Field Of Wastewater Treatment Research Articles

Isolation and identification of a novel aerobic denitrifying bacterium with quorum quenching activity and the effect of environmental factors on its performance

A novel aerobic denitrifying bacterium capable of quorum quenching (QQ), Acinetobacter strain WZL728, was first isolated. WZL728 showed excellent aerobic denitrification performance and QQ activity. Besides, its optimal aerobic denitrification condition was pH 7.1, temperature 32.0 °C, C/N ratio 7.4 and shaking speed 108.0 rpm. However, its optimal QQ condition was pH 7.2, temperature 32.4 °C, C/N ratio 7.1 and shaking speed 96.1 rpm. The QQ activity of WZL728 was more tolerant to environmental changes than its aerobic denitrification performance because of the different response of its denitrification and QQ function genes expression. Moreover, it was revealed that the strain degraded N-acyl-homoserine lactones (AHLs) with long acyl chains by secreting extracellular QQ acylase. Due to the high QQ activity of the aerobic denitrifying bacterium, it may have great potential for controlling membrane biofouling in the field of wastewater treatment. • A novel aerobic denitrifier with QQ activity (WZL728) was isolated and identified. • WZL728 efficiently removed nitrate and degraded AHLs under aerobic conditions. • The QQ of WZL728 was more tolerant to environmental changes than denitrification. • WZL728 hydrolyzed AHLs with long acyl chains by secreting exogenous acylase.

Ultrasound-assisted synthesis of gold nanoparticles supported on β-cyclodextrin for catalytic reduction of nitrophenols

Nitrophenols with high toxicity are well known as one of the main pollutants in water environment while aminophenols, products of the reduction, are important intermediates in the fabrication of several drugs. Thus, the reduction of nitrophenols is considerably attractive in wastewater treatment and pharmaceutical fields. In this work, gold nanoparticles (AuNPs) catalyst was straightforwardly fabricated using β-cyclodextrin as a reducing and stabilizing agent under ultrasound irradiation. The synthetic conditions were explored via the changes in concentration of β-cyclodextrin, environmental pH, temperature and time. The synthesized AuNPs under the optimal condition showed a size distribution in range of 3–21 nm with a mean size of 12 nm. The dynamic lighting scatter and zeta potential data showed the stable colloidal solutions and X-ray diffraction and selected area electron diffraction patterns confirmed crystalline structure of AuNPs. The influence of reagents and the nanoparticles on kinetic data of the reduction was investigated. The kinetic data showed that the performance of 2-nitrophenol reduction is better than that of 4-nitrophenol while rate constants of the reduction is linear to both initial concentrations of nitrophenol substrates and catalyst amount.

Homogeneous ferrous iron oxidation in a pilot-scale electrocoagulation system treating municipal wastewater: a model validation and simulation study.

During an iron-electrocoagulation (Fe-EC) process, floc formation is essential for achieving high contaminants removal. Thus, the complete oxidation of the Fe2+ dosed as coagulant is a critical step for ferric oxides flocs formation. Since the fluctuation in the quality of the influent wastewater affects the kinetics of Fe2+ oxidation, the estimation of optimal operating conditions (i.e. the retention time, dissolved oxygen (DO) concentration, etc.) for high Fe2+ oxidation is required. In this study, the kinetics of Fe2+ oxidation was simulated using PHREEQC software by theoretically optimizing, validating and improving the previously published kinetic models. During model simulation, the process parameters were varied from low to high ranges: Fe2+ dosage (10-100 mg/L) and retention times under the influence of changing pH (7.5-8.2), temperature (12-22 °C), alkalinity (5-10 mEq/L) and initial DO (8.6-10.5 mg/L). Fe2+ oxidation rate was more affected by pH variations in the influent than by temperature variations. A pH increase (+0.4 to +1.7 pH units) was observed due to the low wastewater alkalinity, promoting high Fe2+ oxidation rates. To ensure optimum Fe2+ oxidation levels (≥98%), a minimum retention time of 20 minutes was estimated. Finally, the residual DO concentration should be >3.5 mg/L to avoid a decrease in the oxidation rate. This study contributes to the ongoing research in the field of physico-chemical wastewater treatment with EC by establishing the optimal process parameters required for system optimization and process scalability.

