Nitrate leaching from agricultural systems poses a threat to ecosystems and human health. Integrating 2D carbon-based graphite nano additive (GNA) soil amendments previously demonstrated potential in mitigating nitrate loss, yet the responsible mechanism was unclear. To clarify the causal mechanism, this dissertation aimed to identify and understand mechanisms of how addition of graphite nano-additive (GNA) soil amendment reduces N leaching through agricultural soil by sequential investigation employing laboratory soil incubation tests, batch adsorption experiments, soil column experiments, and greenhouse pot study. Soil incubation tests were conducted with four commercially available graphene nanomaterials to establish that soil microbial activity indicated by respiration was significantly enhanced when soil was amended with graphene (e.g., GNA). Additionally, gene abundance assessment from the same incubation tests indicated a potentially slowed soil nitrification (ammonium to nitrate conversion) by GNA. Separate batch absorption tests indicated that GNA was unlikely to retain nitrate through adsorption. Soil column experiments were designed to probe the dependency of N retention in GNA-amended soil primarily due to altered microbial activity from assessing the impact of temperature, soil saturation, sterility, hydraulic retention time, GNA dose, and soil organic carbon. Finally, a greenhouse plant growth study was designed to assess how GNA impacts soil biology. Enzyme activity indicated GNA could stimulate soil carbon mineralization and improve soil bioavailable carbon. Gene abundance assessment showed total bacterial community size was unimpacted but selected and suppressed certain bacterial groups (e.g., suppressed bacterial amoA gene abundance).16S bacterial community sequencing showed that GNA significantly altered the bulk and rhizosphere soil microbiome composition. GNA-induced selection of certain bacterial classes (e.g., Bacilli) holds significant implications in aspects of plant growth and nutrient acquisition. This dissertation revealed mechanisms behind GNA-induced decrease of nitrate leaching in agricultural soil, aiding progress to its integration into conventional agriculture to improve nitrogen fertilizer efficiency for a food-secure future.

Water quality assessment is essential for maintaining healthy ecosystems and protecting human health. Data interrogation and exploratory data analysis techniques are used to analyze the spatial and temporal variability of water quality parameters, identifying correlations, and to better understand the factors that impacts microbial and chemical quality of water. The seasonal dynamics of microbiome in surface waters were investigated to identify the factors driving these dynamics. Initial investigation analyzed two decades of regional water quality data from 20 various locations in Central Arizona, USA. Leveraging advanced data science techniques, the study uncovered correlations between crucial parameters, including dissolved organic carbon (DOC), ultraviolet absorbance (UVA), and specific ultraviolet absorbance (SUVA). These findings provide foundational insights into the dynamic of overall water quality. A comprehensive 12-month surface water sample collection and study was conducted to investigate potential bias in bacterial detection using EPA approved Membrane Filtration (MF) technique. The results underscore that while MF excels in recovering bacteria of public health significance, it exhibits biases, particularly against small and spore-forming bacteria and Archaea, such as Bacilli, Mollicutes, Methylacidiphilae, and Parvarchaea. This emphasizes the importance of complementing standard microbiology approaches to mitigate technological biases and enhance the accuracy of microbial water quality testing, especially for emerging pathogens. Furthermore, a complementary study of microbial dynamics within a model drinking water distribution systems (DWDSs) using treated water from the same source water as the above study. The influence of pipe material and water temperature on the microbiome and trace element composition was investigated. The research unveiled a preferential link between pipe material and trace elements, with water temperature significantly impacting the microbiome to a higher degree than the chemical composition of water. Notably, Legionellaceae and Mycobacteriaceae were found to be prevalent in warmer waters, highlighting the substantial influence of water temperature on the microbiome, surpassing that of pipe material. These studies provide comprehensive insights into the spatial and temporal variability of water quality parameters. Analyzing microbial data in depth is crucial in detecting bacterial species within a monitoring program for adjusting operational conditions to reduce the presence of microbial pathogens and enhance the quality of drinking water.

