Nitrous oxide (N2O) and nitric oxide (NO) emissions from domestic wastewater treatment had been widely investigated due to their severe greenhouse effect and stratospheric ozone depletion. Researches concerning N2O and NO emissions from industrial wastewater treatment which usually contain high concentrations of nitrogen and refractory organics were still limited. In this study, N2O and NO emissions from a biological aerated filter (BAF) for coking wastewater treatment were investigated that achieved efficient nitrogen and chemical oxygen demand (COD) removal efficiency through short-cut nitrification and denitrification. Notably, emission factor of N2O and NO reached 23.58% and 0.09% respectively, much higher than those emitted from most domestic wastewater treatment plants. Moreover, batch experiments revealed that nitrifier denitrification contributed as high as 97.17% and 93.89% of the total generated N2O and NO, which was supposed to be the main source of green-house gases (GHGs) during coking wastewater treatment. The inhibition of denitrifying reductase by the toxic components in coking wastewater and the severe nitrite accumulations were key factors promoting the high emission of N2O and NO. Microbial community analysis based on high throughput sequencing of 16S rRNA gene revealed that ammonia-oxidizing bacteria and denitrifying bacteria distributed abundantly in the BAF reactor, while nitrite-oxidizing bacteria was almost absent. The huge imbalance between NO and N2O reductase was an underlying explanation for the high N2O emission in the present coking wastewater treatment according to Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) result. This study is of great significance to understanding the high N2O and NO emission and developing the control strategy when treating industrial wastewater with high-strength nitrogen and refractory organics.

Sulfur-modified zero valent iron (S-ZVI) particles have been reported to show improved reactivity and selectivity than conventional ZVI. However, current methods for ZVI sulfidation do not fully utilize the advantages of the material, and S-ZVI has not been tested for U(VI) immobilization. In this work, we synthesized a new type of FeS-modified ZVI core-shell particles (FeS@Fe0) through a facile two-step reaction approach, and then tested for reductive sequestration of U(VI) in water. X-ray diffraction, Scanning transmission electron microscopy, and physical property analyses confirmed the formation of the core-shell structure, surface compositions and magnetic properties. Batch kinetic tests showed that FeS@Fe0 with an Fe0/FeS molar ratio of 1:1 offered the highest U(VI) reduction rate, prolonged reactive life than pristine ZVI, and the reduced uranium was most resistant to re-oxidation when exposed to oxygen. The retarded first-order kinetic model was able to adequately interpret the experimental rate data. FeS@Fe0 performed well over the pH range 5.5–9.0, with higher pH more favoring the reaction. High concentrations (5–10 mg/L) of humic acid, bicarbonate (1–5 mM) and Ca2+ (1 mM) showed only modest inhibition to the U(VI) reduction. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and extraction studies indicated that U(VI) was immobilized via both direct adsorption and reductive precipitation, where Fe0 was the main electron source, with Fe0, sorbed Fe(II) and structural Fe(II) acting as the electron donors. FeS@Fe0 may serve as an improved material for efficient immobilization of U(VI) and other redox-active contaminants in water.

Metal-free photocatalysts have attracted growing concern in recent years. In this work, a new class of carbon quantum dots (CQDs) modified porous graphitic carbon nitride (g-C3N4) is synthesized via a facile polymerization method. With the optimal CQDs loading, the CQDs modified g-C3N4 exhibits ∼15 times higher degradation kinetic towards diclofenac (DCF) than that of pure g-C3N4. The enhanced photocatalytic activity can be ascribed to the improved separation of charge carriers as well as the tuned band structure. Moreover, a photosensitation-like mechanism is proposed to elucidate the photo-generated electrons transfer and reactive radicals formation. CQDs are anchored to g-C3N4 surface via CO bond, which provide channels for the preferential transfer of photo-excited electrons on DCF molecule to the conduction band of g-C3N4. Superoxide radical (·O2−) dominates the degradation of DCF, while holes (h+) show a negligible contribution. Density functional theory (DFT) calculation successfully predicts that the sites on DCF molecule with high Fukui index (f0) are preferable to be attacked by radicals. DCF degradation pathway mainly includes ring hydroxylation, ring closure and CN bond cleavage processes. Acute toxicity estimation indicates the formation of less toxic intermediates/products compared to DCF after photocatalysis. Moreover, the hybrid photocatalysts exhibit good reusability in five consecutive cycles. This work not only proposes a deep insight into photosensitation-like mechanism in the photocatalysis system by using C3N4-based materials, but also develops new photocatalysts for potential application on removal of emerging organic pollutants from waters and wastewaters.

