The aim of this study was to investigate the effect of natural organic matter (NOM) including humic acid (HA) and fulvic acid (FA), intracellular organic matter (IOM) extracted from Microcystis ...aeruginosa (MA) and Chlorella sp. (CH), and their different molecular weight (MW) fractions on the aerobic denitrification performance of bacterial strain WGX-9 by monitoring nitrogen removal efficiency and testing changes in organic matter with HA, FA, MA-IOM and CH-IOM as the sole carbon source. Strain WGX-9 was identified as Acinetobacter johnsonii and exhibited excellent aerobic denitrification capability. The nitrate removal efficiency with IOM as the sole carbon source was relatively higher than that with NOM as the sole carbon source. The prepared NOM and extracted IOM samples were separated into six fractions with MW cut-offs of 100, 30, 10, 5 and 1 kDa. The fraction of MW > 100 kDa contributed the largest amount to the MW distribution, accounting for 77.11%, 29.00%, 44.97% and 24.81% of HA, FA, MA-IOM, and CH-IOM, respectively. Nitrate removal efficiency was improved with decreasing MW of organic matter. For example, nitrate removal efficiency was 26.50%, 32.41%, 27.88% and 43.89% using HA, FA, MA-IOM, and CH-IOM fractions of MW > 100 kDa as the carbon source, whereas with MW < 1 kDa, it increased to 36.67%, 37.88%, 60.90%, and 68.90%, respectively. This is probably because the smaller MW fraction is more suitable for bacterial growth. These results demonstrate that the strain WGX-9 can utilize lower MW organic matter, which lays the foundations for nitrogen removal in actual drinking water reservoirs.
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•Acinetobacter johnsonii WGX-9 has excellent aerobic denitrification performance.•IOM as carbon source show higher nitrate removal relative to NOM, but lower than sodium acetate.•The nitrate removal efficiency was improved with the MW of organic matter decrease.•The tyrosine/tryptophan-like organic matter are preferentially used by microorganisms.
Fungi in aquatic environments received more attention recently; therefore, the characteristics of inactivation of fungal spores by widely used disinfectants are quite important. Nonetheless, the ...inactivation efficacy of fungal spores by chlorine dioxide is poorly known. In this study, the effectiveness of chlorine dioxide at inactivation of three dominant genera of fungal spores isolated from drinking groundwater and the effects of pH, temperature, chlorine dioxide concentration, and humic acid were evaluated. The inactivation mechanisms were explored by analyzing the leakage of intracellular substances, the increase in extracellular adenosine triphosphate (ATP), deoxyribonucleic acid (DNA), and proteins as well as the changes in spore morphology. The kinetics of inactivation by chlorine dioxide fitted the Chick-Watson model, and different fungal species showed different resistance to chlorine dioxide inactivation, which was in the following order: Cladosporium sp.>Trichoderma sp. >Penicillium sp., which are much more resistant than Escherichia coli. Regarding the three genera of fungal spores used in this study, chlorine dioxide was more effective at inactivation of fungal spores than chlorine. The effect of disinfectant concentration and temperature was positive, and the impact of pH levels (6.0 and 7.0) was insignificant, whereas the influence of water matrices on the inactivation efficiency was negative. The increased concentration of characteristic extracellular substances and changes of spore morphology were observed after inactivation with chlorine dioxide and were due to cell wall and cell membrane damage in fungal spores, causing the leakage of intracellular substances and death of a fungal spore.
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•The inactivation kinetic of chlorine dioxide fits Chick-Watson model.•The resistance to chlorine dioxide is in order: Cladosporium sp.>Trichoderma sp.>Penicillium sp.>E. coli.•Chlorine dioxide is more effective in inactivation of fungal spores than chlorine.•Chlorine dioxide inactivates fungi by damaging the cell wall and cell membrane of fungal spores.
