Soil Total Petroleum Hydrocarbon Research Articles

Factors affecting in situ analysis of total petroleum hydrocarbons in contaminated soils by using a mid-infrared diffuse reflectance spectroscopy

The hand-held mid-infrared diffuse reflectance infrared Fourier transform (MIR-DRIFT) spectrometer was used to assess the applicability of on-site and real time monitoring of total petroleum hydrocarbons (TPH) in contaminated soils during site characterization and remediation. Field measurement devices (MIR-DRIFT and turbidimetric screening test kits) were used to analyze reference soils with concentration ranging from 713 to 54790 mg/kg and compared with the results by a gas chromatography/mass spectrometry method (GC/MS). In situ field measurement of 147 petroleum-contaminated soil samples from 11 contaminated sites was correlated with laboratory-determined soil TPH levels by GC/MS. The concentrations of TPH by MIR-DRIFT were significantly correlated to the concentrations of TPH by GC/MS. Detection of TPH by the MIR spectrometer was not affected by the weathering effects of diesel-contaminated soils. Soils contaminated by mixed fuels with high content of gasoline constituents may cause the potential interference in MIR measurement. In field practice, interference may be attributed to soil moisture, soil organic matter, and soil texture. Soil moisture below 5% is required to reduce variation of infrared beam reflected from high level of surface liquid. When measuring the contaminated soil with a high organic matter content, the results may be overestimated due to the possible effects of surface reflection and interference. Clay and partial silty clay soils were not suitable for MIR spectrometer detection due to a potential shielding effect to reduce the infrared radiation absorbed by TPH. Future research is warranted to reduce the variation caused by soil texture and heterogeneity in TPH prediction.

Biodegradation of Total Petroleum Hydrocarbons in Soil: Isolation and Characterization of Bacterial Strains from Oil Contaminated Soil

In this study, we isolated seven strains (termed BY1–7) from polluted soil at an oil station and evaluated their abilities to degrade total petroleum hydrocarbons (TPHs). Following 16 rRNA sequence analysis, the strains were identified as belonging to the genera Bacillus, Acinetobacter, Sphingobium, Rhodococcus, and Pseudomonas, respectively. Growth characterization studies indicated that the optimal growth conditions for the majority of the strains was at 30 °C, with a pH value of approximately 7. Under these conditions, the strains showed a high TPH removal efficiency (50%) after incubation in beef extract peptone medium for seven days. Additionally, we investigated the effect of different growth media on growth impact factors that could potentially affect the strains’ biodegradation rates. Our results suggest a potential application for these strains to facilitate the biodegradation of TPH-contaminated soil.

Predicting total petroleum hydrocarbons in field soils with Vis-NIR models developed on laboratory-constructed samples.

Accurate quantification of petroleum hydrocarbons (PHCs) is required for optimizing remedial efforts at oil spill sites. While evaluating total petroleum hydrocarbons (TPH) in soils is often conducted using costly and time-consuming laboratory methods, visible and near-infrared reflectance spectroscopy (Vis-NIR) has been proven to be a rapid and cost-effective field-based method for soil TPH quantification. This study investigated whether Vis-NIR models calibrated from laboratory-constructed PHC soil samples could be used to accurately estimate TPH concentration of field samples. To evaluate this, a laboratory sample set was constructed by mixing crude oil with uncontaminated soil samples, and two field sample sets (F1 and F2) were collected from three PHC-impacted sites. The Vis-NIR TPH models were calibrated with four different techniques (partial least squares regression, random forest, artificial neural network, and support vector regression), and two model improvement methods (spiking and spiking with extra weight) were compared. Results showed that laboratory-based Vis-NIR models could predict TPH in field sample set F1 with moderate accuracy (R2 >.53) but failed to predict TPH in field sample set F2 (R2 <.13). Both spiking and spiking with extra weight improved the prediction of TPH in both field sample sets (R2 ranged from .63 to .88, respectively); the improvement was most pronounced for F2. This study suggests that Vis-NIR models developed from laboratory-constructed PHC soil samples, spiked by a small number of field sample analyses, can be used to estimate TPH concentrations more efficiently and cost effectively compared with generating site-specific calibrations.

