A comparative study of Box-Behnken, central composite, and Doehlert matrix was performed on the adsorption of Pb (II) by Robinia tree leaves in a batch system. As a case study, uptake capacity (q) and removal efficiency (R) of Pb (II) biosorption have been evaluated with all theses approaches. The advantages and limitations of these different response surface techniques have been experimentally considered. The results show the different statistical predictability of Doehlert matrix and Box-Behnken design at 95% confidence level comparable with some extent with that of central composite design at some extreme conditions. An environmental and economical comparison was also carried out between individual and simultaneous optimization of removal efficiency (R) and uptake capacity (q) using desirability function. Optimization of q proves only to have advantages over R or simultaneous optimization of R and q in this particular biosorption process.

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Statistical experimental design was utilized to optimize removal of aqueous Hg(II) by Fraxinus tree leaves through a batch biosorption process. Sorbent−sorbate behavior was evaluated by fitting equilibrium data by nonlinear and transformed linear forms of the Langmuir, Freundlich, and Redlich−Peterson isotherms. The comparative study showed that nonlinear regression is a better way to model equilibrium data. A 23 full factorial design was used to identify significant factors and interactions. The pH, Hg(II) initial concentration, and sorbent mass were examined as major factors. The contact time was fixed at 30 min. All of the factors were significant at the 95 % confidence level. The amount of Hg(II) was determined by cold vapor atomic absorption spectrophotometry. A regression model was derived by using a response surface methodology through performing central composite design (CCD). Model adequacy was checked by such diagnostic tests as analysis of variance (ANOVA), lack of fit test, residuals distribution, and over-fitting test. On the other hand a residuals distribution was evaluated for normality according to the Ryan−Joiner test. As a result, the optimized condition for Hg(II) biosorption was calculated to be pH = 4.4, s = 0.25 g, and m = 50 mg·L−1, which corresponds to 92.25 % removal efficiency. The biosorption process was kinetically fast and followed a pseudosecond order kinetic model. Fourier transform infrared (FT-IR) and X-ray diffraction (XRD) spectra were used to find more about the biosorption mechanism.

A dependency of the R% and the maximum capacity of sorbent (qmax) was verified. Experimental MaterialsPlatanus tree leaves were collected from a grove in a suburb 2010

A 24−1(IV) half-fractional factorial design was performed to identify significant variables for the biosorption of Cr(VI) by Elaeagnus tree leaves. A face-centered central composite design (FCCD) was carried out to find a suitable response surface relating all significant variables to R (removal) and q (sorption capacity). Simultaneous optimization of both responses (R and q) was carried out, and 80 % of the goal of desirability function was achieved. Simultaneous optimization of R and q and simple optimization of q was more favorable than that of R from an environmental and economical view. A kinetics study was performed by examining pseudofirst-order, second-order, and intraparticle diffusion kinetic models, and the best fit was obtained for the pseudosecond-order kinetics model with q e = (0.624 and 2.657) mg·g−1 for (10 and 50) mg·L−l Cr(VI), respectively. Langmuir, Freundlich, and Dubinin−Radushkevich models were used for the equilibrium study. The equilibrium data had the best fit with the Langmuir isotherm. Biosorption mean free energy (E) was calculated to be 16.2 kJ·mol−1. Considering kinetics and equilibrium studies, one can suggest that adsorption onto the sites is the rate-limiting step and that biosorption goes through chemisorption mechanisms. Fourier transform infrared (FTIR) spectra were recorded to identify functional groups involved in the biosorption.

Worldwide pesticide usage has increased dramatically during the last three decades, coinciding with changing practices and increasing by intensive agriculture. This widespread use of pesticides for agricultural and non‐agricultural purposes has resulted in the presence of their residues in various environmental matrices. The occurrence of pesticides and their metabolite transported in rivers, channels, lakes, sea, air, soils, groundwater, and even drinking water, proves the high risk of these chemicals to human health and the environment. Therefore, pesticide removal is of an increasing concern. In this study, a review of the published literature dealing with pesticides removal process is presented. Firstly, pesticide removal by conventional means is briefly considered. Secondly, the use of the low‐cost sorbent through biosorption process is discussed comprehensively. The effect of factors such as pH, contact time, sorbent dosage, initial pesticide concentration, and optimization of biosorption conditions is also discussed. Kinetic, thermodynamic, and mechanism studies are also given. This study shows that both microorganisms and other materials with biological origin like agricultural by‐products may be used to this end. There is a significant potential for pesticide uptake by the use of various pristine and especially modified biosorbents. In the case of living organisms used as removal agents, degradation may also play a role in the total removal observed.

Ulmus tree leaves were successfully used as a novel and efficient biosorbent for removing cadmium, (Cd(II)), from aqueous solutions in a batch system. A multivariate strategy for optimization of removal efficiency conditions of Cd(II) was carried out. A 2 3 full factorial design with three center points (9 runs) was performed for screening the main variables and reducing the large number of experimental runs. Initial concentration of metal ion (C m ), amount of sorbent (m), and pH were considered as the three main variables at two different levels. The maximum removal efficiency of Cd(II) was achieved within 1 h contact time. It was found that all the main factors and their interactions were significant at p 5 0.05. Doehlert response surface methodology was utilized (13 runs) for finding a suitable mathematical model. The analysis of variance and some statistical tests such as lack-of-fit, coefficient of determination (R 2 ), and residual distribution plot confirmed the validity of the model. The optimum conditions for maximum removal of Cd(II) by Ulmus tree leaves were found as pH ¼ 3.4, m (amount of sorbent) ¼ 0.128 g, C m (initial concentration of metal ion) ¼ 12.1 mg L À1 .