Browsing by Author "Deshusses, Marc A"

An integrated biotrickling filter (BTF)-Anammox bioreactor system was established for the complete treatment of ammonia. Shortcut nitrification process was successfully achieved in the biotrickling filter through free ammonia and free nitrous acid inhibition of nitrite oxidizing bacteria. During transients, while increasing nitrogen loading, free ammonia was the main factor that inhibited the activity of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB). During steady state operation, free nitrous acid was mainly responsible for inhibition of NOB due to the accumulation of nitrite at relatively low pH. Ammonia removal by the BTF reached up to 50 gN m-3 h-1 with 100% removal at an inlet concentration of 403 ppm and a gas residence time of 20.8 s. Average removal of ammonia during stable operation was 95%. The anammox bioreactor could remove 75% of total nitrogen discharged by the BTF when the two reactors were connected. The possibility of operating in complete closed loop mode for the liquid was investigated. However, due to the limited activity of the Anammox bioreactor or the fact that this reactor was undersized, recycling the Anammox effluent back to BTF caused accumulation of nitrite in the system which further inhibited activity of Anammox and progressively caused failure of the system.

A conceptual model of both bioreactors was also developed to optimize the integrated system. The model was developed by including mass balances of nitrogen in the system and inhibition factors in microbial kinetics. Parameters such as hydraulic residence time (HRT), empty bed residence time (EBRT) and pH had significant impact on the partial nitritation process in the BTF. Model simulations also indicated that implementing a recycle for the Anammox bioreactor was needed to reduce the inhibitory effect of nitrite on the performance of the system.

Powdered Activated Carbon (PAC) adsorption was studied in order to determine the influence of natural organic matter (NOM) on the adsorption of two acidic pharmaceutically active compounds (PhACs), clofibric acid and ketoprofen. Suwannee River humic acids (SRHAs) was used as substitute of NOM in natural water. Batch adsorption experiments were conducted to obtain the single compound adsorption kinetics and adsorption isotherm with and without SRHAs in the system. Three main findings resulted from this study. First, the adsorption isotherms showed that the adsorption of clofibric acid was not significantly affected in the presence of SRHAs (5 ppm); however, the adsorption of ketoprofen markedly decreased with SRHAs in the solutions. Higher initial concentrations of clofibric acid than ketoprofen together with the compressed double layer theory helped explain the different behaviors that were observed. Furthermore, the more hydrophobic ketoprofen molecules may increase the possibility that this compound would adsorb less on the surface area which was covered by the more hydrophilic humic acids. Second, the adsorption kinetics of both compounds were not affected by the SRHAs, although more research may be needed, as it is possible that slight differences exist during the initial adsorption phase. Lastly, possible intermolecular forces were discussed and a sequence of importance is proposed for their role in the adsorption process as A). electrostatic forces; B). electron donor-acceptor interaction; C & D). H-bond and London Dispersion forces.

Ammonia is an odorous gaseous compound emitted by a variety of industrial facilities. This study aimed to address the feasibility of ammonia gas removal using a biotrickling filter (BTF) coupled with an anammox bioreactor. In the BTF, the influent ammonia gas partitioned into the trickling water and was converted to nitrite via partial nitrification. The effluent liquid from the BTF, containing nitrite and ammonium concentrations, was fed into the anammox reactor where autotrophic denitrifying bacteria converted the ammonium and nitrite to dinitrogen gas. For the anammox reactor to operate efficiently, the influent ammonium and nitrite concentrations must be in a 1 to 1 molar ratio. To evaluate the feasibility of this system, a lab scale BTF and anammox reactor were constructed and operated and a conceptual model for this system was developed. To obtain a nitrite to ammonium ratio close to 1, it was found that the effluent pH from the BTF must be maintained below 7, and the loading rate could not exceed 8.7 g N/m3h. At this loading rate, complete ammonia gas removal occurred. A recycle rate of 1.4 times that of the influent was implemented in the BTF to increase performance and improve the nitrite to ammonium ratio. The addition of the recycle line achieved a nitrite of ammonium ratio of 0.97 at a pH value of 7.67. The anammox reactor achieved 88% removal of ammonium and nitrite at a loading rate of 10.5 g N /m3h. The fact that the BTF was able to achieve a 1 to 1 nitrite to ammonium ratio indicated that coupling of a BTF with the anammox reactor should be feasible. The mathematical model underpredicted effluent ammonium and nitrite concentrations in the BTF and greatly overpredicted the effluent concentrations from the anammox reactor. To improve the BTF model inhibition factors and oxygen supply need to be accounted for. Further development of the growth kinetics in the annamox model are necessary as well.

Despite significant advances in public health and engineering over the last 100 years, diarrheal disease remains one of the highest global burdens of disease, particularly for children under 5 years of age. Access to clean water, sanitation, and hygiene greatly reduces this risk, but access to improved sanitation remains a challenge for a large percentage of the world. Due to the lack of access to safely managed sanitation and rapid urbanization, sustainable onsite fecal sludge treatment systems need to be developed and deployed to reduce the burden of diarrheal disease.

