Land Treatment Unit Research Articles

A full-scale bioremediation study of diesel fuel-contaminated soil: the effect of plant species and soil amendments

This article presents a comprehensive on-site bioremediation of an excavated diesel fuel-contaminated soil aided by various soil amendments and plant species. In the first 125 days, the excavated soil was placed in a land treatment unit, mixed with compost, and seeded with white clover (Trifolium repens). In the next 155 days, the land treatment unit was re-established and divided into four experimental plots. Experimental plots 2 and 3 were seeded with a mixture of plant seeds (Trifolium alexandrinum, Fagopyrum esculentum Moench, Trifolium incarnatum, Phacelia tanacetifolia, Sinapis alba, Trifolium repens), while experimental plots 1 and 4 were left without seeded vegetation. Moreover, a zeolite and an Ascophyllum nodosum-based biostimulant were added to experimental plots 3 and 4. The objectives were to select the most beneficial plant species for the plant-based bioremediation process, to evaluate applicability of different soil amendments for an enhanced hydrocarbon biodegradation, and to study their effects on the microbial community in soil. Our results showed an overall reduction in hydrocarbon pollution by more than 95% within 280 days. The rates of hydrocarbon degradation and changes in the microbial population were not affected by the presence of the zeolite and the biostimulant. In addition, the use of different plant species did not have a statistically significant effect on hydrocarbon degradation but affected microbial population dynamics, confirming stabile and diverse indigenous hydrocarbon-degrading microbial community in the native soil.

Bioremediation of engine-oil contaminated soil using local residual organic matter.

Soil remediation industries continue to seek technologies to speed-up treatment and reduce operating costs. Some processes are energy intensive and, in some cases, transport can be the main source of carbon emissions. Residual fertilizing materials (RFM), such as organic residues, have the potential to be beneficial bioremediation agents. Following a circular economy framework, we investigated the feasibility of sourcing RFMs locally to reduce transport and assess possible bioremediation efficiency gains. RFMs were recruited within 100 km of the treatment site: ramial chipped wood (RCW), horse manure (MANR) and brewer spent grain (BSG). They were added to the land treatment unit’s baseline fertilizer treatment (FERT, “F”) to measure if they improved the remediation efficiency of an engine oil-contaminated soil (7,500 ± 100 mg kg−1). Results indicate that MANR-F was the only amendment more effective than FERT for petroleum hydrocarbons (PHC) reduction, while emitting the least CO2 overall. RCW-F was equivalent to FERT but retained more moisture. Although BSG contributed the most nitrogen to the soil, BSG-F retained excessive moisture, emitted more volatile organic compounds, contained less soil O2, and was less effective than the baseline treatment. Significantly more of the C16–C22 fraction was removed (63% ± 22%) than all other fractions (C22–C28, C28–C34, C34–C40), which were equally removed. Microbial community-level physiological profiling was conducted with Biolog Ecoplates™, and catabolic diversity differed between treatments (utilization rates of 31 carbon sources). MANR-F has the potential to increase PHC-remediation speed and efficiency compared to inorganic fertilizer alone. Other RFM promote moisture retention and diverse microbial catabolic activity. A variety of RFM are present across the globe and some can offer low-cost amendments to boost remediation efficiency, while reducing treatment time compared to traditional fertilizer-only methods.

Genotoxicity Assessment of Wood-Preserving Waste–Contaminated Soil Undergoing Bioremediation