Nano-alumina wrapped carbon microspheres for ultrahigh elimination of pentavalent arsenic and fluoride from potable water

Materials with ultrahigh adsorption competences are extensively required for effective wastewater remediation. Unfortunately, leaching and agglomeration of nanomaterial-based adsorbents is a common problem to be resolved. Carbon-based hybrid nanocomposite showing enormous capability in the field of wastewater treatment. Arsenic and fluoride in water have unpropitious effects on people’s health, and remediation of these ions through adsorption is one of the foremost challenges and high priority to the research. The present study deals with fabricating a novel composite using alumina wrapped carbon microspheres (Al-CMs) with high adsorption capacities and investigating the mechanism for removing pentavalent arsenic/arsenate (As(V)) and fluoride (F−) at the molecular level. The maximum adsorption capacities for As(V) and F− calculated from the Langmuir model are 68 and 371.1 mg/g, respectively, comparatively higher than other reported nano-adsorbents. Under optimized conditions, Al-CMs are able to remove more than 98% of F− and As(V) under wide range of pH (2–12). Further, the interaction energy of Al-CMs with F− and As(V) was examined using density functional theory (DFT). The reported work exhibits a feasible adsorbent for removing F− and As(V) from the wastewater.

Electrochemical nitrate reduction to produce ammonia integrated into wastewater treatment: Investigations and challenges

Nitrate (NO3−) is widely found in wastewater, which is harmful to human health and water environmental. Electrochemical reduction can convert NO3− to high value-added ammonia (NH3)/ammonium (NH4+) for pollutant removal and resource recovery. Currently, electrochemical nitrate reduction to produce ammonia (ENRA) is mostly focused on the preparation of high-performance catalysts, while ignoring the prerequisite for industrial application as the stable operation and optimal regulation of the process. Therefore, the review focused on wastewater treatment, based on the mechanism of electrochemical nitrate reduction for ammonia production and reactor construction (reactor, power supply system), then summarized the operation control strategies (such as reduction potential, nitrate concentration, inorganic ions, pH) that should be noted for ENRA. Finally, the challenges (system structure, economy) and prospects (ammonia recovery process, construction of large-scale ENRA system, application of real wastewater) of the field as it moves towards commercialization were discussed. It is hoped that this review will facilitate the scaling up of ENRA in the wastewater treatment field.

Facile preparation of recyclable and flexible BiOBr@TiO2/PU-SF composite porous membrane for efficient photocatalytic degradation of mineral flotation wastewater

Various semiconductor nanopowders can photodegrade wastewater efficiently, but their practical application is grievously limited due to poor recycling performance, insufficient sunlight utilization and potential secondary pollution. Membrane materials have been widely used for water treatment, including oil-water separation, desalination and sewage purification. In this paper, a novel BiOBr@TiO2/PU-SF composite porous membrane was prepared via a facile blending-phase separation-impregnation-precipitation method, and this was the first time that the novel membrane material was used as a photocatalyst for mineral flotation wastewater disposal. The PU-SF composite membrane with irregular porous structure acted as a loading substrate, which not only provided abundant space to immobilize BiOBr and TiO2 nanoparticles but also offered more photocatalytically active sites. The as-prepared BiOBr@TiO2/PU-SF composites were well characterized and exhibited higher photocatalytic activity as compared to BiOBr/PU-SF and TiO2/PU-SF. Combining the result of the characterization and free radical capture experiments with correlative theoretical calculations, we confirmed that the significant enhanced photocatalytic performance of BiOBr@TiO2/PU-SF membranes was attributed to the Z-scheme heterojunction formed between BiOBr and TiO2. In addition, the novel composite membrane material is flexible, it can be sheared, folded, and stretched arbitrarily. More importantly, the BiOBr@TiO2/PU-SF membrane can be readily taken out from the photocatalytic reaction system by tweezers, and the catalytic activity was essentially unchanged after being reused for 3 times. This novel recyclable flexible photocatalytic membrane will have promising prospect in field of actual mineral flotation wastewater treatment.

