Biodegradation of Residual Dense Nonaqueous-Phase Liquid Tetrachloroethene: Effects on Mass Transfer

The mass emissions rate of contaminants from nonaqueous-phase liquids (NAPLs) is a driving factor in remediation efforts, whether those efforts are designed to remove, transform, or stabilize the entrapped NAPL or down-gradient aqueous concentrations. Enhancement of mass flux from NAPL source zones has been previously reported in the presence of microbial reductive dechlorination activity in systems containing NAPL with a low proportion of tetrachloroethene (PCE) or a low residual saturation (e.g., 2%). The results reported here demonstrate reductive dechlorination of PCE at residual saturations of 35%, obtained under two different column flow velocities and NAPL configurations. Mass flux in biotic columns was approximately 45% greater than that in uninoculated columns, due to both the presence of daughter products and higher concentrations of PCE in the effluent from biotic columns. Daughter product concentrations were greater in columns with NAPL emplaced only in the lower quarter compared to those with NAPL throughout, and in columns run at the slower velocity. The elevated PCE concentrations in biotic column effluents suggest the influence of microbially generated surfactants, which was supported by surface tension measurements. These results demonstrate the potential significance of bioactivity within NAPL source zones on NAPL longevity and down-gradient aqueous concentrations.     

Feasibility of in situ implementation of vibrations to mobilize NAPL ganglia

A growing number of incidents of nonaqueous phase liquid (NAPL) spills in the recent past have warranted development of innovative and cost‐effective remediation technologies. Of particular concern is the entrapment of LNAPL (NAPL lighter than water) in the form of ganglia or blobs near the water table by virtue of strong capillary forces. The residual ganglia are the leftover component after pumping of free product and typically occupy 20 to 60% of the pore space. Mobilization of these ganglia would require unrealistically high hydraulic gradients and is often beyond the scope of pump‐and‐treat processes. This paper deals with the feasibility of in situ implementation of localized vibrations for controlled mobilization and collection of LNAPL ganglia. Specifically, the paper covers three components. First, the principles involved in soil‐water‐NAPL interactions under the influence of vibrations are discussed. The effects of vibrations on a soil‐NAPL‐water medium are postulated in terms of pore structure and relative density changes, changes in the permeability of the medium as a result of the changes in pore structure, and development of cyclic pore pressures. Second, results from bench‐scale experiments are presented that involved vibrating contaminated soils under the simultaneous influence of hydraulic gradients. A bench‐scale model consisting of a vibrator integrated with an injection and pumping system was found to be successful in these experiments. The results from the tests showed that up to 85% removal of ganglia can be achieved using this process. Third, the principles involved in the vibratory mobilization were applied to in situ conditions to develop a methodology to estimate the zone of influence of the process. The analogy between this process and an existing geotechnical process known as vibroflotation is exploited to demonstrate the methodology.     

Microemulsion‐mediated removal of residual gasoline from soil columns

In situ pumping of micellular solutions of surfactant (S) and cosurfactant (CoS) in water (W) through contaminated soils or aquifers offers potential for enhanced remediation of residual nonaqueous‐phase liquids (NAPLs). Extremely low interfacial tension generated between a W/S/CoS mixture and residual NAPL in soil pores may initially mobilize the NAPL, which is then transported temporarily as a separate phase by immiscible displacement. The NAPL is then solubilized by micro‐emulsification as the W/S/CoS mixture forms a stable W/S/CoS/NAPL micro‐emulsion that undergoes miscible displacement through the pore space. This remediation technique was tested under laboratory conditions by sequentially flushing a saline solution and a W/S/CoS mixture through columns of a sandy soil recently contaminated with residual leaded gasoline (LG). Prior to the flushings, the soil was initially contaminated by applying a W/S/CoS/LG microemulsion. A simple conceptual transport model with kinetic clogging of soil pores adequately described breakthrough curves for gasoline and organolead in the soil columns.     

