Theme: 10. Characterization, Fate and Transport

Topic Area: 10b. Advanced Sampling and Analysis Tools and Techniques

Formatted Title:

A Biogeochemical Model for Enhanced Bioremediation of Chloro-, Nitro- and Amino-Substituted Aromatics Using Advanced Tools and Methods

Background/Objectives:

Conventional tools referenced in current bioremediation research and natural attenuation (NA) protocols are insufficient to assess degradation processes of atypical contaminant mixtures. These tools were primarily developed to address chlorinated solvents and petroleum hydrocarbons, and are often inadequate to assess attenuation mechanisms of various compounds widely used in agrochemical and pharmaceutical manufacturing. This presentation will describe select statistical tools and analytical methods developed to identify bioactivity, compound bond-breaking, and NA at a former chemical manufacturing site in South America. Both vadose and phreatic zones present complex mixtures of volatile and semi-volatile organics, including chlorobenzenes, chloronitrobenzenes, and chloroanilines. The main goal of the biogeochemical model was to conceptualize contaminant-specific degradation processes and geochemical controls to support remedy selection and performance monitoring.

Approach/Activities:

Multiple lines of evidence were integrated to understand contaminant trends at well- and plume-scale over the last 25 years. Multivariate statistics was applied to identify data relationships inapparent using univariate methods, supporting redox zone delineation. International academic collaboration shed light on key genetic strains associated with compound-specific aerobic and anaerobic degradation pathways. ¹³C, ¹⁵N and ³⁷Cl isotope analysis and nuclear magnetic resonance (NMR) were applied to assess biodegradation processes and presence of degradation products, respectively, at pilot- and plume-scale remedy performance monitoring. Spatial distribution and abundance of key microorganisms were compared with the redox zones delineated. Radial diagrams condensed site-wide geochemical conditions as indirect evidence of degradation, from which the attenuation capacity of the aquifer, and effectiveness of natural attenuation, could be evaluated.

Results/Lessons Learned:

Microcosm studies indicated that all tested compounds can be mineralized under aerobic conditions, while chloronitrobenzenes, chloroanilines and chlorobenzenes undergo incompletely transformation under anaerobic conditions. Performance monitoring of the in situ biosparging pilot treatment showed significant reduction in contaminant mass with the temporary transition from predominantly anaerobic conditions to an abundant ammonium-oxidizing archaea medium. ¹³C and ³⁷Cl isotope data suggest an aerobic degradation pathway for 1,2-dichlorobenzene, and H¹ NMR data suggest microbial communities are active during attenuation. Fractionation of ¹⁵N in 2,3-dichloroaniline observed in pilot constructed wetlands were attributed to aerobic degradation processes. Other non-destructive attenuation processes have been investigated via batch tests and numerical modelling. Site-wide, anaerobic biotransformation processes dominate, with localized potential for aerobic mineralization. The distribution of the microbial communities parallel contaminant distribution. Inverse fractionation of ¹³C in chlorobenzene along groundwater flow-paths suggests this compound primarily exists as a degradation intermediate rather than a parent compound, confirming ongoing anaerobic degradation processes in situ. The site aquifer was estimated to be capable of attenuating only 7-18% of the contaminant mass under natural conditions, indicating that a combination of remediation technologies focused on treating degradation intermediates is required to meet remediation goals.

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Maria Cristina Lemes