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Bae, Hyokwan,Paul, Tanusree,Kim, Daeik,Jung, Jin-Young Springer-Verlag 2016 Environmental Earth Sciences Vol.75 No.22
<P>A sequencing batch reactor (SBR) is a suitable system for evaluating an anaerobic ammonium oxidation (ANAMMOX) process. Response surface analysis was employed to optimize the specific ANAMMOX activity (SAA) and evaluate its technical features in a SBR with a range of total nitrogen (TN) concentration as NH4+-N and NO2--N at 1: 1 ratio and an appropriate pH. A partial cubic model adequately fit the response surface with high statistical significance. SAA was optimized at 1.77 mg-N/mg-VSS day with 155.9 mg-N/L TN concentration and pH at 7.34. The inhibition factors of free ammonia, free nitrous acid (FNA), and nitrite gave specific rise to the SAA responses of over 1.4 mg-N/mg-VSS day in square-like boundaries. However, the toxic effect of 2.4 mg-N/L of FNA was identified to induce a drastic decrease at the lowest pH of 5.6. For the most optimized fed-batch mode for ANAMMOX-SBRs, this study found that TN was 100-200 mg/L and pH was 6.5-8, which can become controlling factors for physicochemical reactions at the time of substrate feeding and microbial reacting stages.</P>
Bae, Hyokwan,Park, Jung-Han,Jun, Kwan-Soo,Jung, Jin-Young Marcel Dekker 2011 Journal of Environmental Science and Health. Part Vol.46 No.4
<P>The functional gene of amoA, which produces the 관-subunit of ammonia monooxygenase (AMO), has been analyzed to reveal the microbial community structure of ammonia-oxidizing bacteria (AOB) by culture-independent methods. In this study, the distribution of the amoA gene in 10 wastewater treatment plants (WWTPs) was revealed by the fingerprinting method of terminal restriction fragment length polymorphism (T-RFLP) and comparative sequencing. T-RFLP showed diverse communities of AOB in the modified Ludzack-Ettinger process, in the anaerobic-anoxic-oxic processes, in the hanging biological contactor, and in the sequencing batch reactor. In all of these environments, long solid retention time (SRT) was expected to be the critical factor for maintaining the diverse AOB community structure. Because T-RFLP does not offer sufficient information to confirm the phylogenetic information of AOB, the microbial community structures were analyzed by comparative sequencing for seven samples that were selected by the statistical categorization using principal component analysis (PCA) among 14 samples. The phylogenetic tree of 21 operational taxonomic units (OTUs) among 88 clones obtained in this study revealed that AOB of Nitrosomonas oligotropha and europaea lineages were predominant in WWTPs. Double labeled T-RFLP produced group-specific terminal restriction fragments (T-RFs) representing several groups of AOB and offered advanced resolution comparing with the single labeled T-RFLP.</P>
Bae, Hyokwan,Choi, Minkyu,Chung, Yun-Chul,Lee, Seockheon,Yoo, Young Je Elsevier 2017 Chemical engineering journal Vol.322 No.-
<P><B>Abstract</B></P> <P>A core-shell structured poly(vinyl alcohol)/sodium alginate gel bead was fabricated and the thickness of the outer layer was controlled. Immobilized ammonia-oxidizing bacteria (AOB) and ANAMMOX bacteria in outer and inner parts of the beads, respectively, cooperate to perform single-stage autotrophic nitrogen removal (SANR). As a critical designing factor, oxygen penetration depth according to the oxygen concentration in bulk phase and nitrifying biomass concentration in the outer layer were examined to protect strictly anaerobic ANAMMOX bacteria from oxygen inhibition. Oxygen penetrated up to a depth of 2350±360μm with the lowest nitrifying biomass of 703mg-VSS/L at a dissolved oxygen concentration of 8mg/L. However, a thick shell layer of more than 3mm effectively protected the ANAMMOX bacteria from oxygen inhibition. The applicability of the core-shell structured gel bead for single-stage autotrophic nitrogen removal was validated in batch and continuous modes. A continuous bioreactor with a synthetic ammonia wastewater showed a maximum nitrogen removal efficiency of 80.4±1.20% with a total nitrogen loading rate of 590±12.1g-N/m<SUP>3</SUP>-d. Findings of this study suggest that start-up strategy of SANR using the core-shell structured gel bead can minimize the adaptation period without scarifying the ANAMMOX activity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Interfacial gelling method was applied to fabricate core-shell structured gel beads. </LI> <LI> AOB and ANAMMOX bacteria were immobilized in separate locations. </LI> <LI> AOB protected the ANAMMOX bacteria from oxygen inhibition. </LI> <LI> Single-stage autotrophic nitrogen removal was validated in batch and continuous modes. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Optimization of HPLC-tandem mass spectrometry for chlortetracycline using response surface analysis
