A new type of Au/TiO2/reduced graphene oxide (RGO) nanocomposite was fabricated by the hydrothermal synthesis of TiO2 on graphene oxide followed by the photodeposition of Au nanoparticles. Transmission electron microscopy images showed that Au nanoparticles were loaded onto the surface of both TiO2 and RGO. Au/TiO2/RGO had a better photocatalytic activity than Au/ TiO2 for the degradation of phenol. Electrochemical measurements indicated that Au/TiO2/RGO had an improved charge transfer capability. Meanwhile, chemiluminescent analysis and electron spin resonance spectroscopy revealed that Au/TiO2/RGO displayed high production of hydrogen peroxide and hydroxyl radicals in the photocatalytic process. This high photocatalytic performance was achieved via the addition of RGO in Au/TiO2/RGO, where RGO served not only as a catalyst support to provide more sites for the deposition of Au nanoparticles but also as a collector to accept electrons from TiO2 to effectively reduce photogenerated charge recombination.
In this study, a new water treatment system that couples (photo-) electrochemical catalysis (PEC or EC) in a microbial fuel cell (MFC) was configured using a stainless-steel (SS) cathode coated with Fe0/TiO2. We examined the destruction of methylene blue (MB) and tetracycline. Fe0/TiO2 was prepared using a chemical reduction-deposition method and coated onto an SS wire mesh (500 mesh) using a sol technique. The anode generates electricity using microbes (bio-anode). Connected via wire and ohmic resistance, the system requires a short reaction time and operates at a low cost by effectively removing 94% MB (initial concentration 20 mg?L–1) and 83% TOC/TOC0 under visible light illumination (50 W; 1.99 mW?cm–2 for 120 min, MFC-PEC). The removal was similar even without light irradiation (MFC-EC). The EEo of the MFC-PEC system was approximately 0.675 kWh?m–3?order–1, whereas that of the MFC-EC system was zero. The system was able to remove 70% COD in tetracycline solution (initial tetracycline concentration 100 mg?L–1) after 120 min of visible light illumination; without light, the removal was 15% lower. The destruction of MB and tetracycline in both traditional photocatalysis and photoelectrocatalysis systems was notably low. The electron spinresonance spectroscopy (ESR) study demonstrated that ?OH was formed under visible light, and ?O2– was formed without light. The bio-electricity-activated O2 and ROS (reactive oxidizing species) generation by Fe0/TiO2 effectively degraded the pollutants. This cathodic degradation improved the electricity generation by accepting and consuming more electrons from the bio-anode.
In the recent years, photocatalytic self-cleaning and “depolluting” materials have been suggested as a remediation technology mainly for NOx and aromatic VOCs in urban areas. A number of products incorporating the aforementioned technology have been made commercially available with the aim to improve urban air quality. These commercial products are based on the photocatalytic properties of a thin layer of TiO2 at the surface of the material (such as glass, pavement, etc.) or embedded in paints or concrete. The use of TiO2 photocatalysts as an emerging air pollution control technology has been reported in many locations worldwide. However, up to now, the effectiveness measured in situ and the expected positive impact on air quality of this relatively new technology has only been demonstrated in a limited manner. Assessing and demonstrating the effectiveness of these depolluting techniques in real scale applications aims to create a real added value, in terms of policy making (i.e., implementing air quality strategies) and economics (by providing a demonstration of the actual performance of a new technique).
Effect of different carbon sources on purification performance and change of microbial community structure in a novel A2N-MBR process were investigated. The results showed that when fed with acetate, propionate or acetate and propionate mixed (1:1) as carbon sources, the effluent COD, NH4+-N, TN and TP were lower than 30, 5, 15 and 0.5 mg?L–1, respectively. However, taken glucose as carbon source, the TP concentration of effluent reached 2.6 mg?L–1. Process analysis found that the amount of anaerobic phosphorus release would be the key factor to determine the above effectiveness. The acetate was beneficial to the growth of Candidatus Accumulibacter associated with biological phosphorus removal, which was the main cause of high efficiency phosphorus removal in this system. In addition, it could eliminate the Candidatus Competibacter associated with glycogen-accumulating organisms and guarantee high efficiency phosphorus uptake of phosphorus accumulating organisms in the system with acetate as carbon source.
