Effectiveness of stimulating PCE reductive dechlorination: A step-wise approach (original) (raw)
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Methodology for the evaluation of engineered in situ bioremediation: lessons from a case study
Journal of Microbiological Methods, 1998
Engineered in situ bioremediation is an economically and ecologically sound technology for the clean-up of contaminated soils and aquifers. However, a successful bioremediation requires solid evidence for the detoxification of the contaminants, preferably proven by complete mineralization. This paper discusses a stepwise evaluation leading to the demonstration of successful engineered in situ bioremediation. Five major evaluation steps assess whether: (1) the contaminants can be mineralized by the indigenous microbial population (2) the mineralization rates can be increased (3) the remediation concept can be simulated under continuous flow conditions (4) the increase of mineralization rates can be achieved at the field site (scale-up), and (5) complete mineralization to harmless end products is achieved at the field site. For these evaluations, the applicability of four experimental approaches (field investigations, laboratory aquifer columns, microcosms and microbial cultures) and the relevance of various microbiological or chemical monitoring parameters are discussed. The evaluations are illustrated using a specific engineered in situ bioremediation of a diesel fuel-contaminated aquifer in Menziken, Switzerland. The case study demonstrates that microbiological and chemical monitoring parameters as well as field tracer studies and stable carbon isotopes should be combined for the unequivocal evaluation of engineered in situ bioremediation.
A universal design approach for in situ bioremediation developed from multiple project sites
Remediation Journal, 2012
This article describes a design approach that has been developed for bioremediation of chlorinated volatile organic compound-impacted groundwater that is based upon experience gained during the past 17 years. The projects described in the article generally involve large-scale enhanced anaerobic dechlorination (EAD) and combined aerobic/anaerobic bioremediation techniques. Our design approach is based on three primary objectives: (1) selecting and distributing the proper additives (including bioaugmentation) within the targeted treatment zone; (2) maintaining a neutral pH (and adding alkalinity when needed); and (3) sustaining the desired conditions for a sufficient period of time for the bioremediation process to be fully completed. This design approach can be applied to both anaerobic and aerobic bioremediation systems. Site-specific conditions of hydraulic permeability, groundwater velocity, contaminant type and concentrations, and regulatory constraints will dictate the best remedial approach and design parameters for in situ bioremediation at each site.
Journal of Soils and Sediments, 2011
Purpose In order to provide highly effective yet relatively inexpensive strategies for the remediation of recalcitrant organic contaminants, research has focused on in situ treatment technologies. Recent investigation has shown that coupling two common treatments-in situ chemical oxidation (ISCO) and in situ bioremediation-is not only feasible but in many cases provides more efficient and extensive cleanup of contaminated subsurfaces. However, the combination of aggressive chemical oxidants with delicate microbial activity requires a thorough understanding of the impact of each step on soil geochemistry, biota, and contaminant dynamics. In an attempt to optimize coupled chemical and biological remediation, investigations have focused on elucidating parameters that are necessary to successful treatment. In the case of ISCO, the impacts of chemical oxidant type and quantity on bacterial populations and contaminant biodegradability have been considered. Similarly, biostimulation, that is, the adjustment of redox conditions and amendment with electron donors, acceptors, and nutrients, and bioaugmentation have been used to expedite the regeneration of biodegradation following oxidation. The purpose of this review is to integrate recent results on coupled ISCO and bioremediation with the goal of identifying parameters necessary to an optimized biphasic treatment and areas that require additional focus. Conclusions and recommendations Although a biphasic treatment consisting of ISCO and bioremediation is a feasible in situ remediation technology, a thorough understanding of the impact of chemical oxidation on subsequent microbial activity is required. Such an understanding is essential as coupled chemical and biological remediation technologies are further optimized.