The Anaerobic Digestion Pasteurization Latrine (ADPL) is a concept that was developed by Professor Marc Deshusses to meet this need. The goal of the ADPL was to produce a pathogen-free effluent through pasteurization powered by biogas produced from anaerobic digestion of fecal sludge. The concept was supported through laboratory studies on the anaerobic digestion of a simulant fecal sludge and inactivation of E. coli in a pasteurization system using a heater maintained at 65-75 °C and a tube-in-shell counter-flow heat exchanger for heat recovery.

The goal of this research was to build upon initial laboratory-based research on the ADPL and demonstrate the feasibility of the ADPL concept at full-scale in field conditions, simulate improved digester designs to increase digestion efficiency, evaluate digester effluent post-treatment for residual organic and nutrient removal, and develop a remote data acquisition and controls system to improve system understanding and operation of the pasteurization system. The desired outcome of this work is a complete, self-sustaining system that efficiently digests fecal sludge for maximum biogas production, produces a polished effluent that can be reused, and pasteurizes the effluent efficiently and reliably, all while being low-cost with minimal operation and maintenance requirements.

Two ADPL systems were installed on residential plots with 15-35 residents in a peri-urban area outside of Eldoret, Kenya. Each system was comprised of 3 toilets built above a floating dome digester and heat pasteurization system. The ADPLs are simple systems, with no moving parts and relying on gravity-induced flows. Adoption at two sites was successful, and residents reported that the systems had little to no odor or flies, and the residents were interested in the possibility of excess biogas and effluent reuse. The ADPLs were monitored daily for biogas production and temperatures in the pasteurization system. The ADPL serving 35 residents produced on average 350 Lbiogas d-1, and the temperature in the heating tank was greater than 65 °C on 87% of sampling days. The treated effluent was analyzed periodically for chemical oxygen demand (COD), biochemical oxygen demand (BOD), total ammonia nitrogen (TAN), and pH. On average, the effluent contained 4,500-5,600 mg COD L-1 (an 87-89% reduction of the estimated input), 2,000-3,900 mg BOD L-1, 2,400-4,800 mg NH3-N, and had a pH of 7.4-7.7. Results from this field study show that anaerobic digestion of minimally diluted fecal sludge can provide enough energy to pasteurize the effluent, and that the ADPL can be a suitable option for onsite fecal sludge treatment.

Three variations of a 2 m3 anaerobic digester were simulated with a flow of 120 Lwater d-1 – a reactor with no internal baffle walls (CSTR), a reactor with baffle walls that forced flow to wind in the xy-direction (HABR), and a reactor with baffle walls that forced flow to wind in the xz-direction (ABR). Results showed that increasing the number of baffle walls significantly improved the hydraulic performance of the reactor in terms of residence time, dead space, and Morrill Index. Adding angled portions to the end of baffle walls and adjusting the D:U ratio in the ABR had minimal impact while a variable inflow had a moderate impact on performance. Overall, these results suggest that adding 3-5 baffle walls inside of an anaerobic digester would greatly improve the digester’s hydraulic efficiency and better utilize the reactor volume. These adjustments would thus cause enhanced solids removal and digestion efficiency, resulting in higher biogas production and a cleaner effluent. However, simulation work including solids and biological reactions would be beneficial to future reactor design considerations.

The biological filter study analyzed the treatment of high-strength anaerobic digester effluent using trickling filters for nitrification and then submerged attached growth filters for denitrification. Five media types were tested in the trickling filters (8 L volume): biochar, granular activated carbon (GAC), zeolite (clinoptilolite), Pall rings, and gravel. Five columns were tested for denitrifying filters (4 L volume) using sand, bamboo wood chips, eucalyptus wood chips, bamboo with sand, and eucalyptus with sand. Wood chips were used in denitrifying filters as a supplemental carbon source for denitrification. From six months of operation, biochar, GAC, zeolite, Pall rings, and gravel media had turbidity removal efficiencies of 90, 91, 77, 74, and 74%, respectively, and NH3-N removal efficiencies of 83, 87, 85, 30, and 80%, respectively. The primary mechanism for ammonia removal was nitrification to nitrate, but some adsorption was seen in biochar, GAC, and zeolite filters. From four months of operation, sand, bamboo, bamboo with sand, eucalyptus, and eucalyptus with sand filters had NO3-N removal efficiencies of 30, 59, 51, 31, and 30%, respectively, and turbidity removal efficiencies of 88, 89, 84, 89, and 88%, respectively. Bamboo had the greatest NO3-N removal rate at 0.054 kg N m-3 d-1 and released more COD than eucalyptus (0.076-0.120 gCOD gbamboo-1 compared to 0.012-0.043 gCOD geucalyptus-1). Biochar and bamboo were selected as the best media types from this study for the nitrification and denitrification filters, respectively, due to their low-cost and sustainable supply. Based on an average initial influent of 600 mg NH3-N L-1 and 980 NTU, the biochar filter’s expected effluent would be 97 mg NH3-N L-1, 450 mg NO3-N L-1, and 120 NTU. The bamboo filter would then produce an effluent of 82 mg NH3-N L-1, 180 mg NO3-N L-1, and 13 NTU. This theoretical combined performance would thus result in 56% removal of total N and 98.7% removal of turbidity. Based on nitrate removal rate, full denitrification could be achieved by doubling reactor volume. Total nitrogen removal efficiency of 80-90% could thus be achievable. These filter media were successful in treating high-strength digester effluent and present an alternative for sustainable, low-cost, and low-maintenance post-treatment options for nitrogen management.