A highly promoted nanofiltration membrane by incorporating of aminated Zr-based MOF for efficient salts and dyes removal with excellent antifouling properties

Nowadays, effective removal of dye and salt from aqueous solutions has received widespread attention in the field of wastewater treatment. In this study, Zr-based nanofillers were used to create high-flux polyethersulfone nanofiltration membranes with impressive anti-fouling performance. Three different levels of UiO-66-NH2 concentration (0.01, 0.1, 1 wt%) were used in membrane body. Solvothermal method was used to synthesize the nanoparticles, and their physical and chemical characteristics were examined through FTIR, XRD, EDAX, and FESEM analyses. Membranes properties also were investigated by SEM, porosity, water content, roughness, water contact angle, flux, separation efficiency, and fouling studies. The surface roughness of the blended membrane with 0.01 wt% nanoparticles (M2) was almost halved compared to the pristine membrane (M1). The water contact angle was also reduced from 70.98° for M1 to 39.09° for M2. The water flux of M2 with 0.01 wt% nanoparticles was 2.31 times higher than that of the pristine membrane. The MB, RhB, and RB21 dyes, as well as Na2SO4, MgSO4, MgCl2, and NaCl solutions, were used to investigate the membrane separation efficiency. All modified membranes showed significant dye retention for both cationic and anionic dyes, and sodium sulfate rejection reached up to> 93.2%. The M2 exhibited the best performance for removal of MB (95.8%), RhB (94.2%), and RB21 (83.6%). The FRR was 46.51% for bare membrane, whereas it was increased significantly for the modified samples up to> 86%. The total resistance of the optimal membrane was remarkably reduced compared to the PES pristine membrane.

Enhancing resource recovery via cranberry syrup waste at the Wisconsin Rapids WRRF: An experimental and modeling study

The Wisconsin Rapids Wastewater Treatment Plant (WRWWTP) is faced with a more stringent effluent phosphorus requirement that will drive capital investment between 2020 and 2025. The facility will need to achieve a monthly average value of 0.36 mg L−1 of total phosphorus (TP). While the facility has sufficient influent carbon to drive a conventional enhanced biological phosphorus removal (EBPR) configuration, the existing infrastructure makes the addition of influent selector zones cost prohibitive. Underutilized aeration basin capacity was repurposed for testing return activated sludge (RAS) fermentation. The WRWWTP began pilot testing of RAS fermentation in April 2021. The facility moved through a series of operational setpoints to optimize phosphorus removal in a sidestream RAS (SSR) configuration, including RAS diversion, decrease of DO in aeration basins and chemical dosing shutoff. One of the key implementations was the addition of cranberry syrup waste to provide additional carbon for RAS fermentation, converting the process to a SSR plus carbon (SSRC) configuration. By the end of the testing period, effluent total phosphorus was averaging less than 0.4 mg L−1 with no chemical addition. A model was developed in the SUMO platform and was used to capture orthophosphate trends during the testing period. The model investigated microbial population dynamics and found that the operational changes including RAS diversion, chemical dosing shutoff and cranberry syrup waste addition impacted the enrichment of phosphorus accumulating organisms (PAO). After performing a sensitivity analysis on hydrolysis parameters, the predicted hydrolysis rate around 1.8–1.9 mg COD g VSS−1 hr−1 was found to match the batch rate testing data. This is the first study where cranberry syrup waste was used to successfully enhance EBPR performance, resulting in 90% TP removal. While further research is needed regarding the composition of the waste matrix and the microbial community composition, this expands the routes for resource recovery in the field of wastewater treatment.