Bacterial Adhesion to Soil Contaminants in the Presence of Surfactants

It has been proposed that addition of surfactants to contaminated soil enhances the solubility of target compounds; however, surfactants may simultaneously reduce the adhesion of bacteria to hydrophobic surfaces. If the latter mechanism is important for the biodegradation of virtually insoluble contaminants, then the use of surfactants may not be beneficial. The adhesion of a Mycobacterium strain and a Pseudomonas strain, isolated from a creosote-contaminated soil, to the surfaces of highly viscous non-aqueous-phase liquids (NAPLs) was measured. The NAPLs were organic material extracted from soils from two creosote-contaminated sites and two petroleum-contaminated sites. Cells suspended in media with and without surfactant were placed in test tubes coated with an NAPL, and the percentages of cells that adhered to the surface of the NAPL in the presence and absence of surfactant were compared by measuring optical density. Test tubes without NAPLs were used as controls. The presence of either Triton X-100 or Dowfax 8390 at a concentration that was one-half the critical micelle concentration (CMC) inhibited adhesion of both species of bacteria to the NAPLs. Both surfactants, when added at concentrations that were one-half the CMCs to test tubes containing previously adhered bacteria, also promoted the removal of the cells from the surfaces of the NAPL-coated test tubes. Neither surfactant was toxic to the bacteria. Further investigation showed that a low concentration of surfactant also inhibited the growth of both species on anthracene, indicating that the presence of a surfactant resulted in a reduction in the uptake of the solid carbon source.     

Vacuum‐enhanced recovery of water and NAPL: Concept and field test

Many hydrocarbon‐contaminated soils contain nonaqueous phase liquid (NAPL) following releases from facilities such as underground storage tanks and pipelines. The recovery of free product by pumping from extraction wells or trenches is often an essential prerequisite step prior to further remedial actions. Vacuum‐enhanced NAPL recovery (sometimes referred to as dual‐phase extraction or bioslurping) has attracted recent attention because it offers a means to increase NAPL recovery rates compared with conventional methods, and to accomplish dewatering, while also facilitating vapor‐based unsaturated zone cleanup. A conceptual model is presented that recognizes the effects that vacuum‐enhanced recovery has on soil water and NAPL, with a focus on liquid residing at negative gage pressures and therefore lacking sufficient potential energy to flow into a conventional recovery well or trench. The imposition during vacuum‐enhanced recovery of subatmospheric pressures within the subsurface can reduce the required potential energy (i.e., the entry suction), allowing liquid to be extracted that hitherto had not been able to flow into the well; moreover, it induces both pneumatic and hydraulic gradients toward the vacuum source that increase the rate of water and NAPL recovery. This conceptual model was tested during a 3‐week‐long pilot study at a South Carolina industrial site at which diesel fuel had been discovered in a saprolite formation. During Phase 1 of the pilot study, conventional recovery (liquid only) was carried out from a well screened at the water table, while during Phase 2 dual‐phase extraction was performed at the same well. The application of 27 kPa vacuum resulted in an increase in NAPL recovery from negligible (Phase 1) to approximately 6.6 l/d (Phase 2), with a concurrent increase in water recovery from approximately 190 to 760 l/ d. Neutron moisture probe observations revealed that vadose‐zone liquids underwent redistribution toward the extraction well in response to the onset of Phase 2, also in accordance with the conceptual model. An understanding of soil physical relationships is crucial to the successful application of these and other in situ soil remediation technologies.     

A Preliminary Laboratory Investigation of PCB Flux from Dredge Resuspensions and Residuals

A preliminary laboratory investigation was conducted to understand the relative contributions of major dredge resuspension and residual processes on the releases of polychlorinated biphenyl (PCB) contaminants from sediments to water column. Sediments from New Bedford Harbor were used as test samples. Six sets of experiments were run for simulated resuspension and residual scenarios. During the experiments, water above the sediments was recirculated by peristaltic pumping or orbital shaking and the levels of two PCBs, Aroclor 1248 (PCB-1248) and Aroclor 1254 (PCB-1254), were monitored for 15 days. Analysis of the model predicted data indicated that resulting water column PCB concentrations differed with sediment surface, residual, and resuspension type. Highest PCB water column concentrations were observed for a condition which used a settled fluff from thin sediment slurry as a residual source and the column water was recirculated by orbital shaking. Lowest water column PCB levels were observed for a thick sediment deposit placed over clean sand. The PCB levels in the water column for all six simulated conditions were several orders higher than the USEPA ambient water quality criteria concentrations for aquatic environment and human consumption.     

