Rong Cheng

Removing pentachlorophenol from water using a nanoscale zero-valent iron/H2O2 system.

Nanoscale zero-valent iron (nZVI) is an environmentally benign material that has been widely used as a reducing agent to treat environmental pollutants. In this study, nZVI was used as a heterogeneous Fenton catalyst in an nZVI/H2O2 system to remove pentachlorophenol (PCP) from water. The PCP degradation process in the nZVI/H2O2 system was completed within 1h. The relative Cl(-) concentration increased throughout the test period (6h), indicating that the performance of the oxidative system in terms of dechlorination was excellent. The initial H2O2 concentration significantly influenced the PCP removal rate, and nZVI performed better than commercial zero-valent iron as a catalyst. Moreover, magnetite (Fe3O4), which was the main product of the corrosion of nZVI, was found to perform well as an adsorbent and catalyst, so it allowed the nZVI to be effectively reused.

Nanomaterials for water pollution monitoring and remediation

Water shortage and pollution are serious challenges for many countries. Nanomaterials are promising new tools for water quality management due to unique physicochemical properties, high economic benefit, high removal efficiency and environmental friendliness. Here we describe four types of nanomaterials used for water treatment: nanofiltration membranes, photocatalytic nanomaterials, adsorption nanomaterials and reducing nanomaterials. We discuss their properties, applications and mechanisms for pollutant removal. We also review nanomaterials used for water quality monitoring, notably nanomaterials used for the detection of trace pollutants and pathogens. These nanomaterials include carbon nanotubes, magnetic nanoparticles, noble metal nanomaterials and quantum dots.

The mechanism for bacteriophage f2 removal by nanoscale zero-valent iron.

Nanoscale zero-valent iron (NZVI) has shown excellent performance for pathogenic microorganism removal but the inactivation mechanism has not been understood clearly enough. In this study, the bacteriophage f2 removal by NZVI under aerobic and anaerobic conditions was investigated, and various factors involved in f2 removal were analyzed in detail, including the ion products of NZVI (Fe(II), Fe(III)), solid phase products, the reactive oxygen species (ROS), O2 and H+. In addition, the morphologies of bacteriophage f2 during reaction were observed. The results showed that the removal efficiency of bacteriophage f2 was much higher under aerobic conditions than that in anaerobic systems, and oxygen and pH were determinants for f2 removal. The oxidation of Fe(II) was a fundamental step and played a significant role in bacteriophage f2 removal, especially in the aerobic systems. In the presence of oxygen, the virus removal was attributed to the generation of ROS (namely ·OH and ·O2-) and the oxidized iron, in which the ROS (·OH and ·O2-) made a predominant contribution. And the adsorption of iron oxide was responsible for the removal in oxygen depleted circumstance. In the anaerobic system, the virus removal was mainly attributed to the interaction between NZVI and bacteriophage f2. Besides, from the perspective of TEM images, the virus removal was mainly attributed to the damage of infective ability by NZVI at the initial stage of reaction, and later the virus was inactivated by the ROS generated.

Catalytic oxidation of 4-chlorophenol with magnetic Fe3O4 nanoparticles: mechanisms and particle transformation

Magnetite (Fe3O4) is usually inert and when combined with metal catalysts or enzymes it forms a composite that exhibits both magnetism and catalytic activity. However, it has been reported that Fe3O4 nanoparticles have intrinsic peroxidase-like activity. In this study, super paramagnetic Fe3O4 nanoparticles with a diameter of about 30 nm were synthesized using self-designed experimental devices under mild conditions. Moreover, 4-chlorophenol (4-CP), which is a priority pollutant that widely exists in the environment but is recalcitrant towards chemical and biological degradation, was used as a model compound to test the catalytic activity of the synthesized Fe3O4 nanoparticles and analyse the mechanisms for 4-CP removal. Besides, surface analysis techniques, such as SEM, XRD and Raman spectroscopy, were used to investigate the transformation of the nanoparticles and further verify the interaction between the nanoparticles and 4-CP. The results revealed that the synthesized Fe3O4 nanoparticles show high catalytic activity even after being used several times, and acidic conditions are favourable for the dechlorination of 4-CP. However, 4-CP could also be degraded under neutral and alkali conditions. In the process 4-CP was transformed to formic acid, acetic acid and other byproducts. Adsorption tests indicated that the adsorption process does not play an important role in 4-CP removal, but it occurs between 4-CP and Fe3O4. The surface morphology of the Fe3O4 nanoparticles changed a lot and the reactive sites on the surface increased, which resulted in the higher activity of the particles after being used. The crystal structure of the nanoparticles did not change, suggesting the role of Fe3O4 nanoparticles as catalysts. Moreover, Raman spectra reflected that the adsorption and catalytic oxidation were surface reaction processes. It is proposed that the hydroxyl radical produced during the reaction is the main cause for the degradation of 4-CP. The reaction of H2O2 with ferrous to produce hydroxyl radical is the initial step, and is very important for the overall process.

Electrospinning Cu–TiO2 nanofibers used for photocatalytic disinfection of bacteriophage f2: preparation, optimization and characterization

The presence of pathogenic viruses in drinking water threatens public health severely. However, there is little information about how to use photocatalysts to disinfect viruses. In this report, one-dimensional Cu–TiO2 nanofibers were fabricated using the electrospinning method and used for the removal of bacteriophage f2. The results showed that the optimum doping ratio and calcination temperature of the Cu–TiO2 nanofibers was n(Cu) : n(Ti) = 1 : 8 and 450 °C, respectively. In addition, bacteriophage f2 with an initial concentration of 105 PFU mL−1 was completely inactivated with a dosage of 50 mg L−1 of Cu–TiO2 nanofibers under visible light irradiation for 4 h. Furthermore, the results from characterization of the nanofibers by various techniques, including scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis spectrophotometry demonstrated that TiO2 existed in the anatase phase and Cu2+ substituted Ti4+ in the TiO2 lattice. The introduction of Cu into TiO2 effectively extended the spectral response of TiO2 to visible light. On the basis of this evidence, the mechanism of virus inactivation by Cu–TiO2 nanofibers was proposed.