Biodegradation and post-oxidation of fuel-weathered field soil

Owing to the less volatile and less biodegradable nature of weathered fuel-contaminated soil, it cannot be easily remediated using conventional bioremediation approaches. Therefore, this study was aimed to enhance the landfarming bioremediation process by introducing post-oxidation for the degradation of the residual total petroleum hydrocarbons (TPH) in fuel-contaminated field soil. A laboratory-scale landfarming bioaugmentation process was performed by using oil-degrading microbes, nutrients, and surfactants, followed by chemical oxidation as a post treatment. The results demonstrated that the addition of microbes and nutrients gradually decreased the TPH concentration of the soil (initial TPH = 5932 ± 267 mg/kg) with a removal efficiency of 70–72% (TPH > 800 mg/kg; Korean limit for non-residential sites). However, the use of post-oxidation treatments with 5% KMnO4 decreased the TPH to approximately 401–453 mg/kg (TPH below 500 mg/kg; residential site limit) with an overall efficiency of 92–93% compared to the corresponding value of 13% for the control (water treatment). Performing landfarming through biodegradation followed by chemical oxidation as a post treatment could successfully remove the weathered TPH in soil below the regulatory limits. Furthermore, the post-oxidation treatment may oxidize the less biodegradable portions only after biodegradation, thereby minimizing the oxidant demand and enhancing the soil properties such as the pH, amount of natural substrates and microbial population.

Combined effects of soil particle size with washing time and soil-to-water ratio on removal of total petroleum hydrocarbon from fuel contaminated soil

In this study, total petroleum hydrocarbon (TPH) removal from fuel-contaminated field soil was investigated. The influence of the washing method (washing before/after sieving), washing time, soil-to-water ratio, and soil particle size on TPH removal efficiency was evaluated under constant stirring speed. Washing the whole contaminated soil is more efficient than separating the soils into particle size fractions and separately washing the fractions. Particles with differing diameters would be more in contact with each other resulting in detachment of contaminants from the soil particle surface. Effects of soil washing time and soil-to-water ratio on TPH removal were not significant in coarse soil particles (greater than 0.15 mm diameter) but significantly affected TPH removal in fine particles (less than 0.15 mm diameter). This study suggests a threshold washing time of 1 h and a threshold soil-to-water ratio of 1:6 for the whole soil in soil washing. However, soil particles less than 0.075 mm (<75 μm) should be separated after washing to meet the Korean soil TPH limit of less than 500 mg/kg. This study demonstrates the importance of finer soils as debrading media and particle size fraction composition of fuel-contaminated soil in soil washing.

Optimization and Performance Test of Oil Spill Dispersant at Bioremediation of Contaminated Soil with Heavy Oil by Bioslurry Technique

Petroleum industry activities produce waste such as petroleum hydrocarbons which damage to the soil environment due to changes in soil physical, chemical and biological properties. Oil Spill Dispersant (OSD) is a product that can break down waste of oil into small parts so that it can be dispersed naturally. Laboratory experiments aimed to find out optimize and performance test of OSD in the process of bioremediation with using bio-slurry technique on contaminated soil with heavy oil was carried out at Laboratory of Surfactant and Bio-energy Research Center (SBRC), Research and Community Service Institute of Bogor Agricultural University on January - August 2018 using contaminated soil with heavy oil. The experiment used Response Surface Method (RSM) with two factors, namely the incubation time factor (X1) and the Dispersant to oil ratio (DOR) (X2). The observed variables were soil Total Petroleum Hydrocarbons (TPH), pH, total microbes, and Chemical Oxygen Demand (COD) at soil solution. The results showed that the treatment of incubation time and its combination with DOR significantly reduced soil TPH, increased soil acidity, and increased soil total B. megaterium, but did not significantly affect on COD in soil solutions. Optimization of OSD with RSM showed that the higher DOR of OSD and the longer the incubation time, the higher also the rate of biodegradation of TPH. The optimum conditions were reached at DOR of 1.16:1 and incubation time of 7 days which were able to degrade soil TPH of 54.30%. The optimum conditions of soil pH (8.825) was reached at DOR of 1:1 and incubation time of 5 days, as well as the optimum conditions of B. megaterium (8.35 log CFU g-1) was reached at DOR of 0.86:1 and incubation time of 7 days. Oil spill dispersant (OSD) increased COD in soil solution in both uncontaminated and contaminated soils with heavy oil.

