Mathematical modelling applied to the rate-limiting mass transfer step determination of a herbicide biosorption onto fixed-bed columns.

The herbicide removal of Diuron in a fixed-bed column packed with the Moringa oleifera bark biosorbent was investigated experimentally and through phenomenological mathematical modelling. To understand the physical phenomena involved, the steps of external mass transfer resistance, internal mass transfer resistance and the adsorption phenomenon itself were considered as possible limiting steps in the herbicide mass transfer from the liquid to the solid phase. In the developing process of the internal mass transfer resistance model, two hypotheses were considered: constant mass transfer coefficient and mass transfer coefficient as a function of the herbicide concentration in the biosorbent. The experimental breakthrough curves were obtained for different flow rates and feed concentrations, in order to evaluate the model's predictive capacity. The mass transfer parameter values of the mathematical models were estimated using the simplex downhill optimization method. The model that considers the resistance a mass transfer internal with parameter Ks variable represented effectively the dynamic behaviour of the herbicide biosorption process in fixed-bed column, in the various evaluated conditions, indicating that this mechanism controls the biosorption process. Thus, the phenomenological mathematical modelling proved to be an analysis important tool, understanding and the herbicide adsorption systems design in a fixed-bed column.

Iron-oxide nanoparticles by the green synthesis method using Moringa oleifera leaf extract for fluoride removal.

In this work, we synthesized iron-oxide nanoparticles (NPsFeO) via a green synthesis method, using Moringa oleifera leaf extract, and evaluated its fluoride ion adsorption potential, comparing its efficiency with a commercially available adsorbent (activated carbon of bone [BGAC]). The adsorbent materials were characterized using X-ray diffraction, transmission, and scanning electronic microscopy, X-ray dispersive energy spectrometry, and N2 adsorption/desorption. The results showed that the maximum adsorption occurred in pH 7 for NPsFeO and pH 5 for the BGAC. Adsorption kinetic tests showed that the equilibrium was reached in 40 min for the NPsFeO, and 90 min for BGAC, with adsorption potential of 1.40 and 1.20 mg g-1, respectively. The model that best described the kinetic data was pseudo-first-order for NPsFeO and pseudo-second-order for BGAC. The Langmuir isotherm had a better fit for both adsorbents. The thermodynamic parameters indicated spontaneous and endothermic adsorption at 30°C, 40°C, and 50°C for BGAC, and at 30°C for NPsFeO. The regeneration process showed that it is possible to reuse NPsFeO three times in the fluoride ion adsorption process. As a result of its adsorption capabilities and the shortest contact time to achieve equilibrium, the NPsFeO is a highly promising material for fluoride ion removal.

Water treatment with exceptional virus inactivation using activated carbon modified with silver (Ag) and copper oxide (CuO) nanoparticles.

Continuous flow experiments (450 mL min-1) were performed in household filter in order to investigate the removal and/or inactivation of T4 bacteriophage, using granular activated carbon (GAC) modified with silver and/or copper oxide nanoparticles at different concentrations. GAC and modified GAC were characterized by X-ray diffractometry, specific surface area, pore size and volume, pore average diameter, scanning electron microscopy, transmission electron microscopy, zeta potential and atomic absorption spectroscopy. The antiviral activity of the produced porous media was evaluated by passing suspensions of T4 bacteriophage (∼105 UFP/mL) through filters. The filtered water was analyzed for the presence of the bacteriophage and the release of silver and copper oxide. The porous media containing silver and copper oxide nanoparticles showed high inactivation capacity, even reaching reductions higher than 3 log. GAC6 (GAC/Ag0.5%Cu1.0%) was effective in the bacteriophage inactivation, reaching 5.53 log reduction. The levels of silver and copper released in filtered water were below the recommended limits (100 ppb for silver and 1000 ppb for copper) in drinking water. From this study, it is possible to conclude that activated carbon modified with silver and copper oxide nanoparticles can be used as a filter for virus removal in the treatment of drinking water.