Nitrogen (N) and phosphorus (P) released from the sediment to the surface water is a major source of water quality impairment. Therefore, inhibiting sediment nutrient release seems necessary. In this study, red soil (RS) was employed to control the nutrients released from a black-odorous river sediment under flow conditions. The N and P that were released were effectively controlled by RS capping. Continuous-flow incubations showed that the reduction efficiencies of total N (TN), ammonium (NH4+-N), total P (TP) and soluble reactive P (SRP) of the overlying water by RS capping were 77%, 63%, 77% and 92%, respectively, and nitrification and denitrification occurred concurrently in the RS system. An increase in the water velocity coincided with a decrease in the nutrient release rate as a result of intensive water aeration.
Direct individual analysis using Scanning Electron Microscopy combined with online observation was conducted to examine the S-rich particles in PM2.5 of two typical polluted haze episodes in summer and winter from 2014 to 2015 in Beijing. Four major types of S-rich particles, including secondary CaSO4 particles (mainly observed in summer), S-rich mineral particles (SRM), S-rich water droplets (SRW) and (C, O, S)-rich particles (COS) were identified.We found the different typical morphologies and element distributions of S-rich particles and considered that (C, O, S)-rich particles had two major mixing states in different seasons. On the basis of the S-rich particles’ relative abundances, S concentrations and their relationships with PM2.5 as well as the seasonal comparison, we revealed that the S-participated formation degrees of SRM and SRW would enhance with increasing PM2.5 concentration. Moreover, C-rich matter and sulfate had seasonally different but significant impacts on the formation of COS.
Treating water contaminants via heterogeneously catalyzed reduction reaction is a subject of growing interest due to its good activity and superior selectivity compared to conventional technology, yielding products that are non-toxic or substantially less toxic. This article reviews the application of catalytic reduction as a progressive approach to treat different types of contaminants in water, which covers hydrodehalogenation for wastewater treatment and hydrogenation of nitrate/nitrite for groundwater remediation. For hydrodehalogenation, an overview of the existing treatment technologies is provided with an assessment of the advantages of catalytic reduction over the conventional methodologies. Catalyst design for feasible catalytic reactions is considered with a critical analysis of the pertinent literature. For hydrogenation, hydrogenation of nitrate/nitrite contaminants in water is mainly focused. Several important nitrate reduction catalysts are discussed relating to their preparation method and catalytic performance. In addition, novel approach of catalytic reduction using in situ synthesized H2 evolved from water splitting reaction is illustrated. Finally, the challenges and perspective for the extensive application of catalytic reduction technology in water treatment are discussed. This review provides key information to our community to apply catalytic reduction approach for water treatment.
In this study, FeVO4 was prepared and used as Fenton-like catalyst to degrade orange G (OG) dye. The removal of OG in an aqueous solution containing 0.5 g·L–1 FeVO4 and 15 mmol·L–1 hydrogen peroxide at pH 7.0 reached 93.2%. Similar rates were achieved at pH 5.7 (k = 0.0471 min–1), pH 7.0 (k = 0.0438 min–1), and pH 7.7 (k = 0.0434 min–1). The FeVO4 catalyst successfully overcomes the problem faced in the heterogeneous Fenton process, i.e., the narrow working pH range. The data for the removal of OG in FeVO4 systems containing H2O2 conform to the Langmuir–Hinshelwood model (R2 = 0.9988), indicating that adsorption and surface reaction are the two basic mechanisms for OG removal in the FeVO4–H2O2 system. Furthermore, the irradiation of FeVO4 by visible light significantly increases the degradation rate of OG, which is attributed to the enhanced rates of the iron cycles and vanadium cycles.
