K.T. Klasson

Biological conversion of coal and coal-derived synthesis gas

Recent research has resulted in a number of promising biological pathways to produce clean fuels from coal. These processes all involve two or more steps: either the biosolubilization of coal, followed by bioconversion to ethanol or methane; or conversion of coal to synthesis gas, followed by bioconversion into alcohols or methane. Sulfur may also be removed from the solubilized coal or synthesis gas in a separate, or concurrent, biological step. This paper presents research results from both the direct and indirect conversion of coal to liquid fuels using biological processes. A review of direct conversion techniques in producing liquid fuels from coal in a serial conversion process is presented. In addition, bioreactor design data for the conversion of CO, CO2 and H2 in synthesis gas by Clostridium ljungdahlii in both batch and continuous culture are reviewed and discussed.

The effects of furfural on ethanol production by saccharomyces cereyisiae in batch culture

Browning reaction products such as furfural and 5-hydroxy-methyl-furfural (HMF) have been shown to inhibit microbial growth and metabolism in ethanol fermentations using Saccharomyces cerevisiae. This paper quantifies the extent of furfural inhibition on yeast growth, glucose utilization, and ethanol production as a function of inoculum size (0.1–9 gl−1. Batch culture experiments were conducted using furfural concentrations in the range of 0 to 2.0 gl−1. and mathematical correlations were proposed and tested. The results indicate that the specific growth rate decreased with increasing furfural concentration and inoculum size, while the maintenance coefficients were unaffected. The apparent and true cell yield coefficients on glucose were depressed with the addition of furfural. Specific production rates were unaffected at the furfural levels used but ethanol inhibition was apparent. The specific production rate was less inhibited by ethanol at higher inoculum sizes. Global specific productivities were not affected by the presence of furfural. At a 0.1 gl−1. inoculum size, furfural depletion was complete within 15–20 h, depending upon the furfural concentration employed. At higher inoculum levels (2–9 gl−1. all furfural was depleted in less than 5 h.

Bioreactor design for synthesis gas fermentations

Abstract Bacterial cultures have been isolated for the conversion of synthesis gas (CO, H2 and CO2) into ethanol or methane. These heterogeneous reactions require the transport of substrate through the gas phase, across the interface into the liquid phase, and to the solid micro-organisms. The reactions are generally mass transfer limited due to very low gas solubilities. Bioreactors must maximize mass transport, while achieving high cell densities to promote fast reaction. This paper examines the performance of both dispersed gas phase systems (continuous stirred-tank reactor) and dispersed liquid phase systems (immobilized cell reactor) under mass transfer controlled and non-mass transfer controlled conditions. Mass transfer coefficients are determined and models are developed to predict bioreactor behaviour. Retention times of a few minutes are achieved for these gaseous substrate fermentations.

Biological conversion of synthesis gas into fuels

Liquid and gaseous fuels may be produced from coal biologically by the indirect conversion of coal synthesis gas. Methane has been produced from synthesis gas using acetate and CO2/H2 as intermediates, utilising a number of CO-utilising and methanogenic bacteria. Also, a bacteria has been isolated from natural inocula that is capable of producing ethanol from synthesis gas through indirect liquefaction. This presentation summarises the research to optimise the performance of these cultures. These conversions, involving H2 and CO which are only slightly soluble, are severely mass transfer limited, and methods to enhance mass transport are examined. Experimental results and models for several reactor designs, including CSTR and packed columns, are presented and discussed.

Kinetics of light limited growth and biological hydrogen production from carbon monoxide and water by Rhodospirillum rubrum

The photosynthetic bacterium Rhodospirillum rubrum was studied for its capability of converting CO and water to CO2 and H2 by the water gas shift reaction in batch culture. The specific CO uptake rates were determined and the effects of elevated CO pressures modeled. The results indicate that the specific uptake rate may be related to dissolved CO tension, with substrate inhibition occurring according to Andrews modification of the Monod equation. The yield of H2 from CO and H2O by R. rubrum was 0.87 mol mol−1, or 87% of theoretical. In addition, growth on acetate was studied at light intensities ranging from 100–800 lux in batch culture. Modeling results indicate that growth is dependent upon light intensity according to a Monod-type relationship. The cell yields on acetate and ammonia were 0.42 g g−1 and 13 g g−1, respectively.

Mass-transfer and kinetic aspects in continuous bioreactors usingRhodospirillum rubrum

In designing bioreactors for the conversion of sparingly soluble gases, both mass transfer and kinetic effects must be considered.Rhodospirillum rubrum, an anaerobic photosynthetic bacterium capable of carrying out the water gas shift reaction, is an ideal organism for studying the relative importance of mass-transfer and kinetics since the cell concentration in continuous reactors employingR. rubrum may be regulated by the quantity of light supplied to the bacterium. This article addresses the performance ofR. rubrum in continuous stirred-tank and trickle-bed reactors, with particular attention given to the importance of mass-transfer and reaction kinetics in modeling reactor performance. Estimates of mass-transfer coefficients are made for a trickle-bed reactor system based upon reactor performance equations and experimental observations.

Sulfur gas tolerance and toxicity of CO-utilizing and methanogenic bacteria

Anaerobic bacteria have been shown to be capable of converting CO, H2, and CO2 in synthesis gas to valuable products, such as acetate, methane, and ethanol. However, synthesis gas also contains small quantities of sulfur gases such as H2S and COS, that may inhibit the performance of these organisms. This paper compares the performance of several CO-utilizing and methanogenic bacteria in converting CO, CO2, and H2 to products in the presence of various concentrations of H2S and COS. The sulfur gas toxicity levels, growth, substrate uptake, and product formation for each organism are compared.

Biological conversion of poultry processing waste to single cell protein

Abstract In the processing of poultry for the production of prepared foods such as soups and frozen dinners, waste-water is generated containing significant quantities of fats, protein and starchy materials. These materials must be removed from the wastewater before it is discharged. Typical recovery consists of removing the solids through a combination of dissolved air flotation and filtration. The solids can then be rendered and utilized as poultry feed. This paper investigates an alternative to traditional processing in biologically producing valuable single cell protein from poultry processing waste. The results of fermentation experiments to produce single cell protein by both direct and indirect routes are presented.

Bioreactors for synthesis gas fermentations

Abstract Bacterial cultures have been isolated for the conversion of synthesis gas (CO, H2 and CO2) into ethanol or methane. These heterogeneous reactions require the transport of substrate through the gas phase, across the interface into the liquid phase, and to the solid microorganisms. The reactions are generally mass transfer limited due to very low gas solubilities. Bioreactors must maximize mass transport, while achieving high cell densities to promote fast reaction. This paper examines the performance of both dispersed gas phase systems (CSTR) and dispersed liquid phase systems (immobilized cell reactors) under mass transfer controlled and non-mass transfer controlled conditions. Mass transfer coefficients are determined and models are developed to predict bioreactor behavior. Retention times of a few minutes are achieved for these gaseous substrate fermentations.

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 ofRhodospirillum rubrum, Methanosarcina barken, andMethanobacterium 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 forR. rubrum are considered in bioreactor design.