Paper details

Title:

Is Bioenergy from Residues Really and Always Sustainable? Qualitative Assessment for Policymakers

Author(s):

Giuntoli, J., Vorkapic, V., Garcia-Lledo, L., Agostini, A.

Document(s):

Abstract:

Biomass wastes and residues have an essential role in reaching the EU 2020 renewable energy targets because they are widely available, they are generally cheaper than energy crops, they are regarded as free of environmental burdens (such as iLUC) and they do not compete for agricultural land nor in the food market. In the current version of the Renewable Energy Directive and Fuel Quality Directive, biomass residues are assigned zero GHG emissions from upstream operations and are counted double towards the renewable energy targets. However, a strong promotion of bioenergy from residues needs a clear and comprehensive analysis of the associated direct and possible indirect environmental effects. Such assessment is presented here for a few specific materials relevant to the EU bioenergy market: straw, manure, pruning residues and residues from forestry logging operations. The impacts of increased residues removal on soil health and future productivity, on global GHG emissions and on biodiversity have been analyzed based on the latest literature. Possible impacts are assessed based on the availability and quality of the experimental evidence and the risks associated with such impacts are evaluated. Mitigating actions are also evaluated. Finally, a quantitative assessment is provided for some of the reported impacts based on literature and original data. Straw availability for energy has been estimated to be around 49 Mtoe in EU by 2020. The main impacts of an increased straw removal from agricultural fields include a potential decrease in soil organic carbon (SOC) and in nutrients available for crops. Furthermore, observations indicate that effects on the physical characteristics of the soil might have a negative impact on future yields and potentially cause increased fuel consumption for agricultural operations. The balance of GHG emissions from straw bioenergy should take into account eventual decreases in SOC but also a decrease in N2O emissions. However, straw utilization for energy production may guarantee GHG savings in comparison with fossil fuel alternatives even when taking into account the negative impacts on soil properties. However, straw removal should be accompanied by management practices (e.g., cover crops, diverse crop rotations, and manure application) that minimize potential adverse impacts in order not to jeopardize the future productivity of the soil. Experimental and modeling studies have shown that the fertilizer potential of digestate is higher than for untreated slurries in the short term because of a higher share of mineral­N; however, this advantage disappears in the long­term. Digestate, thus, seems to be as effective fertilizer as undigested slurry with the additional production of energy from biogas to substitute fossil fuels. The GHG balance of biogas, furthermore, benefits of avoided methane emissions from the storage of manure and by lower N2O emissions from field application. However, long­term effects on SOC will need to be carefully assessed as they could significantly reduce the GHG savings obtained. The removal of logging residues from the forest floor seems to have limited impact on the soil health and productivity but higher impacts on biodiversity. GHG emissions are mostly time­dependent (in comparison with slow decomposition on the forest floor) and several analyses have demonstrated that GHG savings are accrued only after one or more decades depending on the nature of the residue and climate conditions. This should be accounted for when estimating the full GHG emissions from forest bioenergy. Pruning residues are rarely used as soil amendments or for bioenergy production and both these options offer a better option for management of these residues than on­site combustion.

Keywords:

life cycle assessment (LCA), waste, residues, risk assessment

Topic:

Biomass Policies, Markets and Sustainability

Subtopic:

Environmental impacts of bioenergy

Event:

22nd European Biomass Conference and Exhibition

Session:

4CO.15.1

Pages:

1407 - 1422

ISBN:

978-88-89407-52-3

Paper DOI:

10.5071/22ndEUBCE2014-4CO.15.1

Price:

FREE