Research Project Descriptions
May 18, 1993 - September 30, 1994
Impact of Soil Microflora on Revegetation Efforts in Southeast, Kansas
M.K. Banks, B.A. Hetrick, and A.P. Schwab, Kansas State University
Goal: The objective is to assess the importance of soil microflora to the revegetation of soil contaminated with heavy metals.
Rationale: Soil microflora may directly improve plant establishment on contaminated sites by mineralizing essential nutrients for plant growth, producing growth regulating substances, or immobilizing heavy metals to reduce their plant availability. Introduction of heavy metal resistant microbes in combination with tolerant plant species may enhance revegetation success in heavily contaminated soils.
Approach: The goal of this project is being achieved through site characterization, greenhouse trials and laboratory studies. A heavy metal contaminated mining site was selected and characterized for chemical and biological properties. Mycorrhizal fungi from uncontaminated soil and moderately contaminated soil were added to chat and moderately contaminated soil which had been previously sterilized to eliminate soil microflora. The fungi also were added to uncontaminated soil as a control. Laboratory research has focused primarily on the mobility of heavy metals in the immediate zone of influence surrounding plant roots (rhizosphere). Two approaches were taken to study the impact of revegetation on metal mobility: (1) a greenhouse experiment testing the effects of plants and microorganisms on the leaching of zinc; and (2) geochemical modeling of the impacts of common rhizosphere organic acids on the solubility of metals.
Status: A lead- and zinc-contaminated site in southeast Kansas was studied in this project. The project involved site characterization for chemical and biological properties, greenhouse studies and laboratory studies. The greenhouse studies measured the importance of soil microbes to revegetation. Results revealed that no plant growth occured in chat, regardless of microbial treatment. Mycorrhizal fungi improved growth of plants in moderately contaminated soil, but the origin of the mycorrhizal fungi did not influence the results. A phosophorus-zinc interaction study indicated that microbial amendments would be insufficient to support plant growth in chat containing high zinc levels. Study of the addition of organic amendments to mycorrhizal fungus inoculation revealed that plant growth was best when nitrogen and phosphorus fertilization was added. The biomass produced in contaminated soil did not equal that of similarly fertilized uncontaminated soil. The influence of mycorrhizal symbiosis on plant growth and zinc tolerance of 44 plant species was studied in mine spoil. Leguminous and non-leguminous forbs established most quickly, followed by cool-season grasses and warm-season grasses. Laboratory research on the mobility of heavy metals in the rhizosphere found that the presence of plants increased zinc leaching either by providing channels for macropore flow of the contaminant or solubilizing the metals by complexing with organics exuded from the roots or associated microflora. Geochemical modeling of the soil-organic system, coupled with laboratory verifications, was performed in order to investigate the potential role of organic acids in altering the mobility of metals in the rhizosphere. As predicted, formic, acetic, oxalic and salicyclic acids did not impact zinc solubility while increasing concentrations of succinic and citric acids produced large increases in zinc solubility. This project's funding ended in 1994.
Clients/Users: The research is of interest to those responsible for revegetation of sites contaminated with heavy metals, including the mining industry and U.S. Bureau of Mines; those involved in restoring production agriculture in Southeast, Kansas are also interested in this research.
Keywords: heavy metals, mycorrhizal fungi, revegetation.
Innovative Treatment and Bank Stabilization of Metals-Contaminated Soils and Tailings Along Whitewood Creek, South Dakota
J.L. Schnoor and L.A. Licht, University of Iowa
Goals: The objectives are two-fold: (1) to determine the efficacy of deep-planted hybrid poplar trees for stabilizing the soils and immobilizing arsenic and cadmium concentrations in the vadose zone via increased evapoconcentration and (2) to investigate a novel treatment system for leachate from tailings deposits that includes photoreduction of iron, oxidation of adsorbed organics or added ligand, and reprecipitation of the iron as oxy-hydroxides with scavenging of metals.
Rationale: Roots can play a key role in the chemistry of surface and groundwater. The risk associated with contaminants at the site can be reduced by growing trees which stabilize the soil and immobilize the heavy metals.
Approach: Poplar trees have been planted at the site using short cuttings and long cuttings. The ability of the trees to survive and grow in the riparian zone and the effect of soil amendments on growth are being investigated. The removal of metals from leachate is being investigated in the laboratory, also.
Status: Review of the literature on iron, arsenic and cadmium chemistry was done. Laboratory investigations have demonstrated that hybrid poplar trees can be grown in pure tailings from the Superfund site along Whitewood Creek. Photolysis experiments on mine tailings have been performed in the laboratory. Irradiation enhanced the photoreductive dissolution of iron from mine tailing samples as compared to dark controls. Arsenic and cadmium concentrations were not greatly affected by photolysis of mine tailings. Coupling of iron photoreduction and oxidative reprecipitation with either arsenic or cadmium removal has been shown to be infeasible. Poplar trees were originally planted along Whitewood Creek in April 1991, and three tree samples were removed in April 1994. Replanting of the site was done in May 1993, and six tree samples were also removed in April 1994. Poplar leaves, stems, roots and soils were extracted for metal analysis using a complete acid digestion method. Samples were analyzed for arsenic and cadmium by graphite furnace atomic adsorption spectrophotometer. Testing done on the trees planted in May 1993 revealed that arsenic and cadmium increased in the leaves of the trees as they grew. Trees established in the replanting have taken up higher concentrations of arsenic and cadmium in the stems and leaves than did the trees in the original planting. A methodology for plant chamber experiments that simulated field uptake of cadmium and arsenic by trees was developed. This project's funding ended in 1994.
Clients/Users: This research is of interest to the mining industry, regulatory community, and other researchers.
Keywords: poplar trees, immobilization, metal stabilization, arsenic.
