Bioremediation Technologies: Background Three main classes - Engineered in situ - Intrinsic in situ - Engineered ex situ Different purposes - Engineered bioremediation: to increase the biotransformation rates significantly - Intrinsic bioremediation: to prevent the migration of contamination away from its source.

Bioremediation Technologies: Contents Scope and characteristics of contaminants Contaminant availability for biodegradation Treatability studies Engineering strategies for bioremediation Evaluating bioremediation

Treatability studies Level Goals Approach 1 Determine if biodegradation is option Thermodynamics Simple lab microcosms 2 Evaluate biodegradation nonidealities (kinetics, multiphasic transport, mixed substrates etc.) Laboratory microcosms of all types (batch, column, slurry etc.) Stoichiometry, thermodynamics, and kinetics 3 Evaluate site-specific issues, such as hydrogeologic conditions and heterogeneity Field pilot scale

Intrinsic bioremediation Essentially in situ bioremediation without human intervention. Removal of contamination source may be necessary prior to intrinsic bioremediation. Although intrinsic bioremediation does not involve active site manipulation, it requires construction and maintenance of a monitoring system. Need to monitor the plume distribution, indicator parameters of biodegradation, and possibility of contamination in previously non-contaminated areas. Need to evaluate the possibility and extent of intrinsic bioremediation in order to examine the effectiveness of “active” groundwater-soil remediation methods (no-treatment control experiment).

Source GW flow Aerobic Margin Anaerobic Core Aerobic Margin

Intrinsic bioremediation Application Diverse microbial populations indigenous to subsurface environments can degrade important classes of organic contaminants. The extent of intrinsic bioremediation depends on the biodegradability of the contaminant and on the site’s hydrogeologic and chemical characteristics. Four types of hydro-geologic and geochemical characteristics determine the successfulness of intrinsic biodegradation instead of an engineered cleanup system. Predictability of groundwater flow. Sufficient amount of electron acceptors. Adequate capacity to buffer against pH changes that may occur with the increased microbial activity. The site must have a natural supply of the elemental nutrients.

Intrinsic bioremediation Limitations. Involves somewhat greater risk of failure than engineered bioremediation because active measures (thorough monitoring) are not used to control plume migration. Pollutant producers may like this approach while regulators, environmental groups, and the public may be unwilling to accept this approach. Plume is mobile. Advantages. Minimizes treatment costs by requiring little or no energy input. Eliminates the chance of remobilizing contaminants or causing additional contamination by pumping.

Method to add degrading bacteria In Situ Bioremediation Nutrients E-acceptor (Biostimulation) *Bioaugmentation Method to add degrading bacteria Surface Soil/Cap Unsaturated Zone Contaminant plume Saturated Zone Biostimulation: addition of nutrients and electron-acceptor into groundwater in order to stimulate subsurface microorganisms (mainly bacteria) to degrade contaminants. Bioaugmentation: addition of efficiently degrading bacteria into contaminated groundwater with nutrients/electron acceptor to enhance biodegradation of contaminant.

In Situ Bioremediation - Hydrocarbons Application Successful method for treating soil and groundwater contaminated with certain types of hydrocarbons (mainly petroleum products and derivatives and others such as refinery wastes, crude oil, fuels, phenols, cresols, acetone and celluloisic wastes.) A specific microbial enhancement feasibility study and a general hydrogeologic site investigation are essential.

In Situ Bioremediation - Hydrocarbons Limitation Geological heterogeneity inhibits the supply of nutrient/e-acceptor or microbes into the contaminated groundwater area. In the cases of slow NAPL dissolution or/and slow desorption, the availability of contaminant to biodegradative microbes is limited. Requirement of a minimal contaminant concentration to remain the population size and to induce the biodegradative pathway (never be complete zero concentration!) Oxygen limitation.

In Situ Bioremediation – Hydrocarbons (continued) Advantage over conventional pump-and-treat approach Completely degrading into non-toxic end products. Less pumping requirement than conventional pump-and-treat. Faster Bacteria move to contaminated zone (chemotaxis)

Air Sparging Vapor Extraction Well Vapor Treatment Air Surface Soil/Cap Unsaturated Zone Saturated Zone Contaminant plume Inject air either directly into the aquifer formation or into specially designed extraction wells. Then, it displaces pore water and rises through the saturated zone into the vadose zone) The air stream must be captured by a properly designed SVE system.

