Browsing by Subject "Wastewater"

Silver nanoparticles (AgNPs) are increasingly being integrated into a wide range of consumer products, such as air filters, washing machines, and textiles, due to their antimicrobial properties [1]. However, despite the beneficial applications of AgNPs into consumer products, it is likely that their use will facilitate the release of AgNPs into wastewater treatment plants, thereby possibly negatively impacting key microorganisms involved in nutrient removal. For this reason, it is important to characterize the effects of AgNPs in natural and engineered systems and to measure the antimicrobial effect of AgNPs on wastewater microorganisms. Polyvinyl alcohol coated AgNPs have already been linked to decreased nitrifying activity [2] and it is important to determine if AgNPs coated with other materials follow similar trends. Furthermore, it is likely that, with repeated exposure to AgNPs microbial communities could evolve and develop resistance to silver. Thus, a long-term effect of silver nanoparticle exposure could be a reduction of the efficacy of such products in a similar fashion to the development of microbial antibiotic resistance [3]. Therefore, it is critical that the impacts of these materials be ascertained in wastewater treatment systems to prevent long-term negative effects.

The objectives of this dissertation were to: 1) characterize the effect of several different AgNPs on the ammonia oxidizing bacterium (AOB) Nitrosomonas europaea and investigate possible mechanisms for toxicity, 2) test the effects of consumer product AgNPs on a wide range of heterotrophic bacteria, 3) evaluate the effects of AgNPs on bench scale wastewater sequencing batch reactors, and lastly 4) assess the impacts on microbial communities that are applied with AgNP spiked wastewater biosolids.

First, Nitrosomonas europaea was was selected because wastewater nitrifying microorganisms carry out the first step in nitrification and are known to be sensitive to a wide range of toxicants [4].The antimicrobial effects of AgNPs on the AOB N. europaea were measured by comparing nitrite production rates in a dose response assay and analyzing cell viability using the LIVE/DEAD® fluorescent staining assay. AgNP toxicity to N. europaea appeared to be largely nanoparticle coating dependent. While PVP coated AgNPs have shown reductions up to 15% in nitrite production at 20 ppm, other AgNPs such as gum arabic (GA) coated showed the same level of inhibition at concentrations of 2 ppm. The first mechanism of inhibition appears to be a post-transcriptional interference of AMO/HAO by either dissolved Ag or ROS, in treatments where membranes are not completely disrupted but nitrite production decreased (2 ppm GA AgNP and 2 ppm PVP AgNP treatments). The disruption of nitrification is dependent on AgNP characteristics, such as zeta potential and coating, which will dictate how fast the AgNP will release Ag+ and ROS production Finally, total membrane loss and release of internal cellular matter occur.

In order to test the effects of AgNP products available to consumers, simple bacterial toxicity tests were carried out on well-studied heterotrophic bacteria. A model gram-positive and gram-negative bacterium (B. subtilis and E. coli, respectively) was selected to assess any differences in sensitivity that may occur with the exposure to AgNPs. A third model gram-negative bacterium (P. aeruginosa) was chosen for its biofilm forming capabilities. In addition to testing pure nanoparticles, three silver supplements meant for ingestion, were randomly chosen to test with these three bacteria. Growth curve assays and LIVE/DEAD staining indicate that the consumer product AgNPs had the most significant inhibition on growth rates, but not membrane integrity. Overall, P. aeruginosa was most negatively affected by all AgNPs with nearly 100% growth inhibition for all 2 ppm AgNP treatments. TEM imaging also confirmed cell wall separation in P. aeruginosa and internal density differences for E. coli. The effects on B. subtilis, a gram-positive bacterium, were not as severe but toxicity was observed for several AgNPs at concentrations greater than 2 ppm. Citrate AgNPs appeared to have the most impact on membrane integrity, while other mechanisms such as internal thiol binding might have been at work for other AgNPs.

The effects of varying concentrations of pure AgNPs on complex microbial wastewater reactors are currently being tested. Eight bench-scale sequencing batch reactors were set up to follow the typical "fill, react, settle, decant, idle" method with an 8 hour hydraulic retention time and constant aeration. Reactors were fed synthetic wastewater and treatment efficiency is measured by monitoring effluent concentrations of COD, NH4+, and NO3-. The reactors were seeded with 500 mL of activated sludge from a local wastewater treatment plant. After reaching steady state, the reactors were spiked with 0.2 ppm gum arabic and citrate coated AgNPs. Treatment efficiency was monitored and results showed significant spikes and ammonia and COD immediately following the first spike, but the microbial community appeared to adapt for future AgNP spikes. Microbial community analysis (terminal restriction fragment length polymorphism) showed confirmed this hypothesis.

