Theme: 01. Remediation Technology Innovations

Topic Area: 01b. Bioremediation: Advances in Amendment Formulations

Formatted Title:

Aerobic and Anaerobic In Situ Bioremediation Evaluation of Chlorinated Ethenes and Chlorinated Benzenes

Background/Objectives:

Background/Objectives. The purpose of the in situ bioremediation (ISB) evaluation was to determine if an aerobic or anaerobic bioremediation approach was appropriate for high levels of chlorinated volatile organic compounds (cVOCs) in groundwater including: tetrachloroethene (PCE), trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE), vinyl chloride (VC), benzene, chlorobenzene (CB), 1,2-dichlorobenzene (1,2-DCB), 1,3-DCB, 1,4-DCB, 1,2,3-trichlorobenzene (1,2,3-TCB) and 1,2,4-TCB. The ISB evaluation used a series of in situ microcosms (ISMs), which evaluated various biostimulation and bioaugmentation options in eight on-site monitoring wells.

Approach/Activities:

Approach/Activities. The following four carbon substrates were evaluated in the ISMs under anaerobic conditions: EOS PRO, EOS ZVI, SRS-ZVI and Wilclear Plus. Three different microbial consortia were evaluated in the anaerobic ISMs including: KB-1, BAC-9, and ZARA-10. EOX and Osmacote were used as oxygen and nutrient sources, respectively, in the aerobic ISM units. ENV486™ and ENV492™ were aerobic microbial consortia that were able to enhance 1,4-DCB and CB aerobic biodegradation, respectively. The ISM units were deployed for a period of 94 days and were analyzed for cVOCs, Dehalococcoides and key genes responsible for reductive dechlorination or aerobic degradation of cVOCs, volatile fatty acids (VFAs), and anions.

Results/Lessons Learned:

Results/Lessons Learned: In the source bedrock well (MW-1), the carbon source amendments, SRS^®-ZVI and EOS PRO were both effective at enhancing PCE, TCE, 1,2,3-TCB and 1,2,4-TCB biodegradation. The SRS^®-ZVI unit was the most effective at degrading PCE, TCE, and VC. However, significant amount of cis-1,2-DCE accumulated in the anaerobic ISM units. In a downgradient well (MW-2), the EOS ZVI showed the highest percent reductions in chlorinated ethenes, CB, DCBs and TCBs. The percent reductions were greater than 80% except for cis-1,2-DCE, which showed a 54% reduction. In this location, bioaugmentation did not enhance biodegradation of the cVOCs within the three-month incubation period. In a further downgradient well (MW-3), EOS PRO was very effective at promoting degradation of chlorinated ethenes (>90% reduction) except for cis-1,2-DCE. The chlorinated benzenes tested were also reduced by greater than 90% in the EOS PRO BioStim unit. EOS PRO was more effective at enhancing biodegradation of cVOCs than SRS^®-ZVI. When the EOS PRO was bioaugmented with BAC-9 or KB-1^®, there was not a significant increase in the percent reduction of the chlorinated ethenes.

EOS PRO was not effective at enhancing degradation of the chlorinated ethenes or 1,2,3-TCB in the downgradient well (MW-4). However, when the oxygen source EOX was provided in the ISM unit, there was greater than 93% reduction in the cVOCs tested and greater than 98% reduction in cis-1,2-DCE, CB, 1,2-DCB, 1,3-DCB, 1,4-DCB and 1,2,3-TCB and 1,2,4-TCB. However, when the EOX ISM unit was bioaugmented with ENV492 and ENV486, the percent reduction in cVOCs was lower in the bioaugmented unit compared to the biostimulation unit. This presentation will demonstrate how the heterogeneity of site groundwater can significantly affect biodegradation rates for various cVOCs and the benefit of evaluating various electron donors and acceptors to enhanced biodegradation of cVOCs.

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Jennifer Warnicke