), vapor (V), and supercritical (SC) . With this system, a reaction scheme may be classified with a three‐character identifier, such as AAO (a system in which the enzyme and substrate are present in an aqueous phase and the product is recovered from an organic phase) . Special cases, such as when the biocatalyst is immobilized or the product forms an insoluble precipitate, are also discussed in the context of this nomenclature. This developed nomenclature and vocabulary also allow categorization of biocatalytic bioprocessing into two distinct classes: traditional (aqueous phase only) and nontraditional, the latter of which may be further subdivided into nonaqueous, aqueous, and supercritical biocatalysis. Such categorization provides a cohesive methodology by which to classify new work within the nontraditional arena, as well as to broaden or refine current research. Furthermore, this paper provides a technology roadmap which outlines nontraditional areas and their associated development issues which still require examination, in terms of both bridging and fundamental research, before these techniques will be adopted by the private sector.

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.

Microbial Removal of Alkanes from Dilute Gaseous Waste Streams: Mathematical Modeling of Advanced Bioreactor Systems

Many industries generate volatile organic compounds (VOCs) in dilute streams which must be removed before being released into the environment. Mathematical models for biological filters which can remediate waste streams are useful both as predictive tools and as a means to better understand the fundamental processes involved. Optimization of the system also necessitates a better understanding of the mechanisms by which biofilters work and can be approached through modeling and maximizing appropriate conditions for removal. In a trickle-bed bioreactor, VOCs (n-pentane and isobutane) were passed over a biofilm-coated packing which degraded the VOCs. Bacterial growth was controlled via liquid nutrient-limited media trickled through the reactor. Results from this trickle-bed system were analyzed by applying a simple mathematical model to accurately describe the processes which are believed to play important roles. The model was based on a two-step process: mass transfer in which the VOCs diffuse into the liquid biofilm, and kinetics by which VOCs are degraded by the biofilm. Modeling results revealed that both kinetic and mass transfer resistances were significant under typical operating conditions.

Solubility of toluene, benzene and TCE in high-microbial concentration systems.

We report measurements of solubility limits for benzene, toluene, and TCE in systems that contain varying levels of biomass up to 0.13 g mL(-1) for TCE and 0.25 g mL(-1) for benzene and toluene. The solubility limit increased from 21 to 48 mM when biomass (in the form of yeast) was added to aqueous batch systems containing benzene. The toluene solubility limit increased from 4.9 to greater than 20mM. For TCE, the solubility increased from 8mM to more than 1000 mM. Solubility for TCE (trichloroethylene) was most heavily impacted by biomass levels, changing by two orders of magnitude as the microbial concentrations approach those in biofilms.

An Integrated Treatment System for Polychlorinated Biphenyls Remediation

Bioremediation is an environmental biotechnology with promise for promoting a sustainable environment. Bioremediation makes use of natural processes and applies the metabolic properties of microorganisms for transforming contaminants to forms that are harmless in the environment. The added capability of biotechnology for tailoring microbial processes to specific problems expands the potential of bioremediation for encouraging a sustainable environment. The process for the biotransformation of polychlorinated biphenyls (PCB) described in this paper is a good example of the enhancement of bioremediation through the tools of biotechnology.