Does rice straw addition and/or Vallisneria natans (Lour.) planting contribute to enhancement in nitrate nitrogen and phosphorus removal in constructed wetlands under low temperature?

It is a global concern that nitrogen and phosphorus removal performances of constructed wetlands (CWs) are limited during cold weather. This study analyzed nutrient removal efficiencies and mechanisms in six CWs including combinations between evergreen submerged vegetation planting and rice straw adding under low temperature. The results showed that both unvegetated and vegetated CWs achieved the highest removal rates of total nitrogen (TN) (85.1-86.6%) and NO3--N (98.2-98.7%) with increases of approximately 56% and 68% by adding rice straw in water, respectively. Moreover, microbial denitrification accounted for reduction in over 70% of influent TN load. Planting vegetation, adding rice straw or their combination could all improve total phosphorus removal. Compared with adding rice straw in sediment, more diversifying bacterial community and higher abundances of some anaerobic fermentative species in the rice straw biofilm might have contributed to higher nitrogen removal in CWs with rice straw added in water.

Occurrence and temporal variation of antibiotics and antibiotic resistance genes in hospital inpatient department wastewater: Impacts of daily schedule of inpatients and wastewater treatment process.

The temporal variation of antibiotics and ARGs as well as the impact of daily schedule of inpatients on their regular occurrence in hospital wastewater (HWW) were previously obscure. In this study, the wastewater of the inpatient department pre- and posttreatment (hydraulic retention time = 8 h) was collected intraday and intraweek. The absolute concentrations of antibiotics/metabolites and ARGs in HWW were analyzed to investigate the temporal variations of their occurrence levels. Fluoroquinolones were the predominant drugs used in the inpatient department (681.30-881.66 ng/mL in the effluent) and the main contaminant in the outlet of the disinfection pond (538.29-671.47 ng/mL). Diurnal variations peaked at 19:00 for most antibiotics and ARGs, while the maximum of them occurred on weekends. Aminoglycoside resistance genes (AMRGs, 21.6-23000 copies/mL) and ß-lactam resistance genes (BLGRs, 1.24-8500 copies/mL) were the dominant ARGs before and after treatment processing, respectively (p < 0.05). The significant removal rates (>50%) of most antibiotics and ARGs, as well as the integrase gene intI1 and 16S rRNA gene, were found to be subjected solely to the chloride disinfection process, suggesting the necessity of the self-contained wastewater treatment process. Meanwhile, the statistically significant correlation among antibiotics, ARGs, intI1, and 16S rRNA (p < 0.05) demonstrated that the risk of selective pressure, horizontal transfer and vertical propagation of ARGs in the effluent of the hospital was warranted. Principal component analysis (PCA) showed that the daily schedule of inpatients and wastewater treatment processes could markedly induce fluctuations in antibiotic and ARG levels in HWW, indicating that they should be considered an impact factor for environmental monitoring. This study demonstrated for the first time the temporal variations in the abundance and dissemination of antibiotics and ARGs in a semiclosed zone and provided new insight into the development of assessments of the associated ecological risk and human health.

Defective Black TiO2: Effects of Annealing Atmospheres and Urea Addition on the Properties and Photocatalytic Activities.

A series of black TiO2 with and without the addition of urea were successfully prepared using a simple one-step synthetic method by calcination under different atmospheres (vacuum, He, or N2). The physicochemical, optical, and light-induced charge transfer properties of the as-prepared samples were characterized by various techniques. It was found that a vacuum atmosphere was more beneficial for the formation of oxygen vacancies (OVs) than the inert gases (He and N2) and the addition of urea-inhibited OVs formation. The samples annealed in the vacuum condition exhibited better visible-light adsorption abilities, narrower bandgaps, higher photo-induced charge separation efficiency, and lower recombination rates. Hydroxyl radicals (·OH) were the dominant oxidative species in the samples annealed under a vacuum. Finally, the samples annealed under vacuum conditions displayed higher photocatalytic activity for methylene blue (MB) degradation than the samples annealed under He or N2. Based on the above, this study provides new insights into the effects of annealing atmospheres and urea addition on the properties of black TiO2.

