RESUMO
Rivers play a significant role in the global nitrous oxide (N2O) budget. However, the microbial sources and sinks of N2O in river systems are not well understood or quantified, resulting in the prolonged neglect of nitrification. This study investigated the isotopic signatures of N2O, thereby quantifying the microbial source of N2O production and the degree of N2O reduction in the Yellow River. Although denitrification has long been considered to be the dominant pathway of N2O production in rivers, our findings indicated that denitrification only accounted for 18.3% (8.2%-43.0%) of the total contribution to N2O production in the Yellow River, with 50.2%-80.2% being concurrently reduced. The denitrification contribution to N2O production (R2 = 0.44, p < 0.01) and N2O reduction degree (R2 = 0.70, p < 0.01) were positively related to the dissolved organic carbon (DOC) content. Similar to urban rivers and eutrophic lakes, denitrification was the primary process responsible for N2O production (43.0%) in certain reaches with high organic content (DOC = 5.29 mg/L). Nevertheless, the denitrification activity was generally constrained by the availability of electron donors (average DOC = 2.51 mg/L) throughout the Yellow River basin. Consequently, nitrification emerged as the primary contributor in the well-oxygenated Yellow River. Additionally, our findings further distinguished the respective contribution of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to N2O emissions. Although AOB dominated the N2O production in the Yellow River, the AOA specie abundance (AOA/(AOA + AOB)) contributed up to 32.6%, which resulted in 25.6% of the total nitrifier-produced N2O, suggesting a significant occurrence of AOA in the oligotrophic Yellow River. Overall, this study provided a non-invasive approach for quantifying the microbial sources and sinks to N2O emissions, and demonstrated the substantial role of nitrification in the large oligotrophic rivers.
Assuntos
Desnitrificação , Monitoramento Ambiental , Nitrificação , Óxido Nitroso , Rios , Óxido Nitroso/análise , Rios/química , China , Poluentes Atmosféricos/análise , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/metabolismo , Bactérias/metabolismoRESUMO
Heterotrophic nitrification-aerobic denitrification (HN-AD) shows innovation potential of wastewater treatment process in a single tank. However, how to enrich HN-AD bacteria in activated sludge to enhance their contribution remained unknown. This study explored the impact of the feast/famine (F/F) ratio on the succession of autotrophic ammonia oxidizing bacteria (AOB) and HN-AD bacteria in a halophilic aerobic granular sludge (HAGS) system. As the F/F ratio decreased from 1/9 to 1/15, the total inorganic nitrogen (TIN) removal performance significantly decreased. The proportion of heterotrophic bacteria was dropped from 79.0 % to 33 %. Accordingly, the relative abundance of Paracoccus decreased from 70.8 % to 25.4 %, and the copy number of the napA gene was reduced from 2.2 × 1010 copies/g HAGS to 8.1 × 109 copies/g HAGS. It found the F/F ratio regulated the population succession of autotrophic AOB and HN-AD bacteria, thereby providing a solution to achieve the enrichment of HN-AD bacteria in HAGS.
Assuntos
Betaproteobacteria , Nitrificação , Águas Residuárias , Esgotos/microbiologia , Desnitrificação , Amônia , Reatores Biológicos , Processos Heterotróficos , Bactérias/genética , Nitrogênio , Oxirredução , AerobioseRESUMO
Nitrogen and phosphate removal from wastewater relies on different functional bacteria. In this study, a novel strain affiliated with Pseudomonas aeruginosa was isolated from activated sludge by gradient dilution and performed heterotrophic nitrification-aerobic denitrification and aerobic phosphate removal (HNADPR). The strain showed an ammonium removal efficiency of 87% and a phosphate removal efficiency of 97% under optimal conditions, such as C/N ratio of 10, P/N ratio of 0.1, temperature of 30°C, and pH of 7.5-8.5. The modified Gompertz model could fit well the heterotrophic ammonium nitrification, aerobic nitrite/nitrate denitrification, and aerobic phosphate removal processes. Functional gene amplification indicated that ammonium removal followed the complete HN-AD pathway (NH4+ â NH2OH â NO2- â NO3- â NO2- â NO â N2O â N2). Phosphate removal only occurred under aerobic conditions and ceased under anaerobic conditions. In successive aerobic cycles, the strain persistently took up phosphate. In wastewater, phosphate was aerobically converted into cell membrane, intracellular and extracellular polymeric substrates (EPS). Phosphorus in the form of phosphate monoester was pooled in EPS. A hypothetic aerobic phosphate removal model for strain SNDPR-01 is proposed to improve our understanding of the novel bacterial function of HNADPR.
