Dynamics of indigenous bacterial communities associated with crude oil degradation in soil microcosms during nutrient-enhanced bioremediation

Ecological impact evaluation by constructing in situ microcosm with porous ceramic arrowhead

In recent years, bioremediation has been used as an effective technique for the cleaning of polluted sites. However, bioremediation treatment efficacy varies considerably; thus, characterization of indigenous pollutant-degrading soil microorganisms and assessment of the changes in microbial composition by pollutants are essential for designing efficient bioremediation methods. In this study, an ecological impact evaluation method that is cost-efficient and has low contamination risk was developed to assess the indigenous microbial composition. An "in situ microcosm" was constructed using a porous ceramic arrowhead. Phenol, a common environmental pollutant, was used to assess the evaluation efficacy of this method. Our data showed that phenol gradually percolated into the soil adjacent to the arrowhead and stimulated unique indigenous microorganisms (Bacillus sp., Streptomyces sp., and Cupriavidus sp.). Furthermore, the arrowhead approach enabled efficient evaluation of the ecological impact of phenol on soil microorganisms. Thus, the arrowhead method will contribute to the development of bioremediation methods.

Biostimulation proved to be the most efficient method in the comparison of in situ soil remediation treatments after a simulated oil spill accident

The use of in situ techniques in soil remediation is still rare in Finland and most other European countries due to the uncertainty of the effectiveness of the techniques especially in cold regions and also due to their potential side effects on the environment. In this study, we compared the biostimulation, chemical oxidation, and natural attenuation treatments in natural conditions and pilot scale during a 16-month experiment. A real fuel spill accident was used as a model for experiment setup and soil contamination. We found that biostimulation significantly decreased the contaminant leachate into the water, including also the non-aqueous phase liquid (NAPL). The total NAPL leachate was 19 % lower in the biostimulation treatment that in the untreated soil and 34 % lower in the biostimulation than oxidation treatment. Soil bacterial growth and community changes were first observed due to the increased carbon content via oil amendment and later due to the enhanced nutrient content via biostimulation. Overall, the most effective treatment for fresh contaminated soil was biostimulation, which enhanced the biodegradation of easily available oil in the mobile phase and consequently reduced contaminant leakage through the soil. The chemical oxidation did not enhance soil cleanup and resulted in the mobilization of contaminants. Our results suggest that biostimulation can decrease or even prevent oil migration in recently contaminated areas and can thus be considered as a potentially safe in situ treatment also in groundwater areas.

Studies on organic and in-organic biostimulants in bioremediation of diesel-contaminated arable soil

In this study, use of inorganic fertilizer (N.P.K) was compared with organic manure (compost) in the bioremediation of diesel-polluted agricultural soil over a two-month period. Renewal by enhanced natural attenuation was used as control. The results revealed that total petroleum hydrocarbon removal from polluted soil was 71.40 ± 5.60% and 93.31 ± 3.60% for N.P.K and compost amended options, respectively. The control (natural attenuation) had 57.90 ± 3.98% of total petroleum hydrocarbon removed. Experimental data fitted second order kinetic model adequately for compost amended option. The fertilizer amended option was found to be 1.04 times slower (k2 = 4.00 ± 1.40 × 10(-7)gmg(-1)d(-1), half-life = 28.15 d) than compost amended option (k2 = 1.39 ± 0.54 × 10(-5) gmg(-1)d(-1), half-life = 8.10 d) but 1.21 times (20.6%) faster than the control (k2 = 2.57 ± 0.16 × 10(-7) gmg(-1)d(-1), half-life = 43.81 d). The hydrocarbon utilizers isolated from the diesel contaminated soil were: Bacillus nealsoni, Micrococcus luteus, Aspergillus awamori, and Fusarium proliferatum. The phytotoxicity test showed that germination indices for natural attenuation (control), fertilizer (NPK) and compost amended options were 34%, 56%, and 89%, respectively.

An evaluation of the impact of multiwalled carbon nanotubes on soil microbial community structure and functioning

This study evaluated the impacts of multiwalled carbon nanotubes (MWNTs) on microbial community composition and functioning in a sandy loam soil over 90 d. We used test concentrations in the range of lower MWNT concentrations (10mg/kg) to extremely high MWNT concentrations (10,000 mg/kg) as a worst case scenario. We observed no effects of MWNTs on soil respiration, enzymatic activities, and microbial community composition at 10, 100 and 1,000 mg/kg. However, increases in fungal fatty acid methyl ester markers were observed at the highest treatment. In addition, pyrosequencing demonstrated a decreased abundance of some bacterial genera like Derxia, Holophaga, Opitutus and Waddlia at the highest treatment while bacterial genera that are considered potential degraders of recalcitrant contaminants (such as polycyclic aromatic hydrocarbons) like Rhodococcus, Cellulomonas, Nocardioides and Pseudomonas increased. These results suggest a shift in soil microbial community composition to more tolerant microbial populations in the presence of extremely high MWNT concentrations. It is unlikely that the change observed at 10,000 mg/kg is due to metal or carbon impurities as the MWNTs used in this study were of high purity. Given the need for wide-ranging data for regulation and risk assessment of nanomaterials, this study provides valuable data.

Spatial variations of hydrocarbon contamination and soil properties in oil exploring fields across China

Successful site remediation is critically based on a comprehensive understanding of distribution of contaminants, soil physico-chemical and microbial properties in oil contaminated sites. One hundred and ten topsoils were sampled from seven typical oil fields in different geoclimate regions across north to south China to investigate the spatial variances of oil contaminations and soil parameters. Oil concentrations and compositions, soil geochemical properties and microbial populations were analyzed and statistic analysis methods were used to analyze the spatial pattern of soil variables. The results indicated that oil contaminations were serious in most oil exploring areas in China, especially with high levels of polycyclic aromatic hydrocarbons (PAHs) from petrogenic origin. Ordination analyses indicated a relatively distinct spatial pattern that all soil samples grouped mainly by geographic locations, instead of distributing along contamination or other geochemical variable gradient. Microbial populations were found to be statistically positively correlated with soil nitrogen, phosphorus and water content, and negatively correlated with salt pH and soluble salts (P<0.05). This study provided insights into the spatial variability of soil variables in hydrocarbon-contaminated fields across large spatial scales, which is important for the environmental protection and further remediation in oil contaminated sites according to local conditions.