Grantee Research Project Results
2003 Progress Report: Dewatering, Remediation, and Evaluation of Dredged Sediments
EPA Grant Number: R828770C007Subproject: this is subproject number 007 , established and managed by the Center Director under grant R828770
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: EAGLES - Atlantic Coast Environmental Indicators Consortium
Center Director: Paerl, Hans
Title: Dewatering, Remediation, and Evaluation of Dredged Sediments
Investigators: Schwab, Arthur Paul , Newman, Lee , Banks, M. Katherine , Nedunari, Krishnakumar
Institution: Purdue University , University of South Carolina at Columbia , Central State University
Current Institution: Purdue University , Central State University , University of South Carolina at Columbia
EPA Project Officer: Aja, Hayley
Project Period: October 1, 2001 through September 30, 2004
Project Period Covered by this Report: October 1, 2002 through September 30, 2003
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (2001) Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management
Objective:
The objectives of this research project are to: (1) determine overall sediment management strategies that will rapidly dewater the dredged sediments and remove contaminants to an acceptable level; (2) select and/or develop plant species that are most suited for the task of dewatering and remediating contaminants; (3) determine the fate of key contaminants, specifically metals, polycyclic aromatic bydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) during the remediation of the sediments; and (4) quantify the residual toxicity of remediated sediments using a suite of protocols, including plant seedling germination, earthworm evaluations, microbial assays, and microarthropods.
The corresponding hypotheses are: (1) a proper combination of plant species selection, application of amendments, and site management will reduce dewatering time by 50 percent or more; (2) the presence of a single combination, or sequence of plant species will significantly enhance biodegradation of target organic contaminants and phytoextraction of metals; (3) the phytoremediation process will degrade the majority of the organic contaminants with few identifiable byproducts. Most of the degraded compounds will be bound to the soil; and (4) toxicity of remediated sediments will be very similar to nontoxic control soils.
Progress Summary:
Approach: Field Studies
Twenty-eight cells approximately 7' x 7' x 2' were constructed in the spring of 2002. These cells were lined with a 36 mil polypropylene liner and filled with sediments collected from 15 feet below the surface of the Jones Island confined disposal facility (CDF) (Milwaukee, WI). The material chosen had been determined previously to be the most contaminated sediments on the CDF. All cells were fertilized just prior to plant establishment and once monthly to provide 2.5mg/kg K and 6.25 mg/kg N.
The cells were planted with poplars (varieties NM6 and OP367, obtained from Sand Creek Consultants, Reinlander, WI), Sesbania exultata, Tripsacum dactyloides, Juncus effusus, and Carex microptera. In Year 1 of the project approximately one-half of the S. exultata germinated; however, they failed to survive the winter. Initially, all poplars leafed out, but the high moisture contents of the sediments did not allow for the trees to establish vigorously and all trees died. The T. dactyloides, J. effusus, and C. microptera failed to germinate. Several replacement species were evaluated, including Helianthus grosseratus, Andropogon gerardii, Spartina pectinata, and C. aquatalis. Of these, the S. pectinata established in one-half of the cells, and the C. aquatalis established robustly in all cells. All other species had shortcomings ranging from no germination to intolerance of prolonged flooding conditions.
In Year 2 of the project, after preliminary dewatering results from greenhouse studies at the University of South Carolina and Purdue University, the plant species we chose to establish in the field were Salix nigra (SX61) (obtained from Sand Creek Consultants, Reinlander, WI) planted with Echinochloa crusgalli, S. pectinata, C. aquatalis, Lolium multiflorum, followed by Morus rubra and Scirpus fluviatilis, followed by M. rubra. In addition to the plant species mentioned above, we have two sets of controls, one which was maintained free of vegetation via broad spectrum herbicide, and the other treatment, which was allowed to develop plant species as they colonized the sediments. The M. rubra was added to the cells, once the water content of the soils was deemed to be not saturated and suitable for growth of this plant species.
In addition to monitoring the moisture content of the soil over time, leaf surface area was estimated, and transpiration was measured with an Infrared Gas Analyzer (IRGA). These data will further elucidate the best plant species for dewatering by quantifying transpiration rate, surface area, and moisture content of the soil.