Air Sparging Application Successful laboratory- and pilot-scale evaluations for volatile and biodegradable contaminants. Permeability of air > 10-3 cm/s the size of the porous medium > 1 mm Henry’s law constant > 10-5 atm-m3/mole Water solubility < 20,000 mg/liter Vapor pressure < 1 mmHg

Air Sparging Limitation Problematic when the depth of air sparing > 10 m. Diffusion limited process will slow cleanup. Clogging problem when ion is oxidized by provided oxygen. Possibly move the residual NAPLs into another locations.

Different Configuration of Air Sparging Injection point for flushing gas Extraction of contaminant gas Surface Soil/Cap Unsaturated Zone Contaminated Zone Saturated Zone Better control of gas (air) flow in subsurface

Air injection well with periodic nutrient flooding Bioventing Air injection well with periodic nutrient flooding *Bioaugmentation Method to add degrading bacteria Vapor Recovery Well Vapor Recovery Well Surface Soil/Cap Unsaturated Zone Saturated Zone Residual LNAPL Microorganisms In situ Bioremediation of the unsaturated zone. Main purpose is to provide oxygen to soil microbes.

Bioventing Application Limitation Successful method for treating petroleum hydrocarbons and some chlorinated solvents. Applicable in permeable soils (sand aquifers). Limitation Possible limitation of nutrient. Change in soil moisture can affect the load-bearing capacity. Significant masses of contaminants in low permeability zone. Advantage over conventional pump-and-treat approach A greater ease of circulating air compared to circulating water. Easy transport of oxygen in air than in water.

Gasoline JP-4 Jet Fuel Diesel KH=102 KH=100 KH=10-2 KH=10-4 Vapor Pressure Too High to Biovent KH=102 KH=100 KH=10-2 Gasoline Vapor Pressure Amenable to Bioventing or Volatilization 1 KH=10-4 JP-4 Jet Fuel 10-3 10-5 Vapor Pressure (atm) Diesel KH=10-6 (atm*m3/mole) Vapor Pressure Too Low to Volatilize 10-9 10-3 103 10-7 Solubility (μM)

In situ Bioremediation – Chlorinated Solvents Application Aerobic cometabolism of chlorinated hydrocarbons. (aerobic TCE degradation by methanotrophs or aromatic degraders) In 1998, a successful case of in-situ aerobic TCE bioremediation by stimulating the cometabolism of TCE by toluene oxidizing bacteria in groundwater. Anaerobic dechlorination (Chlorinated hydrocarbons are electron acceptors) Limitation Toxic intermediates Limitation of food (primary substrate) into the contaminated zone Limitation of biodegradative microorganisms Threshold concentration for biodegradation

In situ Bioremediation - Metals Application Manipulating bacteria to either dissolve the metals (cleanup) or immobilize the metals (containment). Potential mechanisms in anaerobic microorganisms: (1) enzyme reduction of metal, (2) biochemical alteration of red-ox conditions, (3) biogenic chelate, (4) metal sequestration, (5) metal bioaccumulation. Dissolution of metals (Fe2O3, MnO2, CdO, CuO, PbO and ZnO) Immobilization of uranium (VI => IV) Limitation Similar to those for In Situ Bioremediation-Chlorinated solvents. Needs to control the mobilized metals through groundwater. Uncertainties in immobilized metals.

Bio-degradabilities under different respiration conditions Type of bacteria benzene toluene naphthalene Dichloro-benzene TCE Methyl-phenols Penta-chloro-phenol Aerobic De-nitrifying Iron-reducing Sulfate-reducing Methano-genic ++ + -

In situ Reactive Barriers Contamination in saturated zone GW Flow Impermeable Barrier wall Permeable Reaction Wall Treat the contaminant plume as it passes through permeable reactive zones or walls within the aquifer.