Use of surfactants and slurrying to enhance the biodegradation in soil of compounds initially dissolved in nonaqueous-phase liquids

A study was conducted to find means of enhancing the biodegradation of hydrophobic organic compounds in nonaqueous-phase liquids (NAPLs). The effects of surfactants, identity of the NAPL and agitation was investigated. When present in NAPLs, phenanthrene, di-(2-ethylhexyl) phthalate (DEHP) and biphenyl were mineralized slowly in soil. Addition of Triton X-100 or Alfonic 810-60 did not enhance the degradation of phenanthrene initially in hexadecane or dibutyl phthalate. Slurrying the soil increased the rate and extent of mineralization of phenanthrene initially in hexadecane but not in dibutyl phthalate. Addition of either of the two surfactants to the slurries did not promote the transformation. Triton X-100, Alfonic 810-60 and Tergitol 15-S-9 below their critical micelle concentrations increased the rate and sometimes the extent of mineralization in soil slurries of phenanthrene initially in 2,2,4,4,6,8,8-heptamethylnonane, but other surfactants were not stimulatory. Slurrying the soil promoted the initial mineralization of DEHP initially in dibutyl phthalate, and Alfonic 810-60 and Triton X-100 further stimulated the rate and extent of degradation in the slurries. Alfonic 810-60 increased the extent of mineralization in slurries of biphenyl in hexadecane but not in dibutyl phthalate, cyclohexane, kerosene or two oils. Little mineralization of biphenyl or DEHP initially in dibutyl phthalate occurred in soil slurries, but Tween 80, Tergitol 15-S-40 and Tergitol 15-S-9 increased the extent of mineralization. However, vigorous agitation of the slurries of soil acclimated to DEHP or the use of small volumes of the NAPL resulted in marked enhancement of the degradation. Thus, biodegradation of constituents of NAPLs in soil can be increased by the use of some surfactants, slurrying or intense agitation, but the effect will vary with the NAPL and the constituents.     

The Effectiveness of Surfactants for Remediation of Organic Pollutants in the Unsaturated Zone

In laboratory experiments performed to evaluate the efficiency of surfactant flushing for remediation of non-aqueous phase liquid (NAPL) in the unsaturated zone, less than 0.001% of the original mass of tetra-chloroethylene (PCE) remained in the column after 15 pore volumes of a 1% sorbitan monooleate solution or after 7 pore volumes of a 1% Ethomid O/17 solution were passed through the columns. Mass removed as dissolved phase in the effluent accounted for more than 90% of PCE removed; the remainder was lost by volatilization. To determine the influence of parameters that may affect the remediation process, column tests were repeated with different values of parameters, including grain size, application rate, surfactant type, surfactant concentration, and solution viscosity. The results from the column experiments were simulated with the two-dimensional finite element computer code for multiphase flow and transport, MOTRANS. Results of the simulation were similar to those from the experiments. Both experimental and modeling results suggest that surfactant flushing has a great potential to remove mass from NAPL in the unsaturated zone.     

