COMPARATIVE COST AND PERFORMANCE OF TWO NEW BIOLOGICAL PERMEABLE BARRIERS FOR IN SITU BIOREMEDIATION OF CONTAMINATED GROUNDWATER

Key requirements for the success of any bioremediation process are complete detoxification of the contaminant, high removal efficiencies, and process stability. Inadequate control and lack of stability over the microorganisms under specific environmental conditions have been limiting factors for long-term implementation of in situ bioremedian processes.This investigation proposed and examined an innovative combination of two technical concepts that currently have strong market potential for groundwater remediation: in-situ bioremediation and permeable barrier for subsurface groundwater confinement/cleanup. Biological Permeable Barrier (BPB) entails immobilizing microbial organisms, which are acclimated to the target contaminants in unique polymeric beads (PVA, polyvinyl alcohol) or on Granular Activated Carbon (GAC). Ideally, a cost-effective permeable reactive medium should be easy to construct and maintain, remain permeable, and tolerate operational and environmental stresses.A series of column experiments were designed to simulate BPB and to account for any significant changes in removal efficiency of 2,4,6 Trichlorophenol (TCP) from groundwater due to hydraulic retention time (HRT), applied loading, availability of dissolved oxygen (DO), and toxic shock loads of TCP. The results of this laboratory investigation provided the basis for the conceptual design and cost evaluation for a contaminated site with PAH's and BTEX in Louisiana.PVA-immobilized cells were found to be a good permeable barrier media with a 100%-91% TCP removal efficiency at loading up to 300-600 mg/L.d, respectively. The mixture of GAC-immobilized cells (3%) and silica sand (97%) offered 100 % removal for TCP loading up to 1200 mg/L.d (HRT= 14.8 minutes) by a combination of biological and physical adsorption mechanisms. Both media tolerated shock loads of TCP (>550 mg/L) and deficiency of Dissolved Oxygen (DO) of less than 2 mg/L and resume their biodegradation activity in a matter of few days. It was determined that BPB offers a passive and low cost bioremediation process that can be strategically designed to remove contaminants from groundwater in situ. The cost of BPB was determined to be substantially less than any other treatment technology for in situ bioremediation of contaminated groundwater.