Lexikon

an amendment-enhanced bioremediation technology for the treatment of POPs involves the creation of sequential anoxic and oxic conditions. The treatment process involves the following:

1. Addition of solid phase DARAMEND® organic soil amendment of specific particle size distribution and nutrient profile, zero valent iron, and water to produce anoxic conditions.

2. Periodic tilling of the soil to promote oxic conditions.

3. Repetition of the anoxic-oxic cycle until the desired cleanup goals are achieved.

The addition of DARAMEND® organic amendment, zero valent iron, and water stimulates the biological depletion of oxygen, generating strong reducing anoxic conditions within the soil matrix. The diffusion of replacement oxygen into the soil matrix is prevented by near saturation of the soil pores with water. The depletion of oxygen creates a low redox potential, which promotes dechlorination of organochlorine compounds. A cover may be used to control the moisture content, increase the temperature of the soil matrix and eliminate runon/run off.

The soil matrix consisting of contaminated soil and the amendments is left undisturbed for the duration of the anoxic phase of treatment cycle typically 1-2 weeks. In the oxic phase of each cycle, periodic tilling of the soil increases diffusion of oxygen to microsites and distribution of irrigation water in the soil. The dechlorination products formed during the anoxic degradation process are subsequently removed trough aerobic oxic biodegradation processes, initiated by the passive air drying and tilling of the soil to promote aerobic conditions.

Addition of DARAMEND® and the anoxic-oxic cycle continues until the desired cleanup goals are achieved. The frequency of irrigation is determined by weekly monitoring of soil moisture conditions. Soil moisture is maintained within a specific range below its water holding capacity. Maintenance of soil moisture content within a specified range facilitates rapid growth of an active microbial population and prevents the generation of leachate. The amount of DARAMEND® added in the second and subsequent treatment cycles is generally less than the amount added during the first cycle.

The additive enhanced bioremediation was successfully applied for toxaphene and DDT contaminated soil and sediment.

bioremediation uses microorganisms to degrade organic contaminants in soil, sludge, and solids either excavated or in situ. The microorganisms break down contaminants by using them as a food source or cometabolizing them with a food source. Aerobic processes require an oxygen source, and the end products typically are carbon dioxide and water.

Anaerobic processes are conducted in the absence of oxygen, and the end products can include methane, hydrogen gas, sulfide, elemental sulfur, and dinitrogen gas.

Ex situ bioremediation includes slurry-phase bioremediation, in which the soils are mixed in water to form a slurry to keep solids suspended and microorganisms in contact with the soil contaminants, and solid-phase bioremediation, in which the soils are placed in a cell or building and tilled with added water and nutrients.

Land farming, biopiles, and composting are examples of ex situ, solid-phase bioremediation. In situ bioremediation is bioremediation in place, rather than ex situ. In situ techniques stimulate and create a favorable environment for microorganisms to grow and use contaminants as a food and energy source. Generally, this means providing some combination of oxygen, nutrients, and moisture, and controlling the temperature and pH. Sometimes, microorganisms that have been adapted for degradation of specific contaminants are applied to enhance the process.

Source: US-EPA, Clu-In: http://www.clu-in.org/techfocus/default.focus/sec/Bioremediation_of_Chlorinated_Solvents/cat/Overview/

see ecoremediation

ecoremediation is based on the co-operation of plants, soil and soil living microorganisms, mainlyof the rhyzosphere. Ecoremediation comprises systems, processes and technologies which function in natural ecosystems, or as an artificial part of a natural ecosystem. In ecoremedial technologies the man-made artificial ecosystem is able to compensate adverse environmental effects of chemical substances or contaminated environmnetal compartments or phases. Its function is based on the close co-operation of soil microbes and plants, and its proper function depends on the balanced and controlled element- and water-cycle of the artificial ecosystem designed for remedial purposes.

Ecoremedial technologies can be applied for waste water treatment, for the remediation and maintenance of lakes, reservoirs and wetlands, for complex rehabilitation and reclamation of landfills and for the complex rehabilitation or remediation of contaminated or deteriorated soil.

