Biodegradation of aged diesel in diverse soil matrixes: impact of environmental conditions and bioavailability on microbial remediation capacity

While bioremediation of total petroleum hydrocarbons (TPH) is in general a robust technique, heterogeneity in terms of contaminant and environmental characteristics can impact the extent of biodegradation. The current study investigates the implications of different soil matrix types (anthropogenic fill layer, peat, clay, and sand) and bioavailability on bioremediation of an aged diesel contamination from a heterogeneous site. In addition to an uncontaminated sample for each soil type, samples representing two levels of contamination (high and low) were also used; initial TPH concentrations varied between 1.6 and 26.6 g TPH/kg and bioavailability between 36 and 100 %. While significant biodegradation occurred during 100 days of incubation under biostimulating conditions (64.4–100 % remediation efficiency), low bioavailability restricted full biodegradation, yielding a residual TPH concentration. Respiration levels, as well as the abundance of alkB, encoding mono-oxygenases pivotal for hydrocarbon metabolism, were positively correlated with TPH degradation, demonstrating their usefulness as a proxy for hydrocarbon biodegradation. However, absolute respiration and alkB presence were dependent on soil matrix type, indicating the sensitivity of results to initial environmental conditions. Through investigating biodegradation potential across a heterogeneous site, this research illuminates the interplay between soil matrix type, bioavailability, and bioremediation and the implications of these parameters for the effectiveness of an in situ treatment.     

Field Note: Phytoremediation of Petroleum Sludge Contaminated Field Using Sedge Species,Cyperus Rotundus (Linn.) and Cyperus Brevifolius (Rottb.) Hassk

The aim of this study was to degrade total petroleum hydrocarbon (TPH) in a petroleum sludge contaminated site (initial TPH concentration of 65,000–75,000 mg.kg^–1) with two native sedge species namely Cyperus rotundus (Linn.) and Cyperus brevifolius (Rottb.) Hassk. Fertilized and unfertilized treatments were maintained separately to record the influence of fertilizer in TPH degradation. The average biomass production (twenty plants from each treatment) of C. rotundus was 345.5 g and that of C. brevifolius was 250.6 g in fertilized soil during 360 days. Decrease in soil TPH concentration was higher in fertilized soil (75% for C. rotundus and 64% for C. brevifolius) than in unfertilized soil (36% for C. rotundus and 32% for C. brevifolius). In unvegetated treatments, decrease in soil TPH concentration in fertilized (12%) and unfertilized soil (8%) can be attributed to natural attenuation and microbial degradation. TPH accumulation in roots and shoots was significantly higher in fertilized soil in comparison to unfertilized soils (p < 0.05). Most probable number (MPN) in planted treatments was significantly higher than in unplanted treatments (p < 0.05).     

Comparison of bioremediation strategies for soil impacted with petrochemical oily sludge

Different bioremediation techniques (natural attenuation, biostimulation and bioaugmentation) in contaminated soils with two oily sludge concentrations (1.5% and 6.0%) in open and closed microcosms systems were assessed during 90 days. The results showed that the highest biodegradation rates were obtained in contaminated soils with 6% in closed microcosms. Addition of microbial consortium and nutrients in different concentrations demonstrated higher biodegradation rate of total petroleum hydrocarbons (TPH) than those of the natural attenuation treatment. Soils treated in closed microcosms showed highest removal rate (84.1 ± 0.9%) when contaminated at 6% and bacterial consortium and nutrients in low amounts were added. In open microcosms, the soil contaminated at 6% using biostimulation with the highest amounts of nutrients (C:N:P of 100:10:1) presented the highest degradation rate (78.7 ± 1.3%). These results demonstrate that the application of microbial consortium and nutrients favored biodegradation of TPH present in oily sludge, indicating their potential applications for treatment of the soils impacted with this important hazardous waste.     

