Graduate Thesis Or Dissertation
 

Monitoring redox conditions with redox indicators during microbial reductive dechlorination in microcosms and bioaugmented columns

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xw42nb39z

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  • New methods, sensors, and devices based on redox indicators were developed to monitor redox conditions in anoxic and anaerobic laboratory systems and the subsurface environment. The primary application was monitoring redox conditions during the dechlorination of tetrachioroethene (PCE) to ethene (ETH) in packed columns and microcosm bottles containing an enriched chlororespiring culture (Evanite culture). Redox levels were monitored by measuring the absorbance of thionine (THI) or cresyl violet (CV) immobilized on a film that was placed in a unique spectrometric flow cell. This flow cell was incorporated into a flow loop with a pump to create a versatile, flow-based redox sensor for samples in bottles and columns. All components and materials in the flow sensor ioop were optimized to reduce O₂ contamination of pumped solutions to very low levels (30 nmollh). The flow sensor was a critical tool for evaluating O₂ contamination in many laboratory systems and types of sample containers and for monitoring of redox levels of highly O₂-sensitive dechiorinating cultures. The application of a novel fiber-optic redox probe, based on redox indicator film, is also reported. During dechlorination experiments in both columns and bottles, complete reduction of Till indicates redox conditions are appropriate for active dechlorination, and partial reduction of CV is indicative of dechlorination of cis-dichioroethene and vinyl chloride. A new technique was developed and applied to determine a "redox capacity" rather than "redox level". An environmental sample is mixed with a known amount of redox indicator to determine the amount of indicator reduced and an effective concentration of reductant, termed reductive capacity (RC). RC measured with THI ranged from 100 - 400 !iM during active dechlorination of PCE in microcosms and packed columns and increased by a factor of two or greater as dechlorination progressed from PCE to ETH. Redox indicators were immobilized on 20-j.tm particles. These miniature and mobile redox sensors or probes were shown to be useful for evaluating redox conditions inside a packed colunm under dechiorinating conditions and in microcosm bottles under different microbial redox levels. Redox probes based on fitting a redox indicator film to Pt electrodes were also evaluated.
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