Every stream goes somewhere#
SLOP4761 · Week 10 · Waste recovery and integrated balances
Where we are#
The first week the subsystems stop being separate. An arrow drawn wrongly in week 3 shows up here as a balance that will not close.
Your home’s four-week food-waste audit now replaces the 380 kg convention.
This week’s question#
Your household generates food waste, your mushrooms leave five kilograms of spent substrate for every kilogram picked, your fish tank produces sludge, and weeks 4 and 5 sent the meat and dairy away unprocessed.
Where does each of those go, and does the mass balance close?
By the end you can#
- Track every organic stream in dry matter, with a named destination
- Close a balance with stated loss terms rather than a residual line
- Design a compost bay against a named pasteurisation target, in your climate
Balance by stream, in dry matter#
Every stream tracked separately, in kg of dry matter, destination named.
Waste-stream recovery is deliberately not banded. It has no reference calculation behind it, and publishing a band without one would be inventing a number. It is marked from your balances against the rubric instead.
In equals out plus losses. A balance that closes because you wrote the gap into a residual line has not closed. Name the loss and say what process causes it: respiration, leachate, volatilisation.
Hot composting: the target#
The Australian composting standard as described by a state environment regulator:
- core above 55 °C for three consecutive days after each of at least three turns
- manure, food and grease-trap feedstocks: fifteen consecutive days after each of at least five turns
- whole process not less than six weeks
Two scope notes you must carry#
- That is a commercial windrow standard. No household is bound by it — this course uses it as the target a bay is designed against
- It is more demanding than usually quoted: fifteen days after each of five turns, not fifteen in total
WHO’s separate figure for composting excreta is above 50 °C for at least one week — and WHO cautions it is “mainly recommended as an off-site secondary treatment at large scale”.
Anaerobic digestion, and the biogas rule#
Strongly temperature dependent — screening factors run from 0.63 at Darwin to 0.07 at Canberra.
Biogas earns you nothing. It is energy, it belongs to the proposed sequel, and only the digestate’s nutrients count here.
Record it anyway. An unrecorded output is the same mistake as an unrecorded import.
Worked example: Alice Springs#
90 days a year at or above 35 °C. Reaching 55 °C is a question of managing moisture, not of adding heat.
| Stream | Mass | Destination |
|---|---|---|
| Plant-based food waste | 228 kg/yr | Insect unit, then frass to soil |
| Meat, dairy, cooked | 152 kg/yr | Hot compost or digester — 15-day class |
| Spent substrate | ~5 kg per kg picked | Compost and soil |
| Fish sludge | from the system | Compost or digester; never larvae |
| Garden prunings | site-dependent | Mushroom substrate, then compost |
Alice Springs’ trap#
A bay that dries out stops composting and never reaches pasteurisation temperature.
So the water hot composting consumes is a genuine line item on the site’s most constrained resource.
It is easy to write a compost plan here that quietly needs water the site does not have.
Your tutorial task#
- Quiz 4, twenty minutes, on weeks 9 and 10
- Tabulate every stream: wet mass, dry fraction, dry mass, destination, source
- Close it. Name each loss as a process
- Check your bay’s temperature in the month it is hardest
- Record any biogas; credit none of it
Output: a closed dry-matter balance with every stream routed.
Before you leave#
- Is every mass in dry matter, with the dry fraction shown?
- Is there a residual line anywhere? There should not be
- Does your compost design name its target and whose standard it is?
- Does your food-waste input come from your home’s audit?
Full sources in the week 10 notes.