Effects of surfactants on the combined toxicity of TiO2 nanoparticles and cadmium to Escherichia coli

The combined ecological toxicity of TiO₂ nanoparticles (nano-TiO₂) and heavy metals has been paid more attention. As the common pollutants in water environment, surfactants could affect the properties of nanoparticles and heavy metals, and thus further influence the combined toxicity of nano-TiO₂ and heavy metals. In this study, the effects of sodium dodecyl benzene sulfonate (SDBS) and Tween 80 on the single and combined toxicities of Cd^2 + and nano-TiO₂ to Escherichia coli (E. coli) were examined, and the underlying influence mechanism was further discussed. The results showed both SDBS and Tween 80 enhanced the toxicity of Cd^2 + to E. coli in varying degrees. The reaction of SDBS and Cd^2 + could increase the outer membrane permeability and the bioavailability of Cd, while Tween 80 itself could enhance the outer membrane permeability. The combined toxicity of nano-TiO₂ and Cd^2 + to E. coli in absence of surfactant was antagonistic because of the adsorption of Cd^2 + to nano-TiO₂ particles. However, in the presence of SDBS, both SDBS and nano-TiO₂ influenced the toxicity of Cd^2 +, and also SDBS could adsorb to nano-TiO₂ by binding to Cd^2 +. The combined toxicity was reduced at Cd^2 + lower than 4 mg/L and enhanced at Cd^2 + higher than 4 mg/L under multiple interactions. Tween 80 enhanced the combined toxicity of nano-TiO₂ and Cd^2 + by increasing the outer membrane permeability. Our study firstly elucidated the effects of surfactants on the combined toxicity of nano-TiO₂ and Cd^2 + to bacteria, and the underlying influencing mechanism was proposed.     

Effects of disinfection efficiency on microbial communities and corrosion processes in drinking water distribution systems simulated with actual running conditions

The effects of disinfection efficiency on microbial communities and the corrosion of cast iron pipes in drinking water distribution systems (DWDSs) were studied. Two annular reactors (ARs) that simulated actual running conditions with UV/Cl₂ disinfection and chlorination alone were used. High chlorine consumption and corrosion rate were found in the AR with UV/Cl₂. According to functional genes and pyrosequencing tests, a high percentage of iron recycling bacteria was detected within the biofilm of the AR with Cl₂ at early running stage, whereas siderophore-producing bacteria were dominant in the biofilm of the AR with UV/Cl_2. At the early running stage, the sequential use of UV light and an initial high chlorine dosage suppressed the biomass and iron-recycling bacteria in both bulk water and biofilms, thereby forming less protective scales against further corrosion, which enhanced chlorine consumption. Non-metric multidimensional scaling analysis showed that the bacterial communities in the ARs shaped from within rather than being imported by influents. These results indicate that the initial high disinfection efficiency within the distribution system had not contributed to the accumulation of iron-recycling bacteria at the early running stages. This study offer certain implications for controlling corrosion and water quality in DWDSs.     

Protecting the photosynthetic performance of snap bean under free air ozone exposure

Tropospheric ozone(O_3) is a major air pollutant and causes serious injury to vegetation. To protect sensitive plants from O_3 damage, several agrochemicals have been assessed,including cytokinin(e.g., kinetin, KIN) and ethylenediurea(EDU) with cytokinin-like activity.In higher plant, leaves are primarily injured by O_3 and protective agrochemicals are often applied by leaf spraying. To our knowledge, the mitigating abilities of EDU and KIN have not been compared directly in a realistic setup. In the present research, impacts of elevated O3(2 × ambient O_3, 24 hr per day, for 8 days) on an O_3 sensitive line(S156) of snap bean(Phaseolus vulgaris), which is often used for biomonitoring O_3 pollution, were studied in a free air controlled exposure system. The day before starting the O_3 exposure, plants were sprayed with a solution of EDU(300 ppm), KIN(1 mmol/L) or distilled water, to compare their protective abilities. The results demonstrated that 2 × ambient O_3 inhibited net photosynthetic rate and stomatal conductance, increased the minimal fluorescence yield of the dark-adapted state, decreased the maximal quantum yield of PSII photochemistry, and led to visible injury. KIN and EDU alleviated the reduction of the photosynthetic performance, and visible injury under O_3 fumigation. The plants sprayed with EDU showed greater ability to mitigate the O_3 damage than those sprayed with KIN. Chlorophyll fluorescence imaging may have detected more precisely the differences in O_3 response across the leaf than the conventional fluorometer.     