Naphthalene biodegradation from non-aqueous-phase liquids in batch and column systems: comparison of biokinetic rate coefficients

The kinetics of microbial degradation of naphthalene from a two-component non-aqueous-phase liquid (NAPL) coated onto uniformly sized nonporous particles were evaluated in a completely mixed batch reactor (CMBR) system and in flow-through column systems to examine the differences in the biodegradation kinetic coefficients, micro(max), the maximum specific growth rate coefficient, and K(s), the half saturation constant in the two systems. The values of these coefficients were estimated by nonlinear least-squares regression of the naphthalene mineralization profiles obtained from both CMBR and column biodegradation experiments. The results show that the range of values for micro(max) and K(s) obtained from column systems are very similar to the range of values obtained from CMBR systems. This suggests that coefficients estimated from CMBR or column systems are equally applicable for modeling studies. The presence of microorganisms and the development of biofilms at the NAPL-water interface reduced the mass transfer rates of naphthalene from the NAPL by 60% in CMBR and by 70% in column systems. If such changes in mass transfer coefficients are not accounted for, significantly erroneous values of biokinetic coefficients may be obtained.     

Prediction of leachate concentrations in petroleum‐contaminated soils

The efficacy of cleanup methods in reducing gasoline contamination at spill sites is typically determined by measuring benzene, toluene, xylene (BTX), and total petroleum hydrocarbon (TPH) concentrations in soil samples. Although these values may provide a direct measurement of soil contamination, they may not be indicative of what is transferred to percolating water. This study addresses this issue by measuring TPH, toluene, m‐ and p‐xylene, and naphthalene levels in gasoline‐contaminated soil columns before and after forced‐air venting and relating these values to the aqueous‐phase concentrations measured when water is percolated through the same columns.

Sandy soils with and without organic matter were packed into glass columns. The soils were brought to residual water and residual gasoline saturations by applying a vacuum to a ceramic pressure plate at the column bottom. Venting was performed by passing clean, moist air through the columns. The columns were subsequently leached under unsaturated conditions.

Soil samples were taken from the bottom of the columns upon completion of the venting or leaching phases of the experiments. Toluene, m‐ and p‐xylene, naphthalene, and TPH values were measured in soil samples extracted with either freon or methanol. Aqueous phase concentrations of these compounds were predicted using measured soil concentrations and either Raoult's law or organic matter‐water and fuel‐water partitioning theory (Boyd and Sun, 1990). The predicted results were compared with measured leachate concentrations from the same columns.

Mole fractions estimated from soil concentrations and TPH values used in Raoult's law gave good predictions of aqueous phase concentrations for compounds that had a high mole fraction in the residual nonaqueous phase liquid (NAPL). For compounds at low concentrations in the residual NAPL, an approach using a distribution coefficient that accounted for both the organic matter and residual NAPL in the soil provided better estimates than those based on Raoult's law.     

Influence of a nonaqueous phase liquid (NAPL) on biodegradation of phenanthrene

A series of batch reactor experiments was carried out to examine the effect of a nonaqueous phase liquid (NAPL) on the biodegradation of a hydrophobic solute. A mathematical program model that describes physical processes of solute solubilization and partitioning between the NAPL and aqueous phases as well as microbial degradation and oxygen utilization was used to analyze the test data. The model calculates the cumulative changes in concentration of substrate, cell mass, carbon dioxide, and dissolved oxygen as a function of time. The equations incorporate the effects of solute solubilization, partitioning, biodegradation, as well as oxygen availability. Hexadecane was used as the model NAPL and was not biodegraded in the timeframe of the experiments performed. The model solute was the polyaromatic hydrocarbon, phenanthrene. In agreement with several previous studies, experimental measurements showed that hexadecane increased rates of mineralization of 15 mg phenanthrene when present at low mass but decreased rates at high mass. Model results suggest that partitioning of the phenanthrene into the hexadecane phase limits bioavailability at high NAPL mass. Further the model suggests that mineralization rates were higher with the low NAPL mass because aqueous phenanthrene concentrations were higher in those treatments from ca. 20 to 40 h than in other treatments. Finally, experiments showed that the presence of hexadecane, at all masses tested, resulted in a lower cell yield, effectively increasing the amount of CO₂ produced during the experiment. Model results suggest that this is due to changes in phenanthrene metabolism that are induced by the presence of the hexadecane phase. Model studies aimed at increasing rates of biodegradation by modifying operating conditions are described along with practical approaches to implementing these modifications.     

