Browsing by Author "Wang, Zhiwu"

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    Advanced Biofilm and Aerobic Granulation Technologies for Water and Wastewater Treatment
    Sun, Yewei (Virginia Tech, 2020-04-10)
    Attached growth biological processes offer advantages over traditional water purification technologies through high biomass retention, easy sludge-water separation, multiple multispecies synergies in proximity, resilience to shock loading, low space requirements, and reactor operational flexibility. Traditionally, attached growth refers to biofilms that require abiotic carrying media for bacteria to attach and grow on. While biofilms have been broadly applied in wastewater treatment, its potential for potable reuse or stormwater treatment has not been well studied. The treatment trains of pre-ozonation followed by biologically active filtration (ozone- BAF) is an advanced biofilm technology for potable reuse that can generate high-quality potable water at reduced energy and chemical demands by removing pollutant through three different pathways: oxidation, adsorption, and biodegradation. However, these pathways can result in both desirable and undesirable effects, and the mechanism behind it is still unclear. To understand the mechanisms of various pollutant removal, parallel performance comparisons of ozone-BAF treatment trains with spent and regenerated granular activated carbon (GAC), along with a range of pre-oxidant ozone doses were performed. Another common issue of BAF is the headloss buildup during its operation, which has become a significant energy and maintenance burden at many utilities. Thus, a mathematical model was developed to predict BAF headloss buildup in response to organic removal and nitrification. For stormwater treatment, the feasibility of using biofilms for stormwater biological nitrogen removal (BNR) is still largely unknown, as very limited research effort has been dedicated to this aspect. Thus, a mathematical model was developed to evaluate the potential of using BNR techniques for stormwater nitrogen removal. Aerobic granules are an even more advanced attached growth process, which eliminates the need for abiotic carrying media. So far, aerobic granular sludge is only formed in sequential batch reactors but not in a continuous flow system. Therefore, continuous flow aerobic granulation from traditional activated sludge was investigated and, for the first time, successfully achieved in continuous flow plug-flow bioreactors fed with real municipal wastewater. Besides, the role and critical value of an essential operational parameter, feast/famine ratio, for continuous flow aerobic granulation were determined.
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    Advanced Technologies for Resource Recovery and Contaminants Removal from Landfill Leachate
    Iskander, Syeed Md (Virginia Tech, 2019-04-25)
    Landfill leachate contains valuable, recoverable organics, water, and nutrients. This project investigated leachate treatment and resource recovery from landfill leachates by innovative methods such as forward osmosis (FO), bioelectrochemical systems (BES), and advanced oxidation. In this study, a microbial fuel cell (MFC) removed 50-75% of the ammonia from a leachate through the electricity driven movement of ammonium to the cathode chamber followed by air stripping at high pH (> 9). During this process, the MFC system removed 53-64% of the COD, producing a net energy of 0.123 kWh m-3. Similarly, an integrated microbial desalination cell (MDC) in an FO system recovered 11-64% of the ammonia from a leachate; this was affected by current generation and hydraulic retention time in the desalination chamber. The MDC-FO system recovered 51.5% of the water from a raw leachate. This increased to 83.5% when the FO concentrate was desalinated in the MDC and then recirculated through the FO unit. In addition, the project investigated humic acid (HA) recovery from leachate during the synergistic incorporation of FO, HA recovery, and Fenton's oxidation to enhance leachate treatment and to reduce Fenton's reagent requirements. This led to the investigation of harmful disinfection byproducts (DBPs) formation during Fenton's oxidation of landfill leachate. The removal of leachate UV-quenching substances (humic, fulvic, and hydrophilic acids) using an MFC and a chemical oxidant (i.e., sodium percarbonate) with a focus on energy production and cost efficiency were also studied. BES treatment can reduce leachate organics concentrations; lower UV absorbance; recover ammonia; and, in combination with FO, recover water. Although BES is promising, significant work is needed before its use in landfill leachate becomes practical. FO application to leachate treatment must consider the choice of an appropriate draw solute, which should require minimal effort for regeneration. Resources like HA in leachate deserve more attention. Further efforts can focus on purification and application of the recovered products. The emerging issue of DBP formation in leachate treatment also requires attention due to the potential environmental and human health effects. The broader impact of this study is the societal benefit from more sustainable and cost-efficient leachate treatment.
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    Advancing Forward Osmosis for Energy-efficient Wastewater Treatment towards Enhanced Water Reuse and Resource Recovery
    Zou, Shiqiang (Virginia Tech, 2019-05-30)
    Current treatment of wastewater can effectively remove the contaminants; however, the effluent is still not widely reused because of some undesired substances like pathogens and trace organic chemicals. To promote water reuse, membrane-based technologies have emerged as a robust and more efficient alternative to current treatment practice. Among these membrane processes, forward osmosis (FO) utilizes an osmotic pressure gradient across a semi-permeable membrane to reclaim high-quality water. Still, several key challenges remain to be addressed towards broader FO application, including energy-intensive draw regeneration to yield product water and salinity buildup in the feed solution. To bypass energy-intensive draw regeneration, commercial solid fertilizers was utilized as a regeneration-free draw solute (DS), harvesting fresh water towards direct agricultural irrigation. However, using nutrient-rich fertilizers as DS resulted in an elevated reverse solute flux (RSF). This RSF, known as the cross-membrane diffusion of DS to the feed solution, led to deteriorated solute buildup on the feed side, reduced osmotic driving force, increased fouling propensity, and higher operation cost. To effectively mitigate solute buildup while achieving energy-efficient water reclamation, a parallel electrodialysis (ED) device was integrated to FO for DS recovery in the feed solution. The salinity in the feed solution was consistently controlled below 1 mS cm-1 via the hybrid FO-ED system. Considering solute buildup is merely a consequence of RSF, direct control of RSF was further investigated via operational strategy (i.e., an electrolysis-assisted FO) and membrane modification (i.e., surface coating of zwitterion-functionalized carbon nanotubes). Significantly reduced RSF (> 50% reduction) was obtained in both approaches with minor energy/material investment. With two major bottlenecks being properly addressed for energy-efficient water reclamation, FO was further integrated with a microbial electrolysis cell (MEC) to achieve integrated nutrient-energy-water recovery from high-strength wastewater (i.e., the digestor centrate). The abovementioned research projects are among the earliest efforts to address multiple key challenges of FO during practical application, serving as a cornerstone to facilitate the transformation of current water/wastewater treatment plant to resource recovery hub in order to ensure global food-energy-water security.