Heavy Metals Removal from Contaminated Water Solutions
Z. Lewandowski, G.G. Geesey, and F.L. Roe, Montana State University
Goal: The goal of this project is to quantify the process of heavy metals removal by binding to biopolymers from dilute aqueous solutions containing more than one metal.
Rationale: Extracellular polymers extracted from living microorganisms constitute an attractive alternative for heavy metals removal from dilute aqueous solutions. However, demonstrated technologies do not offer any rational means of predicting the process kinetics as a function of water chemical composition. Thus far the documented research effort is largely related to binding single metals from aqueous solutions. Such convenient simplification is unacceptable for most technical applications of the process. For example, it is a rare exception that a water is contaminated with a single heavy metal. In frequently encountered situations when more than one heavy metal is present in the solution, the existing models do not apply, and the result of the process cannot be predicted.
Approach: The investigators propose describing the kinetics and thermodynamics of metals binding to biopolymers from solutions of many metals. The relevant parameters for process modeling will be obtained from measurements of binding constants, binding capacities, selectivity coefficients, diffusion coefficients and rates of metal binding reaction. The predictive value of the models will be experimentally verified.
Status: A medium viscosity sodium alginate was the biopolymer that was selected for study during the first year of the project. The binding capacity for copper has been shown to decrease as pH decreases. The data suggest that there may be a slight drop in binding capacity at higher pH values, but this may be due to unrecognized precipitation of copper resulting in overestimation of actual solution copper concentrations. Biopolymer regeneration has been studied. Once biopolymer beads have been saturated with toxic metals and all binding sites are occupied, the beads must be disposed of or regenerated. Regeneration is the more attractive of the two options, based on monetary and other considerations. Two procedures for regenerating alginate beads have been studied. Both procedures remove metals from the beads, leaving them intact and reusable. The binding capacity of alginate has been shown to be constant whether only copper is present or whether both copper and zinc are present. Construction of a multiequilibrium binding model which includes competitive binding has begun. Field testing of stream remediation using a bio-barrier has been initiated. The test site is located in a mining area north of Butte, Montana, on an unnamed tributary to Jack Creek. The first year of this project has been completed.
Clients/Users: The results are of interest to other researchers, private industry and regulatory personnel.
Keywords: heavy metals, water, biopolymers, sodium alginate
Metals Soil Pollution and Vegetative Remediation
J.L. Schnoor, University of Iowa; G.M. Pierzynski, Kansas State University; L.A. Licht, and M.A. St. Clair, University of Iowa
Goal: The goal of the research is to determine the feasibility and efficacy of vegetative remediation at a variety of sites with heavy metals soil pollution.
Rationale: Mine tailings and metals pollution of soils is a major problem globally, and it has been identified as a primary research priority area of the Great Plains-Rocky Mountain Hazardous Substance Research Center. The New York Times reported recently that mine tailings wastes account for almost half of all hazardous wastes worldwide. Risk assessments at Superfund sites often reveal that exposure to wind-blown dust by inhalation and ingestion of soil by children is the greatest risk to human health.
Approach: The proposed research is a comparative study at two sites (Dearing, Kansas, and Whitewood Creek, South Dakota) with greatly different problems, so the scope of the research is to expand the applications to determine more broadly the potential of this innovative approach. In this research the investigators will attempt to establish vegetation at these sites where it has not already been accomplished and to monitor the movement of metals in the soil profile as a result of the remediation effort. The research will supplement and continue the ongoing research of the investigators at Whitewood Creek.
Status: Revegetation using hybrid poplar trees began at the Dearing, Kansas, site this year. The effects of soil amendments on tree survival have been examined. Metal extractions and measurements have been catalogued in a database. The Kansas site has shown that uptake of cadmium into vegetation may be a problem because concentrations of some native species were as high as 100 mg/kg, while 1-10 mg/kg is considered typical at such sites. Phytoremediation of the sites using hyperaccumulators does not appear practical because of the immense time factor. Soils at both sites have shown a somewhat constant ratio between cadmium and zinc using a total acid digestion. DPTA, a chelate extractant, has been shown to have potential for use at hazardous waste sites as an indicator of bioavailability. KNO3 ion exchange is not effective in extracting arsenic and so a different extraction technique needs to be developed. The first year of this project has been completed.
Clients/Users: This research is of interest to the mining industry, regulatory community, and other researchers.
Keywords: metals, soil, pollution, remediation, poplar trees
The Use of Poplar Trees in Remediating Heavy Metal Contaminated Sites
G.M. Pierzynski, J.C. Tracy, L.C. Davis, L. Reddi, L.E. Erickson, Kansas State University; and J.L. Schnoor, University of Iowa
Goals: The research objectives are to investigate the suitability of deep-planted poplars as a vegetative remediation strategy for heavy metal contaminated sites; to determine the effects of poplar tree cultivar on survivability and growth when deep-planted at a heavy metal contaminated site; to investigate the effects of soil amendments on poplar tree survival and growth; to determine the heavy metal concentrations in poplar leaves, roots and wood when grown in a heavy metal contaminated environment; to investigate the optimum depth of soil cover for establishment of a perennial grass cover; and to extend a current mathematical model that simulates the fate of heavy metals in a vegetated soil and to use the model to develop a protocol for determining the most effective vegetative planting strategies for immobilizing heavy metals in contaminated soil.
Rationale: Abandoned sites associated with old heavy metal mining and smelting activities often have a large proportion of their area without vegetative cover. This allows erosional forces to proceed at a maximum rate, and materials with high heavy metal concentrations are dispersed by wind and water. Little research has addressed the use of poplar trees in such a situation.
