Feedstock engineering for organic fertilizer plants
Feedstock is not what you buy; it is what you design around. Two plants of the same capacity built around the same tonnage of different material are d
01
The calculation
- 01
Measure the feedstock
Moisture by oven or meter, and an estimate of nitrogen from the housing system or from analysis. Assumed numbers are the main source of error.
- 02
Calculate dry matter
Dry matter = fresh mass × (1 − moisture). For 1,000 kg at 75% moisture, dry matter is 250 kg.
- 03
Set the target moisture
For 55% moisture, the total mass needed is dry matter ÷ (1 − 0.55). For 250 kg dry matter, that is 556 kg.
- 04
Work out the water to remove or absorb
The mix already contains 750 kg of water and needs 306 kg, so roughly 444 kg of water has to be absorbed by dry amendment — or removed by dewatering.
- 05
Check the C/N of the mix
Calculate the weighted average of the carbon and nitrogen contributions. If the result is below 25 : 1, increase the carbon-rich share; the moisture calculation and the C/N calculation are then iterated.
- 06
Verify with a squeeze test
A handful of properly mixed material should hold together and release a drop or two of water under pressure. It is a field check, not a measurement, but it catches gross errors immediately.
02
Worked examples
| Feedstock (1 tonne) | Moisture | Dry matter | Amendment needed to reach 55% | C/N after mixing |
|---|---|---|---|---|
| Layer manure | 75% | 250 kg | ≈ 440 kg of straw at 15% moisture | ≈ 25 : 1 with straw |
| Poultry litter | 30% | 700 kg | water or wet material may be required | ≈ 26 : 1 with green waste |
| Cattle manure (separated) | 65% | 350 kg | ≈ 300 kg of green waste or dry compost oversize | ≈ 28 : 1 |
| Pig manure solids | 72% | 280 kg | ≈ 450 kg of wood chip or straw | ≈ 25 : 1 |
| Sewage sludge (dewatered) | 80% | 200 kg | ≈ 600 kg of coarse wood chip | ≈ 27 : 1 with green waste blend |
Indicative examples to show the method. The amendment volume depends on the moisture and C/N of the actual amendment, which should be measured or taken from laboratory data.
03
Practical notes
- One amendment usually corrects both moisture and C/N: dry carbon-rich material absorbs water and raises the ratio.
- Wood chip absorbs water and provides structure but decomposes slowly; straw and green waste contribute more available carbon.
- Screened oversize from your own product is free amendment with an ideal structure — a good reason to size the screener generously.
- Mixing accuracy matters: a 15% error in the amendment share moves moisture and C/N out of range, especially for wet feedstock.
- Record what you mixed, not just what you intended to mix. The recipe that worked is the plant's most valuable record.
Send us your mixing figures
Give us the feedstock, moisture and amendment data; we will return the recipe and the amendment volume the plant should be designed for.
FAQ
Plant engineering questions
What if my feedstock is too dry?
Dry feedstock such as litter can be too dry to compost quickly. Add water, wet material (vegetable or green waste) or fresh manure, and avoid adding carbon amendment which would dry it further.
Can I use the finished compost oversize as amendment?
Yes, and it is one of the best options: it has the right structure, carries an active microbial population, and it is already on site. Screen the material and return the oversize to the mixing area.
How do I know the C/N ratio without a laboratory?
Estimate from the feedstock type and its housing system, then verify by observing the process: an ammonia smell means the ratio is too low; a pile that will not heat means it is too high or the moisture is wrong.
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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