In-vessel composting systems
An in-vessel system puts the fermentation inside a controlled box. Residence time drops to one to two weeks, exhaust air can be treated, and the plant
01
The four design elements
- Aeration floor or plenum — perforated pipe grid embedded in wood chips or gravel, or a concrete floor with cast-in channels. Even distribution matters more than total air volume.
- Blower and control — one blower per pile or per group of piles, with a timer or oxygen-based control. Intermittent aeration on a 5–15 minute cycle is normal for the first 10 days.
- Cover — a breathable fleece blanket keeps heat and moisture in and keeps odour and dust in. A cover is what makes an aerated pile behave like a controlled process rather than a tall heap.
- Leachate and condensate path — the pile must drain to a collection channel; a saturated plenum stops passing air in exactly the place it is needed.
02
Sizing the air supply
| Stage | Typical aeration rate | Control basis | Effect on the pile |
|---|---|---|---|
| Days 0–3 (mesophilic to thermophilic) | 1.0–2.0 m³/kg VS·day | Continuous or 50% duty | Rapid temperature rise; peak oxygen demand |
| Days 4–10 (thermophilic) | 0.5–1.2 m³/kg VS·day | Temperature-controlled | Maintain 55–65 °C for sanitation |
| Days 11–14 (cooling) | 0.3–0.6 m³/kg VS·day | Timer, reduced duty | Heat generation falls; prepare for curing |
| Curing | 0–0.3 m³/kg VS·day | Occasional aeration or turning | Maturation at lower temperature |
Values are planning guidance for manure-based feedstock. Blower selection must account for system pressure drop through the pile, which rises with moisture and compaction.
03
Operating an aerated pile
- 01
Build the pile once, correctly
Mix moisture and amendment before the pile is formed. Re-mixing later means opening the pile and losing the heat and structure the cover was holding.
- 02
Cover immediately
The cover protects the surface zone, which is otherwise too dry and too cool to compost.
- 03
Follow the temperature trend
Probe at three depths daily. Rising temperature with falling oxygen means increase aeration; falling temperature too early usually means the air rate is too high and the pile is being cooled.
- 04
Do not re-handle during thermophilic phase
Every disturbance resets the surface zone. Turning is reserved for curing and for the first mix.
- 05
Break down, cure, then process
After 14–21 days the pile is discharged to curing bays before grinding and granulation.
04
Compared with turning
| Aerated static pile | Turned windrow |
|---|---|
| Air supplied by blowers; no machine on the pile | Air supplied by turning; pile re-built each pass |
| Lower labour, fewer machines to maintain | Higher labour and one large machine to maintain |
| Odour can be captured and treated | Extraction impractical in the open |
| Pile structure fixed at build; mixing errors persist | Turning can correct heterogeneity |
| Suits wetter or more odorous feedstock with a cover | Suits dry, fibrous feedstock and large sites |
| Needs reliable blowers, power and control | Needs a turner, fuel and an operator |
Design an aerated pile plant
Send the daily tonnage, feedstock and site plan; we return the pile layout, blower specification and aeration control philosophy.
FAQ
Plant engineering questions
How high can an aerated static pile be?
Two to three metres is typical. Higher piles reduce footprint but increase pressure drop, which raises blower power and risks channelling — air finding a path of least resistance instead of moving through the pile.
Does an aerated pile need turning?
Not during the thermophilic phase, which is the point of the system. Turning is used at build-up, at breakdown, and occasionally during curing if the material has compacted or dried unevenly.
What cover should be used?
A breathable fleece designed for composting, sized to overhang the pile, with the option of a negative-pressure canopy where odour must be extracted and treated. Plastic sheeting is not suitable because it traps condensate and blocks air.
Is ASP cheaper than in-vessel?
Capital cost is between a turned windrow and an in-vessel system. Operating cost is usually the lowest of the three because there is no turning fuel and no vessel agitation to maintain.
Send us your design basis
Tell us the feedstock, the daily tonnage and the product you want to sell. The engineering team replies with the plant configuration, the equipment scope and the information we still need before layout drawings start.
- Feedstock profile — type, moisture, contamination, seasonal peaks
- Capacity — t/day fresh material or t/h finished fertilizer
- Product — powder, granules, bagged retail, bulk compost
- Site — available area, power supply, water, access road
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