RESUMO
Interfacial Gibbs free energy (IGFE) as a thermodynamic indicator characterize the stability of the natural system. For aerobic granular sludge (AGS), how IGFE determines the stability of sludge remains to be determined. The Gibbs free energy change at the AGS-water interface (ΔGswa) and AGS interfaces (ΔGsc) were selected as the main interfacial thermodynamic factors. Results indicated that the stable AGS was guaranteed with ΔGsc at the range of -31 to - 46 J m-2. Pearson correlation coefficients between ΔGswa/ ΔGsc and relative hydrophobicity, water content, SVI30, integrity coefficient were -0.9, 0.8, 0.85, and 0.84, which illustrated that the IGFE could be a more comprehensive thermodynamic indicator. Microbial community and EPS analysis verified the importance of denitrifiers, Amide III, protein-like substances for AGS stability. This work offers a new insight into the development of AGS stability based on IGFE.
Assuntos
Matriz Extracelular de Substâncias Poliméricas , Esgotos , Aerobiose , Reatores Biológicos , Eliminação de Resíduos LíquidosRESUMO
Aerobic granular sludge (AGS) has excellent performance in wastewater treatment. However, the formation and mechanism of AGS by effluent reflux are not fully understood in sequential batch reactors (SBRs). In this study, two reactors were constructed, among which R1 was the control group, and the R2 reactor refluxed one-fourth of the supernatant of the effluent to the influent water. In the reactor of R2, the granules had better COD and TN removal efficiencies and resistance to external shocks, and AGS produced more extracellular polymeric substances (EPS). Analysis of microbial community indicated that AHLs-mediated microbes, denitrifying microbes, and EPS producers were enriched. At the same time, the correlation between 3OC6-HSL, C8-HSL, C12-HSL and PN was 0.89*, 0.94** and 0.92* respectively, the possible mechanism of enhanced granulation was mainly the promotion of AHLs by effluent reflux. Therefore, the effluent reflux strategy could be an innovative and sustainable strategy that validates the function of AHLs-mediated QS to accelerate aerobic sludge granulation and maintain its structural stability.
Assuntos
Microbiota , Esgotos , Acil-Butirolactonas , Reatores Biológicos , Percepção de QuorumRESUMO
Aerobic granular sludge (AGS) technology has been widely studied as "The Next Generation Wastewater Treatment technology". The effect of hydraulic conditions on the structural stability of AGS has been widely studied. However, the function of flow regime on the AGS stability, especially dissolved oxygen (DO) mass transfer, is still unknown. In this study, we used the Reynolds number (Re) to quantify the flow regime and selected different stages of AGS as experimental subjects. Results showed that the relatively suitable Re (Re = 150) could create lower DO mass transfer limitation (Lc = 27.4 µm) and increase protein (PN) contents and the abundance of hydrophobic functional groups in AGS. At this condition (Re = 150), the interfacial Gibbs free energy of sludge-water (ΔGLSa) was at a lower state (-129.75 ± 2.15 mJ·m-2), which favored the stability of AGS. Principal component analysis (PCA) and correlation analysis indicated that the response of ΔGLSa was affected by Lc, PN, and hydrophobic groups. In addition, results obtained for unstable AGS further verified that suitable Re regulates the structural stability of AGS. This study deepens the understanding of Re as an important hydraulic parameter for structural stability of AGS, which is also of great significance for energy saving of sequential batch reactors (SBRs) with agitation in practical engineering.
Assuntos
Esgotos , Eliminação de Resíduos Líquidos , Humanos , Esgotos/química , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias , Reatores Biológicos , Aerobiose , Termodinâmica , Proteínas , Oxigênio , ÁguaRESUMO
BACKGROUND: Vietnam is experiencing a growing burden of cancer, including among people living with HIV. Stigma acts as a sociocultural barrier to the prevention and treatment of both conditions. This study investigates how cultural notions of "respected personhood" (or "what matters most") influence manifestations of HIV-related stigma and cancer stigma in Hanoi, Vietnam. METHODS: Thirty in-depth interviews were conducted with people living with HIV in Hanoi, Vietnam. Transcripts were thematically coded via a directed content analysis using the What Matters Most conceptual framework. Coding was done individually and discussed in pairs, and any discrepancies were reconciled in full-team meetings. RESULTS: Analyses elucidated that having chu tín-a value reflecting social involvement, conscientiousness, and trustworthiness-and being successful (eg, in career, academics, or one's personal life) are characteristics of respected people in this local cultural context. Living with HIV and having cancer were seen as stigmatized and interfering with these values and capabilities. Intersectional stigma toward having both conditions was seen to interplay with these values in some ways that had distinctions compared with stigma toward either condition alone. Participants also articulated how cultural values like chu tín are broadly protective against stigmatization and how getting treatment and maintaining employment can help individuals resist stigmatization's most acute impacts. CONCLUSIONS: HIV-related and cancer stigma each interfere with important cultural values and capabilities in Vietnam. Understanding these cultural manifestations of these stigmas separately and intersectionally can allow for greater ability to measure and respond to these stigmas through culturally tailored intervention.
