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Browsing by Author "Sun, Yewei"

Now showing 1 - 3 of 3
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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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    Mechanistic understanding of the NOB suppression by free ammonia inhibition in continuous flow aerobic granulation bioreactors
    Kent, Timothy R.; Sun, Yewei; An, Zhaohui; Bott, Charles B.; Wang, Zhi-Wu (2019-10)
    A partial nitritation continuous flow reactor (CFR) was operated for eight months demonstrating that partial nitritation granular sludge can remain stable under continuous flow conditions. The ammonia oxidizing bacteria (AOB)-to-nitrite oxidizing bacteria (NOB) activity ratios were determined for a series of granule sizes to understand the impact of mass diffusion limitation on the free ammonia (FA) inhibition of NOB. When dissolved oxygen (DO) limitation is the only mechanism for NOB suppression, the AOB:NOB ratio was usually found to increase with the granule size. However, the trend is reversed when FA has an inhibitory effect on NOB, as was observed in this study. The decrease in AOB:NOB ratio indicates that smaller granules, e.g. diameter < 150 mu m are preferred for nitrite accumulation when high FA concentration is present, as in the partial nitritation process. The trend was further verified by observing the increase in the apparent inhibition coefficient as granule size increased. Indeed, this study for the first time quantified the effect of diffusion limitation on the apparent inhibition coefficient of NOB in aerobic granules. A mathematical model was then utilized to interpret the observed suppression of NOB and predicted that NOB suppression was only complete at the granule surface. The NOB that did survive in larger granules was forced to dwell within the granule interior, where the AOB growth declines due to DO diffusion limitation. This means FA inhibition can be taken advantage of as an effective means for NOB suppression in small granules or thin biofilms. Further, both FA inhibition and DO limitation were found to be required for the suppression of NOB in mainstream aerobic granules.
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    Metagenomic Analysis of a Continuous-Flow Aerobic Granulation System for Wastewater Treatment
    Gomeiz, Alison T.; Sun, Yewei; Newborn, Aaron; Wang, Zhi-Wu; Angelotti, Bob; Van Aken, Benoit (MDPI, 2023-09-15)
    Aerobic granulation is an emerging process in wastewater treatment that has the potential to accelerate sedimentation of the microbial biomass during secondary treatment. Aerobic granulation has been difficult to achieve in the continuous flow reactors (CFRs) used in modern wastewater treatment plants. Recent research has demonstrated that the alternation of nutrient-abundant (feast) and nutrient-limiting (famine) conditions is able to promote aerobic granulation in a CFR. In this study, we conducted a metagenomic analysis with the objective of characterizing the bacterial composition of the granular biomass developed in three simulated plug flow reactors (PFRs) with different feast-to-famine ratios. Phylogenetic analyses revealed a clear distinction between the bacterial composition of aerobic granules in the pilot simulated PFRs as compared with conventional activated sludge. Larger and denser granules, showing improved sedimentation properties, were observed in the PFR with the longest famine time and were characterized by a greater proportion of bacteria producing abundant extracellular polymeric substances (EPS). Functional metagenomic analysis based on KEGG pathways indicated that the large and dense aerobic granules in the PFR with the longest famine time showed increased functionalities related to secretion systems and quorum sensing, which are characteristics of bacteria in biofilms and aerobic granules. This study contributes to a further understanding of the relationship between aerobic granule morphology and the bacterial composition of the granular biomass.