What is the Difference Between Aeration and Agitation

The key difference between aeration and agitation is that aeration is done using a sparger apparatus in order to provide oxygen for growing cells, while agitation is done using an impeller or an agitator blade in order to distribute oxygen and nutrients uniformly inside the bioreactor.

Fermenters or bioreactors are biological containers that facilitate the growth of target bacteria and fungi in higher quantities. They contain different parts or units to facilitate optimum growth conditions for the growing and multiplying microorganisms inside them. Aeration and agitation are two key factors in a fermenter that facilitate efficient microbial growth. Aeration enhances the delivery of oxygen to growing cells, while agitation enhances the aeration and the uniform mixing of the content inside the reactor.

CONTENTS

1. Overview and Key Difference
2. What is Aeration
3. What is Agitation
4. Similarities – Aeration and Agitation
5. Aeration vs Agitation in Tabular Form
6. Summary – Aeration vs Agitation

What is Aeration?

Aeration is the process where the supply of adequate oxygen to the microorganisms takes place in a submerged culture. This increases the oxygen concentration in the culture. The device that introduces air to the fermenter is called a sparger. During aeration, the air supply to the fermenter should be as fine bubbles with a high surface area. This allows efficient oxygen transfer to the microorganisms to promote fermentation. In some fermenters, aeration also provides agitation. Therefore, a separate agitator will not be required for the fermenter with medium-level or low viscous fluids.

The three types of aeration spargers are porous sparger, orifice sparger, and nozzle sparger. All spargers should consist of air filters to prevent contamination. Porous spargers are used only in lab-scale fermenters, while nozzle spargers are used in larger-scale fermenters. In medium-scale fermenters, the orifice sparger is used for aeration.

What is Agitation?

Agitation is the process of uniform suspension of microbial cells to homogenize the nutrient medium. The function of agitation is to facilitate bulk fluid and gas phase mixing, oxygen transfer, air dispersion, heat transfer, and a uniform condition within the fermenter. The impeller or agitator facilitates the agitation inside the fermenter.

There are four types of impellers: disc impeller, vanned disc impeller, open impeller, and marine impeller. The disc impeller prevents the flooding caused by air bubbles due to the lack of dispersion of air bubbles properly during aeration. Modern fermenters consist of a dual impeller for agitation that provides dual agitation. One impeller is for gas dispersion, and the other impeller is for circulation. Similar to aeration, agitation is a crucial step in fermentation to help the fermenter to provide the required results.

What are the Similarities Between Aeration and Agitation?

• Aeration and agitation are two mechanical processes.
• They play a key role in microbial fermentation.
• Both provide optimum conditions for the growth of microorganisms.
• Moreover, both processes require machinery.
• Both aeration and agitation are controlled processes.

What is the Difference Between Aeration and Agitation?

Aeration uses a sparger apparatus, while agitation uses an impeller or an agitator blade during the fermentation process. Thus, this is the key difference between aeration and agitation. Aeration is the process that supplies adequate oxygen to microorganisms in a submerged culture, while agitation is the uniform suspension of microbial cells to homogenize the nutrient medium. Moreover, there are three key types of aeration systems, while there are four types of agitation systems.

The below infographic presents the differences between aeration and agitation in tabular form for side-by-side comparison.

Summary – Aeration vs Agitation

Fermenters are the vessels used for growing target microorganisms on large scales. They have different parts to facilitate optimum growth conditions for microorganisms. Aeration and agitation are two key factors in a fermenter. Aeration uses a sparger apparatus and supplies oxygen for growing microbial cells. Agitation, on the other hand, uses an impeller or an agitator blade and uniformly mixes the nutrients and oxygen in the medium during the fermentation process. So, this is the key difference between aeration and agitation.

Reference:

1. “Fermentation.” Bioprocessing.
2. “Effect of Agitation and Aeration on the Production of Nitrile Hydratase by RhodococcusErythropolis MTCC 1526 in a Stirred Tank Reactor.” Letters in Applied Microbiology, U.S. National Library of Medicine.

Image Courtesy:

1. “Agitator (6322735090)” By Peter Craven – Agitator (CC BY 2.0) via Commons Wikimedia
2. “Belebungsbecken – aeration tank (12359229313)” By SuSanA Secretariat – (CC BY 2.0) via Commons Wikimedia