•Constructed wetland configuration, TN purification and mechanisms are discussed.•Biochemical process is the main pathway to remove TN in ammonia-dominant wastewater.•Nitrification-denitrification in ...CW needs large O2 and COD consumption in sequence.•Simultaneous nitrification-denitrification can use spatial heterogeneity of biofilm.•Anammox process can save the chemical cost but needs accurate condition control.
Constructed wetland (CW) for wastewater treatment has attracted increasing attention. In this review, the system configuration optimization, purification effect and general mechanisms of nitrogen removal in CW are systematically summarized and discussed. Ammonia oxidation is a crucial and primary process for total nitrogen (TN) removal in domestic or livestock wastewater treatment. Aeration, waterdrop influent and tidal operation are three main methods to strengthen the oxygen supplement and nitrification process in CW. Aeration significantly increases the ammonia removal rate (almost 100%), followed by the removal of chemical oxygen demand (COD) and TN. Solid carbon source, iron and anode material can be filled as electron donor for the denitrification process. The co-adjustment of oxygen and carbon/electron donor can form different conditions for different nitrogen removal pathways (e.g. the simultaneous nitrification-denitrification, the partial nitrification-denitrification and the anammox process), and achieve the optimal removal of nitrogen.
Abstract
Photocatalytic reduction of CO
2
is a promising approach to achieve solar-to-chemical energy conversion. However, traditional catalysts usually suffer from low efficiency, poor stability, ...and selectivity. Here we demonstrate that a large porous and stable metal-organic framework featuring dinuclear Eu(III)
2
clusters as connecting nodes and Ru(phen)
3
-derived ligands as linkers is constructed to catalyze visible-light-driven CO
2
reduction. Photo-excitation of the metalloligands initiates electron injection into the nodes to generate dinuclear {Eu(II)}
2
active sites, which can selectively reduce CO
2
to formate in a two-electron process with a remarkable rate of 321.9 μmol h
−1
mmol
MOF
−1
. The electron transfer from Ru metalloligands to Eu(III)
2
catalytic centers are studied via transient absorption and theoretical calculations, shedding light on the photocatalytic mechanism. This work highlights opportunities in photo-generation of highly active lanthanide clusters stabilized in MOFs, which not only enables efficient photocatalysis but also facilitates mechanistic investigation of photo-driven charge separation processes.
Objective To examine whether the increase in use of electronic cigarettes in the USA, which became noticeable around 2010 and increased dramatically by 2014, was associated with a change in overall ...smoking cessation rate at the population level.Design Population surveys with nationally representative samples.Setting Five of the US Current Population Survey-Tobacco Use Supplement (CPS-TUS) in 2001-02, 2003, 2006-07, 2010-11, and 2014-15.Participants Data on e-cigarette use were obtained from the total sample of the 2014-15 CPS-TUS (n=161 054). Smoking cessation rates were obtained from those who reported smoking cigarettes 12 months before the survey (n=23 270). Rates from 2014-15 CPS-TUS were then compared with those from 2010-11 CPS-TUS (n=27 280) and those from three other previous surveys.Main outcome measures Rate of attempt to quit cigarette smoking and the rate of successfully quitting smoking, defined as having quit smoking for at least three months.Results Of 161 054 respondents to the 2014-15 survey, 22 548 were current smokers and 2136 recent quitters. Among them, 38.2% of current smokers and 49.3% of recent quitters had tried e-cigarettes, and 11.5% and 19.0% used them currently (every day or some days). E-cigarette users were more likely than non-users to attempt to quit smoking, 65.1% v 40.1% (change=25.0%, 95% confidence interval 23.2% to 26.9%), and more likely to succeed in quitting, 8.2% v 4.8% (3.5%, 2.5% to 4.5%). The overall population cessation rate for 2014-15 was significantly higher than that for 2010-11, 5.6% v 4.5% (1.1%, 0.6% to 1.5%), and higher than those for all other survey years (range 4.3-4.5%).Conclusion The substantial increase in e-cigarette use among US adult smokers was associated with a statistically significant increase in the smoking cessation rate at the population level. These findings need to be weighed carefully in regulatory policy making regarding e-cigarettes and in planning tobacco control interventions.
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•Non-suspended microalgae achieve easy biomass recovery and high stress resistance.•TN and TP could get a 90% removal with load rate higher than 150 mg·L−1·d−1.•Above 70% TN and TP ...were transferred from wastewater to microalgae biomass.•The dynamic growth of non-suspended microalgae determined the pollutant removal rate.•The mechanism of pollutant transfer and microalgae growth require investigation.
