Skip to the tool
formerly ielts.gg
Start

Process diagram: Wastewater treatment

Pick out the main features of this process diagram for your overview, write your report on a 20-minute timer, then compare it with a band-8 model answer.

WRITING TASK 1

Process diagram

You should spend about 20 minutes on this task.

The diagram below shows how sewage is cleaned at a treatment plant.

Summarise the information by selecting and reporting the main features, and make comparisons where relevant.

Write at least 150 words.

Wastewater treatment
  1. 1ScreeningLarge objects are removed from the sewage
  2. 2Grit removalSand and stones settle in a channel
  3. 3Primary settlingSolids sink to form sludge
  4. 4AerationAir is pumped in so bacteria digest waste
  5. 5Secondary settlingRemaining particles settle out
  6. 6DisinfectionChlorine or ultraviolet light kills germs
  7. 7DischargeClean water is returned to the river
  8. 8Sludge treatmentSludge is dried and used as fertiliser

GoPrep wrote this practice question in the style of the exam. It is not an official IELTS question.

What your overview should say

An overview names the main trends or differences in one or two sentences, without numbers. These are the features a strong answer picks out:

  1. 1Overall, wastewater treatment is a linear process with eight stages in which sewage is cleaned and returned to the river, while the leftover sludge is processed separately.
  2. 2The water is first screened and passed through a grit channel to remove large objects and sand, then left to settle so solids sink as sludge.
  3. 3Bacteria then digest the remaining waste, the water settles again, and it is disinfected and discharged, while the sludge is dried for fertiliser.

Write it on the clock

Spend the first few minutes planning, then write.

20:00

0 words of 150 minimum

Your answer stays on this page only. Copy it before you leave.

Band-8 model answer

Write your own answer first, then compare: how it answers the exact question, what each paragraph does, and which phrases you could borrow.

Show model answer (189 words)

The diagram illustrates how sewage is cleaned at a wastewater treatment plant, a process with eight stages.

Overall, the water passes through a series of screening, settling and treatment stages before it is discharged, clean, into the river. The solid waste is dealt with separately as sludge. The first three stages remove solid materials, the next two use bacteria and settling to deal with the remaining waste, and the final three disinfect and release the water and treat the sludge.

First, the sewage is screened so that large objects are removed. It then passes through a channel in which sand and stones settle, in the stage called grit removal. In primary settling, solids sink to the bottom and form sludge.

Next, air is pumped into the water in the aeration stage, so that bacteria can digest the waste. Any remaining particles are then allowed to settle out in secondary settling. The water is disinfected with chlorine or ultraviolet light, which kills germs.

Finally, the clean water is discharged back into the river. The sludge that was removed earlier is treated separately, and it is dried and used as fertiliser.

Useful vocabulary

PhraseMeaning
sewagewaste water from homes
screenfilter out large items
settlesink to the bottom
aerationadding air to water
disinfectkill germs
sludgesemi-solid waste

Guides

More questions like this

All process diagram questions

Getting ready for IELTS?

Get your study plan

More free IELTS tools

All free tools

Speaking topic generator

Answer random Part 1, 2 and 3 questions on an exam timer.

IELTS band score calculator

Average your four skill bands, rounded the way IELTS rounds them.

IELTS score converter

Compare an IELTS band with TOEFL, Duolingo and PTE scores and CEFR levels.

University IELTS requirements

Look up the IELTS score a university asks for, with the source.