On-Site Treatment of Contaminated Soils: An Approach to Bioremediation of Weathered Petroleum Compounds

A bench-scale investigation was conducted prior to on-site bioremediation of 52,000 cubic yards of contaminated soil containing weathered, structurally complex petroleum compounds from an inactive oil refinery. Addition of bulking agents was required to improve soil physical properties. A supplemental study was also conducted to evaluate the effectiveness of bio-enhancement products. Loss of n-alkanes was rapid in soil mixtures containing a high nitrogen sludge compost, but very slow in mixtures containing wood products as bulking agents. By completion of the study at day 110, the isoprenoids pristane and phytane had nearly disappeared from mixtures containing sludge compost. Clearly, pristane and phytane are inadequate biomarkers when conditions favor an advanced stage of biodegradation. Nearly half the complex branched and cyclic alkanes in the unresolved complex mixture also degraded. After 70 days, depletion of dibenzo-thiophenes and phenan-threnes was 75 and 90%, respectively. The most stable PAHs within each group were the highly methylated homologues. Because of their complex structures, both steranes and hopanes were stable in all soil mixtures. Data were normalized to hopanes as a conserved internal standard or biomarker. Use of hopane-normalized data successfully eliminated much of the data variability and permitted a more accurate assessment of biodegradation. A relatively slow decline in total hydrocarbons occurred later in the study. This slowing tendency of microbial utilization is caused not only by substrate depletion, but also because remaining hydrocarbons are structurally more complex and persistent. Because of this, it is important to avoid using kinetic data from early stages of bioremediation to predict later hydrocarbon losses, such as the time required to attain a cleanup standard. In the supplemental study, an oleophilic fertilizer product accelerated hydrocarbon degradation when compared with a conventional fertilizer. This product will be tested in combination with organic bulking agents under field conditions to determine its cost effectiveness.     

Surfactant enhances biodegradation of hydrocarbons: Microcosm and field study

The purpose of the present study was to provide new methods that would increase the rates of biodegradation of petroleum hydrocarbons in soil, thus reducing the time required to achieve a satisfactory level of residual hydrocarbon in an ex situ bioremediation. Results of laboratory studies on several techniques were used to guide our implementation of these methods in controlled field studies. Soils contaminated with nonvolatile hydrocarbons were treated with various combinations of (1) an anionic surfactant guanidinium cocoate (CGS), (2) a consortium of hydrocarbon‐degrading microorganisms, (3) a slow‐release form of nitrogen:urea, and (4) the bulking agent vermiculite. Laboratory results describing the activity of CGS have been presented previously (Jain et al., 1992). The amount and rate of hydrocarbon loss in treated soil was compared with hydrocarbon lost in soil that received no amendment other than water (water only). We also used a sheen screen method (Nelson et al., 1995), to assess the effectiveness of our field application of microorganisms.     

Biodegradation of engine oil in soil

Laboratory experiments were conducted with the aim of bioremediation of sandy soil from engine oil in 5% concentration. Bacterial strains, active in degrading oil hydrocarbons as a sole source of carbon and energy were selected and identified. Optimal parameters, such as concentration of inorganic nutrients (expressed as C:N and C:P ratio) and the size of inoculum were established in experiments on 1% engine oil biodegradation. Process enhancing role of surfactants addition, the application of immobilized biomass and reinoculations was also evaluated.     

Bioremediation by Composting of Heavy Oil Refinery Sludge in Semiarid Conditions

The present work attempts to ascertain the efficacy of low cost technology (in our case, composting) as a bioremediation technique for reducing the hydrocarbon content of oil refinery sludge with a large total hydrocarbon content (250–300 g kg⁻¹), in semiarid conditions. The oil sludge was produced in a refinery sited in SE Spain The composting system designed, which involved open air piles turned periodically over a period of 3 months, proved to be inexpensive and reliable. The influence on hydrocarbon biodegradation of adding a bulking agent (wood shavings) and inoculation of the composting piles with pig slurry (a liquid organic fertiliser which adds nutrients and microbial biomass to the pile) was also studied. The most difficult part during the composting process was maintaining a suitable level of humidity in the piles. The most effective treatment was the one in which the bulking agent was added, where the initial hydrocarbon content was reduced by 60% in 3 months, compared with the 32% reduction achieved without the bulking agent. The introduction of the organic fertiliser did not significantly improve the degree of hydrocarbon degradation (56% hydrocarbon degraded). The composting process undoubtedly led to the biodegradation of toxic compounds, as was demonstrated by ecotoxicity tests using luminescent bacteria and tests on plants in Petri dishes.     

