Zhemin Shen

Quantifying air pollution attenuation within urban parks: An experimental approach in Shanghai, China

Parks with various types of vegetations played an important role in ameliorating air quality in urban areas. However, the attenuation effect of urban vegetation on levels of air pollution was rarely been experimentally estimated. This study, using seasonal monitoring data of total suspended particles (TSP), sulfur dioxide (SO(2)) and nitrogen dioxide (NO(2)) from six parks in Pudong District, Shanghai, China, demonstrated vegetations in parks can remove large amount of airborne pollutants. In addition, crown volume coverage (CVC) was introduced to characterize vegetation conditions in parks and a mixed-effects model indicated that CVC and the pollution diffusion distance were key predictors influencing pollutants removal rate. Therefore, it could be estimated by regression analysis that in summer, urban vegetations in Pudong District could contribute to 9.1% of TSP removal, 5.3% of SO(2) and 2.6% of NO(2). The results could be considered for a better park planning and improving air quality.

Adsorption behavior of phosphate on lanthanum(III)-coordinated diamino-functionalized 3D hybrid mesoporous silicates material

An inorganic/organic hybrid adsorbent for phosphate adsorption was synthesized by introducing lanthanum (La) onto diamino modified MCM-41. The adsorbent was characterized by XRD, SEM, BET, TGA, and FTIR spectroscopy. A series of batch tests were conducted to investigate the influence of contact time, initial phosphate concentration, pH of the solution, and competitive ions on the phosphate adsorption capacity. The Langmuir and Freundlich models were used to simulate the sorption equilibrium, and the results indicated that the Langmuir model fitted the experiment data better than the Freundlich model. The maximum adsorption capacity calculated from the Langmuir model is 54.3 mg/g. For kinetic study, phosphate adsorption followed the pseudo-second-order equation well with a correlation coefficient greater than 0.99. Optimum pH value for the removal of phosphate was between 3.0 and 7.0. The presence of Cl(-) and NO(3)(-) has neglectable influence on the phosphate adsorption. F(-)and SO(4)(2-) have negative effects on the adsorption of phosphate. Phosphate on the spent adsorbent can be almost released by 0.01 M NaOH solution in 12 min.

Adsorption behavior of phosphate on Lanthanum(III) doped mesoporous silicates material

A series of lanthanum doped meosoporous MCM-41 (LaxM41, x is Si/La molar ratio) was prepared by sol-gel method. The surface structure of the materials was investigated with X-ray diffraction and N2 adsorption/desorption technique. The content of La in the materials was determined by ICP. It was found that the La content of La25M41, La50M41 and La100M41 was 7.53%, 3.89% and 2.32%, respectively. The phosphate adsorption capacities increased with increasing amount of La incorporation. With 0.40 g La25M41 99.7% phosphate could be removed. The effects of Si/La molar ratio, LaxM41 dose, pH, initial concentration of phosphate solution, co-ions on phosphate adsorption were also evaluated. The phosphate adsorption kinetics of LaxM41 could be well-described by the pseudo second-order model, and Langmuir isotherm fit equilibrium data much better than the Freundlich isotherm.

Metal chlorides loaded on activated carbon to capture elemental mercury

Activated carbon (AC) was considered to be an effective sorbent to control mercury in combustion systems. However, its capture capacity was low and it required a high carbon-to-mercury mass ratio. AC loaded with catalyst showed a high elemental mercury (Hg0) capture capacity due to large surface area of AC and high oxidization ability of catalyst. In this study, several metal chlorides and metal oxides were used to promote the sorption capacity of AC. As a result, metal chlorides were better than metal oxides loaded on AC to remove gaseous mercury. X-ray diffractometer (XRD), thermogravimetric analyzer (TGA) and specific surface area by Brunauer-Emmett-Teller method (BET) analysis showed the main mechanisms: first, AC had an enormous surface area for loading enough MClx; second, Cl and MxOy were generated during pyrogenation of MClx; finally, there were lots of active elements such as Cl and MxOy which could react with elemental mercury and convert it to mercury oxide and mercury chloride. The HgO and HgCl2 might be released from ACs porous structure by thermo regeneration. A catalytic chemisorption mechanism predominates the sorption process of elemental mercury. As Co and Mn were valence variable metal elements, their catalytic effect on Hg0 oxidization may accelerate both oxidation and halogenation of Hg0. The sorbents loaded with metal chlorides possessed a synergistic function of catalytic effect of valence variable metal and chlorine oxidation.

Long-term joint effect of nutrients and temperature increase on algal growth in Lake Taihu, China

To study how global warming and eutrophication affect water ecosystems, a multiplicative growth Monod model, modified by incorporating the Arrhenius equation, was applied to Lake Taihu to quantitatively study the relationships between algal biomass and both nutrients and temperature using long-term data. To qualitatively assess which factor was a limitation of the improved model, temperature variables were calculated using annual mean air temperature (AT), water temperature (WT), and their average temperature (ST), while substrate variables were calculated using annual mean total nitrogen (TN), total phosphorus (TP), and their weighted aggregate (R), respectively. The nine fitted curves showed that TN and AT were two important factors influencing algal growth; AT limited growth as algal photosynthesis is mainly carried out near the water surface; N leakage of phytoplankton and internal phosphorus load from sediment explains why TN was the best predictor of peak biomass using the Monod model. The fitted results suggest that annual mean algal biomass increased by 0.145 times when annual mean AT increased by 1.0 degrees C. Results also showed that the more eutrophic the lake, the greater the effect AT had on algal growth. Subsequently, the long-term joint effect of annual temperature increase and eutrophication to water ecosystems can be quantitatively assessed and predicted.

