Bioemulsification activity assessment of an indigenous strain of halotolerant Planococcus and partial characterization of produced biosurfactants

Halotolerant bacteria are regarded as effective oil-scavengers in the polluted saltern and seawater. In this regard, a halotolerant Planococcus was isolated from oil-contaminated area of Dezful north springs, Iran, due to its capacity in biosurfactant (BS) production. To facilitate hydrocarbons degradation, in the current study, the efficiency of BS production as function of growth rate of the halotolerant Planococcus was investigated in the vicinity of heavy crude oil by emulsification index (E24). Subsequently, the BS characterization was made by thin-layer chromatography (TLC), gas chromatography (GC) and infrared spectra analysis, and the stability was determined by E24 value measurement over a certain pH (5–9), temperature (20–100 °C) and salt concentration (0–10 % w/v) ranges. The BS production was found to be growth-associated. Detection of a unique band on TLC and GC chromatogram showed the extensive refining capacity of the BS purification, using the medium supernatant under acetone alkaline precipitation followed by oil dissolution from the sediment by carbon tetrachloride. Accordingly, it was clarified that the BS ultimately accumulated outside the cells. The glycolipid quality of the BS was further determined by the routine chemical characterization on TLC and by IR spectra analysis. Moreover, there was no protein detected by lowery total protein assay. Finally, the optimal temperature, pH and NaCl concentration to reach highest E24 values (85.7, 77.0, and 79.0 %) were found at respective 40 °C, pH = 9 and 0 % w/v. Our results revealed the practically potential of strain Dezful Isolate for BS large-scale production as environmentally friendly oil-eliminating agents.     

Wave propagation in a transversely isotropic porous ocean bottom

Abstract

The equations of wave motion are considered in this article for three-layered medium which consists of liquid and porous layers with finite depth and solid half-space such as ocean bed. By virtue of scalar potential functions for each layer, complicated differential equations of layers are reduced to ordinary differential equations. An analytical method is applied to determine the Green’s functions of media based on an arbitrary shaped time-harmonic excitation at the interface of liquid and porous layers. A Mathcad code is provided to compute the complex integrals. Displacement and stress fields of three layers are discussed. Comparing with special cases, existing answers represent the validity of the proposed method. Numerical results are carried out for circular patch, ring and point loads, and the effects of various parameters on the behavior of the system are plotted. Finally, the achieved results were under discussion.     

Projections of temperature changes over South America during the twenty-first century using CMIP6 models

A 22-member ensemble from CMIP6 is used to analyze the projected changes and seasonal behavior in surface air temperature over South America during the twenty-first century. In the future projections, CMIP6 models shown a high dependency to the socioeconomic pathway over each country of South America. The multimodel ensemble projects a continuous increase in the annual mean temperature over South America during the twenty-first century under the three future scenarios (SSP1-2.6, SSP2-4.5 and SSP5-8.5). Besides, it was possible to identify consistent positive trends across all the models, with values between 0.45 ± 0.05 and 2.05 ± 0.31 °C cy⁻¹ under the historical experiment, however largest trends occurs for the projection periods (near, mid and far future), with values between − 0.87 ± 0.84 to 2.88 ± 0.60 °C cy⁻¹ (SSP1-2.6), 1.41 ± 0.88 to 5.32 ± 0.81 °C cy⁻¹ (SSP2-4.5) and 4.75 ± 0.58 to 8.76 ± 0.74 °C cy⁻¹ (SSP5-8.5) with maximum values at Bolivia, Brasil, Paraguay and Venezuela whilst minimum values for Argentina and Uruguay, regardless of the SSP scenario used. From the seasonal behavior analysis was possible to identify maximum values between January and March whilst minimum between June and July, except in Brasil, Venezuela and Guyana–Surinam–French Guayana, with annual range decreasing as the latidude decreases. By the end of the twenty-first century the annual mean temperature over South america is projected to increase between 0.92–2.11 °C, 0.97–3.37 °C and 1.27–6.14 °C under SSP1-2.6, SSP2-4.5 and SSP5-8.5 projection scenarios respectively. This projected increase of temperature across the continent will produce negative repercussions in the social, economic and political spheres. The results obtained in this study provide insights about the CMIP6 performance over this region, which can be used to develop adaptation strategies and might be useful for the adaptation to the climate change.