4.1.2.2 Description of Primary Treatment Technology for Alternative 2, Dechlorination and High Temperature Thermal Desorption Alternative 2 involves excavation and transport of contaminated material to the CTF and treatment of the material by a combination of dechlorination and HTTD. Treated wastes would be disposed of in the disposal facility. Figures 4-9 and 4-10 present material flow diagrams for Scenario 1 and Scenario 2 respectively. Dechlorination treatment involves mixing dechlorination chemical reagents with contaminated materials and applying heat to the mixture. The heat is typically provided by a rotary dryer or kiln. The dechlorination reagents are either sprayed on the contaminated materials in a stockpile or before the materials enter the rotary dryer for HTTD. Table 4-1 presents information concerning operational characteristics of several available HTTD systems that use rotary dryers or kilns. Most of these systems can potentially be adapted to include a dechlorination step to treat PCB-contaminated wastes from the CD sites. For the purpose of this FS, however, PRC has selected the SoilTech ATP and the SAREX THERM-O-DETOX systems to illustrate how this alternative would be implemented at the site. The SAREX THERM-O-DETOX system was developed under a license agreement with RREL; ETG Environmental, Inc. (ETG); and Separation and Recovery Systems, Inc. (SRS). These systems were selected because they have been or will be used at full scale to remediate Superfund sites. The operation of the SoilTech ATP and SAREX THERM-O-DETOX systems at the Wide Beach Development (WBD) and Koppers Company (Morrisville Plant) Superfund sites, respectively, are discussed below. General support requirements for dechlorination and HTTD systems are also discussed below. SoilTech ATP Systems, Inc., Anaerobic Thermal Processor In 1991, SoilTech used APEG to dechlorinate PCBs in the ATP at the WBD site in Brant, New York (see Section 4.1.2.1 for description of ATP). During dechlorination, polyethylene glycol monomethyl ethers replace chlorine atoms on the biphenyl ring, resulting in a less toxic compound. The ATP provided the mixing and elevated temperature required for the dechlorination reaction to proceed. The ATP system was modified slightly at the WBD site to include a reagent preparation module to blend dehalogenation reagents and carrier oil when the ATP was used to dehalogenate wastes. The module included an enclosed reagent storage area, reagent mixing tank, reagent and carrier oil blending tank, and feed pump. The reagents were mixed and heated in the reagent mixing tank. The mixed reagents were then blended with carrier oil from the vapor recovery system. The blend of reagents and carrier oil was pumped at a measured rate onto the soil in the preheat zone of the ATP (EPA 1993c). SAREX THERM-O-DETOX Under a license agreement with RREL, ETG and SRS, developed the SAREX THERM-O-DETOX system to demonstrate the BCD process under pilot-scale conditions. The combined system uses both thermal desorption and liquid BCD to extract and dechlorinate chlorinated organic compounds. The process potentially can be applied using any of the HTTD systems supplied by SRS, which range in treatment rates from 1 to 10 tons per hour. Assuming that the 10 ton per hour unit is used and achieves 70 percent mechanical availability and a treatment rate equal 80 percent of the nominal treatment rate, the SAREX THERM-O-DETOX system can treat the contaminated materials from the CD sites in 6.1 years under Scenario 1 and 8.7 years under Scenario 2. The SAREX THERM-O-DETOX system was used to treat soil contaminated with PCPs, dioxins, and furans during a demonstration at the Koppers Company (Morrisville Plant) site in Morrisville, North Carolina. The SAREX THERM-O-DETOX process (see Figure 4-11) consists of the following steps: pretreatment, HTTD, vapor recovery, and liquid decomposition. Pretreatment consists of removing particles with diameters of more than 0.5 inch and homogenizing the soil by mixing. Sodium bicarbonate, a dechlorination agent, is added to the soil as it is being mixed. After pretreatment, the contaminated material is carried by conveyor into the medium temperature thermal desorber (MTTD). Inside the MTTD, the contaminated material is mixed by two screw-type auger shafts as it is heated to 800 澹. A