Hyokwan Bae,Hee-Suk Jung,Jin-Young Jung 대한환경공학회 2018 Environmental Engineering Research Vol.23 No.3
Chlortetracycline (CTC) is one of the most important compounds in antibiotic production, and its distribution has been widely investigated due to health and ecological concerns. This study presents systematic approach to optimize the high-performance liquid chromatography-tandem mass spectrometry for analyzing CTC in a multiple reaction monitoring mode (479 → 462 m/z). One-factor-at-a-time (OFAT) test with response surface analysis (RSA) was used as optimization strategy. In OFAT tests, the fragmentor voltage, collision energy, and ratio of acetonitrile in the mobile phase were selected as major factors for RSA. The experimental conditions were determined using a composite in cube design (CCD) to maximize the peak area. As a result, the partial cubic model precisely predicted the peak area response with high statistical significance. In the model, the (solvent composition) and (collision energy²) terms were statistically significant at the 0.1 α-level, while the two-way interactions of the independent variables were negligible. By analyzing the model equation, the optimum conditions were derived as 114.9 V, 15.7 eV, and 70.9% for the fragmentor voltage, collision energy, and solvent composition, respectively. The RSA, coupled with the CCD, offered a comprehensive understanding of the peak area that responds to changes in experimental conditions.
Hyokwan Bae,Minkyu Choi 대한환경공학회 2019 Environmental Engineering Research Vol.24 No.3
In this study, a poly(vinyl) alcohol/sodium alginate (PVA/SA) mixture was used to fabricate core-shell structured gel beads for autotrophic single-stage nitrogen removal (ASNR) using aerobic and anaerobic ammonia-oxidizing bacteria (AAOB and AnAOB, respectively). For stable ASNR process, the mechanical strength and oxygen penetration depth of the shell layer entrapping the AAOB are critical properties. The shell layer was constructed by an interfacial gelling reaction yielding thickness in the range of 2.01-3.63 ㎜, and a high PVA concentration of 12.5% resulted in the best mechanical strength of the shell layer. It was found that oxygen penetrated the shell layer at different depths depending on the PVA concentration, oxygen concentration in the bulk phase, and free ammonia concentration. The oxygen penetration depth was around 1,000 ㎛ when 8.0 ㎎/L dissolved oxygen was supplied from the bulk phase. This study reveals that the shell layer effectively protects the AnAOB from oxygen inhibition under the aerobic conditions because of the respiratory activity of the AAOB.
배효관 ( Hyokwan Bae ),( Tanusree Paul ),정진영 ( Jin-young Jung ) 한국물환경학회(구 한국수질보전학회) 2020 한국물환경학회지 Vol.36 No.3
Anaerobic ammonium oxidation (AMX) is a cost-efficient biological nitrogen removal process. The coexistence of ammonia-oxidizing bacteria (AOB) in an AMX reactor is an interesting research topic as a nitrogen-related bacterial consortium. In this study, a sequencing batch reactor for AMX (AMX-SBR) was operated with a conventional activated sludge. The AOB in an AMX bioreactor were identified and quantified using terminal restriction fragment length polymorphism (T-RFLP) and real-time qPCR. A T-RFLP assay based on the ammonia monooxygenase subunit A (amoA) gene sequences showed the presence of Nitrosomonas europaea-like AOB in the AMX-SBR. A phylogenetic tree based on the sequenced amoA gene showed that AOB were affiliated with the Nitrosomonas europaea/mobilis cluster. Throughout the enrichment period, the AOB population was stable with predominant Nitrosomonas europaea-like AOB. Two OTUs of amoA_SBR_JJY_20 (FJ577843) and amoA_SBR_JJY_9 (FJ577849) are similar to the clones from AMX-related environments. Real-time qPCR was used to quantify AOB populations over time. Interestingly, the exponential growth of AOB populations was observed during the substrate inhibition of the AMX bacteria. The specific growth rate of AOB under anaerobic conditions was only 0.111 d-1. The growth property of Nitrosomonas europaea-like AOB may provide fundamental information about the metabolic relationship between the AMX bacteria and AOB.