Writing prompt Grade 7 Science
Explain Where Tamsley's Microplastics Go: A Newsletter Article
A grade 7 science writing prompt: explain how a fictional water reclamation plant removes most microplastics, why some still reach the river, and what residents can do.
Objectives
- Students will explain in writing how each treatment stage removes plastic particles from wastewater.
- Students will use plant sampling data to state what share of particles is removed.
- Students will describe a monitoring plan and one way residents can reduce plastics at the source.
Vocabulary
- Clarifier
- A clarifier is a big round or rectangular tank where water sits calmly so solids can sink to the bottom and be scraped away. Treatment plants use clarifiers at more than one stage of cleaning.
- Effluent
- Effluent is the cleaned water that leaves a treatment plant at the end of the process. It is tested carefully before being released to a river, lake, or the ocean.
Also: microplastic, microfiber, sludge, source reduction
Teacher overview
A wastewater plant is unusually good at catching plastic particles even though it was never designed to do so, and explaining why is a clean test of whether a student understands what each treatment stage actually does. This prompt asks students to write a town newsletter article about the fictional Tamsley Water Reclamation Facility, using the plant's own sampling numbers. A common misconception is that anything removed from water is destroyed; the background is written so the article has to account for where the captured plastic ends up, which is in the sludge rather than nowhere.
Prompt
Background. Tamsley and its water reclamation facility are fictional, and every number below was written for this exercise.
Microplastics are plastic pieces smaller than 5 millimeters. Some come from packaging and containers that break down into smaller and smaller pieces. Some are microfibers, which are threads that wash out of fleece, nylon, and polyester clothing in the laundry. Others wash off streets, where tires shed tiny particles as they wear down.
Wastewater from Tamsley homes flows to the reclamation facility. The water passes through several stages. Bar screens catch rags and large debris first. A grit chamber then slows the water so sand and coffee grounds settle out. In the primary clarifier the water sits still for hours, so heavy particles sink into sludge at the bottom and light ones float to the top as scum, which a skimmer removes. Light plastics float, and heavier plastics settle, so both are pulled out here. The water then moves to the aeration basin, where bacteria feed on dissolved waste and clump together. In the secondary clarifier those clumps settle, and plastic particles tangled in them settle too. Last, the water passes through a sand filter and is disinfected before it flows to the river. Treated water leaving a plant is called effluent.
Plant staff sampled the water at four points on the same day. The results were 84 particles per liter entering the plant, 32 after the primary clarifier, 9 after the secondary clarifier, and 3 in the water leaving the sand filter. That is a removal of about 96 percent.
The captured plastic does not disappear. It leaves with the sludge, which Tamsley hauls to a composting site. The plant plans to sample the same four points once a month to watch whether the numbers change with the seasons.
The plant superintendent notes that keeping particles out of the drain costs less than taking them out at the plant. Filters that fit on a washing machine drain catch many microfibers before they leave the house.
Your task. Write an article of 350 to 500 words for the Tamsley town newsletter. Your readers are adults who do not work in water treatment. Your article must explain how at least three treatment stages remove plastic particles, state what share of the particles the plant removes and use the sampling numbers as support, explain why some particles still reach the river, describe the plant's monthly sampling plan, and name one thing residents can do to send fewer particles to the plant. Use a clear, informative voice rather than a persuasive one.
Planning Organizer
Fill in every row before drafting. Each row matches one criterion on the rubric.
| Part of the article | What to write here | My notes |
|---|---|---|
| Opening | One or two sentences naming the topic and why a Tamsley reader should care. | |
| Stage 1 | Which stage, and how it removes particles. | |
| Stage 2 | Which stage, and how it removes particles. | |
| Stage 3 | Which stage, and how it removes particles. | |
| Data sentence | The share removed, plus the two sampling numbers you will quote to support it. | |
| Why some get through | The reason particles still leave in the treated water. | |
| Where the plastic goes | What happens to the particles the plant does capture. | |
| Monitoring plan | How often the plant samples, and at how many points. | |
| What readers can do | One source-reduction step and why it works. |
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Exemplar & Rubric
Exemplar response (grade 7 level, 439 words)
Every load of laundry in Tamsley sends thousands of plastic threads down the drain. Those threads, along with worn tire dust and broken-down packaging, are called microplastics, and most of them end up at the Tamsley Water Reclamation Facility. The plant was built to clean out human waste rather than plastic, and it removes most of the plastic anyway. The reason is in the stages the water passes through on its way to the river.
The first real capture happens in the primary clarifier. Water sits nearly still in a large tank for several hours. In that quiet, heavy particles sink to the bottom as sludge, and light material floats to the top as scum that a skimmer scrapes away. Plastic goes both directions. Dense fragments settle, and buoyant pieces float, so the tank catches both kinds at once.
The aeration basin comes next. Bacteria there feed on dissolved waste and clump into sticky masses. Plastic fibers tangle in those masses. When the water reaches the secondary clarifier, the clumps settle out and carry the tangled fibers down with them. Last, the water passes through a sand filter, where the narrow spaces between grains trap smaller pieces that made it that far.
The plant's own sampling shows how well this works. On one sample day, water entering the plant carried 84 particles per liter. Water leaving the sand filter carried 3. That is a removal of about 96 percent of the particles.
Some particles still get through, and the reason is size. The smallest fragments and the thinnest fibers do not settle quickly, do not float, and can slip between sand grains. Treatment reduces the number sharply, but no stage in the plant is a barrier fine enough to stop every piece.
The captured plastic does not disappear. It leaves the plant in the sludge, which Tamsley trucks to a composting site. The plastic has been moved out of the river's path, but it has not been destroyed.
To keep track of all this, plant staff plan to sample the same four points once a month: the water entering the plant, the water after the primary clarifier, the water after the secondary clarifier, and the water leaving the sand filter. Monthly sampling will show whether the numbers rise in some seasons and whether the plant's performance changes over time.
Residents can help at the source. A filter that fits on a washing machine drain catches many microfibers before they ever leave the house. The superintendent makes a practical point, which is that keeping particles out of the drain costs the town less than taking them out at the plant.
Rubric
| Criterion | Emerging | Developing | Proficient | Advanced |
|---|---|---|---|---|
| Content accuracy | Describes the process incorrectly or too vaguely to check | Describes one stage correctly and others loosely | Describes three stages correctly and explains how each traps particles | Describes three stages correctly and distinguishes settling, floating, and filtering as different mechanisms |
| Use of data | Includes no numbers from the background | Mentions a number without connecting it to a claim | States the removal share and supports it with two sampling numbers | Uses the sampling numbers to show where the largest single drop occurs and what that means |
| Completeness | Misses several required parts | Covers about half the required parts | Covers all required parts, including monitoring and source reduction | Covers all parts and connects the monitoring plan to what the plant would do if numbers rose |
| Audience and conventions | Voice and vocabulary do not suit adult readers; errors block meaning | Some jargon left unexplained; errors distract | Clear, informative voice with terms explained and few errors | Consistently clear for a general adult reader, well organized, with clean conventions |
Differentiation
Support
Provide a labeled flow diagram of the plant with the four sampling points marked, and let students annotate it before writing. Give a paragraph frame for each stage: "In the ___, the water ___. This removes plastic because ___."
Extension
Ask students to write a short second section proposing what the plant should measure to find out whether the microfiber filters are working, including where to sample, how often, and what result would count as success.
ELL supports
Pre-teach "settle," "float," "trap," and "sludge" with a clear jar of water containing sand, cork pieces, and thread, letting students watch what sinks and what floats. Allow students to label the flow diagram in their first language before writing the article in English.