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.
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.
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.
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.