Lactic acid (LA) is a colorless, odorless monocarboxylic acid naturally produced by many organisms. This weak acid has extensively used as an excipient in the food, cosmetics, pharmaceutical and chemical industries. The L-isomer is being preferred for food and pharmaceutical applications. Lactic acid can be produced by several microorganisms classified into bacteria, fungi, yeast, cyanobacteria, and algae. Among these microorganisms, lactic acid production using fungal fermentation showed high efficiency. Widely used method for the production of lactic acid is batch fermentation. Hydrodynamic conditions in the fermenter influence the morphology of the fungus and thus the rheology.
High agitation rates, which are required for optimum mass transfer, lead to high shear stress. Consequently, mycelial networks are fragmented, increasing the amount of free filaments and hence the viscosity. Besides, high viscosity at low agitation rate causes insufficient mass transfer and oxygen limitation. Because of an existing dynamic relationship between fermentation conditions and fungal growth patterns, an improved impeller that was sufficiently flexible for submerged cultures would be an advantage in the design of an efficient enzyme production system.
Increased productivity is one of the most important
objectives in continuous production of ethanol. It is generally accepted that a
high concentration of yeast favors an increased ethanol yield of the
fermentation process . Several techniques that promote the accumulation ofbiomass in fermenters have been used in continuous fermentation processes,
including cell immobilization in polymeric matrices and cell recycle by
centrifugation or filtration through membranes. Good performances have been
reported for processes using immobilized cells; however, procedures and
materials involved in this technique are inaccessible to a large number of
small industrial units . Centrifugation and filtration equipments are extremely
expensive and prone to mechanical problems; the use of these equipments is
limited due to high investment and maintenance costs. Since yeast separation by
conventional methods is an expensive operation in alcoholic fermentation
plants, alternative separation techniques using cheaper equipment such as
hydrocyclones and settlers have been investigated aiming to reduce the costs
involved in ethanol production.
Although solid particles can settle under the action of a
centrifugal force, gravitational sedimentation is understood as the settling of
particles within a fluid under the force of gravity. The factors that controlthe settling velocity are the solids concentration in the slurry, the densities
of solid and liquid, the size and shape of the particles and the viscosity of
the medium. However, the most important factors are the particle size and
particle density.
Woody plants of Tamaulipan Thornscrubs in the semiarid
regions are of great economic importance for various uses such as timber for
furniture, fences, firewood and serve as sources of forage for wild animal
grazing. Few studies are undertaken on nutrient contents of woody plants. The
specific leaf area (SLA, leaf area per unit mass) appears to be correlated with
leaf nitrogen per unit dry mass, photosyntheis and dark respiration sites.
