Abstract: The cost and availability of petroleum and natural gas has generated interest in bioconversion processes that utilize renewable biomass resources for the production of fuels and chemical feedstocks. The bioconversion of biomass to ethanol via anaerobic fermentations offers the promise of renewable liquid fuel and renewable chemical feedstocks. The purpose of this presentation is to review some of the recent studies in my laboratory on thermophilic ethanol fermentations. The emphasis of this review will be on understanding fundamental aspects of the physiology and biochemistry of thermophilic anaerobes that may be of applied interest in developing bioconversion technology for alcohol production. Most of the findings summarized here represent material published elsewhere (1–22).

Abstract: Native wheat straw (WS) was pretreated with various concentrations of H2SO4 and NaOH followed by secondary treatments with ethylene diamine (EDA) and NH4OH prior to enzymatic saccharification. Conversion of the cellulosic component to sugar varied with the chemical modification steps. Treatment solely with alkali yield 51–75% conversion, depending on temperature. Acid treatment at elevated tempeatures showed a substantial decrease in the hemicellulose component, whereas EDA-treated WS (acid pretreated) showed a 69–75% decrease in the lignin component. Acid-pretreated EDA-treated straw yielded a 98% conversion rate, followed by 83% for alkali–NH4OH treated straws. In other experiments, WS was pretreated with varying concentration of H2SO4 or NaOh followed by NH4OH treatment prior to enzymatic hydrolysis. Pretreatment of straw with 2% NaOH for 4 h coupled to enzymatic hydrolysis yield a 76% conversion of the cellulosic component. Acid–base combination pretreatment yielded only 43% conversions. A reactor column was subsequently used to measure modification–saccharification–fermentation for wheat straw conversion on a larger scale. Thirty percent conversions of wheat straw cellulosics to sugar were observed with subsequent fermentation to alcohol. The crude cellulase preparation yielded considerable quantities of xylose in addition to the glucose. Saccharified materials were fermented directly with actively proliferating proliferating yeast cells without concentration of the sugars.

Abstract: A total of 8 yeast and microbial cultures have been grown in the extract derived from the tubers of Jerusalem artichoke (Helianthus tuberosus) and screened according to the following optimization criteria: rates and yields of ethanol production, rates and yields of biomass production, and % of original sugars utilized during fermentation. Batch growth kinetic parameters were also determined for the cultures studied.

Abstract: Daucuscarota cells immobilized in a Ca-alginate performed the bioconversion of gitoxigenin to 5β-hydroxygitoxigenin in a column bioreactor. The smooth spherical shape of the alginate beads was preserved for more than three weeks. The bioreactor was functional for more than thirty days as detected by the bioconversion activity. The rate of bioconversion was influenced by means of aeration.

Abstract: The gases CO, CO2, and H2 were used as substrates in anaerobic fermentations producing organic acids. Various mixed bacterial sources were used, including sewage sludge digester effluent, rabbit feces, and soil. Nonsterile microorganism selection was carried out using CO2/H2 and CO/H2 as the primary carbon and energy sources. Cultures were grown in specially designed, high-pressure (to 70 psig) flasks. Methanogenic bacteria were eliminated from the cultures. Liquid products of the fermentations were acetic through caproic acids, with the even-numbered acids predominating. Carbon balances showed conclusively that acetic acid was formed from carbon contained in the CO or CO2 feed gas. Measurements made included rates of acid product formation, cell density, and degree of gas utilization. Limited characterization of the microorganisms was also performed. Production of organic acids by mixed culture inocula from CO2/H2 or CO/H2 had not been reported previously. Application of this work is to the production of organic chemicals from synthesis gas (SNG), produced by the gasification of fossil fuels (peat, lignite, and various ranks of coals), biomass (agricultural and forest residues, and various biomass crops grown expressly for energy recovery), and municipal solid waste. (Refs. 15).

