Yarrow Nelson

Model for Trace Metal Exposure in Filter-Feeding Flamingos at Alkaline Rift Valley Lake, Kenya

Yarrow M. Nelson et al. — Thu, 20 Jan 2011 12:03:02 PST

Abstract—Toxic trace metals have been implicated as a potential cause of recent flamingo kills at Lake Nakuru, Kenya. Chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) have accumulated in the lake sediments as a result of unregulated discharges and because this alkaline lake has no natural outlet. Lesser flamingos (Phoeniconaias minor) at Lake Nakuru feed predominantly on the cyanobacterium Spirulina platensis, and because of their filter-feeding mechanism, they are susceptible to exposure to particle-bound metals. Trace metal adsorption isotherms to lake sediments and S. platensis were obtained under simulated lake conditions, and a mathematical model was developed to predict metal exposure via filter feeding based on predicted trace metal phase distributions. Metal adsorption to suspended solids followed the trend Pb >> Zn > Cr > Cu, and isotherms were linear up to 60 pg/L. Adsorption to S. platensis cells followed the trend Pb >> Zn > Cu > Cr and fit Langmuir isotherms for Cr, Cu and Zn and a linear isotherm for Pb. Predicted phase distributions indicated that Cr and Pb in Lake Nakuru are predominantly associated with suspended solids, whereas Cu and Zn are distributed more evenly between the dissolved phase and particulate phases of both S. platensis and suspended solids. Based on established flamingo feeding rates and particle size selection, predicted Cr and Pb exposure occurs predominantly through ingestion of suspended solids, whereas Cu and Zn exposure occurs through ingestion of both suspended solids and S. platensis. For the lake conditions at the time of sampling (1.2 g/L suspended solids, 0.23 g/L S. platensis), predicted ingestion rates based on measured metal concentrations in lake suspended solids were 0.71, 6.2, 0.81, and 13 mg/kg-d for Cr, Cu, Pb, and Zn, respectively. Higher exposure doses are predicted when metal concentrations are determined from sediment concentrations rather than suspended solids concentrations. Also, decreases in the S. platensis population would increase the clearing rate of the flamingos and increase predicted metal exposure via ingestion of suspended solids. For example, with metal concentrations calculated based on average metal concentrations in lake sediments and S. platensis concentration of 0.06 g/L, exposure rates would be 13, 10, 4.4, and 38 mg/kg-d for Cr, Cu, Pb, and Zn, respectively. These ingestion rates, except for Cu, are significantly higher than the no observable adverse effects levels.

Chemical Composition of Groundwater Hydrocarbon Mixtures Before and After Aerobic Biodegradation

Eileen Mick et al. — Thu, 20 Jan 2011 12:03:01 PST

Final Report: Production of Biodiesel From Algae Applied to Agricultural Wastewater Treatment

Yarrow M. Nelson et al. — Fri, 07 Jan 2011 12:51:14 PST

Algae Grown on Dairy and Municipal Wastewater for Simultaneous Nutrient Removal and Lipid Production for Biofuel Feedstock

Ian Woertz et al. — Tue, 05 Jan 2010 12:40:38 PST

Algae grown on wastewater media are a potential source of low-cost lipids for production of liquid biofuels. This study investigated lipid productivity and nutrient removal by green algae grown during treatment of dairy farm and municipal wastewaters supplemented with CO₂. Dairy wastewater was treated outdoors in bench-scale batch cultures. The lipid content of the volatile solids peaked at Day 6, during exponential growth, and declined thereafter. Peak lipid content ranged from 14–29%, depending on wastewater concentration. Maximum lipid productivity also peaked at Day 6 of batch growth, with a volumetric productivity of 17 mg/day/L of reactor and an areal productivity of 2.8 g/m²/day, which would be equivalent to 11,000 L/ha/year (1,200 gal/acre/year) if sustained year round. After 12 days, ammonium and orthophosphate removals were 96 and >99%, respectively. Municipal wastewater was treated in semicontinuous indoor cultures with 2–4 day hydraulic residence times (HRTs). Maximum lipid productivity for the municipal wastewater was 24 mg/day/L, observed in the 3-day HRT cultures. Over 99% removal of ammonium and orthophosphate was achieved. The results from both types of wastewater suggest that CO₂-supplemented algae cultures can simultaneously remove dissolved nitrogen and phosphorus to low levels while generating a feedstock potentially useful for liquid biofuels production.