Pervaporation is a membrane process suited to complex and highly contaminated wastewaters. Pervaporation desalination is an emerging area of study where the development of high-performance membranes is necessary to propel the field forward. This research demonstrated that sulfonated block polymer membranes (Nexar™)show excellent permeance (water passage normalized by driving force) of as much as 135.5 ± 29 kg m-2 hr-1 bar-1, with salt removal values consistently equal to or greater than 99.5%. Another challenging water management scenario is in spaceflight situations, such as on the International Space Station (ISS). Spaceflight wastewaters are highly complex, with low pH values, and high levels of contaminants. Current processes produce 70% wastewater recovery, necessitating the handling and processing of concentrated brines. Since recoveries of 85% are desired moving forward, further efforts in water recovery are desirable. An area of concern in these ISS water treatment systems is scalant deposition, especially of divalent ions such as calcium species. Zwitterions are molecules with localized positive and negative charges, but an overall neutral charge. Zwitterions have been used to modify the surface of membranes have shown to decrease fouling. Building a copolymer between zwitterions and other polymers, creates zwitterion layer on top of previously studied Nexar™ membranes. This coating demonstrates great promise to combat scaling, as it increases the hydrophilicity of the membrane surface measured via contact angle. The zwitterion membranes experienced reduced scaling, with the greatest difference being between 1617 ± 241 wt% on control membranes, to 317 ± 87 wt% on zwitterion coated membranes in the presence of CaCl2. In treating spaceflight wastewater, these zwitterion membranes are effective at retaining the acid in the feed, going from a pH value of 2 to 7 and reducing the contamination level of the feed, with a removal value of 99.3 ± 0.4%, measured through conductivity. These membranes also perform well in separation processes that do not require extreme vacuum and can be operated passively. By optimizing both membrane material properties and process conditions, achieving increased high levels of water recovery from spaceflight wastewaters is attainable.

Electrochemical technologies emerge as a feasible solution to monitor and treat pollutants. Although electrochemical technologies have garnered widespread attention, their commercial applications are still constrained by the use of expensive electrocatalysts, and the bulky and rigid plate design of electrodes that restricts electrochemical reactor design to systems with poor electrode surface/ volume treated ratios. By making electrodes flexible, more compact designs that maximize electrode surface per volume treated might become a reality. This dissertation encompasses the successful fabrication of flexible nanocomposite electrodes for electrocatalysis and electroanalysis applications.First, nano boron-doped diamond electrodes (BDD) were prepared as an inexpensive alternative to commercial boron-doped diamond electrodes. Comparative detailed surface and electrochemical characterization was conducted. Empirical study showed that replacing commercial BDD electrodes with nano-BDD electrodes can result in a cost reduction of roughly 1000x while maintaining the same electrochemical performance. Next, self-standing electrodes were fabricated through the electropolymerization of conducing polymer, polypyrrole. Surface characterizations, such as SEM, FTIR and XPS proved the successful fabrication of these self-standing electrodes. High mechanical stability and bending flexibility demonstrated the ability to use these electrodes in different designs, such as roll-to-roll membranes. Electrochemical nitrite reduction was employed to demonstrate the viability of using self-standing nanocomposite electrodes for electrocatalytic applications reducing hazardous nitrogen oxyanions (i.e., nitrite) towards innocuous species such as nitrogen gas. A high faradaic efficiency of 78% was achieved, with high selectivity of 91% towards nitrogen gas. To further enhance the conductivity and charge transfer properties of self-standing polypyrrole electrodes, three different nanoparticles, including copper (Cu), gold (Au), and platinum (Pt), were incorporated in the polypyrrole matrix. Effect of nanoparticle wt% and interaction between metal nanoparticles and polypyrrole matrix was investigated for electroanalytical applications, specifically dopamine sensing. Flexible nanocomposite electrodes showed outstanding performance as electrochemical sensors with PPy-Cu 120s exhibiting a low limit of detection (LOD) of 1.19 µM and PPy-Au 120s exhibiting a high linear range of 5 µM - 300 µM. This dissertation outlines a method of fabricating self-standing electrodes and provides a pathway of using self-standing electrodes based on polypyrrole and polypyrrole-metal nanocomposites for various applications in wastewater treatment and electroanalytical sensing.