Effect of air-exposed biocathode on the performance of a Thauera-dominated membraneless single-chamber microbial fuel cell (SCMFC)

To investigate the effect of air-exposed biocathode(AEB) on the performance of singlechamber microbial fuel cell(SCMFC), wastewater quality, bioelectrochemical characteristics and the electrode biofilms were researched. It was demonstrated that exposing the biocathode to air was beneficial to nitrogen removal and current generation. In Test 1 of 95%AEB, removal rates of ammonia, total nitrogen(TN) and chemical oxygen demand(COD)reached 99.34% ± 0.11%, 99.34% ± 0.10% and 90.79% ± 0.12%, respectively. The nitrogen removal loading rates were 36.38 g N/m~3/day. Meanwhile, current density and power density obtained at 0.7 A/m3 and 104 m W/m~3 respectively. Further experiments on opencircuit(Test 2) and carbon source(Test 3) indicated that this high performance could be attributed to simultaneous biological nitrification/denitrification and aerobic denitrification, as well as bioelectrochemical denitrification. Results of community analysis demonstrated that both microbial community structures on the surface of the cathode and in the liquid of the chamber were different. The percentage of Thauera, identified as denitrifying bacteria, maintained at a high level of over 50% in water, but decreased gradually in the AEB. Moreover, the genus Nitrosomonas, Alishewanella, Arcobacter and Rheinheimera were significantly enriched in the AEB, which might contribute to both enhancement of nitrogen removal and electricity generation.     

Alkali resistance promotion of Ce-doped vanadium-titanic-based NH3-SCR catalysts

The effect of K deactivation on V_2O_5/WO_3-TiO_2 and Ce-doped V_2O_5/WO_3-TiO_2 catalysts in the selective catalytic reduction(SCR) of NOxby NH_3 was studied.Ce-doped V_2O_5/WO_3-TiO_2 showed significantly higher resistance to K deactivation than V_2O_5/WO_3-TiO_2.Ce-doped V_2O_5/WO_3-TiO_2 with K/V = 4(molar ratio) showed 90% NOxconversion at 350°C,whereas in this case V_2O_5/WO_3-TiO_2 showed no activity.The fresh and K-poisoned V_2O_5/WO_3-TiO_2 and Ce-doped V_2O_5/WO_3-TiO_2 catalysts were investigated by means of in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS),NH_3-temperature progress decomposition(NH_3-TPD),X-ray photoelectron spectroscopy(XPS) and H2-temperature program reduction(H_2-TPR).The effect of Ce doping on the improving resistance to K of V_2O_5/WO_3-TiO_2 were discussed.     

Eutectic mixture promoted CO2 sorption on MgO-TiO2 composite at elevated temperature

The development of carbon dioxide(CO_2) sorbents that can operate at elevated temperatures is significant for the advancement of pre-combustion capture technologies.Recently, promoter-based systems composed of alkali/alkaline earth metal nitrates and/or carbonates have been considered as next-generation solid sorbents due to their improved CO_2 uptake and kinetics. However, obtaining stable MgO sorbents against temperature swing regeneration still remained challenging. Herein, we report MgO-TiO_2 solid sorbents promoted by eutectic mixture(KNO_3 and LiNO_3) for elevated temperature CO_2 sorption. The developed sorbents show improved CO_2 sorption capacity, which may be attributed to the alternative CO_2 sorption pathway provided by the ionization of highly dispersed MgO in the eutectic mixture. The MgO-TiO_2 framework was also shown to assist in retaining the MgO configuration by constraining its interaction with CO_2. Furthermore, it is demonstrated that constructing composite structures is essential to improve the CO_2 sorption characteristics,mainly recyclability, at elevated temperatures. The developed promoter integrated sorbents showed exceptionally high CO_2 sorption capacity of 30 wt.% at an elevated temperature(300°C) with pronounced stability under temperature swing operation.     