Methanotrophic Bacteria for Nutrient Removal from Wastewater: Attached Film System

William J. Jewell et al. — Fri, 09 Jan 2009 15:50:39 PST

It was hypothesized that nutrient removal from wastewater could be achieved by using methane oxidizing bacteria (methanotrophs). Because methane is inexpensive. it can be used as an energy source to encourage bacterial growth to assimilate nitrogen and phosphorus and other trace elements. This initial feasibility study used synthetic nutrient mixtures and secondary sewage effluent as feed to a laboratory-scale methanotrophic attached-film expanded bed (MAFEB) reactor operated at 35°C and 20°C. The MAFEB system operated successfully at low nutrient concentrations under a variety of nutrient-limited conditions. Using a synthetic nutrient mixture with a nitrogen:phosphorus feed ratio (w/w) of 9:1, phosphate concentrations were reduced from 1.3 mg P/ L to below 0.1 mg P/ L, and ammonia was reduced from 12 mg N/L to approximately 1 mg N/L on a continuous flow basis, with a bed hydraulic retention time of 4.8 hours. The average nutrient uptake rates from synthetic nutrient mixtures were 100 mg nitrogen and 10 mg phosphorus/L of expanded bed/d. Nutrient assimilation rates increased with increasing growth rate and with increasing temperature. Nitrogen/phosphorus uptake ratios varied from 8 to 13, and the observed yield varied from 0.11 to 0.16 g volatile solids (VS)/g chemical oxygen demand (COD). Nutrient removal from secondary sewage effluent was successfully demonstrated using sewage effluent from two local treatment plants. Nutrient concentrations of 10-15 mg N/L and 1.0-1.8 mg P/L were reduced consistently below 1 mg N/L and 0.1 mg P/L. No supplemental nutrients were added to the sewage to attain these removal efficiencies since the nutrient mass ratios were similar to that required by the methanotrophs. Removal rates were lower at 20°C than at 35°C, but high removal efficiencies were maintained at both temperatures. Effluent suspended solids concentrations ranged from 8 to 30 mg volatile suspended solids (VSS)/L, and the effluent soluble COD concentration averaged 30 mg/L.

Production of Biogenic Mn Oxides by Leptothrix discophora SS-1 in a Chemically Defined Growth Medium and Evaluation of Their Pb Adsorption Characteristics

Yarrow M. Nelson et al. — Fri, 09 Jan 2009 15:50:21 PST

Biogenic Mn oxides were produced by the bacterium Leptothrix discophora SS-1 (= ATCC 3182) in a chemically defined mineral salts medium, and the Pb binding and specific surface area of these oxides were characterized. Growth of SS-1 in the defined medium with pyruvate as a carbon and energy source required the addition of vitamin B₁₂. Complete oxidation of Mn(II) within 60 h required the addition of ≥0.1 μM FeSO₄. Pb adsorption isotherms were determined for the biogenic Mn oxides (and associated cells with their extracellular polymer) and compared to the Pb adsorption isotherms of cells and exopolymer alone, as well as to abiotic Mn oxides. The Pb adsorption to cells and exopolymer with biogenic Mn oxides (0.8 mmol of Mn per g) at pH 6.0 and 25°C was 2 orders of magnitude greater than the Pb adsorption to cells and exopolymer alone (on a dry weight basis). The Pb adsorption to the biogenic Mn oxide was two to five times greater than the Pb adsorption to a chemically precipitated abiotic Mn oxide and several orders of magnitude greater than the Pb adsorption to two commercially available crystalline MnO₂ minerals. The N₂ Brunauer-Emmet-Teller specific surface areas of the biogenic Mn oxide and fresh Mn oxide precipitate (224 and 58 m²/g, respectively) were significantly greater than those of the commercial Mn oxide minerals (0.048 and 4.7 m²/g). The Pb adsorption capacity of the biogenic Mn oxide also exceeded that of a chemically precipitated colloidal hydrous Fe oxide under similar solution conditions. These results show that amorphous biogenic Mn oxides similar to those produced by SS-1 may play a significant role in the control of trace metal phase distribution in aquatic systems.

