M. piri; E. Sepehr; A. samadi; KH. Farhadi; M. Alizadeh khaled abad
Abstract
Introduction: Some of the heavy metals such as cadmium (Cd) and lead (Pb) are toxic and represent hazardous pollutants due to their persistence in the environment. These metals have adverse effects on human health, which include growth retardation, cancer, damage to the nervous and heart system. Heavy ...
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Introduction: Some of the heavy metals such as cadmium (Cd) and lead (Pb) are toxic and represent hazardous pollutants due to their persistence in the environment. These metals have adverse effects on human health, which include growth retardation, cancer, damage to the nervous and heart system. Heavy metals can cause malfunctioning of the cellular processes via the displacement of essential metals from their respective sites. Mainly heavy metals discharge into the environment from industrial and urban sewage. There are different methods to reduce water pollution and the removal of heavy metals from water that one of them is sorption by using organic and inorganic adsorbents such as sepiolite. The low cost of sepiolite along with the high specific surface area, chemical and mechanical stability, and layered structure have made these clay minerals as excellent adsorbent materials for the removal of heavy metals from wastewaters. This study aims to investigate the sorption of Cd and Pb by sepiolite as an inorganic absorbent and optimize process variables (initial concentration, pH and ionic strength) using Response Surface Methodology (RSM) and Box–Behnken design (BBD).
Materials and Methods: Response Surface Methodology (RSM) is a statistical method that uses quantitative data from appropriate experiments to determine regression model equations and operating conditions. RSM is a collection of mathematical and statistical techniques for modeling and analysis of problems in which a response of interest is influenced by several variables. A standard RSM design called Box-Behnken Design (BBD) was applied in this work to study the variables for sorption of Cd and Pb by sepiolite from aqueous solution using a batch process. BBD for three variables (initial Cd and Pb concentrations, pH and ionic strength), each with two levels (the minimum and maximum), was used as an experimental design model. Sepiolite sample used in this study was taken from a mine in Fariman region, northeastern Iran. In the experimental design model, initial concentration (0-200 mg L-1), pH (3-6) and ionic strength (0.01-0.06 mol L-1) were taken as input variables. Design-Expert program was used for regression and graphical analysis of the data obtained. The optimum values of the selected variables were obtained by solving the regression equation and by analyzing the response surface contour plots. The variability independent variables were explained by the multiple coefficients of determination, R2 and the model equation was used to predict the optimum value and subsequently to elucidate the interaction between the factors within the specified range.
Results: The results showed that the sorption of Cd and Pb intensified by increasing initial concentration and pH but ionic strength had an inverse effect. The sorption of Pb and Cd ions onto the sepiolite minerals were lowest at pH =3 and IS=0.06 but increased with an increase in pH and initial concentration of the solution. High value for R2 (0.99) and adjusted R2 (0.99) showed that the removal of Cd and Pb can be described by the response surface method. One-way ANOVA showed (p< 0.0001) that the quadratic model is the best model for determining the interaction variables. According to optimization results, the sorption of Cd and Pb are maximized when pH: 6, concentration: 200 mg.L-1 and ionic strength: 0.02 mol.L-1. The predicted adsorption at these settings for Pb and Cd are 44.4 and 34.28 mg.g-1, respectively. It was found that the initial concentration is the most effective parameter in the sorption of Cd and Pb by sepiolite. Sepiolite adsorbed more lead ions than cadmium ions from aqueous solution.
Conclusion: Response surface methodology using BBD, proved a very effective and time-saving model for studying the influence of process parameters (pH, initial concentration and ionic strength) on response factor (sorb). This model significantly reduces the number of experiments and hence facilitating the optimum conditions. The experimental values and the predicted values are in perfect match with an R2 value of 0.99. The high correlation coefficient between the model and experimental data (R2=0.99) showed that the model was able to predict the removal of Cd and Pb from aqueous solution by using sepiolite. The model revealed that concentration, metal type and pH were the most effective parameters on the response yield (adsorption by sepiolite), respectively. According to the results, sepiolite showed a greater efficiency for sorption of Cd and Pb from aqueous solution, also usage of sepiolite as an inorganic absorbent due to its low cost and abundance can be economically justified.
