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Table 7 Greenhouse gas emissions of different processes to produce the same quantity of energy (maintaining a 500 kWe biogas plant) in the cocksfoot grass-based biomass-biogas-biomass cycle in the 7-year period (in total 39,917 GJ = 66,528 MWh), with area corrections from Table 6 and saved emissions from substituting the European average energy mix with biogas

From: The effect of digestate and mineral fertilisation of cocksfoot grass on greenhouse gas emissions in a cocksfoot-based biogas production system

ProcessSC1SC2SC 3SC 4SC 5SC 6SC7SC8
t CO2-eq%t CO2-eq%t CO2-eq%t CO2-eq%t CO2-eq%t CO2-eq%t CO2-eq%t CO2-eq%
Direct emissions
Soil tillage191.31.775.10.682.30.493.90.969.70.661.90.555.30.454.50.3
Soil cultivation124.31.148.80.453.50.261.10.645.30.440.20.335.90.235.40.2
Sowing53.60.521.00.223.10.126.30.319.50.217.30.115.50.115.30.1
Fertilisation (mineral N)--153.01.2164.70.7----------
Fertilisation (digestate)------141.61.4210.91.8272.22.1323.52.2387.52.3
Grass cutting collection10083.488.64608.235.24949.222.44538.043.73379.629.22897.321.92581.917.62463.214.7
Transportation77.20.766.80.562.00.364.20.669.50.671.00.571.50.573.00.4
Grass storage (ensiling)5.10.04.30.04.10.04.20.04.60.04.70.04.70.04.70.0
Anaerobic digestion process14.10.1211.80.111.30.0511.70.112.70.113.00.113.00.113.30.1
Indirect emissions
Agricultural machinery400.83.5180.41.4194.10.9182.21.8135.61.2116.70.9104.00.799.70.6
Indirect emissions of fertiliser applicationa2278.817.44897.722.24838.446.67203.462.39300.570.411050.575.313236.478.8
Indirect emissions of fertiliser productionb5232.339.911245.350.9
Human work13.50.12546.00.05.90.06.10.14.60.03.90.03.50.03.40.0
Methane loss (0.5% of produced biogas)412.93.6412.93. 2412.91.9412.94.0412.93.6412.93.1412.92.9412.92.5
Total emissions11376.210013099.110022106.110010380.710011568.410013211.810014672.310016799.3100
Alternative emissions− 15079242 − 15081518 − 15082025 − 15063574 − 15053831 − 15044694 − 15037845 − 15027610 
Saved emissions− 15067866 − 15068419 − 15059919 − 15053193 − 15042263 − 15031482 − 15023173 − 15010811 
  1. “Total emissions” are the total GHG emissions from the biomass-biogas-biomass system; “Alternative emissions” are the emissions from the alternative energy system, i.e., the European average energy mix; and “Saved emissions” are the differences between the total GHG emissions from the biomass-biogas-biomass system and those from the alternative European energy mix
  2. aIndirect N2O emissions from soil due to fertiliser application
  3. bIndirect N2O emissions from energy use in industrial fertiliser production