Research on Modified Carbon Nanotubes in Wastewater Treatment

The application of modified carbon nanotubes (MCNTs) in the field of wastewater treatment has received much attention in recent years. To better understand the research progress and trends of MCNTs in wastewater treatment, this paper presents a bibliometric analysis of the scientific literature on the application of MCNTs in wastewater, highlight how it has evolved over the years, and identify the sectors for which the study could be beneficial. The CiteSpace software was used to perform the analysis of the data in which specific maps were used to represent the network of the relationships among countries, journals, organizations, authors, and keywords related to the investigated topic and subtopics. The results show that in the time frame of the study, most attention has been focused on the functional modification of carbon nanotubes, the study of their application in water treatment, and the study of the patterns and mechanisms of pollutant removal. The recycling of MCNTs and their environmental risks have not been sufficiently studied. In conclusion, the recycling and regeneration methods of MCNTs, as well as the potential ecological, environmental and health risks will be the focus of future research and more research should be invested.

Sustainable fabrication of Co-MOF@CNT nano-composite for efficient adsorption and removal of organic dyes and selective sensing of Cr(VI) in aqueous phase

In view of the fascinating applications of hybrid materials, a new nanocomposite is fabricated in order to achieve the excellent adsorption capacity for cationic dye as well as selective sensing ability toward Cr6+ ions in the aqueous phase. The present work deals with the synthesis of metal-organic framework (MOF) based nanocomposite, i.e., Co-MOF@CNT using Co-MOF and functionalized carbon nanotubes (CNTs) by adopting a facile, in-situ solvothermal approach for application in the field of wastewater treatment. The as-synthesized nanocomposite was characterized in detail through Fourier transform infrared spectroscopy (FTIR), Raman, powder X-ray diffraction (PXRD), thermal gravimetric analysis/differential thermal analysis (TGA/DTA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques, revealing the successful fabrication of both parent materials in the hybrid nanocomposite. The developed nanocomposite (Co-MOF@CNT) was assessed for its application in metal sensing as well as for the selective adsorption and elimination of hazardous cationic dyes [from the mixture containing cationic dye, methylene blue (MB) and anionic dye, methyl orange (MO)] from wastewater. The nanocomposite exhibits high selectivity and metal-sensing response towards Cr6+ ion under ambient conditions with an ultra-low detection limit of ∼0.00649 ppm or 0.125 μM, as reported so far. Moreover, the detection ability of Co-MOF@CNT can be restored for up to five cycles significantly. In addition, the developed nanocomposite displayed a high removal rate of about 98% at equilibrium under optimum temperature (25 °C) and neutral pH for cationic (MB) dye with ultimate selectivity. The kinetic studies revealed that the adsorption proceeds via pseudo-second order reaction. The dye adsorption mechanism suggests the presence of electrostatic, ᴫ-ᴫ and hydrogen bonding interactions between nanocomposite and the dye. This hybrid nanocomposite also exhibited high reusability of up to four cycles for MB dye. All in all, Co-MOF@CNT nanocomposite with superior Cr6+ metal sensing performance and MB dye adsorption could pave a promising path for environmental applications in this high-tech industrial era.

An environment-friendly polyurethane composite membrane decorated by superhydrophobic modification of TiC as high efficient separator of oil-water emulsion

The exploring of sustainable, durable and superwetting composite nanofiber membrane as efficient separator for oil-water emulsion is one of the biggest challenges in the field of wastewater treatment. Herin, an environment-friendly polyurethane (bio-PU) was synthesized by introducing biodegradable polycaprolactone diol (PCLd) segments. The superhydrophobic modified titanium carbide nanoparticle (TiCp) by 1H,1H,2H,2H-Perfluorodecyltrimethoxysilane (PFDTS) was decorated on eletrospun bio-PU nanofiber matrix, which could also regulate the microstructure of bio-PU composite membrane. The prepared bio-PU/TiCP membrane displayed superhydrophobicity with WCA of 153.1 ± 1.2°, which attributed to its hierarchical structure composed of nanofibers, microspheres and nanoparticles. Even for oil-water emulsion, the bio-PU/TiCP membrane exhibited the outstanding separation efficiency of 99.65% and high flux of 2464.79 L m−2 h−1. The bio-PU/TiCP membrane also had the excellent self-cleaning, water repellency and recyclability. These characters endowed it great potential application in sustainable separator.

