The loop does not close#
SLOP4761 · Week 4 · Insects, waste streams and conversion limits
Where we are#
Week 3 gave you a stream you cannot feed to the larvae. Week 4 asks what you can feed them, and what it buys.
Still scoping. The 380 kg food-waste figure is a published household convention, not a measurement of this house.
This week’s question#
Search for a closed-loop household diagram and you will find this arrow:
kitchen scraps → black soldier fly larvae → fish → you
drawn as a closed circle, roughly every time.
Size it. What fraction of the fish’s feed do your own scraps actually cover?
By the end you can#
- Apply a dry-matter bioconversion chain with every factor stated
- Decide between outdoor rearing at your climate’s factor and indoor rearing at a counted energy cost
- Put a number on the import arrow instead of omitting it
Thresholds and dry matter#
Black soldier fly larvae have a lower developmental threshold of 10.4–12.3 °C. Below it, development stops.
Egg to adult: 91 days at 19 °C, 42 at 28 °C, 32 at 31 °C. Best population growth near 30 °C.
This course screens each site with a linear productive factor ramping from 12 °C to 27 °C — a simplification, and labelled one.
On food waste, larvae achieve about 52 % substrate reduction and 28 % bioconversion over 14 days on a dry-matter basis. This course uses 20 %, as a conservative course assumption.
Worked example: Darwin, the best site there is#
Productive factor 0.97 — thermally productive essentially all year.
| Step | Factor | Running total |
|---|---|---|
| Household food waste | — | 380 kg/yr |
| Plant-based share (course rule) | × 0.60 | 228 kg/yr |
| Dry matter | × 0.25 | 57 kg DM/yr |
| Bioconversion | × 0.20 | 11.4 kg DM/yr |
| Darwin thermal factor | × 0.97 | 11.1 kg DM/yr |
Demand side — a 4 m² grow bed at the FAO feed rate:
50 g/m² × 4 m² × 365 d = 73 kg feed/year 11.1 ÷ (73 × 0.9) = 17 %
Seventeen per cent. At the best site.#
With the whole household’s plant-based scraps committed.
- An 8 m² bed halves it to about 8 %
- Canberra outdoors, at a thermal factor of 0.19, manages about 3 %
The other 83 % is bought feed. Under this course’s closure definition, fish grown on bought feed are bought fish — so a Darwin excellent design counts 0.27 kg of fish protein a year against a household requirement of 67.5 kg.
That is a result, not a reason to abandon the module.
Your tutorial task#
- Run the five-factor chain, each factor its own row with its source
- Choose outdoor or indoor. Indoor costs about 0.53 everywhere and a counted heating load in watts and hours
- Draw the import arrow, with a percentage on it
- Route meat, dairy and fish sludge away from the larvae, with the reason
Output: a feed mass balance with the import line labelled.
Before you leave#
- Are all five factors on the sheet with their sources?
- Does an arrow enter your diagram from outside, with a number on it?
- If indoors: is the load in watts and hours, flagged for week 12?
- Does your site’s dossier permit the unit where you drew it?
Full sources in the week 4 notes.