Membrane process and adsorption on pine nut shell for removal of dye from synthetic wastewater.

Purification methods such as membrane technology and adsorption have been studied for the purification of textile effluents. This article aimed to evaluate the membrane separation process and adsorption on pine nut shell, separately and sequentially, for reactive dye blue 5G removal from a synthetic effluent. The membrane separation process was carried out in a front filtration module using polymeric membranes. The maximum dye retention was 35.9% using a regenerated cellulose membrane, with agitation and a pressure of 0.5 bar. The permeate flux was fully restored after cleaning the membrane. In the adsorption using pine nut shell, the best results were at pH 2, 50°C, and 50 ppm, with 85% dye removal. The Freundlich isotherm showed the best fit to the data, as did the pseudo-second-order kinetic model. The thermodynamic parameters indicated that the adsorption is of the physical type, with the process being endothermic and spontaneous. In the combined process, the permeate from the membrane separation process was subjected to adsorption on pine nut shell, achieving a removal rate of 98.7 for the initial concentration of 50 ppm. Therefore, this work shows the potential of pine nut shell as an adsorbent, not only to purify textile effluents but also to add value to a waste product, indicating that the combination of membrane technology and adsorption on pine nut shell could be an alternative for the treatment of textile effluents containing the reactive dye 5G blue.

Electrochemical nitrate reduction of brines: Improving selectivity to N2 by the use of Pd/activated carbon fiber catalyst.

Contamination of water by nitrate has become a worldwide problem, being high levels of this ion detected in the surface, and groundwater, mainly due to the intensive use of fertilizers, and to the discharge of not properly treated effluents. This study aims to evaluate the electrocatalytic process, carried out in a cell divided into two compartments by a cation exchange membrane, and with a copper plate electrode as cathode, identifying the effects of current density, pH, the use of a catalyst in the nitrate reduction, and the production of gaseous compounds. The highest nitrate reduction was obtained with a current density of 2.0 mA cm-2, without pH adjustment and, in this condition, nitrite ion was mainly formed. The application of activated carbon fibers with palladium (1% wt. and 3% wt.) in an alkaline medium presented an increase in gaseous compounds formation. With 2.0 mA cm-2, pH adjustment, and applying 3% wt. Pd catalyst, the highest selectivity to gaseous compounds was obtained (95%) with no nitrite detection. These results highlight the viability of using the process developed at this work for the treatment of nitrate contaminated waters.