Integrative approaches for assessing the ecological sustainability of in situ bioremediation
FEMS Microbiology Reviews, 2009
Application of microbial metabolic potential (bioremediation) is accepted as an environmentally benign and economical measure for decontamination of polluted environments. Bioremediation methods are generally categorized into ex situ and in situ bioremediation. Although in situ bioremediation methods have been in use for two to three decades, they have not yet yielded the expected results. Their limited success has been attributed to reduced ecological sustainability under environmental conditions. An important determinant of sustainability of in situ bioremediation is pollutant bioavailability. Microbial chemotaxis is postulated to improve pollutant bioavailability significantly; consequently, application of chemotactic microorganisms can considerably enhance the performance of in situ degradation. The environmental fate of degradative microorganisms and the ecological consequence of intervention constitute other important descriptors for the efficiency and sustainability of bioremediation processes. Integrative use of culture-dependent, culture-independent methods (e.g. amplified rDNA restriction analysis, terminal restriction fragment length polymorphism, denaturing/thermal gradient gel electrophoresis, phospholipid fatty acid, etc.), computational and statistical analyses has enabled successful monitoring of the above aspects. The present review provides a detailed insight into some of the key factors that affect the efficiency of in situ bioremediation along with a comprehensive account of the integrative approaches used for assessing the ecological sustainability of processes. The review also discusses the possibility of developing suicidal genetically engineered microorganisms for optimized and controlled in situ bioremediation.
A systematic approach to in situ bioremediation in groundwater
Remediation Journal, 2003
In situ bioremediation (ISB) melds an understanding of microbiology, chemistry, hydrogeology, and engineering into a strategy for planned and controlled microbial degradation of specific contaminants. ISB creates subsurface environmental conditions, typically through reduction oxidation manipulation, which induce the degradation of contaminants via microbial catalyzed biochemical reactions. In turn, the microbes produce enzymes that are utilized to derive energy and that are instrumental in the degradation of target chemicals. To accomplish this chain of events, the type of microorganisms, contaminant, and the geological conditions at the site must be considered.
Site-specific pre-evaluation of bioremediation technologies for chloroethene degradation
International Journal of Environmental Science and Technology, 2013
Groundwater systems are important sources of water for drinking and irrigation purposes. Unfortunately, human activities have led to widespread groundwater contamination by chlorinated compounds such as tetrachloroethene (PCE). Chloroethenes are extremely harmful to humans and the environment due to their carcinogenic properties. Therefore, this study investigated the potential for bioremediating PCE-contaminated groundwater using laboratory-based biostimulation (BS) and biostimulationbioaugmentation (BS-BA) assays. This was carried out on groundwater samples obtained from a PCE-contaminated site which had been unsuccessfully treated using chemical oxidation. BS resulted in complete dechlorination by week 21 compared to controls which had only 30 % PCE degradation. BS also led to a approximately threefold increase in 16S rRNA gene copies compared to the controls. However, the major bacterial dechlorinating group, Dehalococcoides (Dhc), was undetectable in PCE-contaminated groundwater. This suggested that dechlorination in BS samples was due to indigenous non-Dhc dechlorinators. Application of the BS-BA strategy with Dhc as the augmenting organism resulted in complete dechlorination by week 17 with approximately twofold to threefold increase in 16S rRNA and Dhc gene abundance. Live/dead cell counts (LDCC) showed 70-80 % viability in both treatments indicating active growth of potential dechlorinators. The LDCC was strongly correlated with cell copy numbers (r [ 0.95) suggesting its potential use for low-cost monitoring of bioremediation. This study also shows the dechlorinating potential of indigenous non-Dhc groups can be successfully exploited for PCE decontamination while demonstrating the applicability of microbiological and chemical methodologies for preliminary site assessments prior to field-based studies.
