Water for Schools
Menu

Lesson plan Grade 7 English Language Arts

The Microbes at the Quinnet Mills Plant: Explanatory Writing

A grade 7 ELA lesson on process writing in which students read about the bacteria that treat sewage and explain the four stages to a reader who has never seen a plant.

Objectives

  1. Students will explain a four-stage process in the correct sequence using transition words.
  2. Students will define a technical term in plain language for a named audience.
  3. Students will cite the sentence in a source text that answers a why question.

Vocabulary

Activated sludge
Activated sludge is a living brown mixture of helpful bacteria and other microbes that wastewater plants grow on purpose. The microbes clean the water by eating the waste in it.
Aeration
Aeration means mixing air into water. At a wastewater plant, blowers bubble huge amounts of air through tanks so the helpful microbes have the oxygen they need to eat the waste.
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: microbe, transition

Teacher overview

The misconception this lesson corrects is the belief that a wastewater plant cleans water by straining it, which is a reasonable guess because screens and filters are the equipment a visitor notices first. The treatment tanks at the fictional Quinnet Mills plant hold billions of bacteria that feed on the waste in the water, and the operators' main job is keeping those bacteria fed, aerated, and settled. The reading and the writing task both keep returning to what the microbes consume and why the plant adds air. Students then explain the process to a reader who has never seen a plant, which is where sequencing and transitions matter.

Procedure

Hook (5 min): Ask students to write one sentence answering the question "What actually removes the waste from used water?" Collect two or three answers aloud. Most classes will say filters or screens. Record those answers where the class can see them and tell students they will check the prediction against the source text.

Close reading of the source text (10 min): Distribute the Student Handout. Read the source text aloud once while students follow. On a second pass, students underline every sentence that mentions the microbes and circle every sentence that gives a reason. Ask two students to read a circled sentence and name what it explains.

Mini-lesson on process transitions (10 min): Post a short list of sequence and cause transitions: first, next, after that, once, because, so that, as a result, finally. Model two sentences about the plant in the town of Quinnet Mills, one weak and one strong, and ask the class which transition makes the order of events clear. Point out that a process explanation fails when a reader cannot tell which step comes first.

Guided paragraph (10 min): Work with the class to draft the first two sentences of the four-stage explanation on the board, taking wording from students and revising it aloud. Stop after two sentences so students draft the rest themselves.

Independent drafting (12 min): Students complete handout items 1 through 8. Circulate and check that item 4 is written for a younger reader rather than copied from the text.

Exit check (3 min): Students read their item 6 paragraph to a partner, who signals whether the four stages were in order. Collect any paragraph a partner could not follow and use those for the next day's revision lesson.

The Microbes at the Quinnet Mills Plant: Explanatory Writing — Grade 7 English Language Arts
Name: ____________________________ Date: ______________

Student Handout

Source text: How the town of Quinnet Mills cleans its used water.

Every sink, shower, and toilet in Quinnet Mills drains to one plant beside Camber Brook. The water arriving there is not dirty in the way a muddy shoe is dirty. Most of what has to be removed is food waste, soap, and body waste that is dissolved or in pieces too small for a screen to catch.

The plant removes that waste with living things. In the aeration tank, billions of bacteria and other microbes feed on the waste in the water. Operators call the thick brown mixture of water and microbes activated sludge. Blowers push air through the bottom of the tank all day, because the microbes need oxygen to keep eating. Without air, the useful microbes die off and the tank begins to smell.

After several hours in the aeration tank, the mixture flows to a settling tank called a clarifier. There the water slows down and the heavy clumps of microbes sink. Clear water moves off the top. Operators pump some of the settled sludge back to the front of the aeration tank, so a healthy population of hungry microbes is always waiting for the next load. The rest is removed and treated separately.

The water that leaves the plant is called effluent, and it is tested before it returns to Camber Brook. Secondary treatment standards require a monthly average of 30 mg/L or less for the measures of organic waste and suspended solids, which is roughly 85% removal, since raw sewage usually runs 200 to 300 mg/L. Most fish need dissolved oxygen above 5 mg/L, and waste left in the brook would be eaten by microbes there instead, using up the oxygen the fish need.

  1. In your own words, what job do the microbes in the aeration tank do?
  2. Copy the sentence that explains why blowers push air through the aeration tank.
  3. Copy the sentence that explains why operators pump settled sludge back to the front of the aeration tank.
  4. Write a one-sentence definition of activated sludge that a fifth grader would understand.
  5. List the four stages of the process in the order they happen.
  6. Write a paragraph of four sentences explaining the four stages. Use a different transition word from the posted list in each sentence.
  7. Explain why waste left in Camber Brook would be a problem for fish, using a detail from the last paragraph.
  8. Name one thing a reader who has never seen a plant would still not understand after reading your paragraph, and say how you would fix it.

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: They eat the dissolved waste in the water.
    Accept any answer naming the microbes as the thing that removes the waste. Students still answering "filters" should be sent back to the second paragraph.
  2. Answer: The sentence saying blowers push air through the bottom of the tank all day because the microbes need oxygen to keep eating.
    Accept the sentence copied in full or from the word "because" onward.
  3. Answer: The sentence saying operators pump some settled sludge back so a healthy population of hungry microbes is always waiting for the next load.
    Students who copy the following sentence about removing the rest have found a related but different idea and should recheck.
  4. Answer: Accept any plain-language definition naming a mixture of water and living microbes that eat waste.
    A proficient definition avoids the words aeration and clarifier or explains them. Copying the text word for word does not meet the item, since the audience is younger.
  5. Answer: Arrival at the plant, the aeration tank, the clarifier, and testing before release.
    Accept equivalent wording. The order matters more than the labels.
  6. Answer: Accept any four-sentence paragraph with the stages in order and four different transitions.
    Look for transitions that mark sequence, such as first, next, and finally, and at least one that marks cause, such as because or so that.
  7. Answer: Microbes in the brook would eat the leftover waste and use up the oxygen fish need.
    The text gives the benchmark of 5 mg/L for most fish, so a strong answer connects the leftover waste to lower oxygen rather than to dirt.
  8. Answer: Accept any specific gap with a specific fix.
    Strong responses name something the paragraph assumes, such as what a clarifier looks like or how long the water stays in the tank, and propose a definition, a comparison, or a labeled sketch.

Differentiation

Support

Provide the source text with the four stages already numbered in the margin, and give students a four-box strip with one transition printed in each box so item 6 becomes a matter of filling boxes in order. Allow items 2 and 3 to be answered by highlighting rather than copying.

Extension

Ask students to rewrite their item 6 paragraph twice, once for a second grader and once for a town newsletter aimed at adults, then write two sentences comparing the choices they made about vocabulary and sentence length for each audience.

ELL supports

Pre-teach "microbe," "aeration," and "settle" using a jar of muddy water that clears as the solids sink. Provide the transition list as a printed strip that stays on the desk. Accept phrase-length answers for items 1, 5, and 7, and allow the item 4 definition to be spoken before it is written.

Extensions

Students turn their explanation into a labeled diagram with four boxes and arrows, then compare the diagram with their paragraph and mark which details the diagram carries better and which ones only the sentences can carry.