Kinetic Modelling and Half-Life Study on Bioremediation of Soil Co-Contaminated with Lubricating Motor Oil and Lead Using Different Bioremediation Strategies

The focus of this study was to investigate the effect of nutrient supplement (urea fertilizer) and microbial species augmentation (mixed culture of Aeromonas, Micrococcus, and Serratia sp.) on biodegradation of lubricating motor oil (LMO) and lead uptake by the autochthonous microorganism in LMO and lead-impacted soil were investigated. The potential inhibitory effects of lead on hydrocarbon utilization were investigated over a wide range of lead concentrations (25–200 mg/kg) owing to the complex co-contamination problem frequently encountered in most sites. Under aerobic conditions, total petroleum hydrocarbons (TPH) removal was 45.3% in the natural attenuation microcosm while a maximum of 72% and 68.2% TPH removal was obtained in biostimulation and bioaugmentation microcosms, respectively. Lead addition, as lead nitrate, to soil samples reduced the number of hydrocarbon degraders in all samples by a wide range (11–52%) depending on concentration and similarly, the metabolic activities were affected as observed in mineralization of LMO (3–60%) in soils amended with various lead concentrations. Moreover, the uptake of lead by the autochthonous microorganisms in the soil reduced with increase in the initial lead concentration. First-order kinetics described the biodegradation of LMO very well. The biodegradation rate constants were 0.015, 0.033, and 0.030 day^?1 for LMO degradation in natural attenuation, biostimulation and bioaugmentation treatment microcosms, respectively. The presence of varying initial lead concentration reduced the biodegradation rate constant of LMO degradation in the biostimulation treatment microcosm. Half-life times were 46.2, 21, and 23 days for LMO degradation in natural attenuation, biostimulation and bioaugmentation treatment microcosms, respectively. The half-life time in the biostimulation treatment microcosm was increased with a range between 10.7 and 39.2 days by the presence of different initial lead concentration. The results have promising potential for effective remediation of soils co-contaminated with hydrocarbons and heavy metals.     

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.     

Biostimulation and Phytoremediation Treatment Strategies of Gasoline-Nickel Co-Contaminated Soil

This study investigated the potential effect of poultry dung (biostimulation) and stubborn grass (Sporobolus pyramidalis) (phytoremediation) on microbial biodegradation of gasoline and nickel uptake in gasoline-nickel-impacted soil. In addition, the potential stimulatory effects of nickel on hydrocarbon utilization were investigated over a small range of nickel concentrations (2.5–12.5 mg/kg). The results showed that an increase in nickel concentration increased hydrocarbon degraders in soil by a range of 8.4–17.2% and resulted in a relative increase in gasoline biodegradation (57.5–62.4%). Also, under aerobic conditions, total petroleum hydrocarbons’ (TPH) removal was 62.4% in the natural gasoline-nickel microcosm (natural attenuation), and a maximum of 78.5%, 85.7%, and 95.8% TPH removal was obtained in phytoremediation, biostimulation, and a combination of biostimulation- and phytoremediation-treated microcosms, respectively. First-order kinetics described the biodegradation of gasoline and nickel uptake very well. Half-life times obtained were 28.88, 18.24, 14.44, and 8.56 days for gasoline degradation under natural attenuation, phytoremediation, biostimulation, and combined biostimulation and phytoremediation treatment methods, respectively. The results indicate that these remediation methods have promising potential for effective remediation of soils co-contaminated with petroleum hydrocarbons and heavy metals.     

Upscaling Effects of Soil Improvement by Microbially Induced Calcite Precipitation by Surface Percolation

This study has contributed to the technology of soil stabilization via biocementation based on microbially induced calcite precipitation. The newly described method of in situ soil stabilization by surface percolation to dry soil under free draining environment is tested for its up-scaling potential. Then, 2-m columns of one-dimensional trials indicated that repeated treatments of fine sand (<0.3 mm) could lead to clogging closed at the injection end, resulting in limited cementation depth of less than 1 m. This clogging problem was not observed in 2 m coarse (>0.5 mm) sand columns, allowing strength varying between 850 to 2067 kPa along the entire 2 m depth. Three-dimensional fine sand cementation trials indicated that relatively homogenous cementation in the horizontal direction could be achieved with 80% of cemented sand cementing to a strength between 2 to 2.5 MPa and to a depth of 20 cm. A simple mathematical model elucidated that the cementation depth was dependent on the infiltration rate of the cementation solution and the in-situ urease activity. The model also correctly predicted that repeated treatments would enhance clogging close to the injection point. Both experimental and simulated results suggested that the surface percolation technology was more applicable for coarse sand.     

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 α-Proteobacteria group (genera Sphingomonas and Azospirillum) was the dominant group in all treatments. At later stages, the γ-Proteobacteria group (genus Xanthomonas), the α-Proteobacteria group (genus Sphingomonas), and the Cytophaga-Flexibacter-Bacteroides group (Bacteroidetes) were the dominant groups in the nonnutrient treatment, while the γ-Proteobacteria group (genus Xathomonas), the β-Proteobacteria group (genera Alcaligenes and Achromobacter), and the α-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.     

