Yi Xing

Performance of mesoporous silicas (MCM-41 and SBA-15) and carbon (CMK-3) in the removal of gas-phase naphthalene: adsorption capacity, rate and regenerability

The adsorption isotherms of naphthalene on three typical mesoporous adsorbents, mesosilicas MCM-41 and SBA-15, and mesocarbon CMK-3 were determined by column tests at 125 °C, with feed concentrations ranging from 7.63 × 10−5 to 4.64 × 10−2 mol m−3 (1.88 to 1140 ppm). The Langmuir model and constant-pattern wave propagation model were found to well fit the isotherms and the breakthrough curves, respectively. Regenerabilities of the mesoporous samples and a benchmark activated carbon (AC) were characterized based on thermogravimetric analysis (TGA). The results show mesoporosity significantly reduced the internal mass-transfer resistance, contributing to facile desorption and to fast adsorption kinetics shown by high overall mass-transfer rate coefficient following the order of: CMK-3 > SBA-15 > MCM-41. Micropore–mesopore coexisting structures present in CMK-3 and SBA-15 facilitated the adsorption at very low concentrations due to micropore-filling, while greater surface hydrophobicity and micropore abundance on CMK-3 exhibited larger affinity for nonpolar naphthalene, rendering the highest adsorption capacity (1.014 mol m−3) among all sorbents including ACs. SBA-15 showed higher regenerability with a desorption temperature below 440 K, owing to the weaker binding and diffusion advantages contributed by the interconnectivity between primary mesopores.

Novel Wire-on-Plate Electrostatic Precipitator (WOP-EP) for Controlling Fine Particle and Nanoparticle Pollution

A new wire-on-plate electrostatic precipitator (WOP-EP), where discharge wires are attached directly on the surface of a dielectric plate, was developed to ease the installation of the wires, minimize particle deposition on the wires, and lower ozone emission while maintaining a high particle collection efficiency. For a lab-scale WOP-EP (width, 50 mm; height, 20 mm; length, 180 mm) tested at the applied voltage of 18 kV, experimental total particle collection efficiencies were found as high as 90.9-99.7 and 98.8-99.9% in the particle size range of 30-1870 nm at the average air velocities of 0.50 m/s (flow rate, 30 L/min; residence time, 0.36 s) and 0.25 m/s (flow rate, 15 L/min; residence time, 0.72 s), respectively. Particle collection efficiencies calculated by numerical models agreed well with the experimental results. The comparison to the traditional wire-in-plate EP showed that, at the same applied voltage, the current WOP-EP emitted 1-2 orders of magnitude lower ozone concentration, had cleaner discharge wires after heavy particle loading in the EP, and recovered high particle collection efficiency after the grounded collection plate was cleaned. It is expected that the current WOP-EP can be scaled up as an efficient air-cleaning device to control fine particle and nanoparticle pollution.

Combustion behaviors and kinetics of sewage sludge blended with pulverized coal: With and without catalysts

The combustion behaviors of sewage sludge (SS), pulverized coal (PC), and their blends were studied using a thermogravimetric analyzer. The effect of the mass ratio of SS to PC on the co-combustion characteristics was analyzed. The experiments showed that the ignition performance of the blends improved significantly as the mass percentage of SS increased, but its combustion intensity decreased. The burnout temperature (Tb) and comprehensive combustibility index (S) of the blends were almost unchanged when the mass percentage of SS was less than 10%. However, a high mass percentage of SS (>10%) resulted in a great increase in Tb and a notable decrease in S. Subsequently, the effects of different catalysts (CaO, CeO2, MnO2, and Fe2O3) on the combustion characteristics and activation energy of the SS/PC blend were investigated. The four catalysts promoted the release and combustion of volatile matters in the blended fuels and shifted their combustion profiles to a low temperature. In addition, their peak separating tendencies were obvious at 350-550 C, resulting in high peak widths. All the catalysts improved combustion activity of the blended fuel and accelerated fixed carbon combustion, which decreased the ignition temperature and burnout temperature of the fuels. CeO2 had the best catalytic effects in terms of the comprehensive combustion performance and activation energy, followed closely by Fe2O3. However, the rare-earth compounds are expensive to be applied in the catalytic combustion process of SS/PC blend at present. Based on both catalytic effects and economy, Fe2O3 was potentially an optimal option for catalytic combustion among the tested catalysts.

