Solving the Multifunctionality Dilemma in Biorefineries with a Novel Hybrid Mass–Energy Allocation Method
Njakou Djome S., Knudsen M.T., Parajuli R., Andersen M.S., Ambye-Jensen M., Jungmeier G., Gabrielle B., Hermansen J.E.
Global Change Biology Bioenergy, Volume 9 , 7/2017
Processing biomass into multifunctional products can contribute to food, feed, and energy security while also
mitigating climate change. However, biorefinery products nevertheless impact the environment, and this influence
needs to be properly assessed to minimize the burden. Life cycle assessment (LCA) is often used to calculate
environmental footprints of products, but distributing the burdens among the different biorefinery products
is a challenge. A particular complexity arises when the outputs are a combination of energy carrying no mass,
and mass carrying no energy, where neither an allocation based on mass nor on energy would be appropriate.
A novel hybrid mass–energy (HMEN) allocation scheme for dealing with multifunctionality problems in biorefineries
was developed and applied to five biorefinery concepts. The results were compared to results of other
allocation methods in LCA. The reductions in energy use and GHG emissions from using the biorefinery’s biofuels
were also quantified. HMEN fairly distributed impacts among biorefinery products and did not change the
order of the products in terms of the level of the pollution caused. The allocation factors for HMEN fell between
mass and economic allocation factors and were comparable to energy allocation factors. Where the mass or the
energy allocation failed to attribute burdens, HMEN addressed this shortcoming by assigning impacts to nonmass
or to nonenergy products. Under the partitioning methods and regardless of the feedstock used, bioethanol
reduced GHG by 72–98% relative to gasoline. The GHG savings were 196% under the substitution method, but
no GHG savings occurred for sugar beet bioethanol under the surplus method. Bioethanol from cellulosic crops
had lower energy use and GHG emissions than from sugar beet, regardless of the allocation method used.
HMEN solves multifunctional problems in biorefineries and can be applied to other complex refinery systems.
LCA practitioners are encouraged to further test this method in other case studies.