Applied Microbiology and Biotechnology, 2015
To meet the demand for sustainable energy, aquifer thermal energy storage (ATES) is widely used in the subsurface in urban areas. However, contamination of groundwater, especially with chlorinated volatile organic compounds (CVOCs), is often being encountered. This is commonly seen as an impediment to ATES implementation, although more recently, combining ATES and enhanced bioremediation of CVOCs has been proposed. Issues to be addressed are the high water flow velocities and potential periodic redox fluctuation that accompany ATES. A column study was performed, at a high water flow velocity of 2 m/h, simulating possible changes in subsurface redox conditions due to ATES operation by serial additions of lactate and nitrate. The impacts of redox changes on reductive dechlorination as well as the microbial response of Dehalococcoides (DHC) were evaluated. The results showed that, upon lactate addition, reductive dechlorination proceeded well and complete dechlorination from cis-DCE to ethene was achieved. Upon subsequent nitrate addition, reductive dechlorination immediately ceased. Disruption of microorganisms' retention was also immediate and possibly detached DHC which preferred attaching to the soil matrix under biostimulation conditions. Initially, recovery of dechlorination was possible but required bioaugmentation and nutrient amendment in addition to lactate dosing. Repeated interruption of dechlorination and DHC activity by nitrate dosing appeared to be less easily reversible requiring more efforts for regenerating dechlorination. Overall, our results indicate that the microbial resilience of DHC in biosimulated ATES conditions is sensitive to redox fluctuations. Hence, combining ATES with bioremediation requires dedicated operation and monitoring on the aquifer geochemical conditions. Keywords Reductive dechlorination. Aquifer thermal energy storage (ATES). cis-dichloroethene (cis-DCE). Dehalococcoides. Microbial resilience. Redox potential (E Ag/AgCl)
Engineered and subsequent intrinsic in situ bioremediation of a diesel fuel contaminated aquifer
Journal of Contaminant Hydrology, 2002
A diesel fuel contaminated aquifer in Menziken, Switzerland was treated for 4.5 years by injecting aerated groundwater, supplemented with KNO 3 and NH 4 H 2 PO 4 to stimulate indigenous populations of petroleum hydrocarbon (PHC) degrading microorganisms. After dissolved PHC concentrations had stabilized at a low level, engineered in situ bioremediation was terminated. The main objective of this study was to evaluate the efficacy of intrinsic in situ bioremediation as a follow-up measure to remove PHC remaining in the aquifer after terminating engineered in situ bioremediation. In the first 7 months of intrinsic in situ bioremediation, redox conditions in the source area became more reducing as indicated by lower concentrations of SO 4 2À and higher concentrations of Fe(II) and CH 4 . In the core of the source area, strongly reducing conditions prevailed during the remaining study period (3 years) and dissolved PHC concentrations were higher than during engineered in situ bioremediation. This suggests that biodegradation in the core zone was limited by the availability of oxidants. In lateral zones of the source area, however, gradually more oxidized conditions were reestablished again, suggesting that PHC availability increasingly limited biodegradation. The total DIC production rate in the aquifer decreased within 2 years to about 25% of that during engineered in situ bioremediation and remained at that level. Stable carbon isotope analysis confirmed that the produced DIC mainly originated from PHC mineralization. The total rate of DIC and CH 4 production in the source area was more than 300 times larger than the rate of PHC elution. This indicates that biodegradation coupled to consumption of naturally occurring oxidants was an important process for removal of PHC which remained in the aquifer after terminating engineered measures. D
This report documents the progress of the in situ bioremediation (ISB) remedial component of the Test Area North, Operable Unit 1-07B remedial action for operations performed from November 2003 through September 2004. Activities performed during this reporting period were conducted as part of the Initial Operations Phase. Two ISB strategies were implemented during this reporting period: (1) sodium lactate injections were alternated between TSF-05 and TAN-1859 on a monthly basis from November 2003 through February 2004, and (2) an alternate electron donor (AED) optimization was initiated in March 2004 to evaluate the effectiveness of whey powder in comparison to sodium lactate. The results of data collected during this reporting period indicate that the ISB remedy continues to operate effectively. Implementation of the first ISB strategy continued to maintain reducing conditions appropriate for anaerobic reductive dechlorination of trichloroethene to ethene; however, determining distribution and utilization of electron donor following injections into TAN-1859 was difficult because of vertical transport of sodium lactate within the well during the injection. Data for the second strategy, initiation of the AED optimization, are presented in this report; however, the results will be discussed upon completion of the AED optimization in June 2005.