Mechanism and Parameter Optimization of Fenton’s Reagent Integrated with Surfactant Pretreatment to Improve Sludge Dewaterability

Sludge dewatering can effectively reduce the volume and mass of sludge for subsequent treatment and disposal. The work validated the potential of Fenton’s reagent combined with dodecyl dimethyl benzyl ammonium chloride (DDBAC) in improving sludge dewaterability and proposed the mechanism of joint conditioning. The composite conditioner dosage was optimized using response surface methodology. Results indicated the good conditioning capability of the composite conditioners. The optimum dosages for H2O2, Fe2+, and DDBAC were 44.6, 39.6, and 71.0 mg/g, respectively, at which a sludge cake water content of 59.67% could be achieved. Moreover, a second-order polynomial equation was developed to describe the behavior of joint conditioning. Analysis of the reaction mechanism showed that Fenton oxidation effectively decomposed extracellular polymeric substance (EPS), including loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), into dissolved organics, such as proteins and polysaccharides. The process facilitated the conversion of the bound water into free water. Furthermore, DDBAC further released the bound water through solubilization of TB-EPS and LB-EPS after the Fenton reaction. The bound water content of the sludge conditioned with Fenton’s reagent decreased from 3.15 to 1.36 g/g and further decreased to 1.08 g/g with the addition of DDBAC. High-performance liquid chromatography analysis verified that the composite conditioning could oxidize and hydrolyze EPS into low-molecular-mass organics (e.g., formic and acetic acid), thereby facilitating the release of bound water.

Investigation of free radicals and carbon structures in chars generated from pyrolysis of antibiotic fermentation residue

The effect of pyrolysis on the chemical characteristics of Antibiotic Fermentation Residue (AFR) was studied in this paper. Electron Spin Resonance (ESR) spectrometry, X-ray photoelectron spectroscopy (XPS) and solid state 13C nuclear magnetic resonance (13C NMR) spectroscopy were applied to investigate the variation of free radicals and carbon structures. Results indicated that the free radical concentration (Ng) of AFR/chars changed dramatically during the pyrolysis process, first increasing and then decreasing. Ng reached 1.24 × 1019 spins per g in a N2 atmosphere and 1.11 × 1019 spins per g in a CO2 atmosphere at 320 °C. The g-values monotonically decreased, demonstrating that the chemical structures of free radicals changed during pyrolysis. Bond cleavage in methoxyl groups, aliphatic C–O bonds, aliphatic C–C bonds and CO groups was enhanced with increasing pyrolysis temperature. These carbon structures converted to aromatic C–O bonds and aromatic C–C bonds through polymerization and condensation reactions. Compared with the CO2 atmosphere, the N2 atmosphere was more conducive to the production of free radicals and aromatization of carbon structures in chars during pyrolysis process.

Adsorption thermodynamics and desorption properties of gaseous polycyclic aromatic hydrocarbons on mesoporous adsorbents

Performances of mesoporous materials in removal of polycyclic aromatic hydrocarbons (PAHs) from hot gases were evaluated systematically. The adsorption and desorption natures for PAHs with different aromatic rings, naphthalene (Nap), phenanthrene (Phe) and pyrene (Pyr) on mesosilicas MCM-41 and SBA-15, and mesocarbon CMK-3, were studied. Adsorption equilibria were well described by Langmuir or Freundlich model, giving the order of adsorption capacity of CMK-3 > SBA-15 > MCM-41 and Pry > Phe > Nap. Temperature programmed desorption exhibited the order of ease of desorption of SBA-15 > MCM-41 > CMK-3, along with desorption kinetic triplet determined by combined model fitting analysis. The Johnson–Mehl–Avrami (JMA) rate equation was found to well describe PAH desorption kinetics, except for Phe/SBA-15 and Pyr/CMK-3 due to potential blockage and strong binding, respectively. MCM-41 with simple 1-D mesoporous structure provided smooth diffusion and consistent behavior but very low adsorption capacity for each PAH. SBA-15 with micropores/small mesopores as interconnectivity between primary mesopores not only showed high sorption capacities but also diffusion advantages in desorption. CMK-3 with great microporosity facilitated the adsorption at low concentrations due to micropore-filling, and with surface hydrophobicity rendered high affinities especially for the bulkier Pyr.

Spatial distribution and sources of heavy metals in natural pasture soil around copper-molybdenum mine in Northeast China

The characterization of the content and source of heavy metals are essential to assess the potential threat of metals to human health. The present study collected 140 topsoil samples around a Cu-Mo mine (Wunugetushan, China) and investigated the concentrations and spatial distribution pattern of Cr, Ni, Zn, Cu, Mo and Cd in soil using multivariate and geostatistical analytical methods. Results indicated that the average concentrations of six heavy metals, especially Cu and Mo, were obviously higher than the local background values. Correlation analysis and principal component analysis divided these metals into three groups, including Cr and Ni, Cu and Mo, Zn and Cd. Meanwhile, the spatial distribution maps of heavy metals indicated that Cr and Ni in soil were no notable anthropogenic inputs and mainly controlled by natural factors because their spatial maps exhibited non-point source contamination. The concentrations of Cu and Mo gradually decreased with distance away from the mine area, suggesting that human mining activities may be crucial in the spreading of contaminants. Soil contamination of Zn were associated with livestock manure produced from grazing. In addition, the environmental risk of heavy metal pollution was assessed by geo-accumulation index. All the results revealed that the spatial distribution of heavy metals in soil were in agreement with the local human activities. Investigating and identifying the origin of heavy metals in pasture soil will lay the foundation for taking effective measures to preserve soil from the long-term accumulation of heavy metals.