Influence of Bulking Agents,Fertilizers and Bacteria on the Removal of Diesel from a Newfoundland Soil

Laboratory experiments in culture flasks, containing diesel-contaminated Newfoundland soil samples, were undertaken to compare the influence of fertilizers, microorganisms and bulking agents on bioremediation. In Phase I experiments only one fertilizer (cow manure or poultry manure), one bulking agent (sand or hay), or one inoculum (cold-tolerant indigenous bacteria or exogenous commercial bacteria) was added to a soil sample. In Phase II experiments, Design-Expert® Version 6 design of experiment software determined the combinations of fertilizers, bulking agents and inocula to be mixed with the soil samples to study the interactions among the amendments. The maximum diesel removal at 90 days occurred in the sample with sand (Phase I) and in the sample with cow manure, an inoculum of cold-tolerant indigenous bacteria, and sand (Phase II). Diesel removal at 45 days for the same two samples was 85.4% (Phase I) and 91.9% (Phase II), suggesting the cow manure and/or cold-tolerant bacteria inoclum accelerated the process. The poultry manure, commercial bacteria and hay were less effective than their counterparts. The commercial bacteria were more sensitive to diesel concentration than the indigenous cold-tolerant bacteria. The addition of sand, cow manure, and poultry manure improved diesel removal.     

Compost convective airflow under passive aeration

For composting, passive aeration can save energy costs while being just as efficient as forced or active aeration. Passive aeration requires the proper design of aeration ducts, and thus, the proper prediction of the convective airflow rates created by the temperature differential between the compost and the ambient air. To establish such relationship, the temperature and convective air flow regimes of composts were investigated using three bulking agents (wood shavings, hay and straw), each at three moisture contents (MC-60%, 65% and 70%) spanning the normal values. All bulking agent and aeration treatments were aerated in duplicate under passive and active regimes. Laboratory vessels of 105 L were used for all treatments. Passive aeration treatments produced temperatures above 57 degrees C, as did the treatments actively aerated at 4 mg of air s(-1) kg(-1) of initial dry compost material. Compost MC had an effect only on the peak compost temperature, occurring between day 2 and 6. After 6 days of composting, MC no longer had any effect on temperature regime because of the loss of moisture by each mixture. A relationship was established between the Grasholf number (Gr-ratio of buoyancy to viscous forces) and the convective airflow rates, to size the aeration ducts for passive aeration. In general, convective airflow rates ranged from 1.5 to 0.7 mg of dry air s(-1) kg(-1) of initial compost dry matter, from day 0 to day 20, respectively, and for all compost treatments. This airflow rate sizes the aeration ducts installed under compost piles for passive aeration. As compared to straw where airflow rate dropped over a given level of Gr, wood shavings and hay were found to be more effective as bulking agents, as their airflow rate increased constantly with Gr.     

Bioremediation of Crude Oil-Contaminated Soil Using Slurry-Phase Biological Treatment and Land Farming Techniques

Field-scale experiments on bioremediation of soil heavily contaminated with crude oil were undertaken on the territory of the Kokuyskoye oil field (Perm region, West Urals, Russia) owned by the LUKOIL Company. The pollution consisted of the contents of a oil waste storage pit, which mostly received soils contaminated after accidental oil spills and also the solid n-alkane (paraffin) wastes removed from the surface of drilling equipment. Laboratory analyses of soil samples indicated contamination levels up to 200?g/kg of total recoverable petroleum hydrocarbons (TRPH). Average oil composition consisted of 64% aliphatics, 25% aromatics, 8% heterocyclics, and 3% of tars/asphaltenes. Ex situ bioremediation techniques involved the successive treatment of contaminated soil using a bioslurry reactor and land farming cells. An oleophilic biofertilizer based on Rhodococcus surfactant complexes was used in both treatment systems. An aerobic slurry bioreactor was designed, and the biofertilizer applied weekly. Slurry-phase biotreatment of the contaminated soil resulted in an 88% reduction in oil concentration after 2 months. The resulting reactor product, containing approximately 25?g/kg of TRPH, was then loaded into land farming cells for further decontamination. To enhance bioremediation, different treatments (e.g., soil tilling, bulking with woodchips, watering, and biofertilizer addition) were used. The rates of oil biodegradation were 300 to 600?ppm/day. As a result, contamination levels dropped to 1.0 to 1.5?g/kg of TRPH after 5 to 7 weeks. Tertiary soil management involved phytoremediation where land farming cells were seeded with a mixture of three species of perennial grass. The effect of phytoremediation on the residual decontamination and rehabilitation of soil fertility is being evaluated.     

