Week 3 Activity - Filtration

Our task for Week 3 was to build a rapid water filter in order to filter dirty water collected earlier on.

We were also tasked to evaluate the effectiveness of our rapid water filter as compared to other groups.

To start off, we were asked to formulate some hypotheses about our rapid water filter:

• If the dirty water passed through 6cm charcoal filtration system then the conductivity of the filtered water will increase, because the pH of the filtered water decreased.
• If the dirty water passed through 6cm charcoal filtration system then the dissolved oxygen of the filtered-water will decrease, because carbon will react with oxygen to become carbon dioxide.
• If the dirty water passed through 6cm charcoal filtration system then the pH of the filtered water will decrease because charcoal will acidify the pH of the water.

After that, it was time to get to work! First, we had to prepare the water filter, which consisted of a 6cm filter bed made of charcoal chips,

Figure 1: Preparing the water filter.

then after that we had to take readings of the water before filtering it,

Figure 2: Filtering the dirty water

and then we had to again take readings of the filtered water.

Figure 3: Measured readings.

From these readings, we derived the following conclusions to our hypotheses:

• Hypothesis 1: On the contrary, there was an increase of pH across the board, meaning that after we ran the water through the charcoal filter, it became more alkaline, instead of becoming more acidic as we thought. Why is this so? Did some element in the charcoal filter make the water acidic?
• Hypothesis 2: Since the amount of dissolved oxygen in the dirty water decreased in 2 out of 3 tries, we can safely assume this is true.
• Hypothesis 3: As seen in hypothesis 1, this is true as the conductivity of all three filtered water samples decreased in tandem with the increase of pH.

Next, we then had to compare our water filter against other groups', in order to see how effective ours was against theirs.

We chose 2 groups:

• Group 1, whose filterbed only consists of sand measuring 6cm deep, as the only difference between our filter and theirs is that they have a different material in their otherwise identical filter.
• Group 6, whose filterbed consists of only charcoal measuring 7cm deep, as the only difference between our filterbed and theirs is that their filter is thicker by 1cm.

Against both groups, we found that the pH change was higher than with our own filter.

In conclusion, this week we learnt that it was necessary to work together to divide the workload for the project. As taking the readings for the filtered and unfiltered water samples took plenty of time, we could not afford to have every group member stand and wait for the readings to stabilize. Hence, we decided to split into 2 groups and prepare a second water filter, so that we could do more at the same time.

Also, we learnt that, as the charcoal was dirty and covered in soot at first, we were required to clean the charcoal filter with clear running water. This was because that there was a potential for the soot to affect the experimental readings.

Written by Lucas