Bacterial community response to petroleum contamination in brackish tidal marsh sediments in the Yangtze River Estuary, China

The brackish tidal marsh in the Baimaosha area of the Yangtze River Estuary was severely contaminated by 400 tons of heavy crude petroleum from a tanker that sank in December 2012.The spill accident led to severe environmental damage owing to its high toxicity,persistence and wide distribution.Microbial communities play vital roles in petroleum degradation in marsh sediments.Therefore,taxonomic analysis,high-throughput sequencing and 16 S rRNA functional prediction were used to analyze the structure and function of microbial communities among uncontaminated(CK),lightly polluted(LP),heavily polluted(HP),and treated(TD)sediments.The bacterial communities responded with increased richness and decreased diversity when exposed to petroleum contamination.The dominant class changed from Deltaproteobacteria to Gammaproteobacteria after petroleum contamination.The phylum Firmicutes increased dramatically in oil-enriched sediment by 75.78%,346.19%and 267.26%in LP,HP and TD,respectively.One of the suspected oil-degrading genera,Dechloromonas,increased the most in oil-contaminated sediment,by 540.54%,711.27%and 656.78%in LP,HP and TD,respectively.Spore protease,quinate dehydrogenase(quinone)and glutathione-independent formaldehyde dehydrogenase,three types of identified enzymes,increased enormously with the increasing petroleum concentration.In conclusion,petroleum contamination altered the community composition and microorganism structure,and promoted some bacteria to produce the corresponding degrading enzymes.Additionally,the suspected petroleum-degrading genera should be considered when restoring oil-contaminated sediment.

Mixed surfactant washing of petroleum contaminants from the soils and sediments in the unsaturated zone

A laboratory study was conducted to evaluate the suitability of a mixed surfactant for washing oil from soils in the unsaturated zone. The commercial surfactant used for making mixed surfactant were alcohol polyethoxylate (AEO\|9, nonionic) and sodium alcohol polyethoxylated ethers sulfate (AES, anionic). Based on the properties (critical micelle concentration, hydrophilic/ lipophilic balance and surface tension) of individual surfactants and the mixed surfactant, the preferred composition of an aqueous mixed surfactant solution was determined which consisted of 0 5% AEO\|9 and 0 1% AES. The batch washing experiments have shown that the removal efficiency of oil from soils with mixed surfactant was higher than that with individual surfactants. Soil column washing results have shown that the sequence of oil removal efficiency was mixed surfactant (0.5% AEO\|9 and 0.1% AES)>AEO\|9 (0.1%)>AES (0.2%)>water, and the ratio was 1∶0 84∶0 66∶0 06. Biodegradation experiments by growth cells and resting cells were carried out to evaluate the environmental acceptability of the test surfactants. The results have shown that the surfactants were able to serve as sole carbon source for strains Pseudomonos sp. 52 and Weeksella sp. 6 which were isolated from petroleum contaminated soil. More than 90% of the parent mixed surfactants disappeared in two weeks under growth cell conditions.

Biochar-based materials as remediation strategy in petroleum hydrocarbon-contaminated soil and water:Performances,mechanisms,and environmental impact

Petroleum contamination is considered as a major risk to the health of humans and environment.Biochars as low-cost and eco-friendly carbon materials,have been widely used for the removal of petroleum hydrocarbon in the environment.The purpose of this paper is to review the performance,mechanisms,and potential environmental toxicity of biochar,modified biochar and its integration use with other materials in petroleum contaminated soil and water.Specifically,the use of biochar in oil-contaminated water and soil as well as the factors that could influence the removal ability of biochar were systematically evaluated.In addition,the modification and integrated use of biochar for improving the removal efficiency were summarized from the aspects of sorption,biodegradation,chemical degradation,and reusability.Moreover,the functional impacts and associated ecotoxicity of pristine and modified biochars in various environments were demonstrated.Finally,some shortcoming of current approaches,and future research needs were provided for the future direction and challenges of modified biochar research.Overall,this paper gain insight into biochar application in petroleum remediation from the perspectives of performance enhancement and environmental sustainability.