Abstract: Microbial cells were gel-entrapped with photo-crosslinkable resin prepolymers or urethane prepolymers, respectively. The resulting gels have different tailor-made hydrophobic or hydrophilic character. They were used for successful bioconversion of hydrophobic steroids and terpenoids in watersaturated mixtures of organic solvents. The experiments show the influence of the hydrophobicity of the gels and the polarity of the solvent mixtures, respectively. Use of hydrophobic gels and less polar solvents is preferable for bioconversion of hydrophobic compounds. The selective formation of a desired product among diverse products from a single substrate by appropriate use of hydrophobic or hydrophilic gels is possible. In each case, tests should be made to select the appropriate gel and solvent mixture. Bioconversions tested are: dehydroepiandrosterone to 4-androstene-3,17-dione; cholesterol to cholestenone; β-sitosterol to β-sitostenone; stigmasterol to stigmastenone; pregnenolone to progesterone; testosterone to Δ1-dehydrotestosterone or 4-androstene-3,17-dione, respectively; all with immobilized cells of Nocardia rhodocrous; and stereoselective hydrolysis of dl-menthyl-succinate to yield l-menthol with immobilized cells of Rhodotorula minuta var. texensis.

Abstract: Cereal grain straws are converted into protein-enriched products having significnt amounts of microbial biomass in the form of the fungus, Chaetomium cellulolyticum.

Abstract: Three different techniques having complementary features have been applied to the bioconversion of cellulose to ethanol: (1) membrane biotechnology involving ultrafiltration and reverse osmosis allows conversion of particulate substrates with soluble biocatalysts, continuous removal of inhibitory products, and low-energy upgrading of dilute product streams; (2) co-immobilization of enzymes and microorganisms results in new metabolic combinations, allowing microbial conversion of nondigestible substrates, removal of inhibitory intermediates, and continuous operation; (3) aqueous two-phase systems are biocompatible and allow extractive bioconversions in that soluble biocatalysts and particulate substrates can be partitioned to one phase while products can be partitioned and upgraded in the other phase.

Abstract: A review on the production of EtOH by fermentative and synthetic methods and its industrial uses is presented.

Abstract: After low cost, low energy pretreatment, lignocellulose can be converted directly to volatile (C/sub 2/-C/sub 6/) organic acids by mixed-culture acidogenic fermentation. The principal components of lignocellulose (pectins, hemicellulose, cellulose, and lignin) are all converted to organic acids in high yields. Esterification from dilute aqueous solutions using novel techniques based on adsorption, solvent extraction, or biochemical conversion could be an important method for recovering these acids and simultaneously producing liquid fuels or chemical feedstocks. Uses of organic acid esters and conceptual biomass conversion processes are outlined. The significance of these processes for substantially increasing liquid fuel productivity from biomass feedstocks are discussed.

Abstract: The technological and economic feasibility of producing some selected chemicals by fermentation is discussed: acetone, butanol, acetic acid, citric acid, 2,3-butanediol, and propionic acid. The demand for acetone and butanol has grown considerably. They have not been produced fermentatively for three decades, but instead by the oxo and aldol processes. Improved cost of fermentative production will hinge on improving yields and using cellulosic feedstocks. The market for acetic acid is likely to grow 5% to 7%/yr. A potential process for production is the fermentation of hydrolyzed cellulosic material to ethanol followed by chemical conversion to acetic acid. For about 50 years fermentation has been the chief process for citric acid production. The feedstock cost is 15% to 20% of the overall cost of production. The anticipated 5%/yr growth in demand for citric acid could be enhanced by using it to displace phosphates in detergent manufacture. A number of useful chemicals can be derived from 2,3-butanediol, which has not been produced commercially on a large scale. R and D are needed to establish a viable commercial process. The commercial fermentative production of propionic acid has not yet been developed. Recovery and purification of the product require considerable improvement. Other chemicals suchmore » as lactic acid, isopropanol, maleic anhydride, fumarate, and glycerol merit evaluation for commercial fermentative production in the near future.« less

Abstract: A discussion is given on development of the technology to produce potable grade ethanol from whey.

