Growing plants and then burying them or incorporating them into soil is one of the few practical and efficient things we can do to remove CO2 from the atmosphere and permanently store it. Agricultural wastes such as rice husks, when incorporated into soil at the site of production, readily mineralize, becoming encased in silica, preventing decomposition. It’s estimated that in India, crop wastes produce about 87 million tonnes of mineralized carbon per year. 1
I’ve been reading about carbon offsets lately, as a way to reduce Wikimedia Foundation’s impact on the environment. Carbon offsets are produced by an organisation doing some activity which reduces CO2 in the atmosphere. The offsets are independently verified, most notably by the Gold Standard Foundation. Certificates for CO2 abatement are issued and registered in a market.
The Gold Standard Foundation’s website prominently promotes a waste-to-energy project in Chhattisgarh, India as a carbon offset.2 Offsets against this project can be bought directly from Gold Standard for $11 USD/t. The project aimed to divert 145,920t per annum of rice husks, which otherwise would have been disposed of at the place of production, and to burn them for energy instead. In an attempt to figure out how Gold Standard could justify endorsing this project, I read its Project Design Document (PDD). 3
The document is rigorous in appearance. It adds up the emissions in the “baseline” case, that is, a model for what would have happened if the project was not built. Then it adds up emissions in the “project” case. The difference between these is the carbon offset value.
The baseline case has emissions of 110,881 tCO2e per year, due to electricity generated by the existing mix of generators. 4. In the project case, the emissions are only 3,372 tCO2e per year, mostly due to off-site processing of the rice husks and on-site methane emissions. 5. The emissions due to actually burning the rice husks for energy are supposedly zero — such emissions are dismissed with the phrase “It is assumed that CO2 emissions from surplus biomass residues do not lead to changes of carbon pools in the LULUCF [land use, land-use change, and forestry] sector”.6
This is quite a heroic assumption. If this was new agricultural production, using completely unproductive land (like a desert), you could see how the emissions from burning the plants would be absorbed again by the next year’s crop. But for rice waste which was previously discarded, this is patently not the case. The carbon is diverted from permanent storage in the ground to CO2 emissions in the air, a description which could equally apply to fossil fuels.
Could it be that methane emissions from on-site rice husk dumps are assumed to neatly cancel out the emissions from burning the wastes? Or perhaps was most of the rice was previously burnt by the farmer? No, the PDD conservatively assumes that the total emissions in the baseline case due to decomposition and burning is zero.7
If we adopt these conservative assumptions, but estimate the amount of CO2 actually released by burning rice husks for electricity, the sign of the carbon offset is reversed. That is to say, burning rice husks appears to emit more carbon per unit of electricity than the existing mix of generators. Assuming that rice husks are 38% carbon,8 burning 145,920t of rice husks per annum would release 203,000t of CO2. So the project as a whole would actually increase atmospheric CO2 by 96,000t per annum.
And yet this is being sold as an offset, to absolve wealthy individuals and corporations of their responsibility for emitting yet more CO2!
I set out this entire case to the Gold Standard Foundation by email. On November 3, 2018, they confirmed that they had received the email and that it had been forwarded to their technical team. No further response has been received as of November 12.
The Gold Standard Foundation provided the following response. Essentially they claim that methane emissions from on-site rice husk dumps do indeed cancel out emissions from burning those rice husks for power. I don’t believe this has a firm scientific basis and look forward to a more rigorous approach in future.
The non-fossilized and biodegradable organic material originating from plants for example crop residue is considered carbon neutral – due to no net effect on the biosphere’s carbon concentration. Put simply, the combustion of crop residue releases carbon dioxide which in turn is readily absorbed by plants. Through this cycle, the plants remove carbon from the atmosphere, and carbon is released back to the atmosphere when plants are burned. Since, use of the crop residue for energy use is likely substituting the CO2 emissions from fossil fuel, the energy generation from crop residue such as rice husk burning is considered net carbon neutral.
The permanent sequestration of carbon in rice husks depends on what would happen to the dumped rice husks. As you may already know, the dumped husk will decompose – primarily due to the microbial activity – this will cause anaerobic or aerobic decomposition. In the case of an anaerobic situation, similar to a Municipal Solid Waste (MSW) landfill; the decomposition or organic matter leads to methane emissions, a more potent greenhouse gas as compared to CO2 and further, not one that plants can absorb. While in aerobic decomposition, most of the carbon in the organic material (approximately 2/3) is released into the atmosphere as CO2, which is carbon neutral. In both the cases, the eventual decomposition of the rice husk will happen and it will lead to a release of GHGs (CO2 and/or CH4) in the atmosphere rather than permanent sequestration.
The exclusion of emissions from uncontrolled burning and/or decay in aerobic conditions in baseline scenario is assumed 0 and is conservative. The applied GHGs quantification methodology (ACM0018) keeps it optional for the project to consider these emissions. A likely assumption is that the baseline emissions (primarily CH4 emissions only from burning as CO2 is carbon neutral) would be higher due to inefficient burning or decay as compared to the project situation. Therefore, exclusion of emissions from burning in baseline will lead to net lower emission reductions and is conservative.
Also, the GHGs accounting methodology applied in the project requires an assessment of the availability of the risk husks (annually) to capture any diversion (new) of rice husk from other potential uses. It means the emission reductions estimated or verified are based on field studies of rice husk availability. If any change occurs in potential use of the rice husks (in the project situation) this would be captured and accounted for in the emissions reduction calculations.
Finally, the ex-ante emission reductions in the PDD are estimated based on certain assumptions, for example – potential use of surplus biomass, which is further monitored along with the project operation. The project developer via an independent third party annually conducts field studies to estimate the availability of surplus rice husk within a 50km radius of where the project sources its rice husk. These studies, indicate that the project only uses surplus biomass that would have been dumped in the absence of the project and confirms the initial assumption made in the PDD.
- Rajendiran, S., Coumar, M. V., Kundu, S., Ajay, Dotaniya, M. L., & Rao, A. S. (2012). Role of phytolith occluded carbon of crop plants for enhancing soil carbon sequestration in agro-ecosystems. Current Science (00113891), 103(8), 911. ↩
- https://www.goldstandard.org/projects/20-mw-biomass-power-project-chhattisgarh-india (archive) ↩
- https://mer.markit.com/br-reg/services/processDocument/downloadDocumentById/103000000063706 ↩
- PDD page 38, BEEL,y ↩
- PDD page 40, PEy ↩
- PDD page 15, “Combustion of biomass residues for electricity generation” ↩
- Aerobic decomposition and burning is on PDD page 39, termed BEBR,B1/B3,y. Baseline methane emissions are on page 31, termed BEBR,B2,y. ↩
- Thipwimon Chungsangunsit, Shabbir H. Gheewala, Suthum Patumsawad. Emission Assessment of Rice Husk Combustion
for Power Production. https://waset.org/publications/514/emission-assessment-of-rice-husk-combustion-for-power-production. Adjusting the figure in table 1 to calculate C as a percentage of wet mass. ↩