Potential Role of the Anammoxosome in the Adaptation of Anammox Bacteria to Salinity Stress.

The underlying adaptative mechanisms of anammox bacteria to salt stress are still unclear. The potential role of the anammoxosome in modulating material and energy metabolism in response to salinity stress was investigated in this study. The results showed that anammox bacteria increased membrane fluidity and decreased mechanical properties by shortening the ladderane fatty acid chain length of anammoxosome in response to salinity shock, which led to the breakdown of the proton motive force driving ATP synthesis and retarded energy metabolism activity. Afterward, the fatty acid chain length and membrane properties were recovered to enhance the energy metabolic activity. The relative transmission electron microscopy (TEM) area proportion of anammoxosome decreased from 55.9 to 38.9% under salinity stress. The 3D imaging of the anammox bacteria based on Synchrotron soft X-ray tomography showed that the reduction in the relative volume proportion of the anammoxosome and the concave surfaces was induced by salinity stress, which led to the lower energy expenditure of the material transportation and provided more binding sites for enzymes. Therefore, anammox bacteria can modulate nitrogen and energy metabolism by changing the membrane properties and morphology of the anammoxosome in response to salinity stress. This study broadens the response mechanism of anammox bacteria to salinity stress.

The recovery potential and utilization pathway of chemical energy from wastewater pollutants during wastewater treatment in China.

Research on the potential for chemical energy recovery and the optimization of recovery pathways in different regions of China is still lacking. This study aimed to address this gap by evaluating the potential and optimize the utilization pathways for chemical energy recovery in various regions of China for achieving sustainable wastewater treatment. The results showed that the eastern and northeastern regions of China exhibited higher chemical energy levels under the existing operating conditions. Key factors affecting chemical energy recovery included chemical oxygen demand removal (ΔCOD), treatment scale, and specific energy consumption (µ) of wastewater treatment plants (WWTPs). Furthermore, the average improvement in the chemical energy recovery rate with an optimized utilization pathway was approximately 40% in the WWTPs. The use of the net-zero energy consumption (NZE) model proved effective in improving the chemical energy recovery potential, with an average reduction of greenhouse gas (GHG) emissions reaching next to 95% in the investigated WWTPs.

Effects of physiologic activities of plankton on CO2 flux in the Three Gorges Reservoir after rainfall during algal blooms.

The nutrient supply to the freshwater system may be changed by rainfall, which also encourages the cyclic succession of microorganisms. However, in a highly dynamic land-water reservoir, the microbial metabolic changes brought on by the changes of water nutrients following rainfall are not clearly documented. The study selected the Three Gorges Reservoir (TGR) backwater region during algal bloom seasons as the study area and time, and used the Biolog-EcoPlates technique to examine the heterotrophic metabolism conditions of the water before and after rain. The field monitoring assessed how biotic and abiotic variables affected CO2 flux at the water-air interface. The tests conducted in the laboratory investigated the water-integrated metabolic process was affected by post-rainfall environmental changes. The results showed that the average flux of CO2 at the water-air interface before rainfall was -489.17 ± 506.66 mg·(m2·d)-1, while the average CO2 flux reached 393.35 ± 793.49 mg·(m2·d)-1 after rainfall. This is mostly explained by the heterotrophic metabolic variability of plankton in response to changes in the aqueous environment brought on by precipitation. These discoveries help us better understand how biological metabolisms after rain affect the CO2 flux at the water-air interface and reservoir greenhouse gas (GHG) emission equivalents can be evaluated more accurately.

The acceleration of aerobic sludge granulation by alternating organic loading rate: Performance and mechanism.