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    Anammox-based Technologies for Sustainable Mainstream Wastewater Treatment: Process Development, Microbial Ecology and Mathematical Modeling
    Li, Xiaojin (Virginia Tech, 2018-03-08)
    The nitritation-anammox process is an efficient and cost-effective approach for biological nitrogen removal, but its application in treating mainstream wastewater remains a great challenge. The key objectives of this dissertation are to develop nitritation-anammox process to treat wastewater with low-nitrogen strength, understand the fundamental microbiology, and optimize its operation through experimental studies and mathematic modeling. Chapter 2 showed that the nitritation-anammox process has been successfully developed in an upflow membrane-aerated biofilm reactor, where pure oxygen was delivered via gas-permeable membrane module. Chapter 3 demonstrated that hybrid anaerobic reactor (HAR) could be an effective pretreatment method to provide a relatively low COD/N ratio for nitritation-anammox reactor. In Chapter 4, a novel mathematical model has been proposed to evaluate the minimum DO requirement for the nitritation-anammox reactor to achieve the maximum TN removal under various COD/N scenarios (controlled by HRTHAR). Chapters 5 and 6 designed an OsAMX system by linking nitritation-anammox to forward osmosis to remove the reverse-fluxed ammonium while using ammonium bicarbonate as a draw solute. The microbial community structures and dynamics, spatial distributions in these bioreactors were characterized by high-throughput sequencing and fluorescent in situ hybridization techniques. The studies in this dissertation have demonstrated that nitritation-anammox process is a promising alternative for sustainable mainstream treatment with the appropriate pretreatment approach and operation optimization.
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    Carbon-efficient Wastewater Treatment Through Resource Recovery, Process Intensification, and Partial Denitrification Anammox
    Wang, Jiefu (Virginia Tech, 2024-05-28)
    Facing the pressure of population growth and global warming, this dissertation provided an array of innovative carbon-efficient wastewater treatment technologies for resource recovery, process intensification, and anammox featured next generation biological nutrient removal (BNR) technologies. These technologies aim to supplant traditional carbon-intensive treatment processes with more sustainable alternatives. To this end, the dissertation first comprehensively reviewed what resources can be recovered from wastewater, and how these valuable resources can contribute to the carbon neutrality in water resource reclamation facilities (WRRFs) and help achieve sustainable society development. Then, the effect of mixed liquor recycle (MLR) configurations on the process intensification through continuous-flow aerobic granulation was explored in plug flow reactors. The results demonstrated that MLR configuration could hinder the sludge granulation, but the hindrance could be alleviated to some extent by its location change. In order to eliminate the energy consuming MLR, endogenous denitrification was taken advantage through a synergistic integration with partial nitrification, partial denitrification anammox (PdNA), and enhanced biological phosphorus removal (EBPR). This idea was tested in a pilot setup treating real primary effluent under highly variable influent conditions and low temperatures. The results showcased substantial carbon savings while meeting the stringent effluent requirements. To take a deeper dive into the PdNA performance and the underlying mechanisms, two parallel pilot-scale moving bed biofilm reactor (MBBR) treatment trains fed with methanol and glycerol, respectively, were operated in a local WRRF. Their efficacies in achieving stringent nutrient removal targets and carbon savings were compared. The impacts of operational conditions on the mechanisms and performance were elucidated. In the culmination of this dissertation, a sidestream process intensification and resource recovery technique, namely thermal hydrolysis pretreatment (THP) enhanced anaerobic digestion (AD), was experimented to compare the efficiencies between thermophilic and mesophilic AD when integrated with THP. To sum up, this dissertation not only advanced our understanding of carbon-efficient wastewater treatment processes but also laid the groundwork for their practical implementation, contributing to the global effort towards sustainability.
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    Challege and Opportunities of Membrane Bioelctrochemical Reactors for Wastewater Treatment
    Li, Jian (Virginia Tech, 2016-04-26)
    Microbial fuel cells (MFCs) are potentially advantageous as an energy-efficient approach for wastewater treatment. Integrating membrane filtration with MFCs could be a viable option for advanced wastewater treatment with a low energy input. Such an integration is termed as membrane bioelectrochemical reactors (MBERs). Comparing to the conventional membrane bioreactors or anaerobic membrane bioreactors, MBER could be a competitive technology, due to the its advantages on energy consumption and nutrients removal. By installing the membrane in the cathodic compartment or applying granular activated carbon as fluidized bed materials, membrane fouling issue could be alleviated significantly. In order to drive MBER technology to become a more versatile platform, applying anion exchange membrane (AEM) could be an option for nutrients removal in MBERs. Wastewater can be reclaimed and reused for subsequent fermentation use after a series MFC-MBR treatment process. Such a synergistic configuration not only provide a solution for sustainable wastewater treatment, but also save water and chemical usage from other non-renewable resource. Integrating membrane process with microbial fuel cells through an external configuration provides another solution on sustainable wastewater treatment through a minimal maintenance requirement.