Z. Ahmadpoor; M. Khoramivafa; S. Jalali Honarmand; K. Cheghamirza; M. Khan Ahmadi
Abstract
Introduction: There is necessary to clean up the nitrate and phosphate from surface waters before effluence of them to environment and eutrophication formation because of water health importance and considering to nitrate and phosphate consequences. Nitrate and ammonium as the - forms of inorganic and ...
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Introduction: There is necessary to clean up the nitrate and phosphate from surface waters before effluence of them to environment and eutrophication formation because of water health importance and considering to nitrate and phosphate consequences. Nitrate and ammonium as the - forms of inorganic and nitrogen have been subjected to the center of issues related to environment pollutants and water resources in a long time. The nitrate is more important than other inorganic nitrogen forms such as ammonium because of various reasons such as high dynamics and causing diseases such as some of digestion system and lymph nodes cancers in adults and methemoglobinemia in infants. Therefore the maximum concentration of this ion in drinking water has been determined as 45 mg.Lit-1 by WHO. Regarding the importance of the water health and the complications due to existence of some compounds such as nitrate and phosphate, in this experiment, the possibility of elimination or decreasing excess nitrate and phosphate from water in hydroponic conditions using of two watercress and pennyroyal plants was evaluated. Watercress(Nasturtiumofficinale) and pennyroyal (Menthapulegium)were selected because of some properties such as adaptability with the most climates of Iranamd less requirements care.
Materials and Methods: Two RCD factorial experiments were carried out to evaluate the ability of watercress and pennyroyal to biosorption of nitrate and phosphate from polluted water in hydroponic conditions. First factor was plant species including watercress and pennyroyal. Second factor included nitrate (50, 100, 150 Mg/L) and phosphate (5, 10, 15 Mg/L) in first and second experiment respectively.The final concentrations of nitrate and phosphate in water was measured using spectrophotometer in wavelength of 410 nm and 690 nm by sulphatebrucine and chloride methods , respectively, which are mentioned in Standard Methods for the Examination of Water and Wastewater. At the end of the each experiment, watercress and pennyroyal plants were brought out from the pots carefully and their roots and shoots were separated. Roots and shoots were placed in aluminum foil separately and were dried by oven method (50°C and 48 h). The weights of dried samples were measured by a digital balance scale (0.001 gr accuracy). Three accumulation indices including Bio-concentration Factor, Translocation Factor and Tolerance Index were calculated by measuring of nitrate and phosphate accumulation in roots and shoots
Results and Discussion: According to the results, root phosphate accumulation in two plants was different significantly (p ≤ 0.05). Also, the level values of nitrate and phosphate were resulted to their root accumulation significantly. In this regard, the phosphate accumulation in watercress root changed to 10 mg. Lit-1 significantly and reached to 4.3 mg.Kg-1 dry weight in this concentration. While for pennyroyal, there was no significant increasing in roots phosphate accumulation when its concentration was increased in medium (p ≤ 0.05). Although phosphate accumulation was difference between the two plants in root and shoots, there was similar the alteration of phosphor bioconcentration trend. Because increasing of phosphate concentration resulted in significant decreasing of this index. Whilst both of watercress and pennyroyal accumulated high amount of nitrate and phosphate, quantity of accumulation in shoots was higher than of roots. Consequently, nitrate translocation factor was 1.3 in watercress and 1.07 in pennyroyal, and phosphor translocation factor was 1.07 and 0.94 in watercress and pennyroyal respectively.
Conclusions: Results indicated that two plants were pollutants purified of nitrate and phosphate (The nitrate translocation factors were 1.3 and 1.07 in watercress and pennyroyal and the phosphate translocation factors were 1.07 and 094 in watercress and pennyroyal, respectively). Generally, it was found that watercress and pennyroyal have extractive behavior completely about nitrate and phosphate. Because of the high ability of these plants in biosorption of phosphate and nitrate, with recovery of nitrogen and phosphorus cycle, they can be used as organic resources of nitrogen and phosphor supply in agricultural soil and prevent from entrancing them to seas. It is more important about phosphate, which has slowly cycle. Therefore two main roles for watercress and pennyroyal in aquatic ecosystems are expected. First, perform as bio-filter and returning the nitrogen and phosphor from surface water or wastewater for preventing the environmental pollution and second as secondary saleable or utilizable crop such as green manure and so on.