As a highly promising treatment technology for wastewater, long start-up time is one of the bottlenecks hindering the widespread application of aerobic granular sludge (AGS). This study focused on exploring the possibility of alternating organic loading rate (OLR) in promoting AGS granulation. Under alternating OLR (3.6-14.4 kgCOD/m3·d), AGS granulation was significantly accelerated. The mean granule size under alternating load reached 234.6 µm at 17 d, while under constant OLR (7.2 kgCOD/m3·d), the mean granule size was only 179.2 µm. Moreover, the granule size maintained continuous growth even when the alternating OLR was changed to constant OLR. Alternating load significantly increased the content of extracellular polymeric substances (EPS), especially proteins (PN) in tightly bound EPS (TB-EPS), which was likely the main reason for accelerating AGS granulation. Moreover, alternating load reduced the hydrophilicity of EPS and promoted the content of proteins secondary structures that favored aggregation in TB-EPS, which were also beneficial for granulation. Microbial community results showed that alternating load might promote the enrichment of EPS producing bacteria, such as Thauera, Brevundimonas and Shinella. Meanwhile, the content of enzymes that regulated amino acids metabolism also increased under alternating load, which might be related to the increase of PN in EPS. These results further demonstrated that alternating load promoted granulation through EPS.

The GHG mitigation opportunity of sludge management in China.

Greenhouse gas (GHG) mitigation in wastewater treatment sector is indispensable in China's carbon neutral target. As an important component of wastewater system, sludge generation is rapidly increased with the acceleration of urbanization in China. It is crucial to investigate the carbon footprint of various sludge management strategies and quantify the potential optimization of GHG reduction effect at national scale. Therefore, this study conducted a comprehensive analysis of sludge distribution and GHG profiles of various sludge systems. The overall dry sludge generation in China is 12.15 Mt, with spatial resolution at city level. Different sludge treatment options were categorized into four types: energy recovery, nutrient recovery (e.g. phosphorus and nitrogen), material valorisation (e.g. brick, biochar) and conventional disposal. With various sludge treatment options, the GHG profile of annual sludge management in China ranges from -35.86 Mt/year to 57.11 Mt/year. The best GHG mitigation can be achieved through energy recovery by co-incineration system and the greatest reduction opportunity is concentrated in highly urbanized regions, such as Yangtze River Delta, Pearl River Delta, and Beijing-Tianjin-Hebei urban agglomerations.

Adaptation mechanism of aerobic denitrifier Enterobacter cloacae strain HNR to short-term ZnO nanoparticle stresses.

The adaptation mechanism of a wild type (WT) and resistant type (Re) strain of the aerobic denitrifier Enterobacter cloacae strain HNR to short-term ZnO nanoparticle (NP) stresses was investigated. The results showed that Re maintained higher nitrite reductase (NIR) and nitrate reductase (NR) activities and showed lower increment of reactive oxygen species (ROS) than WT, under ZnO NP stresses. The affinity constant (KA) of WT to Zn2+ was 5.06 times that of Re, indicating that Re was more repulsive to Zn2+ released by ZnO NPs. Transcriptomic analysis revealed that the up-regulation of the nitrogen metabolism of Re helped maintain NIR and NR activities, that the enhancement of purine metabolism lowered the intracellular ROS increment, and that the up-regulation of cationic antimicrobial peptide resistance contributed to the lower KA of Re to Zn2+. These findings provided new insights into the adaptation mechanism of aerobic denitrifying bacteria to ZnO NPs.

Quantitative three-dimensional nondestructive imaging of whole anaerobic ammonium-oxidizing bacteria.

Anaerobic ammonium-oxidizing (anammox) bacteria play a key role in the global nitrogen cycle and in nitrogenous wastewater treatment. The anammox bacteria ultrastructure is unique and distinctly different from that of other prokaryotic cells. The morphological structure of an organism is related to its function; however, research on the ultrastructure of intact anammox bacteria is lacking. In this study, in situ three-dimensional nondestructive ultrastructure imaging of a whole anammox cell was performed using synchrotron soft X-ray tomography (SXT) and the total variation-based simultaneous algebraic reconstruction technique (TV-SART). Statistical and quantitative analyses of the intact anammox bacteria were performed. High soft X-ray absorption composition inside anammoxosome was detected and verified to be relevant to iron-binding protein. On this basis, the shape adaptation of the anammox bacteria response to iron was explored.