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    Characterizing Kinetic Shifts in Nitrifying, Denitrifying, and Phosphorus Removing Biomass Adapting to Low DO
    Kisling, Tyler Houston (Virginia Tech, 2022-11-03)
    Low dissolved oxygen (DO) biological nutrient removal (BNR) is becoming a viable option to improve the energy efficiency of BNR. To properly model and design BNR processes for low DO operation, it is critical to fully understand how nitrifier, denitrifier, and polyphosphate accumulating organism (PAO) oxygen kinetics adapt in a shift from traditional DO operation (2 mg O2/L or more) to low DO operation. Research characterizing how oxygen kinetics shift over time in activated sludge biomass adapting to low DO is limited. Therefore, a method to characterize oxygen kinetics for nitrifiers, denitrifiers, and PAOs simultaneously is lacking. Here a method was developed to simultaneously measure the oxygen kinetics of nitrifiers, denitrifiers, and PAOs. This method, termed the SND and P-Uptake Oxygen Kinetics test, was able to estimate the ammonia oxidizing bacteria (AOB) oxygen half-saturation coefficient, ammonia maximum removal rate, denitrifier oxygen inhibition coefficient, total inorganic nitrogen (TIN) maximum removal rate, PAO oxygen half-saturation coefficient, phosphorus maximum uptake rate, and a simultaneous nitrification and denitrification (SND) optimum operation point. Three tests were conducted on the Virginia Initiative Plant (VIP) BNR Activated Sludge Pilot while it was operating at a process DO of 2 mg O2/L, and one test while it was operating at 1.5 mg O2/L. The measurements among the three initial tests showed high similarity in their parameter estimates. Estimated oxygen half-saturation and oxygen inhibition coefficients were compared to current suggested ranges and were within the expected magnitudes. At 2 mg O2/L, denitrifier oxygen inhibition coefficients and PAO oxygen half-saturation coefficients were estimated to be remarkably low here, under 0.4 and 0.1 mg O2/L, respectively. AOB oxygen half-saturation coefficients were variable here in the range of 0.62 to 2.57 mg O2/L, seeming to vary with available ammonia concentrations. Upon comparison with a previously developed respirometric test for nitrifier oxygen kinetics, termed the Declining DO test, the AOB oxygen half-saturation coefficient from the SND and P-Uptake Oxygen Kinetics test and the Declining DO test, when both were conducted on the VIP BNR Pilot, showed a similar trend. This provided validation for the AOB oxygen kinetics here and the usefulness of the test developed here. Additionally, measuring and plotting AOB and denitrifier oxygen kinetics together produced an intersection point where ammonia removal rates were equal to TIN removal rates. This intersection point was an optimum point for SND during the conditions of the test. This method can be used to characterize and track oxygen kinetic changes in a BNR system adapting from high to low DO.
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    Characterizing the Drivers of Carbon Use in Post-Anoxic Denitrification
    Bauhs, Kayla Terese (Virginia Tech, 2021-07-26)
    Three of Hampton Roads Sanitation District's (HRSD's) conventional activated sludge Water Resource Recovery Facilities (WRRFs) add methanol for post-anoxic denitrification: the Virginia Initiative Plant (VIP), Nansemond Plant (NP), and Army Base (AB). From 2017-2020, VIP averaged 0.49 ± 0.03 lb COD/lb N removed, while NP and AB averaged 1.48 ± 0.06 and 2.11 ± 0.15 lb COD/lb N, respectively. Significant methanol savings at VIP may result from post-anoxic denitrification using internal carbon that was stored in the anaerobic zone. An investigation into the factors affecting internal carbon-driven (internal C) denitrification was done via a series of batch tests. The capacity for internal C denitrification was demonstrated with sludge from all three WRRFs, despite not necessarily being used full-scale. For each WRRF, an increase in these rates correlated to higher phosphorus uptake rates, suggesting a dependence on the PAO population. Shorter aerobic times and more acetate in the anaerobic stage were shown to increase internal C denitrification rates to varying degrees, and this type of denitrification was only observed for bio-P biomass that was also nitrifying. Beyond internal carbon, other denitrification factors explored include moving the methanol dose point further into the anoxic zone, longer post-anoxic residence times, plug-flow conditions, solids residence time (SRT), and anoxic conditions prior to methanol dosing. Contributions from slowly biodegradable COD were minimal. Understanding the conditions that promote denitrification with internal carbon or other carbon sources would be required for effective strategies to achieve methanol savings at NP and AB that would rival those at VIP.
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    A Decision Support System for Indirect Potable Reuse Based on Integrated Modeling
    Lodhi, Adnan Ghaffar (Virginia Tech, 2019-07-01)
    Optimal operation of water reclamation facilities (WRFs) is critical for an indirect potable reuse (IPR) system, especially when the reclaimed water constitutes a major portion of the reservoir's safe yield. It requires timely and informed decision-making in response to the fluctuating operational conditions, e.g., weather patterns, plant performance, water demand, etc. Advanced integrated modeling techniques can be used to develop reliable operational strategies to mitigate future risks associated with water quality without needing high levels of financial investment. The Upper Occoquan Service Authority (UOSA) WRF, located in northern Virginia, discharges nitrified reclaimed water directly into a tributary of the Occoquan Reservoir, one of the major water supply sources for Fairfax County. Among the many operational challenges at UOSA, one is to regulate the nitrate concentration in its reclaimed water based on the denitrifying capacity of the reservoir. This study presents an integrated model that is used to predict future reservoir conditions based on the weather and streamflow forecasts obtained from the Climate Forecast System and the National Water Model. The application captures the dynamic transformations of the pollutant loadings in the streams, withdrawals by the water treatment plant, WRF effluent flows, and plant operations to manage the WRF performance. It provides plant operators with useful feedback for correctly targeting the effluent nitrates using an intelligent process simulator called IViewOps. The platform is powered by URUNME, a new software that fully automates the operation of the reservoir and process models integrating forecasting products, and data sources. URUNME was developed in C#.NET to provide out-of-the-box functionality for model coupling, data storage, analysis, visualization, scenario management, and decision support systems. The software automatically runs the entire integrated model and outputs data on user-friendly dashboards, displaying historical and forecasting trends, on a periodic basis. This decision support system can provide stakeholders with a holistic view for the design, planning, risk assessments, and potential improvements in various components of the water supply chain, not just for the Occoquan but for any reservoir augmentation type IPR system.