Assessing Earthworm Influence on Remediating Potentials of Soil Micro-Organisms, and Bioavailable Hydrocarbon Pollutant in the Niger Delta, Nigeria

In the Niger Delta region of Nigeria, oil explorations and exploitations abound, causing environmental pollution with serious consequences on soil ecosystem and its biodiversity. In spite of the relationship between microbes and fauna in soil ecosystem, such that both organisms can metabolize certain range of petroleum hydrocarbon substrates with the fauna influencing the remediation potentials of bacteria, yet soil fauna is still not fully considered in bioremediation. The influence of earthworm;Lumbricus terrestris on the remediating potentials of soil bacteria in petroleum hydrocarbon contaminated soils was investigated. Eighteen pots were filled with 700 g of soil each, with nine treated with mixture of 3 levels crude oil and remediated with earthworm, while the other nine had no earthworm. The total petroleum hydrocarbon (TPH), soil physical, nutrient compositions, and TPH degrading bacteria biodiversity were determined before contamination or commencement of study and thirty days after. The results showed a decrease in TPH concentration of 55.58%, 62.57% and 67.07% in 1 ml, 2 ml and 3 ml crude oil contaminated soil, respectively. Species richness and abundance of bacteria organisms increased with high relative abundance in soils remediated with earthworms, hydrocarbon utilizing bacteria increased from less than 0.1 cfu/g to 0.4 cfu/g, and total heterotrophic bacteria 1.6 cfu/g at the end of the study. Earthworms increased rate of remediation potentials of bacteria, such that within 30 days post remediation treatment, 34.14% of reduced concentration was achieved over soil samples without earthworms at 3 ml, and 25.14% at 2 ml concentration. Reduction in pH levels in remediated soils was between 6.39 to 6.17 and 6.74 to 6.72 in unremediated soils, while moisture content was 6.73% to 6.77% unremediated and 5.85% to 6.62% in earthworm remediated soils. Total organic carbon, nitrates in soils inoculated with earthworms were lower in concentration than those without earthworms. Reverse was the case with potassium, phosphate and phosphorous concentrations which were above those without earthworms. Results indicate statistically, significant difference between reduction in TPH in earthworm remediated soils and unremediated soils, pointing out that earthworm is a good candidate for facilitation of bacteria remediation-petroleum hydrocarbon contamination.

Groundwater contamination and natural attenuation capacity at a petroleum spilled facility in Korea

As a remedial option, the natural attenuation capacity of a petroleum contaminated groundwater at a military facility was examined. Hydrogeological conditions, such as high water level, permeable uppermost layer and frequent heavy rainfall, were favorable to natural attenuation at this site. The changes in the concentrations of electron acceptors and donors, as well as the relevant hydrochemical conditions, indicated the occurrence of aerobic respiration, denitrification, iron reduction, manganese reduction and sulfate reduction. The calculated BTEX expressed biodegradation capacity ranged between 20.52 and 33.67 mg/L, which appeared effective for the reduction of the contaminants levels. The contribution of each electron accepting process to the total biodegradation was in the order： denitrification 〉 iron reduction 〉 sulfate reduction 〉 aerobic respiration 〉 manganese reduction. The BTEX and benzene point attenuation rates were 0.0058-0.0064 and 0.0005-0.0032 day-1, respectively, and the remediation time was 0.7-1.2 and 2.5-30 years, respectively. The BTEX and benzene bulk attenuation rates were 8.69 × 10^-4 and 1.05 × 10^-3 day-l, respectively, and the remediation times for BTEX and benzene were 7.2 and 17.5 years, respectively. However, most of the natural attenuation occurring in this site can be attributed to dilution and dispersion. Consequently, the biodegradation and natural attenuation capacities were good enough to lower the contaminants levels, but their rates appeared to be insufficient to reach the remediation goal within a reasonable time frame. Therefore, some active remedial measures would be required.

Effect of petroleum on decomposition of shrub–grass litters in soil in Northern Shaanxi of China

