Drinking Water Experiment #2: Determining Chlorine Load for Algae Control

Drinking water disinfection experiment #2: Determining chlorine demand for different concentrations of algae.

Concept: in this test we will use a concentration of bleach, just under the “bleached at 100-minutes” concentrations. But, we will vary the amount of algae in the culture. Why- this will demonstrate that the biomass of the algae requires a specific mass of bleach.
Method

Dilution scheme from the neat culture (use any you want)

bottle	mL Algae Culture	mL culture media (clear)
1	50	0
2	45	5
3	40	10
4	35	15
5	30	20
6	25	25
7	20	30
8	15	35

Record the SSD for each culture
Add the level of bleach that was just under the 100-minute bleached mark from the previous experiment. Feel free to choose different levels of bleaching.
Observe the differences in color by culture density

Results: If you used spirulina and KNOW the dry weight (by filtering out the algae and drying and weighing) AND you know the concentration of the bleach in the water you can create a mass-to-mass ratio of algae killing ability of the bleach. You should be able to answer this question: How much bleach do I need to kill 1-gram of algae?

Drinking water disinfection experiment #2.1: How much chlorine was left in the water?

Concept: The chlorine will oxidize the algae and become inactive. As it expires it will not be detectable by a chlorine determination test kit. Therefore the high concentration of algae will have no chlorine left over and the low concentration of algae will have detectable chlorine levels in it.

Materials:

Chlorine Determination kit
Sniff test!

Method

Measure the level of chlorine in each of the samples from the experiment above

Use chlorine determination kit
Smell the tubes (presence or absence)

Results

Determine chlorine level in each of the using a chlorine determination kit: drippers for color change.