A low-cost data acquisition and controls system with remote, real-time data access was developed using the Particle Electron. This device records temperature and liquid flow data while controlling a gas valve and igniter as part of pasteurization system. The device was tested in lab and field conditions. The power consumption is low, 34 Wh per day, and data acquisition matched the results of standard laboratory devices. The field deployment (Eldoret, Kenya) successfully operated the pasteurization system in its target range while reporting real-time data. This low-cost and low-power device has improved the operation of the onsite pasteurization system, and adaptations of the device would be valuable in many other onsite fecal sludge treatment systems.

Together, these objectives have demonstrated the ADPL concept works in field conditions, digester performance can be improved with simple modifications, digester effluent can be further treated to encourage reuse or for safe disposal with biological filters using sustainable media that have low operational requirements, and low-cost controls can improve the pasteurization system efficiency and reliability while generating more data to expand understanding of the system.

Hydrogen sulfide (H2S) is a toxic gas and common odor nuisance produced in a variety of chemical and environmental processes. The biological oxidation of H2S to sulfate/sulfuric acid is a well-documented treatment method that is efficient both in removal and cost. Sulfate ions produced in a BTF can interact with various cations, specifically calcium, and form insoluble salts. Gypsum (CaSO4*2H2O) formed within a BTF treating H2S can affect system performance by causing pressure buildup and reducing pollutant mass transfer. An experimental approach was developed to quantify gypsum precipitation in BTFs as a function of critical system parameters. Effluent liquid from one laboratory and four industrial BTFs was used to induce gypsum precipitation at various levels of pH, total sulfate concentration, calcium content, and ionic strength. A computer model was developed to predict gypsum precipitation based on the ionic composition of the reactor trickling liquid. The results support the hypothesis that gypsum precipitation in a BTF treating H2S is a realistic concern for industrial systems. The computer model demonstrates the ability to successfully predict gypsum precipitation within a correction factor of 2. The presence of gypsum and elemental sulfur in solid samples collected from industrial BTFs illustrates the feasibility of mineral deposition in full-scale treatment systems. Ethylene diamine tetraacetic acid (EDTA) shows the potential of being an effective additive for the prevention of gypsum formation within a BTF treating hydrogen sulfide.

Upgrading raw biogas (~60% CH4, 40% CO2, 1000-5000 ppmv H2S) to renewable natural gas (RNG) (> 97% CH4, < 2% CO2, < 4 ppmv H2S) for injection into the grid is a desirable endeavor. RNG would allow for a clean alternative to natural gas derived from fossil origin, and it also have a versatile use as a transportation fuel and source of heating energy. Current physical-chemical technologies, such as pressure swing absorption and organic chemical scrubbing, can successfully upgrade raw biogas to meet RNG standards (1,2). However, they are energy intensive, costly, and can remove fractions of methane gas along with the impurities. Recently, biological biogas upgrading technologies have emerged as a promising solution for converting raw biogas to RNG. The method relies on hydrogenotrophic methanogens to reduce the CO2 fraction of raw biogas to CH4 using H2 as the electron donor. This method is advantageous compared to traditional biogas upgrading methods because is sequesters carbon emissions while increasing the volumetric production of methane. While early studies on biological biogas upgrading in continuously stirred tank reactors were conceptually validating, hydrogen mass transfer resistance from the gas-to-liquid phase prevented fast upgrading capacities from being realized. Slow biogas upgrading rates hinder the economic feasibility of the process. Furthermore, these studies only focused on CO2 removal when in reality, other impurities, such as corrosive H2S, must also be removed before RNG injection into the natural gas pipeline.

The overall objective of this thesis research is to develop a biological trickling filter reactor that can upgrade biogas to RNG standards at fast upgrading capacities while biologically co-removing H2S. A biological trickling filter was chosen for this investigation because they are characterized by a high specific surface area for biofilm growth, high biomass density, and are known for their high overall mass transfer coefficients; all factors that contribute to high conversion rates. A proof-of-concept study validated that this approach could achieve upgrading rates that were 5 – 30 times faster than other bioreactor configurations. This finding supported further studies that aimed to investigate hydrogen mass transfer resistance specifically in a biological trickling filter reactor. This was accomplished using a highly sensitive dissolved hydrogen sensor, which collected concentrations in real-time. Using this sensor, experiments were conducted to assess mass transfer resistance in the gas and liquid films. It was discovered that there was no external resistance in the gas-film. Furthermore, the liquid phase was a main barrier for mass transfer and reducing the liquid film thickness can significantly improve biogas upgrading capacities by 20%.