Since the concept of the osmotic microbial fuel cell (OsMFC) was introduced in 2011, it has attracted growing interests for its potential applications in wastewater treatment and energy recovery. However, forward osmosis (FO) membrane fouling resulting in a severe water flux decline remains a main obstacle. Until now, the fouling mechanisms of FO membrane especially the development of biofouling layer in the OsMFC are not yet clear. Here, the fouling behavior of FO membrane in OsMFCs was systematically investigated. The results indicated that a thick fouling layer including biofouling and inorganic fouling was existed on the FO membrane surface. Compared to the inorganic fouling, the biofouling played a more important role in the development of the fouling layer. Further analyses by the confocal laser scanning microscopy (CLSM) implied that the growth of biofouling layer on the FO membrane surface in the OsMFC could be divided into three stages. Initially, microorganisms associated with ß-D-glucopyranose polysaccharides were deposited on the FO membrane surface. After that, the microorganisms grew into a biofilm caused a quick decrease of water flux. Subsequently, some of microorganisms were dead due to lack of nutrient source, in the meantime, polysaccharide and proteins in the biofouling layer were decomposed as nutrient source, thus leading to a slow development of the biofouling layer. Moreover, the microorganisms played a significant role in the formation and development of the biofouling layer, and further studies are needed to mitigate the deposition of microorganisms on FO membrane surfaces in OsMFCs.
This work presents an overall introduction to the Station for Observing Regional Processes of the Earth System–SORPES in Nanjing, East China, and gives an overview about main scientific findings in studies of air pollution-weather/climate interactions obtained since 2011. The main results summarized in this paper include overall characteristics of trace gases and aerosols, chemical transformation mechanisms for secondary pollutants like O3, HONO and secondary inorganic aerosols, and the air pollution–weather/climate interactions and feedbacks in mixed air pollution plumes from sources like fossil fuel combustion, biomass burning and dust storms. The future outlook of the development plan on instrumentation, networking and data-sharing for the SORPES station is also discussed.
We implemented the online coupled WRF-Chem model to reproduce the 2013 January haze event in North China, and evaluated simulated meteorological and chemical fields using multiple observations. The comparisons suggest that temperature and relative humidity (RH) were simulated well (mean biases are–0.2K and 2.7%, respectively), but wind speeds were overestimated (mean bias is 0.5 m?s–1). At the Beijing station, sulfur dioxide (SO2) concentrations were overpredicted and sulfate concentrations were largely underpredicted, which may result from uncertainties in SO2 emissions and missing heterogeneous oxidation in current model. We conducted three parallel experiments to examine the impacts of doubling SO2 emissions and incorporating heterogeneous oxidation of dissolved SO2 by nitrogen dioxide (NO2) on sulfate formation during winter haze. The results suggest that doubling SO2 emissions do not significantly affect sulfate concentrations, but adding heterogeneous oxidation of dissolved SO2 by NO2 substantially improve simulations of sulfate and other inorganic aerosols. Although the enhanced SO2 to sulfate conversion in the HetS (heterogeneous oxidation by NO2) case reduces SO2 concentrations, it is still largely overestimated by the model, indicating the overestimations of SO2 concentrations in the North China Plain (NCP) are mostly due to errors in SO2 emission inventory.
Flow cytometry (FCM) has been widely used in multi-parametric assessment of cells in various research fields, especially in environmental sciences. This study detected the metabolic activity of Escherichia coli and Staphylococcus aureus by using an FCM method based on 5-cyano-2,3-ditolyltetrazolium chloride (CTC); the accuracy of this method was enhanced by adding SYTO 9 and 10%R2A broth. The disinfection effects of chlorine, chloramine, and UV were subsequently evaluated by FCM methods. Chlorine demonstrated stronger and faster destructive effects on cytomembrane than chloramine, and nucleic acids decomposed afterwards. The metabolic activity of the bacteria persisted after the cytomembranewas damaged as detected using CTC. Low-pressure (LP) UV or medium-pressure (MP) UV treatments exerted no significant effects on membrane permeability. The metabolic activity of the bacteria decreased with increasing UV dosage, and MP-UV was a stronger inhibitor of metabolic activity than LP-UV. Furthermore, the membrane of Gram-positive S. aureus was more resistant to chlorine/chloramine than that of Gram-negative E. coli. In addition, S. aureus showed higher resistance to UV irradiation than E. coli.