ABSTRACT Bioremediation represents one of the most cost-effective technologies for treatment of petroleum hydrocarbons in contaminated surface soils. A major concern for regulatory agencies when evaluating bioremediation is how to determine acceptable levels for residual organics in soil. Although guidelines have been developed for some organics in soil, limited information is available to define acceptable levels of the metabolites of biological degradation. The products of oxidative degradation are likely to be more water soluble and may also be more toxic. The purpose of the current study was to monitor changes in compound concentration and genotoxicity in soils undergoing bioremediation. The site selected for this study was a former wood-preserving site in the northwestern United States. Soil samples were collected over a 4-year period from two 6075-m2 land treatment units. Conditions for biodegradation were enhanced by the addition of water and nutrients, as well as by frequent tilling to add oxygen. Due to the location of the facility, the temperature was conducive to a more rapid rate of biodegradation for approximately 6 months per year. Soil samples were collected using a grid system and solvent extracted. Polycyclic aromatic hydrocarbons were quantified in soil extracts using gas chromatography–mass spectrometry (GC/MS), and genotoxicity measured using the Salmonella/microsome assay. After 2 years of treatment, concentrations of total and carcinogenic polycyclic aromatic hydrocarbons (PAHs) were reduced to approximately 10% the concentration in the untreated soil. However, the mean weighted activity of the untreated soil was 293 net revertants per g soil, whereas the extracts of soil collected after 2 years induced a mean weighted activity of 325 net revertants per g soil. Thus, although biodegradation clearly reduced the concentration of total and carcinogenic PAHs in the surface soils, the results from the genotoxicity bioassay indicate that there was a lag in the reduction of mutagenicity in treated soils.

Biodegradation of PAHs and PCBs in Soils and Sludges

Results from a multi-year, pilot-scale land treatment project for PAHs and PCBs biodegradation were evaluated. A mathematical model, capable of describing sorption, sequestration, and biodegradation in soil/water systems, is applied to interpret the efficacy of a sequential active–passive biotreatment process of organic chemicals on remediation sites. To account for the recalcitrance of PAHs and PCBs in soils and sludges during long-term biotreatment, this model comprises a kinetic equation for organic chemical intraparticle sequestration process. Model responses were verified by comparison to measurements of biodegradation of PAHs and PCBs in land treatment units; a favorable match was found between them. Model simulations were performed to predict on-going biodegradation behavior of PAHs and PCBs in land treatment units. Simulation results indicate that complete biostabilization will be achieved when the concentration of reversibly sorbed chemical (SRA) reduces to undetectable levels, with a certain amount of irreversibly sequestrated residual chemical (SIA) remaining within the soil particle solid phase. The residual fraction (SIA) tends to lose its original chemical and biological activity, and hence, is much less available, toxic, and mobile than the “free” compounds. Therefore, little or no PAHs and PCBs will leach from the treatment site and constitutes no threat to human health or the environment. Biotreatment of PAHs and PCBs can be terminated accordingly. Results from the pilot-scale testing data and model calculations also suggest that a significant fraction (10–30%) of high-molecular-weight PAHs and PCBs could be sequestrated and become unavailable for biodegradation. Bioavailability (large Kd, i.e., slow desorption rate) is the key factor limiting the PAHs degradation. However, both bioavailability and bioactivity (K in Monod kinetics, i.e., number of microbes, nutrients, and electron acceptor, etc.) regulate PCBs biodegradation. The sequential active–passive biotreatment can be a cost-effective approach for remediation of highly hydrophobic organic contaminants. The mathematical model proposed here would be useful in the design and operation of such organic chemical biodegradation processes on remediation sites.

Humic Acid Toxicity in Biologically Treated Soil Contaminated with Polycyclic Aromatic Hydrocarbons and Pentachlorophenol

Contaminated soil from a land treatment unit at the Libby Groundwater Superfund Site in Libby, MT, was amended with 14C pyrene and incubated for 396 days to promote biodegradation and the formation of soil-associated bound residues. Humic and fulvic acids were extracted from the treated soil microcosms and analyzed for the presence of pyrene residues. Biologic activity promoted 14C association with the fulvic acid fraction, but humic acid-associated 14C did not increase with biologic activity. The Aboatox flash toxicity assay was used to assess the toxicity of humic and fulvic acid fractions. The fulvic acid gave no toxic response, but the humic acid showed significant toxicity. The observed toxicity was likely associated with pentachlorophenol, a known contaminant of the soil that was removed by solvent extraction of the humic acid and that correlated well with toxicity reduction.