Approach: This study will focus on an abandoned zinc and lead smelter site in southeast Kansas. The investigators propose to begin investigations whose ultimate goal is to immobilize the metals in place. This would be accomplished with grading to 3-5% slope, to encourage runoff without excessive erosion, and the use of rapid growing poplar trees that have a high water demand. This strategy would minimize net percolation through the mine spoil material, thus minimizing the impact on the groundwater. Surface erosion would be effectively controlled once the trees are established. A thin soil cover would be employed to establish a perennial grass cover to prevent surface erosion until the trees had become established.
Status: Characterization data for the soils at the Dearing, Kansas, site indicated that remediation activity at that site will be necessary in the future. Four types of poplar trees have been planted on the site using two different in-trench treatments with three replications. The survival rate of trees was not very good. Surviving trees were predominantly in the first and second replicates, which tend to be wetter than the third replicate. There is a weak association between survival and tree type. The survival rate was slightly higher for the trees which underwent manure treatments compared with trees that received nonmanure treatments. Few of the surviving trees seemed to be suffering from zinc phytotoxicity or any nutrient deficencies. Three possibilities for the low survival rate are: the late planting date followed by hot and dry weather adversely affected the trees, the cuttings did not store well and already had broken dormancy prior to planting, or the trees cannot survive with the high zinc concentrations at the site. It is reasonable to assume that the low survival rate is due to either the growing conditions after planting or storage problems with the cuttings than that the trees are unable to grow due to the high soil metal concentrations. In general, the data suggest that metal bioavailability has been reduced within the trenches as compared to the original state. The soil data are direct evidence and the growth of water hemp in the trenches and the metal concentrations in the plant tissue samples are indirect evidence. The first year of this project has been completed.
Clients/Users: This research is of interest to the mining industry, regulatory community and U.S. Bureau of Mines.
Keywords: heavy metals, soil, poplar trees, zinc, lead.
Alachlor and Atrazine Losses from Runoff and Erosion in the Blue River Basin
E.C. Dickey and D.P. Shelton, University of Nebraska-Lincoln; J.M. Steichen and P.L. Barnes, Kansas State University
Goals: The objectives of this research are to measure the losses of alachlor and atrazine through runoff and erosion from cropland and to determine relationships to tillage practice, land slope, and soil texture. The effects of rainfall intensity and duration on herbicide losses were also investigated.
Rationale: Conservation tillage is an effective management practice for controlling soil erosion. It leaves at least 30% of the soil surface covered with residue after planting. There is a need to understand the effects of tillage practices on surface water quality.
Approach: Investigations were conducted at four experimental sites on farmer tilled fields that have a known pesticide and cropping history. A clean tillage system having less than 5% cover, a conservation tillage system having about 30% cover, and a no-till system having more than 50% cover were evaluated at each site.
Status: Four farmer-owned sites were used in field measurements: two sites in Kansas with medium textured soil on four and eight percent slopes and two sites in Nebraska with finer textured soil on four and six percent slopes. The effect of tillage practice and the method of chemical application on atrazine and alachlor losses through runoff and erosion were evaluated on five treatments: no-till and surface (N.S), disk and surface (D.S), plow and surface (P.S), disk and pre-plant incorporated (D.I) and plow and pre-plant incorporated (P.I). A rainfall simulator was used to create 63.5 mm/hr rainfall for 60 minutes and 127 mm/hr for 15 minutes. Rainfall simulation occurred 24-36 hours after chemical application. The concentration of herbicides in the runoff water decreased with time. No-till treatments had the highest concentration, and disk treatments were higher than plow treatments. The surface application treatments showed significantly higher concentration than the incorporated treatments. Total atrazine losses ranged from 0.078 kg/ha (5.2% of applied mass for N.S treatment) to 0.007 kg/ha (0.4% of applied mass for P.I treatment). Alachlor losses ranged from 0.137 kg/ha (6.1% of applied mass for N.S treatment) to 0.010 kg/ha (0.4% of applied mass for P.I treatment). No-till and surface application treatments had the greatest loss. Plow and incorporated treatments had the least loss. From 74 to 90 percent of herbicide loss for both herbicides occurred through runoff water. Incorporation of herbicides reduced the herbicide loss. This project's federal funding ended in 1992, but the work has continued with other available funds.
Clients/Users: The results are of interest to regulatory personnel and those responsible for pesticide management.
Keywords: atrazine, alachlor, tillage practice, pesticide management.
Laboratory and Field Evaluation of Upward Mobilization and Photodegradation of Polychlorinated Dibenzo- p-Dioxins and Furans in Soil
S. Kapila, R.K. Puri, A.F. Yanders,and D.W. Armstrong, Environmental Trace Substances Research Center, University of Missouri-Rolla
Goals: The objectives of the laboratory experiments are to (1) study the partition behavior of dioxins and co-contaminants in soil and the solvent systems most amenable for photodegradation; (2) study the photodegradation rate of chlorinated dioxins and furans in suitable solvent systems; (3) study the quenching effect of co-contaminants on photodegradation; and (4) study the correlation between soil properties and the degree of solvent saturation required for effective desorption and transport. The objective of the field trials is to evaluate the efficacy of an optimized mobilization-photodegradation process on a pilot scale at contaminated sites in California and Missouri.
Rationale: Photodegradation has been shown to be highly effective in solution. Research on mobilization and photodegradation may lead to a new cost-effective method to remediate soil contaminated with dioxins and furans.
Approach: Mixed solvents such as tetradecane and butanol have been used to mobilize dioxins. Solvents that are amenable to photodegradation will be investigated for their ability to mobilize dioxins. Soil from two contaminated sites will be used.
Status: The remediation approach for this project involves photodegradation of contaminants in solvents. A tiered approach was adopted to achieve the stated goal. The tier one experiments were conducted in the laboratory. These involved evaluation and selection of suitable solvents, optimization of photodegradation, and oxidative carbon regeneration. The tier two experiments were conducted at a contaminated wood treatment facility in Visalia, California. The objective of the tier two field trials was to demonstrate the applicability of solvent-mediated mobilization and subsequent photodegradation of polychlorinated dibenzo-p-dioxins and related compounds in soil at this contaminated site. This project's funding ended in 1994, but work is continuing with other funds.
