Functional UiO-66 for highly selective adsorption of N-nitrosodipropylamine: adsorption performance and mechanisms.

N-Nitrosodipropylamine (NDPA) is a class of nitrogenous disinfection by-products (N-DBPs) with high toxicity. Although NDPA present in water bodies is at relatively low concentrations, the potential risk is high due to its high toxicity and bioaccumulation. Metal-organic frameworks (MOFs), a new type of porous material with remarkable functionality, have shown great performance in a wide variety of applications in adsorption. This is the first study investigating the adsorption of MOFs on NDPA. Herein, UiO-66 with -NH2 and imidazolium functional groups were synthesized by modifying UiO-66 after amination. Adsorption kinetics and isotherm models were used to compare the adsorption properties of the two materials for low-concentration NDPA in water. The results showed that the behavior of all the adsorbents was consistent with the Langmuir model and the pseudo-second-order model and that the adsorption was homogeneous chemisorption. The structures of the nanoparticles were characterized by FTIR, zeta potential, XRD, SEM and BET measurements. Based on the characteristics, four adsorption mechanisms, namely electron conjugation, coordination reaction, anion-π interaction, and van der Waals forces, were simultaneously involved in the adsorption. The influencing factor experiment revealed that the adsorption of UiO-66-NH2 and (I-)Meim-UiO-66 involved hydrogen bonding and electrostatic interactions, respectively.

Removal of N-nitrosopyrrolidine from GAC by a three-dimensional electrochemical reactor: degradation mechanism and degradation path.

Nitrogen-containing disinfection by-products (N-DBPs) produced in the process of drinking water disinfection are widely concerning due to the high cytotoxicity and genotoxicity. It is due to the difficulty of natural degradation of N-DBPs in water and the fact that conventional treatment systems do not effectively treat N-DBPs in drinking water. In this study, N-nitrosopyrrolidine (NPYR) in water was electrocatalytically degraded by a three-dimensional electrode reactor (3DER). This system applied graphite plates as anode and cathode. The granular activated carbon (GAC) was used as third electrode. The degradation of NPYR using a continuous flow three-dimensional electrode reactor was investigated by examining the effects of flow rate, current density, electrolyte concentration, and pollutant concentration on the degradation efficiency, energy consumption, and reaction kinetics of GAC particle electrodes. The results showed that the optimal operating conditions were flow rate = 0.45 mL/min, current density = 6 mA/cm2, Na2SO4 concentration = 0.28 mol/L, and NPYR concentration = 20 mg/L. Under optimal conditions, the degradation of NPYR exceeded 58.84%. The main contributor of indirect oxidation was deduced from free radical quenching experiments. NPYR concentration was measured by GC-MS with DB-5 capillary column, operating in full scan monitoring mode for appropriate quantification of NPYR and intermediates. Based on the identification of reaction intermediates, a possible pathway for the electrochemical oxidation of NPYR on GAC particle electrodes was proposed.

Kinetically and Thermodynamically Favorable Ni-Al Layered Double Hydroxide/Ni-Doped Zn0.5Cd0.5S S-Scheme Heterojunction Triggering Photocatalytic H2 Evolution.

Layered double hydroxide (LDH)-based photocatalysts have attracted more attention in photocatalysis due to their low cost, wide band gaps, and adjustable photocatalytic active sites; however, their low photogenerated carrier separation efficiency limits their photocatalytic efficiency. Herein, a NiAl-LDH/Ni-doped Zn0.5Cd0.5S (LDH/Ni-ZCS) S-scheme heterojunction is rationally designed and constructed from kinetically and thermodynamically favorable angles. The 15% LDH/1% Ni-ZCS displays comparable photocatalytic hydrogen evolution (PHE) activity with a rate of 6584.0 µmol g-1 h-1, which exceeds by ∼6.14- and ∼1.73-fold those of ZCS and 1% Ni-ZCS, respectively, and outperforms most of the previously reported LDH-based and metal sulfide-based photocatalysts. In addition, the apparent quantum yield of 15% LDH/1% Ni-ZCS reaches 12.1% at 420 nm. In situ X-ray photoelectron spectroscopy, photodeposition, and theoretical calculation reveal the specific transfer path of photogenerated carriers. On this basis, we propose the possible photocatalytic mechanism. The fabrication of the S-scheme heterojunction not only accelerates the separation of photogenerated carriers but also decreases the activation energy of H2 evolution and improves the redox capacity. Moreover, there are huge amounts of hydroxyl groups distributed on the surface of photocatalysts, which is highly polar and easy to combine with H2O with a large dielectric constant to form a hydrogen bond, which can further accelerate PHE.