Overall, this dissertation asserts that by examining AgNP coating type, Ag+ dissolution rates and Stern layer surface charge, it may be possible to predict which AgNPs may be more detrimental wastewater treatment, but not all AgNPs will have the same effect. The results obtained herein must be expanded to other types of AgNPs and microorganisms of ecological importance.

Human activities represent a significant burden on the global water cycle, with large and increasing demands placed on limited water resources by manufacturing, energy production and domestic water use. In addition to changing the quantity of available water resources, human activities lead to changes in water quality by introducing a large and often poorly-characterized array of chemical pollutants, which may negatively impact biodiversity in aquatic ecosystems, leading to impairment of valuable ecosystem functions and services. Domestic and industrial wastewaters represent a significant source of pollution to the aquatic environment due to inadequate or incomplete removal of chemicals introduced into waters by human activities. Currently, incomplete chemical characterization of treated wastewaters limits comprehensive risk assessment of this ubiquitous impact to water. In particular, a significant fraction of the organic chemical composition of treated industrial and domestic wastewaters remains uncharacterized at the molecular level. Efforts aimed at reducing the impacts of water pollution on aquatic ecosystems critically require knowledge of the composition of wastewaters to develop interventions capable of protecting our precious natural water resources.

The goal of this dissertation was to develop a robust, extensible and high-throughput framework for the comprehensive characterization of organic micropollutants in wastewaters by high-resolution accurate-mass mass spectrometry. High-resolution mass spectrometry provides the most powerful analytical technique available for assessing the occurrence and fate of organic pollutants in the water cycle. However, significant limitations in data processing, analysis and interpretation have limited this technique in achieving comprehensive characterization of organic pollutants occurring in natural and built environments. My work aimed to address these challenges by development of automated workflows for the structural characterization of organic pollutants in wastewater and wastewater impacted environments by high-resolution mass spectrometry, and to apply these methods in combination with novel data handling routines to conduct detailed fate studies of wastewater-derived organic micropollutants in the aquatic environment.

In Chapter 2, chemoinformatic tools were implemented along with novel non-targeted mass spectrometric analytical methods to characterize, map, and explore an environmentally-relevant “chemical space” in municipal wastewater. This was accomplished by characterizing the molecular composition of known wastewater-derived organic pollutants and substances that are prioritized as potential wastewater contaminants, using these databases to evaluate the pollutant-likeness of structures postulated for unknown organic compounds that I detected in wastewater extracts using high-resolution mass spectrometry approaches. Results showed that application of multiple computational mass spectrometric tools to structural elucidation of unknown organic pollutants arising in wastewaters improved the efficiency and veracity of screening approaches based on high-resolution mass spectrometry. Furthermore, structural similarity searching was essential for prioritizing substances sharing structural features with known organic pollutants or industrial and consumer chemicals that could enter the environment through use or disposal.

I then applied this comprehensive methodological and computational non-targeted analysis workflow to micropollutant fate analysis in domestic wastewaters (Chapter 3), surface waters impacted by water reuse activities (Chapter 4) and effluents of wastewater treatment facilities receiving wastewater from oil and gas extraction activities (Chapter 5). In Chapter 3, I showed that application of chemometric tools aided in the prioritization of non-targeted compounds arising at various stages of conventional wastewater treatment by partitioning high dimensional data into rational chemical categories based on knowledge of organic chemical fate processes, resulting in the classification of organic micropollutants based on their occurrence and/or removal during treatment. Similarly, in Chapter 4, high-resolution sampling and broad-spectrum targeted and non-targeted chemical analysis were applied to assess the occurrence and fate of organic micropollutants in a water reuse application, wherein reclaimed wastewater was applied for irrigation of turf grass. Results showed that organic micropollutant composition of surface waters receiving runoff from wastewater irrigated areas appeared to be minimally impacted by wastewater-derived organic micropollutants. Finally, Chapter 5 presents results of the comprehensive organic chemical composition of oil and gas wastewaters treated for surface water discharge. Concurrent analysis of effluent samples by complementary, broad-spectrum analytical techniques, revealed that low-levels of hydrophobic organic contaminants, but elevated concentrations of polymeric surfactants, which may effect the fate and analysis of contaminants of concern in oil and gas wastewaters.

Taken together, my work represents significant progress in the characterization of polar organic chemical pollutants associated with wastewater-impacted environments by high-resolution mass spectrometry. Application of these comprehensive methods to examine micropollutant fate processes in wastewater treatment systems, water reuse environments, and water applications in oil/gas exploration yielded new insights into the factors that influence transport, transformation, and persistence of organic micropollutants in these systems across an unprecedented breadth of chemical space.