Results: Field Studies
All of the wetland plants removed a high fraction of water from the sediments (see Figure 1). The terrestrial plant adapted to drought conditions and removed more water than the unplanted control, but it did not remove as much water as the wetland plants.
Figure 1. Third Dewatering Cycle. On March 18, all pots were at the saturation point, or with 0 as the fraction lost. NN = no plants, CN = C. aquatalis, FN = S. pectinata, JN = S. fluviatilis, TN = T. dactyloides.
Figure 2. The Percent Moisture in Soils of the Pots Taken Down at the First Destructive Sampling Event. The soils were all brought to the saturation point 2 days earlier.
The three wetland species were able to remove the greatest amount of moisture from the sediments. The S. fluviatilis had the lowest percent moisture as compared to the other wetland plants. S. fluviatilis is a species typically found actually growing in standing water, so it would make sense that this plant would not have had selective pressure to reduce water loss through transpiration. Transpiration rates are illustrated further in Table 1.
Plant Species |
Kg water/pot day |
Transpiration Rate (mmol/mm2 • sec) |
Carex |
1.83 |
0.0076 |
Spartina |
2.10 |
0.0066 |
Scirpus |
2.60 |
0.0070 |
Tripsacum |
0.32 |
0.0037 |
*Transpiration measurements taken under optimal conditions. This number reflects the total surface area of a given plant species in each pot in addition to the transpiration rate per unit surface area measured with the IRGA. |
Select and/or Develop Plant Species That Are Most Suited for the Task of Dewatering and Remediating Contaminants
Field Studies. The C. aquatalis was the most effective dewatering plant on various sampling dates, but the L. multiflorum (annual rye) surpassed the C. aquatalis later in the experiment. The C. aquatalis was the only plant species that was established in the 2002 field season and, therefore, had a considerable advantage over the other species that were established in early 2003. At the end of the 2003 field season, the annual rye had reached its maximum growth and was beginning to senesce. At this point, the C. aquatalis and the L. multiflorum had similar capacity for dewatering (see Figure 2). The S. nigra was excellent in its capacity for dewatering, especially at the beginning of the 2003 field season. This probably is because the trees were put in as whips, and once they established leaves, transpiration was directly proportional to the number of leaves. At this point in the summer, the C. aquatalis was still growing, but, as the summer proceeded, the C. aquatalis overtook the S. nigra and all of the planted treatments, including the natural attenuation plots that had similar soil moisture contents. The unvegetated control continued as the least effective treatment (see Figure 2).
The natural attenuation plots were dominated by Smartweed (spp.). This plant species had a transpiration rate that was similar to that of willow. The surface area of the plant species in an individual cell played an important role in determining the quantity of water removed from a given cell, but many other factors come into play as well. For example, in the annual rye cells, the planting density was so high that the relative humidity next to the leaves was probably close to 100 percent, limiting the total transpiration in these cells. The transpiration measurements are taken under conditions that enhance the transpiration rate and are near the ideal rate; however, these data give us an idea of the relative abilities of these plant species to transpire water. Limiting factors for the transpiration rate of a plant species include available water for transpiration, wind speed, temperature, and relative humidity.
Plant Species |
Transpiration Rate (mmol/m2 • sec) |
L. multiflorum | 3.501 |
C. aquatalis | 2.526 |
S. nigra | 3.993 |
S. fluviatilis | 2.685 |
S. pectinata | 3.294 |
Smartweed (spp.). | 3.125 |
Figure 3. Dewatering Results for the Second Field Season (2003). Results are presented in terms of percent moisture in the soil.
Greenhouse Experiments: University of South Carolina
Sediments. The matrix of the dredged sediments located at the Jones Island CDF is not beneficial for the growth of plants or certain types of bacteria. The soil texture of the sediments has been characterized by AGVISE Laboratories as silt loam, consisting of 22 percent sand, 66 percent silt, and 12 percent clay, making it easily waterlogged leading to anaerobic conditions. Earlier analyses conducted by MDS Harris Laboratories found that the Jones Island sediments contained the following concentrations of macronutrients: nitrogen 42 ppm, phosphorus 55 ppm, and potassium 75 ppm. These amounts were confirmed by MDS Harris as moderately sufficient for plant and microbial growth.