Temperature impacts on anaerobic biotransformation of LNAPL and concurrent shifts in microbial community structure

Thermally-enhanced bioremediation is a promising treatment approach for petroleum contamination; however, studies examining temperature effects on anaerobic biodegradation in zones containing light non-aqueous phase liquids (LNAPLs) are lacking. Herein, laboratory microcosm studies were conducted for a former refinery to evaluate LNAPL transformation, sulfate reduction, and methane generation over a one-year period for temperatures ranging from 4 to 40 °C, and microbial community shifts were characterized. Temperatures of 22 and 30 °C significantly increased total biogas generation compared to lower (4 and 9 °C) and higher temperatures (35 and 40 °C; p < 0.1). Additionally, at 22 and 30 °C methane generation commenced ~6 months earlier than for 35 and 40 °C. Statistically significant biodegradation of benzene, toluene and xylenes was observed at elevated temperatures but not at lower temperatures (p < 0.1). Additionally, a novel differential chromatogram approach was developed to overcome challenges associated with resolving losses in complex mixtures of hydrocarbons, and application of this method revealed greater losses of hydrocarbons at 22 and 30 °C as compared to lower and higher temperatures. Finally, molecular biology assays revealed that the composition and activity of microbial communities shifted in a temperature-dependent manner. Collectively, results demonstrated that anaerobic biodegradation processes can be enhanced by increasing the temperature of LNAPL-containing soils, but biodegradation does not simply increase as temperature increases likely due to a lack of microorganisms that thrive at temperatures well above the historical high temperatures for a site. Rather, optimal degradation is achieved by holding soils at the high end of, or slightly higher than, their natural range.     

Evaluation of Inoculum Addition To Stimulate In Situ Bioremediation of Oily-Sludge-Contaminated Soil

A full-scale study evaluating an inoculum addition to stimulate in situ bioremediation of oily-sludge-contaminated soil was conducted at an oil refinery where the indigenous population of hydrocarbon-degrading bacteria in the soil was very low (10³ to 10⁴ CFU/g of soil). A feasibility study was conducted prior to the full-scale bioremediation study. In this feasibility study, out of six treatments, the application of a bacterial consortium and nutrients resulted in maximum biodegradation of total petroleum hydrocarbon (TPH) in 120 days. Therefore, this treatment was selected for the full-scale study. In the full-scale study, plots A and B were treated with a bacterial consortium and nutrients, which resulted in 92.0 and 89.7% removal of TPH, respectively, in 1 year, compared to 14.0% removal of TPH in the control plot C. In plot A, the alkane fraction of TPH was reduced by 94.2%, the aromatic fraction of TPH was reduced by 91.9%, and NSO (nitrogen-, sulfur-, and oxygen-containing compound) and asphaltene fractions of TPH were reduced by 85.2% in 1 year. Similarly, in plot B the degradation of alkane, aromatic, and NSO plus asphaltene fractions of TPH was 95.1, 94.8, and 63.5%, respectively, in 345 days. However, in plot C, removal of alkane (17.3%), aromatic (12.9%), and NSO plus asphaltene (5.8%) fractions was much less. The population of introduced Acinetobacter baumannii strains in plots A and B was stable even after 1 year. Physical and chemical properties of the soil at the bioremediation site improved significantly in 1 year.     

Oil removal and effects of spilled oil on active microbial communities in close to salt-saturation brines

Abiotic and biotic processes associated with the degradation of a light petroleum in brines close to the salt-saturation (~31 %) and the effect of labile organic matter (LOM) supply (casaminoacids/citrate; 0.2 and 0.1 % w/v, respectively) were followed during an incubation of 30 days. After 4-week incubation at 40 °C under light/dark cycles, a 24 % of abiotic degradation was observed in untreated brines. The stimulation of native brines community with LOM addition allowed an additional 12.8 % oil attenuation due to biodegradation processes. Successional changes in the active microbial community structure due to the oil contamination (16S rRNA DGGE approach) showed the selection of one phylotype affiliated to Salinibacter and the disappearance of Haloquadratum walsbyi in untreated brines. In LOM-amended microcosms, phylotypes related to Salinibacter, Haloarcula, Haloterrigena and Halorhabdus were selected. An effect of hydrocarbon contamination was only observed in the bacterial community with the inhibition of two dominant proteobacterial phylotypes. This study further confirms that short-term and moderate oil biodegradation is possible in LOM-stimulated brines. Biodegradation should be much more reduced under in situ conditions. Self-cleaning capacities of close to saturation hypersaline lakes appears, therefore very limited compared to non-extreme haline environments.     