The control of red water occurrence and opportunistic pathogens risks in drinking water distribution systems: A review

Many problems in drinking water distribution systems (DWDSs) are caused by microbe, such as biofilm formation, biocorrosion and opportunistic pathogens growth. More iron release from corrosion scales may induce red water. Biofilm played great roles on the corrosion. The iron-oxidizing bacteria (IOB) promoted corrosion. However, when iron-reducing bacteria (IRB) and nitrate-reducing bacteria (NRB) became the main bacteria in biofilm, they could induce iron redox cycling in corrosion process. This process enhanced the precipitation of iron oxides and formation of more Fe₃O₄ in corrosion scales, which inhibited corrosion effectively. Therefore, the IRB and NRB in the biofilm can reduce iron release and red water occurrence. Moreover, there are many opportunistic pathogens in biofilm of DWDSs. The opportunistic pathogens growth in DWDSs related to the bacterial community changes due to the effects of micropollutants. Micropollutants increased the number of bacteria with antibiotic resistance genes (ARGs). Furthermore, extracellular polymeric substances (EPS) production was increased by the antibiotic resistant bacteria, leading to greater bacterial aggregation and adsorption, increasing the chlorine-resistance capability, which was responsible for the enhancement of the particle-associated opportunistic pathogens in DWDSs. Moreover, O₃-biological activated carbon filtration-UV-Cl₂ treatment could be used to control the iron release, red water occurrence and opportunistic pathogens growth in DWDSs.     

Simultaneous removal of arsenic and antimony from mining wastewater using granular TiO2: Batch and field column studies

Coexisting arsenic (As) and antimony (Sb) in mining wastewater is a common and great concern. On-site simultaneous removal of As and Sb from mining wastewater was achieved by using a reusable granular TiO₂ column in this study. To evaluate the accuracy of the scale-up procedure, As and Sb adsorption from wastewater was studied in both large (600 g TiO₂) and small columns (12 g TiO₂) based on the proportional diffusivity rapid small-scale column tests (PD-RSSCTs) design. The comparable As and Sb breakthrough curves obtained from small and large columns confirmed the accuracy of the PD-RSSCT theory in the design of large-scale columns. Meanwhile, the consistent As and Sb adsorption results from batch and column experiments suggested that TiO₂ adsorption for As and Sb can be predicted from bench-scale tests. Charge distribution multi-site complexation (CD-MUSIC) and one-dimensional transport modeling integrated in the PHREEQC program were performed to study the adsorption behaviors of As and Sb on the TiO₂ surface. Coexisting ions, such as Ca^2 +, Mg^2 +, and Si^4 +, play an important role in As and Sb adsorption, and the breakthrough curves were well simulated after considering the compound ion effects. The results from this study highlight the surface reactions of As and Sb on TiO₂ and provide a practical way for on-site remediation of industrial wastewater.     

O3-BAC-Cl2: A multi-barrier process controlling the regrowth of opportunistic waterborne pathogens in drinking water distribution systems

Simulated drinking water distribution system (DWDS) treated with O₃-BAC-Cl₂ (ozone-biological activated carbon-chlorine) was constructed to study its effects on the regrowth of five typical opportunistic pathogens (OPs). It was found that O₃-BAC-Cl₂ could significantly reduce the regrowth of target OPs in the effluents of DWDS compared with Cl₂ and O₃-Cl₂ with the same residual chlorine levels. However, the effect of O₃-BAC-Cl₂ on the average numbers of target OPs gene markers in the biofilms of DWDS was not apparent, suggesting that OPs in the biofilms of DWDS were tolerant to the upstream disinfection process. The quantification of target OPs in the BAC-filter column demonstrated that OPs decreased with the increase of depth, which was likely due to the organic nutrient gradient and microbial competition inside the BAC-filter. Increase in the ozone dose could further reduce the OPs at the bottom of the BAC-filter. Spearman correlation analysis demonstrated that some significant correlations existed between target microorganisms, suggesting potential microbial ecological relationships. Overall, our results demonstrated that the BAC-filter may act as a “battlefield” suppressing the OPs through microbial competition. O₃-BAC-Cl₂ could be an effective multi-barrier process to suppress the proliferation of OPs in the bulk water of DWDS. However, OPs protected by the biofilms of DWDS should receive further attention because OPs may be detached and released from the biofilms.     