Clients/Users: The results are of interest to other investigators, regulatory personnel, responsible parties, and private contractors.
Keywords: dioxin, furans, migration, mobilization, photodegradation.
Microbial Transport in Porous Media
A.B. Cunningham and J.W. Costerton, Montana State University
Goal: The objective is to determine how operational variables such as injection flow rate and suspended cell characteristics influence the distribution of cell adsorption along the porous media flow path in an injection/infiltration system. Improved insight into these processes will lead to strategies for beneficial manipulation of the zone of penetration of injected/infiltrated microorganisms.
Rationale: Schemes for enhancing in situ bioremediation of soil and ground water generally involve injection and/or infiltration of fluid, nutrients and oxygen (or other electron acceptors) to stimulate growth of native microbial populations in the subsurface. In addition, suspended cultures of contaminant degrading organisms may be added to the process stream to increase the amount of attached and suspended biomass within the subsurface. Although the success of these schemes depends upon site- specific microbial activity, little is currently known concerning transport, accumulation and fate of the injected microorganisms. Consequently, the rational design and operation of microbial injection/infiltration systems is difficult.
Approach: This project will build on research currently being conducted. This ongoing research has demonstrated the importance of developing a fundamental understanding of porous media microbial transport phenomena to help guide future strategies for bioremediation of contaminated soil and groundwater. This project will investigate the microbial transport processes of advection, dispersion and adsorption in laboratory systems under conditions which minimize the effects of cell growth. Glass beads, sand, soil, diatomaceous earth pellets and field core samples from a spill site will be used.
Status: Data obtained from experiments using three bacterial strains at three pore velocities indicate that the effects of motility and size without regard to adsorption appear to be negligible. When bacterial adsorption velocities begin to approach the pore velocity in the medium, adsorption effects clearly dominate the transport phenomena of the bacteria in a manner that is not related to motility or size alone. With the significant correlation observed between the dimensionless flux ratio and the recoveries of cells in the system, the conclusion was made that the adsorption rate coefficient better predicts transport phenomena than individual cellular characteristics. The following conclusions have also been drawn: 1) phenomenological modeling must be carried out at the microscale in order to consider the interactions among key process variables including biofilm accumulation, biotransformation and mass transport; 2) a porous media model consisting of advection, diffusion and reaction terms can successfully simulate biofilm accumulation and substrate uptake (i.e.biotransformation) in a model porous media biofilm reactor provided the detachment rate function is known a priori. Model mass balance computations are moderately sensitive to the value of the detachment rate function; 3) For biofilm accumulation above a threshold level, biotransformation (as measured by substrate uptake) becomes independent of the amount of biomass present; and 4) porous media mass transport, biofilm accumulation, and biotransformation of growth-limiting substrates are highly interrelated. Flow experiments yielded cell recovery values that were generally similar for saturated and variably saturated flow conditions although significantly higher recoveries were seen in some variably saturated runs. This project's funding ended in 1994.
Clients/Users: This research is of interest to other researchers and to contractors who wish to use bioremediation.
Keywords: microbial transport, adsorption, injection, soil.
Modeling the Use of Plants in the Remediation of Soil and Groundwater Contaminated by Hazardous Organic Substances
J.C. Tracy, South Dakota State University; L.E. Erickson, and L.C. Davis, Kansas State University and J.L. Schnoor, University of Iowa
Goals: The objectives of this project are to (1) develop and verify models to simulate the fate of hazardous organic substances in a transpiring plant's root zone; and (2) use the simulation models to engineer plant remediation strategies for contaminated groundwater and soil sites.
Rationale: Recent studies have shown that many aquifers within U.S. EPA Regions 7 and 8 have been contaminated with hazardous organics that are by-products of agricultural production or have leaked from disposal sites. Due to the large scale nature of the contaminated soil involved in these types of problems, conventional soil and groundwater remediation techniques would prove to be very expensive or completely impractical. Several studies have demonstrated the potential for plants to play an important role in remediating soil and groundwater contaminated with organic substances. However, before this new technology can be put into use, a method will have to be developed to predict the effects that plants have on soil and groundwater remediation, so that effective planting and management plans can be developed.
Approach: The initial step in this study was to perform an exhaustive review of the available literature related to the fate of hazardous organic substances in a plant's root zone. Models have been formulated to simulate the fate of organic substances in a plant's root zone and pilot scale experiments have been developed to examine the effects that vegetative systems have on the degradation of specific hazardous organic contaminants in the saturated and unsaturated zones of a soil. Modeling and experimental results were compared, and sensitivity analyses was performed on the model to determine the most significant factors affecting contaminant degradation. The model can now be used to develop a vegetative remediation system for a field site such as the aquifer underlying the Riley County Landfill, in which several hazardous organic contaminants have been found.
Status: General models describing the fate of hazardous organic contaminants in the root zone of a soil under nonlimiting and limiting degradation conditions were developed early in the project. Hypothetical simulations modeled the effect of remediating atrazine and benzene contaminated soil and groundwater with the use of border planting strategies under nonlimiting degradation conditions. In addition, a hypothetical simulation of the remediation of soil and groundwater contaminated with benzene using shallow and deep rooted vegetation under contaminant degradation conditions limited by the availability of dissolved oxygen and nutrients was performed. Model sensitivity analysis demonstrated that the most critical factor for aiding the degradation of benzene below the water table was the plant's ability to supply oxygen to the ground water via its root system, while degradation in the vadose zone was more dependent on the plant's ability to provide nutrients to the surrounding soil via root exudates. Additionally, the overall performance of a remediation system will be dependent on the climatic conditions present during the remediation process. Experiments that measured the resistance of alfalfa grown in soil to a range of organics showed that only CCl4 and CHCl3 had marked effects on plant survival. A pilot-scale experiment using alfalfa grown in a flow through tank type system containing sandy soil from the Kansas River Valley showed that a majority of the water and contaminants in the system did not exit the down gradient end, with most loss of water being due to evapotranspiration by the alfalfa crop and the loss of contaminants being due to biodegradation which was enhanced by the alfalfa's root system. Toluene and phenol were not detected in the gas phase while trichloroethylene was found in the gas phase above the soil bed. This project's funding ended in 1994.
