Shu-Guang Wang

Removal of fluoride by hydrous manganese oxide-coated alumina: performance and mechanism.

A novel hydrous-manganese-oxide-coated alumina (HMOCA) material was prepared through a redox process. The adsorbent was characterized by SEM, BET surface area measurement, XRD, pH(PZC) measurement, FTIR spectroscopy, and XPS. The manganese oxides were amorphous and manganese existed mainly in the +IV oxidation state. Batch and column experiments were carried out to investigate the adsorption potential of the adsorbent. Fluoride adsorption onto HMOCA followed the pseudo-second-order equation well with a correlation coefficient greater than 0.99. Both external and intraparticle diffusion contributed to the rate of transfer and removal. The adsorption of fluoride was thought to take place mainly by ion-exchange. Optimum removal of fluoride occurred in a pH range of 4.0-6.0. The maximum adsorption capacity calculated from the Langmuir model was 7.09 mg/g. The presence of HCO(3)(-), SO(4)(2-) and PO(4)(3-) had negative effects on the adsorption of fluoride. The adsorbed fluoride can be released by alkali solution. Column studies were performed and 669 bed volumes were treated with the effluent fluoride under 1.0mg/L at an influent F(-) concentration of 5.0mg/L and flow rate of 2.39 m(3)/(m(2)h) (empty bed contact time=7.5 min).

Nano-structured manganese oxide as a cathodic catalyst for enhanced oxygen reduction in a microbial fuel cell fed with a synthetic wastewater

Microbial fuel cells (MFCs) provide new opportunities for the simultaneous wastewater treatment and electricity generation. Enhanced oxygen reduction capacity of cost-effective metal-based catalysts in an air cathode is essential for the scale-up and commercialization of MFCs in the field of wastewater treatment. We demonstrated that a nano-structured MnO(x) material, prepared by an electrochemically deposition method, could be an effective catalyst for oxygen reduction in an MFC to generate electricity with the maximum power density of 772.8 mW/m(3) and remove organics when the MFC was fed with an acetate-laden synthetic wastewater. The nano-structured MnO(x) with the controllable size and morphology could be readily obtained with the electrochemical deposition method. Both morphology and manganese oxidation state of the nano-scale catalyst were largely dependent on the electrochemical preparation process, and they governed its catalytic activity and the cathodic oxygen reduction performance of the MFC accordingly. Furthermore, cyclic voltammetry (CV) performed on each nano-structured material suggests that the MnO(x) nanorods had an electrochemical activity towards oxygen reduction reaction via a four-electron pathway in a neutral pH solution. This work provides useful information on the facile preparation of cost-effective cathodic catalysts in a controllable way for the single-chamber air-cathode MFC for wastewater treatment.

Sorption and detoxification of chromium(VI) by aerobic granules functionalized with polyethylenimine.

This study describes the modification of aerobic granules by grafting polyethylenimine (PEI) for simultaneous sorption and detoxification of Cr(VI). After modification, the uptake capacity of modified aerobic granules (MAG) showed about 401.5 mg/g at pH 5.5 and increased by 274% compared to the control. Adsorption experiments were carried out as a function of contact time, pH and concentration of Cr(VI). It was found that the equilibrium sorption can be attained within 3 h and the process obeys the Redlich-Peterson isotherm model. The adsorption process is a function of pH of the solution, with the greater adsorption at pH 5.2. The interaction characteristics between the Cr and MAG were elucidated by applying FTIR and XPS analyses. FTIR results showed that the -NH2 groups in the sorbent are involved in the adsorption process. XPS results verified the presence of Cr(III) on the MAG surface in the pH range 1.5-8.5, suggesting that some Cr(VI) anions were reduced to Cr(III) during the sorption.

Spectroscopic study of Zn2+ and Co2+ binding to extracellular polymeric substances (EPS) from aerobic granules.

The interacting mechanisms of metallic cations (Zn2+ and Co2+) to active chemical groups on the extracellular polymeric substances (EPS) of the aerobic granules, including loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), were examined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. For Zn2+ and Co2+, LB-EPS showed stronger binding properties than TB-EPS and the process of them was described well by the Langmuir isotherm. Compared to the single-metal system, binary-metal addition induced competitive binding between the Zn2+ and Co2+ with reduction of the maximal binding capacity for both EPS. The main chemical groups involved in the interactions between contaminants were apparently alcohol, carboxyl and amino. These groups were part of the EPS structural polymers, namely, polysaccharides, proteins, and hydrocarbon-like products. When biosorption and flocculation occurred at the same time, the LB-EPS were used not only as chelate sorbents but also as flocculants to further enhance their sorption capacity.

Characteristics and defluoridation performance of granular activated carbons coated with manganese oxides.

Using a redox process, granular activated carbon (GAC) was coated with manganese oxides to enhance its ability to adsorb fluoride from an aqueous solution. Compared with plain GAC, the fluoride adsorption capacity of this new adsorbent was improved and at least three times greater than that of uncoated GAC. The surface characteristics of coated GAC were observed with scanning electron microscopy. The surface area of the new adsorbent was calculated using the Brunauer-Emmett-Teller method. X-ray diffraction revealed that manganese oxides are amorphous. X-ray photoelectron spectroscopy demonstrated that manganese existed primarily in the oxidation state +IV. Kinetic and equilibrium adsorption data showed that the adsorption process follows the pseudo-second order kinetic and Freundlich equation models. The sorption data also indicated that the removal of fluoride by adsorption is a highly complex process, involving both boundary layer diffusion and intra-particle diffusion. The pH value of solution influences fluoride removal, and the optimum equilibrium pH value of fluoride adsorption is 3.0.