portion of the contaminants may be dechlorinated in the MTTD; the remaining contaminants and products of dechlorination are volatilized into a vapor phase. Treated solids exiting the MTTD are cooled in a cooling screw conveyor and then sprayed with water in another screw conveyor to control dust. The treated solids can be disposed of after cooling and remoisturization. The vapor recovery step consists of (1) vapor scrubbing by oil and water scrubbers, (2) oil and water vapor condensation using a water filter, and (3) carbon polishing. Inside the oil scrubber, the contaminated vapor stream comes in direct contact with a petroleum-based scrubber oil. The scrubber oil cools, condenses, and dissolves most VOCs and SVOCs. These condensed and dissolved organic compounds, along with dust particles, are entrained in the scrubber oil, which is stored in an oil tank and treated during the liquid decomposition step. The water scrubbers condense remaining organic vapors and moisture from the vapor stream. Contaminated scrubber water is removed from the system, treated with GAC, and is either used to remoisturize treated soil or discharged in accordance with site-specific regulatory requirements. After exiting the water scrubbers, any remaining oil and water vapor in the vapor stream is condensed in a water filter. The vapor stream is then carbon polished to remove remaining contaminants and finally released to the atmosphere. The liquid decomposition step consists of treating contaminated scrubber oil in the liquid tank reactor (LTR). The contaminated oil is mixed with a hydrogen donor oil and dechlorination reagents consisting of sodium hydroxide and a proprietary catalyst and then heated to the process temperature of about 650 oF. Contaminants are then dechlorinated in the LTR in a continuously mixed batch process. Water vapor produced during treatment is removed from the LTR by a reflux condenser that separates oil entrained in the vapor. Oil is returned to the LTR, and aqueous condensate is held in a condensate tank and then treated with scrubber water by activated carbon. The treated water can be used to quench the treated solids or discharged to a POTW. Treated oil can be disposed of off site or refined and reused. The oil disposal method depends on site-specific regulatory requirements (EPA 1994g). The U.S. Navy has conducted pilot-scale tests of dechlorination and HTTD to treat materials contaminated with PCBs. A stockpile of contaminated material was mixed with sodium bicarbonate in the amount of 10 percent of the weight of the stockpile and heated for about 1 hour at 630 澹 in an HTTD system that uses a rotary dryer as the main process unit. PCBs decompose and partially volatilize in the rotary reactor. Clean soil from the rotary reactor can be returned to the site from which it was excavated. Off-gases from the reactor, which contain dust and trace amounts of PCBs, are sent through a cyclone, baghouse, scrubber, and carbon filters before being vented into the atmosphere. The water from the scrubber and condensate can be discharged to a POTW after being pumped through mixing and settling tanks, filters, and activated carbon. A liquid-phase reaction treats residuals from solid-phase treatment and occurs in a stirred tank reactor (STR). These residuals include vapor condensate, dust, spent carbon, and filter cake. The residuals decomposed after 2 hours at 660 澹 in the STR by a high-boiling-point hydrocarbon oil, a proprietary catalyst, and sodium hydroxide. Nitrogen can be injected into the STR to prevent combustion. The oily residuals left in the STR, which contain dust, sludge, and activated carbon, can be burned in an oil-fired power plant or treated and reclaimed by waste oil recyclers. The STR produces only biphenyls; low- boiling point olefins, which are not water soluble and much less toxic than PCBs; and sodium chloride. Samples of the clean solids would be analyzed and disposed of appropriately (U.S. Department of Navy 1991). Dechlorination and HTTD Support Requirements The support requirements for dechlorination and HTTD are virtually identical to the support requirements for HTTD (see Section 4.1.2.1). The support requirements for site mobilization and access, utilities, contaminated materials pretreatment, and waste residuals post-treatment for dechlorination are negligible.