Characterization of an aerobic denitrifier Enterobacter cloacae strain HNR and its nitrate reductase gene.

Enterobacter cloacae strain HNR was found to grow well and denitrify aerobically at high NO3--N concentrations. When the concentrations of NO3--N were 200, 300 and 500 mg/L, the removal efficiencies of NO3--N were 83%, 74.5% and 75%, respectively. More importantly, the intermediates accumulation of NO2--N and NH4+-N was not obvious during the aerobic denitrification processes, resulting in a high TN removal of 82%, 74% and 70%, respectively. Meanwhile, strain HNR also presented the ability of heterotrophic nitrification. With initial NH4+-N concentrations of 20 and 80 mg/L, the NH4+-N removal efficiency reached 78% and 76%, respectively. The key nitrate reductase enzyme gene relating to denitrification was successfully amplified by polymerase chain reaction (PCR) from strain HNR, and identified it as napA, which encodings the large catalytic subunit A of periplasmic nitrate reductase (NAPA). The sequence analysis of napA indicates that NAPA is a hydrophilic, non-transmembrane protein. The existence of napA might be crucial for strain HNR to denitrify nitrate under aerobic conditions. This study showed prospect to develop novel technology for nitrogen removal by application of E. cloacae strain HNR.

New insights into nitrous oxide emissions in a single-stage CANON process coupled with denitrification: thermodynamics and nitrogen transformation.

The dynamic characteristics of N2O emissions and nitrogen transformation in a sequencing batch biofilm reactor (SBBR) using the completely autotrophic nitrogen removal over nitrite (CANON) process coupled with denitrification were investigated via 15N isotope tracing and thermodynamic analysis. The results indicate that the Gibbs free energy (ΔG) values of N2O production by the nitrifier denitrification and heterotrophic denitrification reactions were greater than that of NH2OH oxidation, indicating that N2O was easier to produce via either nitrifier and heterotrophic denitrification than via NH2OH oxidation. Ammonia-oxidizing bacteria (AOB) denitrification exhibited a higher fs 0 (the fraction of electron-donor electrons utilized for cell synthesis) than NH2OH oxidation. Therefore, AOB preferred the denitrification pathway because of its growth advantage when N2O was produced by the AOB. The N2O emissions by hydroxylamine oxidation, AOB denitrification and heterotrophic denitrification in the SBBRs using different C/N ratios account for 5.4-7.6%, 45.2-60.8% and 33.8-47.2% of the N2O produced, respectively. The total N2O emission with C/N ratios of 0, 0.67 and 1 was 228.04, 205.57 and 190.4 µg N2O-N·g-1VSS, respectively. The certain carbon sources aid in the reduction of N2O emissions in the process.

Role of extracellular polymeric substances in biofilm formation by Pseudomonas stutzeri strain XL-2.

Pseudomonas stutzeri strain XL-2 exhibited significant performance on biofilm formation. Extracellular polymeric substances (EPS) secreted by strain XL-2 were characterized by colorimetry and Fourier transform infrared (FT-IR) spectroscopy. The biofilm growth showed a strong positive correlation (rP=0.96, P<0.01) to extracellular protein content, but no correlation to exopolysaccharide content. Hydrolyzing the biofilm with proteinase K caused a significant decrease in biofilm growth (t=3.7, P<0.05), whereas the changes in biofilm growth were not significant when the biofilm was hydrolyzed by α-amylase and ß-amylase, implying that proteins rather than polysaccharides played the dominant role in biofilm formation. More specifically, confocal laser scanning microscopy (CLSM) revealed that the extracellular proteins were tightly bound to the cells, resulting in the cells with EPS presenting more biofilm promotion protein secondary structures, such as three-turn helices, ß-sheet, and α-helices, than cells without EPS. Both bio-assays and quantitative analysis demonstrated that strain XL-2 produced signal molecules of N-acylhomoserine lactones (AHLs) during biofilm formation process. The concentrations of C6-HLS and C6-oxo-HLS were both significantly positively correlated with protein contents (P<0.05). Dosing exogenous C6-HLS and C6-oxo-HLS also resulted in the increase in protein content. Therefore, it was speculated that C6-HLS and C6-oxo-HLS released by strain XL-2 could up-regulate the secretion of proteins in EPS, and thus promote the formation of biofilm.