Sulfamethoxazole (SMX) and trimethoprim (TMP) are two critical sulfonamide antibiotics with enhanced persistency that are commonly found in wastewater treatment plants. Recently, more scholars have showed interests in how SMX and TMP antibiotics are biodegraded, which is seldom reported previously. Novel artificial composite soil treatment systems were designed to allow biodegradation to effectively remove adsorbed SMX and TMP from the surface of clay ceramsites. A synergy between sorption and biodegradation improves the removal of SMX and TMP. One highly efficient SMX and TMP degrading bacteria strain, Bacillus subtilis, was isolated from column reactors. In the removal process, this bacteria degrade SMX and TMP to NH4+, and then further convert NH4+ to NO3– in a continuous process. Microbial adaptation time was longer for SMX degradation than for TMP, and SMX was also able to be degraded in aerobic conditions. Importantly, the artificial composite soil treatment system is suitable for application in practical engineering.
We designed photoelectrochemical cells to achieve efficient oxidation of rhodamine B (RhB) without the need for photocatalyst or supporting electrolyte. RhB, the metal anode/cathode, and O2 formed an energy-relay structure, enabling the efficient formation of O2– species under ultraviolet illumination. In a single-compartment cell (S cell) containing a titanium (Ti) anode, Ti cathode, and 10 mg·mL–1 RhB in water, the zero-order rate constant of the photoelectrochemical oxidation (kPEC) of RhB was 0.049 mg·L–1·min–1, while those of the photochemical and electrochemical oxidations of RhB were nearly zero. kPEC remained almost the same when 0.5 mol·L–1 Na2SO4 was included in the reactive solution, regardless of the increase in the photocurrent of the S cell. The kPEC of the illuminated anode compartment in the two-compartment cell, including a Ti anode, Ti cathode, and 10 mg·mL–1 RhB in water, was higher than that of the S cell. These results support a simple, eco-friendly, and energysaving method to realize the efficient degradation of RhB.
First-principles calculations were performed to investigate the mechanism of Hg0 adsorption and oxidation on CeO2(111). Surface oxygen activated by the reduction of Ce4+ to Ce3+ was vital to Hg0 adsorption and oxidation processes. Hg0 was fully oxidized by the surface lattice oxygen on CeO2(111), without using any other oxidizing agents. HCl could dissociate and react with the Hg adatom on CeO2(111) to form adsorbed Hg–Cl or Cl–Hg–Cl groups, which promoted the desorption of oxidized Hg and prevented CeO2 catalyst deactivation. In contrast, O–H and H–O–H groups formed during HCl adsorption consumed the active surface oxygen and prohibited Hg oxidation. The consumed surface oxygen was replenished by adding O2 into the flue gas. We proposed that oxidized Hg desorption and maintenance of sufficient active surface oxygen were the rate-determining steps of Hg0 removal on CeO2-based catalysts. We believe that our thorough understanding and new insights into the mechanism of the Hg0 removal process will help provide guidelines for developing novel CeO2-based catalysts and enhance the Hg0 removal efficiency.
Nutrients and water play an important role in microalgae cultivation. Using wastewater as a culture medium is a promising alternative to recycle nutrients and water, and for further developing microalgae-based products. In the present study, two species of microalgae, Chlorella sp. (high ammonia nitrogen tolerance) and Spirulina platensis (S. platensis, high growth rate), were cultured by using poultry wastewater through a two-stage cultivation system for algal biomass production. Ultrafiltration (UF) or centrifuge was used to harvest Chlorella sp. from the first cultivation stage and to recycle culture medium for S. platensis growth in the second cultivation stage. Results showed the two-stage cultivation system produced high microalgae biomass including 0.39 g·L–1Chlorella sp. and 3.45 g·L–1S. platensis in the first-stage and second-stage, respectively. In addition, the removal efficiencies of NH4+ reached 19% and almost 100% in the first and the second stage, respectively. Total phosphorus (TP) removal reached 17% and 83%, and total organic carbon (TOC) removal reached 55% and 72% in the first and the second stage, respectively. UF and centrifuge can recycle 96.8% and 100% water, respectively. This study provides a new method for the combined of pure microalgae cultivation and wastewater treatment with culture medium recycling.
