Lab / experiment Grade 10 Engineering & Design
Comparing Column Filter Media: A Grade 10 Turbidity Design Lab
A grade 10 engineering lab where students build column filters, change the media, and test which design clears cloudy water best while keeping an acceptable flow rate.
Objectives
- Students will build two column filters that differ in one media variable and test each with cloudy water.
- Students will measure clarity on a 1-to-5 scale and calculate flow rate in milliliters per second.
- Students will use their data to recommend one design, weighing clarity against flow rate.
Vocabulary
- Turbidity
- Turbidity is a measure of how cloudy or murky water looks because of tiny particles floating in it. Clear water has low turbidity, and muddy water has high turbidity.
- Flow rate
- Flow rate measures how much water moves past a point in a certain amount of time, like gallons per minute through a garden hose. Bigger pipes and stronger pushes give bigger flow rates.
Also: filter media, independent variable, control
Teacher overview
Real treatment plants clear cloudy water by passing it through layers of media such as sand and carbon, and engineers test different layer designs to find the best one. In this lab, students build two column filters that differ in a single media choice, run the same cloudy water through each, and compare how well each design clears the water and how fast it lets water through. The investigation question is testable: which media design clears the water more without becoming too slow? A classroom filter cannot match a plant's fine control, so the lab uses a simple 1-to-5 cloudiness scale as a stand-in for the precise turbidity readings a plant records.
Procedure
Step 1 (safety, before building): Use only clean tap water stirred with clean soil to make the muddy sample. Do not drink or taste any water in this lab. Wipe up spills right away so the floor stays dry, and keep the columns steady in a holder so they do not tip.
Step 2 (form your hypothesis): Your group will build two columns. Design A is cotton, then gravel, then sand. Design B adds a layer of activated carbon on top of the sand. Write a one-sentence hypothesis predicting which design will clear the water more, and why.
Step 3 (identify your variable): The one thing you change between the two columns is the media design. This is your independent variable. Keep everything else the same: the same muddy water, the same amount poured, and the same column size. These are your controls.
Step 4 (build the columns): Place a cotton plug in the neck of each column. In Design A, add a layer of gravel, then a thick layer of sand. In Design B, add gravel, then sand, then a layer of activated carbon on top. Set each column upright in its holder over a clean collection cup.
Step 5 (rate the starting water): Stir the muddy sample well. Rate its cloudiness on the 1-to-5 card and record it as the "before" rating for both designs.
Step 6 (run Design A): Pour 250 mL of muddy water into Design A. Start the timer as you begin pouring, and stop it when the water stops dripping. Record the time in seconds. Rate the collected water on the 1-to-5 card and record it as the "after" rating.
Step 7 (run Design B): Repeat Step 6 exactly with Design B, using a fresh 250 mL of the same muddy sample. Record the time and the "after" rating.
Step 8 (repeat for a second trial): Run a second trial of each design with fresh samples, so you have two "after" ratings and two times for each design.
Data & Analysis
| Design | Before rating (1-5) | After rating, Trial 1 (1-5) | After rating, Trial 2 (1-5) | Time to drain, Trial 1 (s) | Time to drain, Trial 2 (s) |
|---|---|---|---|---|---|
| A (gravel + sand) | |||||
| B (gravel + sand + carbon) |
What was the average "after" cloudiness rating for Design A across your two trials?
For each design, find the clarity improvement by subtracting the average "after" rating from the "before" rating. Which design improved the clarity more?
If Design B passed 250 mL of water in 40 seconds, what was its flow rate in milliliters per second?
Which variable did you deliberately change between the two designs, and which variables did you keep the same? Name at least two controls.
Suppose one design cleared the water more but drained much more slowly than the other. Explain the trade-off an engineer weighs when choosing between a clearer-but-slower design and a faster-but-cloudier one.
Real plants must reach a finished-water turbidity of 0.3 NTU in nearly all of their monthly samples. Based on your results, could your best classroom design meet that standard on its own? Explain why or why not.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
Answer: varies by group's own data.
The value should equal the average of the group's two recorded Design A "after" ratings. Accept any value from 1 to 5 that matches the group's data.Answer: varies by group's own data.
Clarity improvement equals the "before" rating minus each design's average "after" rating. Most groups will find Design B (sand plus carbon) improves clarity at least as much as Design A. Accept whichever design the group's own numbers support, as long as the subtraction is correct.Answer: 6.25 mL/s.
Flow rate = 250 mL ÷ 40 seconds = 6.25 milliliters per second.Answer: The media design was the independent variable.
The independent variable is the media design (Design A versus Design B). Controls include using the same muddy water, pouring the same 250 mL, and using the same column size. Accept any two valid controls.Answer: Accept any answer explaining that a clearer result is worth more only if the filter can still treat enough water in a reasonable time. A design that clears the water very well but drains very slowly could not keep up with a town's demand, so an engineer balances clarity against flow rate and cost rather than choosing clarity alone.
Answer: No, not on its own.
Accept any answer explaining that a classroom column removes visible cloudiness but cannot reliably reach 0.3 NTU, which is far clearer than the eye can judge on a 1-to-5 card. Real plants add coagulation, fine filtration, and continuous instruments to reach and confirm that standard, steps a simple column filter does not include.
Differentiation
Support (below grade level)
Pre-build one demonstration column as a class so groups see the layering before building their own, and provide a data table that asks for only one trial per design instead of two.
Extension (above grade level)
Have groups design and test a third column that changes a different variable, such as sand depth or an added second carbon layer, and compare its clarity and flow rate to Designs A and B, then explain which single change made the biggest difference.
ELL supports
Provide picture cards for each media layer (cotton, gravel, sand, carbon) labeled with its name, and allow students to record clarity using the numbered 1-to-5 card alone. Provide a sentence frame for the hypothesis in Step 2: "I predict Design ___ will clear the water more because ___."