Spectral and Growth Characteristics of Willows and Maize in Soil Contaminated with a Layer of Crude or Refined Oil

Remote sensing holds great potential for detecting stress in vegetation caused by hydrocarbons, but we need to better understand the effects of hydrocarbons on plant growth and specific spectral expression. Willow (Salix viminalis var. Tora) cuttings and maize (Zea mays var. Lapriora) seedlings were grown in pots of loam soil containing a hydrocarbon-contaminated layer at the base of the pot (crude or refined oil) at concentrations of 0.5, 5, or 50 g·kg−1. Chlorophyll concentration, biomass, and growth of plants were determined through destructive and nondestructive sampling, whilst reflectance measurements were made using portable hyperspectral spectrometers. All biophysical (chlorophyll concentration and growth) variables decreased in the presence of high concentrations of hydrocarbons, but at lower concentrations an increase in growth and chlorophyll were often observed with respect to nonpolluted plants, suggesting a biphasic response to hydrocarbon presence. Absorption features were identified that related strongly to pigment concentration and biomass. Variations in absorption feature characteristics (band depth, band area, and band width) were dependent upon the hydrocarbon concentration and type, and showed the same biphasic pattern noted in the biophysical measurements. This study demonstrates that the response of plants to hydrocarbon pollution varies according to hydrocarbon concentration and that remote sensing has the potential to both detect and monitor the variable impacts of pollution in the landscape.

Soil Odor as An Extra-Official Criterion for Qualifying Remediation Projects of Crude Oil-Contaminated Soil

Unfortunately, many property owners in southeastern Mexico do not trust environmental authorities, and the de facto method they use to evaluate the progress in environmental remediation projects is soil smell. This criterion was evaluated to determine if it was reliable to assess soil fertility and toxicity. Three soils (Fluvisol, Gleysol, and Arenosol), were contaminated with 2% medium or heavy crude oil (30.2, 17.1°API, respectively), and treated for 18 months to simulate bioremediation or natural attenuation. Every two months, field capacity, water repellency, hydrocarbon concentration, acute toxicity and soil odor were measured. Odor was measured in controlled conditions with a group of unexperienced panelists. During remediation, the Fluvisol and Gleysol were perceived to have an odor intensity between slight to low, and were considered acceptable. Meanwhile, in the Arenosol, the odor intensity was between low to medium and was considered unacceptable. After treatment, the hydrocarbon concentration was reduced to low levels, very near Mexican norm, and all the soils, including the Arenosol, were perceived to have an intensity between neutral to slightly agreeable, were considered acceptable, and no toxicity was observed in the earthworm bioassay (no false positives). However, in various soil samples from the Fluvisol and Arenosol, important risks were present with respect to field capacity and water repellency. Due to these observations, even though soil smell may be a trustworthy guide to soil toxicity, it does not ensure that the remediated soil’s fertility has been restored.

Isolation of bacteria from diesel contaminated soil for diesel remediation

This study is aimed at isolating bacterial species that inhabit diesel contaminated soil and also screened these isolates for the ability to be used for remediating diesel contaminated environment using their potential to degrade diesel as carbon and energy source. Top soil sample was collected from an ancient diesel-powered generator house in Minna, Nigeria, in a sterilized plastic container while diesel oil was obtained from local petrol bunk. Four bacterial isolates were isolated from the diesel contaminated soil sample and were screened for their ability to degrade diesel using mineral salt medium (MSM). The isolates with highest biodegradation potential were identified as Bacillus subtilis and Bacillus cereus. The optimum pH (5, 6, 7 and 8) and hydrocarbon concentration (1%, 2%, 5% and 10%) of the isolate was determined by spectrophotometry and the result revealed that the optimum pH for biodegradation of diesel by Bacillus subtilis and Bacillus cereus, was 7 (1.170) and 8 (1.745) respectively while the optimum hydrocarbon concentration degradation for both isolates was 5% (2.22) and 1% (2.37) respectively. The results of this study showed that these isolates were able to degrade diesel and can be useful for large scale bioremediation of diesel contaminated soils. J. bio-sci. 28: 33-41, 2020

Effect of Turbulent Flame Propagation Velocity and Zone Width on the Unburnt Hydrocarbon Concentration and Combustion Efficiency in a Spark-Ignition Engine

The investigation considers how combustion efficiency and exhaust gas (unburnt hydrocarbon) toxicity are linked to the fundamental flame propagation characteristics (flame propagation velocity and reaction zone width). We present combustion efficiency and unburnt hydrocarbon concentration as functions of fundamental flame propagation characteristics, maximum flame temperature, flame failure temperature and thickness of the unburnt fuel layer adjacent to the combustion chamber walls. Comparing combustion efficiency computed according to the equation proposed to combustion efficiency derived by using an experimentally obtained indicator diagram showed that the data are in good agreement. We studied the connection between unburnt hydrocarbon emission and combustion efficiency. We detected that increasing combustion efficiency leads to lower unburnt hydrocarbon emission, which is explained by reduction of the unburnt fuel ratio in the layer adjacent to the wall. We propose a new technique for calculating unburnt hydrocarbon amount in engine exhaust gases. We show that our technique makes it possible to determine the chemical composition of the air-fuel mixture and the values of flame propagation characteristics that ensure a decrease in unburnt hydrocarbon emission. The results of our study may be used to develop or refine methods of increasing combustion efficiency of composite fuels and reducing exhaust gas toxicity in combustion chambers of internal combustion engines and other power plants.