8. Compost & Sludge
Estimation of compost and sludge application
Based on Saveyn & Eder (2013), it is assumed that on average 51% of the compost produced is used in agriculture, and the rest is used in public green, gardening, and horticulture. Compost is assumed to be distributed evenly to all crops except grassland.
For sludge, the amount used for agriculture in each EU member state is provided as input (data source: Eurostat, 2020). Sludge is distributed evenly to all crops except grassland.
Nutrient content in compost
Nutrient content in compost is calculated based on the composition of the compost product ( Regelink et al., 2021). All values are given in g kg–1.
| Compost Type | DM | C | N | P | K |
|---|---|---|---|---|---|
Biowaste |
620 |
114.2 |
7.9 |
1.66 |
4.9 |
Greenwaste |
649 |
145.1 |
4.9 |
0.96 |
5.6 |
According to Geisseler et al. (2021), on average 16-17% of total N was present as mineral N in various organic fertilizers and composts. It is therefore assumed that 16% of the total N in compost is in inorganic form, and the rest is organic.
Nutrient content in sludge
Based on Driessen & Roos (1996), the following assumptions are made on the composition of sludge:
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The average and median organic matter content is ca. 50%.
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C content is assumed to be 50% of organic matter.
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For N, the average and median N content is ca. 44 g kg–1 .
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For P, the content is country-specific, ranging from 0.9% to 6.7%, with an average of 3.3%.
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For K, the average and median K content is ca. 8 g kg–1 DM.
Similar to compost, it is assumed that 16% of the sludge N is inorganic, and the rest is organic.