Two-Dimensional Silicon/Carbon from Commercial Alloy and CO2 for Lithium Storage and Flexible Ti3C2Tx MXene-Based Lithium-Metal Batteries.

Silicon has been considered as the most promising anode candidate for next-generation lithium-ion batteries. However, the fast capacity decay caused by huge volume expansion and low electronic conductivity limit the electrochemical performance. Herein, atomic distributed, air-stable, layer-by-layer-assembled Si/C (L-Si/C) is designed and in situ constructed from commercial micron-sized layered CaSi2 alloy with the greenhouse gas CO2. The inner structure of Si as well as the content and graphitization of C can be regulated by simply adjusting the reaction conditions. The rationally designed layered structure can enhance electronic conductivity and mitigate volume change without disrupting the carbon layer or destroying the solid electrolyte interface. Moreover, the single-layer Si and C can enhance lithium-ion transport in active materials. With these advantages, L-Si/C anode delivers an 82.85% capacity retention even after 3200 cycles and superior rate performance. The battery-capacitance dual-model mechanism is certified via quantitative kinetics measurement. Besides, the self-standing architecture is designed via assembling L-Si/C and MXene. Lithiophilic L-Si/C can guide homogeneous Li deposition with alleviated volume change. With the MXene/L-Si/C host for lithium-metal batteries, an ultralong life span up to 500 h in a carbonate-based electrolyte is achieved. A full cell with a high-energy 5 V LiNi0.5Mn1.5O4 cathode is constructed to verify the practicality of L-Si/C and MXene/L-Si/C. The rational design of a special layer structure may propose a strategy for other materials and energy storage systems.

A novel fractional variable-order equivalent circuit model and parameter identification of electric vehicle Li-ion batteries.

Accurate Li-ion battery modeling is integral to the design of effective battery management systems in electric vehicles. However, the voltage-current (U-I) characteristic of Li-ion batteries presents strong nonlinearity. The application of fractional-order models to create lower-order models to represent physical systems (e.g., the battery characteristics for the state of charge estimation) is interesting and timely. In this paper, a novel fractional variable-order equivalent circuit model (FVO-ECM) is proposed to represent the nonlinear U-I characteristic of Li-ion batteries; its parameter identification is achieved and verified by charge and discharge tests. Compared with the integral-order equivalent circuit model and the fractional constant-order model, the proposed FVO-ECM can identify battery nonlinear characteristics most accurately.

Key role of hydrochar in heterogeneous photocatalytic degradation of sulfamethoxazole using Ag3PO4-based photocatalysts.

To overcome the practical application limitations of Ag3PO4 such as photocorrosion and relatively low efficiency of photogenerated carrier seperation, Ag3PO4 particles were loaded onto hydrochar. The particles in the composite had a smaller crystallite size and different phase structure with more edges than pure Ag3PO4 particles. The as-prepared composite catalyst exhibited a different photocatalytic performance for sulfamethoxazole (SMX) degradation when varying the mass ratio of hydrochar and Ag3PO4. In addition to higher SMX degradation efficiency, the composite exhibited much higher TOC degradation efficiency, recycling stability, and less-toxic intermediate production. The composites enhanced visible light response, and accelerated electron transfer and photogenerated carrier separation as well. The addition of H2O2 to the photocatalytic system enhanced the photocatalytic activity of the composite catalyst. According to a mechanistic examination, the hole (h+) is the dominant reactive species for SMX degradation. This study provides new insight into high-efficiency, low cost, and easily prepared photocatalysts for pollution removal from water.

Allelopathic Effects on Microcystis aeruginosa and Allelochemical Identification in the Cuture Solutions of Typical Artificial Floating-Bed Plants.