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    Development of Integrated Photobioelectrochemical System (IPB): Processes, Modeling and Applications
    Luo, Shuai (Virginia Tech, 2018-04-24)
    Effective wastewater treatment is needed to reduce the water pollution problem. However, massive energy is consumed in wastewater treatment, required to design an innovative system to reduce the energy consumption to solve the energy crisis. Integrated photobioelectrochemical system (IPB) is a powerful system to combine microbial fuel cells (MFCs) and algal bioreactor together. This system has good performance on the organic degradation, removal of nitrogen and phosphorus, and recover the bioenergy via electricity generation and algal harvesting. This dissertation is divided to twelve chapters, about various aspects of the working mechanisms and actual application of IPB. Chapter 1 generally introduces the working mechanisms of MFCs, algal bioreactor, and modeling. Chapter 2 demonstrates the improvement of cathode material to improve the structure and catalytic performance to improve the MFC performance. Chapter 3 describes the process to use microbial electrolysis cell (MEC) to generate biohythane for the energy recovery. Chapters 4 and 5 demonstrate the application of stable isotope probing to study Shewanella oneidensis MR-1 in the MFCs. Chapters 6 to 8 describe the application of models to optimize MFC and IPB system performance. Chapter 9 describes the strategy improvement for the algal harvesting in IPB. Chapter 10 describes the application of scale-up bioelectrochemical systems on the long-term wastewater treatment. Chapter 11 finally concludes the perspectives of IPBs in the wastewater treatment and energy recovery. This dissertation comprehensively introduces IPB systems in the energy recovery and sustainable wastewater treatment in the future.
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    Development of Kinetic Parameterization Methods for Nitrifying Bacteria using Respirometry
    Malin, Kyle George (Virginia Tech, 2022-01-19)
    Understanding how nitrifiers react when exposed to low DO conditions could provide a greater understanding of low DO operations in full-scale biological wastewater treatment. Previous methods to observe nitrifier oxygen kinetics do exist in literature, however they are inefficient and labor intensive. Other more efficient methods require the use of selective inhibitors, which alter the characteristics of the biomass. This study developed a time and labor efficient respirometric method to distinctly measure oxygen half-saturation coefficients for both ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) without the use of selective inhibitors. By eliminating the use of inhibitory substances, representative biomass characteristics were maintained throughout the tests. The developed method, called the declining DO method, consisted of using a high-speed dissolved oxygen (DO) probe to measure relative oxygen uptake rates (OUR) within a batch reactor when varying substrates (ammonia and nitrite) were present in excess within the system. A forward model was developed based on Monod kinetics to simultaneously fit Monod curves to the experimental OUR data. These curves were fit by solving for optimum oxygen kinetic parameters representing endogenous respiration, NOB, and AOB. An inverse model using Markov chain Monte Carlo analysis was applied to the results found in the forward model to provide statistical validation of the proposed respirometric method. A separate method, called the substrate utilization rate test, was conducted in parallel with the declining DO tests to compare and verify oxygen half-saturation coefficient results. Parallel tests were conducted using biomass samples from three different Hampton Roads Sanitation District (HRSD) full-scale facilities. Operating conditions between the three HRSD facilities were considered when performing parallel testing, including averages for DO, solids retention time (SRT), and floc size. Average floc size was found to have a significant effect on the observed oxygen half-saturation values. Observed trends for the KO values estimated using the two methods remained consistent throughout all tests, where KO,NOB was always lower than KO,AOB. The comparison of the two methods highlighted some faults associated with the substrate utilization rate test, which is commonly used in literature to observe nitrifier oxygen kinetics. The declining DO method appeared to be more resistant to potential experimental error and required less than half the time compared to the substrate utilization rate test. The development of the declining DO method without the use of selective inhibitors provided a more time and labor efficient technique for estimating apparent KO values for NOB and AOB without sacrificing biomass characteristics representative of the full-scale treatment process. Biomass samples collected from variable treatment process conditions yielded consistent parallel test results, providing further evidence that the proposed declining DO method can be a robust and reliable technique for distinctly measuring apparent oxygen half-saturation values for NOB and AOB.
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    Development of Transitional Settling Regimen Parameters to Characterize and Optimize Solids-liquid Separation Performance
    Mancell-Egala, Abdul Salim (Virginia Tech, 2016-09-20)
    Novel settling characteristic metrics were developed based on the fundamental mechanisms of coagulation, flocculation, and settling. The settling metrics determined parameters that are essential in monitoring and optimizing the activated sludge process without the need for expensive or specialized equipment. Current settling characteristic measurements that don't require specialized instruments such as sludge volume index (SVI) or initial settling velocity (ISV), have no fundamental basis in solid-liquid separation and only indicate whether settling is good or bad without providing information as to limitations present in a sludge matrix. Furthermore, the emergence of aerobic granulation as a potential pathway to mitigate solid-separation issues further stresses the need for new settling characteristic metrics to enable integration of the new technology with the current infrastructure. The granule or intrinsic aggregate fraction in different types was of sludge was quantified by simulating different surface overflow rates (SOR). The technique named Intrinsic Settling Classes (ISC) was able to separate granules and floc by simulating high SOR values due to the lack of a flocculation time needed for granules. The method had to be performed in a discrete settling environment to characterize a range of flocculation behavior and was able to classify the granular portion of five different types of sludge. ISC was proven to accurately (±2%) determine the granule fraction and discrete particle distribution. The major significance of the test is its ability to show if a system is producing particles that will eventually grow to become granules. This methodology proved to be very valuable in obtaining information as to the granular fraction of sludge and the granular production of a system. Flocculent settling (stokesian) was found to be predominant within ideally operating clarifiers, and the shift to 'slower' hindered settling (non-stokesian) causes both failure and poor effluent quality. Therefore, a new metric for settling characteristics was developed and classified as Limit of Stokesian Settling (LOSS). The technique consisted of determining the total suspended solids (TSS) concentration at which mixed liquor settling characteristics transition from stokesian to non–stokesian settling. An image analytical technique was developed with the aid of MATLAB to identify this transition. The MATLAB tool analyzed RGB images from video, and identified