The impacts of petroleum contamination on the litter decomposition of shrub-grass land would directly influence nutrient cycling, and the stability and function of ecosystem. Ten common shrub and grass species from Yujiaping oil deposits were studied. Litters from these species were placed into litterbags and buried in petroleum-contaminated soil with 3levels of contamination（slight, moderate and serious pollution with petroleum concentrations of 15, 30 and 45 g/kg, respectively）. A decomposition experiment was then conducted in the lab to investigate the impacts of petroleum contamination on litter decomposition rates. Slight pollution did not inhibit the decomposition of any litters and significantly promoted the litter decomposition of Hippophae rhamnoides, Caragana korshinskii, Amorpha fruticosa, Ziziphus jujuba var. spinosa, Periploca sepium, Medicago sativa and Bothriochloa ischaemum. Moderate pollution significantly inhibited litter decomposition of M. sativa,Coronilla varia, Artemisia vestita and Trrifolium repens and significantly promoted the litter decomposition of C. korshinskii, Z. jujuba var. spinosa and P. sepium. Serious pollution significantly inhibited the litter decomposition of H. rhamnoides, A. fruticosa, B. ischaemum and A. vestita and significantly promoted the litter decomposition of Z. jujuba var. spinosa, P.sepium and M. sativa. In addition, the impacts of petroleum contamination did not exhibit a uniform increase or decrease as petroleum concentration increased. Inhibitory effects of petroleum on litter decomposition may hinder the substance cycling and result in the degradation of plant communities in contaminated areas.

In situ Remediation of Petroleum Contaminated Groundwater by Permeable Reactive Barrier with Hydrothermal Palygorskite as Medium

The permeable reactive barrier（PRB） has proven to be a costeffective technique to remediate the petro leum contaminated groundwater at a northeast field site in China. In this study, the geology, hydrogeology and con tamination characterization of the field site were investigated and the natural hydrothermal palygorskite was chosen as a reactive medium. Furthermore, the adsorption of the total petroleum hydrocarbons（TPH） in the groundwater onto hydrothermal palygorskite and the adsorption kinetics were investigated. The results indicate that the removal rates of TPH, benzene, naphthalene and phenantharene could all reach up to 90% by hydrothermal palygorskite with a diameter of 0.25-2.00 mm that had been thermally pretreated at 140 ℃. The adsorption of TPH onto hydrothermal palygorskite after pretreatment followed a pseudosecondorder kinetic model and a Langmuir adsorption isotherm, suggesting that the theoretic adsorption capacity of hydrothermal palygorskite for adsorbate could be 4.2 g/g. Scan ning electron microscopy（SEM）, infrared spectroscopy（IR）, Xray diffraction（XRD） and Xray fluorescence spec troscopy（XRF） were carried out to analyze the adsorption mechanism. The results reveal that hydrothermal palygors kite is a fibrous silicate mineral enriched in Mg and A1 with large surface area and porosity. The dense cluster acicular and fibrous crystal of hydrothermal palygorskite, and its effect polar group OH played an important role in the physical and chemical adsorption processes of it for contaminants. This study has demonstrated hydrothermal paly gorskite is a reliable reactive medium for in situ remediation of petroleum contaminated groundwater at field sites.

Impacts of n-alkane concentration on soil bacterial community structure and alkane monooxygenase genes abundance during bioremediation processes

Petroleum hydrocarbons,mainly consisting of n-alkanes and polycyclic aromatic hydrocarbons(PAHs),are considered as priority pollutants and biohazards in the environment,eventually affecting the ecosystem and human health.Though many previous studies have investigated the change of bacterial community and alkane degraders during the degradation of petroleum hydrocarbons,there is still lack of understanding on the impacts of soil alkane contamination level.In the present study,microcosms with different n-alkane contamination(1%,3%and 5%)were set up and our results indicated a complete alkane degradation after 30 and 50 days in 1%-and 3%-alkane treatments,respectively.In all the treatments,alkanes with medium-chain length(C_(11)-C_(14))were preferentially degraded by soil microbes,followed by C27-alkane in 3%and 5%treatments.Alkane contamination level slightly altered soil bacterial community,and the main change was the presence and abundance of dominant alkane degraders.Thermogemmatisporaceae,Gemmataceae and Thermodesulfovibrionaceae were highly related to the degradation of C_(14)-and C_(27)-alkanes in 5%treatment,but linked to alkanes with medium-chain(C11-C18)in 1%treatment and C21-alkane in 3%treatment,respectively.Additionally,we compared the abundance of three alkane-monooxygenase genes,e.g.,alk_A,alk_P and alk_R.The abundance of alk_R gene was highest in soils,and alk_P gene was more correlated with alkane degradation efficiency,especially in 5%treatment.Our results suggested that alkane contamination level showed non-negligible effects on soil bacterial communities to some extents,and particularly shaped alkane degraders and degrading genes significantly.This study provides a better understanding on the response of alkane degraders and bacterial communities to soil alkane concentrations,which affects their biodegradation process.