Cyperus alternifolius (C. alternifolius) and Canna generalis (C. generalis) are widely used as artificial floating-bed (AFB) plants for water pollution control. This study evaluated the release of anti-cyanobacterial allelochemicals from both plants in AFB systems. A series of cyanobacterial assays using pure culture solutions and extracts of culture solutions of C. alternifolius and C. generalis demonstrated allelopathic growth inhibition of a cyanobacterium M. aeruginosa. After 45 days of incubation by the culture solutions, both final inhibitory rates of M. aeruginosa were more than 99.6% compared with that of the control groups. GC/MS analyses indicated the presence of a total of 15 kinds of compounds, including fatty acids and phenolic compounds, in both plants' culture solutions, which are are anti-cyanobacterial. These findings provide a basis to apply artificial floating-bed plants for cyanobacterial inhibition using allelopathic effects.

Comparison of two different ecological floating bio-reactors for pollution control in hyper-eutrophic freshwater.

The use of ecological floating beds (EFBs) to control water pollution has been increasingly reported worldwide due to the severe situation of eutrophication in water bodies. In this study, two kinds of EFBs were set up under similar condition to compare their purification efficiency in hyper-eutrophic water. The conventional ecological floating bed (CEFB) was made of polystyrene foam board, and the enhanced ecological floating bio-reactor (EEFB) was designed as an innovative hollow, thin floating bed integrated with substrates of zeolite and limestone. The results showed that the EEFB increased treatment efficiency of total nitrogen (TN), total phosphate (TP), and ammonia nitrogen (NH4+-N) to 63.5%, 59.3%, and 68.0%, respectively. Plant accumulation was the main pathway for TN and TP removal in the CEFB. Microbial degradation played an increasingly important role in TN and TP removal in the EEFB. A higher concentration of nitrogen cycling bacteria was recorded in the EEFB than the CEFB (P < 0.05), suggesting that the substrates might enhanced the removal efficiency of the EEFB by promoting the growth of microorganisms rather than their absorption effect.

Influence of nitrogen loading and flooding on seedling emergence and recruitment from a seed bank in Chaohu Lake Basin, China.

Vegetation severely degraded and even disappeared in the water bodies of Chaohu Lake basin, which is the fifth largest freshwater lake in the Yangtze flood plain in China, because of water pollution and eutrophication. Vegetation restoration projects have been carried out. However, the influences of water quality and hydrology on vegetation restoration from seed banks have been rarely investigated. This experiment aimed to identify the effect of water level and nitrogen loading (ammonium and nitrate) on seedling emergence and recruitment from the riparian seed bank of the river in this basin. Most of the species in the seed bank germinated under moist conditions. Under flooding conditions, however, the growth of aquatic species, especially Vallisneria natans (Lour.) Hara, was inhibited when the nitrogen concentration increased. At 0.37 mg/L NH4+-N in the water column, the growth of V. natans was inhibited. The results suggested that flooding was a primary limiting factor of seedling emergence. The inhibitory effect of high nitrogen loading on the growth of aquatic species was one of the main driving mechanisms of macrophyte degradation under flooding conditions; nevertheless, competitive advantage might determine the community pattern in moist habitats. Therefore, water level control and water quality improvement should be the key aspects of vegetation restoration in degraded rivers or lakes.

Triazophos (TAP) removal in horizontal subsurface flow constructed wetlands (HSCWs) and its accumulation in plants and substrates.

