Teaching Sequence

15 minutes – Part A: How much waste is there?
25 minutes – Part B: Can we turn waste materials into energy?
20 minutes – Part C: What are the savings?
15 minutes – Reflection: Can we make improvements?

Work through this resource material in the following sequence:

Part A: How much waste is there?

Step 1.

To begin this lesson, read, project or write on the board the Thought Starter (below and on the Student Worksheet) and allow discussion of ideas or just some quiet time for students to think about this question:

Thought-starter: Is there a way to turn waste into energy?

Now direct students to the Next 20 Years - Waste Production Graph (also available on the Student Worksheet). This graph shows the amount of waste generated by Australia per year from 1996 to 2011, and projected figures up to the year 2036. Allow students a minute or two to comprehend the graph and then explain the following points:

The graph shows a constant (linear) rate of growth from 1996 to 2011.
This rate (or gradient) has been used to make projections up to 2036.
The total amount of waste generated is in megatonnes, which is a million tonnes or a billion kilograms.

Now ask students to calculate the projected percentage increase from 1996 to 2036. They will need to estimate the 1996 value, which is approximately 23 megatonnes. Students can record their responses on Table 1 of the Student Worksheet.

Working:
Percentage increase: difference in amounts / original amount x 100

(109 - 23) / 23 x 100
= 373.9 %

The amount of waste is projected to increase by approximately 374%

Explain the significance of this percentage, pointing out that this value indicates that the original amount has not just doubled or tripled, it has quadrupled. It is almost five times bigger than the original amount. If your class struggles to understand percentage growth you could also point out the following:

100% growth means the population has doubled
200% growth means the population has tripled
300% growth means the population has quadrupled
400% growth means the population has grown to five times the original amount.

Now ask students to estimate the amount of waste generated in 2018 and compare this to the 1996 value. Ask students to think about why these figures have increased by so much, and to list possible reasons.

Step 2.

Now ask the class to analyse these two graphs: Energy From Waste Graph 1 and Energy From Waste Graph 2 (also available on the Student Worksheet) and to read the quote on population growth. Direct students to identify and record any trends or observations on the Student Worksheet.

Students should identify the following:

Despite large growth in waste generation, greenhouse gas emissions have reduced since 1996 (but remained relatively constant from about 2004)
The recycling rate has grown at a rate consistent with waste generation
The amount of waste sent to landfill fluctuated but is approximately the same amount as it was in 1996
Although the population has grown, the growth is not consistent with the amount of waste sent to landfill.

Discuss these trends with students to help them understand the current situation regarding waste generation.

Part B: Can we turn waste into energy?

Step 1.

Remind students of the Thought Starter at the beginning of the lesson: "Is there a way to turn waste into energy?". Allow students to share prior knowledge of sustainable technologies they may be familiar with (e.g. biomass, cogeneration) or other ideas on the topic (students can use the Student Worksheet to record their ideas). Ask students to list the benefits of using waste to make energy. You may prompt students with the following ideas:

Less waste to landfill
Fewer emissions generated from landfill
Generation of electricity (which has not come from fossil fuels).

Step 2.

Explain to students the concept of Waste to Energy (WtE) whereby facilities are able to collect and use waste products to generate energy. Direct students to this Energy Flowchart and explain each of the following steps:

Waste to Energy is a process that captures the energy contained within waste products and uses it to make electricity, whilst also reducing the amount of waste sent to landfill
This flowchart shows waste being collected and delivered to a WtE facility
Once at the facility, the waste is processed (which may involve the removal of recyclables and shredding to reduce particle size)
The processed waste is then placed in a contained combustion chamber where it is exposed to high temperatures (800°C), creating steam
This steam is then used to turn turbines and generate electricity which can be used to run the facility or returned to the grid (represented by the electricity tower)
This process also collects and treats any harmful emissions released from combustion so any gases that are released from the facility are within EPA environmental standards (represented by the leaves above the exhaust)
The remaining ash (from combustion) can be further processed to create new products (e.g. concrete or other construction aggregates)
The whole process is similar to producing electricity from burning coal but is sustainable and more environmentally friendly.

Now explain to students that Viy's waste-to-energy/combined heat and power plants contribute to the electricity and thermal energy requirements of their Coolaroo (VIC), Tumut (NSW) and Gibson Island (QLD) paper mills. Visy’s Kraft Mill in Tumut is one of these facilities. Direct students to watch the video below for some background information regarding this mill. Watch the video from start to 1:09–1:10.

Visy Tumut Showcase 2017 (https://vimeo.com/visyvideos/visytumut)

Step 3.

Explain to your class that they are now going to investigate how much energy can be generated from rubbish, and how efficient WtE facilities are. Direct students to read the quote below and then ask them to calculate the amount of energy that 240,000 tonnes of biomass (from wood) would have.

