It is generally believed that the earth is warming as a result of man's activities, principally the large-scale burning of fossil fuels. This practice generates carbon dioxide emissions, which lead to greenhouse warming by interfering with the re-radiation of accumulated heat into space. The consequences of this warming, including melting ice-caps and rising sea levels, more energetic weather patterns, climate changes, public health issues, etc, are viewed as deleterious to man, to the degree that global action has been mounted to attempt to control the level of carbon dioxide in the atmosphere.
Initial attempts to achieve this control were "front-end" methods, based on restricting emissions. It is now realized that to be effective, these restrictions would have to be so severe as to interfere seriously with industrial activity, development and most human pursuits. Help is needed from "back-end" methods, those which remove carbon from the active cycle after it has served its purpose. This carbon must be collected in a form suitable for segregation; conventionally, this is pure carbon dioxide, which can be pumped to the deep ocean or earth sinks for permanent storage. Suitable sources for quite pure carbon dioxide are natural gas sweetening plants, fermentation operations, etc. More dilute sources like power plant stacks are now being studied to prevent their carbon dioxide from entering the atmosphere; the more dilute the source, the higher the cost for conventional extraction, and this practice could mean noticeably higher energy costs.
An alternative back-end approach has been under study for more than ten years. This process, called AP for Anthropogenic Peat, removes carbon dioxide from the air by the most economical method known, growing biomass. Sugarcane is the most efficient converter now known; its cultivation is well-documented, and an example has been constructed around its use for this purpose. Fresh biomass is digested anaerobically, as in Nature making peat (hence the name Anthropogenic Peat), to produce a digester gas of 70 volume percent methane and 30 carbon dioxide, plus a stabilized organic residue. This solid residue is one which will not produce gas in segregated storage, like a landfill; containing 45% carbon (dry basis) versus 27% for carbon dioxide, this solid may be a good candidate for deep ocean or earth disposal. Extensive small-scale digestion tests have established these gas and residue yields.
What AP does, then, is to use two natural processes to convert carbon dioxide from a very dilute source, the air, first into biomass and then into methane. We also get pure carbon dioxide and organic residue, both of which can be segregated to control carbon dioxide level in the air. AP thus provides for global carbon management; growing sugarcane on about 150 million acres of tropical land produces enough carbon for segregation to stabilize the level of carbon dioxide in the air, with current emission rate. The process also yields about 93 trillion cubic feet of methane at a break-even cost (ex segregation costs) of about $.50 per thousand cubic feet when futures price is above $2.50; this makes methane a renewable fuel, takes pressure off world economies from oil-producing regions, pays for the cost of controlling the level of carbon dioxide in the air, and supplies the clean, cheap energy and economic activity needed to contain other world problems as identified by The World Bank and the Union of Concerned Scientists.
Data acquired in Hawaii over the last fifty years demonstrate that the AP approach will work, that the calculated removal by cultivation is essentially correct, that the atmosphere mixes so well that emissions anywhere (say, Detroit) can be compensated by removal anywhere (say, India), and that the progress of an AP program can be monitored in substantially real time. The data also show that as the level of carbon dioxide in the atmosphere has risen over the last fifty years, at least one aspect of photosynthetic activity (leafing of deciduous trees) has also risen proportionately.
Finally, as anaerobic microorganisms convert biomass to digester gas, there is a stoichiometric shift which increases the energy content of the system by as much as 20%; H/C ratio is increased 68% while 0/C is reduced by 28%. This should be studied, as it represents a large potential benefit to the world energy supply.
Email: H.A.Hartung@py.com