BIOREMEDIATION AND PHYTOREMEDIATION
BTY 884
Process analysis
Site characterization and feasibility studies must determine key chemical,
physical, and microbiological ...
Site Characterization
Main objective of site characterization is to identify the contaminants, their
concentration, and th...
Physical properties of organic contaminants
Octanol/water partition coefficient is defined as the ratio of a compound's
co...
Vapor pressures and Henry's Law constant, HA, measure liquid—air partitioning.
Henry's Law states that the equilibrium par...
In soil bioremediation the rate-limiting step is often the desorption of contaminants,
since sorption to soil particles an...
Measurements of aqueous phase and soil phase concentrations in equilibrium
may be sufficient to indicate potential problem...
Surfactants and cosolvents has been investigated in attempts to increase
bioavailability of contaminants that are strongly...
Microbiological characterization
Measurement of biodegradation rates by indigenous microorganisms is the first
step in mic...
Environmental factors
Chemical analyses that support process design include measurements
of pH, COD, TOC, nitrogen, phosph...
More difficult to optimize are the oxygen and nutrient supply.
Most bacteria capable of degrading organic compounds are he...
A chemical that is cometabolized at one concentration or in one environment
may be mineralized under other conditions
Come...
Biodegradation can occur aerobically or anaerobically.
The most effective biodegradation of hydrocarbon compounds is media...
Predicting degradation rate
Degradation rates and equilibrium properties are useful for process
design.
During wastewater ...
Table is a portion of the 196-compound data base used in a fate model to
estimate volatile emissions, concentrations of to...
The major error in predicting the fate of toxic compounds in wastewater treatment
plants was in estimating the value of th...
A measure of hydrophobicity can be used to estimate relative biodegradation
rates among homologous compounds.
Rates of ana...
An experimental data base that assesses mixed culture biodegradation data
for 800 organic compounds is available
Good pred...
REACTOR OPTIONS
Reactor options are determined primarily by the physical properties of the waste
and the chemical and bioc...
Soils are difficult to transport, so batch reactors are favored.
Agitation is a critical design parameter required for aer...
Groundwater remediation
The technology for the removal of suspended and dissolved contaminants from
municipal and industri...
Activated sludge reactors
Polychlorinated phenols and biphenyls, phenols, phthalates, and PAHs were
tested, with average r...
The advantages of an activated sludge design for treating high-organic-content
wastewaters that produce a flocculating slu...
Fixed film reactors
The BioTrol aqueous treatment system is a good example of a fixed film, continuous
reactor used succes...
Fixed film or attached growth systems require degradative microorganisms with the
ability to attach to the surfaces of an ...
The fixed film reactor used for municipal sewage is the trickling filter reactor,
with large packing, typically 50 mm diam...
Nitrogen and phosphorus may be added to the inflow so that the C: N: P
ratio is approximately 100: 5: 1.
Reactor cells may...
Anaerobic processes
While anaerobic processes for bioremediation of groundwater are uncommon,
anaerobic treatment is used ...
The anaerobic bioreactor is typically an upflow packed-bed reactor. The reactor is
completely filled with liquid except fo...
2,4,6-Trichlorophenol can be degraded to 4-chlorophenol in the anaerobic reactor,
and the 4-chlorophenol was mineralized i...
Soil remediation
With ex situ treatment of contaminated soils, a controlled environment for soil
treatment can be maintain...
Landfarming
Biological soil treatment by landfarming is a relatively simple and inexpensive
method for treating soil conta...
Landfarming has been widely implemented at petroleum production and storage
sites, and at sites contaminated with polynucl...
A potential problem in soil treatment is the residual contaminant concentration
that is slowly or not noticeably degraded ...
Bioremediation presentation1
Bioremediation presentation1
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Bioremediation presentation1

  1. 1. BIOREMEDIATION AND PHYTOREMEDIATION BTY 884
  2. 2. Process analysis Site characterization and feasibility studies must determine key chemical, physical, and microbiological properties of the site.
