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Chemical pesticides and herbicides are one of the most important pollutants in urban, agricultural and industrial wastewaters. Improper discharge of these compounds into water bodies' cause harmful effects on both environment and human health. In this study, photocatalytic degradation of 2,4-Dichlorophenoxyacetic acid (usually called 2,4-D) was investigated using Mn-doped zinc oxide/graphene nanocomposite under light emitting diodes (LED) radiation. FTIR, AFM, DLS, Zeta potential, XRD, and SEM techniques were used to determine the characteristics of the nanocomposite. The effects of process-related parameters, such as the amount of nanocomposite, initial pH, 2,4-D concentrations, and contact time, on the photocatalytic degradation of the 2,4-D were studied. The results showed that the efficiency of photocatalytic degradation of 2,4-D decreased with an increase in the initial concentration of 2,4-D, while photocatalytic degradation efficiency increased by increasing the initial pH and the nano-catalyst content. The results showed that 66.2% of 2,4-D could be photocatalytically degraded using Mn-doped zinc oxide/graphene nanocomposite under LED radiation at optimal conditions (pH 5, initial Zn concentration of 10 mg L−1, nano-composite concentration of 2 g L−1, contact time of 120 min). Findings of this experimental study concluded that photocatalysis using Mn-doped zinc oxide/graphene nanocomposite under LED radiation could efficiently remove 2,4-D herbicide from aqueous media. [ABSTRACT FROM AUTHOR]

The study is a first-time investigation into the use of Eucalyptus leaves as a low-cost herbal adsorbent for the removal of arsenic (As) and mercury (Hg) from aqueous solutions. The adsorption capacity and efficiency were studied under various operating conditions within the framework of response surface methodology (RSM) by implementing a four-factor, five-level Box-Wilson central composite design (CCD). A pH range of 3-9, contact time ( t) of 5-90 min, initial heavy metal (As or Hg) concentration ( C ) of 0.5-3.875 mg/L, and adsorbent dose ( m) of 0.5-2.5 g/L were studied for the optimization and modeling of the process. The adsorption mechanism and the relevant characteristic parameters were investigated by four two-parameter (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich) isotherm models and four kinetic models (Lagergren's pseudo-first order (PFO), Ho and McKay's pseudo-second order (PSO), Weber-Morris intraparticle diffusion, and modified Freundlich). The new nonlinear regression-based empirical equations, which were derived within the scope of the study, showed that it might be possible to obtain a removal efficiency for As and Hg above 94% at the optimum conditions of the present process-related variables (pH = 6.0, t = 47.5 min, C = 2.75 mg/L, and m = 1.5 mg/L). Based on the Langmuir isotherm model, the maximum adsorption or uptake capacity of As and Hg was determined as 84.03 and 129.87 mg/g, respectively. The results of the kinetic modeling indicated that the adsorption kinetics of As and Hg were very well described by Lagergren's PFO kinetic model ( R = 0.978) and the modified Freundlich kinetic model ( R = 0.984), respectively. The findings of this study clearly concluded that the Persian Eucalyptus leaves demonstrated a higher performance compared to several other reported adsorbents used for the removal of heavy metals from the aqueous environment. [ABSTRACT FROM AUTHOR]

In the present study, multi-walled carbon nanotubes (MWCNTs) have been used for the rapid removal of four trihalomethanes (THMs) from aqueous solutions. The adsorption capacity of THMs onto MWCNTs was reasonably constant in the pH range of 5-7 but decreased as the pH exceeded 7. Four equilibrium isotherm models, namely, Langmuir, Freundlich, Temkin, and Sips, were applied to determine the best-fit equilibrium expressions. The results showed that all four experimental adsorption isotherms were best correlated by using the Sips model. The maximum adsorption capacities for the CHCl, CHClBr, CHClBr and CHBr were found to be 10.98, 6.85, 6.57, and 5.95 mg/g, respectively. The rate of adsorption followed the pseudo-second-order kinetic model. Furthermore, four nonlinear regression-based equations were also derived to model THM adsorption from aqueous solutions by MWCNTs. The modeling results clearly indicated that the empirical formulations satisfactorily described the behavior of the present adsorption process for CHCl ( R = 0.949), CHClBr ( R = 0.945), CHClBr ( R = 0.936), and CHBr ( R = 0.919). The overall results confirmed that MWCNTs could be a promising adsorbent material for THMs removal from aqueous solutions. [ABSTRACT FROM AUTHOR]

