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Good use of waste

October 9, 2006 | A version of this story appeared in Volume 84, Issue 41

Many petrochemicals are produced from "syngas" or synthesis gas (carbon monoxide and hydrogen). This versatile gas mixture can be made into a variety of hydrocarbon monomers as well as into pure hydrogen, methanol, ethanol, and pharmaceuticals. Syngas need not be made from petroleum, it can be made from coal and petroleum coke residues by steam reforming. It can also be made from agricultural, municipal, industrial, and sanitary waste. Municipal waste is composed of about 70% carbohydrate, 10% plastic, and 20% incombustibles. Agricultural waste and sewage are mainly cellulose and lignin. Industrial waste is about 60% combustibles.

By steam reforming or partial combustion of organic waste, the current relentless increase in global CO2 emissions may be partially arrested if we make our petroleum fuel products from waste-derived syngas. Virtually all the energy of the precursor carbohydrate molecules can be retained in the hydrocarbon products. By using the energy evolved from a Fischer-Tropsch reaction and by adding a small amount of oxygen or offgas as an additional energy source, the reactions proceed easily. All organics are converted into syngas. Nitrogen and sulfur may be recovered as ammonia and hydrogen sulfide.

The amount of waste generated in the U.S. is large. If all the solid waste (excluding sewage) were placed into steam reforming devices linked to a Fischer-Tropsch or related device, 66% of the nation's total oil supply could be secured. If sewage liquid wastes were included, then the figure could approach 100%.

If 66% of liquid fuel could be generated at home from the nation's solid wastes alone, then fears concerning oil supply interruptions from the Middle East would become groundless. Existing oil exploration and production would not be affected for a long time, as increasing world demand would ensure continued substantial profits. If, eventually, all petroleum used as fuel was derived from waste and all fossil fuel secured as plastic, paint, lube oil, and asphalt, then U.S. carbon dioxide emissions would be substantially curtailed.

I suggest we use our landfills, industrial, agricultural, and municipal waste as our first line of defense against global warming. The very large amounts of waste available on a global scale could substantially impact global CO2 and CH4 emissions. Synfuel could be traded from developing countries to make up for energy deficiencies in industrialized countries.

Another major untapped biological fuel source that could alleviate the current natural gas shortage is sewage. Most U.S. sewage is currently aerobically treated. The organics are all converted to carbon dioxide and water by bacteria. If the sewage plants convert their tanks to anaerobic fermentation, then considerable amounts of natural gas could be generated for heating and lighting purposes.

By emphasizing the natural carbon cycle as a counterbalance to fuels derived from "fossilized" carbon sinks, we may be able to greatly lower our overall CO2 emissions. Hence, any renewable fuel derived from waste or recently living plant tissue will not add CO2 to the atmosphere. If nothing else, the proposal just outlined might give hope to those who believe global warming to be inevitable.

Paul A. Comet


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