ABSTRACT

Degradative Solidification/Stabilization Technology for Chlorinated Hydrocarbons

Remediation of sites contaminated with chlorinated organics and mixtures of chlorinated organics and metals is a major environmental challenge. Degradative solidification/stabilization (ds/s) is potential new technology for such applications. It combines degradative processes for organic contaminants with conventional processes for immobilization of inorganics. It offers potential advantages of the low cost of conventional s/s and the ability to destroy toxic organics. Development of ds/s technologies is particularly timely due to the trend toward more containment-oriented remediation and advances in the science of degradation reactions to be applied in ds/s. Development of ds/s offers the potential for a treatment option that is substantially less expensive than alternatives such as incineration. Costs for s/s treatment typically range from $30 to $300/ton while incineration costs are typically between $200 and $400/ton. Additional costs for ds/s are estimated to range from $5 to $50/ton.

A research program is being established to develop ds/s technologies. A research team has been organized that includes an engineer with expertise in s/s and an environmental chemist with expertise in degradation of organic compounds. The overall goal of the proposed research is to identify combinations of reagents (surfaces, electron carriers, and electron donors), reaction conditions that are appropriate for use in degradative solidification/stabilization systems and to demonstrate the feasibility of using one combination in a commercial ds/s treatment systems. Electron donors such as zero-valent metals and sulfide will be investigated in their ability to degrade tetrachloroethylene (PCE) and its degradation products (TCE, DCE isomers, and VC). To achieve this goal, five objectives are proposed. First, analytical and experimental tools to screen the reagents and reaction conditions will be developed (Objective 1). Then a wide range of reagents and reaction conditions will be investigated to screen those chemical systems that are most likely to become part of a practical treatment technology (Objective 2). These experiments will be conducted in slurry reactors to facilitate sampling and minimize variability in results. Experiments will be conducted at high pH, similar to cementitious s/s systems, and at moderate pH, similar to silicate/phosphate s/s systems. The most promising systems identified in the screening step will be investigated further to characterize their rates of dechlorination more fully so that optimization of the treatment technology can be accomplished (Objective 3). This information will be used to test the most promising technologies under conditions more closely related to those that will be found in the field (Objective 4). Finally, a model describing leaching and degradation in ds/s will be developed to predict the release rate of target organics (Objective 5).