Sustainable Remediation for Protection of Public Health

Scrap rubber tires have been accumulating for decades and are becoming an increasing challenge throughout the US and abroad. Consumption of tires is highest in the US, with an estimated 240 million scrap tires generated annually and no signs of a reduction in this waste stream; this corresponds to an astounding estimate of one scrap tire per person per year in the US has been set forth.

The scrap tires generated daily are added to existing tire dumps and landfills, or are stockpiled for recycling and reuse in construction materials. Leachate from landfills has long been a recognized public health concern, including potential impacts to soil, groundwater, and air quality in large areas around landfills. Exacerbating this concern is the significant risk of fires and ambient air quality posed by tire fires; many such fires last for several days or weeks.

Importantly, tire pile fires produce significant amounts of oils that are flammable and pose threats to air quality through emissions of petroleum hydrocarbon compounds such as polycyclic aromatic hydrocarbons (PAHs); many PAHs are known or suspected carcinogens and are considered highly toxic to human health. To the extent that tires burn with a higher per-pound heat output than most coal, making the increased heat a significant challenge with respect to extinguishment

To help address the above challenges, an innovative method has been developed to recycle large-scale scrap tire piles. The method relies on pyrolysis, which is a form of incineration that chemically decomposes organic materials by heat in the absence of oxygen. This process typically occurs under pressure and at operating temperatures above 430 °C (800 °F). To the extent that some volatile or semi-volatile materials are present in the waste, thermal desorption will also occur.

An important aspect of this methodology is that it transforms organic materials into gases, small quantities of liquid hydrocarbons, steel, and carbon black residue. The off-gases are treated in a secondary thermal oxidation unit and can in fact be used as the source of energy to run a recycling plant, remaining entirely sustainable (Allred et. al., 2000). The hydrocarbons recovered are high-quality fuels which have measurable resale value, while the steel can be readily re-smelted and reused. Lastly, carbon black, when combined with rubber, substantially increases the hardness and durability of the product, with additional applications in development of filters, inks, toners, and paints. As such, this remediation system which serves to protect public health is entirely sustainable.

In addition to the obvious environmental and public health benefits, economic analyses performed on such sustainable recycling systems have yielded measurable financial benefits. Assuming a standard size plant which can handle 100 tons per day of scrap tires, net profit estimates of over $2 million have been estimated. With this size plants, over eighty such plants are needed in the US alone to process the scrap tires generated annually; this does not even consider the more than three billion tires already present in landfills and dumps across the US.

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