Development and Evaluation of Field Sensors for Monitoring Bioaugmentation with Anaerobic Dehalogenating Cultures for In-Situ Treatment of TCE

Principal Investigators

James D. Ingle, Oregon State University

Objectives: The overall objective of this study is to refine and use redox sensors based on redox indicators as monitoring tools for assessing and optimizing redox conditions for treatment of TCE with dehalogenating cultures. Specific objectives are 1) to deploy, evaluate, and refine redox indicators for on-line monitoring of the redox conditions in two collaborative situations involving a bioaugmentation approach, 2) to understand the nature of the redox conditions under which dechlorination microbial processes occur.

Approach: Redox indicators (organic molecules than change color with redox state) will be used to differentiate between different microbial redox levels (Fe(III)-reducing, sulfate-reducing, methanogenic or dechlorinating). These indicators are immobilized in a form (typically a transparent film) amendable for continuous monitoring (e.g., reversible, durable, stable, good kinetics) and placed in optical (or custom) flow cells. These redox indicator flow sensors will be deployed in two primary situations for calibration and demonstration of their applicability: 1) continuous monitoring of redox conditions of cultures inside bioreactors or microcosm bottles as a tool for the optimizing conditions for effective dechlorination of TCE with enriched halorespiratory cultures, 2) on-line monitoring of the redox status of test solutions pumped into and out of wedge-shaped physical aquifer models packed with aquifer sediment (i.e., "push-pull" tests). Redox measurements will be made before and after enriched cultures (developed in microcosm experiments) are injected into the physical model (bioaugmentation) during which characteristics such as electron donor utilization, enzyme activity, biomass, and dehalogenating ability of halorespiratory cultures are being determined. Throughout these studies the design and characteristics of the redox sensors will be improved based on experimental results, and new self-contained, miniature, optical redox sensing modules will be developed.

Expected Results: This research will advance the development of new techniques and devices for monitoring redox status in the laboratory and at contaminated ground water sites that complement existing techniques and provide unique advantages such as rapid on-line monitoring, reversible response, and inexpensive, miniaturized, and portable instrumentation. These on-line monitoring techniques will be beneficial 1) for the initial assessment of laboratory samples and subsurface conditions at a site, 2) for continued assessment of the progress of remediation, and 3) for control of injections of amendments (e.g., substrates, nutrients) during remediation. Developed redox indicator flow sensors should enhance the capabilities of single-well "push-pull" tests developed at OSU and the ability to evaluate the success of bioaugmentation.

Project Status (end of 2002): We have developed a portable flow system for monitoring redox status of solutions in bioreactors and microcosm bottles and physical aquifer models (PAMs)). It is based on a specially constructed peristaltic pump and housing and improved flow cells for immobilized redox indicators. For the pump housing, the gas permeable pump tubing is enclosed and protected by purging with an inert gas or by contact with a deoxygenating solution (e.g., ascorbic acid). This pump can be powered by a small 12-V battery in field applications. Microcosms are easily adapted to the flow system by inserting PEEK or stainless steel tubing through the container wall. The flow system is directly applicable for monitoring redox levels of anaerobic material inside PAMs with minimal oxygen contamination. With this flow system, we have achieved O2 permeation rates as low as 2.4 mL/h.

We have continued to improve the design and fabrication of inexpensive spectrophotometric flow cells suitable for containing redox indicators immobilized on thin transparent films. Critical points in the design of these flow cells include ease of replacing membranes, providing a pathway for trapped bubbles to escape, and rigid construction, which minimizes O2 permeability through the cell walls.

Preliminary work has begun on platinum/redox membrane electrodes constructed with the film of the immobilized indicator press-fit to the surface of a modified platinum electrode. These devices are conceptually simpler than optically based detection systems and could be the basis of simple in-situ redox probes.

Publications

• K. Cantrell and J. D. Ingle, J. (2002, In Press). "The SLIM Spectrometer." Anal. Chem.

Progress Reports: 2003

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