Step 1: Substitution value for fibre fraction to biogas plant
Amount of fibre fraction: 44.857 kg (see figure H.1). N in fibre fraction: 7.17 kg N per 1000 kg fibre fraction (see table C.3 in Annex C). Substitution value: 50% of 7.17 kg per 1000 kg fibre fraction * 44.857 kg fibre fraction / 1000 kg = 0.16081 kg N. This is the substitution value that “belongs” to the fibre fraction that is sent to the biogas plant. This is “input” to the biogas plant.

Step 2: Acknowledging the above, make the weighted sum of the substitution values (liquid and fibre). For raw pig slurry, the substitution value is 75 %.
Here rule (a) applies: “The sum of the “mineral fertiliser replacement value” of the outgoing fractions shall be the same as the “mineral fertiliser replacement value” of the ingoing slurry before separation”.

The mineral fertiliser replacement value of untreated, raw pig slurry is calculated based on the Danish Norm Data (DJF, 2008), which was also done in Annex A (section A.6.1). From the Danish Norm Data tables, the farmer knows the value of 5.00 kg N per kg slurry ex storage (see also table A.5 and A.1). The Danish Norm Data is what the farmer use for the accounts: 5.00 kg N per 1000 kg slurry ex storage (table A. 1).

For the system, the mineral fertiliser substitution value is then: 5.00 kg N per 1000 kg slurry ex storage * 1086 kg slurry ex storage / 1000 kg slurry ex animal * 75% = 4.0725 kg N per 1000 kg slurry ex-animal.

However, there is only 862.963 kg slurry being separated (see figure H.1), i.e. 4.0725 kg/1000 kg * 862.963 kg = 3.51442 kg N.

• Of this 3.51442 kg N, 0.16081 kg N belongs to the fibre fraction (as calculated in step 1).
• The difference i.e.: 3.51442 kg N – 0.16081 kg N = 3.35361 kg N belongs to the liquid fraction.

Mineral fertiliser replacement value for the liquid fraction (at the farm): 3.35361 kg N

Step 3: Make a weighed sum of the substitution values for the materials entering the biogas plant.
Rule (b): “Mass balance in and out of Biogas Plant – i.e. the “mineral fertiliser replacement value” of the outgoing biomass is calculated in accordance with the ingoing biomass”.

• The raw slurry going directly to biogas plant (without separation) has a mineral fertiliser replacement value of 4.0725 kg N per 1000 kg slurry (as described under step 2 above – 75% of 5.00 kg N ex storage). The amount of this raw slurry is 137.037 kg (see figure H.1). Its mineral fertiliser replacement value is: 4.0725 kg N per 1000 kg slurry * 137.037 kg slurry/1000 kg = 0.55808 kg N per 1000 kg slurry ex-animal. This is the substitution value for the raw slurry into the biogas plant.
• At the plant, a biomass mixture is made from this raw slurry and the fibre fraction from step 1, so the substitution value for this input mixture is: 0.16081 kg N (fibre fraction, step 1) + 0.55808 kg N (raw slurry, see above) = 0.71889 kg N.

Mineral fertiliser replacement value for the degassed biomass: 0.71889 kg N

Total amount of substituted mineral N fertiliser in the system
3.35361 kg N + 0.71889 kg N = 4.0725 kg N