Clients/Users: The U.S. Dept. of Energy has an interest in this project. Individuals responsible for landfill closure and management as well as representatives of private industry have expressed interest in the research.
Key words: bioremediation, root zone, plant uptake, transport, organic compounds, oxygen transfer.
Formation and Transformation of Pesticide Degradation Products Under Various Electron Acceptor Conditions
G.F. Parkin and M.A. St. Clair, University of Iowa
Goals: The objectives are (1) year onedevelop and refine the analytical techniques required for identification of the pesticide degradation products, develop and operate batch reactors under each of the four electron acceptor conditions, screen each reactor for the major metabolic products, (2) year twoconduct kinetic experiments to quantify rates of formation and transformation of metabolic products and determine kinetic expressions to describe those reactions, obtain and analyze field samples from research site for metabolites, and (3) year threecomplete kinetic experiments, and develop and test a mathematical model.
Rationale: Recent research has shown that while atrazine and alachlor are transformed in the environment under a variety of conditions, their rates of mineralization are likely much slower than their rates of initial transformation. Thus a number of degradation products are being formed and perhaps accumulating in the environment, and the nature of these products will likely be a function of the particular environment in which they are formed (e.g., the dominant electron acceptor condition). Therefore, it is desirable to gain information regarding the effect of these different environments on the formation and subsequent transformation of the major degradation products.
Approach: The proposed research will employ both batch and column reactor techniques, some with soil-water suspensions. Soil obtained from an Iowa agricultural field known to have been treated in the past with atrazine and/or alachlor will be used. The liquid media used in all experiments will be a "synthetic" groundwater designed to maintain one of the electron acceptor conditions of interest. All experimental reactors will be run at 16 C in an effort to keep the experimental conditions as close as possible to those of a typical Iowa groundwater. Reactors will be seeded with cultures which have been growing under the desired electron acceptor conditions and have been shown to transform atrazine and alachlor. Acetate will be fed as a carbon and energy source. Pesticide, acetate, microbial biomass and electron acceptors will be monitored over time during each experiment. Once a significant fraction of the fed pesticide has been transformed, products of atrazine and alachlor will be assayed in the effluents and/or soil samples of each reactor. Standards for some of the expected transformation products will be obtained. A number of analytical techniques will be employed for the identification and quantification of these metabolic products, including the use of selective GC detectors, GC-MS, or, if necessary, LC-MS. Unknown metabolites may be further analyzed using NMR spectroscopy.
Status: The analytical techniques required for identification of pesticide degradation products have been developed and refined. Batch reactors under each of the four electron acceptor conditions have been developed and operated, and each reactor has been screened for the major metabolic products. Alachlor and atrazine disappeared in batch reactors maintained under all terminal electron acceptor conditions except aerobic conditions. Kinetic experiments to quanitfy the rate of formation and transformation of several of the major metabolic products have been performed and the kinetic expressions most appropriate for describing these reactions have been determined. Several metabolites of alachlor were positively identified. Field samples from an agricultural field research site have been analyzed for all metabolites possible. The second year of this project has been completed.
Clients/Users: This research is of interest to those who are responsible for non-point source pollution control including regulators, farmers, and the USDA.
Keywords: atrazine, alachlor, transformation products, kinetics.
Modeling for Design and Testing of Treatment and Remediation Technologies for Aquifer Soils Contaminated with Organic Waste Chemicals
T.H. Illangasekare, University of Colorado
Goals: The objectives include (1) investigation of NAPL entrapment; (2) mobilization of entrapped NAPL; (3) modeling of interphase mass transfer; (4) development of numerical models; (5) generation of data in soil flumes for model validation; and (6) field validation.
Rationale: Existing models of transport and entrapment behavior of nonaqueous phase organic chemicals based on traditional petroleum engineering formulations are inadequate for situations dealing with complex soils and chemical types found at wastes sites.
Approach: The proposed approach involves continuation of laboratory investigations with more realistic soil types and chemicals which are of relevance to the waste problems in EPA Regions 7 and 8. Model development efforts will be continued, guided by the qualitative results of the fundamental processes and data generated in the laboratory investigations. Issues related to micro- and macro-scale entrapment, preferential flow, mobilization and mass transfer between phases will be investigated further to develop realistic and accurate models. A radically new approach in which the core of the model becomes the available data will be utilized in the transport model development. Basic to this approach is that the models will be driven by the data rather than by a sophisticated numerical algorithm as in existing numerical models. The developed model will then be verified in the laboratory. The developed models will be used to conduct transport simulations to perform a retrospective performance analysis a of field treatment system. A waste site in Region 8 is being used to conduct this case study and field demonstration.