Effect of Oil on Polychlorinated Biphenyl Phase Partitioning during Land Biotreatment of Impacted Sediment

This study evaluated the partitioning of polychlorinated biphenyls (PCBs) during long-term, passive, land biotreatment of PCB-impacted industrial lagoon sediments. Over six years under field conditions, two land treatment units (LTUs) experienced 40% total PCB reductions from initial concentrations of 8–10 mg∕kg . A third LTU with 113 mg∕kg initial total PCBs showed little reduction over five years. In each unit throughout the study, oil concentrations declined at a rate greater than that for PCBs. Measured aqueous equilibrium concentrations for the PCB-impacted sediments were typically an order of magnitude or more smaller than values estimated using correlations based on total organic matter partitioning. Measured aqueous PCB concentrations agreed with predictions based on equilibration with a PCB-containing oil phase, best modeled by Raoult’s law. It was postulated that, as a consequence of PCB oil-phase partitioning, biotreatment would lead to higher PCB concentrations in the oily matter and thus incr...

Sorbent Wicking Device for Sampling Hydrophobic Organic Compounds in Unsaturated Soil Pore Water. II: Chemical Capture, Recovery, and Analysis

Experiments investigated the chemical capture and quantitative recovery of chlorinated hydrophobic organic compounds (HOCs) sampled from the pore-water of unsaturated soils with a new in situ sorbent wicking device. The sampling device is comprised of an annular porous stainless-steel interface encasing granular-activated carbon and a fiberglass wick. Laboratory column studies using Ottawa sand spiked with tri- and tetrachlorobenzenes evaluated the accuracy of the sampling device in assessing average pore-water concentrations. The findings from these experiments showed that the sorbent-wick sampler provided reliable and repeatable estimates of the pore-water concentrations of the chlorobenzenes in the unsaturated soil columns at pore-water concentrations as low as several parts per billion. Field trials were conducted in a land biotreatment unit containing industrial soil/sludge materials to assess the availability of trace levels of aqueous-phase polychlorinated biphenyls (PCBs). The land treatment unit had undergone 5 years of intrinsic remediation and the test results indicated that the samplers were able to replicate the aqueous-phase PCB homolog pattern measured in ex situ aqueous extraction tests. Orthosubstituted PCBs were dominant in sorbent-wick samples and aqueous extracts; these PCBs appear relatively recalcitrant in land biotreatment units. The sorbent-wicking device offers the ability to obtain time-averaged mass and volumetric flux rates of HOCs in land treatment units.

Bacterial succession in a petroleum land treatment unit.

Bacterial community dynamics were investigated in a land treatment unit (LTU) established at a site contaminated with highly weathered petroleum hydrocarbons in the C(10) to C(32) range. The treatment plot, 3,000 cubic yards of soil, was supplemented with nutrients and monitored weekly for total petroleum hydrocarbons (TPH), soil water content, nutrient levels, and aerobic heterotrophic bacterial counts. Weekly soil samples were analyzed with 16S rRNA gene terminal restriction fragment (TRF) analysis to monitor bacterial community structure and dynamics during bioremediation. TPH degradation was rapid during the first 3 weeks and slowed for the remainder of the 24-week project. A sharp increase in plate counts was reported during the first 3 weeks, indicating an increase in biomass associated with petroleum degradation. Principal components analysis of TRF patterns revealed a series of sample clusters describing bacterial succession during the study. The largest shifts in bacterial community structure began as the TPH degradation rate slowed and the bacterial cell counts decreased. For the purpose of analyzing bacterial dynamics, phylotypes were generated by associating TRFs from three enzyme digests with 16S rRNA gene clones. Two phylotypes associated with Flavobacterium and Pseudomonas were dominant in TRF patterns from samples during rapid TPH degradation. After the TPH degradation rate slowed, four other phylotypes gained dominance in the community while Flavobacterium and Pseudomonas phylotypes decreased in abundance. These data suggest that specific phylotypes of bacteria were associated with the different phases of petroleum degradation in the LTU.