Removal of waterborne phage and NO3− in the nZVI/phage/NO3− system: competition effect

Waterborne pathogenic viruses are a threat to public health. Nanoscale zero-valent iron (nZVI) has increasingly been applied to the removal of viruses. However, current studies are usually based on single component systems, which are not consistent with reclaimed water containing various pollutants in complex mixtures. In this study, a coexisting system containing microorganisms and chemical substances was constructed. Phage f2 and NO3− were selected as the model virus and nutrient substance in water to investigate the removal of waterborne phage and a chemical substance in an nZVI/phage/NO3− system. The results showed that phage f2 and NO3− could coexist without interference in a phage/NO3− system, while there was competition between phage f2 and NO3− for nZVI when nZVI was added. The removal efficiency of phage f2 decreased with an increase in NO3− concentration (0–100 mg L−1). When the initial concentration of virus was 8 × 105 PFU mL−1, the virus removal efficiency was not altered by NO3−; however, it was significantly reduced by NO3− when the initial concentration of the virus was increased (8 × 106 to 8 × 107 PFU mL−1). In addition, the virus (8 × 106 PFU mL−1) reduced the NO3− (20 mg L−1) removal by nZVI (60 mg L−1). With an increase in nZVI dosage, the virus removal efficiency first increased and then decreased irrespective of NO3− being present. Nevertheless, the turning point of virus removal efficiency was retard in the presence of NO3−. The removal efficiency of NO3− increased with an increase in the nZVI dosage (20–120 mg L−1) irrespective of whether the virus was present, but the effect of virus on NO3− removal was weakened. Under acidic conditions, phage f2 was superior to NO3− in reacting with nZVI, and NO3− was superior to phage f2 under alkaline conditions.

Nanomaterials for Monitoring and Remediation of Water Pollution

Water shortage and pollution are now serious challenges for many countries. Nanomaterials are promising new tools for water quality management due to their unique physicochemical properties, high economic benefit, high removal efficiency and environmental friendliness. Here we present four types of nanomaterials for water and wastewater treatment: nanofiltration membranes, nano-photocatalytic materials, nano-adsorption materials and nano-reducing materials. We discuss their properties, application scope and mechanism of pollutant removal. We also review nanomaterials used for water quality monitoring, especially for the detection of the extremely low concentration organic pollutants, inorganic pollutants and pathogens. Such nanomaterials include carbon nanotubes, magnetic nanoparticles, noble metal nanomaterials and quantum dots.

Identify driving forces of MBR applications in China

Abstract During the last two decades, MBR applications in China grow exponentially with the first pilot test of 10 m3/d in 1999 and the first application with capacity of 110,000 m3/d commissioned in 2009. It is critical to examine the drivers of MBR applications in China, which can provide sound scientific basis for future development of MBR applications. This study summarized the historical development of MBR applications and analyzed the driving forces by survey, literature review and interviews with MBR suppliers. The results showed that: (1) technical advantages of MBR and public policy related to water resources and environment promoted MBR beyond lab and pilot test into wide commercial applications in China; (2) petrochemical industry needs for wastewater treatment and reuse promoted medium-scale MBRs as public policy and regulation on water resources and environment tightens; (3) when the breakthrough of capacity of a single project above 10 thousand m3/d, the Green Olympic Games and Asian Games and tightening effluent regulations in environmentally sensitive areas incentivized MBR applications; and (4) the emergence of 100,000 m3/d MBR was mainly stimulated by water resources stress. Water resources stress and public policy related on resources and the environment are the primary driving forces in the last several decades. The future drivers of MBR applications in China appear to be decreasing operation cost.

Effect of Sulfate Concentration on Biohydrogen Production by Enriched Anaerobic Sludge

The effect of SO2-4 concentration ranging from 0 to 10 g/L on fermentative hydrogen production by enriched anaerobic sludge was investigated using glucose as substrate at 35°C and initial pH 7.0. The experimental results showed that the hydrogen yield increased with increasing SO2-4 concentration from 0 to 0.05 g/L. The maximum maximum hydrogen yield of 272.2 mL/g glucose were obtained at the SO2-4 concentration of 0.05 g/L. The average hydrogen production rate increased with increasing SO2-4 concentration from 0 to 0.1 g/L and the maximum average hydrogen production rate of 8.4 mL/h was obtained at the SO2-4 concentration of 0.1 g/L. The Han-Levenspiel model could describe the effect of SO2-4 concentration on average hydrogen production rate successfully.

Supported Iron Nanoparticles for Removal of Pentachlorophenol in Water

Two kinds of supported iron nanoparticles by activated carbon/carbon nanotubes were synthesized under ambient condition in this study. And their performance for pentachlorophenol (PCP) removal in water was examined. The SEM images showed that the nanoparticles supported by carbon nanotubes (Fe-CNTs) were of better dispersibility and smaller particle size than that by activated carbon (Fe-C). And the iron content in both of Fe-CNTs and Fe-C system measured by EDS was similar to each other. But the removal rate of PCP in the former system was obviously lower than the latter. It might be due to the more excellent adsorption capacity of activated carbon. And another main reason could be the reduction of adsorption sites due to the occupation of iron nanoparticles. The removal of PCP from the solution was the result of both of the activated carbon/carbon nanotubes adsorption and iron degradation. And the adsorption process was prior to the degradation by iron nanoparticles.