By the end of this lesson
- Describe the structure of an industrial fermenter.
- Explain the need for each condition named in the specification.
- Apply fermenter principles to producing a named product.
BIG QUESTION
Why can’t a giant tank of microbes just be left to grow on its own?
Without control, contamination, heat from respiration, acid build-up and oxygen shortage would reduce yield.
Aseptic precautions
The fermenter, nutrients and air are sterilisedTreated, by heat or chemicals, to kill all microorganisms., for example with steam, before use. Air entering is filtered.
asepticFree from unwanted microorganisms; aseptic techniques, such as sterilising equipment, prevent contamination of a culture. prevent contamination by unwanted microorganisms that would compete for nutrients, produce toxins or reduce the purity of the product.
Nutrients
A nutrient medium supplies a carbon source such as glucose for respiration, a nitrogen source such as ammonium salts for making proteins, plus minerals and vitamins.
Nutrients are needed for growth and for making the desired product.
Optimum temperature and pH
Microbial respiration releases heat. A water jacketA jacket around a fermenter through which cold water flows to remove heat released by respiring microorganisms, keeping the temperature at the optimum. with circulating cold water removes heat so temperature stays at the optimumThe best value of a condition, such as temperature or pH, giving the fastest rate. for the microorganism’s enzymes. Temperature probes monitor it.
Waste products can change the pH. pH probes detect changes and acid or alkali is added to keep the pH at the optimum.
Oxygenation and agitation
Sterile air is bubbled in (oxygenationSupplying oxygen, for example by bubbling sterile air into a fermenter so microorganisms can respire aerobically.) for aerobic respiration, which releases more energy for growth than anaerobic respiration.
agitationStirring the contents of a fermenter so microorganisms, nutrients, oxygen and heat are evenly spread. by paddles (stirrers) keeps microorganisms suspended, mixes nutrients and oxygen evenly and spreads heat so there are no hot spots.
Conditions in an industrial fermenter
Learn the condition, how it is controlled and why.
| Condition | How it is achieved | Why it is needed |
|---|---|---|
| Aseptic | Steam sterilisation; filtered air. | Prevents contamination and competition. |
| Nutrients | Glucose, nitrogen source, minerals. | For respiration, growth and product. |
| Optimum temperature | Water jacket; temperature probe. | Enzymes work best; heat from respiration removed. |
| Optimum pH | pH probe; acid or alkali added. | Enzymes work best. |
| Oxygenation | Sterile air pumped in. | Aerobic respiration for growth. |
| Agitation | Motorised stirrer paddles. | Even mixing of nutrients, oxygen and heat. |
Language that earns precision
- fermenter
- A large vessel in which microorganisms are grown under controlled conditions.
- aseptic
- Free from contaminating microorganisms.
- agitation
- Stirring the contents of a fermenter.
- water jacket
- A surrounding layer of circulating water that removes heat from the fermenter.
Common misconceptions
Claim: The water jacket heats the fermenter.
Correction: It mainly cools it, because microbial respiration releases heat.
Claim: Stirring is only needed to mix the nutrients.
Correction: It also distributes oxygen and heat and keeps microbes suspended.
Claim: Aseptic conditions protect workers.
Correction: Their main purpose is to keep unwanted microbes out of the culture.
Match the answer to the command word
For each condition, state how it is controlled and why it increases growth or product yield.
Be able to label inlets for nutrients and air, the water jacket, paddles, probes and outlet.
Recall, apply, then justify
Explain why an industrial fermenter has a water jacket.
Hint
Source of heat.
Suggested marking points
- Microorganisms release heat from respiration.
- The water jacket removes heat to keep the temperature at the optimum for enzymes.
Explain the need for aseptic precautions and agitation in a fermenter.
Hint
Two conditions, two reasons each.
Suggested marking points
- Aseptic precautions prevent contamination by other microorganisms.
- Contaminants would compete for nutrients or spoil the product.
- Agitation mixes nutrients and oxygen throughout the fermenter.
- It keeps microorganisms in suspension and prevents hot spots.
The pH in a fermenter falls during a run (illustrative data). Suggest a reason and explain the effect on product yield if no action were taken.
Planning hint
Waste products and enzymes.
What a strong design includes
- Microorganisms release acidic waste products such as CO₂ or organic acids.
- The pH moves away from the optimum.
- Enzymes in the microorganisms work less efficiently or denature.
- Growth and respiration slow down.
- Less product is formed.
- A pH probe linked to alkali addition would correct this.