Status: Entrapment and mobilization experiments have been performed. The results of experiments on macro-scale entrapment in sandy soil demonstrated that preferential flow and macro-scale entrapment are not controlled by the properties of a "mixing layer" at the coarse/fine interface. It is believed that these phenomena are dependent solely on the displacement pressure of the fine soil. NAPL mobilization experiments were conducted in a soil column where saturated zone entrapment was established using coarse sand layers embedded in a fine sand matrix. Possible mobilization by changing the water and NAPL fluid pressures which may result during water flooding and water table fluctuations were investigated. An experimental program was developed to investigate macro-scale retention of NAPL in the vadose zone. The experiment showed that macro-scale retention can be observed in a layered system and that it is semi-permanent (high saturations of NAPL found in the fine sand on top of the coarse sand did not decrease measurably in more than a month). Comparison with static pressure distribution profiles for capillary pressure and saturation show that the experimentally-found high saturations cannot be explained under the assumption of a static pressure distribution. Thus it can be concluded that macro-scale retention is controlled by a dynamic process, or more specifically, by the minimum hydraulic conductivity in a soil profile. Modeling of flow and transport processes through fractures in soil formations was performed. Dissolution of trapped fluids has also been studied. Development and laboratory validation of numerical models are ongoing. The second year of this project has been completed.
Clients/Users: This research is partially supported through the Robert S. Kerr Environmental Research Laboratory. Other researchers, regulatory personnel, responsible parties, and private contractors have expressed interest in this research.
Keywords: organic compounds, nonaqueous phase liquids, models, remediation.
Remediation of Soil Contaminated with an Organic Phase
L.E. Erickson and L.T. Fan, Kansas State University
Goal: The objective is to develop knowledge leading to improved methods of quantifying remediation processes for contaminated soil where a hydrocarbon-rich phase is present.
Rationale: Oil-rich phases are found in a variety of contaminated sites including locations of oil and gas exploration or drilling, coal-gas plants, leaking tanks, wood treating and oil refining. Mathematical models of the remediation process should include the composition and geometry of the hydrocarbon phase. Phenomena occurring in the vicinity of or on the hydrocarbon surface may be rate limiting.
Approach: Models will be developed for remediation of a single hydrocarbon deposit through bioremediation, diffusion of the hydrocarbon contaminant through water (pump-and-treat) and volatilization of the contaminant (vacuum extraction). This approach is based on the expectation that phenomena occurring in the vicinity or on the surface of the hydrocarbon deposit may be rate limiting, thereby determining the required remediation time.
Status: Research has shown that for both bioremediation and pump-and-treat models, the aggregate and NAPL blob sizes have the greatest impact on the remediation time, which has been found to be proportional to the square of the characteristic length. Other primary rate-controlling factors are NAPL solubility and diffusivity of the contaminant relative to that of oxygen. Contaminant dissolution is rapid compared to oxygen transfer in the saturated zone for more soluble compound such as benzene than for less soluble compounds. For slightly soluble compounds such as phenanthrene, oxygen transfer is rapid compared to the dissolution. Thus, for phenanthrene, microbial growth at the NAPL interface is expected. A simple equilibrium model has been used to examine bioremediation enhanced pump-and- treat remediation in the saturated zone. Dissolution, sorption and biodegradation are included in the model. Preliminary studies with an advective flow model indicate that the NAPL dissolution rate may be an important factor for some extractive remedies. The second year of this project has been completed.
Clients/Users: This research is of interest to other researchers, contractors, and responsible parties.
Keywords: organic phase, modeling, bioremediation, simulation.
Riparian Poplar Tree Buffer Impact on Non-point Source Surface Water Contamination. A Paired Agricultural Watershed Study
L.A. Licht and J.L. Schnoor, University of Iowa
Goals: The objectives are to develop a paired watershed research site sufficiently instrumented to develop a hydrologic, silt and agricultural chemical movement database; to compile the watershed basin data in a form usable with existing EPA and USDA models to understand the impact of perennial tree buffers on the runoff water quantity and quality from "conventionally" farmed land; to install alternative perennial plant buffer designs to compare the plant survival, biomass growth potential, the sediment interception, the subsurface nitrate movement in near-surface groundwater, and the herbicide movement from up-gradient application to the stream; to test equipment and tillage practices required by farmers to make this plant production practical; and to develop an education and technology exchange program to explain watershed-scale conservation and cropping concepts to agriculturists, farmers, media and all ages of students.
Rationale: Tree-buffered riparian corridors can enhance sustainability of agricultural ecosystems and remove a portion of non-point source pollutants. They can provide a tree crop that does not compete with feed grains.
Approach: Two adjacent agricultural watersheds at Amana, Iowa, have been developed into a field research site, including the in-stream instrumentation required to measure flow and sample at desired intervals. One watershed stream is completely buffered using approximately 15,000 trees; the other watershed is unbuffered; annual tillage and cropping occurs up to the stream bank edge. Both watersheds are predominantly cropped with corn and soybeans; oats and hay are a small portion of the field area. Each watershed contains a portion of upland hardwoods.
Status: The concept of planting poplar trees as a perennial row-crop to manage field edges for reducing non-point source pollutants entering a first-order creek has been demonstrated to farmers, agribusiness, government officials, interested citizens and the media. These watershed buffering concepts were shown to over 20,000 people during the 1993 Farm Progress Show. This demonstration has been called EPA's most successful technology transfer effort. Additionally, other field trips and press conferences have been held. Tours have been given to an agricultural attaché from Egypt, EPA research scientists from Athens Lab, and a press day has been held. A 12-minute video is planned. In-stream water sampling stations have been monitored to measure water quality parameters. The nitrate nitrogen flow from an unbuffered watershed was consistently above the EPA MCL while the buffered watershed was consistently below the MCL. Ground water in the riparian stream border has been monitored for subsurface flows crossing the border. Tile drainage was the primarily source of in-stream nitrate nitrogen. Little nitrate appeared to be added to the stream by base flow after the water flowed through the tree buffer. Buffer plots of grass and different tree varieties have been maintained to test alternative culturing practices. The Universal Soil Loss Equation was used to obtain estimates of the relative soil loss potential in each watershed. The second year of this project has been completed.
Clients/Users: This research is of interest to those who are responsible for non-point source pollution control including regulators, farmers, and the USDA.
