THE BIOMASS REAL POTENTIAL TO REDUCE GREENHOUSE
GAS EMISSIONS: A LIFE-CYCLE ANALYSIS
Bruna de Barros Correia, UNICAMP, +55 19 9257.0711, brunabc@fem.unicamp.br
Tiago de Barros Correia, Ministry of Mines and Energy, +55 61 3319.5842, tiago.correia@mme.gov.br
Arnaldo César da Silva Walter, UNICAMP, +55 19 3521.3283, awalter@fem.unicamp.br
Overview
As the debate surrounding the sustainability of social development based on a heavily oil-depended
economic growth unfolds and increases, alternative energy sources and energy efficiency become the
protagonists in the global effort to limit greenhouse gas emissions. Moreover, biomass becomes more and
more important as a supply-side option to accomplish a low carbon stabilization strategy, mainly because
biomass is a general-purpose energy carrier which can be converted into liquid fuel, electricity, heat and
hydrogen and because biomass presents a high potential to remove carbon dioxide from the atmosphere,
reducing greenhouse gas concentration.
The large scale use of biomass is, however, controversial. The literature reports widely different
conclusions about the possible contribution of biomass in the future global energy supply. The first reason
for the controversy is the uncertainty on the future land availability and yield levels in crop production and
over the detrimental effects on world food production, biodiversity and water availability. The second
reason is the difficulty in establishing a general methodology, based on a given technology and on a
standard productivity level, to measure and to certificate the total (or relevant) greenhouse gas emissions
during the entire biomass’s life-cycle, especially concerning the indirect impact from land use change. This
paper focus on the second point and gives an outline of the controversy surrounding the use of sugar-cane
and corn as bio-energy sources and its contribution to reduce greenhouse gas emissions and offers a
synthesis of a life-cycle analysis methodology to measure the biomass potential to reduce greenhouse gas
emissions.
Methods
As to its methodology, the paper is mainly descriptive, addressing the different aspects of the biomass
potential controversy through a bibliographical revision. The objective is to describe and compute the main
variables needed to measure direct and indirect biomass contribution for greenhouse gas emissions
reduction during its life-cycle, e.g., considering emissions caused by soil loss, fertilizer use, irrigation,
transport, distribution, etc. Nevertheless, the research method adopted presents both explanatory and
analytical remarks on the role played by different cultivating technologies, the relevance of by-products and
of co-generation of other energy carriers and, finally, the importance of biomass certification.
Results
Using the offered synthesis and the data available in the literature we found that energy balance in ethanol
production from sugar-cane is almost 10.2 times better than the corn ethanol ratio, e.g. for each unit of
fossil energy used in the combined ethanol/electricity sugar-cane conversion, 10.5 units of free-carbon
energy may be produced, while the production of ethanol from corn means a balance of 1.03 units of freecarbon energy to each unit of fossil energy used. Moreover, we estimated that the sugar-cane potential to
reduce greenhouse gas emissions is up to 114.81 gCO2e MJ-1 and that the ethanol corn net greenhouse gas
emissions is actually bigger than the gasoline net emissions which means a negative contribution to reduce
greenhouse gas emission. A comparative analysis between corn and sugar-cane energy yield per land area
shows that corn conversion into ethanol produces 2,283 MJ ha -1 of renewable energy; sugar-cane ethanol
produces 144,205 MJ ha-1 of renewable energy; and combined electricity and ethanol from sugar-cane
yields 220,816 MJ ha-1 of bio-energy. We also identify limitations to the life-cycle analysis, especially
when the impacts are more qualitative than quantitative, as well as the need for further discussion about the
relevance of regulatory restrictions and certification systems to mitigate detrimental effects from variables
not included in the quantitative analysis. These limitations are particularly relevant in corn ethanol
production, since its energetic and environmental feasibility relies on the inclusion of co-products credits.
Conclusions
Biomass may be a strong ally to reduce greenhouse gas emission, but its effectiveness relies on production
efficiency, on the intensity of the use of fertilizers, pesticides and fungicides, on the soil loss due to
cultivating and harvest processes and on the fossil fuel consumption to produce, transport and deliver bioenergy. Sugar-cane may be used to produce simultaneously fuel and electricity and to capture carbon and
nitrogen during the production process, which may lead to a zero, or even negative, emission balance. This
makes sugar-cane more competitive than other renewable energy sources; hence available tropical land
should be preferably used to this purpose in the technological path to low carbon stabilization. However,
because biomass potential depends strongly on technology and land use policy, an unsustainable biomass
production may erode any benefit from a large scale investment on bio-energy. Therefore, the adoption of a
minimum sustainability criteria and an efficient certification system for biomass production is as important
as the establishment of a general methodology to measure the biomass potential to reduce greenhouse gas
emissions.
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