the presence of an interface by a dramatic shift in the Red indices. LOSS data for Secondary activated-sludge systems were analyzed for a period of 60 days at the Blue Plains Advanced Wastewater Treatment Plant. LOSS numbers collected experimentally were validated with the Takacs et al. (1991) settling model. When compared to flux curves with small changes in the sludge concentration matrix, LOSS was found to be faster at characterizing the hindered settling velocity and was less erratic. Simple batch experiments based on the critical settling velocity (CSV) selection were used as the basis for the development of two novel parameters: threshold of flocculation/flocculation limitation (TOF/a), and floc strength. TOF quantified the minimum solids concentration needed to form large flocs and was directly linked to collision efficiency. In hybrid systems, an exponential fitting on a CSV matrix was proposed to quantify the collision efficiency of flocs (a). Shear studies were conducted to quantify floc strength. The methods were applied to a wide spectrum of sludge types to show the broad applicability and sensitivity of the novel methods. Three different activated sludge systems from the Blue Plains AWWTP were monitored for a 1 year period to explore the relationship between effluent suspended solids (ESS) and activated sludge settling and flocculation behavior. Novel metrics based on the transitional solids concentration (TOF, and LOSS) were also collected weekly. A pilot clarifier and settling column were run and filmed to determine floc morphological properties. SVI was found to lose sensitivity (r < 0.20) when characterizing ISV above a hindered settling rate of 3 m h-1. ISV and LOSS had a strong correlation (r = 0.71), but ISV was subject to change, depending on the solids concentration. Two sludge matrix limitations influencing ESS were characterized by transition concentrations; pinpoint floc formation, and loose floc formation. Pinpoint flocs had TOF values above 400 mg TSS L-1; loose floc formation sludge had TOF and LOSS values below 400 mg TSS L-1 and 900 mg TSS L-1, respectively. TOF was found to correlate with the particle size distribution while LOSS correlated to the settling velocity distribution. The use of both TOF and LOSS is a quick and effective way to characterize limitations affecting ESS.
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    Diffuser Fouling Mitigation, Wastewater Characteristics And Treatment Technology impact on Aeration Efficiency
    Odize, Victory Oghenerabome (Virginia Tech, 2018-04-18)
    Achieving energy neutrality has shifted focus towards aeration systems optimization, due to the high energy consumption of aeration processes in modern advanced wastewater treatment plants. The activated sludge wastewater treatment process is dependent on aeration efficiency which supplies the oxygen needed in the treatment process. The process is a complex heterogeneous mixture of microorganisms, bacteria, particles, colloids, natural organic matter, polymers and cations with varying densities, shapes and sizes. These activated sludge parameters have different impacts on aeration efficiency defined by the OTE, % and alpha. Oxygen transfer efficiency (OTE) is the mass of oxygen transferred into the liquid from the mass of air or oxygen supplied, and is expressed as a percentage (%). OTE is the actual operating efficiency of an aeration system. The alpha Factor (α) is the ratio of standard oxygen transfer efficiency at process conditions (αSOTE) to standard oxygen transfer efficiency of clean water (SOTE). It is also referred to as the ratio of process water volumetric mass transfer coefficient to clean water volumetric mass transfer coefficient. The alpha factor accounts for wastewater contaminants (i.e. soap and detergent) which have an adverse effect on oxygen transfer efficiency. Understanding their different impacts and how different treatment technologies affect aeration efficiency will help to optimize and improve aeration efficiency so as to reduce plant operating costs. A pilot scale study of fine pore diffuser fouling and mitigation, quantified by dynamic wet pressure (DWP), oxygen transfer efficiency and alpha measurement were performed at Blue Plains, Washington DC. In the study a mechanical cleaning method, reverse flexing (RF), was used to treat two diffusers (RF1, RF2) to mitigate fouling, while two diffusers were kept as a control with no reverse flexing. A 45 % increase in DWP of the control diffuser after 17 month of operation was observed, an indication of fouling. RF treated diffusers (RF1 and RF2) did not show any significant increase in DWP, and in comparison to the control diffuser prevented a 35 % increase in DWP. Hence, the RF fouling mitigation technique potentially saved blower energy consumption by reducing the pressure burden on the air blower and the blower energy requirement. However, no significant impact of the RF fouling mitigation treatment technique in preventing a decrease in alpha-fouling (𝝰F) of the fine pore diffusers over time of operation was observed. This was because either the RF treatment method maintained wide pore openings after cleaning over time, or a dominant effect of other wastewater characteristics such as the surfactant concentration or particulate COD could have interfered with OTE. Further studies on the impact of wastewater characteristics (i.e., surfactants and particulate COD) and operating conditions on OTE and alpha were carried out in another series of pilot and batch scale tests. In this study, the influence of different wastewater matrices (treatment phases) on oxygen transfer efficiency (OTE) and alpha using full-scale studies at the Blue Plains Treatment Plant was investigated. A strong relationship between the wastewater matrices with oxygen transfer characteristics was established, and as expected increased alphas were observed for the cleanest wastewater matrices (i.e., with highest effluent quality). There was a 46 % increase in alpha as the total COD and surfactant concentrations decreased from 303 to 24 mgCOD/L and 12 to 0.3 mg/L measured as sodium dodecyl sulphate (SDS) in the nitrification/denitrification effluent with respect to the raw influent. The alpha improvement with respect to the decrease in COD and surfactant concentration suggested the impact of one or more of the wastewater characteristics on OTE and alpha. Batch testing conducted to characterize the mechanistic impact of the wastewater contaminants present in the different wastewater matrices found that the major contaminants influencing OTE and alpha were surfactants and particulate/colloidal material. The volumetric mass transfer coefficient (kLa) measurements from the test also identified surfactant and colloidal COD as the major wastewater contaminants present in the influent and chemically enhanced primary treatment (CEPT) effluent wastewaters impacting OTE and alpha. Soluble COD was observed to potentially improve OTE and alpha due to its contribution in enhancing the oxygen uptake rate (OUR). Although the indirect positive impact of OUR on alpha observed in this study contradicts some other studies, it shows the need for further investigation of OUR impacts on oxygen transfer. Importantly, the mechanistic characterization and quantitative correlation between wastewater contaminants and aeration efficiency found in this study will help to minimize overdesign with respect to aeration system specification, energy wastage, and hence the cost of operation. This study therefore shows new tools as well as the identification of critical factors impacting OTE and alpha in addition to diffuser fouling. Gas transfer depression caused by surfactants when they accumulate at the gas-liquid interface during the activated sludge wastewater treatment process reduces oxygen mass transfer rates, OTE and alpha which increases energy cost. In order to address