This is a documented response to the document “Woody Biomass for Power and Heat: Impacts on the Global Climate”, author Duncan Brack, that has been recently published by the auto defined Independent Policy Institute based in London, the Royal Institute of International Affairs.

The so-called “research paper”, a claim against the sustainability of the energy use of forest biomass, points out among other things, surprising high values of methane emissions (CH4) from storage of forest biomass before its use. These emission values are taken from a first article by Mirjam Röder et al [1] of the Tyndall Center for Climate Change Research, The University of Manchester. This first article takes the emission values from a second article by Margareta Wihersaari [2] from the VTT center of Finland. Once reviewed this second article, we realize that is not based either on any own experimental measurement but, again, is a review of other articles. It performs an emission modeling that is based on emission factors from another article (Beck-Friis et al.) that deals with “household waste compost” under laboratory conditions[3]. An unfortunate election as household waste and forest biomass are dramatically different.

On the other hand, the most surprising thing is that when we look for the emission factors in the experimental source (that of Beck-Friis), we found out that there is nothing written anywhere about the emissions of CH4 from the experimental tests. One might think that in the Wihesaari article they are confusing grams per milligrams, that is to say the value of 60 g CH4 m2 / day of emission from biomass storage (better said compost) are possibly 60 mg CH4 m2 / day, since once we consulted other sources, we found out that emission orders of magnitude are between 0 and 90 mg CH4 m2 / day in biomass piles. For instance, in sawdust landfills and piles investigates in Tennessee, methane emissions were found where there are long-term deposits in which there is an absence of oxygen and anaerobic microorganisms can then live. In such case the measured emissions gave figures between 1 and 4 mg/m2 hour (average of 40 mg/m2 day) from the pile surface. [4]

In other recent work, [5] developed in the Laboratory of Renewable Resources Engineering, Purdue University, West Lafayette, USA, even when they are considering the case of baled herbaceous biomass in which some anaerobic activity is more likely to occur inside the bales, they conclude that “Net global warming potential from each treatment (0–2.4 gCO2e /kg DM) suggests that direct emission of methane and nitrous oxide from aerobically stored feedstocks have a small effect on net global warming potential of cellulosic biofuels”.

In conclusion, what is the reason for the erroneous information in the Duncan Brack´s article?

Either mistakes or opportunism can be suspected in.

We would like to think that a chain of errors is the cause.

However we would like to emphasise that this is not serious. How can this be admitted? The author has drawn highly negative conclusions against the sustainability of forest lignocellulosic biomass based on wrong data and has published the document in an “in theory” independent institute.

In addition, the article written by Margareta Wihersaari that performs and applies models to forest biomass storage emissions allegedly based on household compost emissions would be a major breach of concept. However the main fault is that the reference CH4 emission value does not exist in the source article from Beck-Friis et al.

Concerning the use of emissions factors in models, we would like to stress that compost has typically has a relative high composition in N (ratio C/N low), very fine particle sizes and an abundant microbial life that generates very different degradation patterns and emissions in quantities and compositions from the ones generated from wood chips or other forest biomass resources in which C/N ratios are much higher. Even so, when composting is properly done, it is an aerobic process and therefore a negligible amount of methane (CH4) is produced. Methane is generated mainly in conditions of oxygen absence by methanogenic microbes.

That is to say that in forest residues in aerobic conditions (most of the situations), methane emissions are very low and quite far from that presented in the mentioned Dunkan Brakes´s article.

 

Elaborated by

Dr Luis Saúl Esteban, Research Scientists at Biomass Unit in CEDER-CIEMAT, Spain)

luis.esteban@ciemat.es

Pablo Rodero, responsable de proyectos europeos en AVEBIOM

pablorodero@avebiom.org

 

References:

[1] Mirjam Röder, Carly Whittaker, Patricia Thornley. How certain are greenhouse gas reductions from bioenergy? Life cycle assessment and uncertainty analysis of wood pellet-to-electricity supply chains from forest residues. Biomass and Bioenergy, Volume 79, August 2015, Pages 50-63

[2] Margareta Wihersaari. Evaluation of greenhouse gas emission risks from storage of wood residueOriginal. Biomass and Bioenergy, Volume 28, Issue 5, May 2005, Pages 444-453

[3] Beck-Friis B, Smars S, Jonsson H, Kirchmann H. “Gaseous emissions of carbon dioxide, ammonia and nitrous oxide from organic household waste in a compost reactor under different temperature regimes.

[4] P.A. Pier, J.M. Kelly. Measured and estimated methane and carbon dioxide emissions from sawdust waste in the Tennessee Valley under alternative management strategies. Bioresource Technology, Volume 61, Issue 3, September 1997, Pages 213-220

[5] Isaac Emery and Nathan Mosier. Direct emission of methane and nitrous oxide from switchgrass and corn stover: Implications for large-scale biomass storage. GCB Bioenergy, 2014.

 

The paper can be downloaded at:

https://www.chathamhouse.org/publication/woody-biomass-power-and-heat-impacts-global-climate

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