Study on Pretreatment Method of Total Petroleum Hydrocarbon in Soil

Study on Pretreatment Method of Total Petroleum Hydrocarbon in Soil

Effects of 5-Aminolevulinic Acid (ALA) on Zinnia hybrida Growth and Phytoremediation Effects in Oil-Contaminated Soil

In this study, we compared plant height, weight, soil TPH concentration, and soil DHA level after 18 weeks of Zennia hybrida cultivation with four different concentrations of 5-Aminolevulinic acid (ALA)-based liquid fertilizer: 1500-fold, 5000-fold, and 8000-fold dilutions, along with a non-treatment control of diluted ALA. The plants of ALA-treated were significantly taller than the non-treatment control. The plants of ALA-treated plants were higher in shoot fresh weight, shoot dry weight, and root dry weight than the non-treatment control. The plot of ALA-based liquid fertilizer with the 5000-fold dilution was significantly highest in shoot fresh weight, shoot dry weight, and root dry weight. ALA-treated plants were lower in the soil Total Petroleum Hydrocarbon (TPH) concentration than the non-treatment control. The plot of ALA-based liquid fertilizer with the 5000-fold was significantly lowest in the TPH concentration. In addition, ALA-treated plants were higher in the soil dehydrogenase activity (DHA) than the non-treatment control. The plot of ALA-based liquid fertilizer with the 5000-fold was significantly highest in the TPH concentration. This study indicated that ALA-applied zinnia-grown oil-contaminated soil is more effective than not. The remediation in oil-contaminated soil with ALA-based liquid fertilizer is more effective than the non-treatment control; furthermore, ALA application with 5000-fold dilution was most suitable in oil-contaminated soil among other plots.

Petroleum hydrocarbons degradation in contaminated soil using the plants of the Aster family.

Oil extraction is one of the causes of soil contamination with the total petroleum hydrocarbons. The objective of this study was to clarify the effect of Asteraceae plants on the degradation of petroleum hydrocarbon in contaminated soil. Initial soils with 40 and 90gkg-1 of total petroleum hydrocarbon (TPH) were prepared. There were three treatments: (1) no addition, (2) addition of FeCl3 and nitrilotriacetic acid (NTA) solution, and (3) addition of FeCl3 + NTA and the cultivation of nine Asteraceae plants. The concentration of TPH was measured using infrared spectrophotometer, 2 and 3months after transplanting (MAT). Shoot and root dry weights were measured 3 MAT. The concentration of TPH in soil cultivated with Cosmos caudatus was lower than that of the initial soil (40gkg-1 TPH), 2 MAT. The concentrations of TPH in soils cultivated with Calendula officinalis, Callistephus chinensis, C. caudatus, and Tagetes sp. were also lower than that in the initial soil, 3 MAT. The concentrations of TPH in soils cultivated with Achillea filipendulina, Anthemis tinctoria, Tagetes erecta, Chrysanthemum coronarium, C. officinalis, C. chinensis, and C. caudatus were lower than that in the initial soil (90gkg-1 TPH), 2 MAT. The concentrations of TPH in soils cultivated with T. erecta, A. tinctoria, Zinnia elegans, C. chinensis, C. caudatus, and Tagetes sp. were lower than that in the initial soil, 3 MAT. A. filipendulina and C. coronarium died at both 40 and 90kg-1 TPH soils. These results suggest that the roots of Asteraceae plants degrade petroleum hydrocarbon in contaminated soil and C. chinensis and Z. elegans are more suitable for using TPH remediation. Plant survival and extensive root system are important factors for the remediation of TPH in contaminated soil.

