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Group 2 List of Activities and Procedures |
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Activities (working template)
- Collect water samples from two locations, stagnant and flowing, at the Brooklyn Bridge Park. Participants will decide sampling area.
- Collect water samples from City Tech or bottled water.
- Measure the temperature of the water sample collected.
- Return to City Tech P304 where the following test will be conducted
- pH – using a pH meter
- Microbial contamination – using phenol red dextrose tubes and phenol red broth.
Procedure
pH reading
To determine the pH of samples collected, follow the following steps.
Note: The pH meter is calibrated and ready to use. However, ensure that the pH reading is around 7 ( the probes are stored in pH 7 buffer).
- Rinse the probe in distilled water.
- Insert the probe into the water specimen.
- Swirl the container and wait until the reading stabilizes.
- Record the displayed reading.
- Give the probe a final rinse and return it to the calibration buffer or continue measuring the pH of other samples.
Microbial level
To measure microbial levels we will use the Colony Forming Unit (CFU) method.
Samples will be collected two days prior. 1 ml of each sample will be used to prepare a 10 fold serial dilution using phenol red glucose broth and nutrient agar plates. This dilution will be carried out to observe the minimum number, usually one, of bacteria in the water sample. All inoculated tubes will be incubated and fermentation and growth will be observed 48 hrs later. (More to come)
Interpretation of results;
Growth or no growth – Nutrient agar plate
Number of colonies – Nutrient agar
Number of different colonies – nutrient agar
Red media - no fermentation
Yellow media – fermentation
Bubble or gas in the upside tube – gas production
To determine the most probable number of bacteria within each sample,
- Observe the change in color of each tube and record the number of positive tubes in each set (3 tubes). The order of positive and negative results in each set is important.
- 2. Use the 3-tubeThe number of positive tubes are then used to determine the number of inoculums in each sample using the 3-tube MPN Table.
- 3. Record your
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