Vinyl Chloride Biodegradation with Methanotrophic Attached Films

Yarrow M. Nelson et al. — Fri, 09 Jan 2009 15:50:03 PST

Methanotrophic degradation of vinyl chloride (VC) is investigated using a laboratory-scale methanotrophic attached-film expanded-bed (MAFEB) bioreactor. This study provides a basis for applying a microbial cometabolizing reaction to practical treatment of toxic chlorinated compounds. The MAFEB reactor was operated at 20°C with influent VC concentrations ranging from 1,800 to 9,600 µg/L and bed hydraulic retention times ranging from 3.7 to 7.6 h. VC effluent concentrations during steady continuous operation ranged from 3 to 140 µg/L, with most values less than 26 µg/L, resulting in removal efficiencies of 96.3% to 99.8%. The maximum continuous-flow VC degradation rate observed at 20°C was 2.5 mg VC per gram volatile solids (VS) per day [2.5 mg VC/(g VS d)] or 30 mg VC per liter expanded bed per day 30 mg VC/L_eb d), under substrate-limited conditions. During semibatch runs at 35°C, vinyl chloride degradation rates up to 60 mg VC/ (g VS d) or 1 g/(Leb d) were observed. Degradation rates increased with temperature between 20°C and 35°C, approximately doubling every 10°C. Dissolved methane concentrations above 0.5 mg/L inhibited VC degradation, with no VC degradation observed with 8 mg/L dissolved methane. The methane consumed during VC degradation was about 40 g CH₄/g VC. Toxic effects were observed after prolonged exposure of the methanotrophic culture to high concentrations of VC.

Lead Binding to Metal Oxide and Organic Phases of Natural Aquatic Biofilms

Yarrow M. Nelson et al. — Fri, 09 Jan 2009 15:49:37 PST

The role of the composition of surface-coating materials in controlling trace metal adsorption in aquatic environments was investigated using natural biofilms that developed on glass slides in three New York State lakes and a water-supply well. Adsorption isotherms were obtained for Pb binding to each of the biofilms in solutions with defined Pb speciation at 25°C and pH 6.0, with Pb concentrations ranging from 0.2 to 2.0 μM. Adsorption isotherms for Pb binding to laboratory-derived metal oxides and surrogate organic materials were determined under the same conditions. These isotherms, combined with characterization of natural biofilm composition, were used to estimate the relative contributions of the organic and metal oxide surface-coating constituents by assuming additivity of adsorption to discrete adsorbing phases. Cells of a diatom (Navicula peliculosa), a green alga (Chlorella vulgaris), the bacterium Leptothrix discophora, and extracellular polymer of the bacterium Burkholdaria cepacia were tested as laboratory analogs for the organic phase of the biofilms. Amorphous Fe oxyhydroxide, γA1₂O₃, and a laboratory-derived biogenic Mn oxyhydroxide were used as laboratory surrogates for biofilm minerals. The sum total of predicted Pb binding to the defined surrogates accounted for at least 90% of the total observed Pb binding in the three lake biofilms and 60% of that observed for the well biofilms. For the lake biofilms, Pb adsorption to Fe and Mn oxides was significantly greater than that estimated for organic materials. The use of biogenic Mn oxide as a model component resulted in an estimated Pb adsorption to Mn oxyhydroxides in the lake biofilms up to four times greater than that estimated for Fe oxyhydroxide. Estimated Pb binding by Al oxide was negligible for all four biofilms. These results suggest that Fe and biogenic Mn oxides exert the greatest influence on Pb adsorption in oxic freshwater environments at pH 6.0.

