Page 16 - Shaping A Sustainable Future

Based on experimental results, it was noted that the CMC Dishwashing Method based on CMC Value
value increases proportionally with the amount of oil in
the solution. Refer to Table 2 for the CMC value of the 1. Add 125 ml of detergent into a 10-litre pail of water
detergent solution with different amounts of oil added. and soak the dishes for 30 mins.
Hence, it proves the hypothesis that more detergent
will be required to clean the dirty dishes than cleaner 2. Wash the dishes in the same pail of detergent
or “no oil” dishes. However, we chose 12.5 ml/l as the solution.
difference in the detergent effect is only 1% between
12.5 ml/l and 14.3 ml/l, which is negligible. Hence, the 3. Place dishes into a pail of 5-litre of water to rinse off
lesser of the two amounts were chosen. the detergent.

Type of Detergent Solution CMC Value (ml/l) Dishwashing Method Based on CMC Value
Experiment
No oil added 11.2

Our team brought a pail of 21 pieces of dirty dishes and
1g oil added 12.5
utensils from the coffee shop back to our laboratory
for testing for our experiment. We soaked the bucket
10g oil added 14.3
of dirty dishes in 10-litre of clean water with 125 ml of
detergent, which had a CMC value of 12.5 ml/l, for 30
Table 2: CMC value of the detergent solution with different min. Refer to Figures 3 and 4 for the dirty dishes and
amounts of oil added. utensils used in the dishwashing experiment.

Dishwashing Method

According to the coffee shop’s dishwashing practice, the
dirty dishes (an average of 20 dirty dishes and utensils)
were soaked in a 10-litre pail of water mixed with an
unknown amount of detergent. We measured the
amount of detergent used on three different occasions,
i.e.155 ml, 210 ml and 175 ml, respectively, with an
average of 180 ml. The dishes were then scrubbed in the
pail before transferring to another bucket of 5-litre of
clean water for a final rinse.
Figure 3: Soaking of a full pail of dishes.

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