Triazophos (TAP) is a widely used phosphorus pesticide in China that possesses a potential risk for water pollution. We have studied the removal efficiency of TAP using pilot-scale horizontal subsurface flow constructed wetlands (HSCWs) as well as the contribution of plants, substrates and other pathways to its removal. For TAP concentrations of 0.12 ± 0.04 mg L-1, 0.79 ± 0.29 mg L-1 and 3.96 ± 1.17 mg L-1, the removal efficiencies were 94.2 ± 3.7%, 97.8 ± 2.9% and 84.0 ± 13.5%, respectively, at a hydraulic loading rate (HLR) of 100 mm d-1; at an HLR of 200 mm d-1, the removal efficiencies were 96.7 ± 1.3%, 96.2 ± 1.7% and 61.7 ± 11.1%, respectively. The isopleth maps of TAP along the direction of flow indicate that most of the TAP removal occurred in the front and middle regions, while the major removal region would move forward with increasing influent TAP. Plant and substrate accumulation accounted for 0.035 ± 0.034% and 4.33 ± 0.43% of the total removal, respectively, indicating that over 95% of the TAP removal was achieved through other mechanisms. Thus, these results suggest HSCWs can be an effective approach with which to treat TAP contaminated water. Furthermore, the longitudinal scale and hydraulic conditions, as well as the roles of plants, substrates and microbes and their interactions, should be further considered in the design and application of CWs for pesticide pollution control.

Increasing phytoplankton-available phosphorus and inhibition of macrophyte on phytoplankton bloom.

We assembled mesocosms to address the coherent mechanisms that an increasing phosphorus (P) concentration in water columns coupled with the phytoplankton bloom and identify the performance gap of regulating phytoplankton growth between two macrophyte species, Ceratophyllum demersum L. and Vallisneria spiralis L. Intense alkaline phosphatase activities (APA) were observed in the unplanted control, with their predominant part, phytoplankton APA (accounting for up to 44.7% of the total APA), and another large share, bacterial APA. These correspond with the large average concentration of total phosphorus (TP), total dissolved phosphorus (TDP) and soluble reactive (SRP) as well as high phytoplankton density in the water column. The consistency among P concentrations, phytoplankton density and APA, together with the positive impact of phytoplankton density on total APA revealed by the structural equation modelling (SEM), indicates that facilitated APA levels in water is an essential strategy for phytoplankton to enhance the available P. Furthermore, a positive interaction between phytoplankton APA and bacteria APA was detected, suggesting a potential collaboration between phytoplankton and bacteria to boost available P content in the water column. Both macrophyte species had a prominent performance on regulating phytoplankton proliferation. The phytoplankton density and quantum yield in C. demersum systems were all significantly lower (33.8% and 24.0%) than those in V. spiralis systems. Additionally, a greater decoupling effect of C. demersum on the relationship between P, APA, phytoplankton density, bacteria dynamic and quantum yield was revealed by SEM. These results imply that the preferred tactic of different species could lead to the performance gap.

Biological mechanisms associated with triazophos (TAP) removal by horizontal subsurface flow constructed wetlands (HSFCW).

Triazophos (TAP) is a widely used pesticide that is easily accumulated in the environment due to its relatively high stability: this accumulation from agricultural runoff results in potential hazards to aquatic ecosystems. Constructed wetlands are generally considered to be an effective technology for treating TAP polluted surface water. However, knowledge about the biological mechanisms of TAP removal is still lacking. This study investigates the responses of a wetland plant (Canna indica), substrate enzymes and microbial communities in bench-scale horizontal subsurface-flow constructed wetlands (HSCWs) loaded with different TAP concentrations (0, 0.1, 0.5 and 5 mg · L(-1)). The results indicate that TAP stimulated the activities of superoxide dismutase (SOD) and peroxidase (POD) in the roots of C. indica. The highest TAP concentrations significantly inhibited photosynthetic activities, as shown by a reduced effective quantum yield of PS II (ΦPS II) and lower electron transport rates (ETR). However, interestingly, the lower TAP loadings exhibited some favorable effects on these two variables, suggesting that C. indica is a suitable species for use in wetlands designed for treatment of low TAP concentrations. Urease and alkaline phosphatase (ALP) in the wetland substrate were activated by TAP. Two-way ANOVA demonstrated that urease activity was influenced by both the TAP concentrations and season, while acidphosphatase (ACP) only responded to seasonal variations. Analysis of high throughput sequencing of 16S rRNA revealed seasonal variations in the microbial community structure of the wetland substrate at the phylum and family levels. In addition, urease activity had a greater correlation with the relative abundance of some functional microbial groups, such as the Bacillaceae family, and the ALP and ACP may be influenced by the plant more than substrate microbial communities.