Extended bioremediation of PAH/PCP contaminated soils from the POPILE wood treatment facility

A study was conducted using two pilot-scale land-treatment units (LTUs) to evaluate the efficacy of different cultivation and maintenance schedules during bioremediation of contaminated soil from a wood treatment facility using landfarming technology. The soil contained high concentrations of polycyclic aromatic hydrocarbons (PAHs, ∼13 000 ppm) as well as of pentachlorophenol (PCP, ∼1500 ppm). An initial 6-month intensive-treatment phase was followed by 24 months of less-intensive treatment. During the first phase, traditional landfarming practice of regular cultivation was compared with a gas-phase composition based cultivation strategy, and both the landfarming units were intensively monitored and maintained with respect to moisture control and delivery of nutrients. The two strategies resulted in similar contaminant concentration profiles with time during this phase, although different microbial populations developed in the two-landfarming units. The second (less-intensive) treatment phase involved no moisture control and nutrient delivery beyond the initial adjustments, and compared natural attenuation (no cultivation) with quarterly cultivation of soil. Both the strategies showed similar behavior again. GC/MS analysis of the soil samples showed PAH removal including four-ring homologues. Leachability tests at zero time and after 6 and 22 months of operation showed significant reductions in leaching of PCP and low molecular weight PAHs. Extended treatment resulted in some leaching of high molecular weight PAHs. Significant biological activity was demonstrated, even at the high contaminant concentrations. Phospholipid ester-linked fatty acid (PLFA) analysis showed an increase in biomass and a divergence in community composition in soils depending on the treatment conducted.

Complex co‐substrate addition increases initial petroleum degradation rates during land treatment by altering bacterial community physiology

AbstractA pilot‐scale land treatment unit (LTU) was constructed at the former Guadalupe oil production field with the purpose of investigating the effect of co‐substrate addition on the bacterial community and the resulting rate and extent of total petroleum hydrocarbon (TPH) degradation. The TPH was a weathered mid‐cut distillate (C10‐C32) excavated from the subsurface and stockpiled before treatment. A control cell (Cell 1) in the LTU was amended with nitrogen and phosphorus while the experimental cell (Cell 2) was amended with additional complex co‐substrate—corn steep liquor. During the pilot LTU operation, measurements were taken of TPH, nutrients, moisture, aerobic heterotrophic bacteria (AHB), and diesel oxidizing bacteria (DOB). The bacterial community was also assayed using community‐level physiology profiles (CLPP) and 16S rDNA terminal restriction fragment (TRF) analysis. TPH degradation in both cells was characterized by a rapid phase of degradation that lasted for the first three weeks, followed by a slower degradation phase that continued through the remainder of the project. The initial rate of TPH‐degradation in Cell 1 (−0.021 day−1) was slower than in Cell 2 (−0.035 day−1). During the slower phase, degradation rates in both cells were similar (−0.0026 and −0.0024 respectively). AHB and DOB counts were similar in both cells during the fast degradation phase. A second addition of co‐substrate to Cell 2 at the beginning of the slow degradation phase resulted in an increased AHB population that lasted for the remainder of the project but did not affect TPH degradation rates. CLPP data showed that co‐substrate addition altered the functional capacity of the bacterial community during both phases of the project. However, TRF data indicated that the phylogenetic composition of the community was not different in the two cells during the fast degradation phase. The bacterial phylogenetic structure in Cell 2 differed from Cell 1 after the second application of co‐substrate, during the slow degradation phase. Thus, co‐substrate addition appeared to enhance the functional capacity of the bacterial community during the fast degradation phase when the majority of TPH was bioavailable, resulting in increased degradation rates, but did not affect rates during the slow degradation phase when the remaining TPH may not have been bioavailable. These data show that co‐substrate addition might prove most useful for applications such as land farming where TPH is regularly applied to the same soil and initial degradation rates are more important to the project goals. © 2003 Wiley Periodicals, Inc.