  3. 3. Site Characterization Main objective of site characterization is to identify the contaminants, their concentration, and the extent of contamination. The distribution of contaminants between soil and groundwater will largely determine whether soil or groundwater treatment is applicable, while the extent of contamination will largely determine the applicability of soil excavation and treatment
  4. 4. Physical properties of organic contaminants Octanol/water partition coefficient is defined as the ratio of a compound's concentration in the octanol phase to its concentration in the aqueous phase of a two-phase system. Measured values for organic compounds range from 10-3 to 107 . Compounds with low values (<10) are hydrophilic, with high water solubilities, while compounds with high values ( > 104 ) are very hydrophobic. Compounds with low water solubilities and high Octanol/water coefficients will be adsorbed more strongly to solids and are generally less biodegradable. Highly soluble compounds tend to have low adsorption coefficients for soils and tend to be more readily biodegradable
  5. 5. Vapor pressures and Henry's Law constant, HA, measure liquid—air partitioning. Henry's Law states that the equilibrium partial pressure of a compound in the air above the air/water interface, PA, is proportional to the concentration of that compound in the water, usually expressed as the mole fraction, XA. PA = HAXA Aeration is often employed to strip volatile organic compounds from water and is favored by large HA values. Conversely, volatilization must be controlled or contained in many bioremediation processes. Henry's Law constant is highly temperature sensitive, and temperature changes of 10 °C can give threefold increases in HA.
  6. 6. In soil bioremediation the rate-limiting step is often the desorption of contaminants, since sorption to soil particles and organic matter in soils can determine the bioavailability of organic pollutants. Bioavailability is also an important toxicity characteristic Rates of in situ soil bioremediation are governed by mass transfer of contaminants (desorption and diffusion), the convective—dispersive flux of oxygen and nutrients, and the microbiological content of the soil. On-site testing to determine the rate and extent of biodegradation can be done immediately in consideration of ex situ process feasibility Desorption tests measure the site-specific soil/water partition coefficients for the contaminants of interest.
  7. 7. Measurements of aqueous phase and soil phase concentrations in equilibrium may be sufficient to indicate potential problems with soil sorption Many organic contaminants are hydrophobic, have a low water solubility, and are tightly held to the soil phase. Desorption of such contaminants is likely to be rate-limiting, especially (on ex situ bioremediation where addition of nutrients and microorganisms and careful control of environmental parameters can minimize these potential rate-limiting effects. Failure to bioremediate polyaromatic hydrocarbon (PAH) compounds has been attributed to strong sorption to soil
  8. 8. Surfactants and cosolvents has been investigated in attempts to increase bioavailability of contaminants that are strongly bound to soil. High surfactant concentrations can be required to achieve small increases in solubility 2% surfactant solutions are needed to remove a high percentage of compounds such as higher-ringed PAHs, polychlorinated biphenyls (PCBs), and higher molecular weight hydrocarbons from soils. High surfactant concentrations can be required to achieve small increases in solubility.
  9. 9. Microbiological characterization Measurement of biodegradation rates by indigenous microorganisms is the first step in microbiological characterization These measurements can be complicated by low microbial populations or by the absence of species capable of degrading contaminants. Also, optimum conditions of temperature, oxygen nutrient supply, and contaminant availability due to low solubility and sorption can limit degradation rates, especially in early tests where these limiting factors are not well defined. Main objective of microbial degradation tests is to determine whether the indigenous microorganisms are capable of bioremediation when conditions are optimized, or if inoculation by nonindigenous microorganisms will be required. Bioremediation sites contaminated by 2-sec-buty-4,6- dinitrophenol (dinoseb), the first site was remediated with indigenous microorganisms, second site required inoculation with microorganisms from the first site
  10. 10. Environmental factors Chemical analyses that support process design include measurements of pH, COD, TOC, nitrogen, phosphorus, and iron; and inhibitory, toxic, or essential metals Soil type, clay and organic matter content, and particle size distribution analyses are used, for water, total suspended solids Microbiological analyses supporting process design include BOD, plate counts, and shake flask and/or column degradation studies with indigenous microbes or introduced cultures Bioremediation is usually carried out near neutral pH, although fungi often require an acidic environment Most microorganisms are mesophilic, requiring temperatures in the 25 to 37 °C range
  11. 11. More difficult to optimize are the oxygen and nutrient supply. Most bacteria capable of degrading organic compounds are heterotrophic and require an organic compound as a source of carbon and energy It may be necessary to add a readily metabolizable carbon source such as glucose to maintain cell viability or to increase cell growth and degradation rates. Many xenobiotic compounds can be transformed by cometabolism, in which the transformation does not serve as an energy source for synthesis of cell biomass, which therefore requires a separate carbon source. Sometimes concept of cometabolism is of limited use in bioremediation process analysis and design.