The mechanism and factors influencing nitrogen loss in the Zhoucun reservoir were explored during the spring. The results showed that the nitrate and total nitrogen concentration decreased from ...1.84 ± 0.01 mg/L and 2.34 ± 0.06 mg/L to 0.06 ± 0.01 mg/L and 0.48 ± 0.09 mg/L, respectively. Meanwhile, the nitrate and total nitrogen removal rate reached 97.02% ± 0.25 and 79.38% ± 3.32, respectively. Moreover, the abundance of nirS gene and aerobic denitrification bacteria increased from 1.04–3.38 × 103 copies/mL and 0.71 ± 0.22 × 102 cfu/mL to 5.36–5.81 × 103 copies/mL and 8.64 ± 2.08 × 103 cfu/mL, respectively. The low MW fractions of DOM (<5 kDa) increased from 0.94 ± 0.02 mg/L in February to 1.51 ± 0.09 mg/L in April. E3/E4 and absorption spectral slope ratio (SR) showed that fulvic acid accounted for the main proportion with autochthonous characteristics. These findings were consistent with the fluorescence components and fluorescence characteristic indices based on EEM-PARAFAC. Meanwhile, the microbial metabolism activity increased significantly from February to April, which contributed to the cycle of nutrients within the reservoir water system. Moreover, the abundance of the bacterial species involved in denitrification (Exiguobacterium, Brevundimonas, Deinococcus, Paracoccus, and Pseudomonas) increased significantly. The relative abundance of KOs related to nitrogen metabolism, were initially increased and then decreased. Specifically, K02567 (napA) represented the main proportion of KOs related to denitrification. The abundance of napA-type denitrifying bacteria (Dechloromonas, Pseudomonas, Azospira, Rhodopseudomonas, Aeromonas, Zobellella, Sulfuritalea, Bradyrhizobium, Achromobacter, Enterobacter, Thauera, and Magnetospirillum) increased significantly during the period of nitrogen loss. Furthermore, the levels of nitrate, T, DO, and AWCD were the most important factors affecting the N-functional bacteria composition. The systematic investigation of the nitrogen loss would provide a theoretical foundation for the remediation of the water reservoir via aerobic denitrification in the future.
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•Microbial aerobic denitrification dominates nitrogen loss of water column in the spring.•The abundance of nirS and aerobic denitrification bacteria increased obviously.•The abundance of N-functional bacteria and napA-type denitrification bacteria both exhibited obvious increase process.
•ZnO@ZIF-8 nanorods were synthesized by a simple self-template method.•A bifunctional electrochemistry platform was constructed based on ZnO@ZIF-8 and.•IL composite film.•The NO2−and immunoassay ...human IgG biosensors exhibited good performance.
The strategy of bifunctional electrochemistry platform based on heterogeneous composite ZnO@ZIF-8 and ionic liquid (IL) composite film for nitrite (NO2−) and immunoassay human IgG biosensors was proposed. On the one hand, the electrocatalytic ability of myoglobin (Mb) modified electrode (ZnO@ZIF-8/IL/Mb-CPE) to NO2− was studied, and a linear response from 10 to 833μM with a detection limit of 3.5μΜ was achieved. On the other, a label-free immunosensor for the determination of human IgG was proposed using ZnO@ZIF-8/IL composite film as immobilization matrix. The differential pulse voltammetry (DPV) response of the developed immunosensor was found to be proportional to logarithm of human IgG concentrations in the two ranges of 0.1-10 and 10–400ng/mL. The lower detection limit was calculated as 0.03ng/mL. The excellent properties of ZnO@ZIF-8 were attributed to the synergistic effects of ZnO nanorods with good conductivity, biocompatibility and ZIF-8 with high porosity. Meanwhile, IL not only prevented the aggregation of ZnO@ZIF-8 nanorods, but also displayed excellent ability in facilitating the electron transfer. Both biosensors exhibited good selectivity, reproducibility and stability, indicating ZnO@ZIF-8 composite film could be a promising matrix in electrochemical biosensor design.