Non-suspended microalgae cultivation technology coupled with wastewater purification has received more scientific attention in recent decades. Since the non-suspended microalgae cultivation is quite different from the suspended ones, the following issues are compared in this study such as advantages and disadvantages, pollutant removal mechanisms and regulations, influential factors, and microalgae biomass accumulation. The analysis aims to support the further application of this technology. The median removal rates of COD, TN, TP, NH4+-N and NO3−-N were 91.6%, 78.2%, 87.5%, 93.2% and 81.7%, respectively, by non-suspended microalgae under the TN & TP load rates up to 150 mg·L−1·d−1. The main pathway for TN & TP removal is microalgae cell absorbance. Light intensity, pollutant composition and microalgae metabolic types are the major factors that influence pollutant removal and the lipid content of microalgae. Meanwhile the mechanism concerning how macro-outer conditions influence the micro-environment and further growth of non-suspended microalgae requires more investigation.
Microalgae is considered an alternative source for biodiesel production producing renewable, sustainable and carbon-neutral energy. Microalgae property changes among species, which determines the ...efficiency of biodiesel production. Besides the lipid content evaluation, multi-principles (including high lipid productivity, high biomass yield, pollution resistance and desired fatty acid, etc.) for superior oil-producing species screening was proposed in this review and three microalgae species (Chlorella vulgaris, Scenedesmus obliquus and Mychonastes afer) with high bio-lipid producing prospect were screened out based on big data digging and analysis. The multilateral strategies for algal-lipid stimulating were also compared, among which, nutrient restriction, temperature control, heterotrophy and chemicals addition showed high potential in enhancing lipid accumulation; while electromagnetic field showed little effect. Interestingly, it was found that the lipid accumulation was more sensitive to nitrogen (N)-limitation other than phosphorus (P). Nutrient restriction, salinity stress etc. enhanced lipid accumulation by creating a stressed environment. Hence, optimum conditions (e.g. N:15–35 mg/L and P:4–16 mg/L) should be set to balance the lipid accumulation and biomass growth, and further guarantee the algal-lipid productivity. Otherwise, two-step cultivation could be applied during all the stressed stimulation. Different from lab study, effectiveness, operability and economy should be all considered for stimulation strategy selection. Nutrient restriction, temperature control and heterotrophy were highly feasible after the multidimensional evaluation.
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•A multi-factor evaluation is proposed to screen algal species for lipid production.•Mychonastes with excellent bio-lipid property is promising but often neglected.•The characters of lipid stimulating strategies are systematically compared.•Nutrient starvation, temperature control and heterotrophy were relatively feasible.•Lipid accumulation is more sensitive to nitrogen stimulating rather than phosphorus.
Three Cu(I) coordination networks, namely, {Cu2(bpz)2(CN)X·CH3CN} n , (X = Cl, 1; I, 3), {Cu6(bpz)6(CH3CN)3(CN)3Br·2OH·14CH3CN} n , (2, bpz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole), were ...prepared by using solvothermal method. The cyanide ligands in these networks were generated in situ by cleavage of C–C bond of MeCN under solvothermal condition. The structures of these networks are dependent on halogen anions. Complex 1 is a ladderlike structure with μ2-CN– as rung and μ2-bpz as armrest. The Cl– in 1 is at terminal position but does not extend the one-dimensional (1D) ladder to higher dimensionalities. Complex 2 is a three-dimensional (3D) framework comprised of novel planar Cu3Br triangle and single Cu nodes, which are extended by μ2-bpz and μ2-CN– to form a novel (3,9)-connected gfy network. Density functional theory calculations showed that single-electron delocalization of Br atom induces the plane structure of Cu3Br. Complex 3 also possesses a similar ladderlike subunit as in 1, but the I– acts as bidentate bridge to extend the ladder to 3D framework with a four-connected sra topology. The three networks show notable catalytic activity on the click reaction. The compared catalytic results demonstrate that complex 2 possesses the best catalysis performance among three complexes, which is ascribed to the largest solvent-accessible void (porosity: 2 (29.4%) > 1 (25.7%) > 3 (17.6%)) and the more Cu(I) active sites in 2. The present combined structure–property studies provide not only a new synthetic route to obtain a new kind of catalyst for click reaction but also the new insights on catalyst structure–function relationships.
Solar‐driven high‐efficiency and direct conversion of methane into high‐value‐added liquid oxygenates against overoxidation remains a great challenge. Herein, facile and mass fabrication of low‐cost ...tungsten single‐atom photocatalysts is achieved by directly calcining urea and sodium tungstate under atmosphere (W‐SA‐PCN‐m, urea amount m = 7.5, 15, 30, and 150 g). The single‐atom photocatalysts can manage H2O2 in situ generation and decomposition into ·OH, thus achieving highly efficient CH4 photooxidation in water vapor under mild conditions. Systematic investigations demonstrate that integration of multifunctions of methane activation, H2O2 generation, and decomposition into one photocatalyst can dramatically promote methane conversion to C1 oxygenates with a yield as high as 4956 µmol gcat−1, superior to that of the most reported non‐precious photocatalysts. Liquid–solid phase transition can induce the products to facilely switch in from HCOOH to CH3OH by pulling the catalyst above water with CH3OH/HCOOH ratio from 10% (in H2O) to 80% (above H2O).
