A poultry manure anaerobic digestion plant can turn chicken litter into biogas, electricity, fertiliser and carbon credits, but ammonia from the manure must be controlled to keep the digesters healthy. In a budget proposal for a poultry producer in the Pacific, about 92 tonnes of manure a day was expected to give roughly 1.7 to 1.8 million Nm³ of biogas a year and 0.4 to 0.5 MW of continuous electrical output.
The challenge: manure that poisons its own digester
Chicken manure is rich in nitrogen. In a digester, nitrogen is released as ammonia, and too much of it inhibits the microorganisms that make methane. At the same time, that nitrogen is valuable as fertiliser. The plant has to manage it, not just tolerate it.
The approach: a phased scheme
The design basis
| Item | Indicative value |
|---|---|
| Feedstock | about 92 t/day of broiler, breeder and layer manure (about 33,500 t/year) |
| Biogas | 1.7 to 1.8 million Nm³/year at about 60% methane |
| Electricity | 0.4 to 0.5 MW continuous (3.6 to 4.2 GWh/year) |
| Digestate | 30 to 35 thousand tonnes/year |
| Recovered nitrogen | 400 to 500 t N/year as liquid ammonium sulphate or ammonium hydroxide |
| Carbon credits | about 13 to 20 thousand tonnes CO₂e/year, to be confirmed |
The process
- Reception and preparation: a reception pit, mixing tanks, screening of oversize material and odour control.
- Digestion: one or more heated, mixed mesophilic digesters.
- Ammonia stripping: a side-stream stripping column to hold digester ammonia at a safe level, with the stripped ammonia captured for fertiliser.
- Power: gas storage, treatment, a combined heat and power engine and heat recovery for the digesters.
- Digestate: solid-liquid separation, with the solid optionally dried or composted and the liquid stored for land application.
- Fertiliser product: conversion of the stripped ammonia to ammonium sulphate or ammonium hydroxide solution.
Waste handling and biosecurity
The outline method statement describes deliveries five days a week with buffer storage for weekends. Litter arrives in covered tipper trucks and wetter manure in sealed tankers. Everything unloads into an enclosed, bunded reception area drained back to the process. Wheel-wash, vehicle wash-down and controlled traffic routes limit disease spread between farms.
The programme
Feasibility study (3 to 4 months), then front-end engineering design (4 to 6 months), then construction and commissioning (14 to 18 months), giving 24 to 30 months from start to operation, subject to permits and procurement.
Why it works
Stripping ammonia protects the biology and creates a product at once. A phased approach lets cost and technical risk be refined before commitment: the feasibility study confirms feedstock quantity and quality at each farm, grid connection and logistics, and the design stage firms up the cost.
For UK readers, the government’s anaerobic digestion guidance covers permitting and digestate use.
What to consider for your own project
- Get feedstock analysis early. Nitrogen and solids content drive digester design.
- Plan for ammonia from day one. Retrofitting stripping is harder.
- Decide the nitrogen product and who will buy it.
- Define civil and permitting responsibility. These were outside the proposed scope.
- Build the monitoring for carbon credits into the design.
For the stripping step itself, see our post on ammonia stripping waste heat.
FAQ
Why is chicken manure hard to digest?
Its high nitrogen content produces ammonia that can inhibit methane-forming organisms.
What happens to the stripped ammonia?
It is converted into a liquid fertiliser such as ammonium sulphate.
Are carbon credits guaranteed?
No. The figures are indicative and depend on the methodology chosen.
How long would the project take?
About two to two and a half years from feasibility to operation.
Considering a manure digester?
Tell us your manure tonnage and location and we will outline a scheme.