Week 11 Tutorial: Where the nitrogen goes, and choosing between the options

Week 11 tutorial — size excreta and greywater to your site's band, find a destination for the nitrogen surplus, then build the options grid Assignment 2 turns on

20 May 2027

Time

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

Graded

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

Due

5 pm, 21 May 2027

What this tutorial is for#

Two halves. First the nitrogen, which is the constraint that caps every site. Then the comparison itself — the grid that Assignment 2’s recommendation comes out of.

Story stage. Design, second last week. This is the last graded checkpoint.

Open these first#

• Your workbook, week 2’s planted area and week 10’s balance.
• Week 11’s lecture for the uptake-limited balance and the storage bands.
• The price schedule — the grid is costed from it.
• Your home’s jurisdiction on its dossier.

If you missed week 10#

You need a planted area and a rough nutrient input. Use PRACTICE — Wattle Street: 120 m² planted, receiving 4 kg of nitrogen a year from compost. Invented round numbers for teaching.

The words this week uses#

• Storage band — the WHO guidance period that excreta must be stored before use, which depends on climate: warmer sites need less time.
• Uptake limit — how much nitrogen a garden can absorb per square metre per year before the surplus becomes pollution rather than fertility. The course uses 12 g N/m²/year.
• Greywater — wastewater from showers, basins and laundry, but not toilets.
• Dominated option — an option that is worse than another on every axis you care about. It can be struck out without further argument, and marking it is part of the exercise.

Do this — part one, nitrogen (45 minutes)#

1. Size the chamber. Storage band from your site’s annual mean, then capacity. Canberra and Adelaide students will find they need roughly 75 % more volume than the warm sites for the same four people, which is worth sitting with.

2. Then the nitrogen. Absorbable N against the household’s 13.6 kg a year. Everybody’s surplus is large. The activity is deciding where it goes — extended storage, alkaline treatment, export to a larger area, or reduced recovery in the first place — and costing that decision.

3. Then the citation exercise, which is the point of the session. Find your jurisdiction’s greywater instrument. Read what it actually requires. Write two sentences: what the law says, and where this course is stricter. Four of the five sites will find the course rule is not their law.

Do this — part two, the options grid (45 minutes)#

4. Write the existing condition down first. From your findings page: what the home currently uses, imports and wastes. Every option is compared against this, and “do nothing” is a legitimate baseline that sometimes wins on one axis.

5. Build three options. Coherent packages, not shopping lists, and all three actually buildable on your site. One should be noticeably cheaper than the others — that is usually the interesting one.

6. Mark the dominated options. An option worse on every row than another is struck out, with a line through it and one sentence of reason. Then identify the cheapest option that meets your client’s stated targets. Anything more expensive than that has to justify itself in Assignment 2, and this grid is where you find out what it would have to justify.

7. Say what you are declining. If mushrooms, insects or aquaponics do not earn their place on your site, write the sentence now, with the number behind it. That is a result, not a gap.

The output#

A nitrogen balance with a destination for the surplus, a cited greywater instrument, and an options grid with the dominated options marked and the cheapest feasible option identified.

Check your own before you submit#

1. Does your chamber capacity match your site’s band, and can you say why the band differs?
2. Does the nitrogen balance show absorbed and surplus separately, with the surplus going somewhere?
3. Have you cited an actual instrument, and said where the course rule is stricter?
4. Does the grid include the existing condition as a column?
5. Are all three options buildable on your site, and is one of them clearly cheaper?
6. Are dominated options marked, each with a one-sentence reason?
7. Is the cheapest option that meets the client’s targets identified?

Where it goes next#

Week 12 assembles everything, runs the five whole-system checks, and finds out which subsystem gives way first.

Back to week 11 overview