The Effects of Chlorine on Harmful Bacteria Group Leow Shawn Tao (1A413, Leader), Sow Jeng Wei (1O220), Justin Soh (1P111), Soh Yee Kiat (1P127)

Contents Overview Materials and Methodology Results and Discussion Conclusion

Rationale To test the ability of chlorine as an disinfectant while also suggesting an alternative to chlorine, in which is Silver Nanoparticles for our case.

Hypothesis Chlorine water is ineffective in killing common harmful bacteria.

MATERIALS AND METHODOLOGY

Variables ControlledDependentIndependent Dilution of bacteria and silver nanoparticles Colonies of bacteria left Type of disinfectant used Amount of bacteria Area of collection of water

Materials Agar Plates Sterile Swabs Chlorine Water (Collected from HCI swimming pool) Pipette & Micropipette Centrifuge Tubes Nutrient Agar & Nutrient Broth Measuring Cylinder De-ionized water E.coli

Materials

METHODOLOGY

DAY 1 Pre-Experimental Procedures

Water Collection Water was collected using centrifuge tubes from the HCI Swimming Pool at the times of 7.50am, 2.30pm and 5.00pm.

Broth and Agar Preparation For broth, 3.25g were displaced into a bottle and mixed with 250ml of de-ionized water. For agar, 14g were displaced into a bottle and mixed with 500ml of de-ionized water.

Broth and Agar

DAY 2 Preparation

Synthesis and Dilution of Silver Nanoparticles 1. 30ml of sodium Borohydride is poured into a small beaker. This small beaker is then placed into a larger beaker. Ice is placed into this larger beaker. Stir for 20 minutes. 2. 2ml of silver nitrate is then dropped into the sodium Borohydride. 1.28g of polyvinyl alcohol is then added into the mixture and heating is carried out.

Agar Spreading Using our agar, the agar was displaced onto Petri dishes to half the Petri dishes height. They were then left to solidify for approximately 15 minutes.

Overnight Culture 1. 10ml of our nutrient broth was displaced into 4 centrifuge tubes each. 2. Then, using a bacteria streaking rod, bacteria was displaced into the tubes. The centrifuge tubes were then placed in the shaking incubator for 1 day.

DAY 3 Experimentation

Dilution 1. Our aim was to reach 1 x 10- ⁶ of bacterial dilution. We filled 6 centrifuge tubes each with 9ml of nutrient broth. 2. Using a micropipette, we displaced 1ml of the bacterial broth from the overnight culture into a centrifuge tube labeled 1 x 10- ¹. This procedure was repeated on the tubes labeled 1 x 10-²to 1 x 10- ⁶.

Bacterial Spreading 1. The plates were labeled accordingly to their content. Triplication was carried out. Also, 3 controls involving sterile water instead of silver nanoparticles or chlorine water was set up. E.g.: First plate consisting of 2.30pm water will be labeled as: 2.30pm, C.Water, 1.

Bacterial Spreading 2. Next, according to the labels, 50 microlitres of bacteria and 50 microlitres of silver nanoparticles or chlorine water accordingly was displaced onto the agar dish with a micropipette. This mixture was then spread and sealed with Parafilm, before being kept in the incubator at 36 Degrees Celsius.

RESULTS DAY 4

Chlorine Water Controls7.50am2.30pm5.00pm Dish 127N/A1533 Dish Dish Average

Results of Chlorine Experiment

Results of Chlorine experiment

Silver Nanoparticles ControlsSilver Nano 1x10-4 Dish 1189 Dish 2213 Dish 3217 Average206.34

Q&A

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