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Abstract
Carbon emitted on account of our continued use of fossil fuel can be offset using carbon capture and storage (CCS). The technology for this exists, however the economics of it is context dependent and CCS is shown not to be very cost effective in oilsands. Committing to the needed large scale sequestration projects without properly considering alternatives can prove costly at both economic and social levels. Charcoal sequestration, discussed earlier by Gupta carries with it a few advantages such as being less costly and lacking any post operation liabilities. Above all, it is reversible allowing flexibility of policy and operation and avoiding long term or large scale commitments.

The economics of the charcoal approach depends mainly on two factors: the cost of the feed biomass and the cost of processing. The first of these is addressed by using municipal waste as feedstock which can be available free of charge. Expectedly the cost of processing, the second factor, depends on the apparatus and the scale of operation.

In this paper, the authors discuss prominent traditional and modern apparatus used for conversion of biomass to charcoal with their benefits and drawbacks and describe a simple and pragmatic apparatus which could be assembled relatively easily, for a small scale operation such as processing industrial camp generated solid organic waste.

Offsetting carbon in this manner can obviously be a good way to initiate demo projects for the charcoal sequestration approach as it also helps with waste management. These demo projects in turn will help evaluate various aspects of this novel method of sequestration, and enhance public awareness on the subject which in turn will help the larger society make an informed choice to embark on a right course of action for atmospheric carbon abatement. Additionally, in light of the growing per capita waste worldwide, use of municipal waste as feedstock for charcoal sequestration can be a significant measure of carbon offset at global scale in its own right.

Introduction
Anthropogenic addition of carbon to the atmosphere on account of our continued significant use of fossil energy can be addressed by employing anthropogenic carbon abatement or offsets. Technological solution to the issue of carbon sequestration, i.e. CCS exists (Benson, 2006). In the current world-wide implementation of CCS (e.g. in Weyburn, Sleipner, Salah projects), its economics are combined with the economics of the associated oil and gas recovery projects, representing win-win opportunities. There is no identified technical reason why it could not be extended to plain capture of CO2 from stack gases and its sequestration in deep saline aquifers. Among the major issues with CCS, as listed by Gupta (2009), are its high cost and unresolved issues around the post operation liability. Even before the post operation liability, its cost is estimated to be in the order of $115-$150 per tonne of sequestered CO2 (Metz, 2005; Harrision, 2008). For an order-of-magnitude estimate, if all the current fossil-fuel produced CO2 were to be sequestered using this technology the world would be spending C$3.5 trillion annually. Therefore, before embarking on CCS on a massive scale for pure sequestration (not associated with oil and gas recovery benefits), we should consider other more sustainable and perhaps less expensive means of sequestration. Charcoal sequestration (Lehmann 2007; Gupta, 2007, 2008, 2009; Gaunt 2008) offers such opportunity with unique benefits. In charcoal sequestration, carbon contained in a portion of naturally produced biomass is preserved in solid form by converting it to charcoal, thus preventing it from entering into atmosphere as CO2.