Current global water scarcity and the spectre of a future critical shortage are driving the need for novel and energy saving water technology approaches. Desalination of seawater and the reuse of treated wastewater effluent, which have historically been viewed as undesirable water sources, are increasingly being explored as sources for reducing water consumption. Although the dominant technologies for taking these water sources to potable quality, energy consumption still makes them unsustainable for widespread application. Membrane distillation (MD) is an innovative water purification method that has shown promise as a technology that can address several of these issues. MD is a membrane process that produces very high quality product water. However, similarly to other thermal desalting processes, MD utilizes heat as the dominant source of energy rather than pressure, and can potentially be used to produce water at higher recoveries (and therefore less waste) than is feasible with existing approaches. Another important advantage of MD is that the water separation occurs at modest temperatures (<90oC), opening the door for the utilization of currently usable waste heat sources. Despite these advantages, MD is primarily a lab scale technology, and key questions concerning process performance, including flux magnitude, energy efficiency, fouling propensity, membrane performance, and long-term system performance must be addressed to fully vet this technology.

This work is represents an attempt to provide insight into several of these issues. The overarching approach taken throughout this project is the parallel evaluation of ceramic membranes alongside commonly used polymeric (PTFE) membranes. The combined factors of MD being a relatively nascent technology and the fundamental separation mechanism point toward initial real-world applications of MD for the treatment of high concentration water that may necessitate membranes exposure to harsher thermal and chemical environments. The robust and inert nature of ceramics make them ideal candidates for such application, although their hydrophilic surface do allow for direct implementation in MD. The first phase of this work details the evaluation of several candidate surface treatments for modifying ceramic membranes and shows that aluminum oxide ceramic membranes can be successfully modified with perfluorodecyltriethoxysilane to possess the necessary hydrophobicity for MD application. The effectiveness of the surface treatment in modifying the membrane surface chemistry was assessed using a multitude of analytical approaches, which showed that the modified ceramic surface attained high hydrophobicity and thus are suitable for application of the membranes in direct contact membrane distillation (DCMD).

The next phase of research details the development and verification of a model for DCMD performance. The relative membrane performance was compared, with the polymeric membrane consistently outperforming the modified ceramics, which was attributed to a combination of superior thermal and physical membrane characteristics. Beyond attempting to evaluate the performance differences, this model allows the consideration of various operational scenarios, focusing on membrane flux and energy performance as various membrane and operational parameters change to determine conditions that maximize MD performance as well as provide insight critical to develop MD-specific membranes.

Finally, membrane performance was evaluated during the treatment water containing various organic foulants as well for the treatment of municipal wastewater. The results showed that the level of fouling was highly dependent on foulant type, with alginate identified as a component that produces severe fouling under all conditions evaluated, and wastewater fouling being relatively minimal. Membrane cleaning solutions were implemented to show that near-complete flux recovery was attainable, and plain deionized water was shown to be as effective as sodium hypochlorite.

The water energy nexus represents the intersection of water use, energy production, electricity generation, and waste generation and disposal. The rapid rise of unconventional natural gas and oil production through the combined processes of horizontal drilling and hydraulic fracturing have shifted the energy dynamic in the United States. Concurrently, the rising utilization of unconventional gas and oil production has intensified the water use for hydraulic fracturing and generation of flowback and produced water associated with shale gas and tight oil production. Among the major environmental risks associated with the rise of unconventional oil and gas exploration water availability, water contamination from leaking or disposal of wastewater, and adequate disposal of the wastewater are the key issues associated with the water-energy nexus. This dissertation aims to quantify the water use for hydraulic fracturing across the U.S., evaluate the water use for electricity production from natural gas in comparison to coal combustion, estimate the flowback and produced water production, and assess possible recycling of oilfield water through irrigation in California.

This dissertation describes the water footprint of hydraulic fracturing by examining total water use, water use per well, water use per length of horizontal well, and the changes in water use through time. The data show that hydraulic fracturing water use per well has been increasing between early stages (2008-2012) to later stages (2012-2016) of operation. In addition to water use, this dissertation estimated waste water generated from unconventional oil and gas wells and find a concurrent increase in flowback and produced water (FP water) per well through time. Using salinity as a marker to distinguish FP water from water injected for hydraulic fracturing, this dissertation observes the sequestration of the injected freshwater, while the return flow composed primarily of more saline formation brines entrapped within the shale formations.

In addition, this this dissertation explored two downstream impacts of the increasing water use and FP water generation. First, as abundant natural gas resources from the expansion of hydraulic fracturing have shifted the electricity sector from primarily coal- to primarily natural gas-fired, this study examined the impact increasing water use associated with hydraulic fracturing has had on power plant lifecycle water consumption and withdrawal. The study found that despite increasing water use for hydraulic fracturing, natural gas-fired generation on average used less water for cooling relative to coal-fired generation. Finally, this this dissertation examined the risks from recycling of oilfield produced water (OPW) as an agricultural makeup water source. The data from field studies in California show that by using low salinity OPW, farmers are able to successfully recycle OPW without risking metals accumulation in soil and consequently in crop and human health.