Organic Bulking Agents for Enhancing Oil Bioremediation in Soil

Soil contaminated with oil is bioremediated by optimizing conditions for microbial activity. Often the question arises about the benefits of bulking with organic materials to improve soil conditions to enhance degradation of the less biodegradable or less bioavailable components. An investigation was undertaken in the laboratory with the objective of measuring the influence of bulking with dried plant material, bermudagrass, and alfalfa on the degradation of oily sludge added to soil. The oily sludge was diluted 50:50 on a weight basis with soil to achieve a final concentration of 100 g oil and grease kg^-1 of final soil mixture. Bulking agents were added 40 d after dilution of the sludge and optimization of environmental conditions to allow time for the readily decomposable fraction to be degraded before amendment with bulking agents. Populations of heterotrophic microorganisms increased approximately ten times by 40 and 80 d after addition of bulking agents, but the numbers of hydrocarbon-degrading microorganisms did not significantly increase above the number in the nonbulked control. Bulking agents increased the quantity of total petroleum hydrocarbons degraded by approximately 20% during the first 40 d after being added. Disappearance of hydrocarbons for bulked treatments was much slower during the next 40 d, such that the total petroleum hydrocarbon content for both bulked and nonbulked treatments generally was not significantly different at the end. It appears that adding bulking agents may enhance the rate of decomposition of total petroleum hydrocarbons by stimulating the general heterotrophic population of microorganisms, but the influence may not be sustained to influence the extent of decomposition.     

Bacterial Community Dynamics during Bioremediation of Diesel Oil-Contaminated Antarctic Soil

The effect of nutrient and inocula amendment in a bioremediation field trial using a nutrient-poor Antarctic soil chronically contaminated with hydrocarbons was tested. The analysis of the effects that the treatments caused in bacterial numbers and hydrocarbon removal was combined with the elucidation of the changes occurring on the bacterial community, by 16S rDNA-based terminal restriction fragment length polymorphism (T-RFLP) typing, and the detection of some of the genes involved in the catabolism of hydrocarbons. All treatments caused a significant increase in the number of bacteria able to grow on hydrocarbons and a significant decrease in the soil hydrocarbon content, as compared to the control. However, there were no significant differences between treatments. Comparison of the soil T-RFLP profiles indicated that there were changes in the structure and composition of bacterial communities during the bioremediation trial, although the communities in treated plots were highly similar irrespective of the treatment applied, and they had a similar temporal dynamics. These results showed that nutrient addition was the main factor contributing to the outcome of the bioremediation experiment. This was supported by the lack of evidence of the establishment of inoculated consortia in soils, since their characteristic electrophoretic peaks were only detectable in soil profiles at the beginning of the experiment. Genetic potential for naphthalene degradation, evidenced by detection of nahAc gene, was observed in all soil plots including the control. In treated plots, an increase in the detection of catechol degradation genes (nahH and catA) and in a key gene of denitrification (nosZ) was observed as well. These results indicate that treatments favored the degradation of aromatic hydrocarbons and probably stimulated denitrification, at least transiently. This mesocosm study shows that recovery of chronically contaminated Antarctic soils can be successfully accelerated using biostimulation with nutrients, and that this causes a change in the indigenous bacterial communities and in the genetic potential for hydrocarbon degradation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

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 Microtox^TM toxicity, and limited hydrocarbon mobility.     

