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Classroom activity Grade 6 Science

Run the Plant: Marlow Bend Water Treatment Rotation

A grade 6 station-rotation where teams act as plant operators, rotating through the five stages of drinking-water treatment and making one decision at each.

Objectives

  1. Students will place the five stages of drinking-water treatment in the correct order.
  2. Students will make an operator decision at each treatment stage using a target reading.
  3. Students will explain why treatment steps must happen in a set sequence.

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.
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.
Disinfection
Disinfection is the step that kills or disables germs in water so it is safe to drink. Water plants usually disinfect with chlorine, ultraviolet light, or ozone.
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

This is a station-rotation role-play for a class working in teams of four or five. Five stations, set around the room in a loop, stand for the five stages a conventional plant uses to turn river water into safe drinking water: intake and screening, coagulation, sedimentation, filtration, and disinfection. Each station's rules map directly onto one real job an operator does. Teams rotate through all five stations, read a status card, make one decision, and log it. The fictional Marlow Bend plant sets a finished-water target of 0.3 NTU for cloudiness, which gives the filtration decision a real goal to aim for.

Activity Directions

  1. Before class, place the five station signs in a loop in this order: Intake, Coagulation, Sedimentation, Filtration, Disinfection. Put one status card at each station. Plan about 5 minutes per station.
  2. Explain that each team is an operator crew at the fictional Marlow Bend plant, and river water must pass through all five stations in order before anyone can drink it. Hand each student an operator log.
  3. Start every team at a different station so the stations are not crowded, but tell teams they must still follow the loop in order, wrapping around from Disinfection back to Intake if they did not start at the beginning. Each status card stands on its own, so teams record each decision in the matching numbered row of the log, and the log ends up in treatment order.
  4. Intake station: the status card says a storm made the river cloudy and full of sticks and leaves. The crew decides whether to open the intake wide or slow it down and run the screens first. They log their choice and why.
  5. Coagulation station: the card says the water is very cloudy today. The crew decides whether to add more or less coagulant to make the tiny particles clump together, and logs the reason.
  6. Sedimentation station: the card says settled sludge is building up on the basin floor. The crew decides whether to leave it or remove it so the basin keeps working, and logs why.
  7. Filtration station: the card says the filter is clogging and the flow is slowing. The crew decides whether to backwash the filter or force more water through to hold the finished water at or below the 0.3 NTU target, and logs the choice.
  8. Disinfection station: suppose today's chlorine reading in the pipes is only 0.1 mg/L, below the usual 0.2 to 2.0 mg/L range. The crew decides whether to add more or less chlorine, and logs why.
  9. Rotate teams every 5 minutes on the timer until each team has completed all five stations.
  10. Debrief with the whole class for the last 8 minutes using the questions in the Answer Key, focusing on why the order of the stations cannot be changed.
Run the Plant: Marlow Bend Water Treatment Rotation — Grade 6 Science
Name: ____________________________ Date: ______________

Student Handout

Operator log for the fictional Marlow Bend plant. Write your crew's decision and reason at each station.

Station Our decision Why we chose it
1. Intake and screening
2. Coagulation
3. Sedimentation
4. Filtration (target 0.3 NTU)
5. Disinfection (0.2 to 2.0 mg/L)

Debrief questions:

  1. Why must the water pass through the stations in this exact order?
  2. What would happen if the plant tried to disinfect the water before removing the cloudiness?
  3. Which two stations are places where operators check a reading against a target?

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: The water must pass through the stations in order because each step prepares the water for the next. Screening removes big debris, coagulation and sedimentation take out most of the cloudiness, filtration removes what is left, and only then does disinfection work well on clean water.
  2. Answer: Disinfecting first would waste chlorine and work poorly, because cloudy water still holds particles that shield germs from the chlorine and use it up, so the water might still be unsafe.
  3. Answer: Filtration and disinfection. At filtration the operator checks cloudiness against the 0.3 NTU target, and at disinfection the operator checks the chlorine residual against the 0.2 to 2.0 mg/L range.

Differentiation

Support

Give students a pre-printed loop diagram of the five stations in order to carry with them, so they can focus on the decisions rather than remembering the sequence. Pair students who need reading support with a partner reader at each status card.

Extension

Ask each crew to write a sixth status card for one station that describes a new problem, along with the correct operator decision and a short reason, then trade cards with another crew to solve.

ELL supports

Provide picture icons for each station (a screen, clumping particles, settling, a filter, and a drop of chlorine) on both the signs and the operator log. Allow students to log decisions with short phrases or by circling a choice.

Extensions

Arrange a virtual or in-person tour of a local drinking-water plant, or a class letter to its operators, and have students match the plant's real steps to the five stations they role-played.