Optimization of dyes and toxic metals removal from environmental water samples by clinoptilolite zeolite using response surface methodology approach.

The present study aimed to remove crystal violet (CV), malachite green (MG), Cd(II), and Pb(II) from an aqueous solution using clinoptilolite zeolite (CZ) as an adsorbent. Response surface methodology (RSM) based on central composite design (CCD) was used to analyze and optimize the process parameters, such as pH, analyte concentration, adsorbent amount, and sonication time. Quadratic models with the coefficient of determination (R2) of 0.99 (p < 0.0001) were compared statistically. The results revealed that the selected models have good precision and a good agreement between the predicted and experimental data. The maximum removal of contaminants was achieved under optimum conditions of pH = 6, sonication time of 22 min, the adsorbent amount of 0.19 g, and analyte concentration of 10 mg L-1. The reusability test of the adsorbent showed that the CZ adsorbent could be used 5 times in water and wastewater treatment processes. According to the results of interference studies, the presence of different ions, even at high concentrations, does not interfere with the removal of contaminants. Applying the CZ adsorbent on environmental water samples revealed that CZ adsorbent could remove CV, MG, Cd(II), and Pb(II) in the range of 84.54% to 99.38% and contaminants present in industrial effluents. As a result, the optimized method in this study can be widely used with high efficiency for removing CV, MG, Cd(II), and Pb(II) from water and wastewater samples.

Application of Taguchi method and response surface methodology into the removal of malachite green and auramine-O by NaX nanozeolites.

In the present study, the simultaneous removal of malachite green (MG) and auramine-O (AO) dyes from the aqueous solution by NaX nanozeolites in a batch system is investigated. Taguchi method and response surface methodology (RSM) were used to optimize and model dye removal conditions. In order to do so, the effect of various factors (dyes concentration, sonication time, ionic strength, adsorbent dosage, temperature, and pH of the solution) on the amount of dye removal was evaluated by the Taguchi method. Then, the most important factors were chosen and modeled by the RSM method so as to reach the highest percentage of dye removal. The proposed quadratic models to remove both dyes were in good accordance with the actual experimental data. The maximum removal efficiencies of MG and AO dyes in optimal operating conditions were 99.07% and 99.61%, respectively. Also, the coefficients of determination (R2) for test data were 0.9983 and 0.9988 for MG and AO dyes, respectively. The reusability of NaX nanozeolites was evaluated during the adsorption process of MG and AO. The results showed that the adsorption efficiency decreases very little up to five cycles. Moreover, NaX nanozeolites were also applied as adsorbents to remove MG and AO from environmental water samples, and more than 98.1% of both dyes were removed from the solution in optimal conditions.

Experimental and numerical assessment of saltwater recession in coastal aquifers by constructing check dams.

Artificial freshwater recharge has been considered as a feasible and effective procedure to mitigate seawater intrusion in coastal regions. The efficiency of freshwater infiltration through a check dam reservoir on saltwater recession (SWR) is investigated using two physical models. The results demonstrate the apparent tendency of recharge freshwater to move horizontally toward the boundaries rather than flowing downward to influence saltwater wedge toe. Thereby, it would affect the saltwater wedge tip instead of its toe due to the new establishment of a positive hydraulic gradient from a dam reservoir to the boundaries. Moreover, numerical dispersive simulations have been carried out on a large-scale aquifer to find the optimum location of the dam as well as the aquifer characteristics impacts on SWR efficiency. The results show that the best location to construct a check dam is immediately above the saltwater wedge toe. It is found that when saltwater head declines, the steeper hydraulic gradient between boundaries is established and the efficiency of recharge performance will be improved. Moreover, the reduction of hydraulic conductivity in vertical direction improves SWR, while higher hydraulic conductivity in the homogeneous cases only accelerates the infiltration rate but has no meaningful effect in the long term. The considered recharge method also works better in scenarios with higher dispersivity. However, the construction of check dams on floodways might be a practical and low-cost solution but it can be concluded that as the dominant direction of the recharged freshwater is toward boundaries, it cannot promptly retreat saltwater around toe position.