Factors influencing the photodegradation of acid orange 8 by nitrocellulose membranes

Nitrocellulose membranes (NCM) have broad application prospects in the field of organic wastewater treatment. In this research, acid orange 8 was used as the target pollutant, and the effects of factors, such as concentration, light intensity, anions, and cations, on the photodegradation of acid orange 8 were investigated under simulated sunlight by NCM. The results showed that the degradation rate constant of acid orange 8 in the NCM system was 1.94 × 10−3 min−1, which was 27.3 times that in the pure water. The photodegradation rate increases with decreasing concentration in the range of 20–120 μmol/L for acid orange 8. The photodegradation rate increased with increasing NCM area. The degradation effect of acid orange 8 increased with the increase of light intensity. Acidic conditions were favorable for the degradation of acid orange 8. The optimal conditions for photodegradation of acid orange 8 were the solution concentration of 20 μmol/L, membrane area of 17.35 cm2, light intensity of 481 μmol/(m2s), and pH value of 3.0. The effect of different components in water on the photodegradation of acid orange 8 was different. Ca2+, Mg2+, and NO3− could promote the photodegradation of acid orange 8, while CO32- could inhibit the photodegradation. The effect of degrading acid orange 8 by NCM under light conditions is obvious, which can provide a new method for the removal of acid orange 8 in wastewater.

Graphene and chitosan innovative materials for water treatment: Review

In recent years Graphene oxide (GO) has become a more usable material due to the excellent electrical, thermal, mechanical and optical properties it contains, Graphene plays an important role in most fields. Chitosan (CS) is a natural polymer that has been extensively studied due to its specific formation, high chemical resistance and better physical properties. Chitosan (CS) is a natural polymer that has been extensively studied due to its specific properties, high chemical resistance and better physical properties. Chitosan has received wide attention due to its high adsorption potential and low cost. Among the advantages of chitosan can bind to heavy metal ions thanks to its form which has hydroxyl and amine groups. However, it also has drawbacks, for example sensitivity to pH, low thermal stability and low mechanical strength, which make it possible to limit the application of chitosan in the field of waste water treatment. The combination of graphene and chitosan allows us to obtain new materials with new properties and with improved adsorption performance. In the following, the preparation of GO-CS fibres, hydrogel and aerogel, and the applications of GO-CS nanocomposites are discussed. Also discusses the results obtained by researchers regarding the ability of the hydrogel to adsorb various contaminants, including cationic and anionic dyes and heavy metals.

Preparation of large-faced flower-like Bi2WO6 using carbon as a template to enhanced photocatalytic activity under visible light

Sewage treatment is a critical issue that needs to be resolved urgently. Accordingly, in this study, a large-faced flower-like Bi2WO6 was prepared via a one-step hydrothermal method using corncob biomass carbon as the carrier; subsequently, its structure and morphology were characterized. The results showed that the as-prepared material exhibited good dispersion properties. Rhodamine B (RhB) and tetracycline (TC) were used as simulated pollutants to detect the photocatalytic activity of the prepared materials. The experimental results showed that Bi2WO6 modified with C demonstrated a good catalytic performance to pure Bi2WO6. Furthermore, it also exhibited excellent stability, the removal rates of RhB and TC reached 98% and 87%, respectively. The proposed material is expected to be of significant application value in the field of wastewater treatment.

Characterization and Mechanistic Study of Heavy Metal Adsorption by Facile Synthesized Magnetic Xanthate-Modified Chitosan/Polyacrylic Acid Hydrogels.

A simple method was used to synthesize magnetic xanthate-modified chitosan/polyacrylic acid hydrogels that were used to remove heavy metal ions from an aqueous solution. Xanthate modification of chitosan significantly improved adsorption performance: individual adsorption capacities of the hydrogel for Cu(II), Cd(II), Pb(II), and Co(II) ions were 206, 178, 168, and 140 mg g−1, respectively. The magnetic hydrogels had good regeneration ability and were effectively separated from the solution by use of a magnet. Adsorption kinetic data showed that the removal mechanism of heavy metal ions from the solution by magnetic hydrogels occurs mainly by chemical adsorption. The equilibrium adsorption isotherms were well-described by the Freundlich and Langmuir equations. Positive values were found for the Gibbs standard free energy and enthalpy, indicating an increase in the disorder at the solid–liquid interface during adsorption. Magnetic xanthate-modified chitosan-based hydrogels that exhibit high adsorption efficiency, regeneration, and easy separation from a solution have broad development prospects in various industrial sewage and wastewater treatment fields.

