Date of Award
Doctor of Philosophy (PhD)
Civil, Construction, and Environmental Engineering
St. Maurice, Martin
Inorganic phosphorus (Pi) is a critical element for all life and a major component of DNA’s backbone. Global agriculture requires Pi to support the rapid growth of plants and high crop productivity. Yet, the mineable Pi supply needed for global agriculture is in short supply in nature and Pi reserves are unevenly distributed around the world. In contrast, surplus Pi in water poses a serious pollution problem as it can cause eutrophication. Scarcity of non-renewable Pi resources combined with pollution in the form of overabundant Pi presents a phosphorus paradox. Tackling this issue is necessary and using innovative approaches targeting Pi removal to ultra-low levels in water/wastewater with subsequent recovery for reuse applications can help. The purpose of this research was to investigate a novel solution utilizing the phosphate-binding protein PstS (PBP) to simultaneously remove and recover Pi from water matrices under controlled conditions. PBP is naturally expressed by many microorganisms as it is responsible for Pi transport into cells under conditions of low surrounding Pi levels. High affinity and selectivity towards Pi even at low concentrations is a superior advantage for removal and recovery efforts addressing the phosphorus paradox. Although PBP offers strong potential for use in engineered systems, more effective water/wastewater configurations are needed before it can be a potential sustainable treatment option for Pi removal and recovery. Specifically, improvements in immobilized PBP’s contact with water, operation in flow-through setup, and adsorption capacity are critical. This research investigated three prospective immobilized PBP-based systems. First, surface-displayed PBP on the outer membrane of E. coli was designed and tested for Pi capture and release. Previous surface displayed efforts did not address both Pi removal and recovery. Increasing temperature and ionic strength increased phosphate release by 20% and 50%, respectively. Both acidic and basic pH conditions promoted Pi release from cells induced to overexpress PBP. Surface-displayed PBP systems increased Pi release under controlled conditions compared to periplasmic PBP overexpressed in the periplasm and control cells without PBP overexpression. Second, micro-structured immobilized PBP (PBP-NHS resin) was tested in fixed-bed column configuration, data from which is needed to support practical implementation. Highly selective Pi separation was observed, and there was no significant decline in the column’s performance over three consecutive cycles for tertiary wastewater samples, substantiating PBP-NHS resin’s reusability. Resin capacity was unaffected by competing anions, whereas a comparative LayneRTTM ion exchange column experienced a 20% drop in capacity in the presence of other anions. Lastly, a PBP-loaded iron oxide particle adsorbent (PBP-IOPs) was shown to improve Pi adsorption capacity beyond the previous systems. The PBP-IOPs offered rapid Pi adsorption kinetics, with near-complete removal in less than 5 min. Higher Pi removal was observed at room temperature, low ionic strength, and slightly acidic conditions. The PBP-IOPs released 99% of total adsorbed Pi whereas IOPs alone (without immobilized PBP) released only 12%, such that PBP-IOPs offer enhanced potential for Pi recovery. Overall research findings advance understanding and system design using immobilized PBP to remove and recover Pi, supporting a more sustainable waste-to-resource paradigm.