Aqueous rechargeable ammonium ion batteries based on MoS2/MXene with a ball-flower morphology as an anode and NH4V4O10 with a layered structure as a cathode.

Due to the small hydrated ionic radius and light molar mass of ammonium ions, aqueous ammonium ion batteries attract much attention, providing high security, environmental friendliness and low cost. However, the lack of suitable electrode materials with high specific capacity is a big challenge for practical application. Therefore, in view of this problem, we fabricated an anode applying a MoS2 material with a ball-flower morphology anchored to MXene nanoflakes, and it shows excellent rate capability in a novel aqueous ammonium ion battery. The corresponding charge capacities of composite electrodes are 279.2, 204.4, 173.2, 118.7, and 80.5 mA h g-1 at 20, 50, 100, 200, and 500 mA g-1, respectively. Meanwhile, polyvanadate was selected as a cathode material for a full aqueous ammonium ion battery, and interestingly it was discovered that the size of this material decreases with increasing synthesis temperature. The discharge capacities of NH4V4O10 electrodes fabricated at 140 °C, 160 °C, and 180 °C at 50 mA g-1 are 88.6, 125.1 and 155.5 mA h g-1, respectively. Furthermore, we also explore the corresponding electrochemical mechanism using XRD and XPS. A full aqueous ammonium ion battery based on both electrodes shows superior ammonium ion storage properties and provides new ideas for the development of this strategy.

Optimized fabrication of Cu-doped ZnO/calcined CoFe‒LDH composite for efficient degradation of bisphenol a through synergistic visible-light photocatalysis and persulfate activation: Performance and mechanisms.

A novel magnetically separable Cu/ZnO/CoFe‒CLDH composite, whose synthesis was optimized using the Taguchi approach, was optimally synthesized by hydrothermally coupling Cu-doped ZnO and calcined CoFe-LDH. The synthesized Cu/ZnO/CoFe‒CLDH was applied to construct a synergistic process of integrating visible-light photocatalysis (VPC) with persulfate activation (PSA) and to degrade bisphenol A (BPA). Various characterizations proved that Cu/ZnO/CoFe‒CLDH possessed excellent physicochemical, optoelectronic and magnetic properties, thereby enhancing the catalytic performance. The Cu/ZnO/CoFe‒CLDH composite achieved highly efficient BPA degradation during the synergistic VPC‒PSA process, and its reaction rate constant (0.74 h-1) was 6.17-, 4.11-, and 2.85-fold higher than that of Cu/ZnO, CoFe‒CLDH, and Cu/ZnO/CoFe‒CLDH (VPC only), respectively. Moreover, the effects of the catalyst dosage, initial pollutant concentration, solution pH, persulfate dosage and coexisting ions on BPA degradation were comprehensively investigated. Radical-trapping experiments revealed that the contributions of ·OH, SO4·â€’, ·O2-, and 1O2 involved in BPA degradation. Based on the intermediates identified by LC/MS, the main BPA degradation pathways were determined, the overall trend of which reflects a decreasing ecotoxicity. This study verified the effectiveness of the synergistic VPC‒PSA process with Cu/ZnO/CoFe‒CLDH, which could be used as a new reference for removing organic micropollutants from water.

Efficient degradation of N-nitrosopyrrolidine using CoFe-LDH/AC particle electrode via heterogeneous Fenton-like reaction.

With the rapid development of drinking water disinfection technology, extensive attentions are paid to the nitrogenous disinfection by-products (N-DBPs) that has strong carcinogenicity, thus their degradation becomes important for the health of human beings. In this work, for the first time, CoFe-LDH material used as particle electrode is proposed to treat trace N-nitrosopyrrolidine (NPYR) in a three-dimensional aeration electrocatalysis reactor (3DAER). The factors on the degradation efficiency and energy consumption of NPYR are systematically investigated, and the results of radical quenching experiments show that the degradation of NPYR is completed by combining with ·OH, ·O2and direct oxidation together. CoFe-LDH particle electrode plays a vital role in generating ·OH via heterogeneous ‾Fenton-like reaction. Moreover, the adsorbed saturated CoFe-LDH particle electrode can be regenerated by electrochemical action to induce further recycle adsorption and form in-situ electrocatalysis. This work pave a way for the removal of NPYR with high efficiency, low energy conservation and environmental protection.

