Towards Sustainable Remediation of Metal Contaminants from Wastewater: A Novel Nano Metal Oxide Impregnated Chitosan-based Adsorption Technology.

摘要

Effective management of industrial wastewater systems for resource recovery and reuse is critical to the long-term sustainability of our planet. With the advancement of science and technology, the increasingly multifaceted nature of mining, fabrication, and transportation industries and consumer use of more complex materials results in significant contamination of our water sources through runoff, discharge, and leaching. The development of technologies to mitigate this environmental impact is immediately necessary to reduce adverse consequences on human health and the environment. This dissertation is focused on addressing this challenge while using sustainable materials and practices through the development of a novel chitosan-based adsorbent technology platform that is effective for the robust remediation of challenging aqueous matrices containing multiple inorganic compounds, including anthropogenic discharges and those occurring naturally.;Metal oxide impregnated chitosan beads (MICB) were synthesized by embedding nanocrystalline metal oxides within a chitosan matrix. This adsorbent was characterized and evaluated for adaptability to various target contaminants and robustness to changing system conditions. Specifically, MICB were successful for the remediation of arsenic and in this context, a mechanistic understanding of the serial oxidation-adsorption of arsenite and arsenate is presented. Selenium remediation was also considered, in a comprehensive and systematic study that included nanocrystalline Al2O3-impregnated chitosan beads (AICB), nanocrystalline TiO2-impregnated chitosan beads (TICB), and their individual components. In both cases, success of MICB was attributed to the synergistic effects of including multiple active components in the adsorbent design, notably including the active role of chitosan in the adsorbent performance. In both system applications, the impacts of background ions were evaluated, and the need to develop a selective adsorption process to target particular contaminants in the presence of background ions was established. To address this need, a mechanistic study on the selective binding of arsenate, selenite, and phosphate to a chitosan-copper complex was studied. Due to electrostatic and steric considerations, phosphate preferentially binds with the monodentate form of the chitosan-copper complex, and arsenate and selenite preferentially bind with the bidentate form of this complex. This enables the potential design of an adsorbent that is selective for the target compounds of interest, such as arsenic and selenium, without losing removal efficiency due to the presence of competitive background ions, such as phosphate.;There are many remediation strategies for aqueous systems, including but not limited to adsorption, available for the treatment of these complex wastewater streams. The MICB technology is a unique approach to this challenge, as it considers environmental health through sustainable practices throughout its usable lifetime. By utilizing the principles of green engineering (Anastas and Zimmerman, 2003) to address this environmental challenge, we can avoid creating new sustainability challenges for the future.