Bioremediation is now an established remediation approach widely used around the world. However, since its early adoption in the 1970s and 80s, there have been relatively few innovations within the sector beyond the increasing sophistication of electron donors and acceptors, and ancillary developments such as improved measurement technologies. Notwithstanding these, the technology remains challenged by a number of factors, from the forefront of which may arguably be singled out two perennial, core issues:
• Bioremediation takes time – despite great headway being made, it remains a relatively slow technology;
• End-points remain uncertain – whilst bioremediation may be employed with confidence to efficiently and inexpensively reduce contamination by one or two orders of magnitude, the (linear) rate of destruction characteristically decreases with time, leading to uncertainty of predictable performance against very low clean-up targets.
This paper presents a new innovation designed to address the above challenges. The technical innovation allows for wide area low-pressure dispersion of a sorptive medium through the aqueous subsurface primary porosity. The medium has a dual function; it sorbs contaminants, quickly removing them from the mobile phase, and provides a high surface area matrix favorable for microbial colonization and growth. Contaminant availability within a risk pathway is therefore reduced while at the same time contaminant destruction is accelerated.
Upon reagent injection, target contaminants partition out of the aqueous phase and into the reagent, thereby removing mobile contaminants from the immediate risk pathway. Concentration of the contaminants in this manner, in a matrix conducive to degrader colonization and activity, results in a direct increase in the overall instantaneous rate of contaminant destruction, given the quasi first-order biodegradation kinetics characteristic of environmental systems. This phenomenon can be doubly important at low contaminant concentrations, which may otherwise prove insufficient to support appreciable growth and activity of a degrading microflora.
The technology can be employed to inhibit spreading of contaminant plumes, to protect sensitive receptors, or to prevent contaminant migration across property boundaries. The technology is also postulated an effective tool for control and treatment of groundwater contamination associated with low-permeability porous formations and matrix back-diffusion, promoting diffusion out of the immobile porosity while preventing groundwater impact.
Field studies confirm wide-area dispersion, with order of magnitude (>90%) dissolved-phase concentration reductions secured at the test sites post-application sampling, increasing to two orders of magnitude (>99%) within two months for both chlorinated solvent and hydrocarbon species alike. Laboratory and field data provide confirmation of post-sorption degradation enhancement, with laboratory data describing a significant increase in the rate of contaminant destruction in biotic matrix systems compared to abiotic matrix and biotic non-matrix controls.
It is anticipated this technology will be of interest to users, prescribers and regulators of bioremediation alike, who may be confronted by the concerns stated above. The technology may be particularly welcomed by those challenged by back-diffusion and performance-tailing issues in dual-porosity or mixed-permeability sites.
Throughout the years, a large (approximately 15000 m²) groundwater zinc contamination plume has developed at a galvanizing company in Maasmechelen, Belgium. The considerable surface of the contamination plume is due to the high permeability of the local aquifer (hydraulic conductivity of approximately 45 m/day), resulting in a high groundwater velocity (0.2 - 1 m/day). Zinc concentrations in the plume fluctuate from 1000 to 100000 µg/L, whereas the legal Flemish limit concentration is 500 µg/L. Groundwater is relatively oxidized, naturally low in DOC (< 1 mg/L) and relatively low in sulphate (40 – 50 mg/L).
This study investigated whether remediation through in-situ zinc bioprecipitation is attainable given the local geophysical and -chemical conditions. Both laboratory feasibility tests and two long-term field pilot test were conducted.
The laboratory microcosm tests demonstrated the occurence of zinc precipitation processes after addition of organic substrate and sulphate, which removed 99 % of zinc from the water phase. Sodium lactate, glycerol and vegetable oil proved equally effective as a substrate. An anaerobic leaching test over 28 days indicated that the precipitates are stable. However, they also suggested that the solubility (leachability) of arsenic and manganese had increased upon substrate addition.
During approximately one year of field testing, an overall zinc concentration reduction of 96 – 97 % was observed both in the zone injected with glycerol and in the zone injected with vegetable oil. Neither one of the test zones showed mobilization of arsenic. Through the formation of iron and zinc sulfides, arsenic may have been coprecipitated. The field observations for manganese corresponded with the laboratory feasibility tests. Manganese groundwater concentrations increased from 0.01 – 0.6 mg/L to 0.4 – 6.5 mg/L.
The results showed that bioprecipitation of zinc is a valuable groundwater remediation technology, even in highly permeable, poorly reduced aquifers.
Given the success of the laboratory and field tests, a full-scale remediation plan was designed, starting with a 7 year monitoring campaign to obtain semi long-term information on the behaviour of the formed precipitates.
At the time of the conference, monitoring results for a period of 3,5 years after the first injection event will be available and presented.
