Polyhydroxyalkanoate as a slow-release carbon source for in situ bioremediation of contaminated aquifers: from laboratory investigation to pilot-scale testing in the field

A pilot-scale study aiming to evaluate the potential use of poly-3-hydroxy-butyrate (PHB) as an electron donor source for in situ bioremediation of chlorinated hydrocarbons in groundwater was conducted. Compared with commercially available electron donors, PHB offers a restricted fermentation pathway (i.e., through acetic acid and molecular hydrogen) by avoiding the formation of any residual carbon that could potentially spoil groundwater quality. The pilot study was carried out at an industrial site in Italy, heavily contaminated by different chlorinated aliphatic hydrocarbons (CAHs). Prior to field testing, PHB was experimentally verified as a suitable electron donor for biological reductive dechlorination processes at the investigated site by microcosm studies carried out on site aquifer material and measuring the quantitative transformation of detected CAHs to ethene. Owing to the complex geological characteristics of the aquifer, the use of a groundwater circulation well (GCW) was identified as a potential strategy to enable effective delivery and distribution of electron donors in less permeable layers and to mobilise contaminants. A 3-screened, 30-m-deep GCW coupled with an external treatment unit was installed at the site. The effect of PHB fermentation products on the in situ reductive dechlorination processes were evaluated by quantitative real-time polymerase chain reaction (qPCR). The results from the first 4 months of operation clearly demonstrated that the PHB fermentation products were effectively delivered to the aquifer and positively influenced the biological dechlorination activity. Indeed, an increased abundance of Dehalococcoides mccartyi (up to 6.6 fold) and reduced CAH concentrations at the installed monitoring wells were observed

Effort to improve coupled in situ chemical oxidation with bioremediation: a review of optimization strategies

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 optimize

Identifying the Burdens and Opportunities for Tribes and Communities in Federal Facility Cleanup Activities: Environmental Remediation Technology Assessment Matrix For Tribal and Community Decision-Makers

The cleanup of this country's federal facilities can affect a wide range of tribal and community interests and concerns. The technologies now in use, or being proposed by the Department of Energy, Department of Defense and other federal agencies can affect tribal treaty protected fishing, hunting and other rights, affect air and water quality thereby requiring the tribe to bear the burden of increased environmental regulation. The International Institute for Indigenous Resource Management developed a tribal and community decision-maker's Environmental Remediation Technology Assessment Matrix that will permit tribes and communities to array technical information about environmental remediation technologies against a backdrop of tribal and community environmental, health and safety, cultural, religious, treaty and other concerns and interests. Ultimately, the matrix will allow tribes and communities to assess the impact of proposed technologies on the wide range of tribal and community interests and will promote more informed participation in federal facility cleanup activities

Using Iron to Treat Chlorohydrocarbon-Contaminated Soil

A method of in situ remediation of soil contaminated with chlorinated hydrocarbon solvents involves injection of nanometer-size iron particles. The present method exploits a combination of prompt chemical remediation followed by longer-term enhanced bioremediation and, optionally, is practiced in conjunction with the method of bioremediation described earlier. Newly injected iron particles chemically reduce chlorinated hydrocarbons upon contact. Thereafter, in the presence of groundwater, the particles slowly corrode via chemical reactions that effect sustained release of dissolved hydrogen. The hydrogen serves as an electron donor, increasing the metabolic activity of the anaerobic bacteria and thereby sustaining bioremediation at a rate higher than the natural rate

Role of Zero Valent Iron and Organic Substrates in Chlorinated Solvent Degradation: An Ex-Situ Remediation Case Study

Field practice suggests that a combination of biotic and abiotic technologies to treat soil impacted by chlorinated solvents positively influences a remediation project’s success rate. Two large remediation programs have used a material containing both zero-valent iron (ZVI) and a dry organic substrate to abiotically reduce contaminants and increase anaerobic bioremediation in soil contaminated with tetrachloroethylene and 1,2-dichloroethylene using ex-situ mixing techniques. This research assesses the contributions made by the dry organic substrate and ZVI to the observed changes in chlorinated solvent concentrations by analyzing field samples collected from the sites previously remediated, as well as conducting bench-scale batch reactor experiments designed to test the individual contributions of the ZVI and the organic substrate to dechlorination processes. Laboratory experiments suggest the mixture of ZVI and organic substrate does not lead to the concentration decreases observed in the full-scale remediation projects, and that volatilization may be the most prominent contributing process for contaminant removal from soil. Field samples analyzed for microorganisms show a community shift in the area remediated as well as a decrease in Dehalococcoides population size, indicating soil mixing is detrimental to microbial dechlorination activity

Electrokinetically-Enhanced Emplacement of Lactate in a Chlorinated Solvent Contaminated Clay Site to Promote Bioremediation

Bioremediation through the injection of electron donors and bacterial cultures is effective at treating chlorinated solvent contamination but faces limitations in low permeability zones where the injected amendments cannot be delivered successfully. Using electrokinetics in combination with bioremediation to enhance the delivery of amendments was tested at a chlorinated solvent contaminated field site, where lactate was injected into clay under a direct current. Advection at locations with higher hydraulic conductivities contributed to lactate transport and dilution of aqueous chlorinated solvents. There was evidence of successful delivery of lactate by electromigration (EM) in all monitoring locations with EM lactate transport rates between 1.3 to 3.0 cm/day. Lactate emplacement resulted in the stimulation of bacterial populations and evidence suggests some biodegradation of chlorinated solvents was observed on site. This research provides evidence that with further field investigation, electrokinetically-enhanced bioremediation has potential as a treatment strategy for contaminated low permeability strata

Phytoforensics tools: The degradation and detection of chlorinated solvents in integrated systems

Due to decades of mismanaged pollutants entering groundwater, subsurface pollution of various compounds has become a widespread challenge. Chlorinated solvents are the most common groundwater contaminants that persist in aquifers, and remediation of these wide-spread plumes is difficult. Bioremediation, permeable reactive barriers, and phytoremediation are remedial technologies that have been developed and applied to chlorinated solvents in groundwater systems. This study integrates these technologies in different combinations to demonstrate the remediation potential of this approach. Zerovalent iron (ZVI) and bioaugmentation with a Dehalococcoides sp. (DHC) culture were applied separately and in combination for degradation of perchloroethene (PCE). Salix pentandra were planted in reactors and concurrently served as monitoring tools. Characteristics studied between reactor combinations included plant health, contaminant degradation rates, and water uptake. By creating an area of lower water potential, trees direct groundwater flow through the reactive zone and uptake the contaminated groundwater after contaminant degradation. Classroom experiential learning of this study was implemented to introduce phytoforensics to students. ZVI and DHC showed degradation of up to 92.0% and 99.3% reduction of PCE, respectively. Combined, ZVI and DHC increased PCE concentration reduction to 99.7%. Dichloroethene (DCE) was only found in all reactors containing DHC, but in no reactors without DHC. Plant sampling was shown to reveal degradation profiles and offer a low impact, low cost approach to monitoring PCE degradation processes in the subsurface. The degradation of PCE by DHC and ZVI was shown to occur through phytoforensics, and the specific mechanism was elucidated --Abstract, page iv

Design of a sequential in-situ anaerobic/aerobic enhanced bioremedication system for a chlorinated solvent contaminated plume

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1996.Includes bibliographical references (leaves 32-33).by Michael M. Collins.M.Eng