BiOI microspheres doped with different amounts of Ti were fabricated and used to remove diclofenac (DCF) from water under visible light irradiation. The fabricated photocatalysts were well characterized. Ti doped BiOI microspheres were found to exhibit higher photocatalytic activity towards DCF under visible light compared with BiOI. Ti doping broadened the band gap of BiOI, which leads to a more negative conduction band edge and a higher reducing activity of photo-generated electrons, thus facilitates ·O2− production during photocatalysis. Among all the fabricated Ti doped BiOI microspheres, TB450 exhibited the highest DCF photocatalytic removal efficiency. Specifically, 99.2% of DCF (C0 = 10 mg L−1) was removed by TB450 (250 mg L−1) at pH 5 within 90 min under visible light irradiation. Scavenger experiments indicated that active species including h+, ·O2− and H2O2 played important roles in the photocatalytic process. The degradation pathway of DCF was elucidated by theoretical density functional theory (DFT) and by-products identification through liquid chromatograph mass spectrometer (LC-MS) analysis. DCF degradation pathway mainly included hydroxylation and the cleavage of CN bond. DFT calculation can well interpret the degradation mechanism and the sites of DCF molecule with high radical-attack Fukui index (f0) exhibit high reactivity. Acidic condition was found to facilitate the DCF photocatalytic removal. Due to strong photo-stability, Ti doped BiOI microspheres contained good visible-light-driven (VLD) photocatalytic removal efficiency for DCF in the fourth consecutive reused cycle. Ti doped BiOI microspheres can be employed as a cost-effective and high-efficient material to efficiently degrade emerging contaminants (e.g., pharmaceutical) from wastewaters under visible light conditions.

Technetium (99Tc) typically exists as pertechnetate (TcO4−) and hydrated oxide (TcO2·nH2O) in soil and groundwater. While the former, Tc(VII), is very soluble and mobile in the environment, the latter is considered sparingly soluble and immobile. Consequently, immobilization of Tc(VII) can be achieved through conversion of Tc(VII) into Tc(IV). In this study, carboxymethyl cellulose (CMC) stabilized FeS nanoparticles (CMC-FeS) were prepared and tested for reductive immobilization of Tc(VII). Effects of nanoparticle dosage and water chemistry, including pH, humic acid and Ca2+ ions, were examined. At a dosage of 100 mg/L of CMC-FeS as Fe, CMC-FeS rapidly removed >96% of 1.2 μM of Tc(VII) within 1 h, with a retarded first-order rate constant (ka) of 150.32 h-1. Higher pH in the range of 5.0–9.0 favored the reaction, with an optimal pH range of 8.0–9.0. While Ca2+ (up to 2 mM) only modestly affected the Tc(VII) removal, high concentrations of humic acid (up to 10 mg/L as TOC) showed increased inhibition on the Tc(VII) removal rate. FTIR and XPS analyses indicated that CMC-FeS immobilized TcO4− through reductive conversion of TcO4− into TcO2(s) and formation of Tc2S7 precipitate. The immobilized Tc remained insoluble when aged for 100 days under anoxic conditions, whereas up to 22.9% of the immobilized Tc was remobilized when it was exposed to air for 100 days.

