Simultaneous saccharification and fermentation of lignocellulose

Simultaneous saccharification and fermentation (SSF) processes for producing ethanol from lignocellulose are capable of improved hydrolysis rates, yields, and product concentrations compared to separate hydrolysis and fermentation (SHF) systems, because the continuous removal of the sugars by the yeasts reduces the end-product inhibition of the enzyme complex. Recent experiments using Genencor 150L cellulase and mixed yeast cultures have produced yields and concentrations of ethanol from cellulose of 80% and 4.5%, respectively. The mixed culture was employed because B.clausenii has the ability to ferment cellobiose (further reducing end-product inhibition), while the brewing yeastS. cerevisiae provides a robust ability to ferment the monomeric sugars. These experimental results are combined with a process model to evaluate the economics of the process and to investigate the effect of alternative processes, conditions, and organisms.     

Adaptive optimal control of fed-batch alcoholic fermentation

An adaptive control scheme is developed for the optimization of a fed-batch ethanol production process. The fermentation process is modeled by an hybrid neural model combining mass balance equations and neural networks, used to represent the kinetic rates. The networks used, the functional link networks (FLN), allow the linear estimation of their parameters; this enables the re-estimation of the parameters at each sampling time, and thus the development of an adaptive optimal control scheme.     

Increased oxygen transfer in a yeast fermentation using a microbubble dispersion

A microbubble dispersion (MBD) was used to supply oxygen for aerobic fermentations in a standard 2 L stirred tank fermenter. The microbubble dispersion was formed using only surfactants produced naturally. Growth rates ofSaccharomyces cerevisiae cultures were found to be equal or greater with MBD sparging than with gas sparging. The oxygen transfer coefficent with MBD sparging was found to be 190/h and independent of impeller speed from 100–580 rpm. The oxygen transfer coefficient with air sparging rose from 55 to 132/h over the same range of impeller speeds. Power requirements for the fermenter systems were estimated.     

Xylose fermentation

The economic impact of conversion of xylose to ethanol for a wood-to-ethanol plant was examined, and the maximum potential reduction in the price of ethanol from utilization of xylose is estimated to be 0.42 per gallon from a base case price of0.42 per gallon from a base case price of 1.65. The sensitivity of the price of ethanol to the yield, ethanol concentration and rate of the xylose fermentation was also examined, and the price of ethanol is most affected by changes in yield and ethanol concentration, with rate of lesser importance. Current performances of various xylose conversion biocatalysts were analyzed, andC. shehatae andP. stipitis appear to be the best yeasts.     

Continuous fermentation of cellulosic biomass to ethanol

Experimental results are presented for continuous conversion of pretreated hardwood flour to ethanol. A simultaneous saccharification and fermentation (SSF) system comprised ofTrichoderma reesei cellulase supplemented with additional β-glucosidase and fermentation bySaccharomyces cerevisiae was used for most experiments, with data also presented for a direct microbial conversion (DMC) system comprised ofClostridium thermocellum. Using a batch SSF system, dilute acid pretreatment of mixed hardwood at short residence time(10 s, 220°C, 1% H₂SO₄) was compared to poplar wood pretreated at longer residence time (20 min, 160°C, 0.45% H₂SO₄). The short residence time pretreatment resulted in a somewhat (10–20%) more reactive substrate, with the reactivity difference particularly notable at low enzyme loadings and/or low agitation. Based on a preliminary screening, inhibition of SSF by byproducts of short residence time pretreatment was measurable, but minor. Both SSF and DMC were carried out successfully in well-mixed continuous systems, with steady-state data obtained at residence times of 0.58–3 d for SSF as well as 0.5 and 0.75 d for DMC. The SSF system achieved substrate conversions varying from 31% at a 0.58-d residence time to 86% at a 2-d residence time. At comparable substrate concentrations (4–5 g/l) and residence times (0.5–0.58 d), substrate conversion in the DMC system (77%) was significantly higher than that in the SSF system (31%). Our results suggest that the substrate conversion in SSF carried out in CSTR is relatively insensitive to enzyme loading in the range 7–25 U/g cellulose and to substrate concentration in the range of 5–60 g/L cellulose in the feed.     

Improved oxygen delivery in a continuous-roller-bottle reactor

Variations to the original aeration system in a continuous roller bottle reactor of novel design have been tested and compared for optimal oxygen (O) delivery. Reactor operating parameters that affect O transfer are rotation rate, liquid-volume level, fresh-feed rate, and supplementary-aeration rate. Design modifications to enhance gas-liquid O transfer include the addition of wall baffles and center baffles. The number and location of each of these baffles are compared for their effect on k_La values in the reaction chamber. The liquid feed into the system has been modified to improve the axial liquid mixing and O transfer.     