This study was conducted in the framework of Life+ InSiTrate project which is developing an in-situ treatment technology for drinking water production from nitrate-polluted groundwater. The objectives of this work are to demonstrate at pilot scale the feasibility of in situ bioremediation technology of nitrate-polluted groundwater and to develop an innovative tool for design and prediction, based on numerical modelling, of the optimal bioremediation strategy and denitrification plant characteristics at any new site. Therefore, Life+ InSiTrate project pretends to demonstrate the adequacy of an innovative technology to restore groundwater quality and recover drinking water wells especially for small communities with a lack of other available freshwater sources.
Initially, the most appropriate organic matter for denitrification was selected. The selection of the organic substrate is a crucial point when implementing biological treatments since it directly affects the feasibility of the technology. To define the optimal organic substrate for in situ denitrification, technical, economic and environmental criteria were taken into account in this project. First, 23 organic carbon sources (8 commercial products, 3 by-products and 12 wastes) were identified as potential substrates to stimulate denitrification. Suitability of these substrates was evaluated from the environmental point of view following the methodology of Life Cycle Assessment (LCA). By means of LCA and considering also the cost of the organic carbon sources, 5 substrates were finally selected for further technical evaluation at lab scale. Experiments were conducted in 5 different columns filled with aquifer soil and fed with nitrate-polluted groundwater spiked with the selected substrates (acetic acid, glycerol, glucose, molasses and wastewater from a fruit juice producer). Acetic acid showed the most promising results for in situ denitrification. Besides, lab experiments permitted to define proper stimulation strategies to minimize bioclogging of the system.
At the same time, the site for the pilot plant implementation was characterized do design the pilot plant based on predictive modeling. In fact, predictive modeling and optimization of the plant design (particularly within thick unconfined aquifers) require detailed hydrologic characterization and moreover, remedial actions depend on adequate characterization of the hydraulic properties of geologic material at the sites. In the alluvial aquifer placed above granitic basement where the plant was to be installed (in the municipality of Sant Andreu de Llavaneres, Spain), different characterization tasks were conducted: hydrogeological study, piezometric maps, drilling of new boreholes, periodical characterization of the groundwater quality and pumping and tracer tests to obtain the hydraulic parameters. These data together with the results of lab experiments were included in the numerical model which considers reactive transport of contaminants. The modeled system had an important 3D component (groundwater flow, variable injection of organic matter and kinetics of chemical reactions…) that could not be reproduced considering only first order kinetics.
Using this tool and considering the physical constraints of the specific site (closed to a road, closed to a stream, with houses around), the pilot plant configuration was defined. It consisted of one extraction well (2.5 L/s) and two injection wells for the organic matter supply (0.1 % acetic acid) located at 30 and 35 m, respectively, from the extraction well. Two control wells in between the injection wells and the extraction well were also built in order to monitor the biological process.
After pilot plant construction, a pumping test was performed to recalculate the hydrogeological parameters of the site and to design the operation strategy.
Injection of organic matter was performed continuously for three months and fast nitrate depletion was observed. Continuous monitoring of nitrate concentration in the extraction well was performed by means of a nitrate sensor based on a UV absorption method. Periodic sampling of control wells and other surrounding wells was performed to monitor main parameters of the process: pH, redox, nitrate, nitrite, organic matter and metals. This work will show the results of the first three months operation.
Background/Objectives.
The success of in-situ remediation technologies requires effective and uniform delivery of remediation reagents through the target treatment area. Traditional amendment delivery techniques based on hydraulic advection mechanisms are often faced with limitations in areas with low permeability materials and/or highly heterogeneous geology. Transport of ionic substances, such as lactate, in an electric field is relatively independent of hydraulic properties and fluid flow. Therefore, electrokinetics-enhanced amendment delivery represents an innovative solution allowing effective in-situ remediation in areas where permeability is limited and heterogeneous.
In 2011, a field pilot test was carried out at the Skuldelev site, Denmark to assess the ability of the novel EK-BIO technology to treat PCE DNAPL source material in clay till with interbedded deposits of sand. The EK-BIO pilot test demonstrated the transport and distribution of amendments (lactate and microbial culture KB-1™) through clay soils in the target area. Results from groundwater and clay soil sampling showed significant reductive dechlorination of PCE to cisDCE, VC, and ethene coupled with significant levels of dechlorinating microorganisms (Dhc with vcrA), indicating that PCE dechlorination in clay soil was achieved by EK-BIO with KB-1™ bioaugmentation. Based on the successful pilot test, a full-scale remediation was implemented.
Approach/Activities.