Effects of tourmaline on nitrogen removal performance and biofilm structures in the sequencing batch biofilm reactor

The effects of tourmaline on nitrogen removal performance and biofilm structures were comparatively investigated in two identical laboratory-scale sequencing batch biofilm reactors(SBBRs)(denoted SBBR1 and SBBR2) at different nitrogen loading rates(NLRs) varying from(0.24 ± 0.01) to(1.26 ± 0.02) g N/(L·day). SBBR1 was operated in parallel with SBBR2, but SBBR1 was filled with polyurethane foam loaded tourmaline(TPU) carriers and another(SBBR2) filled with polyurethane foam(PU) carriers. Results obtained from this study showed that the excellent and stable performance of SBBR1 was obtained. Ammonia nitrogen removal and total nitrogen removal were higher in SBBR1 than that in SBBR2 with increase of NLR. At an NLR of(0.24 ± 0.01) g N/(L·day), the majority of the spherical and elliptical bacteria were surrounded by the extracellular polymeric substance(EPS) and bacillus or filamentous bacteria in two SBBRs biofilms. When NLR increased to(1.26 ± 0.02) g N/(L·day), the clusters were more obvious in the SBBR1 biofilm than that in the SBBR2 biofilm. Bacteria in SBBR1 were inclined to synthesis more EPS, and the formed EPS could protect the bacteria from free ammonia(FA) under extreme condition NLR(1.26 ± 0.02) g N/(L·day). The results of polymerase chain reaction-denaturing gradient gel electrophoresis analysis showed that the microbial community similarity in SBBR2 decreased more obviously than that in SBBR1 with the increase of NLR, which the microbial community in SBBR1 was relatively stable.     

An innovative approach to minimize excess sludge production in sewage treatment using integrated bioreactors

The present investigation deals with an application of integrated sequential oxic and anoxic bioreactor(SOABR) and fluidized immobilized cell carbon oxidation(FICCO) reactor for the treatment of domestic wastewater with minimum sludge generation. The performance of integrated SOABR-FICCO system was evaluated on treating the domestic wastewater at hydraulic retention time(HRT) of 3 hr and 6 hr for 120 days at organic loading rate(OLR)of 191 ± 31 mg/(L·hr). The influent wastewater was characterized by chemical oxygen demand(COD) 573 ± 93 mg/L; biochemical oxygen demand(BOD5) 197 ± 35 mg/L and total suspended solids(TSS) 450 ± 136 mg/L. The integrated SOABR-FICCO reactors have established a significant removal of COD by 94% ± 1%, BOD5 by 95% ± 0.6% and TSS by 95% ± 4% with treated domestic wastewater characteristics COD 33 ± 5 mg/L; BOD59 ± 0.8 mg/L and TSS 17 ± 9 mg/L under continuous mode of operation for 120 days. The mass of dry sludge generated from SOABR-FICCO system was 22.9 g/m~3. The sludge volume index of sludge formed in the SOABR reactor was 32 mL/g and in FICCO reactor it was 46 mL/g. The sludge formed in SOABR and FICCO reactor was characterized by TGA, DSC and SEM analysis. Overall, the results demonstrated that the integrated SOABR-FICCO reactors substantially removed the pollution parameters from domestic wastewater with minimum sludge production.     