In addition to laboratory experiments, a robust and conceptually correct mathematical model was developed for a biogas upgrading biological trickling filter. The model was used to provide deeper insight into process fundamental and identify biological versus mass transfer limitations in the bioreactor. The model successfully replicated complex experimental findings and confirmed that liquid transport through the bioreactor bed was faster than the rates of mass transfer and biological conversion. A sensitivity analysis revealed that the model was most sensitive to the empty bed contact time and the maximum rate of reaction. Interestingly, the mass transfer coefficient for the liquid film (kLa) did not significantly improve the biogas upgrading rate for the bioreactor. This is because the model predicts that the bulk of hydrogen mass transfer occurs from the gas to non-wetted biofilm phase.

Concluding mass transfer resistance testing and process optimization, it was demonstrated that the engineered bioreactor could successfully upgrade various biogas compositions to RNG standards. The rates achieved for these experiments (10 – 20 m3CH4 m-3 d-1) were 1.5 – 25 times faster than other comparable research studies. To determine the economic feasibility of this technology, a paper scale-up cost analysis was conducted to estimate the investment and operation costs of a biological trickling filter upgrading raw biogas (60% CH4, 40% CO2) to RNG (> 97% CH4 < 2% CO2). This was accomplished by using experimental findings to scale the dimensions and determine heating and cooling requirements based on seasonal temperatures. Cost estimates for parts were acquired through vendor quotes. The cost analysis showed that the bioreactor is economically feasible however, the H2 acquisition cost was ~ 650% of the bioreactor investment cost. This is because H2 was acquired from the electrolysis of excess wind and solar energy and the cost of the hydrolyzer was ~ $1,000,000. Despite this significant cost, the total amortized cost of the biological biogas upgrading system was comparable to current physical-chemical upgrading technologies.

The final study of this thesis investigated the potential to biologically co-treat CO2 and H2S using nitrate as the terminal electron donor. Since the addition of nitrate favored undesired oxidation-reduction reaction pathways with hydrogen, a method was developed to map electron transfers. The effect of nitrate on methanogensis was tested with and without sulfur oxidizing bacteria. Under both conditions, nitrate had a negative impact on methanogenesis and ultimately, prevented co-treatment from being achieved. While attempting to co-treat H2S and CO2, it was discovered that dissimilatory nitrate reduction to ammonium was favored over denitrification. The electron balance confirmed that a competition for electrons from hydrogen did exist. This competition required N:S feeding ratios upwards of 16:1, which far exceeded the theoretical ratios of (4:1) for denitrifying bacteria. While the high nitrate loading rates allowed for high H2S removal efficiencies (98%), they inhibited methanogenesis so that carbon dioxide removal efficiencies did not meet RNG standards. Thus, future work should focus on alternative electron donors for sulfur oxidation and quantifying methanogenesis inhibition caused by sulfur-oxidation/denitrification pathways.

Acute Respiratory Distress Syndrome (ARDS), a form of acute lung injury resulting in hypoxic respiratory failure is a frequent and often lethal indication for admission to both adult and pediatric intensive care units (ICUs). Currently, patients in need of oxygen support must rely on conventional methods that use a patient’s lungs to deliver oxygen, such as mechanical ventilation. In severe cases where patients’ lungs are damaged to a point that they are unable to be supported with mechanical ventilation, currently the only option is extracorporeal membrane oxygenation (ECMO). This method of oxygenation bypasses the lungs and directly oxygenates the blood. However, this is a costly, highly sophisticated treatment typically only available in select large hospitals who have the required resources. The onset of the COVID-19 pandemic made clear that the need for alternative, lung-independent, oxygen delivery methods for patients is a dire need in the medical field. Smaller devices that can be easily deployed, used in more hospitals, and are cheaper to manufacture and administer, would find immediate use in the medical field to help patients who would otherwise not have access to ECMO. The hyperbaric intravascular oxygenator catheter is a concept that Dr. Tobias Straube (Duke University) conceived in response to this need. The idea behind this device is to deliver critical levels of oxygen to patients in need with easy to deploy catheter-based devices. The primary objective of this dissertation was to develop the concept of this hyperbaric intravascular oxygenation catheter as a future treatment option in patients with ARDS. The work consisted of the development of a proof-of-concept device using hollow fiber dense membranes and hyperbaric oxygen to diffuse oxygen at transfer rates greater than previous works. A conceptually accurate mathematical model was developed to investigate system limitations in the early prototype, and guide future investigations. Blood mixing methodologies were developed and tested at the bench scale to determine the feasibility of angular oscillation-based mixing on both transport efficiencies and impacts on bubble formation, and the previous model was used to evaluate the system. Finally, an investigation on the mechanisms behind the angular oscillation was conducted using computational fluid dynamics. Initial work demonstrated the technical feasibility of providing oxygen to a bulk medium, such as blood, via diffusion across non-porous hollow fiber membranes (HFM) using hyperbaric oxygen. The oxygen transfer across Teflon AF 2400 membranes was characterized at oxygen pressures up to 2 bars in both a stirred tank vessel (CSTR) and a tubular device mimicking intravenous application. Fluxes over 550 mL min-1 m-2 were observed in well-mixed systems, and just over 350 mL mL min-1 m-2 in flow through tubular systems. Oxygen flux was proportional to the oxygen partial pressure inside the HFM over the tested range and increased with mixing of the bulk liquid. Some bubbles were observed at the higher pressures (1.9 bar) and when bulk liquid dissolved oxygen concentrations were high. High frequency ultrasound was applied to detect and count individual bubbles, but no increase from background levels was detected during lower pressure operation. A conceptual model of the oxygen transport was developed and validated. Model parametric sensitivity studies demonstrated that diffusion through the thin fiber walls was a significant resistance to mass transfer. Promoting convection around the fibers should enable physiologically relevant oxygen supply. This work indicated that a device is within reach that is capable of delivering greater than 10% of a patient’s basal oxygen needs in a configuration that readily fits intravascularly. Proof-of-concept work highlighted the need for an active mixing method that would both improve flux while also limiting conditions favoring bubble formation in such a hyperbaric device. We demonstrated that the introduction of angular oscillation as a form of active mixing allowed for fluxes of up to 400 mL min-1 m-2 at lower pressures than our previous work. This increase of almost 150 mL min-1 m-2 was achieved despite the use of water maintained at body temperature (37 C°) and at the viscosity of blood (3.5 cP), both of which reduce oxygen transfer rates when compared to the 20 C water used in the previous work. Adaptation of the previously developed mathematical model indicated continued improvements maybe achieved with more active mixing. Future work in blood will investigate the effects of angular oscillation on oxygen transport and bubble formation in an in vitro system, and to determine if this method of active mixing has any deleterious effects on red blood cells. A computational fluid dynamics analysis using COMSOL was undertaken on the micro and macro-oscillations used in the active mixing schemes. This analysis revealed reasons why micro-oscillations were reducing the incidence of bubbles on fiber walls in bench testing when the fibers were undergoing rapid small motions, while also producing less overall flux as compared to the large oscillations. This result lends itself to future work to optimize the conditions of micro-oscillations such that bubble formation is reduced in bench top prototypes. Additionally, there is potential to optimize the range of motions used in micro-oscillations to reduce the impact of overall oxygen flux as compared to large consistent motion in real world testing. Overall, this work demonstrated the feasibility of using hyperbaric pressures in an oxygen delivery catheter and that a mixing methodology using angular oscillation could be employed that would increase flux rates while also limiting bubble formation. Mathematical models were developed that gave insight to a hypothetical catheter’s mass transport limitations, and can be used to investigate hypothetical changes to the device. Finally, a CFD model was developed to better understand the angular oscillation mixing that was able to reduce bubble formation in this system.

