# CEE 210 Environmental Biology for Engineers - PowerPoint PPT Presentation

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Lecture 6: Quantifying Microorganisms. CEE 210 Environmental Biology for Engineers. Instructor: L.R. Chevalier Department of Civil and Environmental Engineering Southern Illinois University Carbondale. Objectives. Review the composition of microorganisms

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CEE 210 Environmental Biology for Engineers

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#### Presentation Transcript

Lecture 6: Quantifying Microorganisms

### CEE 210 Environmental Biology for Engineers

Instructor: L.R. Chevalier

Department of Civil and Environmental Engineering

Southern Illinois University Carbondale

### Objectives

Review the composition of microorganisms

Calculated the THOD of bacterial cells

Understand the bacterial growth curve

Calculate the specific growth rate of bacteria

Review methods for measuring bacteria

### Composition

70-90% Water

Dry weight inorganic and organic

On average, carbon is 50% of this dry weight

### Chemical Formula of Microorganisms

Other elements include, but are not limited to, phosphorus, sulfur, potassium, calcium and magnesium

• Most commonly used

• C5H7O2N

• Useful simplification, but not a true chemical formula nor an exact stoichiometric expression

• Compare these values to the elemental composition of E. coli

### Chemical Formula of Microorganisms

• C5H7O2N

• We can use this formula

• Estimate nutrient requirements

• Convert gravimetric cell mass measurements into THOD of cell tissue

• Consider the following example that determines the THOD of microbial cells

### Example: THOD of Bacterial Cells

Determine the theoretical oxygen demand of 1 g of microbial cells using the empirical formula for microbes. Assume that the organic nitrogen in the cells is not oxidized (remains in the -3 oxidation state).

### Bacterial Growth

Source: Stanier et al., 1986

• Binary fission

• 20, 21,22,23…..2n where n is the number of generations

• Generation time a.k.a. Doubling time

• Time it takes for two cells to form from the parent cell

• It is also the time it takes to double the cell numbers

• This varies by species and growth conditions

### Exponential Growth

N = number of cells per volume of medium

t=time

k=specific growth rate

No = number of cells per volume when t=0

td = doubling time

### Bacterial Growth Curve

• Exponential growth can only be carried out up to a certain point

• Limited by environmental conditions, e.g. nutrients depleted

• Closed batch systems consistently show a bacterial growth with 4 distinct phases

• Lag phase

• Exponential growth phase

• Stationary phase

• Death phase

### Bacterial Growth Curve

• lag phase

• Microorganisms initially adjust to the new environment

• Indicative of microbe’s ability to degrade waste

• exponential phase

• Microorganisms start dividing regularly by the process of binary fission

• stationary phase

• Exhaustion of available nutrients

• Limited oxygen

• pH changes due to build up of CO2

• Accumulation of end products;

• Limited space

• death phase

• Number of viable cells decreases geometrically (exponentially), essentially the reverse of growth during the exponential phase

• N=Noe-bt

### Bacterial Growth Curve

Cell numbers (log)

Time

### Example of Exponential Growth

Given the bacterial cell numbers in a batch reactor measure 34,000/L in 4 hours after incubation, and 5.2 x 106/L after 24 hours. Assuming a negligible lag phase, estimate:

The specific growth rate

The initial number of cells

able 1. Some Methods used to measure bacterial growth

### Objectives

Review the composition of microorganisms

Calculated the THOD of bacterial cells

Understand the bacterial growth curve

Calculate the specific growth rate of bacteria

Review methods for measuring bacteria

### References

Chapter 11: Quantifying microorganisms and their activity

Bioremediation Principles, 1998, Ewies, J.B., Ergas, S.J., Chang, D.P.Y., Schroeder, E.D., WCB McGraw Hill.

Todar’s Online Textbook of Bacteriology, K. Todar, http://www.textbookofbacteriology.net/index.html (accessed March 2010)

Stanier, R.Y. et al., 1986, The Microbial World, Prentice-Hall.

### Sources of photographs and images in sidebar

• Professor, Civil and Environmental Engineering

• Fellow, American Society of Civil Engineers (ASCE)

• Diplomat, Water Resources Engineering, American Academy of Water Resources Engineering (AAWRE)

• Board Certified Environmental Engineer, American Academy of Environmental Engineers (AAEE)

• Licensed Professional Engineer, State of Illinois

• Human brain

• http://www.healthnak.com/mind/

• X-rays images

• http://martingallerycharleston.com/index.html

• Cold Virus (altered in Photoshop)

• http://medphoto.wellcome.ac.uk/