Combined water pollution with the coexistence of heavy metals and organic contaminants is of great concern for practical wastewater treatment. In this study, a jaboticaba-like nanocomposite, titanate nanotubes supported TiO2 (TiO2/TiNTs), was synthesized by a two-step hydrothermal treatment. TiO2/TiNTs had large surface area, abundant of –ONa/H groups and fine crystal anatase phase, thus exhibited both good adsorptive performance for Cu(II) and high photocatalytic activity for phenanthrene degradation. The maximum Cu(II) adsorption capacity on TiO2/TiNTs was 115.0 mg/g at pH 5 according to Langmuir isotherm model, and >95% of phenanthrene was degraded within 4 h under UV light. TiO2/TiNTs showed about 10 times higher observed rate constant (kobs) for phenanthrene degradation compared to the unmodified TiNTs. More importantly, the coexistence of Cu(II) promoted photocatalytic degradation of phenanthrene, because the incorporated Cu(II) in the lattice of TiNTs could trap photo-excited electron and thus inhibited the electron-hole recombination. Density functional theory (DFT) calculation indicated that the sites of phenanthrene with high Fukui index (f0) preferred to be attacked by OH radicals. The quantitative structure–activity relationship (QSAR) analysis revealed that the degradation intermediates had lower acute toxicity and mutagenicity than phenanthrene. TiO2/TiNTs also owned high stability, as only slight loss of Cu(II) and phenanthrene removal efficiency was observed even after four reuse cycles. The developed material in this study is of great application potential for water or wastewater treatment with multi-contaminants, and this work can help us to better understand the mechanisms on reaction between Ti-based nanomaterials and different kinds of contaminants.

With different functional groups and hydrophobic/hydrophilic properties, natural organic matters (NOMs) displayed different combining capacities with metal ions. By using XAD-4 and DAX-8 resins, NOMs in natural lake were isolated into three fractions, i.e., HoB (hydrophobic base), HoA (hydrophobic acid) and HiM (hydrophilic matter). Afterwards, influences on Cu(II) adsorption onto titanate nanotubes (TNTs) were compared with varying NOMs and initial pH. As results, HoB can significantly control Cu(II) adsorption at pH 5, with the adsorption capacity increased 15% for 0.5 mg L−1 of HoB (ca. 120 mg g−1), which could be attributed to the formation of HoB-Cu complexation and electrostatic bridge effect of HoB with optimal concentration. Due to the easier ionization and complexation with Cu(II) at lower pH, HoA showed more obvious impaction on Cu(II) adsorption at pH 2. While HiM can influence Cu(II) adsorption at all pH ranges due to its hydrophilic groups and weak affinity to both TNTs and Cu(II). Furthermore, HoB dramatically changed the Langmuir model, with sharp increase of adsorption capacity as equilibrium Cu(II) increased, suggesting its significant involvement in Cu(II) adsorption. X-ray photoelectron spectroscopy (XPS) analysis revealed the absorbed Cu(II) existed in the form of TNTs‑OCu, TNTs‑COOCu and Cu(OH)2, proving Cu(II) adsorption mechanism including both direct adsorption by TNTs and bridging connection with NOMs. Moreover, the CO and OCO groups content ranked as HiM > HoB > HoA, while TNTs‑COOCu content ranked as HoA > HoB > HiM, suggesting HoB had the moderate connection with both TNTs and Cu(II), thus the impact on Cu(II) adsorption was remarkable.

Surface sediments are the inner source of contaminations in aquatic systems and usually maintain aerobic conditions. As the key participators of nitrification process, little is known about the activities and contributions of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in the surface sediments. In this study, we determined the net and potential nitrification rates and used 1-octyne as an AOB specific inhibitor to detect the contributions of AOA and AOB to nitrification in surface sediments of Danjiangkou reservoir, which is the water source area of the middle route of South-to-North Water Diversion Project in China. Quantitative PCR and Illumina high-throughput sequencing were used to evaluate the abundance and diversity of the amoA gene. The net and potential nitrification rates ranged from 0.42 to 1.93 and 2.06 to 8.79 mg N kg−1 dry sediments d−1, respectively. AOB dominated in both net and potential nitrification, whose contribution accounted for 52.7–78.6% and 59.9–88.1%, respectively. The cell-specific ammonia oxidation rate calculation also revealed the cell-specific rates of AOB were higher than that of AOA. The Spearman's rank correlation analysis suggested that ammonia accumulation led to the AOB predominant role in net nitrification activity, and AOB abundance played the key role in potential nitrification activity. Furthermore, phylogenetic analysis suggested AOB were predominantly characterized by the Nitrosospira cluster, while AOA by the Nitrososphaera and Nitrososphaera sister clusters. This study will help us to better understand the contributions and characteristics of AOA and AOB in aquatic sediments and provide improved strategies for nitrogen control in large reservoirs.