  12. 12. A chemical that is cometabolized at one concentration or in one environment may be mineralized under other conditions Cometabolism can often be accelerated by the addition of a mineralizable compound with a structure analogous to the target compound. This method of analog enrichment has been used to enhance the cometabolism of PCBs by addition of biphenyl, in which the unchlorinated biphenyl serves as a carbon source for microorganisms that cometabolize PCBs with the enzymes induced by biphenyl Degradation is often coupled to growth and microbial mass, so the carbon source that best supports growth also gives the highest rate of degradation Since nitrogen and phosphorus supplies in soil systems are inadequate to support microbial growth and degradation of organic compounds, most bioremediation processes supply these two compounds
  13. 13. Biodegradation can occur aerobically or anaerobically. The most effective biodegradation of hydrocarbon compounds is mediated by aerobic bacteria. Oxygen supply can be a rate-limiting factor, and large-scale aerobic bioremediation of hydrocarbons must include an aeration system as a critical design component. Early bioremediation work focused almost exclusively on aerobic systems, but recent improvements in anaerobic technologies have shown that a wide range of nitroaromatic compounds, chlorinated phenols, PAHs, and PCBs can be degraded as well or better by anaerobic processes In the selection of a microbial system and bioremediation method, some examination of the degradation pathway is necessary. At a minimum, the final degradation products must be tested for toxicity and other regulatory demands for closure.
  14. 14. Predicting degradation rate Degradation rates and equilibrium properties are useful for process design. During wastewater or soil treatment, target pollutants can be degraded or mineralized, volatilized, adsorbed onto effluent solids, or discharged in the liquid effluent. Volatilization and sorption must be minimized so that the principal fate of contaminants in a bioremediation process is biodegradation
  15. 15. Table is a portion of the 196-compound data base used in a fate model to estimate volatile emissions, concentrations of toxic compounds in sludges, and removal of toxic compounds during activated sludge wastewater treatment
  16. 16. The major error in predicting the fate of toxic compounds in wastewater treatment plants was in estimating the value of the biodegradation rate constant. For a compound such as tetrachloroethylene, with a low biodegradation rate constant and a high Henry's Law constant, the principal fate will be volatilization. Published biodegradation rate constants do not provide a good comparative basis for process design since experimental conditions vary greatly. Many unreported factors can influence biodegradation rates, including transport effects, Acclimation of microorganisms to toxic chemicals, inhibition, and cometabolism. Degradation rate constants are used mainly for order-of-magnitude estimates, and other approaches to predicting biodegradability have been developed that are based on physical or chemical properties of compounds.
  17. 17. A measure of hydrophobicity can be used to estimate relative biodegradation rates among homologous compounds. Rates of anaerobic degradation of halogenated aromatic compounds are correlated with the strength of the carbon halide bond that is cleaved in the rate-determining step A promising method for predicting biodegradation rates is the group contribution approach, which estimates biodegradability from the type, location, and interactions of the substituent groups that make up a compound.
  18. 18. An experimental data base that assesses mixed culture biodegradation data for 800 organic compounds is available Good predictions of degradation rates can be obtained for mixed-culture aerobic degradation in processes such as activated sludge treatment. The activated sludge reactor can be optimized with respect to aeration using a model to calculate biodegradation and volatilization rates of organics as functions of aeration rate.
  19. 19. REACTOR OPTIONS Reactor options are determined primarily by the physical properties of the waste and the chemical and biochemical properties of the contaminants. If the waste is found in groundwater, then a continuous supported reactor is desirable A suspended batch reactor is preferable with contaminated soil A polar target compound favors an aerobic reactor, while nonpolar compounds favor anaerobic reactors Groundwater is easily treated in a continuous process in which the microbial biomass must be retained in the reactor by adhering to a support.
  20. 20. Soils are difficult to transport, so batch reactors are favored. Agitation is a critical design parameter required for aeration, cell suspension, and transport of contaminants and nutrients during soil remediation.