The properties of nanoparticle sensors intended for real- time monitoring of low concentration of elemental mercury (Hg) vapor and volatile organic compounds (VOCs) are presented and discussed. This sensor for mercury vapors is composed of gold (Au) nanoparticles on single-walled carbon nanotubes (SWNTs) networks. Surface topography was determined by scanning electron microscopy (SEM). The electrical resistance of Au-SWNTs networks drastically increased upon exposure to mercury vapor. The experiment result shows that higher deposition amounts of Au nanoparticles on SWNTs lead to higher sensing responses. A detection limit of this senor to vapor mercury concentrations in the parts-per billion (ppb) was seen. Response features of current mercury sensors are discussed concerning sensitivity, reproducibility and regeneration at room temperature (25°C).

Nanosensors made of conducting polypyrrole (PPY) and tin dioxide (SnO2) on SWNTs were tested for the detection of volatile organics such as benzene, methyl ethyl ketone (MEK), hexane and xylene. The greater sensitivity of these two sensors to lower analytes concentrations compared to previous research studies was demonstrated. Experiments were conducted at room temperature, and the response was shown to be fast and highly sensitive to low concentration of VOCs. Using PPY and SnO2 sensors in a sensor array can identify polar and nonpolar analytes. Sensing mechanisms of these two sensors to analytes are discussed in this thesis.

Further work to improve the sensors that were tested was identified. The main challenge of this sensor is that the response and regeneration time is relatively slow at room temperature, especially for Au nanoparticle sensors. Also, with respect to PPY and SnO2 nanosensors, a high reproducibility in the making of sensors is desired. This improvement can help PPY and SnO2 sensors to have consistency. Finally, since nanosensors that can detect VOCs are not very specific, array sensing and numerical methods that can be used to quantify individual compounds in mixture from nanosensors array data are needed.