Underlying mechanisms of ANAMMOX bacteria adaptation to salinity stress.

Dealing with nitrogen-rich saline wastewater produced by industries remains challenging because of the inhibition of functional microorganisms by high salinity. The underlying mechanisms of anaerobic ammonium-oxidizing bacteria (AnAOB) exposed to salinity stress should be studied to investigate the potential of anaerobic ammonium oxidation (ANAMMOX) for applications in such wastewater. In this study, the total DNA from granular sludge was extracted from an expanded granular sludge bed (EGSB) reactor operated at 0, 15 and 30 g/L salinity and subjected to high-throughput sequencing. The nitrogen removal performance in the reactor could be maintained from 86.2 to 88.0% at less than 30 g/L salinity level. The microbial diversity in the reactor under saline conditions was lower than that under the salt-free condition. Three genera of AnAOB were detected in the reactor, and Candidatus Kuenenia was the most abundant. The predictive functional profiling based on the Clusters of Orthologous Groups of proteins (COGs) database showed that the inhibition of AnAOB under saline conditions was mainly characterised by the weakening of energy metabolism and intracellular repair. AnAOB might adapt to salinity stress by increasing their rigidity and intracellular osmotic pressure. The predictive functional profiling based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database revealed that the inhibition of AnAOB was mainly manifested by the weakening of intracellular carbohydrate and lipid metabolism, the blockage of intracellular energy supply and the reduction of membrane transport capacity. AnAOB might adapt to salinity stress by strengthening wall/membrane synthesis, essential cofactors (porphyrins) and energy productivity, enhancing intracellular material transformation and gene repair and changing its structure and group behaviour. The stability of the nitrogen removal performance could be maintained via the adaptation of AnAOB to salinity and their increased abundance.

Dynamic Dispersal of Surface Layer Biofilm Induced by Nanosized TiO2 Based on Surface Plasmon Resonance and Waveguide.

Pollutant degradation is present mainly in the surface layer of biofilms, and the surface layer is the most vulnerable to impairment by toxic pollutants. In this work, the effects of nanosized TiO2 (n-TiO2) on the average thicknesses of Bacillus subtilis biofilm and on bacterial attachment on different surfaces were investigated. The binding mechanism of n-TiO2 to the cell surface was also probed. The results revealed that n-TiO2 caused biofilm dispersal and the thicknesses decreased by 2.0 to 2.6 µm after several hours of exposure. The attachment abilities of bacteria with extracellular polymeric substances (EPS) on hydrophilic surfaces were significantly reduced by 31% and 81% under 10 and 100 mg/liter of n-TiO2, respectively, whereas those of bacteria without EPS were significantly reduced by 43% and 87%, respectively. The attachment abilities of bacteria with and without EPS on hydrophobic surfaces were significantly reduced by 50% and 56%, respectively, under 100 mg/liter of n-TiO2 The results demonstrated that biofilm dispersal can be attributed to the changes in the cell surface structure and the reduction of microbial attachment ability.IMPORTANCE Nanoparticles can penetrate into the outer layer of biofilm in a relatively short period and can bind onto EPS and bacterial surfaces. The current work probed the effects of nanosized TiO2 (n-TiO2) on biofilm thickness, bacterial migration, and surface properties of the cell in the early stage using the surface plasmon resonance waveguide mode. The results demonstrated that n-TiO2 decreased the adhesive ability of both cell and EPS and induced bacterial migration and biofilm detachment in several hours. The decreased adhesive ability of microbes and EPS worked against microbial aggregation, reducing the effluent quality in the biological wastewater treatment process.