  21. 21. Groundwater remediation The technology for the removal of suspended and dissolved contaminants from municipal and industrial wastewater has been well established for wastes that are readily biodegradable under aerobic conditions. After preliminary treatment such as screening, grit removal, and sedimentation, a biological reactor degrades the organic matter in the wastewater during secondary treatment. The reactor is an aerobic fixed film process or a suspended-growth, activated sludge process. Industry relies heavily on treatment of their chemical wastes by publicly owned wastewater treatment facilities. Removal rates of xenobiotic compounds are not well described
  22. 22. Activated sludge reactors Polychlorinated phenols and biphenyls, phenols, phthalates, and PAHs were tested, with average removal rates of 97%. However, higher concentrations can destabilize an activated sludge system. The presence of cyanide, pentachlorophenol, 1,2-dichloropropane, acrylonitrile, phenolics, and ammonia can cause instability in the operation of activated sludge plants Mobile units are often required for the treatment of groundwater pumped out of a contaminated aquifer, or wash water used to remove chemicals from a contaminated soil.
  23. 23. The advantages of an activated sludge design for treating high-organic-content wastewaters that produce a flocculating sludge are lost in these cases. Low microbial growth, poor flocculation, and instability problems can make an activated sludge process very difficult to apply to groundwater treatment Fixed film processes, similar to the trickling filter designs for wastewater treatment, can generally be operated at lower oxygen supply costs, with retention of bacteria in the reactor and a more stable operation.
  24. 24. Fixed film reactors The BioTrol aqueous treatment system is a good example of a fixed film, continuous reactor used successfully for the treatment of groundwater. This reactor is packed with corrugated polyvinyl chloride media on which a bacterial biofilm is grown The combination of groundwater flow, air sparging, and design of the support media facilitates the upward and lateral distribution of water and air in the reactor. Removal of more than 95% pentachlorophenol (PCP) is achieved at a 1.8 h residence time.
  25. 25. Fixed film or attached growth systems require degradative microorganisms with the ability to attach to the surfaces of an inert packing. Fixed film reactors can treat low concentrations of organics in wastewater because of biomass retention, and they can also treat concentrations as high as 1000 ppm. The high biomass loadings of fixed film reactors render them insensitive to shock loadings, that is, to high fluctuations in organic loadings. The outer layers of the biofilm protect the inner cells from the toxicity of high loadings, and the adsorption of contaminants within the biofilm reduces the soluble concentrations of contaminants
  26. 26. The fixed film reactor used for municipal sewage is the trickling filter reactor, with large packing, typically 50 mm diameter stones or synthetic plastic, and downward liquid flow, producing a liquid film over the biofilm and leaving air voidage within the packed bed. Liquid hold-up is low and retention times are short, so that liquid recirculation is necessary to adequately reduce contaminant concentrations. Recirculated effluent is usually taken from a secondary clarifier output, rather than directly from the trickling filter effluent, to minimize the risk of clogging the trickling filter with biomass released from the filter. Wastewater contaminated with xenobiotics is usually treated in a fixed film reactor with upflow through a submerged plastic packing.
  27. 27. Nitrogen and phosphorus may be added to the inflow so that the C: N: P ratio is approximately 100: 5: 1. Reactor cells may be staged, and typically a 2-hour residence time is sufficient to give a high level of contaminant degradation The major advantage of the upflow fixed film reactor versus the trickling bed reactor is the longer and better control of residence time. A good example of a successful application of a fixed film bioreactor is the treatment of a lagoon contaminated with 36ppm pentachlorophenol (PCP), 37 ppm polynuclear aromatics (PNAs), 52ppm solvents, and a total chemical oxygen demand (COD) of 6700 ppm
  28. 28. Anaerobic processes While anaerobic processes for bioremediation of groundwater are uncommon, anaerobic treatment is used for municipal sludge processing and for agricultural and food-processing wastewaters with a high content of biodegradable matter. The resultant methane production provides a valuable energy source. Since energy production is not an option in the treatment of groundwater, anaerobic processes are considered only for compounds recalcitrant to aerobic degradation. Anaerobic microorganisms have great potential for the reductive dehalogenation of multihalogenated aromatic compounds. With increasing levels of halogenation, bioremediation may be feasible only with an initial anaerobic dehalogenation. Once lightly halogenated or nonhalogenated compounds are produced, subsequent degradations are more rapid in an aerobic environment. This suggests an anaerobic-aerobic process for the degradation of compounds that are highly chlorinated or nitrated, or for PAHs.
