Nitrate (NO3-) pollution in surface and groundwater, worsened by nitrogen-rich fertilizers in agriculture, poses a significant challenge. Conventional methods remove NO3- physically, yielding concentrated reject water needing further treatment. Electrochemical processes use electrons to convert NO3- into ammonia (NH3) or dinitrogen (N2). This project explores photoelectrocatalysis, enhancing selectivity for NH3 as an added-value product using a photocathode based on tri-layers. Titanium oxide (TiO2) nanorods modified with Ag and CuOx nanoparticles that exhibit high NO3- conversion rates and exceptional NH3 selectivity. Mechanism evaluation reveals additive effects between photocatalysis and electrocatalysis, surpassing individual performances. This approach offers promising solution for NO3- pollution remediation and sustainable resource recovery in agriculture.

Due to the use of fertilizers, concentrations of harmful nitrate have increased in groundwater and surface waters globally in the last century. Water treatment plants primarily use separation techniques for nitrate treatment, but these technologies create a high nitrate concentration brine that is costly to dispose of. This dissertation focuses on catalytic hydrogenation, an emerging technology capable of reducing nitrate to nitrogen gas using hydrogen gas (H2). This technology reduces nitrate at rates >95% and is an improvement over technologies used at water treatment plants, because the nitrate is chemically transformed with harmless byproducts and no nitrate brine. The goal of this dissertation is to upgrade the maturity of catalytic nitrate hydrogenation systems by overcoming several barriers hindering the scale-up of this technology. Objective 1 is to compare different methods of attaching the bimetallic catalyst to a hollow-fiber membrane surface to find a method that results in 1) minimized catalyst loss, and 2) repeatable nitrate removal over several cycles. Results showed that the In-Situ MCfR-H2 deposition was successful in reducing nitrate at a rate of 1.1 min-1gPd-1 and lost less than 0.05% of attached Pd and In cumulatively over three nitrate treatment cycles. Objective 2 is to synthesize catalyst-films with varied In3+ precursor decorated over a Pd0 surface to show the technology can 1) reliably synthesize In-Pd catalyst-films with varied bimetallic ratios, and 2) optimize nitrate removal activity by varying In-Pd ratio. Results showed that nitrate removal activity was optimized with a rate constant of 0.190 mg*min-1L-1 using a catalyst-film with a 0.045 In-Pd ratio. Objective 3 is to perform nitrate reduction in a continuous flow reactor for two months to determine if nitrate removal activity can be sustained over extended operation and identify methods to overcome catalyst deactivation. Results showed that a combination of increased hydraulic residence time and reduced pH was successful in increasing the nitrate removal and decreasing harmful nitrite byproduct selectivity to 0%. These objectives increased the technology readiness of this technology by enabling the reuse of the catalyst, maximizing nitrate reduction activity, and achieving long-term nitrate removal.

Generally, porous structures are nano-enabled with a high loading of nanoparticles (NPs) to enhance adsorption capacity, but pore blockage plays a determinant role in kinetics in this approach. The goal of this study is to investigate the effect of NPs loading on the adsorption kinetics and capacity of titanium dioxide (TiO2). To accomplish this, side-emitting optical fibers impregnated with different mass loadings of TiO2 (Ti-NIFs) were developed and characterized. Additionally, taking advantage of the use of optical fibers, the potential influence of ultraviolet light (UV) irradiation in arsenate adsorption over TiO2 was studied. The adsorption kinetics and capacity of Ti-NIFs were compared with slurry TiO2 nanoparticles in batch reactors. Arsenate adsorption was evaluated under both UV irradiation and dark conditions. The Ti-NIF with the lowest TiO2 loading showed comparable adsorption rate to NPs in suspension. Higher loadings resulted in high mass-transfer limitations. Interestingly, the normalized adsorption capacity of the produced Ti-NIFs maintained the adsorption capacity similar as they were freely dispersed. The experiments showed that UV has no influence in arsenate adsorption onto TiO2, contrary to previous literature indicating a positive effect, which was likely due to pH drift. Overall, this study shows that loadings of nanoparticles below 1% effectively enhance nano-enabled surfaces' performance.

