Biosorption of Cr(VI) by free and immobilized Pediastrum boryanum biomass: equilibrium, kinetic, and thermodynamic studies

Background and purpose

The biosorption of Cr(VI) from aqueous solution has been studied using free and immobilized Pediastrum boryanum cells in a batch system. The algal cells were immobilized in alginate and alginate?Cgelatin beads via entrapment, and their algal cell free counterparts were used as control systems during biosorption studies of Cr(VI).

Methods

The changes in the functional groups of the biosorbents formulations were confirmed by Fourier transform infrared spectra. The effect of pH, equilibrium time, initial concentration of metal ions, and temperature on the biosorption of Cr(VI) ion was investigated.

Results

The maximum Cr(VI) biosorption capacities were found to be 17.3, 6.73, 14.0, 23.8, and 29.6?mg/g for the free algal cells, and alginate, alginate?Cgelatin, alginate?Ccells, and alginate?Cgelatin?Ccells at pH?2.0, which are corresponding to an initial Cr(VI) concentration of 400?mg/L. The biosorption of Cr(VI) on all the tested biosorbents (P. boryanum cells, alginate, alginate?Cgelatin, and alginate?Ccells, alginate?Cgelatin?Ccells) followed Langmuir adsorption isotherm model.

Conclusion

The thermodynamic studies indicated that the biosorption process was spontaneous and endothermic in nature under studied conditions. For all the tested biosorbents, biosorption kinetic was best described by the pseudo-second-order model.     

The influence of natural stressors on the toxicity of nickel to <Emphasis Type="Italic">Daphnia magna</Emphasis>

Global warming has become a source of awareness regarding the potential deleterious effects of extreme abiotic factors (e.g., temperature, dissolved oxygen (DO) levels) and also their influence on chemicals toxicity. In this work, we studied the combined effects of nickel and temperature (low and high levels) and nickel and low levels of DO to Daphnia magna, and concentration addition and independent action concepts as well as their deviations for synergism/antagonism, dose ratio and dose level dependency, were applied to survival and feeding rate data. Nickel single exposure showed an LC₅₀ value for 48 h of 7.36 mg l⁻¹ and an EC₅₀ value for feeding impairment at 2.41 mg l⁻¹. In the acute exposures to high and low temperatures, 50% of mortality was observed, respectively, at 30.7°C and 4.2°C whereas 50% reduction on the feeding activity was recorded at 22.6°C and 16.0°C. Relatively to low DO levels, a LC₅₀ value for 48 h of 0.5 mg l⁻¹ was obtained; feeding activity EC₅₀ value was 2 mg l⁻¹. On acute combined experiments, antagonism was observed for the combination of nickel and extreme temperatures, whereas a synergistic behaviour was observed in the combined exposure of nickel and low DO levels. At sublethal levels, nickel showed to be the main inducer of toxicity at high and low temperatures but not at low levels of dissolved oxygen. Toxicokinetics and toxicodynamics modelling studies should be made in the future to understand the toxicological pathways involved on complex combinations of stressors and to validate any conclusions.     

Detection and analysis of xenon isotopes for the comprehensive nuclear-test-ban treaty international monitoring system

The use of the xenon isotopes for detection of nuclear explosions is of great interest for monitoring compliance with the comprehensive nuclear-test-ban treaty (CTBT). Recently, the automated radioxenon sampler-analyzer (ARSA) was tested at the Institute for Atmospheric Radioactivity (IAR) in Freiburg, Germany to ascertain its use for the CTBT by comparing its results to laboratory-based analyses, determining its detection sensitivity and analyzing its results in light of historical xenon isotope levels and known reactor operations in the area. Xe-133 was detected nearly every day throughout the test at activity concentrations ranging between approximately 0.1 mBq/m3 to as high as 120 mBq/m3. Xe-133m and 135Xe were also detected occasionally during the test at concentrations of less than 1 to a few mBq/m3.     

Impacts of land-use and land-cover changes on surface urban heat islands in Addis Ababa city and its surrounding

Environment, Development and Sustainability - Land-use and land-cover (LULC) change as a result of rapid urban expansion cause land surface temperature (LST) variations. The study aims to analyze...     

WATER RESOURCES MANAGEMENT: INTERNATIONAL CHALLENGE AND OPPORTUNITIES1

The entire water resources field is not contemplated, although reference thereto will be registered. Water supply for potable and hygienic purposes will be presented as symbolic of the global issues confronting 4.8 billion people. Some two billion of these live in the so-called developing or less favored countries. They are either underserved or not served at all by utility systems of whatever grade. Targets for meeting their needs were exemplified by the international agencies in the International Water and Sanitation Decade of 1980-1990. Some successes are apparent, but, in general, hopes are not fulfilled. The pace of accomplishment is very slow. Constraints will be reviewed in some detail. Challenges for reducing these and increasing pace of installations are presented. The potential for a global public works program unprecedented in history is reviewed. Several issues will not be discussed in this paper. Their omission rests primarily upon the fact that their resolution is improbable for decades ahead, if ever. Economists have categorized water as any other economic commodity - and should always be subject to benefit-cost scrutiny. I do not share that view. People could well live without the telephone or the automobile, a destroyer. Without water, their survival is a matter of days. Cost-benefit seems unreal and singularly inappropriate under such circumstances. Secondly, the search for quantifying the health impact of safe water goes on forever. My view is that the results speak for themselves - while sturdy souls continue to seek out the exact correlation figure. Thirdly, the population explosion, although softened a bit, proceeds apace while I write. Lastly, the exposition herein is restricted to potable water and its associated sanitation aspects. Other major uses of water, obviously highly important, are not addressed.