Effective oxidation of crude oil in soils by consuming less hydroxyl radical with target iron

To achieve similar oxidative efficiency of long-, medium-, and short-chain alkanes in soils, the mechanism of efficient oxidation of crude oil in soils by consuming less hydroxyl radical (OH) with target iron were investigated. The two contaminated soils (initial total petroleum hydrocarbons (TPH): 9274 mg/kg (S1); 9941 mg/kg (S2)) were subjected to targeted oxidation with target iron (targeted oxidation). The results showed that similar removal efficiencies (25 ± 5%) of each alkane (C14–C24, C26, C28–C30) with 5.6–15.0 of octanol coefficient by unit OH consumption was achieved after targeted oxidation. Under less consumption of OH, considerable removal of TPH (5969 mg/kg; 64%) after targeted oxidation was about 5 times that of the nontargeted oxidation control. The organic functional groups on target iron will combine with each alkane to form targets, which altered the way of OH accessing to all the long-, medium- and short-chain alkanes. A possible explanation of the similar efficiency targeted oxidation of each alkane was achieved by consuming less OH (1.77 ± 0.5 × 10−2 a.u.) was that the TPH in soils can be oxidized as soon as the OH produced in the vicinity of the target, resulting in OH scarcely waste.

Concentration of Total petroleum Hydrocarbons and Selected Heavy Metals In Soil And plant nearby Al-Nassiriya oil Refinery South of Iraq

The present study deal with measure concentration of Total petroleum hydrocarbons (TPHs) and selected heavy metals (HMs) (Cd , Pb , Co , V, and Ni) in soil and plant phragmits austriles (cav.) nearby AL-Nassiriya oil refinery during the period extended from winter up to summer 2018 . Some environmental factors such as , pH, salinity‰ , Electrical conductivity (Ec.) and soil temperature were measured , also total organic carbon (Toc) % content in soil was determined, and soil texture was analyzed and both of them expressed as percentage . The result observed that the range of the following factors were : soil temp. ranged from (26-36) ◦c , pH (7.3-7.9) , Ec. (14.3-25.3) µs/cm and salinity (5.1-7.3)‰ , while the value of Toc ranged from (0.7-8.55)% , soil texture was silty soil in control station , but they were sandy soil at polluted stations . The mean concentration of TPHs in soil , St.1 , St.2 , St.3 and St.4 were (16.47 ,14.78 ,12.65 and 1.36) µg /gm dry weight respectively , while the mean concentration of HMs in the soil for both season were Cd (0.78 ), Pb (26.85), Co (26.83), Ni (227.17) and V (95.67) µg /gm dry weight . In plant (shoot and root) part , mean concentration of TPHs were (4.86 and 8 .44) µg /gm dry weight respectively ,whereas the mean concentration of heavy metals in both parts for both seasons were Cd (0.49 and 0.65) , Pb (30.36 and 49.25).

Degradation of petroleum hydrocarbons in unsaturated soil and effects on subsequent biodegradation by potassium permanganate

To date, the oxidation of petroleum hydrocarbons using permanganate has been investigated rarely. Only a few studies on the remediation of unsaturated soil using permanganate can be found in the literature. This is, to the best of our knowledge, the first study conducted using permanganate pretreatment to degrade petroleum hydrocarbons in unsaturated soil in combination with subsequent bioaugmentation. The pretreatment of diesel-contaminated unsaturated soil with 0.5-pore-volume (5%) potassium permanganate (PP) by solution pouring and foam spraying (with a surfactant) achieved the total petroleum hydrocarbon (TPH) removal efficiencies of 37% and 72.1%, respectively. The PP foam, when coupled with bioaugmentation foam, further degraded the TPH to a final concentration of 438mg/kg (92.1% total reduction). The experiment was conducted without soil mixing or disturbance. The relatively high TPH removal efficiency achieved by the PP-bioaugmentation serial foam application may be attributed to an increase in soil pH caused by the PP and effective infiltration of the remediation agent by foaming. The applied PP foam increased the pH of the acidic soil, thus enhancing microbial activity. The first-order biodegradation rate after PP oxidation was calculated to be 0.068d-1. Furthermore, 94% of the group of relatively persistent hydrocarbons (C18-C22) was removed by PP-bioaugmentation, as verified by chromatogram peaks. Some physicochemical parameters related to contaminant removal efficiency were also evaluated. The results reveal that PP can degrade soil TPH and significantly enhance the biodegradation rate in unsaturated diesel-contaminated soil when combined with bioaugmentation foam.