Effect of surfactants on separate hydrolysis fermentation and simultaneous saccharification fermentation of pretreated lodgepole pine

The effects of surfactants addition on enzymatic hydrolysis and subsequent fermentation of steam exploded lodgepole pine (SELP) and ethanol pretreated lodgepole pine (EPLP) were investigated in this study. Supplementing Tween 80 during cellulase hydrolysis of SELP resulted in a 32% increase in the cellulose‐to‐glucose yield. However, little improvement was obtained from hydrolyzing EPLP in the presence of the same amount of surfactant. The positive effect of surfactants on SELP hydrolysis led to an increase in final ethanol yield after the fermentation. It was found that the addition of surfactant led to a substantial increase in the amount of free enzymes in the 48 h hydrolysates derived from both substrates. The effect of surfactant addition on final ethanol yield of simultaneous saccharification and fermentation (SSF) was also investigated by using SELP in the presence of additional furfural and hydroxymethylfurfural (HMF). The results showed that the surfactants slightly increased the conversion rates of furfural and HMF during SSF process by Saccharomyces cerevisiae. The presence of furfural and HMF at the experimental concentrations did not affect the final ethanol concentration either. The strategy of applying surfactants in cellulase recycling to reduce enzyme cost is presented. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Microbial degradation of phenanthrene by addition of a sophorolipid mixture

The influence of sophorolipids on microbial degradation of poorly soluble phenanthrene in liquid and soil suspension culture was evaluated in the work presented. Experiments were carried out in two parts. In the first part, important basic physico-chemical characteristics of the biosurfactant and the pollutant used were determined. The critical micelle concentration (CMC) and the solubilization ratio of the biosurfactant were found to be in a good range compared with synthetic surfactants. Also, a reduction to 71% of the detectable amount of phenanthrene was measured within 4 d in soil suspension without any biotic influence. In the second part, culture experiments were done with Sphingomonas yanoikuyae, the bacterium used throughout the work presented here with the aim to assess the toxicity of the sophorolipids on these bacteria and the effect of the surfactant on biodegradation. In exponential growth tests, no toxicity up to 1 g l(-1) sophorolipids could be detected, whereas in an agar plate test, slight growth hindrance was measured at a lower concentration of 250 mg l(-1). The above mentioned data were important for planning further experiments. In the following cultivations with liquid and soil suspension media, enhancements of the biodegradation with surfactant addition were measurable. Fluorescence measurements showed that this effect was not due to an increasing biomass, but to an augmentation of bioavailability of the phenanthrene through increasing the apparent dissolved pollutant. Surfactant addition had the consequence of decreasing the residual detectable pollutant concentration (after 36 h 0.5 compared with 2.3 mg l(-1) soil suspension) and increasing the maximal degradation rate (127 instead of 80 mg l(-1) soil suspension x 10 h). Therefore, the two main problems of biological soil remediation techniques, longer process time and residual pollutants, may be solved by the use of surfactants.     

Effect of rhamnolipid on biodegradation of hydrocarbons in non-aqueous-phase liquid (NAPL)

Aliphatic and aromatic hydrocarbons are environmental pollutants of serious concern. Their bioavailability is the major limiting factor that makes the bioremediation process slow. Therefore, the present study focuses on biodegradation of non-aqueous-phase liquids (NAPL) by a halophilic consortium (Pseudomonas aeruginosa and Escherichia fergusonii) in presence of rhamnolipid as well as a rhamnolipid-producing Pseudomonas aeruginosa AMB AS7. The study was performed in microcosms, and the residual hydrocarbons after degradation were estimated by gas chromatography. It was found that the degradation of hydrocarbons in NAPL was more in presence of rhamnolipid in comparison with their biotic controls. However, among NAPL, the degradation of phenanthrene (37.5%) and octadecane (47.8%) was found to be more by co-culture of halophilic consortium and rhamnolipid-producing P. aeruginosa AMB AS7. Denaturing gradient gel electrophoresis was performed to determine the viability of different bacterial strains (halophilic and rhamnolipid-producing bacterial strain). Besides, the results also revealed that during NAPL degradation, the cell surface hydrophobicity (CSH) of halophilic consortium increased from 9.12% to 69.55% when added with 100 mg/L of rhamnolipid, whereas CSH of rhamnolipid-producing P. aeruginosa AMB AS7 was constant at 31.9%, even though it produced about 271.8 mg/L of rhamnolipid.     