In situ Reactive Barriers Application 1) A trench with reactive materials (shallow depth) 2) Slurry well (deeper and larger) 3) Modules to enable periodic replacement. Reactive materials. Activated carbons or biological activated carbons. Redox controls (zero iron). Microbial filters.

In situ Reactive Barriers Limitations 1) Has not been demonstrated in field scale. 2) Difficulties in installing the reactive materials. 3) Difficulties in providing suitable amounts of these reactive materials. Advantages Like in situ bioremediation, it lowers costs of pumping once installed. Safer and more reliable than intrinsic bioremediation. Small and defined zone of reactions: easy to design, monitor and control.

Containment Technologies Isolating contaminant. Physical isolation with low-permeability barriers such as caps, liners, and cutoff walls. Solidifying it in place with either chemical fixatives or extreme heating (a process known as vitrification).

Containment Technologies Application Barriers: lower permeability than the aquifer (compacted clay, synthetic plastics, soil and bentonite mixtures, cement and bentonite mixtures, and sheet piling). Solidification in place Mixing with cementing agents (lime-flyash pozzolan, and asphalt) Heating (1600-2000 oC) it into a molten mass that solidifies upon cooling, a process known as in situ vitrification.

Containment Technologies Limitations The long-term performance of physical barriers is uncertain. Construction difficulties are common. The long-term stability and leaching characteristics of contaminated materials that have been solidified or vitrified are unknown. Vitrification may cause volatilization, mobilization, and migration of contaminants.

NAPLs and Recovered Groundwater to Treatment Soil Flushing Separator NAPLs and Recovered Groundwater to Treatment Surfactants NAPL residual In Saturated Zone Surface Soil/Cap Unsaturated Zone Saturated Zone Enhances contaminant recovery in conventional pump-and-treat systems by injecting chemical agents that mobilize the contaminant residuals in saturated zone.

Soil Flushing Application Chemical agents to improve dissolution of NAPL into groudwater and/or to reduce the viscosity of water. Co-solvents: when mixed with water, they enhance the solubility of some organic compounds (e.g. alcohols). also function as either stimulators or repressors for biodegrading microbes in groundwater. at least 20% of co-solvent is needed to cause efficient mobilization.

Application (continued) Soil Flushing Application (continued) Surfactants: one end with a hydrophilic portion; the other end with a hydrophobic portion. Micelle formation. reducing the interfacial tension bet. NAPLs and water.=> Enhancement of dissolution of contaminant from NAPLs. also enhance recovery of sorbed contaminants. feasible to remove PAHs, PCBs, PCE/TCE, petroleum hydrocarbons etc. can function as biodegradation stimulator or inhibitor.

Soil Flushing NAPL Phase Micelle Formation and Enhanced Dissolution of NAPL by Surfactant Hydrophobic tail of a surfactant monomer (anionic-, cationic-, non-ionic) Hydrophobic Contaminant (solute) Surfactant monomers Hydrophobic tail of a surfactant monomer NAPL Phase

Soil Flushing Limitations Geological conditions can limit the performance of soil flushing systems. Complicating the prediction of transport behavior. - Use of large amount of cosolvent =>changes in density, viscosity and compressibility. Possible to enlarge the zone of contamination by enhancing the mobilization of NAPLs. Uncertain ecological risk due to remaining surfactants.

Land Farming

When do we need bioremediation? Role of Bio-remediation in GW Clean-up River

Bioremedation is useful when a plume (dissolved pollution at low concentration) is widely spread Bioremediation

Evaluating Bioremediation Difficulties in evaluation Definition of success varies among the several parties involved. No one measure is universally applicable (site specific issues, limitation in standardization of methods, etc.) Complexity and heterogeneity in contamination as well as biogeohydrological conditions. NRC’s recommonded evaluation strategy (also see Table 15.11) Documented loss of contaminants from the site Lab assays showing the presence of microorganisms potential for in situ biodegradation One or more pieces of evidence showing that the biodegradation potential is actually realized in the field (p.724-725)

Bioremedation is not everything! (cost, CO2, benefits, impact etc.) Treatment Trains Life Cycle Assessment (cost, CO2, benefits, impact etc.)