In drinking water distribution pipeline systems, the tap water quality is regulated by several biotic and abiotic factors, which can threaten the health of consumers. Stagnation is inevitable in the ...water distribution pipeline however, the combined effects of seasonal changes and stagnation on tap water quality are not well understood. Here, we investigated the seasonal variations in the chemical and biological quality of water after overnight stagnation for a period of one year. The results showed that the tap water quality deteriorated after overnight stagnation, with up to a 2.7-fold increase in the total iron concentrations. The total bacterial cell concentrations increased by 59–231% after overnight stagnation. The total cell and cell-bound adenosine triphosphate (ATP) of the stagnant water samples peaked in summer. In addition, Biolog analysis showed that the metabolic activities of microbes were higher in spring. The bacterial community based on Illumina Miseq DNA sequence analysis found that Proteobacteria dominated the drinking water bacterial community. The bacterial community structure varied significantly among different seasons, where the diversity and richness of the community were much higher in spring. Structural equation modeling (SEM) was constructed to determine the correlations between bacterial metabolic functions and the community structure. The redundancy analysis (RDA) indicated that the residual chlorine played a critical role in the construction of the bacterial community. Altogether, the overall findings from the present work provide novel insights into how the quality of tap water quality impacted by the seasonal changes and overnight stagnation.
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•Water quality deteriorated after overnight stagnation.
•Total iron concentration increased 2.7 times after stagnation.
•The highest cell concentration and ATP was observed in the summer season.
•The water bacterial community metabolic activities were highest in the spring.
•Co-interactions of bacterial communities were explored by SEM and networks.
Low pressure membrane (LPM) filtration is a promising technology for drinking water production, wastewater reclamation as well as pretreatment for seawater desalination. However, wider implementation ...of LPM is restricted by their inherent drawbacks, i.e., membrane fouling and insufficient rejection for dissolved contaminants. Pretreatment of feed water is a major method to improve the performance of LPM, and pre-oxidation has gained extensive attention because it can significantly alter compositions and properties of feed water through chemical reactions. This paper attempts to systematically review efficiency and mechanisms of pre-oxidation in membrane fouling control and permeate water quality improvement. On the basis of briefly discussing major foulants and fouling mechanisms of LPM, advantages and disadvantages of pre-oxidation in mitigating organic fouling, inorganic fouling and biofouling are discussed in detail. Impacts of pre-oxidation on removal of micropollutants, bulk organic matter and inorganic pollutants are summarized, and potential by-products of different oxidants are presented. As a prerequisite for the integration of chemical oxidation with LPM filtration, compatibility of membrane with oxidants at low concentration and long exposure time are highlighted. Finally, the existing challenges and future research needs in practical application of chemical oxidation to improve performance of LPM are also discussed.
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•Effect of pre-oxidation on fouling and permeate quality of LPM is reviewed.•Pre-oxidation effectively mitigates fouling caused by high-MW organics and bacteria.•Pre-oxidation enhances removal of micropollutants and inorganic pollutants.•Compatibility of polymeric membrane with oxidants requires further investigation.
Thermophoresis is of common interest due to its influence on the deposition of particles. Present research on thermophoretic deposition mainly focused on the sub-micron particles, whereas the ...particle size during the radioactive aerosol monitoring process usually exceeds the range. In order to study the effect of thermophoresis on the deposition characteristics of aerosols ranging from 1 to 10 µm, direct numerical simulation (DNS) and experiments of particle deposition are performed in this paper aiming at still and turbulent flow respectively. The results obtained by DNS coupled with Lagrangian particle tracking (LPT) are validated by the experimental data and the theoretical values. The results indicate that thermophoresis has an influence on the deposition of micron-sized particles, and the effect of thermophoresis on deposition velocity depends on particle size. In the still air, when the temperature gradient is 3000 K/m, the deposition velocity of 1 and 10 µm particles will be increased by 87% and 4.8% respectively when compared with gravitational deposition velocity. In the turbulent flow, the motion of particles is dominated by turbulent motion. In the region near the wall, thermophoresis can increase the deposition rate on the cold wall.
•A direct numerical simulation of aerosol thermophoretic deposition is proposed.•Thermophoresis can increase the deposition rate on the cold wall.•In the turbulent flow, the motion of aerosol particles is dominated by turbulence.
lOzonation of fungal spores included two stages with different rate constants.lIncrease in temperature and pH accelerated the ozonation of fungal spores.lOzone destroyed cell wall and membrane, then ...released the intracellular compounds.lOzone was more effective than chlorine and chlorine dioxide in inactivating fungi.