Investigation of Hydrocarbon Phytoremediation Potential of Lupinus Chamissonis in Laboratory Microcosms

Wendy Martin et al. — Fri, 09 Jan 2009 15:49:20 PST

Controlled laboratory microcosms were used to research the phytoremediation potential of lupines (Lupinus chamissonis) for hydrocarbon-contaminated groundwater at a former oil field near Guadalupe, California. During oil production in the Guadalupe Oil Field, a kerosene-like hydrocarbon mixture was used as a diluent to improve the flow of the heavy crude oil. Leaking tanks and pipes resulted in diluent contamination in the soil and groundwater. Native plant species were planted at a pilot-scale field site to investigate the feasibility of using phytoremediation to remediate the groundwater contamination. In the field, biological and hydrological factors make it difficult to determine the specific contributions of individual plant species to hydrocarbon degradation. To overcome the variability of the field site, laboratory experiments with plants grown in glass containers were conducted to examine and quantify the role of plants in contributing to hydrocarbon biodegradation. Earlier experiments, using Salix lasiolepis (Arroyo willows), indicated increased hydrocarbon biodegradation with willows present. Since L. chamissonis plants are a prevalent native species at the site, and because of their potential for nitrogen fixation, the present laboratory study was undertaken to evaluate the contribution of L. chamissonis to phytoremediation and to compare L. chamissonis and S. lasiolepis results. Hydrocarbon-contaminated groundwater from the field site with an initial total petroleum hydrocarbon (TPH) concentration of 5.5 mg/L was recirculated through 1-gallon glass soil chambers for 105 days under conditions mimicking site conditions. Chambers were established in triplicate with 1) soil with active bacteria and one L. chamissonis plant, 2) soil with active bacteria, and 3) sodium azide inhibited soil. Biodegradation was monitored using gas chromatography/mass spectrometry (GC/MS) to determine TPH concentrations on days 0, 24, and 105. TPH concentrations in the L. chamissonis and soil-only chambers were not significantly different from each other after 24 days, suggesting the L. chamissonis did not contribute to bioremediation under these conditions. After 105 days, the final TPH concentrations were 0.95 ± 0.22 for the sodium azide inhibited, 0.67 ± 0.085 for the soil only, and 0.33 ± 0.12 mg/L for the L. chamissonis chambers. Thus, final residual TPH concentrations in the chambers planted with L. chamissonis were less than half of those in the soil-only chambers, and this difference was statistically significant at the 95% confidence level. These results are similar to those for the willows grown under the same conditions, indicating that the nitrogen-fixing ability of the lupines did not lead to enhanced bioremediation relative to willows. Nonetheless, this research shows that lupines enhance biodegradation, most likely by stimulating the hydrocarbon-degrading microorganisms in the soil. Since lupines easily establish themselves at the site they are excellent candidates for use in ecological restoration and phytoremediation at the former Guadalupe Oil Field.

Adsorption of Pb and Cd Onto Metal Oxides and Organic Material in Natural Surface Coatings as Determined by Selective Extractions: New Evidence for the Importance of Mn and Fe Oxides

Deming Dong et al. — Fri, 21 Nov 2008 11:41:31 PST

Surface coatings (biofilms and associated minerals) were collected on glass slides in the toxic surface waters of Cayuga Lake (New York State, U.S.A.) and were used to evaluate the relative contributions of Fe, Mn and Al oxides and organic material to total observed Pb and Cd adsorption by the surface coating materials. Several alternative selective extraction techniques were evaluated with respect to both selectivity and alteration of the residual unextracted material. Pb and Cd adsorption was measured under controlled laboratory conditions (mineral salts solution with defined metal speciation, ionic strength 0.05 M, 25°C and pH 6.0) before and after extractions to determine by difference the adsorptive properties of the extracted component(s). Hydroxylamine hydrochloride (0.01 M NH₂OH·HCl+0.01 M HNO₃) was used to selectively remove Mn oxides, sodium dithionite (0.3 M _{Na₂S₂O₄)} was used to remove Mn and Fe oxides, and 10% oxalic acid was used to remove metal oxides and organic materials. Several other extractants were evaluated, but preliminary experiments indicated that they were not suitable for these experiments because of undesirable alterations of the residual, unextracted material. The selected extraction methods removed target components with efficiencies between 71 and 83%, but significant amounts of metal oxides and organic materials other than the target components were also removed by the extractants (up to 39%). Nonlinear regression analysis of the observed Pb and Cd adsorption based on the assumption of additive Langmuir adsorption isotherms was used to estimate the relative contributions of each surface coating constituent to total Pb and Cd binding of the biofilms. Adsorption of Cd to the lake biofilms was dominated by Fe oxides, with lesser roles attributed to adsorption by Mn and Al oxides and organic material. Adsorption of Pb was dominated by Mn oxides, with lesser roles indicated for adsorption to Fe oxides and organic material, and the estimated contribution of Al oxides to Pb adsorption was insignificant. The fitted Pb adsorption isotherm for Fe oxides was in excellent agreement with those obtained through direct experiments and reported in independent investigations. The estimated Pb distribution between surface coating components also agreed well with that previously predicted by an additive adsorption model based on Pb adsorption isotherms for laboratory surrogates for Mn, Fe and Al oxides and defined biological components.