Bacterial community dynamics and polycyclic aromatic hydrocarbon degradation during bioremediation of heavily creosote-contaminated soil

Bacterial community dynamics and biodegradation processes were examined in a highly creosote-contaminated soil undergoing a range of laboratory-based bioremediation treatments. The dynamics of the eubacterial community, the number of heterotrophs and polycyclic aromatic hydrocarbon (PAH) degraders, and the total petroleum hydrocarbon (TPH) and PAH concentrations were monitored during the bioremediation process. TPH and PAHs were significantly degraded in all treatments (72 to 79% and 83 to 87%, respectively), and the biodegradation values were higher when nutrients were not added, especially for benzo(a)anthracene and chrysene. The moisture content and aeration were determined to be the key factors associated with PAH bioremediation. Neither biosurfactant addition, bioaugmentation, nor ferric octate addition led to differences in PAH or TPH biodegradation compared to biodegradation with nutrient treatment. All treatments resulted in a high first-order degradation rate during the first 45 days, which was markedly reduced after 90 days. A sharp increase in the size of the heterotrophic and PAH-degrading microbial populations was observed, which coincided with the highest rates of TPH and PAH biodegradation. At the end of the incubation period, PAH degraders were more prevalent in samples to which nutrients had not been added. Denaturing gradient gel electrophoresis analysis and principal-component analysis confirmed that there was a remarkable shift in the composition of the bacterial community due to both the biodegradation process and the addition of nutrients. At early stages of biodegradation, the alpha-Proteobacteria group (genera Sphingomonas and Azospirillum) was the dominant group in all treatments. At later stages, the gamma-Proteobacteria group (genus Xanthomonas), the alpha-Proteobacteria group (genus Sphingomonas), and the Cytophaga-Flexibacter-Bacteroides group (Bacteroidetes) were the dominant groups in the nonnutrient treatment, while the gamma-Proteobacteria group (genus Xathomonas), the beta-Proteobacteria group (genera Alcaligenes and Achromobacter), and the alpha-Proteobacteria group (genus Sphingomonas) were the dominant groups in the nutrient treatment. This study shows that specific bacterial phylotypes are associated both with different phases of PAH degradation and with nutrient addition in a preadapted PAH-contaminated soil. Our findings also suggest that there are complex interactions between bacterial species and medium conditions that influence the biodegradation capacity of the microbial communities involved in bioremediation processes.     

生物反应器法处理油泥污染土壤的研究

采油过程产生的油泥是整个石油烃污染源的重点。在陆地生态环境中 ,烃类的大量存在往往对植物的生物学质量产生不利影响 ,更重要的是石油中的一些多环芳烃是致癌和致突变物质 ,这些致癌和致突变的有机污染物进入农田生态系统后 ,在动植物体内逐渐富集 ,进而威胁人类的生存和健康[1 ,1 1 ] 。大量的废弃油泥 ,不仅污染农田 ,同时也给石油行业带来巨大的经济损失。污染土壤的治理主要有物理、化学和生物 (生物修复 )方法 ,生物修复方法被认为最有生命力。污染土壤生物修复技术主要有 3种 ,即原位处理、挖掘堆置处理和反应器处理。反应器处理是…     

Bioremediation of PAH-contaminated soil by composting: A case study

Composting technique was used for bioremediation of industrial soil originating from a former tar-contaminated site. The composting process was regulated by aeration to keep optimal temperature gradient and concentrations of O₂ and CO₂ inside the composting pile. The efficiency of bioremediation was evaluated by performing analysis of 11 individual three- to six-ring unsubstituted aromatic hydrocarbons (PAH) and estimating of changes in ecotoxicity of the contaminated soil. After 42 d of composting, PAH with 3–4 rings were removed from 42 to 68%, other higher-molar mass PAH from 35 to 57%. Additional 100 d of compost maturation in open-air field did not result in a further decrease of PAH. Ecotoxicity tests performed with bioluminescent bacteriaVibrio fischerii showed a decrease in toxicity both after composting and maturation phases. However, toxicity tests on mustard-seed germination did not reveal any significant changes during composting and maturation phases.     

Effects of Bacillus subtilis O9 biosurfactant on the bioremediation of crude oil-polluted soils

The application of a surfactant from Bacillus subtilis O9 (Bs) on the bioremediation of soils polluted with crude oil was assayed in soil microcosms under laboratory conditions. Three concentrations of biosurfactant were assayed (1.9, 19.5, and 39 mg kg(-1) soil). Microcosms without biosurfactant were prepared as controls. During the experiment, the crude oil-degrading bacterial population, the aliphatic and aromatic hydrocarbons were monitored in each microcosm. The results indicated that applying Bs did not negatively affect the hydrocarbon-degrading microbial population Concentrations of 19 and 19.5mg (Bs) per kilogram of soil stimulated the growth of the population involved in the crude oil degradation, and accelerated the biodegradation of the aliphatic hydrocarbons. However, none of the assayed Bs concentrations stimulated aromatic hydrocarbon degradation.     