Heterogeneous Fenton-like reaction has been extensively investigated to eliminate refractory organic contaminants in wastewater, but it usually shows low catalytic performance due to difficulty in reduction from Fe(III) to Fe(II). In this study, enhanced catalytic efficiency was obtained by employing Cu-doped BiFeO3 as heterogeneous Fenton-like catalysts, which exhibited higher catalytic performance toward the activation of H2O2 for phenol degradation than un-doped BiFeO3. BiFe0.8Cu0.2O3 displayed the best performance, which yielded 91% removal of phenol (10 mg L–1) in 120 min. The pseudo first-order kinetic rate constant of phenol degradation in BiFe0.8Cu0.2O3 catalyzed heterogeneous Fenton-like reaction was 5 times higher than those of traditional heterogeneous Fenton-like catalysts, such as Fe3O4 and goethite. The phenol degradation efficiency could still reach 83% after 4 cycles, which implied the good stability of BiFe0.8Cu0.2O3. The high catalytic activity of BiFe0.8Cu0.2O3 was attributed to the fact that the doping Cu into BiFeO3 could promote the generation of Fe(II) in the catalyst and then facilitate the activation of H2O2 to degrade the organic pollutants.
Ammonia has emerged as a promising hydrogen carrier with applications as an energy source in recent years. However, in addition to being toxic, gaseous ammonia is a precursor of secondary inorganic aerosols. The concentration of ambient fine particulate matter (PM2.5) is intrinsically connected to public health. In this study, PM2.5-related health impacts of utilizing ammonia-hydrogen energy in Kanto Region, Japan, were investigated. It was assumed that 20% of the electricity consumption in Kanto Region, the most populated area in Japan, was supplied by ammonia-hydrogen energy. The PM2.5 resulted from incomplete ammonia decomposition was simulated by a chemical transport model: ADMER-PRO (modified version). Based on the incremental PM2.5 concentration, health impacts on the elderly (individuals over 65 years old) were quantitatively evaluated. The ammonia emission in this scenario increased PM2.5 by 11.7% (0.16 μg·m–3·y–1) in winter and 3.5% (0.08 μg ·m–3·y–1) in summer, resulting in 351 premature deaths per year. This study suggests that costeffective emissions control or treatment and appropriate land planning should be considered to reduce the associated health impacts of this type of energy generation. In addition, further in-depth research, including cost-benefit analysis and security standards, is needed.
The development of cost-effective and highly efficient anode materials for extracellular electron uptake is important to improve the electricity generation of bioelectrochemical systems. An effective approach to mitigate harmful algal bloom (HAB) is mechanical harvesting of algal biomass, thus subsequent processing for the collected algal biomass is desired. In this study, a low-cost biochar derived from algal biomass via pyrolysis was utilized as an anode material for efficient electron uptake. Electrochemical properties of the algal biochar and graphite plate electrodes were characterized in a bioelectrochemical system (BES). Compared with graphite plate electrode, the algal biochar electrode could effectively utilize both indirect and direct electron transfer pathways for current production, and showed stronger electrochemical response and better adsorption of redox mediators. The maximum current density of algal biochar anode was about 4.1 times higher than graphite plate anode in BES. This work provides an application potential for collected HAB to develop a cost-effective anode material for efficient extracellular electron uptake in BES and to achieve waste resource utilization.
A spent fluid catalytic cracking (FCC) catalyst containing lanthanum (La) was used as a novel adsorbent for phosphorus (P) in simulated wastewater. The experiments were conducted in a batch system to optimize the operation variables, including pH, calcination temperature, shaking time, solid-liquid ratio, and reaction temperature under three initial P-concentrations (C0 = 0.5, 1.0, and 5.0 mg/L). Orthogonal analysis was used to determine that the initial P-concentration was the most important parameter for P removal. The P-removal rate exceeded 99% and the spent FCC catalyst was more suitable for use in low P-concentration wastewater (C0 <5.0 mg/L). Isotherms, thermodynamics and dynamics of adsorption are used to analyze the mechanism of phosphorus removal. The results show that the adsorption is an endothermic reaction with high affinity and poor reversibility, which indicates a low risk of second releasing of phosphate. Moreover, chemical and physical adsorption coexist in this adsorption process with LaPO4 and KH2PO4 formed on the spent FCC catalyst as the adsorption product. These results demonstrate that the spent FCC catalyst containing La is a potential adsorbent for P-removal from wastewater, which allows recycling of the spent FCC catalyst to improve the quality of water body.
