Search

The Kingdom of Saudi Arabia (KSA) has millions of date palm trees for commercial scale date-fruit production. The respective industry also generates agricultural waste including date palm tree branches. This rich bio-resource can be used for several beneficial applications. The present study therefore investigated the application of granular activated carbon (GAC) produced using date palm tree branches to successfully remove phenol, p-cresol, and copper from synthetic wastewater. The respective adsorption equilibrium results fitted well to the Langmuir-type adsorption isotherm. Furthermore, the pH-dependent adsorption results both for phenol and p-cresol appeared to follow an anionic-type adsorption behavior (i.e., decreasing adsorption with an increase in aqueous phase equilibrium pH). However, the pH-dependent adsorption finding for copper showed a cationic-type adsorption behavior. These adsorption trends were explained employing the pH-dependent speciation of the respective pollutants. In general, findings from the present work indicate that a high-specific-surface-area (SSABET) GAC material from the date palm tree branches can be successfully employed for aqueous phase pollution control. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) has become the most attractive material for membrane technology owing to its potential application as a nanofiller in water treatment, purification, and desalination. In this study, we incorporated mica as a cross-linking reagent to increase the interlayer spacing and stability of GO sheets and fabricated a mica/GO (MGO) membrane for the first time. The MGO membrane (260 ± 10 nm) exhibits 100% rejection for biomolecules such as tannic acid (TA) and bovine serum albumin (BSA) and >99% rejection for multiple probe molecules, such as methylene blue, methyl orange, congo red, and rhodamine B. The high rejection of membranes can be attributed to the surface interaction of mica with GO nanosheets through covalent interaction, which enhances the stability and separation efficiency of the membranes for probe ions and molecules. This ultrathin MGO membrane also exhibits much better water permeability at 870 ± 5 L m−2 h−1 bar−1, which is 10–100 times greater than that reported for pure GO and GO-based composite membranes. Additionally, the membrane shows high rejection for salt ions (70%). Furthermore, the stability of the MGO membranes was evaluated under various conditions, and the membranes demonstrated remarkable stability for up to 60 days in a neutral environment. [ABSTRACT FROM AUTHOR]

Aqueous phase bromate (BrO3 -) treatment using a commercial granular activated carbon (GAC, FILTRASORB 400) indicated that bromate removal is highly influenced by the operational factors such as pH, initial bromate concentration, contact time and the adsorbent dosage. The effect of pH on bromate treatment indicated higher to significant bromate removal at pH = 4, whereas for pH range 5-9 ~ 50% bromate removal was noted. At pH higher than 9, a significant decrease in the bromate removal was noted that was ascribed to changes in the GAC surface speciation. Furthermore, a higher mass-based bromate removal transpired with an increase in the initial bromate concentration that was explained based on higher mass transfer and diffusion. Also, the bromate adsorption experimental data fitted well to the Freundlich adsorption isotherm, indicating a multilayer bromate ions accumulation on the GAC surface. Furthermore, an increasing 'qe vs. Ce' trend also implied a multilayer bromate ions attachment on the GAC surface. Moreover, the kinetics experiments showed that the pseudo-second-order kinetic model better describes the respective GACbased bromate removal as compared to pseudo-first-order kinetic model. This indirectly indicated that the removal of bromate using granular activated carbon is a more involved process, with both adsorption and reduction causing the noted bromate removal (GAC-BrO3 - GAC-BrO - GAC-Br). It is suggested that initially the adsorbed BrO3 - ion is reduced to BrO-(hypobromite) followed by a further reduction of BrO- to Br- (bromide) ion. Additionally, as the surface bound bromate ion is reduced to bromide, it would cause further mass transfer of solution phase bromate ion towards the GAC surface, which is also indirectly supported by the aforementioned Freundlich based multilayer bromate removal trend. [ABSTRACT FROM AUTHOR]

Selenium as a nutrient has a narrow margin between safe and toxic limits. Hence, wastewater discharges from selenium-containing sources require appropriate treatment that considers health concerns and stringent selenium-related water treatment standards. This work examined the use of a photocatalysis-cum-adsorption system based on a layered double hydroxide coupled with TiO2 (LDH-TiO2) to remove aqueous phase selenocyanate (SeCN−), which is difficult to treat and requires specific treatment procedures. The synthesized LDH and LDH-TiO2 composite samples were characterized using the X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and thermogravimetry analysis (TGA) methods. The XRD results for the uncalcined LDH indicated a hydrotalcite mass with a rhombohedral structure, whereas increasing the calcination temperature indicated transition to an amorphous state. FESEM results for the LDH-TiO2 matrix indicated round titanium dioxide particles and LDH hexagonal layers. The TGA findings for uncalcined LDH showed a gradual decrease in weight up to 250 °C, followed by a short plateau and then a sharp decrease in LDH weight from 320 °C, with a net weight loss around 47%. Based on the characterization and initial selenocyanate adsorption results, the 250 °C calcined LDH-TiO2 matrix was used for the selenocyanate photocatalysis. A ~100% selenium removal was observed using LDH:TiO2 at a 1.5:1 w/w ratio with a 2 g/L dose, whereas up to 80% selenium removal was noted for LDH:TiO2 at a 0.5:1 w/w ratio. The respective difference in the efficiency of selenium treatment was attributed to enhanced LDH-based adsorption sites in the enhanced LDH:TiO2 w/w ratio. Furthermore, the selenite and selenate that occurred during SeCN− photocatalytic degradation (PCD) were also nearly completely removed via adsorption. An optimization exercise using response surface methodology (RSM) for total selenium removal showed R2 values of more than 0.95, with a prediction accuracy of more than 90%. In summary, the present findings show that the use of a photocatalysis-cum-adsorption system based on LDH-TiO2 is a promising technique to treat industrial wastewater discharges for selenocyanate and also remove the resulting intermediates. [ABSTRACT FROM AUTHOR]