Fuel ethanol production: process design trends and integration opportunities.

Past technoeconomic modeling work has identified the relatively large contribution that enzymatic hydrolysis adds to the total cost of producing ethanol from lignocellulosic substrates. This cost was primarily due to the high concentration of enzyme and long incubation time that was required to obtain complete hydrolysis. Although enzyme and substrate concentration and end-product inhibition influenced the rate of hydrolysis, the effect was less pronounced during the initial stages of hydrolysis. During this time most of the cellulases were adsorbed onto the unhydrolyzed residue. By recycling the cellulases adsorbed to the residual substrate remaining after an initial 24 h, a high rate of hydrolysis, with low overall residence time and minimal cellulase input, could be achieved for several rounds of enzyme recycle. A comparison of the front end (pretreatment, fractionation, and hydrolysis) of a softwood/hardwood to ethanol process indicated that the lignin associated with the softwood-derived cellulose stream limited the number of times the cellulose containing residue could be recycled. (c) 1996 John Wiley & Sons, Inc.

Factors affecting cellulose hydrolysis and the potential of enzyme recycle to enhance the efficiency of an integrated wood to ethanol process

A method for extracting nucleic acids from a biological material such as blood comprises contacting the mixture with a material at a pH such that the material is positively charged and will bind negatively charged nucleic acids and then eluting the nucleic acids at a pH when the said materials possess a neutral or negative charge to release the nucleic acids The nucleic acids can be removed under mildly alkaline conditions to the maintain integrity of the nucleic acids and to allow retrieval of the nucleic acids in reagents that are immediately compatible with either storage or analytical testing

Isolation of nucleic acids

https://cyberleninka.org/article/n/642770.pdf

Lipid recovery from wet oleaginous microbial biomass for biofuel production: A critical review

The present work reviews and critically discusses the aspects that influence yeast flocculation, namely the chemical characteristics of the medium (pH and the presence of bivalent ions), fermentation conditions (oxygen, sugars, growth temperature and ethanol concentration) and the expression of specific genes such as FLO1, Lg-FLO1, FLO5, FLO8, FLO9 and FLO10. In addition, the metabolic control of loss and onset of flocculation is reviewed and updated. Flocculation has been traditionally used in brewing production as an easy and off-cost cell-broth separation process. The advantages of using flocculent yeast strains in the production of other alcoholic beverages (wine, cachaca and sparkling wine), in the production of renewal fuels (bio-ethanol), in modern biotechnology (production of heterologous proteins) and in environmental applications (bioremediation of heavy metals) are highlighted. Finally, the possibility of aggregation of yeast cells in flocs, as an example of social behaviour (a communitarian strategy for long-time survival or a means of protection against negative environmental conditions), is discussed.

https://sfamjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2672.2010.04897.x

Flocculation in Saccharomyces cerevisiae: a review.

The desorption of Trichoderma reesei cellulase from Avicel by a wide range of desorbents was measured. Emphasis was placed on desorption at alkaline pH. A maximum desorption of 65-68% Avicelase activity was achieved by contact with NaOH, pH 10.0, at 40 degrees C for 5 min in the presence of 0.005% Triton X-100 or Tween 80. The design of a suitable desorption process using these conditions is discussed. Glycerol was also effective as a desorbent either alone or in combination with alkali and detergent. However, relatively high concentrations of glycerol were needed and the maximum desorption achieved, 68%, was not significantly greater than that with only alkali and detergent.

Desorption of Trichoderma reesei cellulase from cellulose by a range of desorbents

Liquid extraction is one means of removing metabolic products continuously during a fermentation and so reducing product inhibition. It is known that microbial organisms are attracted to liquid-liquid interfaces, and it is important for the design of extraction systems to establish if this has a detrimental effect on the rate of extraction. The extraction of ethanol from aqueous suspensions of yeast (Saccharomyces cerevisiae) using n-decanol is described in this paper. It was found that the presence of the yeast cells severely reduced the rate of ethanol extraction. The overall mass transfer coefficient was reduced from 5.0 x 10/sup -6/ to 0.7 x 10/sup -6/ m/s. This reduced overall mass transfer coefficient was unaffected by yeast concentration in the range of 0.1-20 kg/cubic m. The results are consistent with the yeast cells absorbing to the interface in closely packed layers and preventing mass transfer by simply reducing the available interfacial area. Optical microscope observations confirmed that a yeast layer several cell diameters thick rapidly built up at the interface when a small decanol droplet was added to a yeast suspension. 12 references.

Effect of microorganisms on rate of liquid extraction of ethanol from fermentation broths.

Up to 45% of bound cellulase (Avicelase) could be recovered from crystalline cellulose by pH adjustment with NaOH (0.008–0.01 M) to pH 10.0 (40°C). Enzyme was simultaneously desorbed and inactivated as the pH increased and both events occurred within 1 minute. Enzyme desorption and stability were also temperature dependent and desorption increased to approximately 65% by adding detergents.

Elution of Trichoderma reesei cellulase from cellulose by pH adjustment with sodium hydroxide

A novel technique for settling microorganisms has been described. The technique involves adding a dense, inert powder to a suspension of microorganisms under conditions where flocculation of the microorganism with the inert poweder occurs. The flocs formed are small and relatively dense and settle rapidly. Suspensions of Saccharomyces cerevisiae yeast have been flocculated with several different inert seed materials achieving rapid settling and separations of up to 99.9%. Nickel powder was used as a seed material for most experiments described here, and iron sand showed promise as a cheaper seed for large-scale use. The degree of flocculation and cell separation obtained depended largely on the seed concentration and the components in solution. Temperature and pH had little effect. When the method was initially applied to a practical fermentation, flocculation was poor because of inhibiting compounds in the fermentation medium, but modification of the technique produced good flocculation in the medium.

New concepts for rapid yeast settling. I. Flocculation with an inert powder.

Two rate equations have been developed to model the hydrolysis of ground lean meat protein by Alcalase. The first equation was based on classical Michaelis-Menten kinetics and the second on the adsorption of enzyme to the protein prior to reaction. It was assumed that this adsorption could be modelled by a Langmuir-type adsorption isotherm. Each equation considered the enzyme to be competitively inhibited by reaction product, and considered enzyme inactivation to be first order. Both rate equations have been fitted to experimental data obtained from the hydrolysis of meat protein by Alcalase. Initial rate data indicated that the adsorption model was more appropriate. However, both equations gave satisfactory fits to 11 reaction progress curves determined over a wide range of enzyme and substrate concentrations.

P. A. Munro

Papers

Desorption of Trichoderma reesei cellulase from cellulose by a range of desorbents

Effect of microorganisms on rate of liquid extraction of ethanol from fermentation broths.

Elution of Trichoderma reesei cellulase from cellulose by pH adjustment with sodium hydroxide

New concepts for rapid yeast settling. I. Flocculation with an inert powder.

Kinetics of the hydrolysis of lean meat protein by alcalase: Derivation of two alternative rate equations and their fit to experimental data.