Effects of Asian dust events on atmospheric bacterial communities at different distances downwind of the source region

Aeolian dust particles arising from arid and semiarid zones are known to carry microbes by air currents. The effect of wind-borne bacteria on atmospheric bacterial population at various downwind distances from the dust source regions must be clarified, but has not yet been reported. This study monitored the bacterial abundance and community composition in outdoor aerosol samples in Beijing, China, which is close to the Asian dust source regions, and compared them with the results obtained in a distant region(Osaka, Japan).The Asian dust collected in Beijing contained(4 ± 3) × 10~4 bacterial cells/m~3, approximately~4 times higher than in Osaka. On 15 April 2015, Beijing experienced severe Asian dust events with a 1000-fold increase in bacterial abundance, relative to non-Asian dust days. Dominant bacterial phyla and classes in Asian dust collected in Beijing were Actinobacteria, Bacilli and Acidobacteria, and the bacterial community composition varied more widely than in Osaka.The bacterial community compositions differed between the Beijing and Osaka dusts, even for the same Asian dust events. These results indicated that aerosol bacterial communities nearer the dust source are more affected by eolian dust than their distant counterparts.     

On-going nitrification in chloraminated drinking water distribution system (DWDS) is conditioned by hydraulics and disinfection strategies

Within the drinking water distribution system (DWDS) using chloramine as disinfectant, nitrification caused by nitrifying bacteria is increasingly becoming a concern as it poses a great challenge for maintaining water quality. To investigate efficient control strategies, operational conditions including hydraulic regimes and disinfectant scenarios were controlled within a flow cell experimental facility. Two test phases were conducted to investigate the effects on the extent of nitrification of three flow rates (Q = 2, 6, and 10 L/min) and four disinfection scenarios (total Cl₂=1 mg/L, Cl₂/NH₃-N=3:1; total Cl₂=1 mg/L, Cl₂/NH₃-N=5:1; total Cl₂=5 mg/L, Cl₂/NH₃-N=3:1; and total Cl₂=5 mg/L, Cl₂/NH₃-N=5:1). Physico-chemical parameters and nitrification indicators were monitored during the tests. The characteristics of biofilm extracellular polymetric substance (EPS) were evaluated after the experiment. The main results from the study indicate that nitrification is affected by hydraulic conditions and the process tends to be severe when the fluid flow transforms from laminar to turbulent (2300<Re<4000). Increasing disinfectant concentration and optimizing Cl₂/NH₃-N mass ratio were found to inhibit nitrification to some extend when the system was running at turbulent condition (Q = 10 L/min, Re = 5535). EPS extracted from biofilm that was established at the flow rate of 6 L/min had greater carbohydrate/protein ratio. Furthermore, several nitrification indicators were evaluated for their prediction efficiency and the results suggest that the change of nitrite, together with total organic carbon (TOC) and turbidity can indicate nitrification potential efficiently.     

Engineering of responsive polymer based nano-reactors for facile mass transport and enhanced catalytic degradation of 4-nitrophenol

Silver nanoparticles with average diameter of 10 ± 3 nm were synthesized within the sieves of poly(N-isopropylacrylamide-2-hydroxyethylmethacrylate-acrylic acid)(p(NIPAAm-HEMA-AAc))polymer microgels. Free radial emulsion polymerization was employed for synthesis of p(NIPAAm-HEMA-AAc) polymer microgels. Silver nanoparticles were introduced within the microgels sphere by in situ reduction method. Microgels and hybrid microgels were characterized by Fourier transform infrared spectroscopy, ultra violet-visible spectroscopy,transmission electron microscopy and dynamic light scattering measurements. Catalytic activity of Ag-p(NIPAAm-HEMA-AAc) hybrid microgels was studied using catalytic reduction of 4-nitrophenol(4-NP) as a model reaction in aqueous media. The influence of sodium borohydride(Na BH4) concentration, catalyst dose and 4-NP concentration on catalytic reduction of 4-NP was investigated. A linear relationship was found between catalyst dose and apparent rate constant(kapp). The mechanism of catalysis by hybrid microgels was explored for further development in this area. The deep analysis of catalytic process reveals that the unique combination of NIPAAm, HEMA and AAc does not only stabilize silver nanoparticles in polymer network but it also enhances the mass transport of hydrophilic substrate like 4-NP from outside to inside the polymer network.     