Use of Rice Husk as Bulking Agent in Bioremediation of Automobile Gas Oil Impinged Agricultural Soil

Evaluation of rice husk (RH) as bulking agent in bioremediation of automobile gas oil (AGO) hydrocarbon polluted agricultural soil using renewal by enhanced natural attenuation (RENA) as control was the subject of the present investigation. The effect of different parameters such as total petroleum hydrocarbon (TPH), dehydrogenase activity (DHA), optical density and pH on bioremediation performance were evaluated. The studied parameters such as microbial dynamics, percentage degradation and DHA were found to be higher in RH-amended system and differed significantly with control at P < 0.05. RH resulted in high removal efficiency of 97.85 ± 0.93% under a two-month incubation period, while RENA had lesser removal efficiency of 53.15 ± 3.81%. Overall hydrocarbon biodegradation proceeded very slowly in the RENA particularly from week 0 to 4. Experimental data perfectly fitted into the first-order kinetic and generated high r² values (0.945), first-order degradation constant (0.47 day^?1), and shorter degradation half-life (1.50 d)—t_1/2 = Ln2/K and Ln2 numerically equals to 0.693 and hence written as 0.693/K. Micrococcus luteus and Rhizopus arrhizus were isolated in the present study, which displayed extreme AGO hydrocarbon biodegradative abilities. The use of RH in hydrocarbon-polluted soil significantly increased biodegradation rate and resulted in effective AGO cleanup within 2 months period. Therefore, RH provides an alternative source of bioremediation material in field application for abundant petroleum hydrocarbon soil pollution.     

Effects of alkylphosphates and nitrous oxide on microbial degradation of polycyclic aromatic hydrocarbons

We conducted a series of liquid-culture experiments to begin to evaluate the abilities of gaseous sources of nitrogen and phosphorus to support biodegradation of polycyclic aromatic hydrocarbons (PAHs). Nutrients examined included nitrous oxide, as well as triethylphosphate (TEP) and tributylphosphate (TBP). Cultures were established using the indigenous microbial populations from one manufactured gas plant (MGP) site and one crude oil-contaminated drilling field site. Mineralization of phenanthrene was measured under alternative nutrient regimes and was compared to that seen with ammoniacal nitrogen and PO(4). Parallel cultures were used to assess removal of a suite of three- to five-ring PAHs. In summary, the abilities of the different communities to degrade PAH when supplemented with N(2)O, TEP, and TBP were highly variable. For example, in the MGP soil, organic P sources, especially TBP, supported a considerably higher degree of removal of low-molecular-weight PAHs than did PO(4); however, loss of high-molecular-weight compounds was impaired under these conditions. The disappearance of most PAHs was significantly less in the oil field soil when organophosphates were used. These results indicate that the utility of gaseous nutrients for PAH bioremediation in situ may be limited and will very likely have to be assessed on a case-by-case basis.     

Low temperature bioremediation of oil-contaminated soil using biostimulation and bioaugmentation with a Pseudomonas sp. from maritime Antarctica

AIMS: To identify native Antarctic bacteria capable of oil degradation at low temperatures. METHODS AND RESULTS: Oil contaminated and pristine soils from Signy Island (South Orkney Islands, Antarctica) were examined for bacteria capable of oil degradation at low temperatures. Of the 300 isolates cultured, Pseudomonas strain ST41 grew on the widest range of hydrocarbons at 4 degrees C. ST41 was used in microcosm studies of low temperature bioremediation of oil-contaminated soils. Microcosm experiments showed that at 4 degrees C the levels of oil degradation increased, relative to the controls, with (i) the addition of ST41 to the existing soil microbial population (bioaugmentation), (ii) the addition of nutrients (biostimulation) and to the greatest extent with (iii) a combination of both treatments (bioaugmentation and biostimulation). Addition of water to oil contaminated soil (hydration) also enhanced oil degradation, although less than the other treatments. Analysis of the dominant species in the microcosms after 12 weeks, using temporal temperature gradient gel electrophoresis, showed Pseudomonas species to be the dominant soil bacteria in both bioaugmented and biostimulated microcosms. CONCLUSIONS: Addition of water and nutrients may enhance oil degradation through the biostimulation of indigenous oil-degrading microbial populations within the soil. However, bioaugmentation with Antarctic bacteria capable of efficient low temperature hydrocarbon degradation may enhance the rate of bioremediation if applied soon after the spill. SIGNIFICANCE AND IMPACT OF THE STUDY: In the future, native soil bacteria could be of use in bioremediation technologies in Antarctica.     