the adverse effect of surfactants on OTE and alpha, another study was designed to evaluate 4 different wastewater secondary treatment strategies/technologies that enhances surfactant removal through enhanced biosorption and biodegradation, and to also determine their effect on oxygen transfer and alpha. A series of pilot and batch scale tests were conducted to compare and correlate surfactant removal efficiency and alpha for a) conventional high-rate activated sludge (HRAS), b) optimized HRAS with contactor-stabilization technology (HRAS-CS), c) optimized HRAS bioaugmented (Bioaug) with nitrification sludge (Nit S) and d) optimized bioaugmented HRAS with an anaerobic selector phase technology (An-S) reactor system configuration. The treatment technologies showed surfactant percentage removals of 37, 45, 61 and 87 %, and alphas of 0.37 ±0.01, 0.42 ±0.02, 0.44 ±0.01 and 0.60 ±0.02 for conventional HRAS, HRAS-CS, Bioaug and the An-S reactor system configuration, respectively. The optimized bioaugmented anaerobic selector phase technology showed the highest increased surfactant removal (135 %) through enhanced surfactant biosorption and biodegradation under anaerobic conditions, which also complemented the highest increased alpha (62 %) achieved when compared to the conventional HRAS. This study showed that the optimized bioaugmented anaerobic selector phase reactor system configuration is a promising technology or strategy to minimize the surfactant effects on alpha during the secondary aeration treatment stage
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    Effect of Process Intensification Techniques on Biosolids Management
    Zhang, Dian (Virginia Tech, 2020-04-10)
    This study is aimed to provide comprehensive evaluation and mechanistic understanding of the impact of process intensification techniques applied in main and side stream wastewater treatment on biosolids management in terms of anaerobic digestion enhancement, dewaterability improvement, odor mitigation, as well as phosphorus and nitrogen removal. The first part of this study was conducted to understand the effect of anaerobic digester solids retention time (SRT) on odor emission from biosolids. A kinetic model and inhibitory studies showed the emission of methanethiol (MT), a representative odor compound, was primarily determined by the dynamic concurrence of MT production from amino acid and utilization by methanogens in the course of anaerobic digestion. MT emission pattern follows a bell-shape curve with SRT in anaerobic digesters. However, for digested and dewatered biosolids, SRT ranging from 15 to 50 days in anaerobic digesters demonstrated insignificant effect on the odor emission from biosolids. In contrast, the peak odor emission was found to exponentially increase with both shear intensity and polymer dose applied during dewatering. The second part of this study investigated the impact of process intensification practices on sludge dewatering performance. The integration of high-rate activated sludge process and anaerobic digestion elevated the sludge orthophosphate level, leading to struvite scaling and dewaterability deterioration. Superior orthophosphate removal, significant improvement of sludge dewaterability, and favorable economics were achieved through sludge conditioning by cerium chloride. Continuous flow aerobic granulation technology offered significant process intensification of mainstream treatment trains. However, its impact on biosolids management was not studied. This study showed that there was little dewaterability difference between aerobic granular sludge and activated sludge when polymer was not added. However, about 75% polymer saving and improved dewatering performance were observed with polymer addition. When subjected to high shear, a greater dewaterability deterioration was observed for granular sludge than activated sludge. The last part of this study is focused on the impact of anaerobic digestion process intensification through thermal treatment including pre-pasteurization, thermophilic anaerobic digestion, temperature phased anaerobic digestion, and thermal hydrolysis pretreatment. Improved methane production, pathogen reduction, dewatering performance, and odor mitigation were observed with the involvement of these high-temperature processes. However, special cautions and measure should be taken during the start-up of these high rate processes as they are more liable to digester souring. In addition, the in-depth understanding of the mechanism of recalcitrant dissolved organic nitrogen formation during sludge thermal pretreatment was provided.
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    Evaluation of Digital PCR (dPCR) for the Quantification of Soil Nitrogen Turnover Bacteria in Wetland Mesocosms in Response to Season, Fertilization, and Plant Species Richness
    Shah, Parita Raj (Virginia Tech, 2019-02-11)
    Excess nutrients from nonpoint sources are an ongoing problem that is expected to worsen as population and fertilizer usage rise. Conventional centralized treatment systems are not well suited to address nonpoint source pollution. More distributed best management practices (BMPs) like constructed wetlands are a promising alternative and have been widely implemented in the US since the 1970's. Constructed wetlands are multi-functional systems that can effectively store and transform harmful contaminants using primarily natural processes. However, the removal of pollutants like nitrogen by wetlands is highly variable, likely due to a combination of factors such as plant species-specific assimilation behavior, the effects of plant communities on microbial diversity and function, and variable nitrogen inputs. In this study, the effect of plant species richness (i.e., number of plant species in a system) and seasonal nutrient loading (i.e., nitrogen fertilization) on the microbial community responsible for regulating nitrogen turnover in wetland mesocosm soils was investigated. The chip-based QuantStudio 3D digital PCR (QS3D dPCR) system was used to quantify ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), comammox, anammox, and denitrifiers. Principal component analysis (PCA) was used to identify dominant patterns in the microbial community and nitrogen species. Resampling-based analysis of variance (ANOVA) was used to assess statistical significance of any observed differences caused by nitrogen fertilization or plant species richness. Results indicated that fertilization or season, which was convolved with fertilization, was the dominant factor influencing the microbial community in the study environment (27% variance explained), as indicated by the disparate clustering of fall (fertilized) and spring (unfertilized) samples about principal component 1 (fall: negative PC1, spring: positive PC1). Because unplanted unfertilized controls sampled in November clustered within the season in which they were collected rather than with other unfertilized samples collected in May, season may have influenced microbial community shifts more than fertilization for unplanted systems. This finding should be interpreted cautiously, however, given the small number of unplanted unfertilized controls (N = 2) and the absence of similar controls in the planted systems. The most abundant bacterial groups detected in May (November) were AOB, nirK, anammox, and Nitrospira spp. NOB (AOB, anammox, Nitrospira spp. NOB, and nosZ). The effects of plant species richness were more nuanced, with greater richness significantly impacting the abundance of only a subset of bacterial groups (i.e., the nitrifying bacteria AOB, Nitrospira spp. NOB, and comammox, but not the denitrifying bacteria). Different relationships between richness and microbial abundance were observed in different seasonal nutrient loadings (i.e., interaction effects between richness and fertilization were detected for some bacterial groups).