Keywords: non-point pollution, poplar trees, pollution prevention, nitrate, atrazine.
The Effect of Redox Conditions on Transformations of Carbon Tetrachloride
G.F. Parkin, The University of Iowa
Goals: The objectives of this research are to investigate the effect of redox conditions on the transformation of carbon tetrachloride, to identify pathways and metabolites, to investigate abiotic transformation and the effect of carbon tetrachloride concentration on its transformation.
Rationale: Soil and groundwater contamination by carbon tetrachloride has been documented at several sites within the 10-state area served by EPA Regions 7 and 8. In order to engineer in situ or above-ground biological treatment systems to remediate these sites, research is needed to understand the transformations of carbon tetrachloride under a variety of conditions.
Approach: Experiments are being conducted in laboratory reactors under aerobic, denitrifying, sulfate-reducing and methanogenic conditions. Redox potential is being measured using an electrode system.
Status: Investigations have been undertaken to assess the lasting effects of the biotransformation of carbon tetrachloride (tetrachloromethane, CT) and its reductive dechlorination product, chloroform (trichloromethane, CF), by a mixed, methanogenic culture. Initial experiments determined that the fraction of CT converted to CF was about 60%. Dichloromethane (DCM) persisted in all studies. Inactivation assays were conducted in two rounds. In Round 1, treatments were spiked with various concentrations of CT and/or CF. Following transformation to DCM, treatments were stripped with N2/CO2 gas. In Round 2, treatments were amended with 400 mg/L acetic acid, and methane production was measured over time. Correlation analysis revealed a linear, inverse relationship between the total mass of CF and CT transformed in Round 1 and the maximum specific methane production rate in Round 2. CF biotransformation inactivated acetoclastic methanogens to a much greater degree than CT biotransformation. The use of elemental metals to abiotically reduce the chlorinated solvents has been studied. Metallic iron may serve two purposes under methanogenic conditions: (1) as a reducing agent coupled to reduction of CT and CF and (2) as an ultimate electron donor for hydrogenotrophic methanogens. Preliminary results indicate that supporting a methanogenic consortia on elemental iron may hold promise for the transformation of chlorinated solvents such as CT or CF. In addition, it is clear that such a combined chemical-microbiological treatment system has a considerable advantage over abiotic systems utilizing elemental iron as a reducing agent only. This project's funding ended in 1994.
Clients/Users: The research is of interest to other researchers and to those responsible for the remediation of soil contaminated with carbon tetrachloride. Regulatory personnel have expressed interest in this project.
Keywords: carbon tetrachloride, cometabolism, bioremediation, anaerobic.
Nano-Scale Metal Oxide Particles as Reagents for Destruction and Immobilization of Hazardous Substances
K.J. Klabunde, Kansas State University
Goal: The investigators are attempting to develop a new technology for the one-step destruction of hazardous substances, including chlorocarbons, chlorofluorocarbons, organosphosphorus, nitrogen and sulfur compounds. This new technology is based on ultrahigh surface area metal oxides with reactive surfaces that behave as "destructive adsorbents" (surfaces that adsorb and break chemical bonds in the hazardous adsorbate). The research objectives are (1) to develop the best ways of synthesizing the destructive adsorbents, (2) to understand the surface chemistry going on during the adsorption/destruction process, and (3) to develop a second generation of better destructive adsorbents based on multilayer oxide/oxide composites. Destructive adsorbent technology has promise as an alternative to incineration and for air purification systems.
Rationale: Organic compounds containing halogens can be completely destroyed under mild conditions using metal oxides. Destructive adsorbent technology has promise as an alternative to incineration and for air purification systems. Further research is needed to develop this technology so that it can be used in field applications.
Approach: Research work on the production of magnesium oxide, ferric oxide on magnesium oxide and calcium oxide in nano-scale particle size and reactivity studies are being carried out. The adsorption and transformation of chlorinated hydrocarbons, phenols, and phosphorous compounds are being investigated.
Status: For MgO and CaO, the best method to date of synthesizing aerogel/autoclave-prepared AP-MgO and AP-CaO has been developed. Compared with conventionally-prepared samplesCP-MgO and CP-CaOthe AP samples continually show better performance in destructive adsorption chemistry. However, the AP-preparation schemes would be expensive on a large scale. Further work is needed on improved non-aerogel/autoclave approaches in synthesis. Great progress has been made in understanding surface morphology, the effect of surface-OH groups, and basicity/acidity of the CaO surfaces. Also, progress in understanding physiosorption and chemisorption of CCl4 on CaO has been made. Work on developing a second generation destructive adsorbent has yielded the discovery that a thin coating of Fe2O3 on MgO or CaO allowed the capacity for CCl4 destructive adsorption to increase by tenfold. This so-called spillover catalysis is a new phenomenon and appeared to be unique to nanoscale particles. Design and testing of a continuous flow reactor has begun. Theoretical studies have predicted that a Multi-tube Entrained Flow Reactor coupled with electrostatic precipitators constitutes one possible design. Also, fluidized bed reactors with special characteristics for handling ultrafine powders are under consideration. Scale-up of the preheat treatment step is in process and will be followed by studies of the destructive adsorption process. The first year of this project has been completed.
Clients/Users: The results of this research are of interest to other researchers and to those in private industry. Representatives from several government agencies have expressed interest in the research.
Keywords: magnesium oxide, carbon tetrachloride, adsorption, calcium oxide.
The Fate and Transport of Munitions Residues in Contaminated Soil
S.D. Comfort, P.J. Shea, D.L. McCallister, W.L. Powers, University of Nebraska-Lincoln
Goals: The goals are to establish accurate predictions of desorption kinetics of munitions residues by elucidating changes in sorption characteristics over time, to characterize transport properties of both freshly added and aged RDX, TNT and principal degradates, and to predict the fate and transport of munitions residues over time with a computer transport model.