Determination of Iron Colloid Size Distribution in the Presence of Suspended Cells: Application to Iron Deposition onto a Biofilm Surface

Waihung Lo et al. — Fri, 21 Nov 2008 11:41:10 PST

Transport and deposition of colloidal Fe, Mn and Al oxides play key roles in the cycling of toxic transition metals in aquatic environments because these colloids strongly bind transition metals. Further, attachment of biological cells and biofilm growth on surfaces can indirectly affect toxic metal distribution by influencing the deposition of colloidal oxides to surfaces. To elucidate the mechanisms governing these processes, deposition of colloidal oxides onto surfaces must be evaluated in the presence of suspended and adherent bacterial cells. Both particle size and concentration are expected to influence deposition. An experimental protocol was developed to determine the size distribution of iron colloids in mixtures with suspended cells. A Ti(III) reagent was used to reduce and dissolve colloidal Fe(III) from mixtures containing both suspended cells and Fe colloids. The size distribution of Fe(III) colloids in the original solution was then determined from the difference between size distributions before and after dissolution of Fe with Ti(III). The Ti(III) reagent dissolved over 95% of the Fe colloids without altering the size distribution of suspended bacterial cells, and the method accurately determined the size distribution of Fe colloids added to cell suspensions. The applicability of this protocol was tested by applying it to a study of the deposition of Fe(III) oxide particles onto glass surfaces with and without biofilms of the bacterium Burkholdaria cepacia 17616. Experimental results using a laboratory biofilm reactor indicated that the deposition rate of Fe(III) colloids was not significantly affected by the presence of B. cepacia biofilms or by the presence of previously deposited Fe. However, deposition of Fe to reactor surfaces other than the glass surfaces may have interfered with the analyses, and atomic absorption measurements showed a slight increase in Fe deposition onto glass surfaces with biofilms present. Fe deposition to the composite of all reactor surfaces increased with increasing colloidal particle size, indicating a dominance of interception and/or sedimentation in controlling Fe deposition on surfaces in the biofilm reactor.

Lead Distribution in a Simulated Aquatic Environment: Effects of Bacterial Biofilms and Iron Oxide