水相中CCl4和CHCl3的紫外光解机理

利用瞬态吸收光谱技术研究水体污染物CCl₄和CHCl₃在紫外光照条件下的转化和归宿,表明在248nm激光作用下,CCl₄解离为CCl₃和Cl自由基;CHCl₃在此条件下不解离,但加入少量的苯后即发生明显解离,产生CHCl₂和Cl自由基.在有氧条件下,光解产生的CCl₃和CHCl₂自由基均与O₂反应分别生成CCl₃O₂和CHCl₂O₂;在无氧条件下,CCl₃和CHCl₂则发生偶合反应分别生成C₂Cl₆和C₂H₂Cl₄.本研究还得出了一些微观速率常数.     

Inhibitive effects of chlortetracycline on performance of the nitritation-anaerobic ammonium oxidation (anammox) process and strategies for recovery

The short-and long-term effects of chlortetracycline(CTC) on the nitritation-anaerobic ammonium oxidation(anammox) process were evaluated. The half maximal inhibitory concentration of CTC in the batch tests of the nitritation-anammox process was 278.91 mg/L at an exposure time of 12 hr. The long-term effects of CTC on the process were examined in a continuous-flow nitritation-anammox reactor. Within 14 days, the nitrogen removal rate significantly decreased from 0.61 to 0.25 kg N/m~3/day with 60 mg/L CTC in the influent.The performance suppressed by CTC barely recovered, even after CTC was removed from the influent. Furthermore, the inhibition of CTC also reduced the relative abundance of ammonium oxidizing bacteria(AOB) and anaerobic ammonium oxidizing bacteria(An AOB)in the reactor, resulting in both a decreased amount of and an imbalance between AOB and An AOB. When fresh anammox sludge was reseeded into the nitritation-anammox reactor,the nitrogen removal rate recovered to 0.09 ± 0.03 kg N/m~3/day.     

Dairy farm CH4 and N2O emissions,from one square metre to the full farm scale

The greenhouse gas emissions from agricultural systems contribute significantly to the national budgets for most countries in Europe. Measurement techniques that can identify and quantify emissions are essential in order to improve the selection process of emission reduction options and to enable quantification of the effect of such options. Fast box emission measurements and mobile plume measurements were used to evaluate greenhouse gas emissions from farm sites. The box measurement technique was used to evaluate emissions from farmyard manure and several other potential source areas within the farm. Significant (up to 250 g CH₄ m⁻² day⁻¹and 0.4 g N₂O m⁻² day⁻¹) emissions from ditches close to stables on the farm site were found.Plume emission measurements from individual manure storages were performed at three sites. For a manure storage with 1200 m³ dairy slurry in Wageningen emission factors of 11 ± 5 g CH₄ m⁻³ manure day⁻¹ and 14 ± 8 mg N₂O m⁻³ manure day⁻¹ were obtained in February 2002.Mobile plume measurements were carried out during 4 days at distances between 30 and 300 m downwind of 20 different farms. Total farm emissions levels ranged from 14 to 95 kg CH₄ day⁻¹ for these sites. Expressed as emission per animal the levels were 0.7 ± 0.4 kg CH₄ animal⁻¹ day⁻¹ for conventional farms. For three farms that used straw bedding for the animals1.4 ± 0.2 kg CH₄ animal⁻¹ day⁻¹ was obtained. These factors include both respired methane and emission from manure in the stable and the outside storages.For a subset of these farms the CH₄ emission was compared with monthly averaged model emission calculations using FarmGHG. This model calculates imports, exports and flows of all products through the internal chains on the farm using daily time steps. The fit of modelled versus measured data has a slope of 0.97 but r² = 0.27. Measurements and model emission estimates agree well on average, for large farms within 30%. For small farms the differences can be up to a factor of 3. CH₄ emissions during winter seem to be underestimated.     