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.     

Multi-substrate biodegradation interaction of 1, 4-dioxane and BTEX mixtures by <Emphasis Type="Italic">Acinetobacter baumannii</Emphasis> DD1

This study evaluated substrate interactions during the aerobic biodegradation of 1, 4-dioxane and BTEX mixtures by a pure culture, Acinetobacter baumannii DD1, which is capable of utilizing 1, 4-dioxane for growth. A. baumannii DD1 could utilize BTEX as a sole carbon source, but could not utilize m-xylene and p-xylene. In binary mixtures, there was a lag of about 14 h before the degradation of BTE, and 1, 4-dioxane only started to be utilized when BTE was completely degraded by 1, 4-dioxane-grown DD1. Furthermore, the biodegradation rate of 1, 4-dioxane decreased from 73.33 to 40.74 mg/(h g dry weight) after the biodegradation of benzene. 1, 4-dioxane could not be degraded after the biodegradation of o-xylene in 80 h. DD1 could also not degrade m-xylene and p-xylene coexisting with 1, 4-dioxane. The ability of DD1 to degrade BTEX occurred in the following order: benzene > ethylbenzene > toluene > o-xylene > m-xylene = p-xylene. The biodegradation of 1, 4-dioxane was not activated in the mixture with o-xylene, primarily because of the accumulation of the specific toxic intermediate, 2, 3-dimethylphenol. The lag in BTE degradation was presumably because of the induction of enzymes necessary for BTE degradation. Additionally, SDS-PAGE analysis demonstrated that there were different proteins during the degradation of benzene and 1, 4-dioxane.     

Biodegradation of high concentration of nitrobenzene by Pseudomonas corrugata embedded in peat-phosphate esterified polyvinyl alcohol

Efficiency on biodegradation of high concentration of nitrobenzene (NB) by peat-phosphate esterified polyvinyl alcohol-embedded NB-degrading bacteria Pseudomonas corrugata was conducted compared to free bacteria cells. Its biodegradation kinetics, reuse ability, degradation effect in the absence of the essential element needed for the growth of bacteria and degradation efficiency of the raw water from the contaminated site were also invested. Results show that the degradation rate when the concentration of NB was at 600, 750, and 900 mg/L reached 91.02, 83.23, and 55.9 %, which was higher than that observed in free bacteria at the same concentration levels. Biodegradation kinetics of the material could be well described by first- and zero-order kinetics when the concentration of NB was at 300, 450 mg/L and 600, 750, 900 mg/L, respectively. Stable degradation activity (stayed at a level of approximately 70 %) was displayed during the 11th repeat-batch experiment. The affect of absence of phosphorus in the medium can be abated ascribed to the addition of peat, which contributes with organic matter and other elements such as nitrogen and phosphorus necessary to maintain metabolically active the microorganisms. Effective biodegradation of the raw water from the experimental site revealed that the material can be a potential candidate for treating NB-contaminated wastewater in the practical setting.     

Decomposition pathways of 13C-depleted leaf litter in forest soils of the Swiss Jura

