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Process diagram: Biogas production

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 biogas is produced from farm waste.

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

Write at least 150 words.

Biogas production
  1. 1Collecting wasteManure and crop waste are gathered
  2. 2Mixing tankWaste is mixed with water
  3. 3DigesterBacteria break down waste without oxygen
  4. 4Gas collectedMethane rises and is stored in a dome
  5. 5Gas cleanedImpurities are removed
  6. 6GeneratorBiogas fuels an engine
  7. 7Electricity and heatPower is supplied to the farm
  8. 8DigestateLeftover slurry is spread 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, biogas production is a linear process of eight stages, in which farm waste is converted into energy for the farm and fertiliser.
  2. 2Manure and crop waste are collected, mixed with water and broken down by bacteria in an airtight digester.
  3. 3The methane produced is stored, cleaned and burned in a generator to supply electricity and heat, while the leftover slurry is spread on fields.

Write it on the clock

Spend the first few minutes planning, then write.

20:00

0 words of 150 minimum

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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 (176 words)

The diagram shows how biogas is produced from farm waste, a process that has eight stages.

Overall, the process is linear. Farm waste is converted into methane gas by bacteria, and the gas is cleaned and used to generate power, while the leftover waste is used as fertiliser. The first three stages prepare the waste, the next three produce and clean the gas, and the last two make use of the energy and the by-product.

First, manure and crop waste are gathered, and the waste is then mixed with water in a mixing tank. The mixture is fed into a digester, where bacteria break the waste down without oxygen.

As a result, methane rises and is collected and stored in a dome. After that, impurities are removed from the gas in the cleaning stage. The biogas is used to fuel an engine in a generator.

The generator produces electricity and heat, and the power is supplied to the farm. In the final stage, the leftover slurry, known as digestate, is spread on the land as fertiliser.

Useful vocabulary

PhraseMeaning
biogasfuel gas made from waste
digestertank where waste breaks down
without oxygenin the absence of air
methanea fuel gas
remove impuritiestake out unwanted substances
digestatematerial left after digestion

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