Towards highly salt-rejecting solar interfacial evaporation: Photothermal materials selection, structural designs, and energy management

With the development of the industry, water pollution and shortage have become serious global problems. Owing to the abundance of seawater storage on earth, efficient solar-driven evaporation is a promising approach to relieve the freshwater shortage. The solar-driven evaporation has attracted tremendous attention due to its potential application in the seawater desalination and wastewater treatment fields. Also, the solar-driven evaporation efficiency can be enhanced by designing both solar absorbers and structures. Up to now, many strategies have been explored to achieve high solar-driven evaporation efficiency, mainly including the selection of photothermal conversion materials and structure optimization. In this review, the solar absorbers, structural designs, and energy management are proposed as the keys for high performance solar-driven evaporation systems. We report four kinds of solar absorbers based on different photothermal conversion mechanisms, substrate structure designs, and energy management methods for the purpose to achieve high conversion efficiency. And we also systematically investigate the available salt-rejections strategies for seawater desalination. This review aims to summarize the current development of efficient solar-driven evaporation systems and provide insights into the photothermal conversion materials, structural designs, and energy management. Finally, we propose the perspectives of the salt-rejection technologies for seawater desalination.

Disinfection during Iron Electrocoagulation: Differentiating between Inactivation and Floc Entrapment for Escherichia coli and Somatic Coliphage ØX174

Electrochemical water treatment is gaining increasing popularity due to its wide range of potential applications, its decreasing costs, and its suitability as a decentralized treatment alternative, but mainly due to it being considered a ”green technology”. In the field of municipal wastewater treatment, the use of iron electrocoagulation (Fe-EC) has been marginal and although disinfection has been reported, its underlying mechanisms are not fully understood, for which significant controversy remains. In this study, microbial inactivation during Fe-EC was evaluated as a two-component process, namely, physical removal by microbial floc sorption/entrapment, and inactivation by reactive oxygen species (ROS) produced by (semi)Fenton reactions. Using the fecal indicators Escherichia coli WR1 and somatic coliphage ØX174 suspended in a synthetic water matrix, the role of ROS and the role of flocculation were quantitatively evaluated. Fenton inhibitor TEMPOL was used to quench ROS production during Fe-EC. At circumneutral pH, ROS were found to be highly detrimental to E. coli, yet only mildly damaging for phage ØX174 (≈3.9 log10 and ≈0.8 log10 inactivation, respectively). Inactivation for both indicators increased under acidic conditions (pH 5.5), likely due to the formation of hydroxyl radicals (•OH), exceeding 5.1 log10 for E. coli and 1.5 log10 for phage ØX174. The ROS inactivation pathway is linked to the oxidation of ferrous iron (Fe2+), being independent of flocculation settings. Experiments involving different flocculation settings demonstrated that there is a strong positive correlation between orthokinetic-like flocculation conditions, floc sedimentation, and microbial removal, meaning that floc entrapment is a major removal pathway following Fe-EC. When compared to control experiments in which no proper flocculation stage was introduced, orthokinetic flocculation produced additional 3.1 log10 and 4.4 log10 removal for E. coli and phage ØX174, respectively. We conclude that ROS production is not a prerequisite for removal of E. coli and phage ØX174, however, it does offer an additional disinfection barrier, which increases the robustness of Fe-EC for water treatment.