Yarrow M. Nelson et al. — Fri, 21 Nov 2008 11:40:54 PST

Biofilms influence the transport and fate of heavy metals in aquatic environments both directly by adsorption and complexation reactions and indirectly via interactions with oxides of iron and manganese. These reactions were investigated by introducing lead into a continuous-flow biofilm reactor that was designed to simulate conditions in a flowing freshwater aquatic environment. The reactor provided controlled conditions, and use of a chemically-defined growth medium allowed calculation of lead speciation with a chemical equilibrium program (MINEQL). Pseudomonas cepacia was employed as a test cell strain because of its ability to grow and form biofilms in the defined medium. This bacterium affected lead distribution in the reactor by adsorbing lead both to adherent and suspended cells. When the aqueous bulk lead concentration was 1.4 ± 0.1 µM and biofilm coverage (measured as chemical oxygen demand, COD) was 50 mequiv COD/m², lead adsorption was increased by about a factor of five relative to bare glass. Of the total lead in solution, only 1% was adsorbed to suspended cells (5 x 10⁷ cells/ml). Lead adsorption to biofilms followed a Langmuir isotherm with a maximum adsorption (Γ max) of 56 µmol Pb/equiv COD and an adsorption equilibrium constant (K) of 0.64 liter/µmol Pb. Lead complexed with dissolved bacterial exopolymer was below detection limits. Pretreatment of glass slides with colloidal iron also significantly increased lead adsorption relative to bare glass. Lead adsorption to adsorbed iron fit a Langmuir isotherm with Γ_max = 50 µmol Pb/mol Fe, and K = 1.3 liter/µmol Pb. Lead binding to glass coated with both cells and iron was additive, and could be predicted by summing adsorption predicted using isotherms for each constituent. The presence of iron surface coatings increased initial biofilm formation rates, but after reaching steady state conditions, biofilm coverage was similar for slides treated with iron and untreated slides. A concentration of 1 µM lead produced a transient reduction in suspended cell counts. Cell counts recovered to the original cell density over the course of five to ten reactor retention times. With iron present, the magnitude of the reduction in cell concentration in response to the addition of lead was greatly reduced, suggesting that toxic effects of lead may be reduced by iron.

Kinetics of Mn(II) oxidation by Leptothrix discophora SS1

Jinghao Zhang et al. — Fri, 21 Nov 2008 11:40:40 PST

The kinetics of Mn(II) oxidation by the bacterium Leptothrix discophora SS1 was investigated in this research. Cells were grown in a minimal mineral salts medium in which chemical speciation was well defined. Mn(II) oxidation was observed in a bioreactor under controlled conditions with pH, O>sub>2, and temperature regulation. Mn(II) oxidation experiments were performed at cell concentrations between 24 mg/L and 35 mg/L, over a pH range from 6 to 8.5, between temperatures of 10°C and 40°C, over a dissolved oxygen range of 0 to 8.05 mg/L, and with L. discophora SS1 cells that were grown in the presence of Cu concentrations ranging from zero to 0.1 µM. Mn(II) oxidation rates were determined when the cultures grew to stationary phase and were found to be directly proportional to O₂ and cell concentrations over the ranges investigated. The optimum pH for Mn(II) oxidation was approximately 7.5, and the optimum temperature was 30°C. A Cu level as low as 0.02 µM was found to inhibit the growth rate and yield of L. discophora SS1 observed in shake flasks, while Cu levels between 0.02 and 0.1 µM stimulated the Mn(II) oxidation rate observed in bioreactors. An overall rate law for Mn(II) oxidation by L. discophora as a function of pH, temperature, dissolved oxygen concentration (D.O.), and Cu concentration is proposed. At circumneutral pH, the rate of biologically mediated Mn(II) oxidation is likely to exceed homogeneous abiotic Mn(II) oxidation at relatively low (≈µg/L) concentrations of Mn oxidizing bacteria.

Biotreatment of Synthetic Drill-Cutting Waste in Soil

Laleh Rastegarzadeh et al. — Tue, 18 Nov 2008 16:09:26 PST

Oil and gas drilling operations create drill cutting wastes around the world. Drill cutting waste includes synthetic drilling fluids typically consisting of petroleum-based compounds mixed with clay-type materials and water. Biological treatment is an effective means of disposing of drill cutting wastes, but proper biodegradation conditions are critical. In this study biological treatment of drill cutting wastes containing Saraline® (synthetic paraffin mineral oil) was examined using a variety of amendments to study the effect of different conditions on the biodegradability of synthetic drill cutting wastes. Soil was collected from a drilling site in Southeast Asia and soil microcosms were incubated in a sealed and controlled environment to mimic the dry season of the field site. Amendments evaluated included native soil as a bulking agent and as a source of inoculum, rice hulls as a bulking agent to improve aeration and moisture retention, and urea as a source of nitrogen fertilizer. All microcosms were maintained with 15 – 20 % moisture and kept at 30^o C. Hydrocarbon biodegradation was evaluated using gas chromatographic (GC) analysis of total petroleum hydrocarbon (TPH) concentration of each microcosm. Microcosms were sampled every 30 days for a period of 4 months.