Application of PROSPECT for estimating total petroleum hydrocarbons in contaminated soils from leaf optical properties.

Recent advances in hyperspectral spectroscopy suggest making use of leaf optical properties for monitoring soil contamination in oil production regions by detecting pigment alterations induced by Total Petroleum Hydrocarbons (TPH). However, this provides no quantitative information about the level of contamination. To achieve this, we propose an approach based on the inversion of the PROSPECT model. 1620 leaves from five species were collected on a site contaminated by 16 to 77 g.kg-1 of TPH over a 14-month period. Their spectral signature was measured and used in PROSPECT model inversions to retrieve leaf biochemistry. The model performed well for simulating the spectral signatures (RMSE < 2%) and for estimating leaf pigment contents (RMSE ≤ 2.95 μg.cm-2 for chlorophylls). Four out of the five species exhibited alterations in pigment contents when exposed to TPH. A strong correlation was established between leaf chlorophyll content and soil TPH concentrations (R2 ≥ 0.74) for three of them, allowing accurate predictions of TPH (RMSE =3.20 g.kg-1 and RPD = 5.17). The accuracy of predictions varied by season and improved after the growing period. This study demonstrates the capacity of PROSPECT to estimate oil contamination and opens up promising perspectives for larger-scale applications.

Characterization and Initial Application of Endophytic Bacillus safensis Strain ZY16 for Improving Phytoremediation of Oil-Contaminated Saline Soils.

Hydrocarbon-degrading and plant-growth-promoting bacterial endophytes have proven useful for facilitating the phytoremediation of petroleum-contaminated soils with high salinity. In this study, we identified Bacillus safensis strain ZY16 as an endophytic bacterium that can degrade hydrocarbons, produce biosurfactants, tolerate salt, and promote plant growth. The strain was isolated from the root of Chloris virgata Sw., a halotolerant plant collected from the Yellow River Delta. ZY16 survived in Luria-Bertani (LB) broth with 0–16% (w/v) sodium chloride (NaCl) and grew well in LB broth supplemented with 0–8% NaCl, indicating its high salt tolerance. The endophytic strain ZY16 effectively degraded C12–C32 n-alkanes of diesel oil effectively, as well as common polycyclic aromatic hydrocarbons under hypersaline conditions. For example, in mineral salts (MS) liquid medium supplemented with 6% NaCl, ZY16 degraded n-undecane, n-hexadecane, n-octacosane, naphthalene, phenanthrene, and pyrene, with degradation percentages of 94.5, 98.2, 64.8, 72.1, 59.4, and 27.6%, respectively. In addition, ZY16 produced biosurfactant, as confirmed by the oil spreading technique, surface tension detection, and emulsification of para-xylene and paraffin. The biosurfactant production ability of ZY16 under hypersaline conditions was also determined. Moreover, ZY16 showed plant-growth-promoting attributes, such as siderophore and indole-3-acetic acid production, as well as phosphate solubilization. To assess the enhanced phytoremediation of saline soils polluted by hydrocarbons and the plant-growth-promotion ability of ZY16, a pot trial with and without inoculation of the endophyte was designed and performed. Inoculated and non-inoculated plantlets of C. virgata Sw. were grown in oil-polluted saline soil, with oil and salt contents of 10462 mg/kg and 0.51%, respectively. After 120 days of growth, significant enhancement of both the aerial and underground biomass of ZY16-inoculated plants was observed. The soil total petroleum hydrocarbon degradation percentage (a metric of phytoremediation) after incubation with ZY16 was 63.2%, representing an elevation of 25.7% over phytoremediation without ZY16 inoculation. Our study should promote the application of endophytic B. safensis ZY16 in phytoremediation by extending our understanding of the mutualistic interactions between endophytes and their host plants.