Synergistic effect of a triethanolamine-modified carbon-based layered double hydroxide for efficient removal of nitrate from micro-polluted water.

Owing to the ubiquitous existence and low concentrations of detrimental nitrogen pollutants in micro-polluted water, simple adsorption-oriented approaches are becoming increasingly appealing for the effective removal of NO3- from wastewater. Triethanolamine (TDA) modified carbon-based layered double hydroxide (LDH) composites (TDA@LDH/CS) were synthesized by a supersaturated co-precipitation method for efficient NO3- adsorption. The characterization results showed that TDA@LDH/CS, formed by the stacking of irregular nanosheets and lamellar aggregates, has a mesoporous structure and a specific surface area of 67.15 m2 g-1. The Langmuir and pseudo-second-order kinetic models were well fitted with the adsorption of NO3- by TDA@LDH/CS, with the maximum adsorption capacity reaching 14.45 mg g-1, and the adsorption process was consistent with the spontaneous exothermic entropy increasement. Furthermore, the synergistic adsorption mechanism of NO3- by the TDA-modified materials was proposed using XPS analysis, which indicated that TDA modification greatly enriched the surface of TDA@LDH/CS with tertiary amine groups (R3N) and hydroxyl groups (-OH), providing more adsorption sites and active sites. After five cycles, the NO3- removal rate could still reach 64.2%, which exhibited its high potential to be utilized as an adsorbent for the removal of nitrogen pollutants from micro-polluted water.

Efficient treatment of aged landfill leachate containing high ammonia nitrogen concentration using dynamic wave stripping: Insights into influencing factors and kinetic mechanism.

Aged landfill leachate is challenging to treat owing to its extremely high ammonia concentration and poor biodegradability. We constructed pilot-scale dynamic wave stripping equipment to separate ammonia from landfill leachate and achieved excellent results. To further expand the usage of pilot-scale equipment in actual water treatment process and implement it in a sewage plant, we established the mass transfer kinetic physics and mathematical model of the dynamic wave stripping process based on the surface renewal theory and the traditional stripping method. The surface renewal theory and the traditional stripping method are employed to analyze the mechanism of various experimental parameters affecting the stripping process, predict the stripping effect of the equipment under different conditions, and verify the calculation results of the model using the kinetic fitting results of the experimental data. These calculation results of the model indicate that the mass transfer kinetic coefficients of ammonia stripping at 20 °C, 25 °C, and 30 °C are 85.62 min, 75.34 min, and 65.88 min, respectively, when the gas-liquid ratio is 129. When the gas-liquid ratios are 62, 129, and 163 at 25 °C, the mass transfer kinetic coefficients of ammonia stripping are 102.61 min, 75.34 min, and 61.43 min, respectively. With increasing temperature and gas-liquid ratio, the particle size and number of bubbles in the wave tube of the stripping equipment gradually decrease and the mass transfer efficiency of free ammonia between the gas and liquid phases improves, enhancing the stripping efficiency of ammonia nitrogen.

Synergistic denitrification and phosphorus removal performance of a biofilm-microflocculation system and its microbial community variations: A pilot-scale study for a wastewater treatment plant.

AIMS: For upgrading and reconstructing a municipal wastewater treatment plant, a biofilm-microflocculation filter system was designed and established towards synergistic improvement of denitrification and phosphorus removal from the secondary effluent. METHODS AND RESULTS: The establishment of the biofilm-microflocculation filter system underwent several processes, including sludge inoculation, biofilm formation and polyaluminum chloride (PAC) addition as flocculating agent. Microbial community analysis indicated that the dominant denitrification bacteria of the biofilm filter were in the phylum Proteobacteria and the genera Hydrogenophaga and Dechloromonas. On the basis of the initiation of filter system under optimal parameters such as C/N ratio of 5.3, hydraulic retention time of 1.06 h and PAC of 5 mg L-1 , approximately 75% COD, 80% TN and 75% TP could be effectively removed to satisfy discharge standards. Comparing the variations of microbial community structure at the genus level during the operating period of the filter system, it was found that the relative abundance of denitrification bacteria merely shifted from 53.14% to 48.76%, demonstrating that the effect of PAC addition on the main micro-organisms is marginal. CONCLUSIONS: From the above results, it can be verified that the established biofilm-microflocculation filter system has practical and reliable performance for simultaneous biological denitrification and phosphorus removal. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides a reference method for improving the advanced treatment of wastewater plant secondary effluent.

