Abstract
Today, traditional biomass contributes 75% to total bioenergy use, but the share of modern biomass, e.g., for biofuels or electricity, increases. Bioenergy derives from first (food crops), second (energy crops or agricultural residues) and third (algae) generation feedstocks. There is an ongoing debate about the competition between energy and food crops. Energy crops do not compete with food directly, but indirectly, using the same natural resources like freshwater. Instead of food or energy crops, crop residues can also be used for bioenergy supply. This paper uses the water footprint (WF) concept and compares WFs of first, second and third generation bioenergy (m3/GJ). Next, it compares WFs of future bioenergy demand based on different bioenergy feedstocks. WFs of energy from residues is smallest, WFs of energy crops largest. Bioenergy from algae has the largest blue WF (surface and groundwater). From a resource-use perspective, environmental impacts of green WFs (precipitation) are smaller than impacts of blue WFs. If bioenergy production rises, impacts on freshwater also go up. Increased production of first generation biofuels and energy crops contributes to global water scarcity. Third generation bioenergy, substantially increases the global blue WF. Comparing feedstocks in the IEA 450 scenario shows that all feedstocks, except residues, generate WFs larger than the global WF over the period 1996–2005. Technology to convert residues into bioenergy is developing, e.g., thermochemical or biochemical conversions. There is large potential for residues, but new possibilities to convert residues into bioenergy need to be explored, combined with possible residue use elsewhere.
Highlights
To decrease carbon dioxide emissions, biomass feedstocks for bioenergy seem a good alternative to replace fossil fuels
Future energy mixes might change due to factors like shale gas development, larger implementation of wind or solar energy, changes in population characteristics or differences between reality in 2040 and the scenario outcomes. & The results indicate that the International Energy Agency (IEA) 450 scenario, in which modern bioenergy is supplied by crop residues, has the smallest water footprint (WF)
This study gives an overview of average water footprints (WFs) of first, second and third generation bioenergy per unit of energy, and shows the consequences of the global application of these types of bioenergy on water resources for 2040
Summary
To decrease carbon dioxide emissions, biomass feedstocks for bioenergy seem a good alternative to replace fossil fuels. In 2014, the world energy demand was 574 EJ of which biomass provided 59 EJ and other renewables, i.e., hydropower, wind, geothermal and solar energy, another 21 EJ (IEA 2016). With a contribution of 10% to total energy demand in 2014, biomass provided the largest share of all renewables. Traditional biomass comprises wood, charcoal, crop residues and animal dung, and is mainly used for heating purposes (IEA 2012). Modern biomass for energy includes food crops, energy crops, crop residues, or algae, for example. The supply of traditional biomass to the total bioenergy supply is around 75% and modern biomass contributes another 25% (Fritsche and Iriartre 2014). Energy scenarios indicate a larger contribution of bioenergy to the total energy supply in the future (IEA 2016). Modern biomass will probably increase its share of the bioenergy supply. Modern biomass is produced in agricultural systems, including forestry, and requires freshwater for the growth of crops, trees and algae
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