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    Exploring Forward Osmosis Systems for Recovery of Nutrients and Water
    Wu, Zhenyu (Virginia Tech, 2018-01-19)
    Livestock wastewater contains a large amount of nutrients that are available for recovery. In this study, a proof of concept process based on forward osmosis (FO) was proposed and investigated for in-situ formation of struvite from digested swine wastewater. This FO system took advantage of a drawback reverse solute flux (RSF) and used the reversed-fluxed Mg^{2+} for struvite precipitation, thereby accomplishing recovery of both water and nutrient. With 0.5 M MgCl2 as a draw solution, high purity struvite formed spontaneously in the feed solution and the water flux through the FO membrane reached 3.12 LMH. The precipitated struvite was characterized and exhibited a similar composition to that of commercial struvite. The FO system achieve >50% water recovery, >99% phosphate recovery (given sufficient magnesium supply), and >93% ammonium nitrogen removal from the digested swine wastewater. The recovered products (both struvite and water) could potentially generate a value of 1.35 $ m^{-3}. The results of this study have demonstrated the feasibility of nutrient recovery from livestock wastewater facilitated by FO treatment.
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    Feasibility of using Waste Heat as a power source to operate Microbial Electrolysis Cells towards Resource Recovery
    Jain, Akshay (Virginia Tech, 2020-05-05)
    Wastewater treatment has developed as a mature technology over time. However, conventional wastewater treatment is a very energy-intensive process. Bioelectrochemical system (BES) is an emerging technology that can treat wastewater and also recover resources such as energy in the form of electricity/hydrogen gas and nutrients such as nitrogen and phosphorus compounds. Microbial electrolysis cell (MEC) is a type of BES that, in the presence of an additional voltage, can treat wastewater and generate hydrogen gas. This is a promising approach for wastewater treatment and value-added product generation, though it may not be sustainable in the long run, as it relies on fossil fuels to provide that additional energy. Thus, it is important to explore alternative renewable resources that can provide energy to power MEC. Waste heat is one such resource that has not been researched extensively, particularly at the low-temperature spectrum. This was utilized as a renewable resource by converting waste heat to electricity using a device called thermoelectric generator (TEG). TEG converted simulated waste heat from an anaerobic digester to power an MEC. The feasibility of TEG to act as a power source for an MEC was investigated and its performance compared to the external power source. Various cold sources were analyzed to characterize TEG performance. To explore this integrated TEG-MEC system further, a hydraulic connection was added between the two systems. Wastewater was used as a cold source for TEG and it was recirculated to the anode of the MEC. This system showed improved performance with both systems mutually benefitting each other. The operational parameters were analyzed for the optimization of the system. The integrated system could generate hydrogen at a rate of 0.36 ± 0.05 m3 m-3 d-1 for synthetic domestic wastewater treatment. For the practical application, it is necessary to estimate the cost and narrow the focus on the functions of the system. Techno-economic analysis was performed for MEC with cost estimation and net present value model to understand the economic viability of the technology. The application niche of the BES was described and directions for addressing the challenges towards a full-scale operation were discussed. The present system provides a sustainable method for wastewater treatment and resource recovery which can play an important role in human health, social and economic development and a strong ecosystem.
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    Gravity selector-enabled kenaf recirculation and reuse as a renewable ballasting agent for sludge settleability enhancement in a municipal wastewater secondary process: A real wastewater pilot-scale study
    Roy, Pranta (Virginia Tech, 2025-01-14)
    Sludge densification can be achieved through granulation/densification, migrating carriers, ballasted flocculation, or a combination of these approaches. Hydrocyclone-enabled continuous flow densification has been applied for full-scale applications; however, it requires long startup times and, in some instances, results in poor stability of the densified floc. Migrating carriers hold promise to offset these disadvantages for continuous flow processes where reasonable feast-famine or plug flow conditions cannot be achieved while drawing on the strength of hydrocyclones to retain and return the ballasting agent. This idea was tested by dosing kenaf, a plant-based renewable migrating carrier in a pilot-scale plug flow reactor equipped with a gravity selector to mimic a hydrocyclone. Results showed that kenaf could gradually reduce the sludge volume index from 170 to 50 mL/g and increase zone settling velocity from 2.5 to 7 m/h over 110 days without compromising treatment performance. Because of the selective retention of the inert plant-based carrier represented as a volatile solid in the gravity selector underflow, a traditional SRT calculation based on mixed liquor volatile suspended solids tended to overestimate daily Waste Activated Sludge (WAS) requirements and resulted in active sludge inventory loss. An oxygen utilization rate-based method was developed and verified for easy SRT correction to avoid kenaf interference with the sludge wasting protocol. Denser kenaf incorporated into the sludge matrix during flocculant settling contributed to the settleability improvements. However, a lack of biofilm formation on the kenaf surface was observed even after 110 days of treatment is intriguing and different from other studies. Challenges with initial kenaf floating and interference with conventional SRT calculations were two significant lessons learned from this study, and countermeasures were provided accordingly. It was concluded that kenaf could work in synergy with gravimetric ballast separation, such as with a hydrocylone, for quick and sustainable sludge settleability improvements.