MODELOS DE CALIBRACIÓN PARA LA CUANTIFICACIÓN ESPECTROFOTOMÉTRICA DE HIDROCARBUROS TOTALES DEL PETRÓLEO EN SUELO

Calibration models used in analytical chemistry must be previously validated to achieve their aim. Generally, this is achieved by means of regression analysis. This study proposes strategies of internal and external validation of simple linear calibration models (LCM) to determine total petroleum hydrocarbons (TPH) by means of ultraviolet visible spectrometry (UV-Vis). In the crossed validation, the model is used to estimate one by one the reference concentrations with which it was constructed/calibrated, whereas in the external validation the model estimates reference concentrations that were not used in its calibration, which demonstrates its robustness. Four models were constructed and validated, demonstrating in all cases the linearity and robustness of the MCLS in the studied range. All the models were adequate for the spectrometric quantification of TPH in soils or in water extracted by different solvents, in quantities that comply with the maximum permissible limits established by Mexican regulations. In the calibrated models, the matrix effect was identified due to the type of solvent used to dilute the hydrocarbons and the type of hydrocarbon, which is influenced by the limits of detection and quantification.

Impacts of Anthropological Activities on Soils of Some Parts of Rivers State, Nigeria

The study is a post project implementation Environmental Monitoring (EM) of impacts of anthropological activities on levels of soil physicochemical parameters. The study evaluates levels of physicochemical parameters in soils of 9 locations in Port Harcourt and its environs in Rivers State, Nigeria, grouped into 3 categories; urbanized, industrialized and agricultural. Composite soil samples were collected between April to October 2018. Concentration levels of Benzene, Toluene, Ethyl-benzene, and Xylene (BTEX), Total Petroleum Hydrocarbon (TPH), Percent Total Organic Carbon (% TOC), Lead (Pb), Iron (Fe), Copper (Cu), Cadmium (Cd), Zinc (Zn), Calcium (Ca), Nickel (Ni), Sodium (Na), Potassium (K), Chromium (Cr), Magnesium (Mg), Manganese (Mn), and Sulphur (S) in soil was measured using standard analytical procedures. The study evaluates the impact magnitude (IM) of the obtained test values against control values. In industrial area, BTEX recorded the highest Impact Magnitude (IM) of 100% while TOC and TPH recorded 100.00% and 88.89% respectfully, and were classified as severely impacted (S). In the agricultural areas, TOC and Ni recorded IM of 88.89% while BTEX had an IM of 77.78% which were highest and were classified as severe impact (S). In urbanized areas, Ni and (Phosphate) PO43- recorded the highest IM of 88.89% and were classified as severe (S). The study establishes that urbanization, industrialization and agricultural activities do affect the level of physicochemical parameters in the study areas. Activities in industrial areas negatively impact on levels of BTEX, % TOC and TPH in soils. Activities in agricultural areas negatively impacted on levels of BTEX, NO3-, NO2- and SO42- in soils, and activities in urban areas negatively impact on levels of Ni, PO43-, Zn, Mn, TPH, % TOC and Ca in soils of the study areas. These findings form a reliable baseline data for future researchers in EM in the study areas. The study recommends EM of soil physicochemical parameters in the study area in order to ensure a healthy soil for food production in order for realization of Sustainable Development Goals (SDGs); Good Health and well-being, and sustainable cities and communities.

Growth of zinnia, Italian ryegrass, and alfalfa and their remediation effects in diesel oil-contaminated soils

Our objective in this study was to compare the growth of zinnia, Italian ryegrass, and alfalfa, and their remediation effects in oil-contaminated soils. The soils were prepared by mixing 2, 4, or 8% diesel oil by weight with soil. The plant height and dry weights of shoots and roots were highest for zinnia in the 2 and 4% oil treatments, and highest for Italian ryegrass in the 8% oil treatment. The reduction ratios in soil total petroleum hydrocarbons concentration (TPH) for 3 plants were lower in the 4 and 8% oil treatments than those in the 2% treatment. The reduction ratios for Italian ryegrass and zinnia contaminated with 2, 4, and 8% diesel oil treatments were significantly higher than those for alfalfa and the non-cultivation treatment at 45 days after sowing, and there were no significant differences in reduction ratios between Italian ryegrass and zinnia. The reduction ratio of soil TPH concentration brought about by zinnia was also comparable to that of Italian ryegrass. Therefore, we conclude that zinnia shows growth and remediation effects that are equivalent to those of Italian ryegrass, in soils contaminated with less than 8% oil.

