Development of a Biological Permeable Barrier To Remove 2,4,6‐Trichlorophenol from Groundwater Using Immobilized Cells

Abstract

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‐tonitrogen‐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.