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    Intensification of Biological Nutrient Removal Processes
    Klaus, Stephanie Anne (Virginia Tech, 2019-10-29)
    Intensification refers to utilizing wastewater treatment processes that decrease chemical and energy demands, increase energy recovery, and reduce the process footprint (or increased capacity in an existing footprint) all while providing the same level of nutrient removal as traditional methods. Shortcut nitrogen removal processes; including nitrite shunt, partial nitritation/anammox, and partial denitrification/anammox, as well as low-carbon biological phosphorus removal, were critically-evaluated in this study with an overall objective of intensification of existing infrastructure. At the beginning of this study, granular sidestream deammonification was becoming well-established in Europe, but there was virtually no experience with startup or operation of these processes in North America. The experience gained from optimization of the sidestream deammonification moving bed biofilm reactor (MBBR) in this study, including the novel pH-based aeration control strategy, has influenced the startup procedure and operation of subsequent full-scale installations in the United States and around the world. Long startup time remains a barrier to the implementation of sidestream deammonification processes, but this study was the first to show the benefits of utilizing media with an existing nitrifying biofilm to speed up anammox bacteria colonization. Utilizing media with an established biofilm from a mature integrated fixed film activated sludge (IFAS) process resulted in at least five times greater anammox activity rates in one month than virgin media without a preliminary biofilm. This concept has not been testing yet in a full-scale startup, but has the potential to drastically reduce startup time. False dissolved oxygen readings were observed in batch scale denitrification tests, and it was determined that nitric oxide was interfering with optical DO sensors, a problem of which the sensor manufacturers were not aware. This led to at least one sensor manufacturer reevaluating their sensor design and several laboratories and full-scale process installations were able to understand their observed false DO readings. There is an industry-wide trend to utilize influent carbon more efficiently and realize the benefits of mainstream shortcut nitrogen removal. The A/B pilot at the HRSD Chesapeake Elizabeth Treatment provides a unique chance to study these strategies in a continuous flow system with real wastewater. For the first time, it was demonstrated that the presence of influent particulate COD can lead to higher competition for nitrite by heterotrophic denitrifying bacteria, resulting in nitrite oxidizing bacteria (NOB) out-selection. TIN removal was affected by both the type and amount of influent COD, with particulate COD (pCOD) having a stronger influence than soluble COD (sCOD). Based on these findings, an innovative approach to achieving energy efficient biological nitrogen removal was suggested, in which influent carbon fractions are tailored to control specific ammonia and nitrite oxidation rates and thereby achieve energy efficiency in the nitrogen removal goals downstream. Intermittent and continuous aeration strategies were explored for more conventional BNR processes. The effect of influent carbon fractionation on TIN removal was again considered, this time in the context of simultaneous nitrification/denitrification during continuous aeration. It was concluded that intermittent aeration was able to achieve equal or higher TIN removal than continuous aeration at shorter SRTs, whether or not the goal is nitrite shunt. It is sometimes assumed that converting to continuous aeration ammonia-based aeration control (ABAC) or ammonia vs. NOx (AvN) control will result in an additional nitrogen removal simply by reducing the DO setpoint resulting in simultaneous nitrification/denitrification (SND). This work demonstrated that lower DO did not always improve TIN removal and most importantly that aeration control alone cannot guarantee SND. It was concluded that although lower DO is necessary to achieve SND, there also needs to be sufficient carbon available for denitrification. While the implementation of full-scale sidestream anammox happened rather quickly, the implementation of anammox in the mainstream has not followed, without any known full-scale implementations. This is almost certainly because maintaining reliable mainstream NOB out-selection seems to be an insurmountable obstacle to full-scale implementation. Partial denitrification/anammox was proven to be easier to maintain than partial nitritation/anammox and still provides significant aeration and carbon savings compared to traditional nitrification/denitrification. There is a long-standing interest in combining shortcut nitrogen removal with biological phosphorus removal, without much success. In this study, biological phosphorus removal was achieved in an A/B process with A-stage WAS fermentation and shortcut nitrogen removal in B-stage via partial denitrification.
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    Mechanistic understanding of biogranulation for continuous flow wastewater treatment and organic waste valorization
    An, Zhaohui (Virginia Tech, 2022-04-20)
    Aerobic granular sludge has been regarded as a promising alternative to the conventional activated sludge which has been used for a century in that granular sludge offers advantages in high biomass retention, fast sludge-water separation, and small footprint requirement. However, this technology has been rarely applied in continuous flow reactors (CFRs) which are the most common type of bioreactors used in water resource recovery facilities across the world. Hence, the overarching goal of this study is to provide advanced understanding of biogranulation mechanism to enable industrial application of this technology. The lack of long-term stability study in CFRs has restricted its full-scale acceptability. The high settling velocity-based selection pressure has been regarded as the ultimate driving force towards biogranulation in sequential batch reactors (SBRs). In this study, this physical selection pressure was firstly weakened and then eliminated in CFRs to investigate its role in maintaining the long-term structural stability of aerobic granules. Given the fact that implementing settling velocity-based selection pressure only can cultivate biogranules in SBRs but not in completely stirred tank reactors (CSTRs), the essential role of feast/famine conditions was investigated. Seventeen sets of data collected from both literature and this study were analyzed to develop a general understanding of the granulation mechanisms. The outcome indicated that granulation is more sensitive to the feast/famine conditions than to the settling velocity-based selection pressure. The theory was tested in a CFR with 10-CSTR chambers connected in series to provide feast/famine conditions followed by a physical selector separating the slow-settling bioflocs and fast-settling biogranules into feast and famine zones, respectively. Along with successful biogranulation, the startup performance interruption problem inherent in SBRs was also resolved in this innovative design because the sludge loss due to physical washout selection was mitigated by returning bioflocs to the famine zone. Then, a cost-effective engineering strategy was put forward to promote the full-scale application of this advanced technology. With this generalized biogranulation theory, pure culture biogranules with desired functions for high value-added bioproducts were also investigated and achieved for the first time in this study, which paves a new avenue to harnessing granulation technology for intensifying waste valorization bioprocesses.