Fungal contamination of drinking water sources is increasingly threatening the environment and human health. In this study, the inactivation of three genera of dominant fungi in drinking water sources using ozone was first reported. The inactivation of the fungal spores by ozone could be divided into two distinct stages: first a rapid reduction in survival, and then the inactivation at a slower rate. The secondary stage inactivation fitted the Chick–Watson model well, and there was no significant difference in the second-order inactivation rate constants of the three fungal spores (0.199–0.209 L mg−1 min−1). The inactivation rate constants of fungal spores by molecular ozone were much lower than those of viruses, which were equivalent to that of Cryptosporidium. The increase in pH and temperature showed a positive effect on the inactivation rate. Damage to cell membranes, leakage of intracellular compounds, and changes of reactive oxygen species and esterase activity in the spores were detected after inactivation. The results indicated that ozone inactivated fungal spores by firstly destroying cell walls and membranes and then causing the release of intracellular compounds. The fungicidal efficiency of ozone was superior to those of chlorine and chlorine dioxide. In addition, the inactivation efficiency of ozone on fungal spores in real water matrices was reduced to 50.7–91.2% of the efficiency in phosphate buffer. In conclusion, ozone showed high efficiency in the inactivation of fungal spores and could be used as an alternative disinfectant for fungal contamination in drinking water sources.
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Jinpen Reservoir is a deep, stratified reservoir in Shaanxi province, located in a warm temperate zone of Northwest China. Influenced by a temperate monsoon climate, more than 60% of the annual ...precipitation is concentrated from late summer to autumn (July-September). In recent years, extreme rainfall events occurred more frequently and strongly affected the thermal structure, mixing layer depth and evolution of stratification of Jinpen Reservoir. The reservoir's inflow volume increased sharply after heavy rainfall during the flooding season. Large volumes of inflow induced mixing of stratified water zones in early autumn and disturbed the stratification significantly. A temporary positive effect of such disturbance was the oxygenation of the water close to the bottom of the reservoir, leading to inhibition of the release of nutrients from sediments, especially phosphate. However, the massive inflow induced by storm runoff with increased oxygen-consuming substances led to an increase of the oxygen consumption rate. After the bottom water became anaerobic again, the bottom water quality would deteriorate due to the release of pollutants from sediments. Heavy rainfall events could lead to very high nutrient input into the reservoir due to massive erosion from the surrounding uninhabited steep mountains, and the particulate matter contributed to most nutrient inputs. Reasonably releasing density flow is an effective way to reduce the amounts of particulate associated pollutants entering the reservoir. Significant turbid density flow always followed high rainfall events in Jinpen Reservoir, which not only affected the reservoir water quality but also increased costs of the drinking water treatment plant. Understanding the effects of the storm runoff on the vertical distributions of water quality indicators could help water managers to select the proper position of the intake for the water plant in order to avoid high turbidity outflow.
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•Strain LSL 251 was identified as Paracoccus thiophilus using 16S rRNA gene.•LSL 251 removed 98.78% of nitrate and 94.79% of TOC under aerobic condition.•RSM model found that the ...maximum TN removal efficiency was 98.43%•13C-MFA revealed that carbon flux distributions were ED pathway and TCA cycle.•Electrons were primarily donated as electron donor-NADH through TCA cycle.
The intracellular carbon metabolic flux pathways of denitrifying bacteria under aerobic conditions remain unclear. Here, a newly strain LSL251 was identified as Paracoccus thiophilus. Strain LSL251 removed 94.79% and 98.78% of total organic carbon and nitrate. 74.66% of nitrogen in culture system was lost as gaseous nitrogen. Moreover, 13C stable isotopic labeling and metabolic flux analyses revealed that the primary intracellular carbon metabolic pathways were the Entner-Doudoroff pathway and the tricarboxylic acid (TCA) cycle. Electrons are primarily donated as direct electron donor-NADH through the TCA cycle. Furthermore, response surface methodology modeled that the highest total nitrogen removal efficiency was 98.43%, where the optimal parameters were C/N ratio of 8.00, 32.98 °C, 50.18 rpm, and initial pH of 7.73. All together, these results have shed new lights on intracellular central carbon metabolic distribution and flux pathways of aerobic denitrifying bacteria.
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