Sunday, September 7, 2008

Carbonization of Waste is a UH-based Trash Management Option

Technology developed by University of Hawaii researcher Michael J. Antal Jr. to produce charcoal from green waste can reduce the burden on the Waimanalo Gulch landfill.

Dr. Antal's flash carbonization process uses heat and pressure to turn scrap tires, corn cobs, macadamia nut shells and green waste into a high-quality, clean alternative to wood or coal.

Flash Carbonization™ of raw sewage sludge produced in Honolulu's Ewa treatment plant was converted into charcoal. Charcoal yields of about 30% (dry basis) were produced from the sewage sludge.

Charcoal is the sustainable fuel replacement for coal. Coal combustion is the most important contributor to climate change. On the other hand, the combustion of charcoal - sustainably produced from renewable biomass - adds no CO2 to the atmosphere! Thus, the replacement of coal by charcoal is among the most important steps we can take to ameliorate climate change.

Combustion of charcoal does not add to the CO2 burden of the atmosphere because charcoal is produced from renewable biomass that would otherwise decompose (i.e. rot) in a landfill or in the ground and become CO2. Thus the combustion of charcoal is a small part of nature's carbon cycle upon which life depends.

We burn coal to generate a good portion of the electrical power in Hawaii. Oahu has a 180 MW coal fired power plant. The highest priority for knowledgeable people who care about the environment is the replacement of coal by cleaner, renewable fuels.

The Sand Island sewage treatment plant converts its sewage sludge to dry pellets which can be used to enrich the soil. However, the other sewage plants continue to send their sludge to the landfill. Installing a carbon diversion system at all the other plants could not only reduce the burden on our landfill but cut down on the import and use of coal to generate electricity.

The replacement of coal by charcoal has other benefits. Coal is laden with mercury and sulfur. Mercury is a deadly toxin. Coal is also laden with sulfur and the combustion of coal leads to the release of sulfur oxides into the atmosphere. Sulfur oxides are a principal cause of acid rain. In contrast, charcoal contains no mercury and virtually no sulfur. In fact, our drug stores sell charcoal tablets to eat as an aid for digestion! Moreover, on a pound per pound basis, charcoal contains much more energy than most coals.

Just this year, in July and August, thousands of discarded old tires were found in Kapolei. At least two recycling companies apparently have had problems with old tires. They can serve as feedstock for a carbon diversion system and produce tons of charcoal in the process. My personal preference, however, is to use old, used and discarded tires in the asphalt pavement mix, which offers a cheaper re-use path and an improved final product, i.e., more durable asphalt pavements.

Oahu has thousands of acres devoted to growing seed corn for the mainland. The system can process corn cobs into miniature charcoal corn cobs which could probably be sold at a premium. It takes only a half acre to install a carbon diversion system which can process up to four tons of waste material per hour.

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