In the present paper, the removal of ethidium bromide (EtBr) from aqueous solutions in a batch system using natural (NP) and aluminium-coated pumice (ACP) as alternative low-cost adsorbents was investigated. The maximum adsorption capacity, q m (mg/g) was 58.82 and 76.92 mg/g for NP and ACP, respectively, operating at an initial pH of 8, an adsorbent dose of 8 g/L, a contact time of 210 min and an initial EtBr concentration of 30 mg/L. The equilibrium data of both adsorbents fitted the Freundlich isotherm model, indicating the heterogeneity of the adsorbent surface. In addition, the adsorption rate of both adsorbents was well described by the pseudo-second-order kinetics model. This indicated chemisorption was the rate-controlling step of the adsorption process which occurred by ion exchange. Within the performed study, a three-layer artificial neural network (ANN) model was also developed to predict the efficiency of EtBr removal. Computational results clearly demonstrated that the ANN model was able to predict the combined effect of initial pH, adsorbent dose, contact time and initial EtBr concentration on the adsorption efficiency with a very high determination coefficient ( R 2 = 0.998) and a low relative error (RE = 0.037). [ABSTRACT FROM AUTHOR]

Highlights: [•] LECA modified by aqueous solution of MgCl2 and H2O2 are used to remove toxic chromium. [•] Spent natural and surface modified LECA with MgCl2 and H2O2 are best regenerated with HCl acid. [•] XRD and FTIR studies of surface modified LECA do not show any structural distortion. [•] The modification of adsorbents improve specific surface area and metal sorption capacity. [•] Studied adsorbents partially increase the solution conductivity and turbidity. [Copyright &y& Elsevier]

The efficiency of new and nano-scale adsorbents including multi-walled carbon nanotubes (MWCNTs) and γ-alumina in the removal of cobalt(II) from aqueous solutions was experimentally evaluated in a batch-system reactor. To the best of our knowledge, no previous study has specifically attempted to introduce a hybrid strategy based on artificial neural network and genetic algorithm techniques for modelling and optimizing adsorptive removal of cobalt(II) from aqueous solutions via the proposed nanoparticles. The analyses of SEM, TEM, and FTIR were used to characterize both adsorbents. The response surface methodology (RSM) approach suggested a second-order polynomial model with a p -value < 0.0001 and R 2 of 0.9980 for MWCNTs adsorbent and a p -value < 0.0001 and R 2 of 0.9992 for γ-alumina adsorbent. The artificial neural network (ANN) approach suggested a three-layered feed-forward backpropagation model with R 2 of 0.9794 for MWCNTs adsorbent and R 2 of 0.9823 for γ-alumina adsorbent. The results linked to optimization by RSM showed that the maximum cobalt(II) removal efficiency of about 90% was achieved in the case of the MWCNTs adsorbent under the conditions of pH = 10, contact time = 38.6 min, MWCNTs dosage = 1.57 mg/L, and initial cobalt(II) concentration = 56.57 mg/L. About 93% of cobalt(II) removal could be obtained in the case of γ-alumina adsorbent under the conditions of pH = 10, contact time = 35.5 min, γ-alumina dosage = 1.63 g/L, and initial cobalt(II) concentration = 52.15 mg/L. The optimization values using the genetic algorithm (GA) technique were almost the same as those obtained from the RSM method. The kinetic model of Ho and McKay's pseudo-second order (PSO) and the isotherm model of Dubinin–Radushkevich were found to be the best-fitted to the experimental for both MWCNTs and γ-alumina. In addition, the maximum monolayer adsorption capacity of MWCNTs and γ-alumina adsorbents for the adsorption of cobalt(II) was 78.94 mg/g and 75.78 mg/g, respectively. Also, a thermodynamic study exhibited a favorable and spontaneous adsorption process for both materials. The present study clearly concluded that the proposed adsorbents could be effectively used for the removal of cobalt(II) from aqueous solutions at lower adsorbent dose and shorter contact times than various adsorbents reported in literature. Unlabelled Image • Adsorptive removal of cobalt (II) was explored via MWCNTs and nano-alumina. • ANN and genetic algorithm were proposed for this first time in cobalt (II) adsorption. • Isotherms and kinetic data followed Dubinin–Radushkevich and PSO models, respectively. • A cobalt (II) removal efficiency above 90% was possible at pH = 10 and 1 g adsorbent/L. • Favorable and spontaneous removal was corroborated by thermodynamic study. [ABSTRACT FROM AUTHOR]