Auto-aggregation properties of a novel aerobic denitrifier Enterobacter sp. strain FL.

Enterobacter sp. strain FL was newly isolated from activated sludge and exhibited significant capability of auto-aggregation as well as aerobic denitrification. The removal efficiencies of NO3--N, total nitrogen (TN), and TOC by strain FL in batch culture reached 94.6, 63.9, and 72.5% in 24 h, respectively. The production of N2O and N2 in the presence of oxygen demonstrated the occurrence of aerobic denitrification. The auto-aggregation index of strain FL reached 54.3%, suggesting a high tendency that the cells would agglomerate into aggregates. The production of extracellular polymeric substances (EPSs), which were mainly composed of proteins followed by polysaccharides, was considered to be related to the cell aggregation according to Fourier transform infrared (FT-IR) and confocal laser scanning microscopy (CLSM). The proteins in EPS were evenly and tightly combined to cells and altered the protein secondary structures of cell surface from random coils to ß-sheets and three-turn helices. The alteration of protein secondary structures of cell surface caused by the proteins in EPS might play a dominant role in the auto-aggregation of strain FL. To further assess the feasibility of strain FL for synthetic wastewater treatment, a sequencing batch reactor (SBR), solely inoculated with strain FL, was conducted. During the 16 running cycles, the removal efficiency of NO3--N was 90.2-99.7% and the auto-aggregation index was stabilized at 35.0-41.5%. The EPS promoted the biomass of strain FL to aggregate in the SBR.

Net-Zero-Energy Model for Sustainable Wastewater Treatment.

A large external energy input prevents wastewater treatment from being environmentally sustainable. A net-zero-energy (NZE) wastewater treatment concept based on biomass energy recycling was proposed to avoid wasting resources and to promote energy recycling in wastewater treatment plants (WWTPs). Simultaneously, a theoretical model and boundary condition based on energy balance were established to evaluate the feasibility of achieving NZE in WWTPs; the model and condition were employed to analyze data from 20 conventional WWTPs in China. A total of six WWTPs can currently export excess energy, eight WWTPs can achieve 100% energy self-sufficiency by adjusting the metabolic material allocation, and six municipal WWTPs cannot achieve net-zero energy consumption based on the evaluation of the theoretical model. The NZE model offset 79.5% of the electricity and sludge disposal cost compared with conventional wastewater treatment. The NZE model provides a theoretical basis for the optimization of material regulation for the effective utilization of organic energy from wastewater and promotes engineering applications of the NZE concept in WWTPs.

[Analysis of Endocrine Disruptor: Triphenyltin Chloride with Raman Spectroscopy].

Triphenyltin Chloride (TPhT) is one of the only two kinds of metal compounds known in the endocrine disruptors. TPhT is widely used in industry, agriculture and transportation fields, which can cause great impact on soil, marine and inland freshwater environment. This experiment collects the Raman signal of TPhT standard powders by applying laser confocal Raman spectroscopy to explore the feasibility of the method and to acquire optimized parameters. In this paper, we combined the application of laser confocal Raman spectroscopy with TPhT physical property. Due to different functional groups of TPhT molecules shows different vibration modes, the Raman spectra was divided into three wavenumber areas(1 500~3 200, 900~1 500 and 100~900 cm-1) to attribute and analyze their assignments of the Raman peaks, obtaining the characteristics of TPhT vibration modes and the corresponding characteristic peaks. Finally, a standard Raman spectra library was established with the spectral range between 100~3 200 cm-1. The results showed that the Raman spectra with high signal-to-noise ratio can be obtained in a short time when the laser power options decayed to 0.5% of the original power (500 mW) after 10s exposure and 2 times integration. Strong Raman signals observed in the Raman spectroscopy at 212, 332, 657, 997 and 1 577 cm-1 could be used as the characteristic peaks of TPhT in Raman detection. Otherwise, the co-occurrence of the Raman peaks at 657 and 997 cm-1 can be considered as the presence of TPhT in complex environmental samples. Experimental results are given to identify the presence of TPhT. The results would be used to identify the presence of TPhT residual in real environmental samples, which provide a theoretical basis and data base on Raman spectroscopy.

