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Life-Cycle Assessment of Existing Biochar Systems
Figure 5.11 Contribution Analysis for Net Climate Change Impact per Tonne of Dry Feedstock for Rice Husk Biochar System in Vietnam with 100 Percent Allocation for Rice Wafer Stove and Upstream Impacts
Emissions / reductions
–
Net = –0.6
+
0
0.1
0.2
0.3 0.4 GHG (t CO2e t–1 DM)
Stable C in biochar
SOC
Avoided burning
Stove emissions
0.5
0.6
0.7
NPK fertilizer
Source: World Bank. Note: The upper bar (–) represents the GHG reductions, the lower bar (+) is GHG emissions, and the difference represents the net GHG balance of the system. C = carbon; SOC = soil organic compound; NPK = nitrogen, phosphorus, and potassium (fertilizer); GHG = greenhouse gas; CO2e = carbon dioxide equivalent.
transportation revenue is higher than the feedstock and biochar transportation costs. The costs of the rice wafer feedstock and stove are small, again because of the economic allocation. If these impacts were allocated at 100 percent of biochar production, then the rice husk cost increases from $0.09 to $17 per tonne of dry matter and the stove from $0.002 to $0.40 per tonne of dry matter, for a net balance of $918 per tonne of dry matter. A biochar “payback period” provides an estimate of the number of years it would take biochar used as a soil amendment to pay for itself. The payback period is calculated assuming the baseline price of peanuts, and is achieved in the first cropping season. For a one-crop biochar effect, the results are presented in figure 5.12b. With the peanut surplus per crop only $7 per tonne of dry matter, the scale on the x-axis is greatly reduced. The transportation cost of the biochar becomes more apparent (–$6 per tonne of dry matter), and the avoided manure transport cost is minimal. The revenues from avoided manure and fertilizer are also decreased. There is a distinction between the net revenue per functional unit and the net revenue for the farmer (table 5.11). For the farmer, the cost of the biochar incorporates the cost of the feedstock, the stove construction, and the biochar Biochar Systems for Smallholders in Developing Countries • http://dx.doi.org/10.1596/978-0-8213-9525-7