In the present study, defluoridation study of liquid phase with the help of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) were well investigated and elucidated. The impact of different experimental conditions such as solution pH, initial fluoride concentration, adsorbent dose, and contact time was well studied and optimized for the maximum fluoride removal from water. The experimental data were fitted by the Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherm models and the related equilibrium constants were calculated. The results of the isotherm studies showed that fluoride removal by both adsorbents followed the Freundlich isotherm model. Kinetic studies were conducted and the results demonstrated that the experimental data were fitted well with the pseudo-second order kinetic model. Furthermore, two multiple regression-based equations were also derived to model the removal of fluoride from aqueous solutions by the carbon nanotubes. This study demonstrated that the polynomial equations satisfactorily described the behavior of the present defluoridation process for both MWCNTs ( R 2 = 0.913) and SWCNTs ( R 2 = 0.941). [ABSTRACT FROM AUTHOR]

Humic substances (HSs) are a group of complex macromolecular polymeric compounds originating from the decomposition of plant residuals and other organic matter. Within the presence of micro-pollutants and heavy metals, HSs negatively act upon potable water quality by contributing to aesthetic problems such as yellowish or brownish color and annoying taste and odor. They are also responsible for re-growth of pathogenic microorganisms and fouling of membranes in water distribution systems. More importantly, these high-molecular-weight polymers have been noted to be the major contributor to the formation of disinfection by-products (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs). Considering these harmful effects, removal of HSs is one of the significant tasks in drinking water treatment. For this purpose, this study aimed to explore the effects of various operating parameters (initial concentration, initial pH, electrical conductivity, pulse time, pulse number, and process time) on the humic acid (HA) removal efficiency and energy consumption. In this study, a new current supply method called alternating pulse current electrocoagulation-flotation (APC-ECF) process was proposed, and a detailed comparative optimization of four different ECF processes (direct current (DC)-simple electrode, DC-perforated electrode, pulse current-simple electrode, and pulse current-perforated electrode) was conducted within the framework of Taguchi-based experimental design methodology. According to scanning electron microscopy (SEM), the morphology of electrode surfaces with APC and perforated electrode showed less disordered (irregular) pores and a regular structure of aluminum compared to the DC, which confirmed the difference in the corrosion rates. Moreover, the proposed APC-ECF method led to the production of less dewatered and dense sludge. The results of the performance analysis revealed that the APC with a perforated electrode provided 3.2-fold lower energy consumption and 2.5-fold lower aluminum consumption compared to the DC with a simple electrode. Considering the expenses associated with power consumption and sludge disposal costs for the electrocoagulation unit, the experimental findings corroborated that the proposed APC-ECF process could be used as a promising and cost-effective technology in water treatment for the removal of HSs. [ABSTRACT FROM AUTHOR]

Azinphos-methyl and chlorpyrifos are the organophosphorous pesticides which pose serious threats to the environment including their detrimental effect on humans and, therefore, their removal from the environment is a must. Hence, in the present paper the ultrasound technique was applied to remove the above-mentioned hazardous compounds. For this, the effect of influential parameters such as pH, initial pesticide concentration, frequency, electric power and treatment time on the ultrasound degradation of azinphos-methyl and chlorpyrifos was well investigated and elucidated. The results obtained showed that azinphos-methyl and chlorpyrifos were effectively and rapidly degraded by the ultrasound technique. Thus, the operating optimal conditions (initial pH 9, initial pesticide concentration 1 mg/L, frequency 130 kHz, electric power 500 W and treatment time 20 min) lead to a degradation of 78.50% for azinphos-methyl and of 98.96% for chlorpyrifos with in 20 min of contact time. Two multiple regression-based equations were derived to describe the degradation process of the pesticides by the ultrasound treatment. The result of this study showed that the polynomial equations satisfactorily described the behavior of the present process for various operating conditions. [ABSTRACT FROM AUTHOR]

In Section 2.3 on page 105, it was stated that: "Two L-shaped aluminium electrodes were embedded in the reactor in unipolar mode with an effective surface area of 100cm SP 2 sp at 1cm distance from each other, and 20 pores with a diameter of 4mm were created on the surface of each electrode." In Section 3.3.2 on page 109, it was stated that: "At the beginning of the process, the removal efficiency of HA versus time is increased with a steep slope, so that the highest HA removal rate in experiments shown in Fig. This sentence should be replaced by: "At the beginning of the process, the removal efficiency of HA versus time is increased with a steep slope, so that the highest HA removal rate in experiments shown in Fig. [Extracted from the article]