Greenhouse. Each experimental run will be conducted for approximately 6 weeks in a controlled greenhouse environment located at the Savannah River Site in Aiken, SC. An attempt will be made to recreate the environmental conditions found at the Jones Island CDF in our greenhouse. Two 600W high-pressure sodium light fixtures will provide the supplemental lighting necessary for efficient plant growth. The lights will be on a 16/8, on/off cycle to provide supplement lighting on overcast days and during winter growth.
Plant Species. Numerous plants were identified as candidates for this study based on physiological and morphological characteristics that indicate that they may be well suited for dewatering and/or enhancing the biodegradation of contaminants in the soil: L. multiflorum (annual rye), Phleum pratense (timothy), Agrostis alba (red top), Trifolium repens (white clover), and S. exaltata (swamp pea). These characteristics may include traits such as high water requirements, high biomass yield, deep rooted, high germination rates of seeds, and an adaptation to a wide range of environments.
Growth Tubes. The experiment is being conducted in 36 5.7 liter rigid, clear acrylic tubes (height = 88.9 cm; inside diameter 8.9 cm). The tubes are designed to allow collection of sediment samples at predetermined depths along the length of the tube. This will allow us to gather moisture data and bacteria counts along a profile of the growing tubes. Because of the clear design, we also will be able to determine root penetration and growth in the tubes. The tubes will be arranged into a table with a complete randomized block design generated from a GW-BASIC program. There will be three controls (C1-C3, C4-C6) and five species (Sets 1-5, Sets 6-10) per treatment, with each planted tube replicated three times. Sets 1-5 and controls C1-C3 will have only sediments (i.e., no amendments); sets 6-10 and controls C4-C6 will have sediments amended with biosolids (20 percent of total volume). Controls C1-C6 will have no plants, which will represent the effects of evaporation alone. The planted tubes will represent the combined effects of evaporation and transpiration. The sediments in each tube initially will be resaturated to a moisture content of 65.4 percent. This value was determined by AGVISE Laboratories to be the saturation point of the sediment.
Variables. The independent variables that will be monitored are light intensities, temperature (maximum, minimum), relative humidity (maximum, minimum), wind-speed (maximum, average), root growth, root density (subjective analysis), plant height, and plant biomass. Light intensity, temperature, relative humidity, and wind speed will be measured every second day using standard monitoring equipment. An attempt will be made to measure root growth and weight by separating the roots from the sediments at the conclusion of the study, although this may not be possible because of the nature of the sediments. Separated roots will be measured for growth and weighed. Plant height will be measured throughout the experiment to monitor aerial growth. All above-ground portions of the plants will be cut and weighed at the conclusion of the study. We will use these independent variables to model total moisture loss (evapotranspiration), and bacteria populations will be enumerated from the rhizosphere and nonrhizosphere region of the tubes. Moisture loss in the sediment will be determined gravimetrically at 3 and 6 weeks.
Microbial Analysis. Sediment samples will be divided into rhizosphere and nonrhizosphere samples. Rhizosphere samples will be taken by shaking soil directly off the roots at the conclusion of the study. Nonrhizosphere samples will be taken from the sediments furthest away from any roots. A comparison between rhizosphere/nonrhizosphere bacteria populations to our controls will allow us to determine which plant species will sustain the greatest bacteria populations. Bacteria populations will be enumerated by acridine orange direct counts (AODC) at the initiation and conclusion (0 and 6 weeks) of the study (Hobbie, et al. 1997).
