Bioremediation of Petroleum and Polyaromatic Hydrocarbons: Theory and Applications

1. Bioremediation of Petroleum and Polyaromatic Hydrocarbons: Theory and Applications Dr. Carol Litchfield Dept. Environmental Science & Policy George Mason University Manassas, Virginia, U.S. A. October 2005

2. Outline • Brief introduction to hydrogeology and the subsurface • Overview of the theory of bioremediation

3. What is Bioremediation? • In the most general terms, this is the process by which organisms (from any domain) transform chemicals. • For our purposes it is the transformation of chemicals considered to be contaminants or pollutants. • When aerobic microorganisms are involved, it means the production of CO2, biomass, water, and perhaps other ions such as Cl-

4. Some Terms and Understanding of the Subsurface • Groundwater: subsurface water • Water Table: water level in the subsurface where the pressure of the water equals the atmospheric pressure and soil pores are completely saturated with water • Hydraulic Conductivity: water flow rate per cross sectional area; units of cm2/m/day or meters/day • Vadose Zone: zone of unsaturation above the water table. It may or may not include the interface. • Saturated Zone: soils where water is always present • NAPL: nonaqueous phase liquid • DNPL: dense nonaqueous phase liquid

5. Soil Texture & Porosity

6. Aerobic Heterotrophic Metabolism • Molecular oxygen provides the electron acceptor for the oxidation of organic compounds • Organic carbon is used for energy and growth and this includes methane but not carbon dioxide • Examples: mammals, birds, fish, bacteria

7. Anaerobic Metabolism • Anaerobic bacteria live and grow in the presence of reduced compounds and with either the total absence of molecular oxygen or its greatly reduced concentration • Compounds which can serve as terminal electron acceptors for anaerobes are: carbon dioxide, nitrate, sulfate, iron, humates and glucose (producing lactic acid and ethanol)

8. Co-metabolism • The transformation of a nongrowth compound when an organism is growing on another substrate and deriving its carbon and energy from the second substrate. That is, the first compound is “accidentally” transformed and provides no benefit to the organism

9. Some Terms and Understanding of the Subsurface • Retardation: the extent to which substances or chemicals are prevented from moving in soils or in the subsurface: sorption entrapment cation exchange capacity Kow (octanol:water partition coefficient) chemical reactions porosity composition other organic matter gases microbial action

10. Retardation of Bacteria

11. Cross Section of the Subsurface

12. Hydraulic Conductivities of Different Soil Types

13. Traditional Technologies • Pump and Treat if a Liquid • Excavate and treat on site • with soil washing • incineration • landfill

14. Remediation Options • Excavate and remove to landfill or incinerate • Containment • Slurry wall • Vitrification • Stabilize • Pump and Treat • Free-phase removal • Pump groundwater and air strip or carbon filter • Chemical/physical oxidation • Hydrogen peroxide • UV • Reverse Osmosis • Thermal treatment • Use In Situ treatments • Soil venting • Bioremediation

15. Advantages of Bioremediation • Can be highly specific • Less expensive than excavation or incineration processes • If mineralization occurs get complete degradation and clean up • Does not transfer contaminants from one environment to another • Uses a natural process • Good public acceptance • Process is simple • If using ISB you will treat the groundwater and soil at the same time

16. Disadvantages to Bioremediation • Not instantaneous • Often need to develop a system • Always need to test and optimize conditions empirically – not with computer models • May have inhibitors present • Compounds may not be in a biodegradable form – polymers, plastics • Compounds may be recalcitrant – higher congeners of PCBs

17. How Do We Begin Bioremediation? • Determine there is a problem • Monitor the surface/subsurface soils and water

18. Types of Organisms • Natural • Pure cultures • Flavobacterium spp. • Pseudomonas spp. • Mixed cultures • Consortia • Methane-utilizing bacteria (anaerobes) • Genetically engineered microorganisms

19. What Types of Organisms Have Been Used? • Fungi • Plants (Phytoremediation) • Bacteria • The natural community • Bioaugmentation

20. What Types of Compounds Can Be Treated Biologically? • Petroleum Hydrocarbons • Gasoline • Diesel Fuel • Gasoline Additives such as MTBE • Polyaromatic Hydrocarbons • Creosote • Chlorinated Hydrocarbons • Chlorinated Aliphatics: trichlorethylene • Chlorinated Aromatics : PCB’s, Pentachlorophenol • Explosives • RDX, TNT • Inorganics via Reduction to a Lower Valence Causing Precipitation • Uranium, Technicium • Sulfur and Sulfuric Acid • Ammonia or Nitrate/Nitrite