Peracetic acid (PAA) is a sanitizer with increasing use in food, medical and water treatment industries. Amino acids are important components in targeted foods for PAA treatment and ubiquitous in natural waterbodies and wastewater effluents as the primary form of dissolved organic nitrogen. To better understand the possible reactions, this work investigated the reaction kinetics and transformation pathways of selected amino acids towards PAA. Experimental results demonstrated that most amino acids showed sluggish reactivity to PAA except cysteine (CYS), methionine (MET), and histidine (HIS). CYS showed the highest reactivity with a very rapid reaction rate. Reactions of MET and HIS with PAA followed second-order kinetics with rate constants of 4.6 ± 0.2, and 1.8 ± 0.1 M−1⋅s−1 at pH 7, respectively. The reactions were faster at pH 5 and 7 than at pH 9 due to PAA speciation. Low concentrations of H2O2 coexistent with PAA contributed little to the oxidation of amino acids. The primary oxidation products of amino acids with PAA were [O] addition compounds on the reactive sites at thiol, thioether and imidazole groups. Theoretical calculations were applied to predict the reactivity and regioselectivity of PAA electrophilic attacks on amino acids and improved mechanistic understanding. As an oxidative disinfectant, the reaction of PAA with organics to form byproducts is inevitable; however, this study shows that PAA exhibits lower and more selective reactivity towards biomolecules such as amino acids than other common disinfectants, causing less concern of toxic disinfection byproducts. This attribute may allow greater stability and more targeted actions of PAA in various applications.

The discovery of complete ammonia oxidizing bacteria (CAOB) capable of performing the two-step nitrification process on their own has fundamentally upended our traditional perception. However, their environmental distribution and ecological significance in driving ammonia oxidation are still urgently awaited to be assessed. In this study, the diversity and abundance of CAOB amoA gene in wastewater treatment plants (WWTPs) were presented taking advantage of a newly designed primer pair specifically targeting CAOB amoA gene. Phylogenetic results demonstrated the novel amoA gene formed a clearly distinct cluster from the canonical amoA and pmoA genes. Among the five well-supported sub-clusters, Nitrospira nitrosa cluster accounted for 94.34% of all the currently retrieved sequences from WWTPs. More importantly, qPCR results demonstrated a remarkably high abundance of CAOB amoA gene, which were up to 182.7-fold more abundant than AOB amoA gene. This study provided new dimension and fundamental basis for future researches towards biogeochemical nitrogen cycle.

A composite comprises a carbonaceous and a metallic nanotube conjugated with a carbonaceous support. The composite may be used to remove contaminants from water.

ZrO2 modified BiOCl0.5I0.5 composites (ZBCI), synthesized via a facile precipitation method at room temperature, were utilized to photocatalytically oxidize and adsorb arsenite from water under visible light irradiation. The composites were well characterized by using various techniques. With visible light irradiation, 5 mg L−1 of As(III) could be completely removed by ZBCI (0.25 g L−1) in 90 min. Particularly, we found that ZBCI composites not only could oxidize As(III) into As(V) with visible light irradiation, but also could effectively capture the generated As(V), leading to the negligible residual As(III) or As(V) in aqueous solutions after 90 min treatment. In the fabricated composites, ZrO2 acted as the main adsorption sites while BiOCl0.5I0.5 served as the primary photocatalysis center. Because of the heterostructure of ZBCI, e- generated by BiOCl0.5I0.5 would be transferred to ZrO2 and inhibited e–h+ recombination rate, contributing to the improved photocatalytic efficiency. ZBCI could effectively remove As(III) over a broad range of pH from 3 to 11. Chloride and nitrate did not obviously affect the photocatalytic As(III) removal, while sulfate and phosphate yet reduced the capture of As(III). Moreover, ZBCI composites exhibited high photocatalytic As(III) removal efficiency during the fourth reused cycles. The facile synthesized ZBCI could be employed to capture and oxidize As(III) from water.