Abstract: Progress in the following process development studio is reported: economic evaluation of hydrolysis and ethanol fermentation schemes, economic evaluation of alternative fermentation processes, raw materials evaluation, and evaluation of pretreatment process. Microbiological and enzymatic studies reported are: production of cellulase enzyme from high yielding mutants, hydrolysis reactor development, xylose fermentation, and xylanese production. Fermentation and separation processes include: process development studies on vacuum fermentation and distillation, evaluation of low energy separations processes, large scale hollow fiber reactor development. (MHR)

Abstract: A schematic representation of the variety of products which can be obtained by microbial conversion of cellulose is presented. Alkaline pre-treatment has been used after milling in all the experiments. Solka-floc or sugarcane bagasse was used as sources of cellulose. A cellulolytic strain of Aspergillus terreus (ATCC 30514) was cultivated in batch-, fed batch and continuous culture up to 7 liter stirred tank fermenter. The general growth characteristics were determined by growing on glucose. Results of experiments on the growth of A. terreus for production of biomass on Solka-floc or Sugarcane bagasse are given, also the ability of crude cellulases to produce sugar syrups by enzymatic hydrolysis of cellulose has been evaluated.

Abstract: Staged autohydrolysis of wood at 175 to 225/sup 0/C without chemical addition results in polysaccharide solubilization. The first stage at 175/sup 0/C solubilized hemicellulose, and subsequent stages at 200 to 225/sup 0/C solubilized cellulose, but carbohydrate decomposition also occurred, yielding furan compounds. Over 70% of the wood carbohydrates were solubilized in this three-stage treatment. The anaerobic bioconvertibility of the autohydrolysis soluble product was evaluated with both batch assays and continuously fed anaerobic filter treatment, and both gave comparable results of 76% bioconvertibility to methane of three-stage autohydrolysis soluble product chemical oxygen demand (COD), or 26% bioconversion efficiency referenced to the original wood COD against 2% bioconversion without pretreatment.

Abstract: In the bioconversion of solid agricultural biomass to energy carriers one can distinguish various stages: liquefaction, saccharification and fermentation to the desired fuel. Liquefaction and saccharification are indispensable if immobilized micro-organisms or enzymes are used for the fermentation step. Sugar-beet pulp which is a waste product of the beet sugar industry was chosen as a model for agricultural biomass. The pulp was treated with a combination of pectolytic and cellulolytic enzymes. This resulted in almost complete liquefaction and saccharification. The polygalacturonase from the pectic enzyme plays a major role during the liquefaction process; its optimal action is at pH 3,5. The solubilized neutral sugars were in monomeric form. The sugar solution consisted of glucose, fructose, arabinose and galacturonic acid. Cellulose was hydrolysed extensively: 91% was converted to glucose. The hemi-cellulose fraction, which consists mainly of araban was hydrolysed for 93%. From the pectic substances 91% was brought into solution. Residual saccharose of the pulp was converted to glucose and fructose. The obtained sugar solution is a versatile product and can be used for subsequent conversion to several fuels like ethanol, hydrogen or methane.

Abstract: Two kinds of bacteria were isolated from soil as biotransformers of dehydrocholic acid (DHCA) to 12-ketochenodeoxycholic acid (KCDCA), and identified as Brevibacterium fuscum and Lactobacillus xylosus, respectively. DHCA was converted via 7, 12-diketolithocholic acid (DKLCA) to KCDCA by both strains, and the product and the intermediate were purified and chemically identified. By using an immobilized cell system of B. fuscum stable production of KCDCA was observed over more than 600 hrs with a fair yield. On the other hand, a two-stage continuous culture of L. xylosus was conducted to verify the possibility of increasing the yield of KCDCA by changing pH and dilution rate as operational parameters. KEYWORDS Chenodeoxycholic acid; dehydrocholic acid; 7,12-diketolithocholic acid; 12-ketochenodeoxycholic acid; cholic acid; immobilized whole-cell system; continuous culture system; continuous biotransformation; bioconversion.