Assuntos
Infecções por HIV , Neoplasias , Estigma Social , Humanos , Vietnã/epidemiologia , Infecções por HIV/psicologia , Infecções por HIV/epidemiologia , Masculino , Feminino , Neoplasias/psicologia , Neoplasias/terapia , Adulto , Pessoa de Meia-Idade , Pesquisa QualitativaRESUMO
Efficient substrate metabolism is the premise for stable operation of aerobic granular sludge and can be regulated by quorum sensing (QS). In this study, starch and acetate were selected to represent complex and simple substrates to provide comparable amount of metabolic energy for granules cultivation. Starch-fed granules were larger in size and contained higher EPS content than acetate-fed granules, though both granules exhibited similar substrate-degradation rates during sequencing batch reactor (SBR) cycle. Three N-acylhomoserine lactones (AHLs), including C8-HSL, 3OHC8-HSL and 3OHC12-HSL, were detected as dominant autoinducers in granules. They accumulated more in starch-fed granules than acetate-fed granules. The batch experiments were implemented to investigate QS regulation for granular stability in terms of substrate hydrolysis and transformation. The addition of three AHLs increased the activity of α-amylase, the main starch hydrolase, 4-6 times, significantly (p < 0.01) higher than the control treatment without AHLs amendment. While activity of dehydrogenase, the main simple substrate degradation enzyme, was increased only 1-2 times. Higher enzyme activity, especially α-amylase, significantly (p < 0.05) promoted the substrate-degradation rate (65 % than control group) and EPS yield in starch-fed system. Overall, QS can facilitate complex substrate uptake via hydrolysis enhancement and EPS secretion, which together promote sludge granulation and stability.
Assuntos
Acil-Butirolactonas , Homosserina , Esgotos , alfa-Amilases , AmidoRESUMO
Calcification of anaerobic granular sludge causing the decrease of microbial activity has been focused for several decades, but the mechanism of calcification and deactivation of calcified granule are still lacking. In this study, the calcification process of anaerobic granular sludge was analyzed in the UASB reactor with long-term exposure to a high calcium level of 2 gCa2+L-1. Greyish-white calcified granules with larger size and density first appeared at the bottom of sludge bed. Characterization of granular surface demonstrated that calcified granules had smaller specific surface area and pore volume with the disappearing channels in granules visualized over calcification. The coverage of calcite on granular surface with a thickness of 500-600 µm was observed by a microscope, which is responsible for the blockage of channels for substrate diffusion and transport. The evaluation of mass transfer showed that the 'effectiveness factor' η of calcified granules was higher than 1.23, proving the existence of mass transfer resistance. Furthermore, the interactions between calcium and extracellular polymeric substances (EPS) revealed the possible mechanism of calcite location at the outer layer of anaerobic granular sludge: The bulk calcite directly binds the EPS such as humic acids via charging functional groups, and bulk CO32- could react easily with Ca2+ bound to EPS according to thermodynamic analysis.
Assuntos
Esgotos , Eliminação de Resíduos Líquidos , Anaerobiose , Reatores Biológicos , CálcioRESUMO
According to the relationship among microbial activity, quorum sensing (QS) and structural stability of aerobic granular sludge, the mechanism of QS regulation for microbial activity and granular stability was investigated in AGS process. Results showed that ATP content decreased sharply from 1.8⯵mol/gVSS of stable granules to 0.8⯵mol/gVSS of disintegrating granules, and the relative abundance of QS-activity microbes, Rhodobacter spp. and Xanthomonadaceae decreased in initially unstable granules compared with stable granules. The main AHLs were detected in this study, and C8-HSL, 3OHC8-HSL and 3OHC12-HSL decreased significantly when structure of granules changed from stability to disintegration. Accompanying with the decrease of AHLs level, the extracellular polymeric substances (EPS) content in initially unstable granules decreased sharply from 226.8 to 163.6â¯mg/gVSS with the ratio of extracellular protein to exopolysaccharide (PN/PS) decreasing from 3.6 to 2.2, despite EPS-secretion microbes enriched. The effect of QS on microbial activity was proved by AHL add-back study, results indicated that ATP and EPS content in sludge increased significantly (pâ¯<â¯0.05) with AHLs added, but EPS production was limited when ATP synthesis was disrupted. It was concluded that the AHLs-based QS favored the granular stability via the enhancement of ATP synthesis in microbes. This study provides a new perspective for QS regulation in aerobic granular sludge system, because the ATP regulated by QS could be the energy currency for cellular metabolism, such as nutrient removal, degradation of emerging pollutants, microbial growth and other aspects.