Characterizing the antibiotic resistance genes in a river catchment: Influence of anthropogenic activities

Previous studies on environmental antibiotics resistance genes(ARGs) have focused on the pollution sources such as wastewater treatment plants, aquaculture and livestock farms,etc. Few of them had addressed this issue in a regional scale such as river catchment. Hence,the occurrence and abundances of 23 ARGs were investigated in surface water samples collected from 38 sites which located from the river source to estuary of the Beijiang River.Among them, 11 ARGs were frequently detected in this region and 5 ARGs(sul I, sul II, tet B,tet C, and tet W) were selected for their distribution pattern analysis. The abundances of the selected ARGs were higher in the upstream(8.70 × 10~6 copies/ng DNA) and downstream areas(3.17 × 10~6 copies/ng DNA) than those in the midstream areas(1.23 × 10~6 copies/ng DNA), which was positively correlated to the population density and number of pollution sources. Pollution sources of ARGs along the Beijiang River not only had a great impact on the abundances and diversity, but also on the distribution of specific ARGs in the water samples. Both sul I and sul II were likely originated from aquaculture farms and animal farms,tet W gene was possibly associated with the mining/metal melting industry and the electric waste disposal and tet C gene was commonly found in the area with multiple pollution sources.However, the abundance of tet B was not particularly related to anthropogenic impacts. These findings highlight the influence of pollution sources and density of population on the distribution and dissemination of ARGs at a regional scale.     

Hollow TiO2 spheres with improved visible light photocatalytic activity synergistically enhanced by multi-stimulative: Morphology advantage, carbonate-doping and the induced Ti3 +

Great efforts have been devoted to improve the photocatalytic activity of TiO_2 in the visible light region. Rational design of the external structure and adjustment of intrinsic electronic status by impurity doping are two main effective ways to achieve this purpose. A facile onepot synthetic approach was developed to prepare C-doped hollow TiO_2 spheres, which simultaneously realized these advantages. The synthesized TiO_2 exhibits a mesoporous hollow spherical structure composed of fine nanocrystals, leading to high specific surface area(~180 m~2/g) and versatile porous texture. Carbonate-doping was achieved by a postthermal treatment at a relatively low temperature(200°C), which makes the absorption edge red-shifted to the visible region of the solar spectrum. Concomitantly, Ti~(3+) induced by C-doping also functions in improving the visible-light photocatalytic activity by reducing the band gap. There exists a synergistic effect from multiple stimulatives to enhance the photocatalytic effect of the prepared TiO_2 catalyst. It is not out of expectation that the asprepared C-doped hollow TiO_2 spheres exhibits an improved photocatalytic activity under visible light irradiation in organic pollutant degradation.     

Revealing the changes of bacterial community from water source to consumers tap: A full-scale investigation in eastern city of China

This study profiled the bacterial community variations of water from four water treatment systems, including coagulation, sedimentation, sand filtration, ozonation-biological activated carbon filtration (O₃-BAC), disinfection, and the tap water after the distribution process in eastern China. The results showed that different water treatment processes affected the bacterial community structure in different ways. The traditional treatment processes, including coagulation, sedimentation and sand filtration, reduced the total bacterial count, while they had little effect on the bacterial community structure in the treated water (before disinfection). Compared to the traditional treatment process, O₃-BAC reduced the relative abundance of Sphingomonas in the finished water. In addition, ozonation may play a role in reducing the relative abundance of Mycobacterium. NaClO and ClO₂ had different effects on the bacterial community in the finished water. The relative abundance of some bacteria (e.g. Flavobacterium, Phreatobacter and Porphyrobacter) increased in the finished water after ClO₂ disinfection. The relative abundance of Mycobacterium and Legionella, which have been widely reported as waterborne opportunistic pathogens, increased after NaClO disinfection. In addition, some microorganisms proliferated and grew in the distribution system, which could lead to turbidity increases in the tap water. Compared to those in the finished water, the relative abundance of Sphingomonas, Hyphomicrobium, Phreatobacter, Rheinheimera, Pseudomonas and Acinetobacter increased in the tap water disinfected with NaClO, while the relative abundance of Mycobacterium increased in the tap water disinfected with ClO₂. Overall, this study provided the detailed variation in the bacterial community in the drinking water system.