Some of the worst air quality is found in enclosed indoor spaces that do not have the capability for sufficient ventilation. Despite the major health risk of indoor air pollutants, such as volatile organic compounds (VOCs), current technologies to treat indoor VOC pollution could be improved. There is a critical need for a new technology that can effectively control VOCs in enclosed indoor environments. Biofiltration can potentially be adapted for indoor air treatment by intensifying the process with miniaturization. Microbioreactors have maximized surface-to-volume ratios, which allows for increased mass transfer of pollutants and oxygen to bacteria in the aqueous phase, resulting in superior biodegradation of VOCs. Accurate measurements of mass transfer coefficients are critical for reliable characterization of bioreactors. While standardized methods to measure mass transfer coefficients have been established for simple stirred tank reactors, existing methods to characterize MTCs have not yet been standardized for alternative reactor types such as miniaturized and biofiltration reactors, leading to inconsistencies in implementation and confusion about the validity of comparisons across different methodologies, volume scales, or reactor types. The accuracy of two commonly used lab-scale methods were critically evaluated for the measurement of mass transfer coefficients in a miniature plug-flow reactor. A detailed mathematical model was developed and applied to each experimental method, which enabled accurate calculation of the mass transfer coefficients. Building upon promising preliminary microbioreactor prototypes, a systematic study of major reactor design parameters was carried out with the aim of improving reactor performance. A design-build-test-learn pipeline was developed that enabled new reactor design prototypes to be rapidly designed using CAD software, manufactured with 3D printing, and inserted interchangeably in an experimental testing system. Several microbioreactors were manufactured with varying microchannels sizes and configurations. The mass transfer coefficients were characterized and a selection of microbioreactor prototypes were evaluated in a study of toluene biodegradation in continuously operated microbioreactors. The results of the microbioreactor evaluation studies indicate good performance for biological treatment of toluene and methanol as single model VOC substrates. Realistic treatment environments will have mixtures of pollutants, with several to potentially hundreds of separate volatile pollutants. The biological treatment of pollutant mixtures has been shown be more difficult for many microorganisms to treat effectively. Recently, several tools have emerged to enable a rational approach to design of microbial communities. Community metabolic network modeling was evaluated for use in engineering a microbial consortium to effectively and resiliently biodegrade VOCs. Model-predicted microbial communities were experimentally assessed alongside pure strains and conventionally enriched cultures for biodegradation of toluene and styrene as a model VOC mixture. Altogether, the aim of this dissertation was to engineer a high-performing microbioreactor-microbiome system for biological VOC removal. An experimental and mathematical modeling method was developed to accurately characterize the oxygen mass transfer coefficients of microbioreactors. The impact of key design parameters on the mass transfer of microbioreactors and the biodegradation of VOCs was evaluated. Finally, the potential to employ metabolic network modeling for the rational design of synthetic VOC-degradation consortia was explored.

Volatile organic compounds (VOCs) are a family of chemicals which are known to have adverse effects on climate change and health, and thus emissions of VOCs are regulated. One such control method is via biodegradation in a biofilter and other similar reactors. Many hydrophobic VOCs, however, are difficult to degrade in such devices. Biphasic bioreactors are designed to remove and treat hydrophobic compounds from waste gas streams. In addition to the water phase, a biphasic bioreactor includes a secondary (2°) liquid phase where hydrophobic VOCs are absorbed and made available for degradation by bacteria. A viable 2° phase is non-miscible with water, non-toxic to bacteria in the bioreactor, and has a strong affinity for target pollutants. In this work, methods were explored by which candidate 2° phases may be screened for suitability to treat two commonly studied hydrophobic VOCs, toluene and hexane. 2° phases included the commonly used silicone oil, paraffin oil and several ionic liquids (ILs), a novel type of solvent popular with the chemical industry. The air-liquid partition coefficient of toluene and hexane with each 2° phases was determined. Additionally the effect on the oxygen uptake rate (OUR) and cell growth in a flask of each 2° phase on biological cultures enriched on toluene and hexane was studied. It was determined that OUR is a poor method of screening 2° phases for biophasic bioreactors. Additionally, cell growth studies failed to capture accelerated degradation of the target pollutants in biphasic cultures. The presence of ILs resulted in significant biological inhibition, and thus do not appear to be promising 2° phase candidates for biodegradation purposes.

Supercritical water oxidation (SCWO) had been investigated as an advanced technology for the removal of inert and stable organics found in wide range of wastes. Ammonia and nitrous oxide are confirmed in outlet of SCWO system treating municipal sludge. In this study, a mathematical model was established to simulate nitrogen reaction, in order to explore the kinetics of ammonia reaction and reduce the nitrous oxide generation. This developed mathematical model was trained by data from Duke Sanitation Solution group where a pilot-scale supercritical water oxidation facility is invested to treat municipal sludge. The final model was validated by practical data obtained from this facility, and give instruction on SCWO operation.

The problem of inadequate sanitation in less developed countries has dire health consequences such as diarrheal diseases. A household-scale sanitation system consisting of an anaerobic digester, heat exchanger, and biogas-powered heater, was developed to provide a simple, potentially low cost and low carbon-footprint solution to this problem. A conceptual model was developed to predict the effectiveness of the heat sterilization system in reaching the appropriate temperatures to significantly inactivate pathogens such as E. coli, helminthe ova, and viruses. Lab experiments with a stainless steel heater and exchanger were used to establish model parameters and to verify the model. Though the model sometimes predicts higher or lower values than the experimental data, probably due to uncertainties in pathogen decay constants and in the different heat transfer coefficients, the model adequately predicts temperature across the heat exchanger and heater, and can provide a preliminary estimate of pathogen inactivation within the system. Both disinfection experiments showed the system reduces E. coli concentrations to below the WHO limit, which was predicted by the model.