Ecotoxicological Risks Associated with Land Treatment of Petrochemical Wastes. I. Residual Soil Contamination and Bioaccumulation by Cotton Rats (Sigmodon Hispidus)

Petrochemical waste contains both organic and inorganic contaminants that can pollute soil and may pose significant ecological risks to wildlife. Petrochemical waste typically is disposed of in land treatment units, which are widespread throughout Oklahoma and the United States. Few studies have been conducted evaluating possible toxicity risks to terrestrial organisms residing on these units. In this study, the extent of soil contamination with fluoride (F), metals, and organic hydrocarbons, the bioaccumulation of F and metals in cotton rats (Sigmodon hispidus), the relationship between contaminants in soil and in tissues of cotton rats, and the level of potentially toxic polycyclic aromatic hydrocarbons (PAHs) in soil were determined on land treatment units. Over a 2-yr period, cotton rats and soils were collected and analyzed from 5 land treatment and matched reference units. The number of land treatment units with soil metal contamination (in parentheses) included: Cr, Cu, Pb (5); Al, As, Ni, Sr, Zn (4); Ba (3); and Cd, V (2). The number of land treatment units with soil PAH contamination (in parentheses) were naphthalene, phenanthrene, benzo[g,h,i]perylene (3); acenaphthene, anthracene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[a]pyrene, indeno[1,2,3-c,d]pyrene, dibenz[a,h]anthracene (2); and acenaphthylene, fluorene, fluoranthene, benzo[k]fluoranthene (1). Total PAH and total petroleum hydrocarbons (TPH) were elevated at all five land treatment units. Mean sums of benzo[a]pyrene (BaP) equivalents (BaP equiv ) were not affected on land treatment units as compared to reference units. Units 1 and 3 were significantly higher in levels of metals, total PAH, TPH, and BaP equiv than the other units. Pb and F bioaccumulated in bone and Pb bioaccumulated in kidney of cotton rats. F in bone of 496 to 2212 mg/kg was 3- to 15-fold greater than mean F in bone of cotton rats from reference units. Elevated levels of Pb in bone of 4.6 to 24.8 mg/kg were 460- to 2500-fold greater than mean Pb in bone of cotton rats from reference units. Elevated levels of Pb in kidney of 0.31 to 1.08 mg/kg were 10- to 36-fold greater than mean Pb in kidney of cotton rats from reference units. Bone F was an accurate predictor of the severity of dental fluorosis. Strong relationships were found between bone F and HCl-extractable F and bone F and total F in soils of land-treatment units. A strong relationship was discovered between Pb in bone and Pb in soil. Land treatment appears to have been effective as a remediation technology in reducing levels of individual PAHs and the sum of BaP equivalents to background levels on units 2, 4, and 5 but not on units 1 and 3. This study shows that certain contaminants such as Pb and F tend to bioaccumulate in cotton rats collected from land treatment units. Land treatment was ineffective in reducing levels of these contaminants to background levels that will not pose an increase in risk to terrestrial mammals. Therefore, to avoid accumulation of these contaminants in cotton rats and their possible deleterious effects, these contaminants should be measured, and land application rates of petrochemical waste should be managed to avoid excessive loading into soil systems.

Assessment of fungal diversity using terminal restriction fragment (TRF) pattern analysis: comparison of 18S and ITS ribosomal regions

Assessment of fungal diversity in environmental samples is currently a challenge. Several recently developed molecular methods offer new avenues for determining the presence and diversity of fungi in complex microbial communities. Terminal restriction fragment (TRF) pattern analysis was tested as a method for assessing the fungal molecular diversity of a terrestrial microbial community. Community DNA was isolated from sand samples taken from a pilot-scale petroleum-contaminated land treatment unit. PCR amplification was carried out using primers, one of which was fluorescently labeled, designed to hybridize to conserved sequences in the fungal ribosomal small subunit (18S) or the internal transcribed spacer ITS1-5.8S-ITS2 (ITS) ribosomal region. Amplicons were then digested separately with HpaII or HaeIII; fluorescently labeled TRFs were detected by capillary gel electrophoresis. ITS region TRF patterns were predicted and observed to generate a greater richness than 18S TRF patterns. Unique TRF patterns were also observed for each community examined. Finally, the ITS region showed a higher degree of specificity in matching observed TRF profiles to those generated from GenBank sequence data for species identification. These data suggest that ITS rDNA TRF pattern analysis has great potential as a rapid and specific method for fungal community analysis and species identification.