Principal component analysis reveals microbial biomass carbon as an effective bioindicator of health status of petroleum-polluted agricultural soil

ABSTRACT We investigated a number of microbiological activities in the soil to serve as biomonitoring tools in assessing the ecotoxicity of diesel-contaminated soil samples during the different periods of bioremediation. Sawdust was used as the biostimulant for the biodegradation of artificial diesel-polluted soil samples. Soil microbial population, soil microbial enzymatic activities (catalase, lipase, dehydrogenase, urease, phosphatase and β-glucosidase), soil microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP), soil microbial respirometric index and total petroleum hydrocarbon (TPH) concentration were monitored to evaluate the efficiency of the bioremediation process. After a period of 56 d, total petroleum hydrocarbon content reduced from 14,221 to 270 mg/kg. The parameter estimation using the nth-order kinetic model revealed that the first-order rate constants (k) for TPH removal were 4.417 d−1 and 0.2670 d−1 for sawdust-amended and unamended soil, respectively. This implied that, the sawdust amendment resulted in reaction rate 16.5 times faster than unamended soil. Thus, the biological indicators were generally more pronounced in biostimulated soil than the attenuated soil. However, to evaluate the efficiency of the sawdust-assisted bioremediation, principal component analysis, which was used in selecting the most sensitive bioindicators. It was observed that microbial biomass carbon, catalase, lipase and dehydrogenase were the most responsive bioparameters. A positive relationship between TPH removal and the four most sensitive bioparameters suggests that the use of four biological activities have proven to be effective monitoring tools for evaluating the efficiency of a bioremediation strategy.

Response of soil bacterial community to bioaugmentation with a plant residue-immobilized bacterial consortium for crude oil removal

Both the crude oil removal efficiency of the Eichhornia crassipes dried straw-immobilized bacterial consortium and shifts in soil bacterial community in response to the bioaugmentation strategy were unmasked in this study. After 30 days of bioremediation, total petroleum hydrocarbon in soil was determined and immobilized consortium showed a removal percentage (51.7%) better than either Eichhornia crassipes dried powder (37.0%) or bacteria solution (36.0%) alone. Bacterial community and soil properties analyses demonstrated that the relative abundances of Cytophagales and Rhizobiales increased with increasing total organic carbon and total nitrogen contents because of the addition of Eichhornia crassipes dried powder. The genus Burkholderia which may play a key role in hydrocarbon degradation among the inoculated bacterial consortium proliferated when immobilized on the Eichhornia crassipes dried powder. Such a cell immobilization technology using plant residue materials as carriers helps to improve soil fertility and mitigate competition between indigenous and inoculated microorganisms for nutrients, which offers a promising way to enhance the removal of crude oil from contaminated soils.

Bioremediation of petroleum-contaminated soil enhanced by aged refuse

In this study, the effect of aged refuse on biodegradation of total petroleum hydrocarbons (TPH), microbial counts, soil ecotoxicity, dehydrogenase activity and microbial community compositions were investigated in solid phase reactors during a 30-week period. The results demonstrate that the removal efficiency of TPH was significantly higher in the soil supplemented with aged refuse than in the soil without aged refuse. After 30 weeks, the removal efficiencies of TPH in soils were 29.3%, 82.1%, 63.7% and 90.2% in the cases of natural attenuation, nutrient addition (with NH4NO3 and K2HPO4), supplement with 20% (w/w, dry weight basis) of aged refuse and the combination of nutrient and aged refuse. Nutrient plus aged refuse made the TPH concentration decrease to below the threshold level of commercial use required for Chinese soil quality for TPH (<3000 mg/kg) in 30 weeks. It was also found that dehydrogenase activity, bacterial counts and degrader abundance in the soil were remarkably enhanced by the addition of aged refuse (20%,w/w). Total organic carbon analysis demonstrates that large amounts of hydrocarbon intermediates occurred in the soil after bioremediation.