Alteration in cell surface properties of <Emphasis Type="Italic">Burkholderia</Emphasis> spp. during surfactant-aided biodegradation of petroleum hydrocarbons

Chemical surfactants may impact microbial cell surface properties, i.e., cell surface hydrophobicity (CSH) and cell surface charge, and may thus affect the uptake of components from non-aqueous phase liquids (NAPLs). This work explored the impact of Triton X-100, Igepal CA 630, and Tween 80 (at twice the critical micelle concentration, CMC) on the cell surface characteristics of Burkholderia cultures, Burkholderia cepacia (ES1, aliphatic degrader) and Burkholderia multivorans (NG1, aromatic degrader), when grown on a six-component model NAPL. In the presence of Triton X-100, NAPL biodegradation was enhanced from 21% to 60% in B. cepacia and from 18% to 53% in B. multivorans. CSH based on water contact angle (50–52°) was in the same range for both strains while zeta potential at neutral pH was −38 and −31 mV for B. cepacia and B. multivorans, respectively. In the presence of Triton X-100, their CSH increased to greater than 75° and the zeta potential decreased. This induced a change in the mode of uptake and initiated aliphatic hydrocarbon degradation by B. multivorans and increased the rate of aliphatic hydrocarbon degradation in B. cepacia. Igepal CA 630 and Tween 80 also altered the cell surface properties. For B. cepacia grown in the presence of Triton X-100 at two and five times its CMC, CSH increased significantly in the log growth phase. Growth in the presence of the chemical surfactants also affected the abundance of chemical functional groups on the cell surface. Cell surface changes had maximum impact on NAPL degradation in the presence of emulsifying surfactants, Triton X-100 and Igepal CA630.     

Biodegradation kinetics of naphthalene in nonaqueous phase liquid-water mixed batch systems: comparison of model predictions and experimental results

A model is formulated to describe dissolution of naphthalene from an insoluble nonaqueous phase liquid (NAPL) and its subsequent biodegradation in the aqueous phase in completely mixed batch reactors. The physicochemical processes of equilibrium partitioning and mass transfer of naphthalene between the NAPL and aqueous phases were incorporated into the model. Biodegradation kinetics were described by Monod's microbial growth kinetic model, modified to account for the inhibitory effects of 1,2-naphthoquinone formed during naphthalene degradation under certain conditions. System parameters and biokinetic coefficients pertinent to the NAPL-water systems were determined either by direct measurement or from nonlinear regression of the naphthalene mineralization profiles obtained from batch reactor tests with two-component NAPLs comprised of naphthalene and heptamethylnonane. The NAPLs contained substantial mass of naphthalene, and naphthalene biodegradation kinetics were evaluated over the time required for near complete depletion of naphthalene from the NAPL. Model predictions of naphthalene mineralization time profiles compared favorably to the general trends observed in the data obtained from laboratory experiments with the two-component NAPL, as well as with two coal tars obtained from the subsurface at contaminated sites and composed of many different PAHs (polycyclic aromatic hydrocarbon compounds). The effects of varying the NAPL mass and the naphthalene mole fractions in the NAPL are discussed. It was observed that the time to achieve a given percent removal of naphthalene does not change significantly with the initial mass of naphthalene in a fixed volume of the NAPL. Significant changes in the mineralization profiles are observed when the volume (and mass) of NAPL in the system is changed.     

