Name _________________________

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Exercise 6: A Trip to the Sewage Treatment Plant Sample Collection and Quantitative Analysis

INTRODUCTION In this exercise we will assess the effect of Bard's drinking water plant on its input (water from the Sawkill) and the effect of the sewage treatment plant on its input (raw sewage). To do this, we will collect water samples from the input and output of each plant and we will determine the concentration of bacteria in each. The four samples in mind are quite instructive, but you can take more if you are curious about anything in particular. PROCEDURE 1. Obtain four autoclaved milk dilution bottles. Label them

SAWKILL INPUT DRINKING WATER OUTPUT

RAW SEWAGE INPUT TREATED SEWAGE OUTPUT

2. After this we will head to the Bard College drinking water and sewage treatment

plants to take tours and to collect samples. Bring plastic gloves and a strong stomach for the latter.

3. After the tours bring the samples back to lab to determine the concentration of

bacteria in each sample. To do this, we will prepare dilutions of each of samples. This will involve making a series of 10-fold dilutions and will be described in detail in the lab. We will make 100 (undiluted), 101, 102, 103, 104, 105, 106, and 107 dilutions of each.

4. After the dilutions are made, pipette 1.0 mL of each dilution (NO MOUTH

PIPETTING ) into separate screw-cap culture tubes containing molten agar at

BIOLOGY 112: BIOLOGY OF INFECTIOUS DISEASE LABORATORY MANUAL EXERCISE 6: A TRIP TO THE SEWAGE TREATMENT PLANT

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47 C. Mix each 47 C tube swiftly but thoroughly, without making any bubbles, then immediately pour the agar into the bottom of a sterile Petri dish. The tech-nique will be demonstrated. KEEP THE 47 C TUBES OUT OF THE 47 C WATER BATH FOR ABSOLUTELY AS LITTLE TIME AS POSSIBLE, OR THEY WILL GEL ON YOU!

5. Incubate the plates at room temperature until colonies have grown sufficiently for

counting. The colonies confined in the agar will be much smaller than those growing freely on the agar. Since all colonies are presumably the product of a single cell, count them all equally, no matter what the size.

RESULTS 1. For each water sample, find a plate that has between 30 and 300 colonies, count

the colonies and record the number below. Indicate the dilution of the sample used for each plate counted. Use this data to calculate how many bacteria there were for each sample per milliliter before diluting.

Water Sample Colonies per

Plate

Cells per mL of Dilution

Dilution Factor

Cells per mL of Original

Sample Sawkill Input

Drinking Water Output

Raw Sewage Input

Treated Sewage Output

DISCUSSION 1. Was the concentration of bacteria in the Sawkill input to the drinking water plant

higher than that of the drinking water output? What procedures in the drinking water plant are designed to reduce the bacterial

count?

BIOLOGY 112: BIOLOGY OF INFECTIOUS DISEASE LABORATORY MANUAL EXERCISE 6: A TRIP TO THE SEWAGE TREATMENT PLANT

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2. Was the concentration of bacteria in the treated sewage output lower than that of the raw sewage input?

What procedures in the sewage treatment plant are designed to reduce the

bacterial count?

BIOLOGY 112: BIOLOGY OF INFECTIOUS DISEASE LABORATORY MANUAL EXERCISE 6: A TRIP TO THE SEWAGE TREATMENT PLANT

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