Results. In our results, we are interested in screening those plant species that have the greatest moisture loss as a function of root growth and still are able to maintain a high rhizosphere bacteria population. The results in Figure 9 show that the greatest microbial populations were sustained by A. alba in the unamended tube, with a count of 1.02 E9 bacteria. S. exaltata and L.lium multiflorum had the second (9.01 E8) and third (8.75 E8) highest microbial counts in the amended tubes, respectively. With the exception of A. alba, microbial populations followed as expected in the growth tubes, with counts generally higher in the amended tubes. The greatest moisture loss, shown in Figure 10, was exhibited by S. exaltata (final sediment moisture of 28.53 percent) followed by L. multiflorum (final sediment moisture of 30.41 percent). S. exaltata and L. multiflorum also had the greatest root growth in both the unamended and amended tubes (see Figure 11). Root growth was observed along the full length of the growth tubes (88.9 cm) in both species, except for the amended tube containing L. multiflorum. Overall, S. exaltata and L. multiflorum exhibited the best results in dewatering and sustaining the highest bacteria populations in the contaminated sediments at all depths.
Figure 9. Bacterial Counts of Initial Versus Final (Rhizosphere) in Tube Experiment One
Figure 10. Average Moisture Content in Tube Experiment One
Figure 11. Average Root Depth/Growth (cm) for Tube Experiment One
Modeling Water Loss From Contaminated Sediments Placed in the Greenhouse Pots Subjected to Different Plant Treatments: Central State University
The second phase of this research project proposed use of an unsaturated flow model to estimate the dewatering potential of different wetland species. Several models have been reviewed to determine their suitability to the dewatering of sediments. The literature review and the mathematical modeling were reported elsewhere (Schwab, et al. 2003).
Simulation Results. The unsaturated flow model was used to simulate dewatering of Milwaukee sediments using wetland species in greenhouse studies at Purdue University (Ms. Euliss Katy, the graduate student provided the experimental data). The sediments were dewatered using S. pectinata, C. aquatalis, T. dactyloides, and S. fluviatis.
Ms. Katy determined transpiration rates (fluxes) for these plant species in the greenhouse. These were expressed in mm/day so that these values could be directly incorporated as boundary conditions at the sediment-atmosphere interface for water movement. The transpiration rates for different wetland species used in the study are given below.
Plant Species | Replicates | Evapotranspiration (mm/day) | Crop Coefficients |
S. pectinata | 9 | 7.16 | 1.42 |
C. aquatalis | 9 | 10.77 | 2.13 |
T. dactyloides | 12 | 5.04 | 1.00 |
S. fluvatius | 7 | 10.63 | 2.11 |
Crop coefficients were computed using T. dactyloides, because this species satisfied conditions of a reference crop, which include the presence of an extensive surface of green grass of uniform height, actively growing, completely shading the ground, and with adequate water. Currently, these coefficients are being used to estimate corresponding transpiration rates from these plants in the field at the Milwaukee site. The transpiration rates in the greenhouse reported in Table 3 were used in the model to determine the drying fronts within Milwaukee sediments. The sediments have a bulk density of approximately 1.4 gm/cc and composition of 61 percent silt, 5 percent clay, and 34 percent sand. The sediments were packed to a depth of 8.5 cm. The following are the sediment hydraulic characteristics predicted by Rosetta (Personal communications with Dr. Kluitenberg at the Department of Agronomy, Kansas State University; Schaap and van Genuchten, 1999) based on sediment composition and bulk density:
• Theoretical saturated water content (10 percent uncertainty) = 0.4836
• Residual water content (corresponding to wilting point) = 0.0926
• Saturated hydraulic conductivity (20 percent uncertainty) = 0.459 cm/hour
• van Genuchten soil moisture retention curve parameters (Schaap and Bouten,
1996), a = 0.0089 and N = 1.49
• Same values are used for parameters describing hydraulic function (Schaap and
van Genuchten, 1998).
Moisture Movement Within the Sediments
Soil hydraulic characteristics predicted above were used to model the dewatering of sediments using an unsaturated flow model. The sediments initially were assumed uniformly saturated. Steady evapotranspiration rates, as shown in Table 1, for different plant species were used to represent typical water losses from different wetland species during the growth period. Figures 4-8 show corresponding drying fronts (changes in water content along the depth of the sediment) at different times (40, 80, 120, 160, and 240 hours since the drying process began). One can observe steeper gradients in drying fronts as drying progresses in time. While monitoring the rate of drying within the sediments, it is often a challenge to find the optimal locations for the placement of moisture probes to capture the overall drying process within sediments. Our simulations have indicated that most changes in water content would occur only in the top 8 cm of the sediment. A sensor near the surface is recommended to capture the rate of drying at the surface. Another sensor near the bottom 15-20 cm will capture the relatively constant rate of moisture reduction in that region. Two to three sensors placed between 2 cm and 8 cm depths (exact locations can be determined using an exponential distribution at increasing depths) will be ideal to capture the drying fronts and estimate the overall water loss and rate of drying within sediments.
