Chicken processing generates two different waste streams. Manure suits anaerobic digestion. Carcass remains and dried digestate suit pyrolysis. A proposal for a slaughterhouse in the Middle East put both together: a 60 tonne-per-day continuously mixed digester producing around 575 Nm³/h of biogas and about 1.34 MW, and a 1.85 tonne-per-hour pyrolysis unit.
The challenge: one site, several waste types
Not everything a poultry plant discards can be digested. Parts such as bone and feathers digest slowly. Digestate also needs final disposal. A complete solution must treat all of it.
The digester
- Feed: 60 tonnes a day at 25% moisture, diluted to a flow of about 560 m³ a day.
- Reactor: one glass-fused-to-steel tank of about 10,000 m³, with a flexible roof that stores gas.
- Retention: about 17 days, with biomass recycled.
- Gas: about 575 Nm³/h at 60% methane, giving around 1.34 MW.
- Gas storage: about 1,500 m³ under the roof, around 2.5 hours for a 1 MW engine.
- Gas train: bioscrubber (2,000 ppm H₂S in, 150 ppm out), dewatering, duty-standby booster and standby flare.
Poultry waste is rich in nitrogen and COD, which is why a compact tank was preferred to a lagoon. The covered lagoon, UASB and CMAR options were compared in the proposal: the UASB was considered unsuitable for this substrate.
Dry and destroy the rest
Digestate leaves wet. A mechanical dryer followed by a thermal dryer reduces its moisture so it can be pyrolysed with the carcass remains. A macerator breaks up carcasses ahead of the feed. The pyrolysis unit has three tubes and processes up to 1,850 kg of waste per hour (about 1,480 kg dry). Waste is converted into syngas and ash, and the gas is burned in an oxidiser at 850 to 1,050°C, a range stated to give complete combustion and destroy dioxin precursors.
Why combine them
- Biogas from the digester powers the site.
- Pyrolysis deals with what the digester cannot, including digestate.
- Both fit within one battery limit, so one supplier is responsible.
What to consider for your own project
- Split the waste by type. Carry out a waste audit first.
- Watch ammonia. Poultry feed raises ammonia in digesters, so check inhibition.
- Dry the digestate before thermal treatment; moisture costs energy.
- Plan 12 months from order to commissioning.
For UK projects, digestion and thermal plants need an environmental permit. See also the Anaerobic Digestion Strategy and Action Plan.
FAQ
Can all poultry waste be digested?
No. Slow-degrading parts are better treated thermally.
What does the digester produce?
Biogas for engines, and digestate that is dried.
Why a glass-fused-to-steel tank?
It resists corrosion over a long life.