Final Report: Bioremediation of Contaminated Sediments and Dredged Material

EPA Grant Number: R825513C019
Subproject: this is subproject number 019 , established and managed by the Center Director under grant R825513
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: HSRC (1989) - South and Southwest HSRC
Center Director: Reible, Danny D.
Title: Bioremediation of Contaminated Sediments and Dredged Material
Investigators: Ward, C. Herb , Hughes, Joseph B
Institution: Rice University
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1992 through January 1, 1995
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (1989) RFA Text |  Recipients Lists
Research Category: Hazardous Substance Research Centers , Land and Waste Management


The goal of this project was to develop the technical basis for evaluating the potential of bioremediation processes for cost-effective treatment and risk reduction of contaminated sediments (CS) and dredged material (DM).

Specific objectives of this project included:

1) Determine the unique properties of sediment-associated contaminants that influence their biodegradability.
2) Identify and quantify the factors that control the biodegradation of contaminants in sediments.
3) Assess the limits (how clean is clean?) of realistic field approaches to the bioremediation of CS and DM.
4) Use mass balance approaches to assess the potential risk reduction benefits of bioremediation systems.
5) Explore the feasibility of in-situ and in place bioremediation of CS and DM based on knowledge of sediment structure and mechanics and dredging and disposal operations.

Summary/Accomplishments (Outputs/Outcomes):

The biodegradation of PAHs was studied in laboratory-scale slurry systems. Sediments for use in these experiments were collected on several occasions. Initially, sampling focused on four locations in the Houston Ship Channel - Turning Basin, Vince Bayou, San Jacinto Monument and Patrick Bayou. An additional sediment sampling location was identified approximately 30 miles south of the ship channel in Dickinson Bayou. Following sample collection, sediments were stored at 4 C in sealed wide-mouth glass containers. Prior to use in experimental systems, individual containers were homogenized and large debris (shells, sticks, etc.) were removed. Initially, studies were conducted to assess the ability of indigenous bacteria to mineralize PAHs. These experiments have clearly demonstrated mineralization of naphthalene, fluorene, and phenanthrene. In most cases, PAH degradation occurs without an observable lag (less than 24 hours). However, PAH mineralization rates are relatively slow - presumably due to their limited aqueous solubility. To develop an elevated population of indigenous PAH degraders for use in experimental systems, an enrichment culture was established using Dickinson Bayou sediments (10% to 15% solids) by routinely adding naphthalene, fluorene, and phenanthrene and other PAHs.

Slurry reactors were used to evaluate factors including: adsorption/desorption rates; the rate and extent of phenanthrene mineralization (by indigenous sediment bacteria); the rate and extent of contaminant biodegradation from sediments; and factors which may influence the design/operation of engineered bioreactors for use in remediation of contaminated sediments. Lab-scale slurry reactors ranged in size from 60 mL to 250 mL total volume depending on the requirements of an individual experiment. Mass balances were facilitated by the use of 14C-labeled PAHs.

A focus of this project was to assess the ability to increase biodegradation rates through addition of surfactants. In theory, surfactants have the potential to increase degradation rates by enhancing hydrocarbon solubility and reducing interfacial tension, but there are conflicting reports on the effect of surfactants on biodegradation rates in the literature. Studies focused on non-ionic surfactants and their impact in the rate and extent of biodegradation were achieved.

It can be concluded from this series of experiments that resuspension of anaerobic sediments can affect the degradation of phenanthrene sorbed to them. Sediments with contamination levels of 50 ppm phenanthrene were remediated in lab scale slurry reactors to the point that only tract phenanthrene (below GC-PID detection limit) was found after 7 days. Mixing and aeration, natural byproducts of the resuspension process, were the only treatment used.

Contaminant release from the sediments to the liquid phase is rapid under mixed conditions. Mixing was also found to be the main factor affecting rate and extent of compound mineralization. After a consistent 2-day lag period seen before appreciable activity, mineralization was rapid, reaching maximum extent within 3 days.

Mass balance analysis of radioactive carbon, in the radiolabeled phenanthrene added as a tracer, indicated that the PAH is used as a growth substrate and is biodegraded by bacteria indigenous to the sediments. Due to the time required to see complete degradation, it is unlikely that the mixing and aeration provided solely by dredging can be considered to be a remedial treatment.

The lab scale slurry reactors used , demonstrate that this type of reactor holds promise as a potential remediation methodology. A slurry reactor can be defined as an enclosed system where sediments and water are maintained in a homogeneous slurry over a period of time. It is envisioned that the reactors will be a batch treatment process. As such its size will be limited. Ex-situ reactors for sediment remediation could be built on barges or on shore. Both the bottom sediments and a liquid phase would have to be moved to the reactor to form the slurry. If hydraulic dredges are used, the sediments are removed in a slurry form and could be pumped directly to the reactors. In-situ reactors would isolate small areas of the contaminated bottom and utilize the overlying water to make the slurry. Potential methods of isolation include caissons, sheet piling, or other types of physical barriers.

