El tratamiento de las aguas residuales urbanas es un problema no resuelto. Las nuevas tecnologías, como los humedales construidos (HC), ayudan a conservar y proteger los cuerpos de aguas. En esta revisión se analizan los estudios publicados durante los últimos 10 años sobre los HCs como alternativa de tratamiento de las aguas residuales en zonas urbanas. La búsqueda sobre HCs se realizó para el período 2010-2020 en las bases de datos Scopus y Web of Science. Es de esperar un continuo aumento de la introducción de estos sistemas en los ambientes urbanos, por ser soluciones basadas en la naturaleza; de bajo costo; fáciles de diseñar, construir y explotar; que brindan servicios ecosistémicos y que son amigables con el medio ambiente y el entorno. Las áreas que requieren de investigaciones priorizadas para el desarrollo eficiente de los HCs son (1) la búsqueda de nuevas especies de plantas propias de cada zona climática; (2) el fortalecimiento de la sostenibilidad y la potenciación de diferentes servicios ecosistémicos; (3) la continuación del proceso de innovación de los diferentes diseños para aumentar la confiabilidad y el desempeño de estos sistemas; y (4) la integración con otros sistemas de tratamiento para aumentar las posibilidades de reúso del agua.

Adsorption is one of the most successful physicochemical approaches for removing heavy metal contaminants from polluted water. The use of residual biomass for the production of adsorbents has attracted a lot of attention due to its cheap price and environmentally friendly approach. The transformation of Sargassum—an invasive brown macroalga—into activated carbon (AC) via phosphoric acid thermochemical activation was explored in an effort to increase the value of Sargassum seaweed biomass. Several techniques (nitrogen adsorption, pHPZC, Boehm titration, FTIR and XPS) were used to characterize the physicochemical properties of the activated carbons. The SAC600 3/1 was predominantly microporous and mesoporous (39.6% and 60.4%, respectively) and revealed a high specific surface area (1695 m2·g−1). To serve as a comparison element, a commercial reference activated carbon with a large specific surface area (1900 m2·g−1) was also investigated. The influence of several parameters on the adsorption capacity of AC was studied: solution pH, solution temperature, contact time and Cr(VI) concentration. The best adsorption capacities were found at very acid (pH 2) solution pH and at lower temperatures. The adsorption kinetics of SAC600 3/1 fitted well a pseudo-second-order type 1 model and the adsorption isotherm was better described by a Jovanovic-Freundlich isotherm model. Molecular dynamics (MD) simulations confirmed the experimental results and determined that hydroxyl and carboxylate groups are the most influential functional groups in the adsorption process of chromium anions. MD simulations also showed that the addition of MgCl2 to the activated carbon surface before adsorption experiments, slightly increases the adsorption of HCrO4− and CrO42− anions. Finally, this theoretical study was experimentally validated obtaining an increase of 5.6% in chromium uptake.

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