Assessment of fungal diversity using terminal restriction fragment (TRF) pattern analysis: comparison of 18S and ITS ribosomal regions

Assessment of fungal diversity in environmental samples is currently a challenge. Several recently developed molecular methods offer new avenues for determining the presence and diversity of fungi in complex microbial communities. Terminal restriction fragment (TRF) pattern analysis was tested as a method for assessing the fungal molecular diversity of a terrestrial microbial community. Community DNA was isolated from sand samples taken from a pilot-scale petroleum-contaminated land treatment unit. PCR amplification was carried out using primers, one of which was fluorescently labeled, designed to hybridize to conserved sequences in the fungal ribosomal small subunit (18S) or the internal transcribed spacer ITS1–5.8S–ITS2 (ITS) ribosomal region. Amplicons were then digested separately with HpaII or HaeIII; fluorescently labeled TRFs were detected by capillary gel electrophoresis. ITS region TRF patterns were predicted and observed to generate a greater richness than 18S TRF patterns. Unique TRF patterns were also observed for each community examined. Finally, the ITS region showed a higher degree of specificity in matching observed TRF profiles to those generated from GenBank sequence data for species identification. These data suggest that ITS rDNA TRF pattern analysis has great potential as a rapid and specific method for fungal community analysis and species identification.

Immunotoxicity risks associated with land-treatment of petrochemical wastes revealed using an in situ rodent model

Land-treatment of petrochemical wastes is a widely used method to dispose of hazardous and non-hazardous waste by biodegradation. However, no comprehensive assessment of the impact of such disposal techniques on terrestrial ecosystems has been conducted. Despite the presence of suspected immunotoxicants in the soil, wild rodents frequently reside on these waste sites after closure or abandonment. We explored the seasonal sensitivity of the immune system of the hispid cotton rat ( Sigmodon hispidus) to in situ exposures on sites land-treated with petrochemical wastes. Animals were monitored on five contaminated land-treatment sites and five ecologically matched-reference sites in Oklahoma, USA, over two seasons (summer and winter). Most hematological parameters were not adversely affected by land-treatment; however, platelet counts were 26% greater in cotton rats from land-treatment sites compared to reference sites in winter. Significant treatment-related differences were observed in total serum protein concentrations, organ mass and organ cellularity, but these differences were not consistent across the five land-treatment units. Lymphoproliferative responses of cotton rat splenocytes stimulated in vitro were elevated for a T-cell mitogen and depressed for a B-cell mitogen in animals from land-treatment compared to reference sites. The ability of splenocytes to proliferate in response to interleukin-2 receptor-binding was not influenced by treatment. Total yields of peritoneal cells, yield of peritoneal macrophages, and yield of peritoneal lymphocytes were influenced to varying degrees by land-treatment. Functionally, in vitro metabolic activity of peritoneal macrophages was 114% greater in cotton rats from land-treatment sites compared to reference sites during summer. These results indicate that petrochemical wastes applied to soils on these five land-treatment sites had variable immunomodulatory effects in resident cotton rats. Immune alterations for some assays were indicative of enhancement on some land-treatment sites while suppressive on other land-treatment sites, which could have been a function of type and concentration of immunotoxicants present on each site and highlights the uniqueness of each land-treatment site.