The connection between aeration regimes and EPS composition in nitritation biofilm.

The effects of aeration regimes (intermittent and continuous aeration) on nitritation performance and biofilm EPS composition were evaluated in moving bed biofilm reactors (MBBRs), and a hypothesis that the aeration regimes affect EPS composition by affecting the microbial activity and sludge discharge content was proposed. The effluent NO2-/NH4+ ratio corresponded to that of an anammox reaction (1.07 ± 0.20) for the MBBR with continuous aeration (MBBRcon.), while that in the MBBR with intermittent aeration (20 min on/15 min off) (MBBRint.) was relatively lower (0.75 ± 0.19). Furthermore, the activity of ammonia-oxidizing bacteria in MBBRcon. was 0.4-7.9 mg-N·L-1·h-1 more than that in MBBRint., which was consistent with the lower proportion of dead cells in MBBRcon. compared with MBBRint. (9.4% vs. 31.8%). The higher microbial activity in MBBRcon. led to more sludge discharge than MBBRint., which was reflected in the higher biofilm detachment rate in MBBRcon. compared with MBBRint. (0.15 ± 0.02 vs. 0.11 ± 0.02 g m-2·d-1). The ratio of humic substances to polysaccharides in the EPS was high (0.96 ± 0.08) in the detachment biomass, while the ratios in the nitritation biofilm on carriers from MBBRcon. and MBBRint. were 0.52 ± 0.13 and 0.72 ± 0.16, respectively. We hypothesized that biofilm matrix with high ratios of humic substances to polysaccharides are structurally unstable and prone to fall off. In addition, the higher proportion of dead cells in MBBRint. made the proportion of humic substances in EPS high. Meanwhile, less sludge discharge in MBBRint. than MBBRcon. caused more humic substances to accumulate in the biofilm. These was responsible for the higher ratio of humic substances to polysaccharides in MBBRint. compared with MBBRcon. The findings elucidate the connection between aeration regimes and biofilm EPS composition, and guide the choice of aeration regimes in the design of biofilm reactors for partial nitritation.

Visual evidence for anammox granules expanding their size by aggregation of anammox micro-granules.

Granular sludge is superior in sustainable wastewater treatment; however, no consensus has achieved in its formation mechanism. In this study, we provide visual and experimental evidences to reveal how the large anammox granules formed. Micro-observation of anammox granules illustrated that some special anammox granules were clearly composed of numerous micro-granules, which enveloped by transparent extracellular polymeric substances (EPS). Static culture experiment proved that anammox granules were easy to aggregate and form a larger entirety within approximately 14 days when there were no severe external disturbances (mainly hydraulic shear force). Stratified EPS extraction and selective enzymatic digestion tests further elucidated that tightly-bound EPS and extracellular proteins were the most vital constituents in maintaining the structure of anammox granules, and the minimal size of anammox micro-granules that aggregated to form large anammox granules was approximately 100-150 µm in the reactor studied herein. Our findings highlight that anammox granules could expand their size and form larger granules by the aggregation of anammox micro-granules, representing a natural but significant granule formation and enlargement mechanism. Understanding the enlargement mechanism could consummate the granulation process and help to culture large size anammox granules.

Reduction and immobilization of Cr(VI) in aqueous solutions by blast furnace slag supported sulfidized nanoscale zerovalent iron.

In this study, an industrial waste-blast furnace slag (BFS) supported sulfidized nanoscale zerovalent iron (S-nZVI@BFS) was prepared and used for synergistic reduction and adsorptive removal of Cr(VI) from aqueous solutions. The characterization analysis showed that Fe0 and FeS were well dispersed on the surface of BFS, and the specific surface area of S-nZVI@BFS was 141.986 m2 g-1. Batch experiments demonstrated that the removal capacity of Cr(VI) was as high as 184 mg/g for S-nZVI@BFS. The pseudo-second-order kinetic model fitted the Cr(VI) removal kinetics well. Cr(VI) removal on the S-nZVI@BFS relied highly on pH values. The reduced Cr(VI) precipitated on S-nZVI@BFS mainly as CrxFe(1-x)(OH)3, CrxFe(1-x) OOH and Cr2S3, and the alkaline capacity of the BFS could efficiently prevent the release of Cr(III) from the precipitations in acid condition. Thus, supporting S-nZVI on BFS was an effective and safe method for Cr(VI) removal from aqueous solutions.