21. Environmental Conditions for Bioremediation • Aerobic – where oxygen in some form is added to the treatment environment • Anaerobic – where nitrate, iron, or other electron acceptor is added to the treatment environment • Combinations - where a combination of the above is used, often in pulses

22. What Biological Technologies Are Available? • In situ Bioremediation (ISB) or Enhanced Bioremediation • Natural Bioremediation • Biopiles • Bioreactors • Bioventing/ Biosparging • Engineered Treatment Cells

23. Bioreactor Design Considerations • Type of contaminant: soil, sludge, water • Hydraulic residence time • Bacterial residence time • Mixing • Oxygen transfer • Contaminant levels and likelihood of interactions • Discharge standards and air emission controls • Sludge disposal • Operational costs: capital equipment, personnel, chemicals, duration

24. Bioaugmentation • Definition: The addition of microorganisms to the reaction chamber whether in situ or above ground • Considerations before bioaugmenting: • Ability to survive • Ability to function • Assurances that they are nonpathogenic to higher life forms

25. Types of Bioremediation Using Indigenous Microorganisms • On Site • Above ground bioreactor for soils and/or water • Solid phase treatment cells for soils • Landfarming for soils but could use for water if not much water is contaminated • Composting of soils • In situ bioremediation

26. Composting • A process for treating contaminated soils using microorganisms in a heat generating process so that the contaminants are degraded at an accelerated rate.

27. Definition of In Situ Bioremediation (ISB) • The treatment in place without excavation of contaminated soils or sediments. This may require construction in the soils/sediments of barriers to contain the movement of the groundwater, nutrients, or contaminants

28. Factors to Consider in Any In Situ Process • Geochemistry – the interaction of any treatments with the soil mineralogy • Hydrogeology – how does the subsurface water move • Biodegradability – rate, extent, and pathways of degradation • Redox condition – is this an oxidizing or reduced environment

29. Principles of ISB • Bacteria occur naturally in subsurface soils and water. • These bacteria have adapted to their environment • Microbial activity is limited by environmental or nutrient factors • When these limiting factors are corrected, the microbial community can degrade the contaminants to biomass, carbon dioxide, water, and salts if appropriate • Growth stimulation can be controlled by controlling the addition of the nutrients. • Aerobic biodegradation is preferred because it is faster and tends to result in more complete degradation • Microbial transformations can lead to more toxic materials or complete degradation

30. Information Required for any ISB Process • Is there an acclimated population? • How many are there? • Is there a reducing zone indicating that bacteria are already active there? • What is the hydrology of the site? • What is the vertical and horizontal distribution of the contaminants? • What are the concentrations of the contaminants? • What is the lithology of the subsurface?

31. Steps in Performing an ISB • Historical background • Obtain fresh core and groundwater samples Run a screening study to determine if adapted organisms are there, their numbers, and whether they can degrade the contaminant Duration: 1- 4 weeks Cost: Minimal Optimize the conditions to determine the best electron acceptor, optimal nutrient mixture, and evaluate the rate and extent of biodegradation Duration: 14-20 weeks Cost:$10,000 - $100,000

32. Steps in Performing an ISB, cont’d. Perform a soil-nutrient interaction study Duration: 1-5 days depending on conductivity Cost: Minimal Engineering Designs Construction Implementation: monitoring soils and/or groundwater to show biodegradation is occurring Closure

33. Indicators of an Acclimated Microbial Community • Depressed oxygen levels in the area of the spill • Increased numbers of colonies capable of growing on the contaminant • Increased levels of ATP • Demonstration in microcosm studies that have degradation of the contaminants • If appropriate, increased levels of salts in the groundwater

34. How to Enhance the Indigenous Microbial Community • Add nutrients: nitrogen, phosphorus, trace metals, co-substrates • Add electron acceptor: oxygen, nitrate, humates, etc.

35. Information Required for In Situ Bioventing • Adapted microorganisms are present • Radius of influence of the wells- permeability of the soils to gases • Likely flow paths • Presence of natural biogenic gases: carbon dioxide, methane, and oxygen • Evidence of in situ respiration