Sorption and biodegradation of tetracycline by nitrifying granules and the toxicity of tetracycline on granules

This paper examines the simultaneous sorption and biodegradation performance of tetracycline (TC) by the nitrifying granular sludge as well as the short-term exposure toxicity of TC. The removal of TC was characterized by a quick sorption and a slow process of biodegradation. The adsorption process fits pseudo-second-order kinetic model, with a complex mechanism of surface adsorption and intra-particle diffusion. Both temperature and mixed liquor suspended solid (MLSS) influenced TC sorption to the granules. TC biodegradation was enhanced with the increase of COD and NH(4)(+)-N concentrations, with except of the NH(4)(+)-N concentrations higher than 150 mg/L. With the ATU addition, TC degradation was weakened remarkably, indicating a synergistic effect of multiple microbes. Results of the short-term exposure (12h) effects showed that the respirometric activities of the microbes decreased greatly. The addition of TC also decreased the rate of NH(4)(+)-N utilization considerably, with the half saturation constant (K(s)) increasing from 297.7 to 347.2 mg/L.

Enhanced Cu(II) and Cr(VI) biosorption capacity on poly(ethylenimine) grafted aerobic granular sludge

The biosorption characteristics of cations and anions from aqueous solution using polyethylenimine (PEI) modified aerobic granules were investigated. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis exhibit the presence of PEI on the granule surface. Compared with the raw granule, the modified aerobic granules with PEI showed a significant increase in sorption capacity for both metal ions. The monolayer biosorption capacity of granules for Cu(II) and Cr(VI) ions was found to be 71.239 and 348.125mg/g. The optimum solution pH for adsorption of Cu(II) and Cr(VI) from aqueous solutions was found to be 6 and 5.2, respectively. The biosorption data fitted better with the Redlich-Peterson isotherm model. FTIR showed chemical interactions occurred between the metal ions and the amide groups of PEI on the biomass surface. XPS results verified the presence of Cr(III) on the biomass surface, suggesting that some Cr(VI) anions were reduced to Cr(III) during the sorption.

Integration of a microbial fuel cell with activated sludge process for energy-saving wastewater treatment: Taking a sequencing batch reactor as an example†

In the research and application of microbial fuel cell (MFC), how to incorporate MFCs into current wastewater infrastructure is an importance issue. Here, we report a novel strategy of integrating an MFC into a sequencing batch reactor (SBR) to test the energy production and the chemical oxygen demand (COD) removal. The membrane‐less biocathode MFC is integrated with the SBR to recover energy from the aeration in the form of electricity and thus reduce the SBR operation costs. In a lab‐scale integrated SBR‐MFC system, the maximum power production of the MFC was 2.34 W/m3 for one typical cycle and the current density reached up to 14 A/m3. As a result, the MFC contributed to the 18.7% COD consumption of the integrated system and also recovered energy from the aeration tank with a volume fraction of only 12% of the SBR. Our strategy provides a feasible and effective energy‐saving and ‐recovering solution to upgrade the existing activated sludge processes. Biotechnol. Bioeng. 2011; 108:1260–1267.

Changes of the reactor performance and the properties of granular sludge under tetracycline (TC) stress

In this study, the response of nitrifying granules (NG) and conventional granules (CG) to tetracycline (TC) was compared. The presence of TC made granules break down into small fractions and led to nitrite accumulation in nitrifying system; while it had little toxic effect on CG system. Specific oxygen uptake rate tests showed 3.3% inhibition of ammonium oxidizing bacteria and 25.7% inhibition of nitrite oxidizing bacteria in the NG system. Granules produced more extracellular polymeric substances (EPS) to protect themselves from the TC stress, with higher production of proteins compared to polysaccharides. FTIR data also revealed significant changes of protein functional groups, while only small changes in polysaccharides functional groups were found. Three dimensional excitation-emission matrix fluorescence spectroscopy showed a decrease of peak intensity, indicating quenching effect of TC on EPS fluorescence, and also a blue shift of peak position, indicating chemical changes of EPS components.

Aerobic granulation for nitrogen removal via nitrite in a sequencing batch reactor and the emission of nitrous oxide.

In this study, the granulation of nitrifying-denitrifying via nitrite process in a sequencing batch reactor (SBR) as well as N(2)O emission patterns was investigated. After 60 days of operation, 0.8 mm granules were obtained, and partial nitrification was achieved after NH(4)(+)-N was raised to 350 mg/L. Fluorescence In-Situ Hybridization (FISH) analysis indicated that a fairly large proportion of ammonia-oxidizing bacteria (AOB) was close to the surface but nitrite-oxidizing bacteria (NOB) were rarely found. Batch experiments showed that 64.0% of NH(4)(+)-N in influent was transformed into NO(2)(-)-N, which showed the granules had excellent partial nitrification ability. Inhibition of free ammonia (FA) and limited DO diffusion within granules may contribute to the development and stabilization of partial nitrification. This process did not simultaneously lead to increased N(2)O production. N(2)O emissions at the anoxic and aerobic phases were 0.06 and 13.13 mg N(2)O/cycle, respectively.