Remediation of Petroleum Refinery Waste Pond Contents: A Case Study

The objectives of this field study were to (1) remediate the contents of a pond containing petroleum refinery waste products, and (2) characterize the performance of the remediation effort in terms of changes in chemical concentration, toxicity of the waste material, and mobility of the remediated waste constituents. The study was conducted in a field land treatment unit (LTU) in two phases over 140 weeks. Site remediation and closure decisions should be based on criteria that indicate that protection of human health and the environment has been achieved. Thus, criteria used to determine performance should include measures of chemical loss as well as measures of mobility (leaching) and toxicity. In this field study, changes in both general (oil and grease, total petroleum hydrocarbons) and specific (benzene, toluene, ethylbenzene and xylene compounds and polycyclic aromatic hydrocarbons) were determined. Several measures of chemical mobility and LTU soil toxicity also were used. The data indicated that the land treatment of this waste material reduced the concentrations of general and specific hydrocarbons, reduced the toxicity of the material being treated, and contained the waste constituents, that is, little to no vertical migration of the chemicals measured occurred. At the end of both field phases of the study, considerable amounts of general hydrocarbons remained in the LTU soil, as indicated by total petroleum hydrocarbons, oil and grease, and total polycyclic aromatic hydrocarbon compound measurements. However, there were little chemical mobility and relative toxicity of the soil at the end of these phases.

Decreased Release of PAHs from Soils as a Result of Field Bioremediation

In this study, the relationship between the release characteristics of contaminants from soil and the biodegradability of the contaminants was evaluated. The soils used were from a large-scale field site. A batch rate of release procedure was used to quantify the release of polynuclear aromatic hydrocarbons (PAHs) from manufactured gas plant site soils before and during bioremediation in a field land treatment unit (LTU). This evaluation assessed the performance of the field-scale LTU with respect to changes in the soil PAH concentrations and to changes in chemical release parameters. The practical implications of the evaluation are discussed. During 147 days of LTU operations, the concentrations of specific PAHs were reduced 39–93%. ROR studies were conducted on LTU soil samples obtained at Days 0, 58, 72, and 147 of treatment. As a result of 147 days of treatment in the LTU, the fraction of a PAH released rapidly (F) had decreased for 8 of 10 PAHs, and the value of k2 (the first-order rate constant describing slow release) had decreased for 5 of 10 PAHs. There were no increases in F or k2 for any of the PAHs as a result of treatment in the field LTU. The results indicated that (1) only a fraction of the total concentration of the individual PAHs in the LTU samples was readily available to be released from the soil; (2) the remainder was released at a much slower rate; and (3) the mass of PAH released from the LTU soils to the aqueous phase decreased considerably. In addition, the fraction of the chemical released rapidly (F) for the Day 0 soil sample provided a reasonable prediction of the extent of PAH loss during 147 days of biological treatment in the field LTU.

Prepared Bed Land Treatment of Soils Containing Diesel and Crude Oil Hydrocarbons

An ex situ, field-scale, prepared bed land treatment unit (LTU) was used to bio-remediate soils containing petroleum hydrocarbons. Two soils were treated in side-by-side units to compare performance: (1) a clayey silt containing crude oil hydrocarbons from releases 30 to 40 years ago and (2) a silty sand containing diesel fuel hydrocarbons from a leak about three years prior to the bioremediation. The effectiveness of the bioremediation in the LTU was evaluated over a period of 18 months. The results indicated that: (1) prepared bed bioremediation reduced the hydrocarbon concentration, mobility, and relative toxicity in the soil with the diesel fuel, and (2) chemical bioavailability appeared to limit bioremediation of the soil containing the crude oil hydrocarbons. Although the soils containing the crude oil hydrocarbons contained an average of 10,000 mg TPH/kg dry soil, these soils had limited hydrocarbon availability, nontoxic conditions, and low potential for chemical migration. For the soils containing the diesel fuel, active prepared bed bioremediation of about 15 weeks was adequate to reach an environmentally acceptable endpoint. At that time, there was little further TPH loss, no MicrotoxTM toxicity, and limited hydrocarbon mobility.