Explicitly state that ‘calorific value’ refers to the amount of energy contained within different types of materials (e.g. wood, coal, oil). Students will assume that the calorific value of biomass from wood is approximately 18 MJ per kg (source).

Direct students to read the quote below (source). Invite them to record their responses on the Student Worksheet:

Working:
1000 kg in a tonne
240,000 tonnes = 240,000,000 kg

240,000,000 x 18
= 4,320,000,000 MJ

Step 4.

Now introduce the concept of efficiency. Explain to students that even though this biomass contains over 4 billion MJ, a WtE facility will not be able to capture this entire amount. State that a standard WtE facilitate has a minimum efficiency of 15% and a maximum efficiency of 27%. This means that the WtE process is only able to obtain about 20% of the total energy available in the biomass (source).

Ask students to calculate the total amount of MJ generated by the Tumut mill if it has an approximate efficiency of 20% (students can record their responses on the Student Worksheet).

Working:
4,320,000,000 x 20 / 100
864,000,000 MJ

The mill can generate 864,000,000 megajoules of energy within a year, from 240,000 tonnes of wood-related biomass.

Step 5.

Now ask your students to repeat these calculations using the calorific value and efficiency of coal in coal power stations, and household waste in WtE facilities. Students will use the 240,000 tonnes as the input value for both, so comparisons can be made. Students can record their working and responses on Table 2 of the Student Worksheet.

Energy Values	Biomass (wood) in WtE facility	Household waste (processed) in WtE facility	Coal
Energy (total) in 240,000 tonnes	Calculated in step 4	Calorific value of processed waste: 15.5 MJ/kg 240,000,000 x 15.5	Calorific value of coal: 22 MJ/kg 240,000,000 x 22
Energy (total) in 240,000 tonnes	= 4,320,000,000 MJ	= 3,720,000,000	= 5,280,000,000
Energy produced	Calculated in step 4	Efficiency of WtE: 20% 3,720,000,000 x 20/100	Efficiency of Coal power station: 33% 5,280,000,000 x 33/100
Energy produced	= 864,000,000 MJ	= 744,000,000 MJ	= 1,742,400,000 MJ

Source: https://www.wastenet.net.au/

To complete this section of the lesson, ask students to write a paragraph that compares the data in the table as well as the environmental costs and benefits of each method, to decide whether producing waste from energy is a viable or practical alternative to coal. Encourage students (particularly those who are highly able) to complete further calculations (e.g. finding differences or percentages of coal production) if they wish to justify their claims.

Students can write their paragraph in their workbooks or in the space provided on the Student Worksheet.

Example response: The amount of energy generated at WtE facilities is less than half of that at a coal facility, for the same weight of input. Using biomass from wood produced about 50% of the total amount of energy produced from coal, whilst using household waste only produced 42%. Despite this, however, waste production is a growing issue in Australia and the WtE method will not only reduce the amount of waste sent to landfill but also lower Australia’s reliance on coal. Although we will need to process twice as much waste as coal, the environmental benefits will outweigh the reduction in efficiency.

864,000,000 / 1,742,400,000 x 100
= 49.6%

744,000,000 / 1,742,400,000 x 100
= 42.7%

Part C: What are the savings?

Note: Now that students have an idea of how waste can be used to create energy, they can examine how reductions in landfill will help to reduce emissions. Students will focus on how much ‘bottom ash’ may end up in landfill compared to current projections and how many emissions this will prevent.

Step 1.

Direct students to look back on the waste projections from Part A. Remind them that in 2036 we, as a country, are projected to create 109 megatonnes of waste. Point out that this figure represents just the yearly value for 2036 alone, and have students imagine all 109 megatonnes piled up on top of 20 previous years of rubbish, plus the current volumes of landfills.

Now have students think back to the WtE flowchart and how the combusted material produces ash that may end up in landfill. Explain the following:

This ash weighs 20–30% of the original weight of the waste
This ash takes up only 10% of the volume of the original waste
Ash is not typically repurposed in Australia but can be made into construction aggregates (including concrete) or into biochar which can be used to improve soil conditions. (Source: https://www.wastenet.net.au/Profiles/wastenet/Assets/ClientData/Document-Centre/W2EDiscussionPaper_FINAL.pdf)

Explain to students that we are currently producing about 64 million tonnes of waste of which 27 million tonnes is ending up in landfill. Ask students to calculate how much waste (from ash) will go to landfill if our waste is first sent to a WtE facility. As it is unreasonable to expect 100% of waste to go to a WtE facility in just one year, have students work out progressive percentages of the waste, using the table below. Double-check that students know to use the 27 million tonnes per year as the base figure, and the approximate of 25% for the ash figure. (Source: https://www.environment.gov.au/system/files/resources/d075c9bc-45b3-4ac0-a8f2-6494c7d1fa0d/files/national-waste-report-2016.pdf)

Students can record their responses in Table 3 of the Student Worksheet.