A novel composite material which is referred to as activated carbon fibre supported titanate nanotubes (TNTs@ACF) was used for the removal of methylene blue (MB) from water through the combined adsorption and photocatalysis. TNTs@ACF was synthesized through a one-step hydrothermal method, which was composed of the activated carbon fibre as the skeleton and supported titanate nanotubes. TNTs@ACF showed a large surface area of 540.7 m2/g, thus, facilitating adsorption and interaction with MB. TNTs@ACF could first pre-concentrate MB molecules onto the material and then degrade under UV light irradiation. The first-order model simplified from the Langmuir-Hinshelwood (L-H) model can well describe the photodegradation of MB on TNTs@ACF. Moreover, TNTs@ACF could be reused without significant capacity loss by UV light photo-regenerated. The structure and morphology of TNTs@ACF were indicated by TEM, SEM, and EDS, and it is found that TNTs were highly dispersed on the surface of ACF. XRD, FTIR, and XPS analyses of TNTs@ACF before and after the MB photodegradation also indicated the stability of the material. The combined adsorption and photodegradation suggests that TNTs@ACF is an attractive material for maintainable remediation of organic pollution in the environment.

Abstract Magnetic Fe3O4@BiOI@AgI (FBA) spheres were synthesized through a multi-step process. The fabricated photocatalysts were characterized by different techniques. To testify the visible light driven photocatalytic activity of FBA, Rhodamine B and Bisphenol A were chosen as model common and emerging organic contaminants, respectively. While, gram-negative strain Escherichia coli was selected as model waterborne bacteria. The results showed that under visible light irradiation, \FBA\ contained strong photocatalytic degradation capacity towards both RhB and BPA. Moreover, \FBA\ was also found to exhibit excellent disinfection activity towards E. coli. The photocatalytic mechanisms for different pollutants by \FBA\ were determined and found to vary for different pollutants. Specifically, scavenger experiments, degradation intermediates determination, as well as theoretical density functional theory (DFT) analysis showed that RhB and \BPA\ were degraded via photosensitization (dominated by e- and ·O2−) and direct photocatalytic oxidation (contributed by h+, e- and ·O2−), respectively. Whereas, E. coli cells yet were found to be inactivated by the generation of e- and ·O2− rather than by the released Ag+. Since it contained superparamagnetic property, \FBA\ could be easily separated from the reaction suspension after use. Due to the excellent photo stability, \FBA\ exhibited strong photocatalytic activity in the fourth reused recycle. Therefore, \FBA\ could serve as a promising alternative for water purification.

Abstract A niobate/titanate nanoflakes (Nb/TiNFs) composite was synthesized through a one-step hydrothermal method. Nb/TiNFs displayed a heterojunction structure owing to deposition of a small fraction of niobate onto tri-titanate nanoflakes. Tri-titanate (Na1.6H0.4Ti3O71.7H2O) was the primary crystal phase, and the molar ratio of niobate (Na2Nb2O6H2O) to titanate was determined to be 1:15.9. Nb/TiNFs showed rapid adsorption kinetics and high adsorption capacity for U(VI) (Langmuir Qmax = 298.5 mg/g). Ion-exchange and surface complexation were the key mechanisms for U(VI) uptake, and the adsorption was further enhanced by the unique tunnel lattice structure of the heterojunction. Moreover, Nb/TiNFs were able to convert U(VI) into its immobile form, UO2(s) under solar light through photocatalytic reduction. More than 89.3% of (VI) was transformed into U(IV) after 4 h of solar irradiation (initial U(VI) = 20 mg/L, pH = 5.0). Diffuse reflectance UV–vis absorption spectra and Mott-Schottky plots indicated a narrowed band gap energy of Nb/TiNFs compared to neat TNTs. Density functional theory (DFT) calculation on band structure and density of states further confirmed the heterojunction architecture of niobate and titanate, resulting in offset of the conduction bands for the two phases in the composite material. Therefore, transfer of photo-excited electrons from titanate to niobate leads to inhibition of recombination of the electron-hole pairs. In addition, the trapping of uranium in the tunnel lattice of titanate and niobate heterojunction prevents re-oxidation of U(IV) to U(VI), thus achieving long-term immobilization of uranium. Remobilization tests indicated that only 18.7% of U(VI) was re-oxidized to U(VI) and almost no U dissolved into the aqueous phase when exposed air for 90 days. The new material is promising for separation and safe disposal of high strength radionuclides in water.