Release Of Petroleum Hydrocarbons From Bioremediated Soils

This article presents a qualitative evaluation of the extent to which the bioavailability (release) of a chemical is related to the biodegradation of hydrocarbons in a field bioremediation unit. The objectives of this research were to (1) quantify the rate of release of petroleum hydrocarbons from two soils that were bioremediated, (2) explore hydrocarbon release as a process affecting bioremediation; and (3) investigate the impact of bioremediation on chemical release in the two soils. An experimental protocol was used to quantify the rate of release of these hydrocarbons from two soils that had been bioremediated in a field-scale prepared bed land treatment unit. One soil showed little change in hydrocarbon concentration during 55 weeks of prepared bed bioremediation. The field study results indicated that, prior to the bioremediation, this soil had reached an environmentally acceptable endpoint. The second soil showed considerable hydrocarbon loss as a result of the bioremediation. The rate of hydrocarbon release was determined for the first soil and for the second soil at time zero and after 1, 2, and 7 months of prepared bed bioremediation. The results indicated: (1) the fraction (F) of the specific hydrocarbons that were released rapidly from the soil and the rates of release (k2) of the residual hydrocarbons that were released slowly, (2) that the mass of each chemical of concern that was released from the first soil was very low; and (3) that the hydrocarbon released rapidly from the second soil decreased as treatment progressed. The experiments also verified, qualitatively, that some portion of each chemical evaluated was not able to be released, and thus was unavailable for bioremediation in the prepared bed land treatment unit.

Leaching of PCB compounds from untreated and biotreated sludge-soil mixtures

Column experiments were conducted to evaluate the aqueous leachability of polychlorinated biphenyls (PCBs) from sludge-soil mixtures contaminated with PCBs and hydraulic oils. Untreated and biotreated sludge-soil samples were obtained from a two-month, pilot-scale field test of PCB biodegradation in land treatment units. Column leachate comprised mainly di- and trichlorobiphenyls. In comparison to untreated samples, column leachate from biotreated samples showed 34 to 63% reduction in PCBs; average values of total PCB concentrations in the column effluent ranged from 0.36 to 0.82 μg 1 −1 for untreated samples and 0.25 to 0.30 μg 1 −1 for biotreated samples. Only a small fraction, less than 6%, of the PCB mass in the untreated sludge-soil mixtures was removed by prolonged flushing with up to 2400–3000 pore volumes of water, suggesting long-term, slow release of PCBs at low aqueous concentrations. It should be noted that flushing rates for the column experiments were much higher than typical ground-water flow rates and the two-month period for column experiments can be qualitatively compared to a greatly extended duration for ground-water flow. The leaching of PCBs from a nonaqueous phase liquid (NAPL) in the column experiments was modelled as a predominantly dissolution-governed process based on first-order kinetics. The estimated dissolution rate coefficients ranged from 0.02 to 0.04 min −1 for various PCB homolog groups. This investigation helps support the concept of biostabilization, in which contaminated materials may be actively biotreated to remove the potentially mobile organic contaminants leaving a residual material that is more stable against leaching. Natural attenuation processes like sorption and intrinsic biodegradation further reduce the PCB leachability potential. Additional long-term monitoring of the land treatment units under passive conditions is under progress to evaluate such reductions.

Soil Gas Oxygen Tension and Pentachlorophenol Biodegradation

Laboratory tests were conducted to determine the effect of soil gas oxygen concentration on the degradation and mineralization of spiked 14C-pentachlorophenol and nonlabeled pentachlorophenol (PCP) present in soil taken from a prepared-bed land treatment unit at the Champion International Superfund Site in Libby, Mont. This soil was contaminated with wood preserving wastes including creosote and PCP. Degradation rates of 14C-PCP and nonlabeled PCP were found to be enhanced under soil gas oxygen concentrations between 2 and 21% in the contaminated soil. Between 48 and 64% of 14C-PCP spiked onto the soil was mineralized after 70 days at soil gas oxygen levels between 2 and 21%. No statistically significant mineralization of PCP was found to occur at 0% oxygen concentrations. Mineralization of 14C-PCP in contaminated soil poisoned with mercuric chloride was determined to be less than 0.2%. Degradation of indigenous nonradiolabeled PCP in the nonpoisoned soil was statistically significantly greater than in po...