Investigation into cyclic utilization of carbon source in an advanced sludge reduction, inorganic solids separation, phosphorus recovery, and enhanced nutrient removal (SIPER) wastewater treatment process.

An advanced wastewater treatment process (SIPER) was developed to simultaneously reduce sludge production, prevent the accumulation of inorganic solids, recover phosphorus, and enhance nutrient removal. The ability to recover organic substance from excess sludge to enhance nutrient removal (especially nitrogen) and its performance as a C-source were evaluated in this study. The chemical oxygen demand/total nitrogen (COD/TN) and volatile fatty acids/total phosphorus (VFA/TP) ratios for the supernatant of the alkaline-treated sludge were 3.1 times and 2.7 times those of the influent, respectively. The biodegradability of the supernatant was much better than that of the influent. The system COD was increased by 91 mg/L, and nitrogen removal was improved by 19.6% (the removal rate for TN reached 80.4%) after the return of the alkaline-treated sludge as an internal C-source. The C-source recovered from the excess sludge was successfully used to enhance nitrogen removal. The internal C-source contributed 24.1% of the total C-source, and the cyclic utilization of the system C-source was achieved by recirculation of alkaline-treated sludge in the sludge reduction, inorganic solids separation, phosphorus recovery (SIPER) process.

Survey and analysis of the current state of residency training in medical-school-affiliated hospitals in China.

BACKGROUND: Since the global standards for postgraduate medical education (PGME) were published in January 2003, they have gained worldwide attention. The current state of residency training programs in medical-school-affiliated hospitals throughout China was assessed in this study. METHODS: Based on the internationally recognized global standards for PGME, residents undergoing residency training at that time and the relevant residency training instructors and management personnel from 15 medical-school-affiliated hospitals throughout China were recruited and surveyed regarding the current state of residency training programs. A total of 938 questionnaire surveys were distributed between June 30, 2006 and July 30, 2006; of 892 surveys collected, 841 were valid. RESULTS: For six items, the total proportions of "basically meets standards" and "completely meets standards" were <70% for the basic standards. These items were identified in the fields of "training settings and educational resources", "evaluation of training process", and "trainees". In all fields other than "continuous updates", the average scores of the western regions were significantly lower than those of the eastern regions for both the basic and target standards. Specifically, the average scores for the basic standards on as many as 25 of the 38 items in the nine fields were significantly lower in the western regions. There were significant differences in the basic standards scores on 13 of the 38 items among trainees, instructors, and managers. CONCLUSIONS: The residency training programs have achieved satisfactory outcomes in the hospitals affiliated with various medical schools in China. However, overall, the programs remain inadequate in certain areas. For the governments, organizations, and institutions responsible for PGME, such global standards for PGME are a very useful self-assessment tool and can help identify problems, promote reform, and ultimately standardize PGME.

The logistic growth of duckweed (Lemna minor) and kinetics of ammonium uptake.

Mathematical models have been developed to describe nitrogen uptake and duckweed growth experimentally to study the kinetics of ammonium uptake under various concentrations. The kinetics of duckweed ammonium uptake was investigated using the modified depletion method after plants were grown for two weeks at different ammonium concentrations (0.5-14 mg/L) in the culture medium. The maximum uptake rate and Michaelis-Menten constant for ammonium were estimated as 0.082 mg/(g fresh weight x h) and 1.877 mg/L, respectively. Duckweed growth was assessed when supplied at different total nitrogen (TN) concentrations (1-5 mg/L) in the culture medium. The results showed that the intrinsic growth rate was from 0.22 to 0.26 d(-1), and TN concentrations had no significant influence on the duckweed growth rate.