The full-scale EK-BIO implementation targeting a PCE source area at the Skuldelev site was initiated as a World’s First in December 2012. The treatment zone, addressed by a network of 15 electrode wells, covers an area of 100 m2 to a maximum depth of 10 m bgl. The overall area is divided into two sub-areas, which are treated in alternating stages, each for a period of three months. The polarity of the electrodes is changed to alter the current directions and electric field orientations in alternating stages in order to optimize the EK transport efficiency and to achieve treatment of the entire target zone for remediation. Performance monitoring comprises monthly water sampling for TOC and field measurements, as well as quarterly water sampling for complete characterization of contaminant composition and degradation processes. In addition, soil sampling is also performed at the end of select stages of operation to assess treatment in clay materials.
Results/Lessons Learned.
Result from the first two years of EK-BIO operation will be presented. At present, five stages (approximately 20 months) of operation and monitoring have been completed with very encouraging and expected results. Both electron donor and Dhc have been distributed throughout the treatment area and complete reductive dechlorination of PCE to ethene has been well established where the degree of dechlorination continues to increase. Orders of magnitude increases of Dhc have been observed between clay soil samples collected before remediation and following one year of implementation. Soil sampling data support the groundwater monitoring data and confirm that EK-BIO implementation has achieved active reductive dechlorination treatment within low-permeability clay materials. Successful implementation of this EK-BIO project will broaden the applicability of various in-situ remediation technologies.
Rail yard facilities are highly specialized facilities consisting of one or more areas including engine maintenance buildings, fueling areas, track and switching areas, and track maintenance/material storage yards. The raw materials associated with this industry are primarily used in fueling and maintenance operations. During the early 20th century, the railway infrastructure developed rapidly in a number of European cities. The railways at that time needed gas for lightning and other purpose, and a great number of gas production plants were established in the central part of many cities. In the Northern part of Berlin an oil gas production was running between 1909 and 1922. During that period, an oil tank was situated at the site and a tar pit was established for the remaining tar from the gas production. The handling of the oil and tar resulted in considerable soil and groundwater contamination of the area. The contamination mainly consists of tar oil with a high content of PAH and other aromatic compounds. Today, the contamination is located below buildings, constructions and active railways tracks, making it both difficult and expensive to apply traditional remediation strategies. On the contrary, the use of in situ biological remediation can provide an excellent solution, enabling efficient clean ups below constructions, requiring relatively less energy, and generating less waste and less costs.
Thus the objective of this study was to develop and evaluate tools for predicting the optimal strategy for bioremediation in a PAHs contaminated former gas plant in Berlin.
The site is characterized by deep-lying contamination of both soil and groundwater. Several meters of free phase tar oil are present in the source area, and a plume of contaminants, in varying concentrations, was detected down-gradient of it.
A multidisciplinary approach was established, as a combination of physiochemical analyses (groundwater monitoring), treatability study (based on batch incubations), and microbial population analyses (based on next-generation DNA-sequencing techniques), in order to evaluate the potential of the in situ microbial communities to biodegrade the target contaminants and thus choose the optimal bioremediation approach for the site.
Different sets of amendments (e-acceptors and e-donors/carbon sources) where tested in batch incubations of soil samples over a period of about 90 days. The temporal evolution of the microbial degradation of naphthalene and additional chemical compounds was monitored on line with a non-invasive sampling technique, Solid Phase Microextraction (SPME). The presence and identity of the dominating organisms catalyzing the degradation of the hydrocarbons in the contaminated soil was evaluated by comparing samples with similar soil types, from contaminated and uncontaminated areas.
The DNA-based analyses showed that the microbial community from the heavily contaminated soil samples is different to that of the uncontaminated soil sample. Further, it was clear that proliferation of specific bacteria occurred for most treatments revealing that specific changes in the microbial compositions can be induced by addition of defined compounds.
The best degradation rates were achieved with addition of oxygen as e-acceptor (> 99.9% in 90 days). Alternatively, with nitrate as e-acceptor, in combination with DAP (diammonium phosphate) (97.5% in 90 days). Furthermore, the effect of the addition of different external carbon sources was evaluated. A complete biodegradation (final concentrations below detection limit) of naphthalene, and the other monitored chemical compounds, was reached during our treatability study in less than 98 days. However, already after 20 and 50 days it was possible to get a clear overview of degradation rates and trends.
Overall, the results indicate that organisms able to degrade of aromatic hydrocarbons are already present in this contaminated soil, and that the growth can be stimulated by adding the right nutrients and e-acceptors. These findings are used to choose the optimal bioremediation treatment for an in situ field scale test.
The use of newly developed microbial and molecular tools, such as NGS (next generation sequencing) technology and batch incubations, to implement our decisional platform a great potential, especially if used together.
The ultimate goal of such study is the coupling of models of microbial growth and metabolism in contaminated environments with existing geochemical and hydrological models, to predict accurately the likely outcome of engineered strategies to accelerate bioremediation. In fact, the results from such pre-studies have the potential to help companies to efficiently and quickly decide which bioremediation strategy should be chosen for a specific contamination problem.