Simulations in Figures 4-8 show that both S. fluviatus and C. aquatalis can achieve similar rates of dewatering sediments. It is obvious that these species can rapidly dewater sediments because of their high transpiration rates. It is evident from Figures 4-8 that these species yield steep gradients in drying fronts during the early stages of drying, which essentially means that upper portions of the sediments carrying these species dry out rapidly relative to the bottom. T. dactyloides dries the sediments slowly and uniformly along the depth initially, and subsequently dries the top portion more rapidly relative to the bottom. Drying rates for S. pectinata are greater than those for T. dactyloides and lower than those for S. fluviatus and C. aquatalis. These species, however catch up with the later species after about 120 hours of drying in terms of rapid drying. Careful observation of these drying fronts is critical in determining the endpoint in drying before the remediation phase of sediments to clean up PCBs may start. It also helps in assessing the time required to dry sediments to an optimal depth. As is evident from the simulations, it takes considerable time to reduce the moisture content near the lower portion of sediments relative to the surface.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Future Activities:
In the next year, we will reduce the concentrations of PAHs and PCBs in the selected sediments. A future study will include a culture-based method of identifying aerobic PCB-degrading bacteria associated with our selected plant species. Sediment samples will be taken directly from the roots of the test plants for culturing. The bacteria from the samples will be cultured under laboratory conditions, and the resulting population will be sent out for DNA sequencing. Biphenyl will be used as the sole carbon source for the bacteria under investigation to facilitate specific growth in the PCB degradation study. The results of this portion of the study will allow us to better understand the microbial communities involved in the degradation PCBs in our greenhouse experiments.
We will continue to screen for beneficial plant species that can best dewater and condition dredged sediments. At the conclusion of the study, plant species that are most suitable for the task of remediating the sediments will be chosen for field sites. All of the investigated variables will be taken into consideration in determining the most favorable plant species.
Journal Articles:
No journal articles submitted with this report: View all 16 publications for this subprojectSupplemental Keywords:
dewatering, remediation, dredged sediments, vegetative dewatering, bioavailability, biodegradation, bioremediation of soils, contaminants in soil, contaminated sediment, contaminated soil, degradation, earthworms, genetics, microbes, microbial degradation, phytoremediation, polycyclic aromatic hydrocarbon, PAH, polychlorinated biphenyl, PCB., RFA, Scientific Discipline, Waste, Water, Contaminated Sediments, Environmental Chemistry, Analytical Chemistry, Environmental Microbiology, Hazardous Waste, Molecular Biology/Genetics, Bioremediation, Hazardous, Environmental Engineering, microbiology, degradation, dewatering, vegetative dewatering, microbial degradation, genetics, bioavailability, biodegradation, contaminated sediment, contaminated soil, microbes, contaminants in soil, bioremediation of soils, earthworms, remediation, phytoremediation, dredged sedimentsRelevant Websites:
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Progress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R828770 EAGLES - Atlantic Coast Environmental Indicators Consortium Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R828770C001 Technical Outreach Services for Communities
R828770C002 Technical Outreach Services for Native American Communities
R828770C003 Sustainable Remediation
R828770C004 Incorporating Natural Attenuation Into Design and Management
Strategies For Contaminated Sites
R828770C005 Metals Removal by Constructed Wetlands
R828770C006 Adaptation of Subsurface Microbial Biofilm Communities in Response to Chemical Stressors
R828770C007 Dewatering, Remediation, and Evaluation of Dredged Sediments
R828770C008 Interaction of Various Plant Species with Microbial PCB-Degraders
in Contaminated Soils
R828770C009 Microbial Indicators of Bioremediation Potential and Success
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
Main Center: R828770
108 publications for this center
14 journal articles for this center