Enhancing the water purification efficiency of a floating treatment wetland using a biofilm carrier.

Floating treatment wetlands (FTWs) and biofilm carriers are widely used in water purification. The objective of the present work was to explore whether and to what extent an FTW integrated with plants and biofilm carriers (FTW-I) could enhance the nutrient removal efficiency. Significantly higher removal rates of ammonia nitrogen (85.2 %), total phosphorus (82.7 %), and orthophosphate (82.5 %) were observed in the FTW-I treatment relative to the FTW with plants (FTW-P; 80.0, 78.5, and 77.6 %, respectively) and the FTW with biofilm carriers (FTW-B; 56.7, 12.9, and 13.4 %, respectively) (p < 0.05). The mass balance results indicated that plant uptake was the main pathway for N and P removal (accounting for 58.1 and 91.4 %, respectively) in FTW-I, in which only 1.2 % of the N and 5.7 % of the P was deposited on the bottom of the tank. In addition, the plants translocated 43.9 and 80.2 % of the N and P in the water and 83.5 and 88.3 % of the absorbed N and P, respectively, into their aboveground tissues. The combination of an FTW and biofilm carriers can improve the efficiency of water purification, and nutrients can be rapidly removed from the system by harvesting the aboveground plant tissues.

Acclimation of Hydrilla verticillata to sediment anoxia in vegetation restoration in eutrophic waters.

Sediment anoxia generally results from intense organic enrichment and is a limiting factor in the restoration of vegetation in eutrophic waters. To investigate the effect of sediment anoxia on a typical pollution-tolerant submerged macrophyte species, Hydrilla verticillata, and acclimation mechanisms in the plant, a gradient of sediment anoxia was simulated with additions of sucrose to the sediment, which can stimulate increased concentrations of total nitrogen, NH4(+) and Fe in pore water. H. verticillata growth was significantly affected by highly anoxic conditions, as indicated by reduced total biomass in the 0.5 and 1% sucrose treatments. However, slight anoxia (0.1% sucrose addition) promoted growth, and the shoot biomass was 22.64% higher than in the control. In addition to morphologic alterations, H. verticillata showed physiological acclimations to anoxia, including increased anaerobic respiration and changes in carbon and nitrogen metabolism in roots. The soluble protein and soluble carbohydrate contents in roots of the 1% treatment were both significantly higher compared with those in the control. The increase in alcohol dehydrogenase activity and pyruvate content in the roots suggested that H. verticillata has a well-developed capacity for anaerobic fermentation. This study suggests that highly anoxic sediments inhibit the growth of H. verticillata and the species has a degree of tolerance to anoxic conditions. Further in situ investigations should be conducted on the interactions between sediment conditions and macrophytes to comprehensively evaluate the roles of sediment in the restoration of vegetation in eutrophic waters.

Seed banks and their implications of rivers with different trophic levels in Chaohu Lake Basin, China.

The seed banks of three rivers, with different trophic levels in Chaohu Lake Basin, China, were investigated to explore the dynamics of seed bank under the pressure of eutrophication. A total of 60 species from 25 family 43 genera were identified from the seed banks of the three rivers. In the eutrophic Paihe River, the species richness and mean seed density were the highest, followed by the oligotrophic Hangbuhe River and the hypereutrophic Nanfeihe River. Various compositions of three functional group assemblage of hydro-ecotypes were found in different rivers. The dominant and endemic species were aquatic, wetland, and terrestrial species in Hangbuhe River, Paihe River, and Nanfeihe River, respectively. The shift trend of seed bank in three rivers probably presented past vegetation dynamics under the trophic process in the rivers of Chaohu Lake Basin. Seed bank in the river bed might be quickly assessed by its trophic level. Additionally, it might imply that the seed bank with more aquatic species in the oligotrophic river would be a potential seed resource for vegetation restoration of severely degraded river ecosystems.