Difference Between Solid State Fermentation and Submerged Fermentation

The key difference between solid state fermentation and submerged fermentation is that solid-state fermentation involves the cultivation of microorganisms on a solid substrate with a low moisture content while submerged fermentation involves the cultivation of microorganisms in a liquid medium which has more than 95% water content.

Microorganisms are beneficial in various types of industries. Bacteria and fungi especially have a wide variety of applications in industries. Microorganisms should be grown on a large scale during the industrial fermentation process to extract the necessary products resulting from microbial metabolism. Solid-state fermentation and submerged fermentation are two main types of fermentation that help to produce enzymes industrially. In solid-state fermentation, fermentation occurs by microorganisms grown on a solid substrate while in submerged fermentation, fermentation occurs by microorganisms grown in a liquid medium. Each method has advantages as well as disadvantages.

CONTENTS

1. Overview and Key Difference
2. What is Submerged Fermentation
3. What is Submerged Fermentation
4. Similarities Between Solid State Fermentation and Submerged Fermentation
5. Side by Side Comparison – Solid State Fermentation vs Submerged Fermentation in Tabular Form
6. Summary

What is Solid State Fermentation?

Solid state fermentation is a type of fermentation used in the enzyme production. As the name suggests, fermentation occurs by microorganisms grown on a solid surface or solid substrate that has very low moisture content. A single insoluble substrate provides nutrients such as carbon, nitrogen, etc., for growing microbes. Microorganisms grow adhered to the solid substrate. Solid-state fermentation often uses composite and heterogeneous products of agriculture or by-products of agro-industries such as rice husk, wheat bran, sugar beet pulp, wheat and corn flour, etc. Hence, the substrates are cheaper and readily available.

Furthermore, filamentous fungi are the ideal microorganisms for solid-state fermentation. Also, bacteria, yeast and other fungi can also grow on solid substrates and can be used in solid-state fermentation.

Advantages of Solid State Fermentation

Similar to other fermentation processes, solid-state fermentation also has many advantages as listed below.

• The medium is simple, easily available, and inexpensive
• Substrates need less pretreatment compared to liquid media
• Contaminations are restricted since the moisture content is low
• Forced aeration is often easier
• Simplified and minimized downstream process and waste disposal
• Simple fermentation equipment
• High volumetric productivity

Although solid-state fermentation provides many advantages, it also has several disadvantages as well as listed below.

Disadvantages of Solid State Fermentation

• Low moisture level may restrict the growth of microorganisms
• Removing of metabolic heat is a problem in large scale solid-state fermentations
• Difficulties in monitoring the process parameters

What is Submerged Fermentation?

Submerged fermentation is another fermentation method we use in industrial enzyme production. Moreover, it needs a large-scale aseptic fermentation vessel which can provide a controlled environment that consists of optimum temperature, pH, degree of agitation, oxygen concentration, etc., for the growing microorganisms. Submerged fermentation occurs in a liquid medium where microorganisms are present. Thus, the water content is high, and all the nutrients are present in the liquid medium for the growth of microorganisms. Most importantly, the nutrients are evenly available throughout the medium for microorganisms in submerged fermentation. Agitation facilitates the even distribution of nutrients and the microbial cells.

Similar to solid-state fermentation, submerged fermentation also has advantages and disadvantages as mentioned below.

Advantages

• Easiness of measuring process parameters
• Even distribution of nutrients and microorganisms
• Ability to control growth conditions
• Availability of high water content for the growth of microbes

Disadvantages

• Use of expensive media and expensive equipment
• Complex and expensive downstream process and difficulty in the waste disposal
• High power consumption

What are the Similarities Between Solid State Fermentation and Submerged Fermentation?

• Solid-state fermentation and submerged fermentation are two types of common fermentations in enzyme production.
• Furthermore, microorganisms carry out both processes.

What is the Difference Between Solid State Fermentation and Submerged Fermentation?

Microbes grow on a solid surface in solid-state fermentation while microbes grow in a liquid medium in submerged fermentation. So, this is the key difference between solid state fermentation and submerged fermentation.

The below infographic summarizes the difference between solid state fermentation and submerged fermentation.

Summary – Solid State Fermentation vs Submerged Fermentation

Solid-state fermentation uses a solid substrate to grow microorganisms while submerged fermentation uses a liquid medium to grow microorganisms. Thus, this is the key difference between solid state fermentation and submerged fermentation. Solid-state fermentation takes place under low moisture level while submerged fermentation takes place under high water content.

Reference:

1. Filer, Keith, et al. “Production of Enzymes for the Feed Industry Using Solid Substrate Fermentation.” Engormix, Engormix, 20 Apr. 2007, Available here.

Image Courtesy:

1. “Schema FMS En” By SOUFFLET S.A. – SOUFFLET S.A (CC BY-SA 3.0) via Commons Wikimedia
2. “Penicillin bioreactor” By Matt Brown – Flickr (CC BY 2.0) via Commons Wikimedia