Lesson plan Grade 10 Science
Driftwood Springs Water Treatment: Breaking Down the Treatment Train
A grade 10 lesson where students sequence a fictional plant's treatment stages and use turbidity data to judge compliance with a real federal limit.
Objectives
- Students will sequence the five stages of conventional drinking water treatment and explain what each stage removes.
- Students will analyze a turbidity data table to identify which treatment stage removes the most particulate matter.
- Students will compare a finished-water turbidity reading to the federal regulatory limit to judge compliance.
Vocabulary
- Coagulation
- Coagulation is the first cleaning step at a drinking water plant. Operators quickly mix in a chemical that makes tiny bits of dirt stop pushing each other away so they can start sticking together.
- Flocculation
- Flocculation is the slow, gentle stirring step at a water plant that lets tiny sticky particles bump into each other and clump into bigger pieces called floc, heavy enough to settle out of the water.
- Sedimentation
- Sedimentation is the step where water sits almost still in a big basin so the heavy clumps of dirt can sink to the bottom. The cleaner water on top then moves on to the filters.
- Filtration
- Filtration is the step where water passes through layers of sand, gravel, or other materials that trap the small particles still left in it. It works like a very fine strainer.
- 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.
Teacher overview
Driftwood Springs Water Treatment Plant (a fictional plant used for this lesson) turns cloudy raw reservoir water into water clear enough to drink. This lesson breaks that large problem into the five smaller engineering problems a conventional treatment train solves in sequence: coagulation, flocculation, sedimentation, filtration, and disinfection. A common misconception is assuming disinfection is what makes water clear; disinfection kills pathogens, but it is the earlier stages, especially sedimentation and filtration, that remove the particles causing cloudiness, or turbidity, in the first place.
Procedure
Hook (5 min): Describe or show two water samples: raw reservoir water that looks cloudy and finished tap water that looks clear. Ask students to guess how many separate steps it takes to turn one into the other.
Direct instruction (15 min): Walk through the treatment train stage by stage: coagulation (a chemical is added that neutralizes charges holding tiny particles apart so they clump together), flocculation (gentle mixing grows those clumps larger), sedimentation (the clumps settle out under gravity), filtration (remaining fine particles are trapped as water passes through sand and other media), and disinfection (chlorine is added to kill remaining pathogens). Frame each stage as solving one smaller, manageable piece of the larger problem of making raw water safe to drink, the same decomposition strategy engineers use for any complex design problem.
Guided practice (15 min): In small groups, students study a turbidity data table showing nephelometric turbidity units (NTU) measured after each stage of treatment on a sample day at the fictional Driftwood Springs plant:
| Stage | Turbidity (NTU) |
|---|---|
| Raw water | 18.0 |
| After coagulation/flocculation | 9.5 |
| After sedimentation | 3.2 |
| After filtration | 0.18 |
| After disinfection | 0.18 |
Groups calculate the drop in NTU at each stage and identify which single stage removes the most turbidity in absolute terms.
Independent practice (10 min): Students compare the finished-water reading (0.18 NTU) to the federal requirement that conventional filtration plants keep finished-water turbidity at or below 0.3 NTU in 95 percent of monthly samples, and write one sentence stating whether Driftwood Springs' sample meets that requirement and by how much.
Closure / exit ticket (5 min): Students answer one question on an index card: "Why does breaking water treatment into five separate stages make the engineering problem easier to solve than trying to remove everything in one step?" Collect and scan responses for a reasoned explanation, such as each stage being designed, monitored, and adjusted separately, before dismissal.
Student Handout
Driftwood Springs Water Treatment Plant (a fictional plant used for this lesson) recorded these turbidity readings, in nephelometric turbidity units (NTU), after each stage of treatment on one sample day.
| Stage | Turbidity (NTU) |
|---|---|
| Raw water | 18.0 |
| After coagulation/flocculation | 9.5 |
| After sedimentation | 3.2 |
| After filtration | 0.18 |
| After disinfection | 0.18 |
- Find the drop in turbidity at each stage in the table. Which single stage removes the most turbidity in absolute terms?
- Conventional filtration plants must keep finished-water turbidity at or below 0.3 NTU in 95 percent of monthly samples. Driftwood Springs' finished water measured 0.18 NTU. By how much does this sample clear that limit?
- Why does breaking water treatment into five separate stages make the engineering problem easier to solve than trying to remove everything in one step?
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: Coagulation and flocculation.
That stage dropped turbidity from 18.0 to 9.5 NTU, a decrease of 8.5 NTU, larger than the decrease at any other single stage (sedimentation dropped it 6.3 NTU, and filtration dropped it about 3.0 NTU). - Answer: 0.12 NTU.
Yes, the sample meets the requirement. Driftwood Springs' finished water measured 0.18 NTU, below the federal limit of 0.3 NTU, clearing it by 0.3 − 0.18 = 0.12 NTU. - Answer: model response.
A reasonable exit-ticket answer explains that breaking treatment into five stages lets engineers design, test, and troubleshoot each step on its own, so if turbidity or another problem shows up in the finished water, operators can check each stage's readings to find exactly where the process is falling short instead of fixing one enormous, all-in-one system at once.
Differentiation
Support (below grade level)
Provide the five stage names in order as a labeled reference strip, and pre-fill the "drop" column of the turbidity table so students only need to compare values rather than subtract them.
Extension (above grade level)
Ask students to calculate, using only the fictional Driftwood Springs data table provided, what percent of the total turbidity removal (18.0 to 0.18 NTU) happened during the coagulation and flocculation stage alone, and explain what that percentage suggests about where a plant operator should focus troubleshooting effort first.
ELL supports
Pre-teach "coagulation," "sedimentation," "filtration," and "turbidity" with a labeled diagram of the treatment train showing water becoming clearer at each stage. Allow students to complete the guided-practice comparison using the data table and simple over/under symbols instead of written sentences.