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Remediation of Soils Contaminated with Wood-Treatment Chemicals

Principal Investigators
R.K. Bajpai, S.K. Banerji, and R.K. Puri, University of Missouri; M.E. Zappi, U.S. Army Corps of Engineers


Goal: The goal of this project is to develop a slurry biotreatment process for soils contaminated with Pentachlorophenol (PCP) and creosote.

Rationale: PCP and creosote polyaromatic hydrocarbons (PAHs) are found in most contaminated soils at wood-treatment sites. Treatment methods currently being used for such soils include soil washing, incineration, and biotreatment. Soil washing involves removal of hazardous chemicals from soils using solvents, but the solvent stream must still be treated for destruction of contaminants. Incineration is an effective tool for destruction of contaminants but is costly and lacks public acceptance. Bioremediation has been considered and used for treatment of soils contaminated with wood-treatment chemicals, but bioremediation leaves the most toxic, carcinogenic, and regulated chemicals in the soil. Slurry-phase biotreatment of contaminated soils and sediments is an innovative treatment technology. Its advantages include easy manipulation of physicochemical variables and operating conditions to enhance rates of biodegradation and ease of containment of exhaust gases and effluent. Bioslurry technology is currently hampered by some bottlenecks that need to be relieved.

Approach: Engineering and process development aspects of bioslurry treatment of PCP- and creosote-contaminated soils from a Superfund site will be studied in this project in shake flasks and in 14-liter well-instrumented fermentors. Use of surfactants and cosolvents will be explored in order to enhance aqueous solubility of hydrophobic and sparingly soluble contaminants. The effect of cosolvents on microbial activity will be studied. Kinetic studies for biodegradation of PCP and PAHs will be carried out in sealed bioreactors so that accurate material balances can be taken. Experiments are planned to investigate the role of surfactant/cosolvent, temperature, carbon source, and oxygen delivery by sparging of pure oxygen in reduction of concentrations of PAHs and PCP in the contaminated soil slurry. Reactors with power measurement devices will be used to investigate several different types of mechanical agitators in order to keep the solids in suspension. The power requirement under aerated and unaerated conditions will be correlated with geometrical and system parameters such as particle size, nature of soil, solid density, and physical dimensions in the reactor. Oxygen transfer rate and oxygen transfer efficiency in the slurries with sufficient power input for minimal and complete suspension will also be studied in this reactor. All of the information will be used to develop a flow diagram of the bioslurry treatment process for cleanup of contaminated sites and to generate cost data that may be used to determine cost effectiveness of this process for field-scale treatment.

Status: Start-up activities have been completed. These include collection of contaminated and uncontaminated soils, procurement of agitators, assembly of set-up, and development of experimental protocols for the first phase of study. Studies of solubility enhancement, measurements of surfactants' adsorption equilibria in different soils, and mixing studies are currently being conducted. Procedures for analysis of surfactant concentrations are being standardized and will be followed by measurements of adsorption equilibrium isotherms in soil suspensions. PAH-solubility enhancements will be conducted mostly with contaminated soil and will be related to soil-characteristics, PAH partition coefficients, and surfactant adsorption isotherms. Measurements of power number versus Reynold number for the different impellers in soil-free systems are being conducted with and without aeration; these will be followed by measurements in different soil slurries. Rheology of soil slurries is also being measured. This project is in its first year.

Clients/Users: This project will interest those in the wood-treatment industry and federal agencies such as U.S. Environmental Protection Agency and U.S. Department of Defense.

Key words: soil, PCP, creosote, slurry bioreactor, wood treatment

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