Design factors that should be considered include mixing intensity, aeration, and the use of sequential treatment cells. The lab scale reactors used had minimal to insufficient mixing capacity. Any field or full scale test should be designed to provide adequate mixing for the desired slurry. Mixing not only enhances mass transfer of the contaminant from the sediment to the aqueous phase, but also helps to maintain oxygenation of the slurry when open to the atmosphere.

Tests conducted demonstrate that the intermittent aeration can substantially lower volatilization without detrimentally affecting mineralization. Optimum design will utilize intermittent aeration or some form of chemical oxidation, e.g., peroxide addition. The purpose will be to minimize contaminant loss due to volatilization or stripping. No tests have been made in slurry reactors using chemical oxidants. However, previous research looking at peroxide as a potential oxidant for injection into ground water aquifers has shown this chemical to be inhibitory at high concentrations.
It was shown that augmenting the reactor with aged slurry eliminated the lag period. Treatment times were reduced by 40% when the reactors were seeded, going from 5 to 3 days to reach maximum extent of mineralization.

Step desorption studies using the Dickinson Bayou sediments showed that desorption was fast and reversible. In sediment-slurry reactors desorption may not be a limiting factor to achieve biodegradation. PAHs in both liquid and sediment phases degraded in less than 10 days to below detection limits. This implies that PAHs were readily bioavailable. However, the current study has a lower limit on sediment concentration (1 ppm). Assuming one ppm is a reasonable value for environmentally acceptable end-point for practical purposes, bioremediation of contaminated sediments by slurry-type reactors can be considered to be a potential remedial technology.

A key element in mixing intensity is that it breaks up the sediment aggregates that entrap a fraction of the contaminant, and allowing for that fraction to be available for degradation by the microorganisms.

Sediments are strong adsorbents for nonionic surfactants as well as for PAHs. Sorption of surfactant molecules to sediment affected surfactant performance as a solubility enhancer by necessitating greater surfactant concentrations in order to achieve surface tension minima and micelle formation. When considering the use of surfactants in soil or sediment systems, a detailed consideration of surfactant sorption is necessary to evaluate the potential performance of the surfactant in enhancing contaminant solubilization and/or mobilization.

Sorption of low (less than 0.5 mg/L) phenanthrene concentrations to sediments may not limit the rate of phenanthrene biodegradation. The apparent lack of rate-limiting effect of desorption on biodegradation may be due to the relatively short (4 days) equilibration time used, since longer equilibration times have been implicated in increased degrees of sorption.

All but one of the nonionic surfactants tested at concentrations in excess of thier CMC were inhibitory to the short-term (less than 6 days) extent of phenanthrene mineralization. As many nonionic surfactants are noted for their cellular membrane solubilizing characteristics, disruption of membrane-mediated cellular events or destruction of membrane integrity are likely explanations for inhibition of phenanthrene mineralization by nonionic surfactants.

Nonionic surfactants at concentrations greater than CMC, if not toxic or irreversibly inhibitory to the microbes capable of phenanthrene degradation, can enhance the extent of phenanthrene mineralization within short time periods when supplied with inorganic nutrients and oxygen. In the absence of sediment, addition of a nonionic surfactant in excess of it CMC reduced the initial rate of phenanthrene mineralization but enhanced the extent of mineralization after 1 week. The presence of as little as 2% sediment prevented this initial inhibitory effect, perhaps by acting as an adsorbent for surfactant molecules, reducing the free concentration of surfactant and thus its possible inhibitory effect on phenanthrene-degrading microorganisms. A greater concentration of micelles in the absence of sediment may have reduced the fraction of phenanthrene in molecular solution, thereby rendering the phenanthrene more difficult to degrade. This is a possibility since phenanthrene was at a concentration below its aqueous solubility. A sediment-specific property not relating to sorptive capacity for the surfactant may also be a factor in eliminating the initial inhibitory effect by the surfactant in the absence of sediment. Subtle structural differences among the surfactants within the same class may result in dramatically different biological effects, and any surfactant considered for use must be evaluated individually.

Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other subproject views: All 22 publications 10 publications in selected types All 3 journal articles
Other center views: All 392 publications 154 publications in selected types All 106 journal articles
Type Citation Sub Project Document Sources
Journal Article Jee V, Beckles D, Ward CH, Hughes JB. Aerobic slurry reactor treatment of phenanthrene contaminated sediment. Water Research 32(4):1231-1239. R825513C019 (Final)
R825513C020 (Final)
not available
Journal Article Tsomides HJ, Hughes JB, Thomas JM, Ward CH. Effect of surfactant addition of phenanthrene biodegradation in sediments. Environmental Toxicology and Chemistry 1995;14(6):953-959. R825513C019 (Final)
R825513C020 (Final)
not available
Journal Article Ward CH, Hughes JB. Microbes may help clean up contaminated sediments. Centerpoint 1994;2(1):6-8. R825513C019 (Final)
not available

Supplemental Keywords:

bioavailability, volatile organics, and remediation., RFA, Scientific Discipline, Waste, Water, Chemical Engineering, Contaminated Sediments, Environmental Chemistry, Analytical Chemistry, Hazardous Waste, Bioremediation, Ecology and Ecosystems, Hazardous, Environmental Engineering, environmental technology, sediment treatment, hazardous waste management, hazardous waste treatment, risk assessment, biodegradation, decontamination of soil, risk management, contaminated sediment, slurry reactors, chemical contaminants, PAH, contaminated soil, bioremediation of soils, contaminants in soil, PAHs, remediation, biotransformation, anaerobic biotransformation, waste mixtures, technology transfer, contaminated soils, metal compounds

Progress and Final Reports:

Original Abstract
  • 1992
  • 1993

  • Main Center Abstract and Reports:

    R825513    HSRC (1989) - South and Southwest HSRC

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R825513C001 Sediment Resuspension and Contaminant Transport in an Estuary.
    R825513C002 Contaminant Transport Across Cohesive Sediment Interfaces.
    R825513C003 Mobilization and Fate of Inorganic Contaminant due to Resuspension of Cohesive Sediment.
    R825513C004 Source Identification, Transformation, and Transport Processes of N-, O- and S- Containing Organic Chemicals in Wetland and Upland Sediments.
    R825513C005 Mobility and Transport of Radium from Sediment and Waste Pits.
    R825513C006 Anaerobic Biodegradation of 2,4,6-Trinitrotoluene and Other Nitroaromatic Compounds by Clostridium Acetobutylicum.
    R825513C007 Investigation on the Fate and Biotransformation of Hexachlorobutadiene and Chlorobenzenes in a Sediment-Water Estuarine System
    R825513C008 An Investigation of Chemical Transport from Contaminated Sediments through Porous Containment Structures
    R825513C009 Evaluation of Placement and Effectiveness of Sediment Caps
    R825513C010 Coupled Biological and Physicochemical Bed-Sediment Processes
    R825513C011 Pollutant Fluxes to Aquatic Systems via Coupled Biological and Physicochemical Bed-Sediment Processes
    R825513C012 Controls on Metals Partitioning in Contaminated Sediments
    R825513C013 Phytoremediation of TNT Contaminated Soil and Groundwaters
    R825513C014 Sediment-Based Remediation of Hazardous Substances at a Contaminated Military Base
    R825513C015 Effect of Natural Dynamic Changes on Pollutant-Sediment Interaction
    R825513C016 Desorption of Nonpolar Organic Pollutants from Historically Contaminated Sediments and Dredged Materials
    R825513C017 Modeling Air Emissions of Organic Compounds from Contaminated Sediments and Dredged Materials title change in last year to "Long-term Release of Pollutants from Contaminated Sediment Dredged Material"
    R825513C018 Development of an Integrated Optic Interferometer for In-Situ Monitoring of Volatile Hydrocarbons
    R825513C019 Bioremediation of Contaminated Sediments and Dredged Material
    R825513C020 Bioremediation of Sediments Contaminated with Polyaromatic Hydrocarbons
    R825513C021 Role of Particles in Mobilizing Hazardous Chemicals in Urban Runoff
    R825513C022 Particle Transport and Deposit Morphology at the Sediment/Water Interface
    R825513C023 Uptake of Metal Ions from Aqueous Solutions by Sediments
    R825513C024 Bioavailability of Desorption Resistant Hydrocarbons in Sediment-Water Systems.
    R825513C025 Interactive Roles of Microbial and Spartina Populations in Mercury Methylation Processes in Bioremediation of Contaminated Sediments in Salt-Marsh Systems
    R825513C026 Evaluation of Physical-Chemical Methods for Rapid Assessment of the Bioavailability of Moderately Polar Compounds in Sediments
    R825513C027 Freshwater Bioturbators in Riverine Sediments as Enhancers of Contaminant Release
    R825513C028 Characterization of Laguna Madre Contaminated Sediments.
    R825513C029 The Role of Competitive Adsorption of Suspended Sediments in Determining Partitioning and Colloidal Stability.
    R825513C030 Remediation of TNT-Contaminated Soil by Cyanobacterial Mat.
    R825513C031 Experimental and Detailed Mathematical Modeling of Diffusion of Contaminants in Fluids
    R825513C033 Application of Biotechnology in Bioremediation of Contaminated Sediments
    R825513C034 Characterization of PAH's Degrading Bacteria in Coastal Sediments
    R825513C035 Dynamic Aspects of Metal Speciation in the Miami River Sediments in Relation to Particle Size Distribution of Chemical Heterogeneity