Week 10 Tutorial: Closing the mass balance

Week 10 tutorial — route every organic stream to a destination and prove, in dry matter, that nothing has quietly disappeared

13 May 2027

Time

90 minutes in the room, plus about 30 to tidy the output

Graded

Checkpoint 9 of 10, 2 % — a good-faith attempt at the output below

Due

5 pm, 14 May 2027

What this tutorial is for#

Every stream goes somewhere. Today you tabulate all of them, give each a destination, and find out whether the arithmetic closes — which is the first week the separate subsystems stop being separate.

Story stage. Design. Your home’s four-week food-waste audit replaces the 380 kg convention you used in week 4. This is the week an arrow drawn wrongly in week 3 shows up.

Open these first#

• Your home’s specialist findings, for the food-waste audit, from clients.
• Your workbook, weeks 3, 4 and 5 — spent substrate, frass and fish sludge.
• Week 10’s lecture for the stream-by-stream method and the temperature check.

If you missed weeks 3 to 5#

Use the labelled practice streams and redo it later: PRACTICE — Wattle Street: 70 kg fresh spent substrate, 8 kg dry frass, 15 kg wet fish sludge a year. Invented round numbers for teaching.

The words this week uses#

• Dry matter — mass after the water is taken out. Streams are compared on a dry basis because wet masses of different materials are not comparable.
• Frass — insect droppings plus shed skins and leftover substrate from the larval unit.
• Residual line — the gap you write in to make a balance appear to close. It is not a loss term; it is the absence of one.
• Pasteurisation target — the time-at-temperature a compost process is designed to reach to kill pathogens. It belongs to a named standard, and the standard has a jurisdiction.

Do this#

1. Quiz 4 (20 minutes). On paper, on weeks 9 and 10.

2. Tabulate every stream (25 minutes). Food waste split by type, prunings, spent substrate, frass, sludge. Mass in dry matter for each, destination for each:

3. Then close it (25 minutes). In equals out plus losses. A balance that closes only because you wrote the gap into a residual line has not closed — name the loss and say what process causes it. Respiration, leachate and volatilisation are processes; “balance” is not.

4. Then check the temperatures (20 minutes). Can your bay actually reach and hold its pasteurisation target in your climate, in the month it is hardest? Canberra students should look at a July bay honestly. Alice Springs students should look at where the moisture comes from. Name the standard you are designing against and whose it is.

5. Biogas, if any (5 minutes). Record it. Do not credit it. Only the digestate’s nutrients count toward anything in this course, and the scope page says why.

The output#

A closed dry-matter balance in which every organic stream has a named destination and every loss term is stated as a process.

Check your own before you submit#

1. Is every stream’s mass in dry matter, with the dry fraction shown?
2. Does every stream have a destination — including meat and dairy?
3. Is there a residual line anywhere? There should not be.
4. Is each loss term named as a process, with a reason?
5. Does your compost design name its pasteurisation target and whose standard it is?
6. Does your food-waste input come from your home’s audit rather than the 380 kg convention?
7. Is biogas, if present, recorded and uncredited?

Where it goes next#

This table is the waste-stream recovery evidence in Assignment 2. It is not banded, so the table itself is what gets marked — not a number derived from it.

Back to week 10 overview