Moisture sorption isotherms are useful in food dehydration, storage and packaging. Because of the complex food composition, experimental measurements are necessary for prediction of the isotherms. Moisture sorption isotherms of Thompson seedless raisins were determined at 30, 40, 50, 60, 70 and 80oC, using the standard static gravimetric method developed by the European cooperation project COST 90. GAB, Smith, Oswin, Halsey, Henderson and Arcy-Watt equations were fitted to the experimental data. The experimental data were fitted well with D’Arcy-Watt equation at 30 to 70 and with GAB equation at 80ºC. The Isosteric heat of sorption was determined (4.79) kj/mol.

Chromium VI is a frequent pollutant of industrial liquid effluents. It is a substance classified as a carcinogen group I. In this study, a Cr VI sorption mechanism was developed by using nanocellulose spheroids (hydrogel) obtained from ivory nut. Cr VI was detected in water by a colorimetric method, using 1, 5-diphenylcarbazide at λ 540 nm. Then, the sorption capacity of nanocellulose spheroids was tested by varying the solution's pH and temperatures. The outcome of the experiment shows that the most efficient pollutant’s adsorption conditions are occur at pH 4 and 25 °C. Removal percentages of Cr VI reached 91.29% (+/-1.36) and 95.33% (+/- 0.86). Additionally, the sorption kinetics showed that the adsorption reaction on the material reaches its equilibrium 20 to 30 minutes after the reaction starts. Finally, an analysis of adsorption isotherms showed a high adjustment with the Langmuir and Freundlinch isotherms. In this frame, this work’s results show that nanocellulose beads are an interesting alternative to efficiently reduce Cr VI from industrial and drinking water.

Background and objectives: Organic black grapes produced in Sardasht, West Azerbaijan province in Iran, contain resveratrol and flavonoids and high amount of melatonin with health benefits. The relationship between equilibrium moisture content and water activity at specified temperature is expressed as sorption isotherms. Moisture sorption isotherms are useful in predicting shelf-life stability and in calculating the variations of moisture content during drying, storage and packaging. In physical, chemical and microbial analysis of food, data obtained from adsorption and desorption curves are very important factors. Isotherm curves are able to predict the maximum moisture retention in foods during processing. In this study, the moisture sorption isotherms of grape pulp (Siah-Sardasht cultivar) were determined using a static-gravimetric method at 30, 40, 50, 60 and 70° C with water activities over the range of 0. 1-0. 9. Material and methods: Black grapes were obtained from a vineyard in Sardasht (West Azerbaijan province). Nine saturated salt solutions with degree of purity over 98% were used for generating a range of relative humidity. In order to describe the sorption moisture isotherms, the BET, GAB, Henderson, Darcy-watt and Halsey equations were tested to fit the experimental data by using non-linear regression analysis method. The models were sorted based on the least mean absolute percentage error (P<10%), RMSE and χ 2, and the highest R-square. The isosteric heat was determined using the Claussius– Clapeyron equation. Results: At all of temperature levels, moisture sorption isotherm curves of grape pulp were of type III, according to BET. Moisture sorption isotherms obtained in this work were affected by temperature, and the equilibrium moisture content generally increased with temperature elevation. According to the evaluated parameters in the tested models, P-value of Darcy-Watt model was consistently less than 10 % and its RMSE and χ 2 were lowest, indicating its reliability in predicting moisture sorption behavior of grape pulp. According to results of predicting moisture sorption in the grape pulp, it is concluded that BET and GAB models can be used only at high temperatures. The isosteric heat showed a marked increase with decreasing moisture content especially at the levels less than 0. 3% (d. b). Conclusion: At the studied range of water activity, the equilibrium moisture content values of grape pulp increased with increasing temperature, and no reverse temperature effect was observed in the range of water activities studied here. In spite of presence of sugar in the black grape pulp, no inversion phenomenon was observed in the relationship between equilibrium moisture content and water activity. Darcy-Watt was found to be the best model offering fits over the entire water activity and temperature range. The isosteric heat decreased with increasing the moisture content probably due to the fact that pulp water properties approached to that of free water.

Varieties of St. John’s wort (Hypericum perforatum L.) native to Iran possess the largest percentage of hypercin in their leaves and flowers. Isotherm curves show the relationship between the relative humidity and moisture content of the plant at a constant temperature. It is essential to understand the isotherms curves for successful storage and drying of the plant. This study used adsorption and desorption to determine the moisture equilibrium of St. John’s wort flowers at 40o, 50 o, 60 o and 70 o C. Moisture content was determined to be 0.11-0.84 using the gravimetric static method. Five mathematical models (modified Henderson, modified Oswin, modified Halsey, modified Chung-Pfost and GAB equations) were used to compare the experimental data. The modified Halsey and Chung-Pfost models were found to be the best models for describing desorption and adsorption isotherms curves.

The adsorption of a mono azo dye methyl-orange (MeO) onto granular pinecone derived activated carbon (GPAC), from aqueous solutions, was studied in a batch system. Seven two-parameter isotherm models Langmuir, Freundlich, Dubinin-Radushkevic, Temkin, Halsey, Jovanovic and Hurkins-Jura were used to fit the experimental data. The results revealed that the adsorption isotherm models fitted the data in the order of Jovanovic (X2=1.374) > Langmuir > Dubinin-Radushkevic > Temkin > Freundlich > Halsey > Hurkins-Jura isotherms. Adsorption isotherms modeling showed that the interaction of dye with activated carbon surface is localized monolayer adsorption. A comparison of kinetic models was evaluated for the pseudo-second order, Elovich and Lagergren kinetic models. Lagergren first order model was found to agree well with the experimental data (X2=9.231). In order to determine the best-fit isotherm and kinetic models, two error analysis methods of Residual Mean Square Error and Chi-square statistic (X2) were used to evaluate the data.

Chromium (VI) which exists in many industrial wastewater is considered highly toxic. The aim of the present investigation was to study the reduction of chromium (VI) to chromium (III) and then removing it with the help of weathered basalt andesite products. Reduction of the chromium (VI) to chromium (III) by hydrazinium sulfate was investigated. The influence of hydronium ion concentration, contact time, hydrazinium sulphate dosage and temperature has been tested in batch runs. The process was found to be acid, temperature and concentration dependent. The suitability of weathered basalt andesite products as a potential sorbent was assessed for the removal of chromium (III) following batch mode of operation. The effect of various parameters such as hydronium ion concentration, shaking time, sorbent dose, initial metal ion concentration and temperature on the removal of chromium (III) from aqueous solution was studied. Thermodynamic parameters (DHo, DSo and DGo) for the sorption process were evaluated. Analysis of sorption obtained results showed that the sorption pattern followed the Freundlich, Langmuir and Dubinin-Kaganer-Radushkevich isotherms. The process follows pseudo second order rate and surface diffusion is identified as the predominating mechanism. The sorption process was shown to be reversible by the recovery of sorbed chromium (III) upon extraction with 0.5 M nitric acid. The sorbent, before and after sorption, was characterized by fourier transform infrared spectrometer, X-ray diffraction, scanning electron microscope, transmision electron microscope and thermogravimetric analyse methodes. An increase in crystallanity after sorption of chromium was observed. An industrial effluent was successfully treated with the same sorbent with convincing results.