The objective of this study is to design and develop bio-based hydrogels aligned with the goals of green engineering for arsenic removal from aqueous solutions. A sub-objective is to evaluate the potential for regeneration of these materials and any subsequent impact on performance to estimate functional lifetime. Additionally, end of life strategies will be evaluated, including biodegradation. To close the loop, a feasibility analysis will be conducted to evaluate the recovery of arsenic from the waste stream for use as a feedstock to industrial processes. By considering the entire life cycle of the system including the material itself and the waste streams from the process, the design of an arsenic removal system for water purification has an increased likelihood of optimizing performance of the entire system while aligning environmental and economic objectives. The study involves the functionalization of chitosan, a biopolymer, and its use in arsenic removal. This research presents potential benefits for improved health and quality of life for those whose groundwater source contains toxic arsenic levels. The team will work with the Yale Peabody Museum staff to develop an exhibit communicating global water issues, particularly as they relate to water quality and scarcity in developing communities. Also, the team will work with high school students in the Evolutions Program at Peabody to develop exhibits about global water issues, and additionally high school students will work in the team?s laboratories over summers. Undergraduate and graduate students will be actively engaged in the research throughout the year.
Industrial manufacturing and mining processes produce wastewaters that are laden with a variety of inorganic contaminants. As these metal solutions are released into the environment, there is a high potential for contamination of surface and groundwater, which can serve as the primary drinking water source for many communities as well as the basis for ecological habitats. Further, there are geologic sources for many of these contaminants as well, which can further contribute to degraded water sources. Exposure to these contaminated water sources raises significant concerns for human and ecosystem health. Many technologies have seen success at the lab scale for removal of arsenic from aqueous solutions, but very few have been appropriate for wide-scale, long-term use due to broken mechanical components, electrical supply malfunction, or lack of economies of scale and appropriate infrastructure. In addition, these technologies lack important characteristics for sustainable implementation, including minimal energy requirements and sustainable materials sourcing. Intellectual Merit To address this limitation, a novel, sustainable technology to remove arsenic from aqueous systems, titanium dioxide (TiO2)-impregnated chitosan beads (TICB), has been developed. TICB realizes the benefits of high surface area adsorbents by embedding nano-sized TiO2 in a chitosan matrix. Chitosan, an aqueous-stable biopolymer that is derived from insect and shellfish exoskeletons, has a desirable lifecycle as it is an abundant waste product that is readily accessible with minimal environmental cost. Rather than energy-intensive filtration, ready and passive self-separation of the adsorbent from solution is possible simply by density. To leverage this novel technology, that is, to increase the capacity for removal and to potentially apply this design to other contaminant metals, the TICB platform was evolved to incorporate an additional active component, nano-aluminum oxide (Al2O3). The resulting mixed metal oxide chitosan beads (MICB) successfully remove arsenic from aqueous solutions with higher efficacy and higher efficiency than TICB. These enhancements are based on fundamental synergistic effects between Al2O3 and TiO2 while maintaining the desirable sustainable attributes of the original technology. In addition, MICB enable a more rigorous mechanistic understanding of this metal-oxide impregnated chitosan sorbent system. Although Al2O3 is unable to oxidize arsenite like TiO2, our experiments indicate that nano-Al2O3 has a significantly higher affinity for arsenate than does nano-TiO2. The new design exploits this chemistry by optimizing the ratio of TiO2 and Al2O3 in the system for arsenite oxidation and arsenate sorption resulting in performance exceeding that of the original system and currently available technologies. A mechanism for the observed performance enhancement is proposed wherein TiO2 oxidizes arsenite to arsenate in the presence of UV light and the subsequent arsenate complexes with Al2O3. Pseudo-second order kinetic models were used successfully to validate this probable mechanism and to mathematically describe the observed performance of the adsorbent. This system is currently under further development to address other inorganic contaminants of concern, particularly selenium. In this case, selenate needs to be reduced to selenite, reverse to the arsenic system. Further, other nano metal oxides are being explored with a focus on various forms of iron oxides due to their abundance and low toxicity. Broader Impacts. This research contributed to the development of a World’s Water class at Yale focusing on the broad range of issues – from technical to social to cultural – related to water and water systems. This course engaged a more diverse enrollment than the average for Yale STEM majors, which reflects the growing consensus that if the right questions are asked, more and different students see a role for themselves in developing sustainable scientific and technical solutions. Beyond integration into this new course and other existing courses, such as Green Engineering and Sustainable Design, this project also enabled the launch of "Pathways to Engineering" and "Pathways FOR GIRLS to Engineering". These programs are designed to engage middle and high school students from the City of New Haven for a day long visit to campus that includes lab tours, design challenge events, faculty discussions, and brief experiments.