  29. 29. The anaerobic bioreactor is typically an upflow packed-bed reactor. The reactor is completely filled with liquid except for gas formed during the process. Coarse packing (2 to 6 cm) is used since anaerobic organisms can form large floes instead of thin attached films, causing clogging. Anaerobic reactors have a number of advantages, including high efficiency at low organic loading, high loading capacity, stability with toxic substances, and low energy requirements. COD reductions of 4 to 10kg/m3/day can be obtained with residence times from 4 to 18 h. A two-stage anaerobic-aerobic biofilm reactor process has been used to metabolize hexachlorobenzene (HCB), tetrachloroethylene (PCE), and chloroform (CF) Reductive chlorination is relatively rapid for these compounds and other highly chlorinated compounds such as polychlorinated biphenyls, trichloroethylene, carbon tetrachloride and 1,1,1-trichloroethane. These are some of the most pervasive groundwater contaminants.
  30. 30. 2,4,6-Trichlorophenol can be degraded to 4-chlorophenol in the anaerobic reactor, and the 4-chlorophenol was mineralized in the subsequent aerobic operation. A sequential anaerobic—aerobic process similar to the process shown in Figure 1.1 has been used to degrade nitrobenzene. Under anaerobic conditions nitrobenzene was converted to aniline, a reaction accelerated by the addition of glucose. Complete mineralization of aniline was accomplished in the aerobic stage. Anaerobic—aerobic processes have a high potential for the treatment of pulp mill wastewater containing xenobiotic compounds. The pulp and paper industry is under great pressure to remove chlorophenols, chlorinated aliphatic hydrocarbons, and chlorinated dioxins and furans from wastewater.
  31. 31. Soil remediation With ex situ treatment of contaminated soils, a controlled environment for soil treatment can be maintained. With mixing, nutrient addition, aeration, and other environmental controls, mass transfer rates that typically limit in situ bioremediation can be greatly increased. The disadvantages of ex situ bioremediation are the costs of soil excavation and reactor operation. Thus, ex situ bioremediation is favored by localized, shallow soil contamination.
  32. 32. Landfarming Biological soil treatment by landfarming is a relatively simple and inexpensive method for treating soil contaminated by compounds that are readily degraded Aerobically. Contaminated soil is evacuated and usually treated in pits lined with a high-density synthetic or clay liner (Figure 1.2). Perforated pipes can be placed in a layer of sand between the liner and contaminated soil to collect drainage that can be separately treated or recycled. Alternatively, the treatment area can be graded to a sump where runoff is collected. Aeration can be accomplished by tilling the soil or with forced aeration. With tillage, soil is usually spread to a depth of 15 to 50 cm. For forced aeration, soil is placed above slotted PVC pipes that are manifolded to a blower (Figure 1.2). Nutrients may be added and pH adjusted. Phosphorus is typically added as a salt of phosphoric acid and nitrogen as an ammonium salt, a nitrate salt, or urea. Nutrient requirements are estimated from contamination concentrations or laboratory treatability tests, and water is added or sprayed onto the soil to maintain optimum moisture.
  33. 33. Landfarming has been widely implemented at petroleum production and storage sites, and at sites contaminated with polynuclear aromatic residues (PNAs) or pentachlorophenol (PCP). The efficacy and design of land treatment for petroleum-contaminated soil has been studied in controlled laboratory experiments. The effects of soil type, fuel type, contamination level, and temperature on the kinetics of fuel disappearance were determined for a land treatment process using lime to raise the pH to 7.5-7.6, addition of 60 µ mol of N as NH4NO3 and 5 µ mol of P as K2HPO4, and tilling Disappearance of hydrocarbons was maximal at 27 °C. The C6 to C9 components of gasoline were removed primarily by evaporation. The C10 to C 11 components were removed by biodegradation. The medium distillates responded well to bioremediation and increased in persistence in this order: jet fuel, heating oil, and diesel oil. Biodegradation can be accelerated in a prepared bed reactor with forced aeration. These reactors are used at many Superfund sites for bioremediation of PAHs and BTEX (benzene, toluene, ethylbenzene, and xylene).
  34. 34. A potential problem in soil treatment is the residual contaminant concentration that is slowly or not noticeably degraded by soil microorganisms. This nonbioavailable fraction is recognized by its slow transport out of soil micropores. Slow desorption can result from entrapment in intraparticle micropores, especially in the presence of organic matter, which can tightly bind nonionic organic contaminants. Soil leaching experiments can demonstrate whether contaminants are slowly Released from the soil matrix, and the addition of surfactants can increase the Desorption rate. However, the mixing and surfactant addition that may be necessary to release contaminants increase the cost of landfarming and favor the use of more intensive bioremediation methods such as slurry reactors.

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