The mass fabrication of low‐cost tungsten single atom photocatalysts is achieved by directly calcining urea and sodium tungstate under atmosphere. These single‐atom photocatalysts can manage H2O2 in situ generation and decomposition into ·OH to achieve highly efficient CH4 photooxidation in water vapor, and the products can be facilely switched from HCOOH to CH3OH by the liquid–solid phase transition.
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•Fe addition in partially unsaturated CW could achieve high TN/TP removal (＞75%).•Extra biochar addition decreased Fe dosage but achieved the equivalent TN/TP removal.•Electron ...generation and transport by Fe-C enhanced denitrification to above 95%.•Fe-metabolic bacteria and electroactive bacteria were enriched by Fe-C addition.•Metallic bonded P and organic P dominated TP removal in Fe-C added CW.
Insufficient dissolved oxygen (DO) for ammonia oxidation and limited electron donor for denitrification inhibit the nitrogen removal performance of constructed wetlands (CWs). To solve the problems, partially unsaturated CWs filled with biochar (C) and/or iron shavings (Fe) as functional substrate were proposed in this study and its mechanism on pollutant removal was thoroughly analyzed from the aspects of micro-environment property surrounding substrate, microbial function, plant toxicity, among others. Results showed that partially unsaturated section significantly improved the removal of NH4+-N from 25.1 ± 0.3 mg/L to <10 mg/L. The addition of Fe and Fe-C combination resulted in a better total nitrogen removal of 76.1 ± 0.6% and 86.5 ± 1.7% respectively compared with traditional CWs. For Fe-C combination, Fe, rather than C, was supposed to be the electron donor for nitrate (NO3–-N) removal. Moreover, the lower oxidation–reduction potential (ORP) in the micro-environment surrounding Fe-C combination than that surronding Fe proved that biochar accelerated the transfer process once Fe released electron, which guaranteed the nitrogen removal with less Fe dosage (only 60% v/v). Massive Fe2+ and Fe3+ were produced by Fe, and biochar provided large surface for the bacterial adhesion and co-precipitation of Fe cations and phosphate (P). The enhanced formation of Fe,Ca,Al-P and Porg after Fe-C addition led to a high total phosphorus (TP) removal of 98%. The import of biochar reduced the dosage of Fe and its toxicity to Iris wilsoni. Therefore, compared with Fe, Fe-C combination is a high-efficiency and environmental-friendly functional substrate in CWs.
Compared with suspended microalgae cultivation, attached microalgae cultivation for wastewater treatment has advantages of low biomass recovery costs and high robustness. As a heterogeneous system, ...the variation of photosynthetic capacity along biofilm depth lacks quantitative conclusions. The distribution curve of oxygen concentration along the depth of attached microalgae biofilm (f(x)) was detected by dissolved oxygen (DO) microelectrode, and a quantified model was built based on mass conservation and Fick's law. It revealed that the net photosynthetic rate at a certain depth (x) in the biofilm showed a linear relationship with the second derivatives of the distribution curve of oxygen concentration (f″(x)). In addition, the declining trend of photosynthetic rate along attached microalgae biofilm was relatively slow compared with the suspended system. The photosynthetic rate at 150–200 μm depth of algae biofilm was only 3.60 %–17.86 % of that at the surface layer. Moreover, the light saturation points of the attached microalgae got lower along the depth of biofilm. Compared to 400 lx light intensity, the net photosynthetic rate of microalgae biofilm at the depths of 100–150 μm and 150–200 μm increased by 389 % and 956 % under 5000 lx, respectively, showing the high photosynthesis potential with increasing light.
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•Quantified photosynthetic rate changes along algae biofilm depth were first reported.•Light attenuation in microalgal biofilm was different from suspended cultivation.•Photosynthetic rate at 150–200 μm depth was 3.60 %–17.86 % as much as surface biofilm.•Deep layer algae could regain high photosynthesis under enhanced illuminance.•Deep layer microalgae had relatively low light saturation point.
Nanoscale inorganic wheel-shaped structures are one of the most striking types of molecular aggregations. Here, we report the synthesis of a gigantic lanthanide wheel cluster containing 140 Gd3+ ...atoms. As the largest lanthanide cluster reported thus far, {Gd 140 } features an attractive wheel-like structure with 10-fold symmetry. The nanoscopic molecular wheel possesses the largest diameter of 6.0 nm and displays high stability in solution, which allows direct visualization by scanning transmission electron microscopy. The newly discovered lanthanide {Gd 140 } cluster represents a new member of the molecular wheel family.
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