Maximum biodegradation was observed with a 1:1 mixture of soil and drill cuttings containing 1% urea and 10% rice hulls. Biodegradation proceeded with a half-life of about 30 days under these optimal conditions. After 4 months, 91% of the TPH was biodegraded under optimum conditions. Little or no biodegradation was observed for drill cuttings without amendments suggesting addition of soil bulking agent and fertilizer is essential. No decrease in TPH concentration was observed for a control with 1% sodium azide, indicating observed decreases in TPH were due to biodegradation alone. No volatilization was observed in the sealed soil microcosms. A separate volatilization experiment in open containers showed evaporation could contribute significantly to TPH loss in the field.

Characterization of Aerobic and Anaerobic Microbial Activity in Hydrocarbon-Contaminated Soil

Lynne C. Maloney et al. — Tue, 18 Nov 2008 16:09:22 PST

Microbial activity in hydrocarbon-contaminated soil was characterized and quantified to determine the potential for natural attenuation at a former oil field in California. Plate counts, direct microscopic counts, and carbon dioxide and methane production rates were used to quantify the populations and activity of soil microorganisms. Terminal restriction fragment (TRF) analysis provided preliminary identification of dominant microorganisms and community shifts as depth and contaminant concentrations changed. Plate counts under aerobic conditions resulted in 1.5 to 22 × 10⁶ colony-forming units (CFU) per gram of soil, and direct microscopic counts of total bacteria were 3 to 33 × 10⁶ cells per gram. Carbon dioxide production rates of 1.3 to 5.5 μL CO₂/g soil per day were measured in the aerobic samples. Methane production rates in sealed anaerobic microcosms were higher in samples with more highly contaminated soil, and ranged from 0 to 20.9 ppmv CH₄/day. Terminal restriction fragment analysis revealed the presence of three distinct microbial communities at the site. The aerobic non-contaminated zone included Actinomyces, Pseudomonas, and other microorganisms. The transition zone included Streptomyces, and the zone with the highest TPH concentrations was characterized by microorganisms including Mycobacteria and Actinobacteria. Communities of both aerobic and anaerobic bacteria appear to be biodegrading hydrocarbons in situ.

Biodegradability and Toxicity of Hydrocarbon Leachate From Land Treatment Units

Sandy L. Scott et al. — Tue, 18 Nov 2008 16:09:17 PST

The biodegradability of leachate from the land treatment of hydrocarbon-contaminated soil was investigated in the laboratory using respirometry and toxicity testing in combination with total petroleum hydrocarbon (TPH) measurements. Soil in land treatment units (LTU) had been contaminated with a diesel-like hydrocarbon mixture formerly used as a diluent for crude oil at an oil field in California. Leachate was collected from two different LTUs for treatability testing in a respirometer under aerobic conditions. Only about 12% reduction in TPH concentration was observed after aeration for 161 days, indicating limited biodegradability of the hydrocarbon constituents in the leachate. Similarly, Microtox® toxicity did not change after 130 days. Leachate biodegradability was further tested by comparison to diluent-contaminated groundwater from the same site. Leachate diluted to the same TPH concentration as the contaminated groundwater was three times less toxic, but was much less biodegradable. The recalcitrance of the leachate hydrocarbons may be attributable to their high molecular weight, since the majority of the TPH was long-chained hydrocarbons of C₂₀ or greater for leachate. In contrast, the diluent contaminated groundwater has a majority of its TPH concentration in short-chained hydrocarbons of C₂₀ or less, which were more easily biodegraded. These short chain hydrocarbons are typically more toxic than the longer chain hydrocarbons, which would explain the observed decrease in toxicity of the diluent-contaminated groundwater during biodegradation.