Pharmaceutically active compounds (PhACs) are widely detected emerging contaminants in water environments and possess high potential risks to human health and aquatic life; however, conventional water treatment processes cannot remove them sufficiently. The boom in nanoscience and nanotechnology offers opportunities to leapfrog on the back of these new technologies to develop innovative techniques in the field of water treatment. The extraordinary properties of nanomaterials, such as large surface area, quantum effect, electrochemical and magnetic properties, and other size-dependent physical and chemical properties, offer nanotechnologies great advantages over conventional technologies. To date, nanomaterials have been extensively applied or investigated in adsorption, photocatalysis, catalytic ozonation and filtration processes and have been shown to have many promising potential application prospects. Among the various nanomaterials, graphene and carbon nanotubes have shown a superior adsorption capacity for the removal of PhACs and possess great potential for modifying photocatalysts; moreover, they can also act as highly efficient catalysts for ozonation. The nano-sized photocatalysts, i.e. nano-TiO2, graphitic carbon nitride, MoS2 nanosheets, and ZnO, generally exhibit higher photocatalytic activity than bulk photocatalysts. The involvement of nanomaterials in a membrane can improve the permeability, selectivity, and anti-fouling properties of the membrane for improved filtration processes. However, some challenges, such as high cost, poor separation performance and environmental risks, are still impeding their engineering application. Aiming to provide readers with a comprehensive insight into the application of nanotechnologies for PhACs' remediation, the current review summarizes the recent advances and breakthroughs made in nanotechnology for PhACs' removal, highlights the modification methods for improving the effectiveness of treatment methods using nanomaterials, and proposes a number of possible further research directions.

Chromium contamination can be remediated by catalytic reduction with precious metal palladium (Pd). Thus, enhancing Pd catalytic performance is of strong interest. An environmentally friendly and nontoxic approach for production of palladium nanoparticles (Pd-NPs) is to use microorganisms. Herein, the biosynthesis of Pd-NPs by Shewanella loihica PV-4 is reported for the first time. Both extracellular and intracellular bioreduction of Pd(II) has contributed this bio-fabrication, with the production of Pd0 particles in the size range of 4-10 nm. It was found that several factors including a higher initial Pd(II) concentration, weak acid medium condition, and a lager dosage of sodium formate and biomass amount could facilitate this synthesis process. The biosynthesized Pd-NPs exhibited excellent catalytic activities for chromium (VI) reduction, with complete removal of Cr(VI) after 3-h operation with a catalyst amount of 0.5 mg/mL, an initial Cr(VI) concentration of 0.5 mM, and formic acid as electron donor; these are significant advantages to chemically prepared Pd0. Cr(VI) reduction catalyzed by biosynthesized Pd-NPs was promoted with factors such as a higher dosage of formic acid, lower pH, and a lower initial Cr(VI) concentration. Density functional theory calculations of formic acid decomposition on Pd-NPs revealed that Pd-NPs facilitated formic acid to decompose into CO2 and H2. These results have collectively demonstrated the feasibility of the biosynthesis of Pd-NPs by Shewanella loihica PV-4 and its potential application as a promising catalyst for remediation of chromium contamination.