Decomposition of leaf litter and its incorporation into the mineral soil are key components of the C cycle in forest soils. In a ¹³C tracer experiment, we quantified the pathways of C from decomposing leaf litter in calcareous soils of a mixed beech forest in the Swiss Jura. Moreover, we assessed how important the cold season is for the decomposition of freshly fallen leaves. The annual C loss from the litter layer of 69–77% resulted mainly from the C mineralization (29–34% of the initial litter C) and from the transfer of litter material to the deeper mineral soil (>4 cm) by soil fauna (30%). Although only 4–5% of the initial litter C was leached as dissolved organic carbon (DOC), this pathway could be important for the C sequestration in soils in the long term: The DOC leached from the litter layer was mostly retained (95%) in the first 5 cm of the mineral soil by both physico-chemical sorption and biodegradation and, thus, it might have contributed significantly to the litter-derived C recovered in the heavy fraction (>1.6 g cm^?3) at 0–4 cm depth (4% of the initial litter C). About 80% of the annual DOC leaching from the litter layer occurred during the cold season (Nov–April) due to an initial DOC flush of water-soluble substances. In contrast, the litter mineralization in winter accounted for only 25% of the annual C losses through CO₂ release from the labelled litter. Nevertheless, the highest contributions (45–60%) of litter decay to the heterotrophic soil respiration were observed on warm winter days when the mineral soil was still cold and the labile litter pool only partly mineralized. Our ¹³C tracing also revealed that: (1) the fresh litter C only marginally primed the mineralization of older SOM (>1 year); and (2) non-litter C, such as throughfall DOC, contributed significantly to the C fluxes from the litter layer since the microbial biomass and the DOC leached from the litter layer contained 20–30% and up to 60% of unlabelled C, respectively. In summary, our study shows that significant amounts of recent leaf litter C (<1 year) are incorporated into mineral soils and that the cold season is clearly less important for the litter turnover than the warm season in this beech forest ecosystem.     

Biodegradation Kinetics of Hydrocarbons in Soil during Land Treatment of Oily Sludge

This study focuses on the processes influencing hydrocarbon residue persistence in soil, following land treatment of refinery oily sludge. Treating sludge applied to soil resulted in 70% to 90% degradation of total petroleum hydrocarbon (TPH) during 2 months, regardless of their initial concentrations (9 to 60 g/kg soil). Kinetic analyses performed on TPH degradation, in laboratory and field systems, revealed a degradation pattern characterized by two consecutive first-order kinetics reactions in all experimental settings. The first stage lasted about 3 weeks and was characterized by a temperature dependent rate constant of 0.047 day^-1 at 24°C. That value was comparable to the rate constant obtained when combining the individual rate constants of the saturated, aromatic, asphaltene and polar fractions. The subsequent slower stage rate constant was 0.012 day^-1, insensitive to temperature and to hydrocarbon composition. The transition between the two stages (about 21 days) was independent of the experimental temperature and the biodegradation extent during the first stage. It was concluded that the extent of residual accumulation in the soil was determined by the biodegradation efficiency during the first three weeks of treatment when biological processes dominated. During the following period, abiotic processes leading to reduced bioavailability of the TPH were limiting the degradation rate. Practically, as the first few weeks of treatment determine its efficiency, efforts to enhance the biological activity should be directed to that period.     

Influence of substratum on the degradation processes in diesel polluted sub-Antarctic soils (Crozet Archipelago)

Biodegradation by naturally occurring populations of microorganisms is a major mechanism for the removal of oil hydrocarbons from the environment. Therefore, follow-up of bacterial populations and chemical indices of biodegradation are important components of contaminated site assessment studies. Over a 4-year period following an accidental diesel contamination of the sub-Antarctic Crozet Archipelago (51°51′E–46°25′S), a field study was carried out in the contaminated area that is located in a transition zone between an arid fell-field (upstream) and a wet vegetated area (downstream). This study included a monitoring of heterotrophic and hydrocarbon-degrading bacterial abundance and chemical analysis of the remaining hydrocarbons. Significant higher number of heterotrophic and hydrocarbon-degrading bacterial counts revealed a rapid acclimation of sub-Antarctic microbial soil communities to the diesel fuel contamination. A chemical survey conducted during the last 2 years (2002 and 2003) showed that the total extractable hydrocarbons (TPH) content in arid fell field was reduced to ≤50% of their value while it was reduced only to ≤65% in vegetated soil. In addition, the decrease of TPH was always higher in the presence of fertilizer in the arid contaminated area, while fertilizer addition was almost inefficient in the wet contaminated one. All these results demonstrate a serious influence of the soil properties on the degradation rate. However, all chemical indices showed a significant reduction of alkanes and light aromatics in both contaminated area confirming a regular oil degradation process.     

