Presentation on

“Heat generation in aerobic culture”

Submitted for self study evaluation for the course“Biochemical engineering”

Fifth Semester, Chemical Engineering - 2016

Submitted by :

Name : Sirajudheen K V

USN : 1RV13CH032

SYNOPSIS

Introduction Heat generation and removal

A typical study to understand heat production by ruminal bacteria in continuous culture and its relationship to maintenance energy.

INTRODUCTIONThe growth of microorganisms is accompanied by the production

of heat which is closely related to the catabolic activity of the cell. A large part of the heat is generated during the degradation of the

organic substrate, which serves as a carbon and energy source. The catabolic process is associated with a significant free-energy

decrease. Part of the released energy is conserved is, high-energy bonds of

adenosine triphosphate (ATP) providing energy for biosynthesis of cellular components and other-cell activities when required.

The rest of the substrate's original energy is released as heat. In addition to the heat production during the catabolism of the energy-rich nutrient 1 molecules, most of the' ATP_ energy is also

liberated as heat during its utilization in the cellular activities, providing support for the microbial growth and other cell functions. The amount of the produced heat is dependent on the type of

catabolic pathway through which the organic substrate is metabolized.

It is also dependent on the energetic coupling of ATP generation and cell biosynthesis

Variations in the microbial heat parameter reflect the type of metabolic activities of the cell as weIl as the degree of perfection with which the cellular catabolism and anabolism are completed.This indicates that the heat generation during the growth of

microbial culture may be used to evaluate the regulatory mechanism of the cellular energy metabolism.

Aerobic Culture: A bacterial culture in which growth is allowed to occur in a state of ambient normal oxygenation.

HEAT GENERATION AND REMOVAL

All fermentations generate heat. In submerged cultures, typically 3-15ka’3 comes from microbial activity. In addition, mechanical

agitation of the broth produces up to 15 kW m'3. Consequently, a fermenter must be cooled to prevent a rise in temperature and

damage to the culture. Heat removal tends to be difficult, because typically the temperature of the cooling water is only a few degrees

lower than that of the fermentation broth. Therefore industrial fermentations are commonly limited by their heat-transfer

capability.

The ability to remove heat depends on: the surface area available for heat exchange; the temperature difference between the broth

and the cooling water; the properties of the broth and the coolant; and the turbulence in these fluids. The geometry of the fermenter

determines the surface area that can be provided for heat exchange. Heat generation due to metabolism depends on the rate

of 0; consumption, and heat removal in large vessels becomes difficult as the rate of Oz consumption approaches5 kg m‘3 h ‘l.

A fermenter must provide for heat transfer during sterilization and subsequent cooling, as well as removing metabolic heat. Liquid

medium, or slurry, for batch fermentation may be sterilized using batch or continuous processes. In batch processes, the medium or

some of its components and the fermenter itself are commonly sterilized together in a single step, by heating the medium inside the fermenter. Steam maybe injected directly into the medium, or

heating may take place through the fermenter wall.

Heating to high temperatures (typically 121°C) during sterilization often leads to undesirable reactions between components of the medium. Such reactions reduce the yield, by destroying nutrients or by generating compounds which inhibit growth. This thermal damage can be prevented or reduced by sterilizing only certain components of the medium in the fermenter and adding other, separately sterilized components, later. Sugars and nitrogen

containing components are often sterilized separately.

Dissolved nutrients that are especially susceptible to thermal degradation may be sterilized by passage through

hydrophilic polymer filters, which retain particles of 0.45 pm or more. Even finer filters (e.g. retaining particles of 0.2 pm) are also

available.

The heating and cooling of a large fermentation batch takes time, and ties up a fermenter unproductively. In addition, the longer a medium remain sat a high temperature, the greater the thermal degradation or loss of nutrients. Therefore, continuous sterilization of the culture medium en

route to a presterilized fermenter is preferable, even for batch fermentations. Continuous sterilization is rapid and it limits nutrient loss

however, the initial capital expense is greater, because a separate sterilizer is necessary.

A TYPICAL STUDY TO UNDERSTAND HEAT

PRODUCTION BY RUMINAL BACTERIA IN CONTINUOUS

CULTURE AND ITS RELATIONSHIP TO MAINTENANCE ENERGY.

Selenomonas ruminantium HD4 and Bacteroides ruminicola B(1)4 were grown in continuous culture with glucose

as the energy source, and heat production was measured continuously with a microcalorimeter. Because the bacteria were

grown under steady-state conditions, it was possible to calculate complete energy balances for substrate utilization and

product formation (cells, fermentation acids, and heat).

As the dilution rate increased from 0.04 to 0.60 per h, the heat of fermentation declined from 19 to 2% and from 34 to 8% for S.

ruminantium and B. ruminicola, respectively.

Since the heat due to growth-related functions was small compared to maintenance expenditures, total heat production provided a reasonable estimate

of maintenance under glucose-limiting conditions. As the dilution rate was increased, glucose eventually accumulated in the chemostat vessel and the specific rates of heat production

increased more than twofold. Pulses of glucose added to glucose-limited cultures (0.167 per h)

caused an immediate doubling of heat production and little increase in cell protein.

These experiments indicate that bacterial maintenance energy is not necessarily a constant and that energy source accumulation was

associated with an increase in heat production.

REFERENCESJ Bacteriol. 1986 Nov; 168(2): 694–701. PMCID: PMC213537; Heat

production by ruminal bacteria in continuous culture and its relationship to maintenance energy; J B Russell.

Fermentation (Industrial): Basic Considerations; Yusuf Chistl, Department of Chemical Engineering; University of Almeria,

Spain; Copyright © 1999 Academic Press.

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