Lenore S. Clesceri

Recycle of the cellulase-enzyme complex after hydrolysis of steam-exploded wood

Cellulases can be recovered in high yields by contacting fresh substrate with hydrolysis filtrate and by extraction of spent hydrolysis residue with pH 7 buffer. Recycled enzymes give hydrolysis rates about equal to those with fresh enzymes. Steam-exploded wood (SEW) is washed with water to remove sugars and byproducts from breakdown of hemicellulose, and recycle of enzymes proceeds better if lignin is also removed prior to hydrolysis. Oven drying of SEW interferes with recycle, and the recovery of enzymes is only one-half of that with SEW that is kept moist.Effectiveness of enzyme recovery depends on the completeness of hydrolysis, as determined by contact time and enzyme concentration. For cost-effective operation, enzyme should not be recovered until appreciable filter paper activity and carboxylmethylcellulase activity appear in the hydrolysate.

Inhibition of cellulases by impurities in Steam-Exploded wood.

Steam explosion of hardwood chips produces impurities that reduce the activity and stability of cellulases. Washing the exploded wood with water removes the inhibitors and permits hydrolysis equivalent to that with purified cellulose.

Continuous culture, feedback control and auxostats

Abstract Improved sensing methods and computerized control of bioreactors are encouraging the development of auxostats, continuous culture systems in which, unlike the chemostat, the growth rate (dilution rate) can vary. Auxostats are useful, in particular, for studying cultures growing at rates close to their maxima and they can be used to select fast-growing cultures. Although development is at an early stage, it is clear that, in order to operate commercially, auxostats would probably require some form of effluent recycle or multistage reactor configuration.

Recovery of enzymes from the insoluble residue of hydrolyzed wood

During the enzymatic hydrolysis of steam-exploded wood, enzymes are adsorbed on both the cellulosic and noncellulosic components. Significant amounts of enzymes are recovered from the spent hydrolysis residue, which consists mostly of lignin, by neutralizing the pH from 4.5, the optimum for hydrolysis.

Aluminum exposure: a study of an effect on cellular growth rate

Aluminum effects on cultured human brain cells were examined. Human brain cells (neuroblastoma IMR-32) were cultured to examine possible effects of soluble aluminum at a cellular level. The cellular growth rate was measured by counting the number of cells with a hemocytometer under an optical microscope over a period of time. No significant change in cell growth was found during a three-week exposure period to aluminum at concentrations from 0.1 to 10 mg/l. However, after 3 weeks Al started to reduce the growth rate relative to the control, and the decrease became more pronounced as the exposure period to aluminum increased. The effect was greatest at the higher Al-concentration.

Aerobic formation of ethanol by Saccharomyces cerevisiae in a computerized pHauxostat

Abstract A computerized pHauxostat was used for investigating oxidoreductive metabolism of yeast. Elevated glucose concentrations due to high dilution rates overloaded aerobic respiratory capacity and induced formation of ethanol. Although specific productivity of ethanol was excellent at low concentrations of glucose, ethanol toxicity caused diminished productivity and uneconomic concentrations of ethanol with industrial-strength substrate.

AUTO-SELECTION OF VERY RAPIDLY GROWING MICROORGANISMS

ABSTRACT With very rapid flow rates, in a continuous culture vessel almost all cells are young because of the low probability of long residence. In contrast to a conventional chemostat which is unstable as the washout rate is approached, controlling the limiting nutrient to achieve a high rate is self-adjusting and stable. Convenient, rapid detection of nutrient concentration presents problems, but pH is an index of glucose consumption when organic acids are formed. A feedback control system that adjusted dilution rate to hold pH constant was used to investigate the effects of pH set point, nutrient strength, and buffer capacity of the medium. A dilution rate exceeding 6.6 hr−1 could be maintained with the proper selection of pH and buffer capacity of the medium, and the organisms tended to pure culture.

Chemical Control of Pests and Vectors

Chemical poisons can be used in the control of pests and vectors. The term “poison” is very broad, referring to practically any chemical that can produce sickness or death if its concentration is high enough. Thus even nutrients can become poisons. For example, copper, which is highly toxic to all forms of plant life, is an essential element for plant growth at the trace level [1].

Role of Cyanide on Polycyclic Aromatic Hydrocarbon Degradation in Manufactured Gas Plant Soils

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants that are formed during the incomplete combustion of organic material. This paper reports on a study of soils from manufactured gas plant (MGP) sites that contain PAHs as well as other gas byproducts including ammonia, cyanide, coal tars and phenols. These methane production byproducts were removed from the gas prior to distribution. The byproducts were then disposed of on the land, and many sites still have high concentrations of these byproducts even though MGP plants in the United States have not been operating for the past 40 years.

Multivariable Control of a Continuous Culture

Multivariable control of both pH and ammonium levels in an aerobic continuous yeast culture was demonstrated. A buffered glucose feed was used for pH control. This control loop was coupled with ammonium control using an on-line ammonia electrode suspended above a pH-adjusted sample stream from the fermentor. The dilution rate of the culture was the sum of the two individual feed rates. The advantages and implications of multivariable feedback control in continuous fermentation are discussed.