Co-Metabolic Biodegradation of DBP by Paenibacillus sp. S-3 and H-2

Two di-n-butyl phthalate (DBP)-degrading strains, designated as S-3 and H-2, were isolated from DBP-polluted soil and both identified as Paenibacillus sp. When DBP was provided as the sole carbon source, about 45.5 and 71.7 % of DBP (100 mg/L) were degraded by strain S-3 and H-2, respectively, after incubation for 48 h. However, DBP (100 mg/L) was degraded completely by co-culture of strain S-3 and H-2 after incubation for 60 h. Four phthalic acid (PA) esters could be utilized by co-metabolism in the study and the degradation rates followed the order of dimethyl phthalate > diethyl phthalate > DBP > dioctyl phthalate. The metabolic pathway of DBP was elucidated based on the results of metabolites identification and enzyme assays. For strain S-3, DBP was degraded into butyl hydrogen phthalate which was degraded to PA by carboxyesterase further. But PA could be not hydrolyzed further because strain S-3 lacked 3,4-phthalate dioxygenase. Different with S-3, strain H-2 could hydrolyze PA into 3,4-dihydroxy-PA by 3,4-phthalate dioxygenase. Then 3,4-dihydroxy-PA was converted to protocatechuate and benzoic acid. Finally, the aromatic ring was cleavage and mineralized to CO₂ and H₂O. Above all, co-metabolism could increase the activity of 3,4-phthalate dioxygenase and accelerated the degradation of DBP. This study highlights an important potential use of co-metabolic biodegradation for the in situ bioremediation of DBP and its metabolites-contaminated environment.     

Pesticide dissipation and microbial community changes in a biopurification system: influence of the rhizosphere

The dissipation of atrazine, chlorpyrifos and iprodione in a biopurification system and changes in the microbial and some biological parameters influenced by the rhizosphere of Lolium perenne were studied in a column system packed with an organic biomixture. Three column depths were analyzed for residual pesticides, peroxidase, fluorescein diacetate activity and microbial communities. Fungal colonization was analyzed by confocal laser scanning microscopy to assess the extent of its proliferation in wheat straw. The L. perenne rhizosphere enhanced pesticide dissipation and negligible pesticide residues were detected at 20–30 cm column depth. Atrazine, chlorpyrifos and iprodione removal was 82, 89 and 74% respectively in the first 10 cm depth for columns with vegetal cover. The presence of L. perenne in contaminated columns stimulated peroxidase activity in all three column depth sections. Fluorescein diacetate activity decreased over time in all column sections with the highest values in biomixtures with vegetal cover. Microbial communities, analyzed by PCR-DGGE, were not affected by the pesticide mixture application, presenting high values of similarity (>65%) with and without vegetal cover. Microbial abundance of Actinobacteria varied according to treatment and no clear link was observed. However, bacterial abundance increased over time and was similar with and without vegetal cover. On the other hand, fungal abundance decreased in all sections of columns after 40 days, but an increase was observed in response to pesticide application. Fungal colonization and straw degradation during pesticide dissipation were verified by monitoring the lignin autofluorescence loss.     

Assessment of hydrocarbon degradation potentials in a plant–microbe interaction system with oil sludge contamination: A sustainable solution

A pot culture experiment was conducted for 90 days for the evaluation of oil and total petroleum hydrocarbon (TPH) degradation in vegetated and non-vegetated treatments of real-field oil-sludge-contaminated soil. Five different treatments include (T1) control, 2% oil-sludge-contaminated soil; (T2), augmentation of microbial consortium; (T3), Vertiveria zizanioides; (T4), bio-augmentation along with V. zizanioides; and (T5), bio-augmentation with V. zizanioides and bulking agent. During the study, oil reduction, TPH, and degradation of its fractions were determined. Physico-chemical and microbiological parameters of soil were also monitored simultaneously. At the end of the experimental period, oil content (85%) was reduced maximally in bio-augmented rhizospheric treatments (T4 and T5) as compared to control (27%). TPH reduction was observed to be 88 and 89% in bio-augmented rhizospheric soil (T4 and T5 treatments), whereas in non-rhizospheric and control (T2 and T1), TPH reduction was 78 and 37%, respectively. Degradation of aromatic fraction after 90 days in bio-augmented rhizosphere of treatments T4 and T5 was found to 91 and 92%, respectively. In microbial (T2) and Vertiveria treatments (T3), degradation of aromatic fraction was 83 and 68%, respectively. A threefold increase in soil dehydrogenase activity and noticeable changes in organic carbon content and water-holding capacity were also observed which indicated maximum degradation of oil and its fractions in combined treatment of plants and microbes. It is concluded that the plant–microbe soil system helps to restore soil quality and can be used as an effective tool for the remediation of oil-sludge-contaminated sites.