Ecoremediation is used for long term and sustainable protection, restoration and complex rehabilitation of environment of damage or exposed to potential damage. Ecoremedial technologies are cost- and eco-efficient in protection of water resources, streams, rivers, lakes, groundwater and the sea and in ensuring the sustainable quality of the environment on long term.The most important characteristics of ecoremedial technologies are their adaptive character, their high buffer and self-protective capacities against adverse affects of antropogenic origin, and they are highly potent in preservation of natural habitats and biological diversity.

Eco-remediation has more areas, such as bioremediation, utilising soil microflora; phytoengineering utilising plants for many purposes, artifically built lakes, aerobic and anaerobic wetlands, reactive soil zones, etc., are all considered as ecoremedial technologies.

electrokinetics relies upon application of a low-intensity direct current through the soil between ceramic electrodes that are divided into a cathode array and an anode array. This mobilizes charged species, causing ions and water to move toward the electrodes. Metal ions, ammonium ions, and positively charged organic compounds move toward the cathode. Anions such as chloride, cyanide, fluoride, nitrate, and negatively charged organic compounds move toward the anode.

Removal of contaminants at the electrode may be accomplished by several means, among which are: electroplating at the electrode; precipitation or co-precipitation at the electrode; pumping of water near the electrode; or complexing with ion exchange resins.

Source: US-EPA, Clu-In: http://www.clu-in.org/techfocus/default.focus/sec/Electrokinetics%3A_Electric_Current_Technologies/cat/Overview/

treatment of contaminated or otherwise damaged environmnetal compartments or phases such as soil, groundwater, soil gas, surface water and sediment after excavation, dredging or extraction. The remedial treatment may be executed on site or off-site by applying physical, chemical, thermal, biological or ecological technologies.

see also ex situ soil treatment

an increasing variety of nanoscale materials with environmental applications has been developed over the past several years. For example, nanoscale materials have been used to remediate contaminated soil and groundwater at hazardous waste sites, such as sites contaminated by chlorinated solvents or oil spills. As indicated above, many types of nanoscale materials are being applied across various fields of science and technology; this website focuses on the use of engineered nanoscale materials for environmental site remediation. Nanoscale materials are of interest for environmental applications because the surface areas of the particles are large when compared with their volumes; therefore, their reactivity in chemical or biological surface mediated reactions can be greatly enhanced in comparison to the same material at much larger sizes (U.S. EPA 2007). They can be manipulated for specific applications to create novel properties not present in particles of the same material at the micro- or macroscale. Nanoscale materials can be highly reactive in part because of the large surface area to volume ratio and the presence of a larger number of reactive sites; but may also exhibit altered reaction rates that surface-area alone cannot account for. These properties allow for increased contact with contaminants, thereby resulting in rapid reduction of contaminant concentrations. Furthermore, because of their minute size, nanoscale materials may pervade very small spaces in the subsurface and remain suspended in groundwater if appropriate coatings are used. Appropriate coating may allow the particles to travel farther than macro-sized particles, achieve wider distribution, and therefore improve contaminant reduction.

Some applications of nanoscale materials for environmental remediation are in the research phase but others are rapidly progressing from pilot-scale to full-scale implementation. For example, certain nanoscale materials hold promise for environmental applications in addressing challenging sites, such as sites contaminated with chlorinated solvents. Ongoing bench- and pilot-scale research is being performed to investigate particles such as TiO₂, self-assembled monolayers on mesoporous supports (SAMMS^TM), dendrimers, carbon nanotubes, metalloporphyrinogens, and swellable organically modified silica (SOMS). This research is evaluating how to apply the unique chemical and physical properties of these nanoscale materials for use in full-scale environmental remediation (see the Nanotechnology Products with Potential Remediation Applications section). In addition, there are many unanswered questions about nanotechnology. For example, more research is needed to understand the fate and transport of free nanoscale materials in the environment, whether they are persistent, whether they have toxicological effects on various biological systems, and whether the theoretical benefits of nanoscale materials can be realized in broad commercial use (U.S. EPA 2008). Furthermore, nanoscale materials are also being considered for use in sensing and monitoring environmental contaminants; however, research and development of nanosensors are still in progress (U.S. EPA 2007).