Rationale: Past disposal practices of munitions production facilities have resulted in contamination of terrestrial and aquatic ecosystems. Efforts to date have documented the extent of contamination and estimated potential migration routes. To predict the fate and transport of munitions in soils, an accurate description of the adsorption-desorption process is critical.
Approach: The investigators hypothesize that munitions residues residing in soils for extended periods may be more tightly bound into a soil organic fraction and that this bound fraction may be more important in predicting the long-term fate and transport of munitions residues. The proposed research will elucidate the changes in transformations, mechanisms and reversibility of munitions residues in soils with traditional sorption experiments and diffuse reflectance (FTIR) spectroscopy. The validity of using transport equations that assume instantaneous equilibrium, isotherm linearity and adsorption-desorption singularity in field contaminated soils will also be tested. The proposed research will characterize the sorption of munitions residues in soil and provide improved predictions on desorption kinetics.
Status: Progress in this project has been in the areas of fate and transport, microbiology and remediation. Column experiments have been conducted, and the data clearly indictated a concentration dependence of both transport and the amount of amino degradate formation. Results also supported the nonlinear adsorption behavior of TNT in soil. A long-term sorption study has been completed. This study was conducted with and without the presence of solid phase TNT. These results exemplify the importance of bound residue formation. they support the nonlinear adsorption behavior of TNT in soil. Experiments conducted without solid phase TNT show that TNT applied to the soil degrades to an extractable concentration below the EPA preliminary remediation goal. A continuous core down to approximately 300 cm below grossly contaminated surface soil has been obtained and is being analyzed. Microbiology experiments have revealed that Pseudomonas savastoni has the capacity to degrade and partially mineralize TNT. Experiments have been completed showing the potential of the Fenton reaction to destroy and mineralize TNT. The Fenton reaction will work with soil extracts and can be used to destroy a number of munitions residues. Soil washing can remove TNT from contaminated soils and the wash water can be effectively remediated by Fenton oxidation. The first year of this project has been completed.
Clients/Users: This research will be of use to those in munitions production facilities, the US Department of Defense and others.
Keywords: fate and transport, munitions, soil, adsorption, diffuse reflectance spectroscopy.
Intelligent Process Design and Control for the Minimization of Waste Production and Treatment of Hazardous Waste
L.T. Fan, Kansas State University
Goal: The goal of this research is to develop intelligent or computer-aided systems tools for synthesizing and designing environment-friendly processes and controlling such processes with minimum waste generation.
Rationale: Waste minimization can be realized through source reduction and recycling. Efficient process synthesis and design, robust control, reliable diagnosis, and flexible production scheduling are important techniques to effectuate source control of waste.
Approach: The approach being employed is comprehensive and unique. The comprehensiveness of the proposed approach arises from the fact that all three levels of synthesis and design of processes and the control systems for these processes, namely, macroscopic, mesoscopic and microscopic levels, are incorporated into it. The uniqueness arises from the fact that the approach resorts to the most modern graph-theoretic methods, which are mathematically and theoretically rigorous, and to the techniques of artificial intelligence and neural networks, which are logically sound and computationally efficient.
Status: Theoretical, mathematical and logical foundations of process synthesis, design and control at the macroscopic, mesoscopic and microscopic levels have been established. Methodologies based on such foundations have been developed. These efforts have been enhanced with emphasis on problem solving and application. The results have been widely disseminated through publications and presentations. Particular attention has been paid to developing procedures that can be readily implemented by practicing designers and to preparing publications that can be read by them without excessive difficulty. The feasibility of starting up a synthesized process network has been investigated through literature review. No publication on this subject could be identified in spite of its importance to the process and allied industries. A limited number of the available publications on process start-up deal only with individual process units, but not with a process network comprising two or more units. Start-up characteristics of such a network are being studied through exhaustive computer simulation. Several cases have been completed. The second year of this project has been completed.
Clients/Users: The results are of interest to design engineers who wish to incorporate waste minimization into process synthesis and control system design.
Keywords: waste minimization, process synthesis, robust control, pollution prevention, graph theory.
Evaluation of Biosparging Performance and Process Fundamentals for Site Remediation
R.R. Dupont, Utah State University
Goal: The goal of this project is to conduct a detailed investigation of air sparging systems operated in a pulsed mode to provide a fundamental framework from which to evaluate the applicability and effectiveness of biosparging technology for a given set of site, soil and waste constraints.
Rationale: Air sparging represents a highly attractive remediation alternative for contaminants located below the groundwater table. It has been shown through anecdotal evidence that contaminant emission rates increase and groundwater concentrations are greatly reduced at groundwater monitoring well points. The specific mechanisms of air sparging system performance are yet to be investigated, and adequate monitoring of field scale systems to quantitatively document their performance throughout effected areas of injection well influence are yet to be developed.
Approach: The proposed research project will involve two integrated components, companion field scale and laboratory scale studies. The field study will be utilized to provide mass transfer and contaminant biodegradation rates resulting from a field scale biosparging system, as affected by media property and heterogeneity limitations inherent at field sites. The laboratory component of the proposed research will provide detailed analysis of mass transfer and contaminant degradation rates under controlled conditions. Laboratory investigations will include an evaluation of the effect of bubble size, air injection rate, air injection depth, media properties and contaminant properties on observed mass transfer and contaminant degradation rates. Air injection versus inert gas injection will allow the separate evaluation of mass transfer and degradation, while air injection in clean water systems will allow an evaluation of system mass transfer relationships independent of effects due to contaminant properties and/or contaminant/media interactions.
Status: Funding for this project will begin early in 1995. An extensive review of the literature has been conducted.
Clients/Users: The results from this project will be of interest to other researchers, the US Department of Defense, private industry and regulatory personnel.
Keywords: biosparging, biodegradation, mass transfer.