Esterification using a liquid lipase to remove residual free fatty acids in biodiesel

Lately, the price of liquid formulated lipase enzymes, usable in biodiesel production, has been significantly reduced. This enables one-time use of these enzymes for transesterification, and the process is used industrially. However, the process suffers a drawback by leaving 2−3 % free fatty acids in the crude biodiesel, which reduces the profitability. This article discusses a novel enzymatic FFA esterification reaction utilizing liquid lipase B from Candida antarctica (CALB) along with glycerol at low water concentrations to eliminate the residual FFA. The reaction setup was found able to reduce the free fatty acid concentration to within biodiesel specifications of < 0.25 wt.% FFA. Additionally, two alternative process setups are proposed, which were both found viable through a combination of experiments and simulations, and can be developed into full-scale processes. The resulting two-step enzymatic biodiesel process - transesterification followed by esterification - provides a potential process layout for the industrial production of biodiesel.     

Physical properties of oil-particle aggregate (OPA)-containing sediments

ABSTRACT

Sediments composed of oil-particle aggregates (OPAs) have unique physical characteristics. These in situ deposited sediments develop at locations where a continual or nearly continual discharge of non-aqueous phase liquids (NAPLs) have occurred, or are occurring through time. The NAPL discharged into the surface water body interacts with suspended particles in the water column. The particles adhere to the suspended NAPL, which generally is in the form of a bead, and produce a discrete aggregate. As the aggregate grows in response to additional particle adherence, the density of the unit increases and deposition occurs. The resulting sediment consists of a collection of discrete OPAs that form a network with small pores, where oil is tightly bound and/or contained. Porosity, water content, and dry bulk density measurements indicate the sediment formed by OPA deposition is physically unique. Although the sediment consists of a very open pore structure, the pore openings are relatively small, typically being less than 5 microns in diameter. These small pores inhibit fluid movement. Results of physical property testing suggest the OPA structure is retained upon deposition. Although the sediment contains NAPL, this original OPA structure inhibits the oil beads from coalescing, which would enable NAPL flow.     

Seasonal sedimentation trends in a mesotrophic lake: Influence of diatoms and implications for phosphorus dynamics

To quantify the extent to which biomass and phosphorus in particular is removed from an aquatic system via sedimentation as well as to identify factors that influence sedimentation of nutrient elements, various characterizations of suspended and settling particulate matter were made in Trout Lake, Wisconsin, USA. The proportion of water column phosphorus reaching sediment traps showed a seasonal component with a minimum during late summer. Biogenic silicon analysis indicated that relatively high rates of phosphorus removal were associated with the sedimentation of siliceous algae (diatoms) from the water column. Estimates of the impact of nutrient removal through diatom sedimentation indicate that this process can reduce primary production by decreasing the amount of nutrient remineralization in the water column during the stratified period.     

Thermal variation of organic fluid properties and impact on thermal remediation feasibility

Preliminary evaluations of the feasibility of thermal remediation techniques such as hot water flooding and steam flushing can be conducted with a knowledge of the influence of temperature on organic fluid properties such as interfacial tension, density, viscosity, solubility, vapor pressure, and Henry's constant. Relationships quantifying the effect of these fluid properties on organic removal and empirical equations for predicting the thermal variation of fluid properties are reviewed. Methods for measuring these properties are reviewed and applied to the characterization of perchloroethylene and a transformer oil. The importance of various removal mechanisms associated with thermal remediation is evaluated for these two fluids. Perchloroethylene solubilities increased by approximately 60% as temperature increased from 30°C to 90°C, suggesting that increased solubilization at higher temperatures would not be a significant removal mechanism. Viscosity and density reductions for both NAPLs were small, indicating that hydraulic displacement of NAPL would not be greatly enhanced with hot water or steam flushing. Interfacial tension decreases were not great enough to cause concem about downward remobilization of pools and residual zones of NAPLs. Capillary numbers for hot water flooding decreased for both NAPL, suggesting that hot water flooding would not enhance hydraulic removal of entrapped NAPL.