U.S. Environmental Protection Agency (U.S. EPA). 2008. Nanotechnology for Site Remediation Fact Sheet. Solid Waste and Emergency Response. EPA 542-F-08-009. October 2008. Available at: http://www.clu-in.org/download/remed/542-f-08-009.pdf.

U.S. EPA. Science Policy Council. 2007. Nanotechnology White Paper. U.S. Environmental Protection Agency. February 2007. Available at: http://www.epa.gov/ncer/nano/publications/whitepaper12022005.pdf.

minimizing waste generation from site remediation by recovering and reprocessing usable products that might otherwise become waste (Source: EUGRIS).

for the in situ or ex situ remediation of hydrocarbons, pesticides, chlorinated substances contaminated soils the altering oxic-anoxic or aerobic-anaerobic treatment is an efficient bioremediation alternative. The steps of the technology application are:

1. Addition of organic soil amendment, zero valent iron, and water to produce anoxic conditions.

2. Periodic tilling of the soil to promote oxic conditions.

3. Repetition of the anoxic-oxic cycle until the desired cleanup goals are achieved.

The addition of DARAMEND® organic amendment, zero valent iron, and water stimulates the biological depletion of oxygen, generating strong reducing anoxic conditions within the soil matrix. The diffusion of replacement oxygen into the soil matrix is prevented by near saturation of the soil pores with water. The depletion of oxygen creates a low redox potential, which promotes dechlorination of organochlorine compounds. A cover may be used to control the moisture content, increase the temperature of the soil matrix and eliminate runon/run off.

The soil matrix consisting of contaminated soil and the amendments is left undisturbed for the duration of the anoxic phase of treatment cycle typically 1-2 weeks. In the oxic phase of each cycle, periodic tilling of the soil increases diffusion of oxygen to microsites and distribution of irrigation water in the soil. The dechlorination products formed during the anoxic degradation process are subsequently removed trough aerobic oxic biodegradation processes, initiated by the passive air drying and tilling of the soil to promote aerobic conditions.

all kind of risk reduction options which are able to mitigate risk of contaminated soil. During the decision-making procedure the remediation options should be collected, enlisted, evaluated and based on the priority point of views make the selection between them to find the best possible solution for a certain problem.

soil bioremediation based on aerobic oxidation means that the soil remediation is based on aerobic biodegradation. The microbiological biodegradation occurs in this case on a high redoxpotential of +0,8-+0,6 Volt. The degrading microorganisms utilise the pollutant as enbergy sources. The source of oxigen is the atmospheric air, soil air, or dissolved oxigen in soil moisture or ground water. If the oxigen-concentration is low, the technologist can increase it by aeration of the soil or the groundwater as well as by adding peroxide substances or other oxigene release compounds ORC to serve as oxigene source for the activation of the aerobic soil microbes.

soil remediation based on aerobic biodegradation is an oxidative process catalysed by microbes. Microbes, mainly bacteria utilise the contaminant as substrate for producing energy. Aerobic bacteria use athmospheric oxigen for the oxidation of the polluting organic compounds and produce inorganic products, such as CO₂, NO₃ and H₂O. This process is also called mineralisation.

When athmospheric oxigen is limited, the biodegradation is catalysed by facultative anaerobic microbes, which use NO₃ for their alternative respiration. In this case the oxidation/mineralisation products from the substrate the contaminant are alcohols or aldehydes.

anaerobic biodegradation of soil contaminants is based on the aternative respiration of soil microorganisms, using oxigen from NO₃^2-, SO₄^2-or CO₂, as hydrogen-acceptor instead of atmospheric oxigen. Paralel to the oxidation of the contaminant energy source in this case, nitrate, sulfate and carbonate are reduced into N₂ via nitrite NO₂⁻, nitric oxide NO, nitrous oxide N₂O, H₂S and CH₄ respectively.

