Incineration, soil cleanup

Thermal desorption systems can be broken into three key components pretreatment, the TDU, and posttreatment (Fig. 1) as discussed below. Additionally, thermal desorption systems are often used in conjunction with other treatment technologies as part of a treatment train. At previous RCRA and Superfund sites, thermal desorption has been used in conjunction with bioremediation, dechlorination, incineration, soil vapor extraction, soil washing, and solidification/ stabilization. " In these cases, the combination of technologies was required to meet the site s cleanup goals. 

According to EPA s initial plans, cleanup of the Times Beach area was to begin in 1984. However, a number of lawsuits delayed that process until 1990, when the EPA hired the Syntex Corporation to remove and incinerate contaminated soil and restore Times Beach to a safe area. That process was finally completed in July 1997, when the area was reopened as the 409-acre Route 66 State Park. 

Until very recently, explosives-contaminated soils have been remediated by incineration, a process whose high cost has stimulated the search for a more economical cleanup method (Roberts et al., 1993). Microbially mediated degradation of explosives is a promising technology. Many researchers have studied microbial consortia and various pure cultures for their ability to degrade TNT and other nitroaromatic compounds (for a review see Crawford, 1995), bringing about the development of bioremediation processes that can remove TNT and other explosives from contaminated soil and water (Funk etal., 1995 Williams a/., 1992). 

SET , incineration and plasma arc are very effective at achieving regulatory cleanup standards. However, SET is a nonthermal process, whereas the other processes are thermal. Thermal processes have the potential to produce hazardous by-products such as dioxins. SET does not form dioxins because it is a reduction process. Furthermore, the SET process is a closed system without an exhaust stack. When the SET process is used in soils, residual ammonia remains in the soil. This is typically on the order of 1-3%. Ammonia is a fertilizer which farmers pump (anhydrous) into their fields, so this residue is usually not harmful. 

Cleaning the Times Beach site was a massive estimated 200 million effort that included installation of a temporary incinerator to burn the contaminated soil, and the erection of a 15 ft high barrier around the incinerator to protect that area from regular flooding by the Meramec River. Contaminated soils were dug up, burned, and the resulting waste ash was buried on site. Cleanup of the site was completed by the end of 1997 by the US EPA and Syntex Agribusiness, the company that assumed responsibility for the site s cleanup. More than 265 000 tons of dioxin-contaminated soil from the site and 27... 

In another mobile incinerator, oxy/fuel was successfully used, instead of the conventional air/fuel system, to meet very stringent particulate emissions regulations at a Superfund cleanup site where the soil contained a significant amount of sand.22... 

In some applications, the waste material may directly contain dioxins and furans, or it may contain halogens that could lead to the formation of dioxins and furans. Many of the U.S. Superfund cleanup sites contain soil that has been contaminated with halogenated compounds. One common method to clean the soil is to process it through an incinerator which reduces the contaminants to trace levels (see Chapter 8). 

Ex situ remediation techniques require the excavation of polluted soil for subsequent treatment or disposal. Ex situ treatments can be broadly classified into extraction versus stabilization treatments that will render the polluted soil less harmful and suitable for deposition in a landfill or backfill. Soil washing is an example of an ex situ extraction technique in which the treated soil can either be returned to its original site (backfill) or be land filled, depending on the success of the cleanup stage. Asphalt incorporation, thermal treatment, and encapsulation are ex situ stabilization techniques in which the metal(loid)-contaminated soil is either incorporated (e.g., asphalt) or contained (encapsulation) by secondary materials that are subsequently land filled. Thermal treatments involve the incineration of the metal(loid)-polluted soil and the conversion of the pollutants into their metallic (zero-valent) states. In the following section we present an overview of the various technologies based on their mechanism of action. 

Effectiveness With sufficiently long residence time and a sufficiently high temperature, incineration usually reduces levels of organics to below nondetection levels, which simplifies handling of treated soil and reduces overall site cleanup levels. 

Soil washing is generally accepted as preferable to more conventional methods such as incineration for wastes where soil washing will provide cost-effective cleanup. The soil washing operation will have minimal effect on the off-site population or environment. However, soil washing produces a small volume of residual requiring further treatment or disposal. 

Incineration ashes are used as fill material for roads and in construction.Municipal solid waste, mixed biofuel, and heating plant ashes were analyzed by Sohxlet extraction in toluene, deactivated silica gel cleanup, and GC-MS to show SPAHis levels of 140 to 77,000 /rg kg. The highest levels measured were for ashes from biofuels incineration with NAP and PHN as the predominant PAHs. Since volatile PAHs are lost in the Soxhlet sample preparation process, actual levels of NAP and PHN may have been underestimated. B[a]P ranged from 1 to 1327 /rg kg. Bottom ashes contained more of the less volatile PAHs as expected. Results for the mixed biofuel ash were in excess of the Swedish EPA soil limits for less sensitive land use of 7 /rgkg of carcinogens and 40 /rg kg for noncarcinogenic PAHs. 

Traditional environmental cleanup methods include approaches such as excavation and incineration of contaminated soil or pumping and aboveground treatment of groundwater. These techniques are both expensive and politically unpopular. Affordable, innovative technologies are needed by the environmental restoration industry. Bioremediation is such a technology. 

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