Preparation of needle coke composite cathode and its treatment of RhB wastewater

A novel Fe-loaded needle coke composite electro-Fenton electrode was prepared, characterized, and investigated as the heterogeneous catalytic cathode for oxygen reduction and OH generation for the first time. The novel electro-Fenton system constructed with the cathode and DSA anode was employed to degrade rhodamine B (RhB) in an aqueous solution. Optimal conditions for electrode preparation for the treatment of RhB were obtained by single-factor experiments. The occurrence of the Fenton reaction was verified by hydroxyl radical quenching experiments, and the RhB degradation pathway was inferred by spectroscopic analysis. The decolorization rate of RhB of nearly 100% and the COD removal efficiency of 81.6% were achieved. RhB was degraded by N-de-ethylation, chromophore cleavage, opening-ring, and mineralization in the presence of reactive oxygen species, mainly OH. The cost of RhB simulated wastewater treatment was estimated at RMB 13 yuan per cubic meter of wastewater. As a cheap carbon cathode material, needle coke can catalyze the two-electron transfer of O2 to produce H2O2, reducing the material cost of the electrode, and also increasing the conductivity of the electrode, reducing the cost of water treatment. The needle coke composite electrode can serve as a cost-effective electro-Fenton cathode in the field of refractory organic wastewater treatment represented by dye wastewater.

Synthesis of a Z-scheme ternary photocatalyst (Ta3N5/Ag3PO4/AgBr) for the enhanced photocatalytic degradation of tetracycline under visible light

Solar photocatalysis is a green and sustainable technology that has been widely studied in the field of wastewater treatment. Herein, a ternary photocatalyst (Ta3N5/Ag3PO4/AgBr) with dual Z-scheme heterojunctions was synthesized by the hydrothermal, chemical precipitation and anion exchange methods. The morphology and structure properties of the photocatalysts were systematically characterized by SEM, TEM, EDS, XRD and XPS. Tetracycline was used as the model pollutant to examine the photocatalytic activity under visible light (>420 nm). The results indicated that the unique micron flower-like structure of Ta3N5 made it to be a good substrate for the deposition of Ag3PO4/AgBr. Over the ternary photocatalyst, tetracycline was efficiently degraded, and 95% of tetracycline could be removed in 30 min. The degradation rate constant over the ternary photocatalyst (0.089 min−1) was 1.98 and 15.89 times that over Ta3N5/Ag3PO4 and Ta3N5, respectively. Meanwhile, the stability of the ternary composite was also significantly improved. Additionally, the trapping experiments verified that ·O2− and h+ played major roles during photocatalysis, while ·OH had relatively little impact on the tetracycline removal. Accordingly, the photocatalytic mechanism with respect to dual Z-scheme heterojunctions was proposed. On one hand, the components of the ternary photocatalyst were all visible light driven semiconductors, which endowed the composite catalyst with good light absorption capacity. On the other hand, facilitated by the dual Z-scheme heterojunctions, the photo-generated charge carriers with stronger redox ability could be separated more efficiently, thus leading to a better photocatalytic performance.

Preparation of low-cost functionalized diatomite and its effective removal of ammonia nitrogen from wastewater.

A low-cost functionalization method was used to treat diatomite, and an efficient adsorbent for ammonia nitrogen was prepared by optimizing the functionalization conditions. The functionalized diatomite (DTCA-Na) was characterized by SEM, EDS, BET, XRD, FT-IR, and TG. The results demonstrate that DTCA-Na has excellent adsorption performance after being modified with H2SO4 (60.00 wt.%), NaCl (5.00 wt.%), and calcination at 400°C for 2h. While studying the effect of adsorption factors on the removal of ammonia nitrogen, the kinetic and thermodynamic behaviors in the adsorption process were discussed. The removal efficiency of the simulated wastewater with the initial ammonia nitrogen concentration of 10.00mg L-1 by the DTCA-Na was more than 80% when the contact time was 60min, pH was 6-10, the dosage of adsorbent was 1.00g, and the temperature was 25°C. The adsorption process of ammonia nitrogen was conformed to the pseudo-first-order and Langmuir isothermal model. The removal efficiency of ammonia nitrogen was still above 80% after 5 times adsorption-desorption experiments. The DTCA-Na has a brighter prospect of application in the field of ammonia nitrogen wastewater treatment due to its excellent adsorption performance and low-cost advantage.