Solution:

Percentage of waste going to WtE

No. of tonnes sent to WtE

No. of tonnes sent to landfill as ash (following WtE)

No. of tonnes diverted from landfill

% of waste diverted from landfill

100%

27,000,000

27,000,000 x 25/100

= 6,750,000

27,000,000 - 6,750,000

= 20,250,000

20,250,000 / 27,000,000
= 0.75 x 100

= 75%

80%

27,000,000 x 80/100

= 21,600,000

21,600,000 x 25/100

= 5,400,000

21,600,000 - 5,400,000

= 16,200,000

16,200,000 / 27,000,000
= 0.6 x 100

= 60%

60%

27,000,000 x 60/100

= 16,200,000

16,200,000 x 25/100

= 4,050,000

16,200,000 - 4,050,000

= 12,150,000

12,150,000/ 27,000,000
= 0.45 x 100

= 45%

40%

27,000,000 x 40/100

= 10,800,000

10,800,000 x 25/100

= 2,700,000

10,800,000 - 2,700,000

= 8,100,000

8,100,000 / 27,000,000
= 0.3 x 100

= 30%

20%

27,000,000 x 20/100

= 5,400,000

5,400,000 x 25/100

= 1,350,000

5,400,000 - 1,350,000

= 4,050,000

4,050,000 / 27,000,000
= 0.15 x 100

= 15%

Step 2.

Now direct students to the quote below. (Source: https://www.lms.com.au/assets/Media-Resources/Fact-Sheet-on-Emissions.pdf). Ask students to calculate the amount of carbon pollution that will be prevented due to sending all or a percentage of our waste to a WtE facility before landfill. Students can record their answers on Table 4 of the Student Worksheet.

Percentage of waste going to WtE	No. of tonnes diverted from landfill Calculated in Step 1	No. of tonnes of CO₂e prevented each year
100%	= 20,250,000	20,250,000 x 1.2 = 24,300,000
80%	= 16,200,000	16,200,000 x 1.2 = 19,440,000
60%	= 12,150,000	12,150,000 x 1.2 = 14,580,000
40%	= 8,100,000	8,100,000 x 1.2 = 9,720,000
20%	= 4,050,000	4,050,000 x 1.2 = 4,860,000

Reflection

Step 1.

Using the Student Worksheet, invite students to reflect on all of the new content and information they have covered in this lesson. Ask the following questions and advise students to give reasons as to why WtE facilities are useful and practical in Australia.

How much waste we are making?
How much energy can we make from waste?
How much carbon pollution will this prevent?

Step 2.

Explain to students that WtE is just another process or technology that is bound to improve in the next 5–10 years. Ask students to imagine that, in the next 5–10 years, they will be working as an engineer and designing or inventing new methods that will improve the WtE process. Ask students to record what they think are the most important parts to focus on for improvement.

Step 3.

Encourage your class to continue to think about the future. Ask them to imagine how different Australia might look if we utilised WtE across the country. Allow students some time to process their thoughts, or discuss with a peer, and ask them to record what improvements they would hope and/or expect to see.

Differentiated Learning

Extension – This lesson could be extended by reducing the amount of scaffolding and teacher direction. High ability students or extension classes may not need as much teacher guidance and may enjoy completing the lesson at their own pace. This lesson could be a student-led investigation whereby groups of students access resources and complete tasks independently of the class. There are also several sections of this lesson that could be extended to include higher math skills or terminology. See the list below for ideas:

Part A
- Treat graphs as straight-line functions and describe trends using relevant terminology (e.g. positive gradient).
- Explain how this graph is showing a constant rate.
Part B and C
- Could make explicit use of the efficiency formula (efficiency = useful energy/ total energy x 100).
- Could also set a research task for the class to investigate the running costs of a WtE facility to ensure that operating costs are not outweighing that the savings made from landfill diversion.

Since there are large numbers used throughout this lesson, you could also encourage students to express these numbers in scientific notation and use index laws to multiply.

Provisions for Learning Support – Depending on support requirements, students requiring learning support could work in a pair or group or receive additional scaffolding. The number of tasks within each part of this lesson could also be reduced (completing just one or two) or completed across the class (e.g. every different group completes a different percentage row for the tables in Part C).

Teacher Reflection

Take this opportunity to reflect on your own teaching:

What did you learn about your teaching today?
What worked well?
What didn't work so well?
What would you share?
Where to next?
How are you going to get there?

The information and statistics included in this document are approximate and have been simplified for educational/illustrative purposes. They should not be relied upon for any other purpose.

Visy Education - Waste to Energy

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