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PhD Defenee by Zeou Dou

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School of Civil and Environmental Engineering 

 

Ph.D. Thesis Defense Announcement 

Precise Ion Separation by Engineered Polymer Composites for Phosphorous Recovery
 

By:

Zeou Dou

Advisor: 

Dr. Xing Xie

Committee Members: 

Dr. Ching-Hua Huang, Dr. Sotira Yiacoumi, Dr. Yongsheng Chen, Dr. YuHang Hu

Date & Time: 07/21/2022, 10am

Location: Zoom meeting ID: 941 4411 3546

Nutrient recovery is pressingly needed for advancing the sustainability of global food production. Given the composition of nutrient streams, nutrient separation and enrichment are needed for high recovery efficiency and market viability. Membrane-based processes providing precise separation are well studied for nutrient recovery. However, the capital cost and energy consumption remain the main challenges before large scale commercialization. Ionic hydrogels offer sufficient ion selectivity especially within a concentration range comparable to the nutrient level in wastewaters, presenting promising potential for cheap and sustainable solutions to nutrient recovery from wastewater. Therefore the overall objective of this research was to develop and test nutrient, particularly phosphorous, enrichment, recovery, and reuse technologies based on engineered ionic hydrogels, with the specific objectives to: i) investigate the phosphate rejection and enrichment performance of commercial ionic hydrogels through spontaneous water absorbing and reveal the mechanisms driving the selective ion exchange and transport in the swelling hydrogel scaffold; ii) develop advanced composite hydrogels with high ion rejection at elevated concentration for enhanced enrichment capability; iii) develop green composite hydrogels to recovery and reuse nutrients through adsorption and controlled release. 
This research demonstrated the phosphate enrichment by negatively charged ionic hydrogels as a self-driven dewatering agent under different conditions. The effects of the pH, ionic strength of the nutrient stream, and the swelling ratio of hydrogels on the rejection of phosphate were investigated. The interactions of anionic hydrogel chains with phosphate and heavy metal ions were elucidated through molecular dynamic simulations. 
To further enhance the selectivity of hydrogels, we developed a core-shell polymer composite (CSPC) for effective ion rejection at high concentration. These flexible and easy-to-use CSPCs exhibit high-capacity and selective water absorption, which presented unique possibilities for recovering valuable resources from waste streams. Extensive characterizations have been done on the nanofilm shell.
Chitosan nanocomposite hydrogel was developed in this research as a controlled release nutrient excipient formula to increase the nutrient use efficiency. By introducing elastic and flexible physical crosslinking induced by 2-dimensional (2D) montmorillonite (MMT) nanoflakes into the chitosan hydrogel, highly swellable and degradable chitosan-MMT nanocomposites were fabricated. The chitosan-MMT nanocomposite hydrogel achieved a well-controlled overall fertilizer release in soil. In the meantime, the nanocomposites improved the water retention of the soil, thanks to its excellent water absorbency. Based on chitosan-MMT controlled release formulation, ferric (Fe) salt was added for enhanced phosphate adsorption capability of the composite as a phosphate adsorbent and controlled releaser to bridge recovery from wastewater and reuse in soil as a fertilizer. Sorption kinetics and isotherm were quantified in batch experiments. Versatile sorption pathways enabled stable capacity across a range of pH. With additional water retaining capability, the P-laden hydrogels can be reused in soil amendment as a controlled release P fertilizer.
Accessible, affordable, and effective P recovery and reuse solutions could close the loop for P establishing a supply cycle of fertilizer for sustainable agriculture. The solutions developed in this study provides new opportunities to further lower the cost and energy consumption of wastewater P recovery and efficient reuse, making P recovery more economically viable compared to unsustainable phosphate mining. P recovery at scale not only ensures the long-term food security globally but also paves way to sustainable agriculture.
 

Status

  • Workflow Status:Published
  • Created By:Tatianna Richardson
  • Created:07/06/2022
  • Modified By:Tatianna Richardson
  • Modified:07/06/2022

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