An exploratory study of peat and sawdust as enhancers in the (bio)degradation of n-dodecane

Current practice for dealing with oil spills involves the use of adsorbent materials to contain the pollution prior to bioremediation of the contaminated soil and adsorbent. This work presents a study of the effects of bioavailable carbon sources in the adsorbents peat and sawdust as organic nutrients for microorganisms specialized in degrading n-dodecane in soil and sawdust contaminated with hydrocarbon mixtures. An experimental bioremediation system was developed using n-dodecane, biomass adapted to n-dodecane, inorganic nutrients and the two adsorbents (sterilized). Bioreactors containing peat enhanced cell growth the most and also evolved more CO(2). An advantage of peat is that its soluble carbon sources can sustain higher cell densities compared to sawdust, and this may prove decisive when cultivating endogenous microorganisms for the aerobic bioremediation of soils contaminated with hydrocarbons. However, at the end of the 68-day experiment slightly higher n-dodecane removal was identified in the system containing sawdust-n-dodecane (99.6%) than in that with peat-n-dodecane (98.5%), evidencing the higher hydrocarbon retention capacity of peat. Based on this study, the use of sawdust instead of peat is recommended when an adapted inoculum is available for aerobic bioremediation of organic contaminants, whereas the use of peat is advisable to boost cell densities in order to improve the probability of sustaining a viable biomass in unfavorable conditions.     

Influence of biochar and compost on phytoremediation of oil-contaminated soil

The use of pyrolyzed carbon, biochar, as a soil amendment is of potential interest for improving phytoremediation of soil that has been contaminated by petroleum hydrocarbons. To examine this question, the research reported here compared the effects of biochar, plants (mesquite tree seedlings), compost and combinations of these treatments on the rate of biodegradation of oil in a contaminated soil and the population size of oil-degrading bacteria. The presence of mesquite plants significantly enhanced oil degradation in all treatments except when biochar was used as the sole amendment without compost. The greatest extent of oil degradation was achieved in soil planted with mesquite and amended with compost (44% of the light hydrocarbon fraction). Most probable number assays showed that biochar generally reduced the population size of the oil-degrading community. The results of this study suggest that biochar addition to petroleum-contaminated soils does not improve the rate of bioremediation. In contrast, the use of plants and compost additions to soil are confirmed as important bioremediation technologies.     

Comparative bioremediation of soils contaminated with diesel oil by natural attenuation, biostimulation and bioaugmentation

Bioremediation of diesel oil in soil can occur by natural attenuation, or treated by biostimulation or bioaugmentation. In this study we evaluated all three technologies on the degradation of total petroleum hydrocarbons (TPH) in soil. In addition, the number of diesel-degrading microorganisms present and microbial activity as indexed by the dehydrogenase assay were monitored. Soils contaminated with diesel oil in the field were collected from Long Beach, California, USA and Hong Kong, China. After 12 weeks of incubation, all three treatments showed differing effects on the degradation of light (C12-C23) and heavy (C23-C40) fractions of TPH in the soil samples. Bioaugmentation of the Long Beach soil showed the greatest degradation in the light (72.7%) and heavy (75.2%) fractions of TPH. Natural attenuation was more effective than biostimulation (addition of nutrients), most notably in the Hong Kong soil. The greatest microbial activity (dehydrogenase activity) was observed with bioaugmentation of the Long Beach soil (3.3-fold) and upon natural attenuation of the Hong Kong sample (4.0-fold). The number of diesel-degrading microorganisms and heterotrophic population was not influenced by the bioremediation treatments. Soil properties and the indigenous soil microbial population affect the degree of biodegradation; hence detailed site specific characterization studies are needed prior to deciding on the proper bioremediation method.