Xiuyun Sun

Evaluation of zeolites synthesized from fly ash as potential adsorbents for wastewater containing heavy metals.

The pure-form zeolites (A and X) were synthesized by applying a two-stage method during hydrothermal treatment of fly ash prepared initial Cu and Zn gel. The difference of adsorption capacity of both synthesized zeolites was assessed using Cu and Zn as target heavy metal ions. It was found that adsorption capacity of zeolite A showed much higher value than that of zeolite X. Thus, attention was focused on investigating the removal performance of heavy metal ions in aqueous solution on zeolite A, comparing with zeolite HS (hydroxyl-solidate) prepared from the residual fly ash (after synthesis of pure-form zeolite A from fly ash) and a commercial grade zeolite A. Batch method was used to study the influential parameters of the adsorption process. The equilibrium data were well fitted by the Langmuir model. The removal mechanism of metal ions followed adsorption and ion exchange processes. Attempts were also made to recover heavy metal ions and regenerate adsorbents.

Influence of NaOH concentrations on synthesis of pure-form zeolite A from fly ash using two-stage method

Synthesis of pure-form zeolite A were investigated using four concentrations of NaOH solution to dissolve Si source form fly ash, and with the addition of Al source, to prepare initial gel. Experimental results demonstrated, for two-stage method, that NaOH concentrations in initial gel played an important role in synthesis of pure-form zeolite A using fly ash as raw materials. Generally, pure-form zeolite A could be synthesized when following conditions were used: NaOH concentrations, 1.67, 5 and 6.67 M; the synthesis temperature, 100 degrees C; the corresponding crystallization time, 340, 250 and 190 min. However, a mixture phases of zeolites A and X were obtained at the condition of 3.33 M NaOH solution during various crystallization times. It was found that the higher NaOH concentration was used, the shorter crystallization time of zeolite A was required and the narrower particle size distribution of zeolite A was achieved. In addition, zeolite A submicron-crystals were first synthesized from fly ash using two-stage method in our study.

Biodegradation of 2,4,6-trinitrophenol by Rhodococcus sp. isolated from a picric acid-contaminated soil.

A picric acid-degrading bacterium, strain NJUST16, was isolated from a soil contaminated by picric acid and identified as a member of Rhodococcus sp. based on 16S rRNA sequence. The degradation assays suggested that the strain NJUST16 could utilize picric acid as the sole source of carbon, nitrogen and energy. The isolate grew optimally at 30 degrees C and initial pH 7.0-7.5 in the mineral salts medium supplemented with picric acid. It was basically consistent with degradation of picric acid by the isolate. Addition of nitrogen sources such as yeast extract and peptone accelerated the degradation of picric acid. However, the stimulation was concentration dependent. The degradation was accompanied by release of stoichiometric amount of nitrite and acidification. The degradation of picric acid at relatively high concentrations (>3.93 mM) demonstrated that the degradation was both pH and nitrite dependent. Neutral and slightly basic pH was crucial to achieve high concentrations of picric acid degradation by the NJUST16 strain.

Synthesis of nanoscale zero-valent iron/ordered mesoporous carbon for adsorption and synergistic reduction of nitrobenzene.

Nanoscale zero-valent iron (NZVI) supported on ordered mesoporous carbon (OMC) was synthesized through liquid phase reduction route. The NZVI/OMC composite was characterized by X-ray diffraction, N(2) adsorption/desorption and transmission electron microscopy. Results reveal that the composite possesses ordered mesostructure with NZVI distributing homogeneously on the surface of OMC support. The removal effects of nitrobenzene (NB) in water with OMC, NZVI/OMC and non-supported NZVI were evaluated. Results indicate that NZVI/OMC shows enhanced removal efficiency, which is attributed to its adsorption and synergistic reduction for NB. The transformation process of NB was further investigated by HPLC. Nitrosobenzene and phenylhydroxylamine were detected as intermediate products and aniline was the final reductive product.

Biodegradation of 2,4,6-trinitrophenol (picric acid) in a biological aerated filter (BAF).

This study demonstrated the microbial purification of a model wastewater containing 2,4,6-trinitrophenol (TNP), which was carried out in a continuously working biological aerated filter (BAF). The main emphasis was on the operating performance of the reactor as a function of the pollution load. TNP was degraded at a maximum volumetric removal rate of 2.53gTNP/Ld, with low residual COD and TNP concentration. Overloading of TNP inhibited the nitrite-oxidizing activity, resulting in poor TNP degradation performance in the BAF system. The inhibition depended on some factors, such as influent concentrations and flow rates of the influent. It is assumed that nitrite-oxidizing occurred spontaneously during TNP degradation in the BAF system, could have significant influence on TNP wastewater treatment. One year after the reactor start-up, the dominance of Rhodococcus, which was initially inoculated in the reactor, was confirmed by analysis of 16S rDNA sequence of the PCR products separated by DGGE.