Extractive fermentation of acetic acid

In this technoeconomic evaluation of the manufacture of acetic acid by fermentation, the use of the bacterium:Acetobacter suboxydans from the old vinegar process was compared with expected performance of the newerClostridium thermoaceticum bacterium. Both systems were projected to operate as immobilized cells in a continuous, fluidized bed bioreactor, using solvent extraction to recover the product. Acetobacter metabolizes ethanol aerobically to produce acid at 100 g/L in a low pH medium. This ensures that the product is in the form of a concentrated extractable free acid, rather than as an unextractable salt. Unfortunately, yields from glucose by way of the ethanol fermentation are poor, but near the biological limits of the organisms involved.     

Computer simulation of the dartmouth process for separation of dilute Ethanol/Water mixtures

High energy costs are associated with the recovery of ethanol from fermentation broths. This paper discusses a computer simulation of the Dartmouth Process, which aims to reduce these costs by the use of IHOSR distillation, extensive heat integration, and extractive distillation using a salt. To resolve the uncertainty in modeling alcohol-water-salt vapor-liquid equilibrium, a new and more accurate activity coefficient model was used. An Aspen™ model was used to generate capital and energy costs for a range of ethanol concentrations in the feed. Simulation results show that the Dartmouth Process offers substantial economic advantages over benzene azeotropic distillation, particularly at low feed concentrations.     

A novel fermentation pathway in anEscherichia coli mutant producing succinic acid,acetic acid,and ethanol

Escherichia coli strain NZN111, which is unable to grow fermentatively because of insertional inactivation of the genes encoding pyruvate: formate lyase and the fermentative lactate dehydrogenase, gave rise spontaneously to a chromosomal mutation that restored its ability to ferment glucose. The mutant strain, named AFP111, fermented glucose more slowly than did its wild-type ancestor, strain W1485, and generated a very different spectrum of products. AFP111 produced succinic acid, acetic acid, and ethanol in proportions of approx 2:1:1. Calculations of carbon and electron balances accounted fully for the observed products; 1 mol of glucose was converted to 1 mol of succinic acid and 0.5 mol each of acetic acid and ethanol. The data support the emergence in E.coli of a novel succinic acid:acetic acid:ethanol fermentation pathway.     

Simulation and optimization of a cell recycle system

This article describes the simulation and subsequent optimization of a cell recycle fermentar and membrane filter in a wheat-to-ethanol process. The optimum conditions with respect to economic operating performance were found using a search method similar to steepest gradients. Optimum fermentor cell and inlet substrate concentrations were 54 and 127 g/L, respectively. The study also involved the effects of parameter variations on net cost, and the effects of raw material and product prices on profitability. The net cost was found to be most sensitive to the product yield and wheat costs.     

Optimization of sucrose ethanol fermentation for K,Na, Ca,and cu metal contents

The effect of the trace metals Cu, K, Na, and Ca, separately or in mixture, on fermentation time, ethanol production rate, and cell growth in the fermentation of synthetic media containing sucrose is discussed. The results are related to the range of contents found in raw materials, molasses and raisins, in order to determine their optimum concentrations for alcohol production.     

A mathematical model of ethanol fermentation from cheese whey

The cybernetic approach to modeling of microbial kinetics in a mixedsubstrate environment has been used in this work for the fermentative production of ethanol from cheese whey. In this system, the cells grow on multiple substrates and generate metabolic energy during product formation. This article deals with the development of a mathematical model in which the concept of cell maintenance was modified in light of the specific nature of product formation. Continuous culture data for anaerobic production of ethanol byKluyveromyces marxianus CBS 397 on glucose and lactose were used to estimate the kinetic parameters for subsequent use in predicting the behavior of microbial growth and product formation in new situations.     

A new kinetic approach to the fermentation of multisubstrate complex media

Ethanol production from natural complex media has been studied in this work. A new kinetic approach is presented for two-substrate media, such as hardwood hemicellulose hydrolysate, which predominantly consists of a mixture of xylose and glucose. It has been founded on the supposition that the whole ethanol production and biomass growth can be subdivided into two separated components imputable to glucose and xylose consumptions, respectively. A model describing the continuous fermentation in CSTR byPachysolen tannophilus has been also presented, and experimentally verified; it takes into account the different substrate consumption rates of these sugars contained in both natural and synthetic complex media.     