Pre-treatment of hydrogen sulfide is required before the utilization of biogas to eliminate the detrimental effects of corrosive hydrogen sulfide to the following combustion engines and pipelines. Biotrickling filters as one of the biotechnological methods have been investigated in desulfurizing biogas in recent years. Although high removal efficiency has been achieved by conventional biotrickling filters, clogging of the biotrickling filter bed due to the accumulation of excess biomass and elemental sulfur, has been widely reported (Janssen et al. 1997, Fortuny et al. 2008). In this context, a novel biotrickling filter using a monolith as its filter bed has been proposed and studied in this work to investigate its performance in removing H2S and solving the bed-clogging problem through pigging, a common method used for pipeline and tubular reactor cleaning. The inlet H2S concentration was controlled around 1000 ppmv, corresponding to a loading rate of 122 g S–H2S m−3 h−1, and the empty bed gas residence time (EBRT) was 41 s. The influence of different H2S/O2 ratios on the removal performance was investigated at these conditions and results indicated that at H2S/O2 molar ratio of 1:2, an average removal efficiency of 95% was obtained. Under all conditions investigated, elemental sulfur and sulfate were measured to be the two dominant products and covered up to 93% of total end products. The monolith bed design also served to demonstrate that the risk of clogging was greatly reduced under this kind of design and bed-clogging problems could be resolved when bed pigging was implemented to remove excess biomass and elemental sulfur accumulated inside the bed. Based on the results reported here, the monolith filter bed can be an effective alternative to the conventional packing material with a high specific surface area and a comparable performance could also be achieved by this novel bioreactor.

The main goal of this dissertation was to develop practical water and bioaerosol monitoring strategies for resource limited settings. This goal was established because there are ~2.2 billion people who lack access to safe drinking water services, ~4.6 billion without access to safe sanitation services, and, in February 2021, more than 95% of the world population was susceptible to COVID-19 infection. Herein, widely available drinking water quality testing technologies were used to develop a scalable methodology to standardize water quality monitoring in cities. Passive and active aerosol sampling methods were optimized to facilitate bioaerosol monitoring near open wastewater canals in cities with poor sanitation. Stochastic mathematical models were used to estimate the risk of infection, illness, and mortality posed by bioaerosols near open wastewater canals, translating monitoring data into potential health outcomes. Lastly, a stochastic mathematical model was developed and converted into a web-application to facilitate the understanding of long-range aerosol transmission of COVID-19 indoors. It was demonstrated that sampling drinking water at the point of consumption provided a more accurate characterization of water safety than access to a type of water infrastructure. Passive aerosol sampling can provide quantitative fecal coliform data in low-resource settings, and active aerosol sampling allowed the collection of pathogen-specific data to identify which pathogens may pose an exposure risk. Risk assessment models indicated that bacterial pathogens present non-negligible risks of infection in La Paz, Bolivia, warranting future longitudinal investigations. The risk assessment application that was developed and applied for both assessment of exposure to fecal bioaerosols and SARS-CoV-2 contributed to the understanding of aerosol transmission of infectious diseases.

The United States Environmental Protection Agency (EPA) defines environmental justice (EJ) as “The fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income, with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies.” Environmental injustices are not just a symptom of environmental conditions themselves, but are a manifestation of legal, economic, political, and social structures of oppression.

Globally, there are over 4.5 billion people who lack access to safely managed sanitation, with the largest burden of inadequate infrastructure being most greatly felt by communities which are marginalized based on income, indigeneity, and race. The work herein explores three different case studies of engagement with environmental injustices, leveraging academic environmental science and engineering, with three different theories of change: philanthropy-led research, academic-led research, and community-led research, respectively.

Case 1: The Philippines has poor access to improved sanitation, declining national food security, and water scarcity during the dry seasons. Although the country does not contribute as much to man-induced climate change, the Philippines is considered to be one of the most vulnerable countries to be disproportionately affected by climate change, further exacerbating lack of access to sanitation. Through the Gates Foundation’s Reinvent the Toilet Challenge theory of change to privatize innovative technologies to develop for-profit businesses around innovative sanitation systems, a novel modular laboratory anaerobic digestate nitrification and denitrification post-treatment bioreactor system was is developed and operated for 200 days. The system achieved a combined removal of chemical oxygen demand (COD), total nitrogen (TN), and phosphorus (PO4-P) up to 84%, 69%, and 89%, respectively, and have successfully recovered vital nutrients for agricultural development by precipitating ammonium magnesium phosphate hydrate, a documented valuable slow-release solid fertilizer.

Case 2: A predominately African American community in Wake County, North Carolina which, despite being surrounded by White neighborhoods with municipal water distribution lines, relies on private wells for their water supply and relies on on-site septic tanks for sanitation needs. Residents have reason to believe that both on-site water and sanitation infrastructure are compromised, and contamination is of concern. An academic-led community assessment was conducted to determine exposure to standard pathogens and chemical contaminants using culture-based and qPCR methods. Cross contamination septic tanks and wells were evaluated by comparing antibiotic resistance gene profiles, microbial source tracking, and geostatistical models. From samples of 14 household wells, 6 tested positive for total coliforms, 4 for E.coli, 10 for sucralose, and 80% and 20% of total E.coli isolates tested positive for antibiotic resistance to amoxicillin and ceftriaxone, respectively.