There are some metals which can also be reduced and function as electronacceptor, such as ferric ion Fe³⁺reduction to Fe²⁺ or Fe⁰, manganic ion Mn⁴⁺ reduction to Mn²⁺, selenate SeO₄^2- reduction to selenite: SeO₃^2- and Se⁰, arsenate AsO₄^3- reduction to arsenite: AsO₃^3- or uranyl ion UO₂²⁺ reduction to uranium dioxide UO₂ for the electron transport chain.

The anaerobic biodegradation of xenobiotics needs a microorganism- and metabolism-specific redoxpotential. The soil remedial biotechnology is responsible for ensuring the proper redoxpotential in the soil to control the process and run biodegradation on the optimum.

To control the redoxpotential the technologist should ensure sufficient quantity of nitrate, sulfate or any other electronacceptors in the soil.

Surfactant Enhanced Aquifer Remediation (SEAR), in its most basic form, could thus be considered a chemical enhancement to pump and treat. A chemical solution is pumped across a contaminated zone by introduction at an injection point and removal from an extraction point. To cover the entire contaminated zone, a number of injection and extraction wells are used; the well configuration is determined by the subsurface distribution of NAPL and the hydrogeologic properties of the aquifer.

SEAR is a source zone remediation technology. SEAR removes the residual phase contamination from which the dissolved phase plume is derived. Free phase contamination is typically removed by conventional pumping before SEAR is employed. SEAR does not have an immediate effect on the dissolved phase plume concentrations and is not a dissolved phase plume remediation technology. Removal of the source does however cause an intermediate and long-term reduction in dissolved phase contaminant concentrations.

Surfactants are unique chemical agents that greatly enhance the solubility of organic contaminants in aqueous media. They are also able to reduce the interfacial tension (IFT - that force existing where two fluids meet that keeps them as separate fluids) between the aqueous and organic phases to mobilize the organic phase. To illustrate the two mechanisms, we can use the familiar examples of the cleaning action of household cleaning detergents, which contain surfactants as a common constituent. We have witnessed surfactant-induced solubilization in the oily solution resulting from soaking oily pots and pans in dish detergent; we have observed a reduction in IFT from oil droplets or a sheen of oil coming off the pan due to the presence of a detergent. A surfactant flood can be designed to remove contaminants either primarily by solubilization or primarily by mobilization. Surfactant mobilization can remove more DNAPL in less time; however, there is greater risk of uncontrolled downward movement of DNAPL, as DNAPL is being physically displaced by the surfactant solution. Thus, to conduct a mobilization flood, it is necessary to have an aquitard as a barrier to prevent vertical DNAPL migration. It is important to identify from the outset whether solubilization or mobilization of DNAPL is desired, because not all surfactants can be used to conduct a mobilization flood.

The primary objective in SEAR design is to remove the maximum amount of contaminant with a minimum amount of chemicals and in minimal time while maintaining hydraulic control over the injected chemicals and contaminant. Each step in the design process must keep this in mind. Design challenges include precisely locating the DNAPL, finding the optimum surfactant solution for a given DNAPL composition and soil type, and fully characterizing the hydraulic properties of the aquifer, particularly the heterogeneities typically present in the subsurface environment. Because it is impossible to know with certainty the variations in aquifer properties over the treatment zone, numerical modeling tools are used to simulate how the system may respond in the presence of these unknown factors. Numerical modeling is also necessary to understand the dynamics of the flooding process under the hydrogeologic conditions at the site. SEAR has been acknowledged to be a promising, innovative technology for the removal of DNAPLs primarily because of the history of the use of surfactant-enhanced oil recovery by the petroleum industry.

Source: http://www.cpge.utexas.edu/ee/sear.html