Development of a biological permeable barrier to remove 2,4,6-trichlorophenol from groundwater using immobilized cells

This investigation developed and evaluated a new biological permeable barrier media designed to remove 2,4,6-trichlorophenol (TCP) in situ from groundwater. There are many potential, expensive barrier media, such as ion-exchange resins and granular activated carbon. Therefore, developing low-cost, yet effective, barrier materials would expand potential applications of permeable barrier technology. A polyvinyl alcohol matrix that immobilized microbial cells (PVA-immobilized cells) was selected as the media for a series of column studies under various operating conditions to simulate a biological trench permeable barrier. Column experiments were designed to account for any significant changes in removal efficiency as a result of hydraulic retention time, applied loading, availability of dissolved oxygen (DO), and nutrient carbon-to-nitrogen-to-phosphorus ratio added to groundwater. During 166 days of continuous operation, PVA columns (10- and 20-cm beds) reacted to insufficient DO and high loading rate, The PVA-immobilized cells were found to be a good permeable barrier media with a 99.9 to 91% TCP removal efficiency at loading as great as 300 to 600 mg/L.d with corresponding hydraulic retention times of 24.5 and 12.3 minutes, respectively. The PVA-immobilized cells remained permeable and structurally sound during 166 days of continuous operation. The cells also tolerated low DO and resumed biological activity to a steady state once they received sufficient DO. Finally, the cells completely dehalogenated TCP without formation of chlorinated intermediates or phenol.