Controllable Synthesis of Functional Hollow Carbon Nanostructures with Dopamine As Precursor for Supercapacitors

N-doped hollow carbon spheres (N-HCSs) are promising candidates as electrode material for supercapacitor application. In this work, we report a facile one-step synthesis of discrete and highly dispersible N-HCSs with dopamine (DA) as a carbon precursor and TEOS as a structure-assistant agent in a mixture containing water, ethanol, and ammonia. The architectures of resultant N-HCSs, including yolk-shell hollow carbon spheres (YS-HCSs), single-shell hollow carbon spheres (SS-HCSs), and double-shells hollow carbon spheres (DS-HCSs), can be efficiently controlled through the adjustment of the amount of ammonia. To explain the relation and formation mechanism of these hollow carbon structures, the samples during the different synthetic steps, including polymer/silica spheres, carbon/silica spheres and silica spheres by combustion in air, were characterized by TEM. Electrochemical measurements performed on YS-HCSs, SS-HCSs, and DS-HCSs showed high capacitance with 215, 280, and 381 F g(-1), respectively. Moreover, all the nitrogen-doped hollow carbon nanospheres showed a good cycling stability 97.0% capacitive retention after 3000 cycles. Notably, the highest capacitance of DS-HCSs up to 381 F g(-1) is higher than the capacitance reported so far for many carbon-based materials, which may be attributed to the high surface area, hollow structure, nitrogen functionalization, and double-shell architecture. These kinds of N-doped hollow-structured carbon spheres may show promising prospects as advanced energy storage materials and catalyst supports.

Biological denitrification of high-nitrate wastewater in a modified anoxic/oxic-membrane bioreactor (A/O-MBR)

A modified anoxic/oxic-membrane bioreactor has been applied to the denitrification of a high strength nitrate waste (about 3600 mg/L nitrate-N) generated from an initiating explosive factory. Nitrate removal efficiency and nitrite accumulation in the treated water were investigated under various conditions set by several factors including the type of carbon source used, ratios of carbon to nitrogen, pH and hydraulic retention times (HRTs). The results of the preliminary experiments, which were carried out in parallel CSTR systems, demonstrated that sodium acetate had shown the best performance as the external carbon source. The optimal reaction parameters in the anoxic/oxic-membrane bioreactor were pH 7.5-8.5, C/N 1.56 and HRT 30 h, with over 99.9% of nitrate removed and without accumulation of nitrite. Explicitly high average-specific denitrification rate of 324 mg NO(3)(-)-N/g VSS/h could be attained under these conditions. The aerobic process and membrane module used subsequently could remove the residual COD, excessive biomass and soluble microbial products generated during the denitrification process.

Electrochemical degradation of pyridine by Ti/SnO2-Sb tubular porous electrode.

Diffusion in electrochemistry is a critical issue for water purification. Electrocatalytic reactor system in improving water quality is a useful way to induce convection to enhance diffusion. This study focuses on the preparation and the characterization of Ti/SnO2-Sb tubular porous electrode for degrading pyridine wastewater. The electrode as an anode in reactor system is prepared by coating SnO2-Sb as an electro-catalyst via Pechini method on the tubular porous Ti. Scanning Electron Microscopy, Energy Dispersive Spectrum, X-ray Diffraction and Pore Distribution are employed to evaluate the structure and morphology of the electrodes coatings, and Linear Sweep Voltammetry and Cyclic Voltammetry are used to illustrate the electrochemical properties of the electrodes coatings. Furthermore, the electrochemical oxidation performance of Ti/SnO2-Sb tubular porous electrode is characterized by degrading pyridine wastewater. The effects of flow and static pattern, initial pyridine concentration, supporting electrolyte concentration, current density and pH on the performance of the reactor were investigated in the electrocatalytic reactor system. The results indicated that the removal ratio of pyridine reaches maximum which is 98% under the optimal operation conditions, that are 100 mg L(-1) initial pyridine concentration, 10 g L(-1) supporting electrolyte concentration, 30 mA cm(-2) current density and pH 3. Transition state calculation based on the density function theory was combined with High Performance Liquid Chromatography, Gas Chromatography and Ionic Chromatography results to describe the pathway of pyridine degradation.

Coupling of a bioelectrochemical system for p-nitrophenol removal in an upflow anaerobic sludge blanket reactor.

Coupling of a bioelectrochemical system (BES) into the upflow anaerobic sludge blanket (UASB) was developed for enhanced p-nitrophenol (PNP) removal in this study. Compared to the control UASB reactor, both PNP removal and the formation of its final reductive product p-aminophenol (PAP) were notably improved in the UASB-BES system. With the increase of current density from 0 to 4.71 A m(-3), the rates of PNP removal and PAP formation increased from 6.16 ± 0.11 and 4.21 ± 0.29 to 6.77 ± 0.00 and 6.11 ± 0.28 mol m(-3) d(-1), respectively. More importantly, the required dosage of organic cosubstrate was significantly reduced in the UASB-BES system than that in the UASB reactor. Organic carbon flux analysis suggested that biogas production from organic cosubstrate was seriously suppressed while direct anaerobic reduction of PNP was not remarkably affected by current input in the UASB-BES system. This study demonstrated that the UASB-BES coupling system had a promising potential for the removal of nitrophenol-containing wastewaters especially without adequate organic cosubstrates inside.

Bioelectrochemical system for recalcitrant p-nitrophenol removal

Bioelectrochemical system (BES) for recalcitrant p-nitrophenol (PNP) removal was investigated in this study. Effective removal of PNP at rates up to 9.14 ± 0.48 mol m(-3)d(-1) was achieved at an energy consumption as low as 0.010 ± 0.002 kWh mol(-1) PNP. PNP removal rate was enhanced with negative cathode potential, increased influent PNP concentration and shortened hydraulic retention time (HRT). Although the coulombic efficiencies at the anode did not exceed 40%, coulombic efficiencies for PNP removal at the cathode were above 70% at various cathode potentials. Compared with conventional anaerobic process, the cosubstrate dosage in BES was significantly reduced due to the high coulombic efficiencies at the cathode. p-Aminophenol (PAP) was identified as the dominant product of PNP reduction at the abiotic graphite cathode of BESs. This study demonstrated that the BES had a potential for efficient removal of nitrophenol pollutants from wastewater.