Weathering Effects on Biodegradation and Toxicity of Hydrocarbons in Groundwater

Marie G. Dreyer et al. — Tue, 18 Nov 2008 16:09:13 PST

This study examined the effect of weathering on hydrocarbon biodegradation and toxicity at a former oil field near Guadalupe, California. Soil and groundwater at this site contains residual diesel-range hydrocarbons formerly used to dilute the viscous crude oil to facilitate pumping (Lundegard and Garcia, 2001). Natural attenuation is being considered at this site as a means of remediating residual hydrocarbons in soil and groundwater. To provide the lines of evidence required for use of natural attenuation at this site, this research was undertaken to determine if the hydrocarbons continue to be biodegradable after extensive weathering in the field. Observed hydrocarbon biodegradation rates were directly proportional to initial total petroleum hydrocarbon (TPH) con-centration, suggesting first-order kinetics. Highly weathered hydrocarbons most distant downgradient from the source zones exhibited slightly lower biodegradation rate con-stants. Microtox® toxicity decreased rapidly during 20 days of biodegradation in laboratory microcosms.

Biological Feasibility and Optimization of Biosparging at a Hydrocarbon-Contaminated Site

Jason G. Waudby et al. — Tue, 18 Nov 2008 16:09:09 PST

The purpose of this study was to identify any biological/chemical factors which may be limiting the biodegradation of total petroleum hydrocarbon (TPH) contaminants at a biosparge site located at a former oil field near Guadalupe, California. Laboratory experiments using a combination of respirometry and TPH analyses were conducted to determine if biodegradation of TPH at the site is limited by a lack of hydrocarbon-degrading microorganisms, depleted inorganic nutrient concentrations, insufficient dissolved oxygen supply, or the chemical composition of the partially biodegraded petroleum constituents in the groundwater. No increase in total CO₂ production was observed in samples with added nutrients, inoculum, or both, over the 28-day experiment. No significant TPH biodegradation benefit could be attributed to the addition of nutrients or inoculum indicating both were sufficiently available at the site. Decreasing dissolved oxygen (DO) concentration decreased short-term CO₂ production, but considerable CO₂ production was observed even in samples with DO concentrations as low as 0.5 mg/L. In a long-term experiment, TPH degradation rates decreased significantly after initial observed biodegradation.

Biodegradation of Weathered Hydrocarbons in Laboratory Microcosms and Soil Columns Simulating Natural Attenuation Field Conditions

C. Robin Cunningham et al. — Tue, 18 Nov 2008 16:09:05 PST

Abstract of paper presented at conference.

Optimization of High-Strength Hydrocarbon Biodegradation Using Respirometry

Bunkim G. Chokshi et al. — Tue, 18 Nov 2008 16:09:00 PST

Laboratory respirometry experiments were conducted on mixtures of soil and oily sludge to estimate biodegradation rates by CO₂ production rates and determine optimum conditions for biodegradation of high-strength hydrocarbon waste products. These experiments were used to determine a suitable range of total petroleum hydrocarbon (TPH) concentration for biological treatment and to optimize for nutrient addition and moisture content. CO₂ production rates from biological respiration of hydrocarbon-contaminated soil were maximized at concentrations of 3-9% TPH (30,00090,000 mg/kg TPH). CO₂ production rates decreased dramatically at concentrations above 9% TPH, indicating that either these concentrations are lethal to microbes present, or this high sludge content inhibits aeration of the soils. Addition of 120 mg/kg nitrogen, 40 mg/kg phosphorous, and 40 mg/kg potassium to the soils resulted in a three fold increase in CO₂ production rates. No significant increase in CO₂ production was observed when the nutrient addition was increased to 240 mg/kg nitrogen, 80 mg/kg phosphorous, and 80 mg/kg potassium. Maximum CO₂ production rates were observed at 15-20% moisture content. CO₂ production rates decreased significantly at and below 10% moisture and at and above 25% moisture. Maximum CO₂ production rates observed for soil with 50,000 mg/kg TPH, with added nutrients at optimum moisture content, were 30-35 μL CO₂/g/hr. Assuming all CO₂ was generated from hydrocarbon degradation, this maximum CO₂ production rate corresponds to a hydrocarbon biodegradation rate of approximately 500 mg TPH/kg/day (assuming 100% respiration for a conservative estimate). If ideal conditions are maintained and rates of respiration remain high, clay soil contaminated with 60,000 mg/kg TPH sludge could probably be remediated in 2 months.