© 2015 John Wiley & Sons Ltd
Edited By: Steve Long
Impact Factor: 4.248
ISI Journal Citation Reports © Ranking: 2013: 2/79 (Agronomy); 12/83 (Energy & Fuels)
Online ISSN: 1757-1707
Associated Title(s): Global Change Biology
Accounting for algae
Algal material is increasingly being considered as a feedstock for bioenergy production. The fossil carbon removed during algae growth and then released during combustion of algae is similar to that of other biomass types. Yet, according to Pena and coauthors, there are many unknowns regarding accounting for the carbon removed and released from algal bioenergy production, especially when algae is grown using captured CO2 from exhaust streams of fossil fuel power plants or industrial processes. In this review, the authors consider whether the release of fossil carbon should be accounted for by the industrial emitter when the carbon is first created or when it enters the atmosphere. To do this, they evaluate four accounting approaches and their implications.
The two options under the Kyoto Protocol (KP) are Source Reduction and Sink Enhancement. Both account for carbon capture and sequestration (CCS) where waste carbon dioxide is captured from an industrial source and used or permanently stored instead of being released into the atmosphere. Under KP Source Reduction, if CCS is employed, captured carbon dioxide emissions are not counted for when produced by the industrial source, but instead if and when it enters the atmosphere during biomass production, transportation, preparation, and combustion. An industrial emitter capturing and transferring carbon dioxide to CCS would only report the portion of carbon dioxide that did not get captured. Under Kyoto’s Sink Enhancement, the industrial emitter reports its total waste carbon dioxide production, whether CCS is employed or not. Any reduction in carbon dioxide emissions by CCS would be reported as negative emissions.
The third value chain approach considers all emissions including those caused by production of the biomass, its conversion to a liquid fuel, and the transportation of biomass and fuels to a point of fuel distribution. The sum is not used for accounting in this approach. Rather, it is a relative value that can be taken into account when determining whether a biofuel can be used to meet a renewable fuel mandate.
The fourth approach, Point of Uptake and Release (POUR), counts only emissions. All emissions of carbon dioxide from the use of biomass are counted as positive emission values and uptake of atmospheric carbon dioxide into biomass are counted as negative emission values. No emissions are attributed to the carbon stored in harvested biomass until it is released by combustion or decay.
The authors evaluated each accounting approach against four criteria: completeness, simplicity, sectoral accuracy, and scale independence. Completeness describes the approaches’ ability to count all carbon dioxide emissions and removals once but only once. Simplicity reflects the degree to which a system uses commonly accepted procedures. Sectoral accuracy represents accuracy over space and time. Scale independence is an evaluation of how an accounting system operates spatially (e.g. at both national and local levels).
The authors concluded that neither proposed KP accounting approach for algae leads to correct accounting of emissions for all uses. Both value chain and POUR approaches more correctly and consistently account for algal emissions across uses. POUR offers the potential to provide comprehensive, consistent emission accounting across all uses of biomass, which represents a major step forward in accounting for carbon dioxide emissions.
Pena, N., Frieden, D. and Bird, D. N. (2012), Accounting for Algae. GCB Bioenergy. doi: 10.1111/j.1757-1707.2012.01194.x Read this paper.
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