Freshwater as the resource for the survival of humans and all lives on earth is very precious but scarce. The shortage of the original freshwater resources and the interfering activities by human and other natural factors form this issue together. To reduce the water supply pressure and deterioration of freshwater systems (for example, river, wetland, and groundwater), the quantity-increase and the quality-increase strategies should be implemented at the same time. Therefore, corresponding membrane technologies have been developed to achieve water purification with high efficiency and low cost. For desalinating seawater and other types of saline water, pervaporation has been proved that has the potential to complete desalination with salt rejection rate over 99 % when dealing with high salinity water that reverse osmosis (RO) cannot handle. In this dissertation, except the discussion of commonly used materials to synthesize pervaporation membranes, two types of novel pervaporation desalination membranes (nanophotonic-enhanced membrane and free-standing sulfonated membrane) have been presented and discussed. The novel membranes were tested to see the potential of pervaporation to desalinate seawater and saline water with more complex ionic composition, and the possibility of achieving zero liquid discharge in the desalination field when having pervaporation as the assistance. For mitigating polluted water that is caused by human activities, especially agricultural activities, electrodialysis is an effective method to remove specific ions from water, and it does not require extra chemical cost or regeneration. A type of anion exchange membranes inspired by ion exchange resins was synthesized and tested, and the performance on nitrate removal has been evaluated in this dissertation.

The developing world has witnessed a rapid growth in crop production since the green revolution in the 1960s. Even though the population has almost doubled since then, food production has tripled; most of this growth can be attributed to crop research, fertilizers, infrastructure, and market development. Although the green revolution came with benefits, it has been widely criticized for its negative impact on the environment. The excessive and inappropriate use of fertilizers has led to human and livestock diseases, polluted waterways, loss of soil fertility, and soil acidity. Even though the green revolution was started to ensure food security, it has unintended consequences on human health and the surrounding environment. This dissertation focuses on the surface characteristics of graphene nanomaterials (GNMs) and their application in agriculture. Among the nutrients needed for crops, some can be easily obtained from the environment (e.g., carbon, hydrogen, oxygen, etc.), while others, like nitrogen (N), phosphorus (P), and potassium (K), often requires supplementation by fertilizers. However, conventional fertilizers have caused problems associated with soil pH changes, stunted plant growth, and disrupted beneficial microbial processes. Implementing nano-fertilizers, which can act as controlled-release fertilizers, is important. GNMs have shown some promising characteristics for the controlled release of drugs and other chemicals. Therefore, in the first part of this study, the loading capacity of the three macronutrients (N, P, and K) over GNMs of different surface chemistry was characterized. In the second part of this thesis, the effect of graphene oxide (GO) addition on wheat germination was evaluated. Rapid germination is essential for crop establishment to ensure low-cost and high-quality products and keep in check the sustainable use of resources in commercial agriculture. The results of this thesis indicated that the application of GO significantly enhanced the seed germination potential of the wheat crops. It not only increases the root weight but also improves its volume. Future work should focus on the impact of surface chemistry of GNMs on germination, which, when combined with the materials’ ability to bind nutrients, could help better guide the use of GNMs in agriculture.

Plastics, when released into the environment, undergo surface weathering due to mechanical abrasion and ultraviolet (UV) exposure that leads to the formation of microplastics. Weathering also introduces oxygen functional groups on the surface, which will affect surface interactions compared to pristine plastics. In this study, the adsorption of selected model contaminants of high environmental relevance was evaluated at different level of abiotic and biotic transformation to understand how microplastics aging influences contaminant adsorption on high density polyethylene (HDPE) and polypropylene (PPE). Microplastics were aged through an accelerated weathering process using UV exposure with or without hydrogen peroxide. The effect of UV aging on the microplastics’ morphology and surface chemistry was characterized by Fourier Transform Infrared Spectroscopy, X-Ray Photoelectron Spectroscopy, streaming Zeta potential, Brunauer–Emmett–Teller Krypton adsorption analyses and Computed X-Ray Tomography. Sorption of organic contaminants was found to be higher on aged microplastics compared to pristine ones for all contaminants investigated. This increase in sorption affinity was found to be associated with a change in the surface chemistry and not in an increase in specific surface area after aging. Biological surface weathering (i.e., biofilm formation) was carried out at a lab-scale setting using model biofilm-forming bacteria followed by adsorption affinity measurement of biofilm-laden microplastics with the model organic contaminants. The amount of microbial biomass accumulated on the surface was also evaluated to correlate the changes in sorption affinity with the change in microplastic biofilm formation. The results of this study emphasize the need to understand how contaminant-microplastics interactions will evolve as microplastics are altered by biotic and abiotic factors in the environment.