Assuntos
Compostos de Amônio , Nitrificação , Aerobiose , Desnitrificação , Processos Heterotróficos , Nitritos/metabolismo , Nitrogênio/metabolismo , Dióxido de Nitrogênio , Fosfatos , Pseudomonas aeruginosa/genética , Pseudomonas aeruginosa/metabolismo , Águas ResiduáriasRESUMO
The utilization of halophilic bioresources is limited due to a lack of isolation and characterization work. A halophilic bacterium strain SND-01 of Exiguobacterium mexicanum was isolated in this study, which is the first report on its novel function in heterotrophic nitrification-aerobic denitrification (HN-AD). The strain SND-01 is slightly halophilic, surviving at 0 up to 9% (w/v) salinity. When utilizing ammonium, nitrate or nitrite as the sole nitrogen source in aerobic conditions, the isolated strain showed the maximum nitrogen removal rate of 2.24 ± 0.14 mg/(L·h), 3.63 ± 0.21 mg/(L·h) and 2.30 ± 0.23 mg/(L·h), respectively. Functional genes and key enzymes involved in heterotrophic-aerobic nitrogen transformations were characterized, establishing the pathway of HN-AD. The nitrogen removal via HN-AD is dependent on the C/N ratio, salinity and temperature. The halophilic Exiguobacterium mexicanum strain SND-01 shows a significant potential in biotreatment of saline wastewater in an easy and cost-effective way.
Assuntos
Compostos de Amônio , Nitrificação , Aerobiose , Desnitrificação , Exiguobacterium , Processos Heterotróficos , Nitritos , Nitrogênio , Águas ResiduáriasRESUMO
Granulation of halophilic activated sludge is an important solution to solve the problem of solid-liquid separation in biological treatment of saline wastewater. This study demonstrated that by adding divalent cations into the saline influent with low organic load, halophilic granular sludge with an average diameter of 910 ± 10 µm can be cultivated. The close correlation between divalent cations and particle size indicated that Ca2+ played a major role in the granulation process. Ca2+ was accumulated in halophilic granular sludge, which provided an inorganic carrier for microbial aggregation and leaded to the dominance of halophilic bacteria of the family Flavobacteriaceae. The halophilic bacteria secreted a large amount of extracellular polymeric substances (EPS), which contained 70.0 ± 0.02% protein. By enhancing the EPS network of protein and Ca2+, halophilic granular sludge was formed. The addition of Mg2+ enhanced the network of Mg2+ and loosely bound EPS, which could be destroyed due to Na+ substitution. This study provides an effective granulation method for halophilic activated sludge.
Assuntos
Esgotos , Águas Residuárias , Reatores Biológicos , Cátions Bivalentes , Matriz Extracelular de Substâncias Poliméricas , Eliminação de Resíduos LíquidosRESUMO
As a solution of the sludge loss in the treatment of saline wastewater, the granulation of halophilic sludge was explored in this study. The inoculated estuarine sediment was granulated to an average diameter of 1155⯱â¯102⯵m under the selective settling pressure in the airlift sequencing batch reactor (SBR) when the influent organic loading rate (OLR) was doubled to 0.36â¯g COD/L·day. The results indicated that the OLR doubled the amount of total extracellular polymeric substance (EPS) and that protein was predominant in the EPS (72.8⯱â¯2.0%). The correlation between aggregate size and protein content was better than that between aggregate size and polysaccharide content. The amount of alginate-like exopolysaccharides (ALE) increased linearly at the mature granular stage, co-occurring with the compact and elastic structure of the granules. According to the results of 16S rRNA high -throughput sequencing, the Shannon-Weaver index of mature granule decreased by >50% compared to the inoculated sediment. Bacteria of Propionibacteriaceae family constituted 34% of the population in granules and were in symbiotic relationship with halophiles of family Rhodocyclaceae, Vibrionaceae, Flavobacteriaceae, and Cryomorphaceae. The aerobic halophilic granular sludge showed COD removal efficiency of 90.9⯱â¯0.8% and ammonia removal efficiency of 72.6⯱â¯4.0% for 30â¯g/L saline wastewater. An average nitrite accumulation ratio of 94.5⯱â¯2.9% was observed during nitrification. Granulation of halophilic sludge provides an effective solution to the saline sludge loss problem, which is a step forward to realize the biological treatment of saline wastewater by halophiles.
Assuntos
Eliminação de Resíduos Líquidos/métodos , Amônia , Bactérias , Reatores Biológicos , Estuários , Matriz Extracelular de Substâncias Poliméricas , Sedimentos Geológicos/química , Nitritos , Nitrogênio , Pressão , Esgotos/química , Águas Residuárias/químicaRESUMO
Chronic pharyngitis is a common disease, which has a long duration and a wide range of onset. It is easy to misdiagnose by mistaking it with other diseases, such as chronic tonsillitis, by using common diagnostic methods. In order to reduce costs and avoid misdiagnosis, the search for an affordable and rapid diagnostic method is becoming more and more important for chronic pharyngitis research. Speech disorder is one of the typical symptoms of patients with chronic pharyngitis. This paper introduces a convolutional neural network model for diagnosis based on the typical symptom of speech disorder. First of all, the voice data is converted into a speech spectrogram, which can better output the speech characteristic information and lay a foundation for computer diagnosis and discrimination. Second, we construct a deep convolutional neural network for the diagnosis of chronic pharyngitis through the design of the structure, the design of the network layer, and the description of the function. Finally, we perform a parameter optimization experiment on the convolutional neural network and judge the recognition efficiency of chronic pharyngitis. The results show that the convolutional neural network has a high recognition rate for patients with chronic pharyngitis and has a good diagnostic effect.