Novel quantification of formation trend and reaction efficiency of hydroxyl radicals for investigating photocatalytic mechanism of Fe-doped TiO2 during UV and visible light-induced degradation of acid orange 7.

A detailed mechanistic investigation of the hydroxyl radical (•OH) formation and organic pollutant degradation over transition metal-doped and undoped TiO2 photocatalysts was performed by the quantitative measurement of •OH and the identification of intermediate products under various experimental conditions. The Fe-doped TiO2 as a typical subject was prepared, characterized and used to degrade an azo dye Acid Orange 7 (AO7). It is indicated that the enhanced photocatalytic activity of Fe-doped TiO2 for AO7 degradation was attributed to the increase in surface area, the facilitated charge transfer via Fe-dopant, and a red shift of absorbable wavelength, maintaining a great formation of •OH under visible irradiation. The oxidation of H2O by holes was estimated as the major pathway of •OH formation rather than the reduction of dissolved O2 by electrons, and their formation trends reached to approximately 75% and 25%, respectively. Meanwhile the synergistic effect of Fe-dopant produced nearly 10% of extra •OH by visible light photoactivation. The intermediate products and pathways of AO7 degradation varied greatly with different photocatalysts and conditions of the process, involving several reaction mechanisms such as the azo bond cleaving, naphthalene oxidation, desulfonation, and hydroxylated products generation. Through the quantification of •OH-reacted efficiency we proposed, a stoichiometry of •OH affecting overall reaction mechanisms in the TiO2-assisted photodegradation of AO7 was further established. This study can provide new insights on how to better clarify the variation regularity of organic pollutant degradation from different treatments of the •OH-based advanced oxidation processes.

Removal of organics by combined process of coagulation-chlorination-ultrafiltration: optimization of overall operation parameters.

To gain the run parameters of the combined process of coagulation/in situ chlorination/ultrafiltration (UF) so that the system can remove as much organic contaminants as possible without serious membrane fouling, the impacts of operation conditions in coagulation and pre-chlorination unit were investigated in a pilot-scale test. The characteristics of organics in UF influent were examined by excitation emission matrix spectroscopy to find out fouling behavior of different natural organic matter compositions to UF membrane. Thereafter, the operation parameters of different processing units of the hybrid device were optimized by response surface methodology (RSM). The results showed that the tests with the agitation speed of 40 r min-1 had the lowest membrane fouling rate and the highest CODMn removal, in addition, inappropriate dosage of sodium hypochlorite in membrane influent might exert negative impacts on membrane by lowering UV254 rejection, especially during the high algae laden period. The predominant factors of membrane fouling were the existence of tryptophan protein-like substances and the soluble microbial products. Optimum values of the mechanical rotation speed in coagulation unit, chemical dosage in pre-chlorination unit, and membrane flux in UF unit of the integrative process were 41.79 r min-1, 1.40 mg L-1, and 82.26 LMH, respectively.

[Impact of dissolved oxygen on the activity of anaerobic granular sludges].

The effect of dissolved oxygen (DO) on the methanogenic activity of anaerobic granular sludges introduced into the expanded granular sludge bed (EGSB) reactor was measured in serum flasks. Results show that the specific methanogenic activity (SMA) decreases with DO increases. At 22 degrees C, the SMA drops from 75.9 mL x (g x d)(-1), 91.1 mL x (g x d)(-1) to 47.6 mL x (g x d)(-1), 71.4 mL x (g x d)(-1), respectively as DO increases from 0.00 mg/L to 7.00 mg/L. Higher temperature can weaken this trend and significantly promote SMA. As the control levels of temperature is 28 degrees C, 35 degrees C, the SMA average increases by 54.0%, 114.4% compared with that of the first gas production experiment. The study confirms that the presence of dissolved oxygen in the influent of an EGSB reactor does not constitute any evidently detrimental effect on the performance of anaerobic treatment process. Anaerobic granular sludges are demonstrated high tolerance for dissolved oxygen so that in practice this factor can be neglected.