This study investigated the difference in biofilm growth on pristine and aged polypropylene microplastics exposed to Tempe Town Lake water for 8 weeks. The research question here is, does the aging of microplastic (MPs) change the biofilm formation rate and composition of the biofilm in comparison with the pristine MPs. To answer this question, the biofilm formation was quantified using different methods over time for both pristine polypropylene and aged polypropylene using agar plate counts and crystal violet staining. Colony counts based on agar plating showed an increase in microbial growth over the 8 weeks of treatment, with the aged MPs accumulating higher microbial counts than the pristine MPs. The diversity of the biofilm decreased over time for both MPs and the aged MPs had overall less diversity in biofilm, based on phenotype enumeration, in comparison with the pristine MPs. Higher biofilm growth on aged MPs was confirmed using crystal violet staining, which stains the negatively charged biological compounds such as proteins and the extracellular polymeric substance matrix of the biofilm. Using this complementary approach to colony counting, the same trend of higher biofilm growth on aged MPs was found. Further studies will focus on confirming the phenotype findings using microbiome analysis following DNA extraction. This project created a methodology to quantify biofilm formation on MPs, which was used to show that MPs may accumulate more biofilms in the environment as they age under sunlight.

Membrane fouling, especially inorganic fouling, is a significant obstacle to treatinghighly saline brine using membrane distillation (MD). In this study, microbubbles (MBs) were injected into the feed tank of a lab-scale direct contact membrane distillation (DCMD) system, and its effect on permeate flux over time was examined. A synthetic inland reverse osmosis (RO) brine with a high scaling tendency was used as a feed solution. Results showed a sharper flux decline in the absence of MBs compared to when MBs are continuously injected into the feed tank. The introduction of MBs reduced the formation of salt precipitations on the membrane surface, which was the primary cause of the decline in flux. The use of intermittent MBs injection instead of continuous MB injection was evaluated as a way to reduce energy consumption; with a 15 min MBs injection every 2h, similar benefits were found for intermittent injection compared to continuous injection, indicating that providing MBs continuously is not needed to mitigate scale formation. These results show that MBs can be a potential chemical-free method to prevent scaling in desalination systems treating high saline solutions.

Megapolitan cities have emerged due to unprecedented urban migration. These changes strain urban resources, especially water distribution and treatment systems. The recent rise of Legionella cases linked to water distribution systems highlights this issue.Bacterial growth and biofilm formation are influenced by factors, such as type and concentration of residual disinfectant, pipe material, water temperature. Experiments were conducted in identical model water distribution systems (WDSs) constructed of three different pipe materials: galvanized steel, copper, and cross-linked polyethylene (PEX) operated under a continuous flow rate of 15 L/min. Each model WDS includes 11 steel coupons screwed to the water distribution pipes. City of Tempe (Arizona) municipal water was used in the experimentation, with no nutrients added. Following biofilm growth, coupons were removed and processed by scrubbing biofilm into phosphate-buffered saline (PBS). Reasoner's 2A (R2A), Trypticase Soy Agar (TSA), Brilliant, and buffered charcoal yeast extract (BCYE) agar media were used to examine biofilm samples for heterotrophic plate counts (HPC), metabolically active bacteria, E coli, and Legionella. Simultaneously, water samples from the reservoirs of model WDSs were also collected and examined for the same bacteria.Next, an electrochlorination cell maintained free chlorine residuals in unheated PEX and copper model WDSs. These two systems maintained free chlorine residuals for one week and evaluated biofilm and bacterial kinetics. Higher water temperature increased biofilm development. Bacterial counts in biofilms were higher on new (fresh) coupons compared to the old coupons. Heterotrophic and metabolically active bacteria behaved similarly. Only control and heating systems in copper water reservoirs have Legionella spp. Biofilms formed less on copper systems than steel and PEX systems. Initially, PEX had more HPC than copper. After electrochlorination, HPC concentration in the PEX system rapidly declined to non-detect, whereas in the copper system dropped to 0.54 log CFU/mL. Thus, higher temperature increases biofilm growth on all pipe materials and reservoirs bacterial concentration. Electrochlorination is a potential biofilm and microbial disinfection method. This thesis topic investigated how these parameters affect the model distribution system bacterial populations and biofilm growth.