Amelioration of methane yield in cheese whey fermentation by controlling the pH of the methanogenic stage

A two-stage, no-mix anaerobic digester of 145 L capacity was used to investigate the effect of controlling the pH of the methanogenic stage on the biogas production and the pollution potential reduction of acid cheese whey. The digester was operated at a 15-d hydraulic retention time, and a temperature of 35°C. Controlling the pH of the methanogenic stage increased the biogas production rate and methane yield by 77.77 and 289.00%, respectively. Reductions of up to 32.19, 44.44, and 35.86% in the COD, solids and nitrogen were achieved.     

Synthesis of Cyclodextrin Glucosyl Transferase byBacillus cereus for the production of cyclodextrins

A potent indigenous bacillus isolate identified asBacillus cereus (RJ-30) was found to produce Cyclodextrin Glucosyl Transferase (CGTase) extracellularly. Process optimization of various fermentation parameters has been established for optimal growth of bacillus and the maximum enzyme synthesis. The organism had the highest specific growth rate (0.7μ) with a generation time of 1 h in glucose containing medium at the conditions of pH 7.0, 37°C at 300 rpm, 1.5 vvm of agitation, and aeration. At these conditions, it exhibited the maximum activity of 54 U/mL at the synthesis rate of 2.7 U/L/h. CGTase was produced from the early exponential growth and peaked during the midsporulating stage of about 16 h thereafter maintained at the same level of 50 U/mL. Saccharides containing media were better inducers than starch, and the influence of carbohydrate substrates has shown that enzyme synthesis is promoted by xylose (65 U/mL) and, more remarkably, by the supplementation of wheat bran extract in glucose medium (106 U/mL). This organism produced CGTase stably in a chemostat culturing over a period of 400 h with a maximum productivity of 5.4 kU/L/h (threefold higher than obtained in batch culturing [1.75 kU/L/h]). Comparatively, CGTase was produced by immobilized cells in a continuous fluidized bed reactor for over approx 360 h, at a relatively high dilution rate of 0.88 h⁻¹ resulting in the productivity of 23.0 kU/L/h.     

Purification and partial characterization of two lectin isoforms fromCratylia mollis mart. (camaratu bean)

Two additional electrophoretically distinct molecular forms, isoforms (iso) 2 and 3, with lectin properties were isolated fromCratylia mollis Mart, seeds (FABACEAE), by extraction with 0.15M NaCl and ammonium sulfate fractionation, followed by chromatography on Sephadex G-75 and Bio-Gel P-200 (iso 2), as well as CM-Cellulose and Sephadex G-75 (iso 3). Both isoforms were human group nonspecific and showed distinct specificity. Polyacrylamide gel electrophoresis resolved iso 2 and 3 in polypeptides of apparent mol wts 60 and 31 kDa, respectively; a distinct isoelectric focusing pattern was obtained for iso 2 and 3, under denaturing and reducing conditions.     

Heterogeneous modeling for the alcoholic fermentation process

In this paper a heterogeneous model is developed for the alcoholic fermentation process. The model is expressed in terms of intracellular and extracellular concentrations of ethanol and sugar as well as biomass concentration as state variables. The model takes into consideration the floc size and the mass transfer rates of both ethanol and sugar. The intrinsic kinetics of the process used in the model was developed from published data which includes the inhibitory effects of ethanol and cells. The model development is achieved through comparison with one set of experimental results given by Novak et al. (1). The model is then checked against two other sets of experimental results. The developed model is also used to simulate an industrial fed-batch fermentar.     

Effects of arachidonic acid concentration on prostaglandin biosynthesis and feasibility of semibatch processes

The reaction characteristics of prostaglandin E2 biosynthesis by PGH-synthase and PGE2 isomerase and the substrate dependency of this biosynthesis were studied. The activity of PG-synthases was blocked by the inhibitory action of one or more byproducts, probably resulting from the action of PGH-synthase. This inhibitory action then appeared to be partly reversible, indicating that the substrate and the inhibitor compete for the catalytic sites. According to these findings, the feasibility of a successful semibatch biosynthesis was investigated. A combination of the substrate concentration reducing procedure and the semibatch process resulted in an about 3.5-fold higher increase in the total amount of PGE2 formed in comparison with the batch results obtained at the substrate concentration of 1.0 mg/cm3. Since the cost of enzyme is a governing factor in this biosynthesis, development of semibatch biosynthesis of PGE2 becomes a matter of economic importance.