Case 3: Lowndes County is a predominantly Black rural county in Alabama which has a rich history and present climate of racial discrimination, economic oppression, and social activism. Over 80 % of the county relies on on-site sanitation infrastructure and most of them are failing, exposing many to raw wastewater. Under the Center of Rural Enterprise and Environmental Justice’s ownership and management, a community assessment of exposure to untreated sewage was conducted using samples from residential drinking water, surface swabs, public surface waters, and both residential and public soil samples using culture-based and qPCR methods. From samples of 43 households, 68% and 55% of houses had detectable presence of human fecal matter in their residential soils and on their doorsteps, respectively. Of the 18 publicly accessible surface waters which were sampled, 50% had detectable amounts of human fecal matter present.

To assess justice and equity components of the theories of change, each case study was contextualized within an equity framework and recommendations are presented regarding the execution of these strategies. Although different theories of change have various broader implications and limitations, the work herein supports the notion that environmental science and engineering can be utilized to address environmental injustices if inclusive and equitable frameworks are used in the research processes.

Non-thermal plasma (NTP) technology is an emerging method to degrade otherwise recalcitrant volatile organic compounds (VOCs) in air. Here, a dielectric barrier discharge (DBD) NTP was used to evaluate the degradation efficiency of several VOCs (toluene, benzene, ethylbenzene, MEK (methyl ethyl ketone), MTBE (methyl-tert-butyl ether) 3-pentanone and n-hexane) under constant experimental conditions (6.6 L/min, 95 and 100 ppm average inlet concentrations). The efficiency with which toluene, ethylbenzene, benzene, MEK, MTBE, 3-pentanone, and n-hexane were removed was 74.03 ± 0.30%, 80.94 ± 0.07%, 57.82 ± 0.06%, 50.00 ± 0.20%, 80.00 ± 1.40%, 76.00 ± 1.4%, and 90.00 ± 0.30 %, respectively, at an inlet concentration 95 ppm, gas flow rate 6.6 L/min, and a specific input energy (SIE) of 350 J/L. The effects of various operating conditions on pollutant removal were investigated. Interestingly, the highest removal efficiencies were observed for compounds that have the highest percentage of hydrogen in the molecular structure.

During treatment of toluene and ethylbenzene, a deposit was formed inside the plasma reactor. This deposit was dark brown in color and gave off an oil-like odor, suggesting the formation of higher-order hydrocarbon compounds. The deposit mass was quantified and the impact of the deposit on the DBD reactor performance was discussed. It was noted that the time required for the deposit to clog the reactor depended on the experimental conditions. The clogging time when treating toluene in dry air conditions was more than 1.5 times greater than under humidified conditions (30% RH), suggesting that attention to the treated air relative humidity is critical. The quantity and structure of the deposits depended on both input VOC molecular structure as well as the experimental conditions. Thus, this study provides recommendations for the current applications of this technology.

Introduction: Municipalities often struggle to build and maintain basic infrastructure for informal slums in urban cities for its most vulnerable populations. One impact of inadequate water and sanitation access is the creation of an environment that breeds water borne pathogens that are the agents of infectious disease. Escherichia coli is a common bacteria found in water, often as an indicator of fecal contamination in the water supply. This study looks at one of the most common diseases found in women that results from E. coli growth, urinary tract infection. Specifically, this study aims to examine and describe factors of water, sanitation, and hygiene that are associated with positive E. coli urine results among women. The study took place in Ahmedabad, Gujarat, one of India's wealthier cities, in which heavy investments have been made in improving slum settlements throughout the rapidly expanding city.

Method: This was a cross-sectional study of 250 women recruited from households in urban Ahmedabad from October to December 2017. To determine positive cases of E. coli urinary tract infection, urine samples were collected from each participant. A commercial laboratory performed the urine analyses using a culture method. The threshold for positive cases was 10,000 CFU/mL or greater for E. coli. To obtain information on the water, sanitation, and hygiene practices, each participant completed a structured survey that included questions on demographics, working environment, reproductive health, sanitation access, family relationships, public toilets and social customs.

Results: Of the 250 participants, 23 (9.2%) were above the 100,000 CFU/mL threshold for E. coli, and therefore defined as a positive case. There were 124 (49.6%) participants who attempted a treat method, such as over the counter medicine or home self-treatments, for feminine health in the last three month. There were three factors that significantly correlated with positive cases. The first was the location of the handwashing facility, which could be either inside or outside of the dwelling. The second factor was antibiotic use in the last three weeks. The third factor was a participant living in a home with a child under the age of 5 years old, who experienced diarrhea.

Conclusion: This study identified a higher point prevalence of positive E. coli urine cultures than what we would want or would have expected for a sample population that all had access to piped water and a toilet inside of the dwelling. There is evidence to suggest that hygiene management around water use has an impact on a woman's susceptibility for E. coli causing infections in the urinary tract. Because half of the participants sought a form of treatment over the last three months for feminine health, a longitudinal study that tracks these women over a three month period, could provide relevant information on the incidence of new infections as well as prolonged urinary tract infections, particularly since multi-drug resistant E. coli infections are on the rise.