Biosorption of Hexavalent Chromium by Bacillus megaterium and Rhodotorula sp. Inactivated Biomass

Due to the adverse effects of hexavalent chromium (Cr6+) on human health and the quality of the environment, the scientific community has invested a lot of effort to solve this pollution problem. Thus, implementing sustainable alternatives for Cr6+ elimination by exploiting the capacity of microbial biomass to retain heavy metals by biosorption is considered an economic and eco-friendly solution, compared to the conventional physico-chemical processes. However, the ability of microorganisms to remove Cr6+ from liquid effluents can strongly be affected by biotic and abiotic factors. With these issues in mind, the main purpose of this paper was to investigate Cr6+ biosorption on Bacillus megaterium and Rhodotorula sp. biomass inactivated by thermal treatments, exploring the effects of some factors such as: pH, biosorbent dose, initial concentration of the metal in solution, temperature and contact time between the biosorbent and the metal ions on process effectiveness. The results showed that Cr6+ removal by biosorption on the selected microorganisms was strongly influenced by the pH of the solution which contains chromium, the reduction being the principal mechanism involved in hexavalent chromium biosorption. Equilibrium and kinetic studies were also performed, together with SEM-EDX and FTIR spectra, to explain the mechanisms of the biosorption process on the selected biomasses. Maximum uptake capacities of 34.80 mg/g biosorbent and 47.70 mg/g biosorbent were achieved by Bacillus megaterium and Rhodotorula sp., respectively, at pH 1, biosorbent dosage of 8 g/L, 25 °C, after a contact time of 48 h and an initial Cr6+ concentration in solution of 402.52 mg/L. The experimental results showed that Cr6+ biosorption by selected microorganisms followed the Elovich model, the values of the correlation coefficients being 0.9868 and 0.9887, respectively. The Freundlich isotherm model best describes the Cr6+ biosorption by Bacillus megaterium and Rhodotorula sp., indicating that a multilayer biosorption mainly controls the process and is conducted on heterogeneous surfaces with uniformly distributed energy.

CO2 Adsorption on Activated Carbons Prepared from Molasses: A Comparison of Two and Three Parametric Models

Activated carbons with different textural characteristic were derived by the chemical activation of raw beet molasses with solid KOH, while the activation temperature was changed in the range 650 °C to 800 °C. The adsorption of CO2 on activated carbons was investigated. Langmuir, Freundlich, Sips, Toth, Unilan, Fritz-Schlunder, Radke-Prausnitz, Temkin-Pyzhev, Dubinin-Radushkevich, and Jovanovich equations were selected to fit the experimental data of CO2 adsorption. An error analysis (the sum of the squares of errors, the hybrid fractional error function, the average relative error, the Marquardt's percent standard deviation, and the sum of the absolute errors) was conducted to examine the effect of using various error standards for the isotherm model parameter calculation. The best fit was observed to the Radke-Prausnitz model.

Clinoptilolite Microparticles as Carriers of Catechin-Rich Acacia catechu Extracts: Microencapsulation and In Vitro Release Study

The main goal of the present study was to investigate the microencapsulation, in vitro release capacity and efficiency of catechin-rich Acacia catechu extract by Clinosorbent-5 (CLS-5) microparticles by in-depth detailed analyses and mathematical modelling of the encapsulation and in vitro release kinetics behaviour of the polyphenol-mineral composite system. The bioflavanol encapsulation and release efficiency on/from the mineral matrix were assessed by sorption experiments and interpretative modelling of the experimental data. The surface and spectral characteristics of the natural bioactive substance and the inorganic microcarrier were determined by Fourier Transform Infrared Spectroscopy (FTIR) and Ultraviolet/Visible (UV/Vis) spectrophotometric analyses. The maximum extent of catechin microencapsulation in acidic medium was 32%. The in vitro release kinetics study in simulated enzyme-free gastric medium (pH = 1.2) approved 88% maximum release efficiency achieved after 24 h. The in vitro release profile displayed that the developed bioflavanol/clinoptilolite microcarrier system provided sustained catechin in vitro release behaviour without an initial burst effect. Thus, the results from the present study are essential for the design and development of innovative catechin-CLS-5 microcarrier systems for application in human and veterinary medicine.

Modelling and Interpretation of Adsorption Isotherms

The need to design low-cost adsorbents for the detoxification of industrial effluents has been a growing concern for most environmental researchers. So modelling of experimental data from adsorption processes is a very important means of predicting the mechanisms of various adsorption systems. Therefore, this paper presents an overall review of the applications of adsorption isotherms, the use of linear regression analysis, nonlinear regression analysis, and error functions for optimum adsorption data analysis.