Per- and polyfluoroalkyl substances (PFAS) are anthropogenic chemicals used for a wide variety of products and industrial processes, including being an essential class of chemicals in the fabrication of semiconductors. Proven concerns related to bioaccumulation and toxicity across multiple species have resulted in health advisory and regulatory initiatives for PFAS in drinking and wastewaters. Among impacted users of PFAS, the semiconductor industry is in urgent need of technologies to remove PFAS from water. Specifically, they prefer technologies capable of mineralizing PFAS into inorganic fluoride (F-). The goal of this thesis is to compare the effectiveness of photo- versus electrocatalytic treatment in benchtop reactor systems PFAS in industrial wastewater before selecting one technology to investigate comprehensively. First, a model wastewater was developed based upon semiconductor samples to represent water matrices near where PFAS are used and the aggregate Fab effluent, which were then used in batch catalytic experiments. Second, batch experiments with homogenous photocatalysis (UV/SO32-) were found to be more energy-intensive than heterogeneous catalysis using boron-doped diamond (BDD) electrodes, and the latter approach was then studied in-depth. During electrocatalysis, longer chain PFAS (C8; PFOA & PFOS) were observed to degrade faster than C6 and C4 PFAS. This study is the first to report near-complete defluorination of not only C8- and C6- PFAS, but also C4-PFAS, in model wastewaters using BDD electrocatalysis, and the first to report such degradation in real Fab wastewater effluents. Based upon differences in PFAS degradation rates observed in single-solute systems containing only C4 PFAS versus multi-solute systems including C4, C6, and C8 PFAS, it was concluded that the surfactant properties of the longer-chain PFAS created surface films on the BDD electrode surface which synergistically enhanced removal of shorter-chain PFAS. The results from batch experiments that serve as the basis of this thesis will be used to assess the chemical byproducts and their associated bioaccumulation and toxicity. This thesis was aimed at developing an efficient method for the degradation of perfluoroalkyl substances from industrial process waters at realistic concentrations.

Light-driven reactions can replace chemical and material consumption of advanced water treatment technologies. A barrier to light-driven water treatment is optical obstructions in aquafers (i.e. granular media) or built infrastructures (i.e. tubing) that limits light propagation from a single source such as the sun, or lamps. Side emitting optical fibers (SEOFs) can increase light distribution by > 1000 X from one-point source, but absorbance of UV light by conventional optical fibers limits their application to visible light only.

This dissertation assessed how SEOFs can enable visible through ultraviolet light-driven processes to purify water. I first used an existing visible light polymer SEOF and phototrophic organisms to increase the dissolved oxygen level of a granular sand reactor to > 15 mg DO/L. The results indicated that SEOFs successfully guide light past optical obstructions for environmental remediation which encouraged the fabrication of UV-C SEOFs for microbial inactivation.

I was the first to obtain consecutive UV-C side emission from optical fibers by placing nanoparticles on the surface of a UV transmitting glass core. The nanoparticles induced side-emission via Mie scattering and interactions with the evanescent wave. The side emission intensity was modulated by tuning the separation distance between the nanoparticle and fiber surface. Coating the fiber with a UV-C transparent polymer offered the optical fiber flexibility and prevented nanoparticle release into solution. One SEOF coupled to a 265 nm LED achieved 3-log inactivation of E. coli. Finally, a method was developed to quantify the zone of inhibition obtained by a low flux output source. By placing a SEOF connected to a UV-C LED over a nutrient-rich LB agar plate, I illustrated that one SEOF inhibited the growth of P. aeruginosa and E. coli within 2.8 cm along the fiber’s length. Ultimately this research informed that side-emitting optical fibers can enable light-driven water purification by guiding and distributing specific wavelengths of light directly to the microbial communities of interest.