Open hardware · 2024 design

Compost Energy: heat from what we throw away.

Composting microbes run hot, 55 to 70 °C, for weeks. I designed a home unit to capture that heat and return enriched fertiliser to the soil, then let the numbers decide where it actually works.

Open hardware · prototype design (2024)

How Compostito works, in about two and a half minutes: composting, aerobic and anaerobic, the four chambers, the phases, where the heat goes, and why aerobic compost makes a better fertiliser. Captions are in the video. The temperature curves are simulated and labelled as such.

From the home to the farm

I started by designing Compostito for individual homes: food scraps in at the top, heat for the house, and enriched fertiliser out at the bottom. After doing the maths, it did not add up at that scale, so I pivoted the design to farm scale.

Author: Maxime Kadri; I own the IP and all deliverables
Started: 2024, with a French provisional patent, since lapsed and now published openly
Status: Design, costed prototypes and a simulation; no physical build measured yet
Licences: Hardware CERN-OHL-P 2.0 · documents, data and video CC BY 4.0 · code MIT

~59 WAverage heat in one household's food waste. A 50 W fan and controller cancel it out.Model

~50 WWhat a 3 m pipe buried in compost really collects. The 2024 sizing said 3.5 kW; compost conducts heat poorly.Model

38 %Share of microbial heat that reached the water in an enclosed composter on a 150-cow dairy farm (Kojima et al., 2022).Measured, third party

Drawings

Five drawings, generated from one script so a dimension changes in one place. Dimensions are indicative: they come from the prototype bill of materials, not from a verified build.

**CE-01 · Compostito, isometric cutaway.** Four phase chambers, mesh baskets, vents, drip line and the coil in chamber B.

**CE-02 · Prototype 2 build drawing.** Front, side and top views with a parts list keyed to the bill of materials.

**CE-03 · Exchanger coil.** One tube against two, and where the thermal resistance sits.

**CE-04 · Water loop P&ID.** By-pass on a heating return, with the logger's sensor tags.

**CE-05 · Farm-scale layout.** Reactors, exhaust-air heat recovery, maturation and storage.

Known and still open

The home unit is designed, costed and simulated, but not yet built and measured. At farm scale, the open questions are a nearby heat user, moving tonnes of mixed material through enclosed reactors, and the recovery rate in a large reactor. Each needs a pilot, not a model.

And the loop closes

Working on heat, soil or waste?

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