Total lifecycle greenhouse gas emissions from cassava-based ethanol from post-mining land are up to 17% lower than from gasoline

The IKI project “Cultivation of Energy Crops on Post-Mining Sites” aims to develop and test ways to cultivate biomass as a feedstock without competing for land or causing negative environmental impacts through land use change (LUC). While the first phase of the project (2015-2018) focused on developing suitable cropping systems, the second phase (2020-2025) now focusses on scaling up the results of the first phase. As the production of bioethanol from cassava proved to be the most promising approach from a climate and environmental perspective in the first phase, 1.6 ha of post-mining land in central Viet Nam (Lam Dong Province) was pilot cultivated with cassava. As part of the proof of concept and to support the exploitation, the Independent Institute of Environmental Issues (UfU), together with Hanoi University of Science and Technology, investigated the CO_2eq mitigation potential of using cassava as a bioethanol feedstock under real-life conditions.

To determine the GHG emissions of the pilot, the study conducted a life cycle assessment (LCA) of the cassava-based ethanol pathway using the results and boundary conditions of the Lam Dong Province pilot. The stages of the value chain included in the LCA are land-use change; cassava cultivation, chipping, feedstock production, conversion and delivery to the ethanol plant, biomass processing into biofuels, and biofuel transportation, storage, and distribution. As the cassava yield at the experimental site varied considerably, two scenarios were considered in the LCA:

1. Scenario 1: yield’s mean value of all plots on the experimental site = 8.4 t of tubers /ha
2. Scenario 2: 0,75-quantile of all plots in Lam Dong (upper 25% of the values) = 11.7 t of tubers/ha

The total GHG emissions of the cassava-based ethanol in Scenario 1 are 94.4 g CO₂eq/MJ ethanol, of which 63.0 % are from cassava cultivation and 32.0 % from ethanol processing. Thus, the average yield of 8.4 t tubers/ha which is relatively low compared to the agricultural average of 19.0 t of tubers/ha of cassava, is already sufficient to result in GHG emissions equivalent to those of gasoline (94.0 g CO₂eq/MJ petrol). The total GHG emissions from vehicles using the blended product as E5-biofuel are 235.0 g CO₂eq/km compared to 241.0 g CO₂eq/km for gasoline (mainly because the fuel efficiency and heat consumption per kilometer of biofuels like E5 are higher than that of gasoline). The use of E5 blended with cassava-based ethanol thus saves 2.5 % of GHG compared to gasoline. In Scenario 2, the total GHG emissions from the production of cassava-based ethanol (77.67 g CO2eq/MJ ethanol) are 17.4 % lower than those from gasoline (94.0 g CO₂eq/MJ petrol). Thus, the average yield of 11.7 t/ha of cassava is sufficient to achieve GHG emission savings throughout the production process. Furthermore, the total GHG emissions of vehicles using the blended product as E5-biofuel are 233.0 g CO₂eq/km compared to 241.0 g CO₂eq/km for gasoline. The use of E5 blended with cassava-based ethanol therefore saves 3.4 % of GHG emissions compared to gasoline.

As calculated for the two Lam Dong’s scenarios, the LCA shows that the total GHG emissions from the life cycle of the cassava-based ethanol of Scenario 2, which corresponds to the 25 % of the best-grown and highest-yielding plants, are about 17 % lower than the total GHG emissions from the life cycle of gasoline. The results also show that the GHG emissions come mainly from the cassava cultivation and ethanol processing stages. In addition, the co-benefits on soil ecosystems services through recultivation such as flood and climate regulation as well as carbon sequestration are not balanced here.

Analysis of the computing data shows that the potential for reducing GHG emissions at these two stages is still large. In cassava cultivation, the amount of fertilisers used per ha is quite high compared to the yield, resulting in a large amount of GHG emissions per kg of cassava. Therefore, if the yield per ha is improved, the GHG emissions per kg of cassava would be reduced. Regarding the ethanol production, the cassava wastewater discharged from the ethanol factory could be used to recover biogas for steam production. The steam can in turn be used directly in the ethanol factory to generate electricity for ethanol production. There is a need to invest in advanced technologies to improve the efficiency of biogas recovery in order to reduce the GHG emissions during the ethanol production. In addition, the share of total GHG emissions from transporting cassava chips to the bioethanol plants would be lower if more bioethanol plants were in operation to reduce the distance between the cultivation area and the ethanol plant. Although Viet Nam has put in place a relatively comprehensive legal framework to promote energy transition, biofuel development and GHG emissions reduction, the promotion of renewable energy in Viet Nam is being held back by influential energy enterprises that support the existing energy system and decision-makers who doubt its sufficient availability. In addition, Viet Nam’s bioethanol production technology is outdated, lags behind foreign standards and is often uncompetitive with conventional fossil fuels. It is therefore crucial to promote technology transfer and convince decision-makers that a well-established bioethanol industry will reliably contribute to the country’s energy security. In July 2023, Viet Nam’s Prime Minister approved a new plan for the extraction of mineral resources, which will significantly increase the area required for mining after 2030. In the near future, Viet Nam is therefore expected to see a significant increase in post-mining land, and therefore potential areas for energy crop cultivation and areas requiring recultivation.

Contact: Dr. Arne Reck, arne.reck@ufu.de; Niklas Müller, Niklas.mueller@ufu.de; Prof. Nguyen Thi Anh Tuyet, Hanoi University of Science and Technology, tuyet.nguyenthianh@hust.edu.vn

For more information about the project, please visit: Cultivation of energy plants on set-aside mining sites in Viet Nam – pilot project II | Internationale Klimaschutzinitiative (IKI)