Removal of phosphate by Fe-coordinated amino-functionalized 3D mesoporous silicates hybrid materials

Phosphate removal from aqueous waste streams is an important approach to control the eutrophication downstream bodies of water. A Fe(II) coordinated amino-functionalized silicate adsorbent for phosphate adsorption was synthesized by a post-grafting and metal cation incorporation process. The surface structure of the adsorbent was characterized by X-ray diffraction, N2 adsoropion/desoprotion technique, and Fourier transform infrared spectroscopy. The experimental results showed that the adsorption equilibrium data were well fitted to the Langmuir equation. The maximum adsorption capacity of the modified silicate material was 51.8 mg/g. The kinetic data from the adsorption of phosphate were fitted to pseudo second-order model. The phosphate adsorption was highly pH dependent and the relatively high removal of phosphate fell within the pH range 3.0-6.0. The coexistence of other anions in solutions has an adverse effect on phosphate adsorption; a decrease in adsorption capacity followed the order of exogenous anions: F- > SO4(2-) > NO3- > Cl-. In addition, the adsorbed phosphate could be desorbed by NaOH solutions. This silicate adsorbent with a large adsorption capacity and relatively high selectivity could be utilized for the removal of phosphate from aqueous waste streams or in aquatic environment.

Development of a trickle bed reactor of electro-Fenton process for wastewater treatment

To avoid electrolyte leakage and gas bubbles in the electro-Fenton (E-Fenton) reactors using a gas diffusion cathode, we developed a trickle bed cathode by coating a layer composed of carbon black and polytetrafluoroethylene (C-PTFE) onto graphite chips instead of carbon cloth. The trickle bed cathode was optimized by single-factor and orthogonal experiments, in which carbon black, PTFE, and a surfactant were considered as the determinant of the performance of graphite chips. In the reactor assembled by the trickle bed cathode, H2O2 was generated with a current of 0.3A and a current efficiency of 60%. This performance was attributed to the fine distribution of electrolyte and air, as well as the effective oxygen transfer from the gas phase to the electrolyte-cathode interface. In terms of H2O2 generation and current efficiency, the developed trickle bed reactor had a performance comparable to that of the conventional E-Fenton reactor using a gas diffusion cathode. Further, 123 mg L(-1) of reactive brilliant red X-3B in aqueous solution was decomposed in the optimized trickle bed reactor as E-Fenton reactor. The decolorization ratio reached 97% within 20 min, and the mineralization reached 87% within 3h.

Effects of electrokinetics on bioavailability of soil nutrients

There is growing interest in the potential for applying an electric field to soil to move and stimulate the degradation of contaminants; however, we know little of the impact of this method on the bioavailability of soil nutrients. The effect of electrokinetics (EK [1 V·cm−1]) on the bioavailability of nutritional elements in the soil was examined. Soil organic matter, pH, electrical conductivity, oxidation-reduction potential, available nitrogen, phosphorus, and potassium were monitored before and after remediation. After 60 h of EK remediation, the available N, phosphorus, and potassium in soil were increased by an average of 0.44, 3.31, and 1.25 fold, respectively; whereas the content and speciation of organic carbon in soil changed little. At the same time, the average cadmium (Cd) removal efficiency was approximately 68% for Cd-amended soil (100.63 mg Cd kg−1). Overall, there was an obvious increase in the bioavailability of nutrients after EK remediation. It is concluded from this study that the application of EKs cannot only remove soil pollutants effectively but also enhance the bioavailability of nutrients, thus showing its validity as a viable soil remediation technology.

QSAR models for removal rates of organic pollutants adsorbed by in situ formed manganese dioxide under acid condition

Manganese dioxide formed in oxidation process by potassium permanganate exhibits promising adsorptive capacity which can be utilized to remove organic pollutants in wastewater. However, the structure variances of organic molecules lead to wide difference of adsorption efficiency. Therefore, it is of great significance to find a general relationship between removal rate of organic compounds and their quantum parameters. This study focused on building up quantitative structure activity relationship (QSAR) models based on experimental removal rate (rexp) of 25 organic compounds and 17 quantum parameters of each organic compounds computed by Gaussian 09 and Material Studio 6.1. The recommended model is rpre = −0.502 − 7.742 f(+)x + 0.107 EHOMO + 0.959 q(H+) + 1.388 BOx. Both internal and external validations of the recommended model are satisfied, suggesting optimum stability and predictive ability. The definition of applicability domain and the Y-randomization test indicate all the prediction is reliable and no possibility of chance correlation. The recommended model contains four variables, which are closely related to adsorption mechanism. f(+)x reveals the degree of affinity for nucleophilic attack. EHOMO represents the difficulty of electron loss. q(H+) reflect the distribution of partial charge between carbon and hydrogen atom. BOx shows the stability of a molecule.

Enhanced electrokinetic remediation of Cd and Pb spiked soil coupled with cation exchange membrane

Electrokinetic (EK) remediation is one of the popular and promising in situ remediation techniques for metal-contaminated soils, but the remediation effect is strongly affected by soil type and chemical species of contaminants; moreover, pH is very difficult to control. This paper investigates the species of cadmium (Cd) and lead (Pb) in simulating contaminated soil before and after EK remediation, and the soil is a typical silt loam soil from Shanghai. Heavy metal speciation in the soil sample was analysed through a sequential extraction procedure. Cation-exchange membrane (CEM) and conductive solution were applied to improve the remediation efficiency. Both methods help to keep acid conditions and CEM can prevent anions in the cathodic compartment from penetrating into the soil sample system. The pH of the soil specimen was acidic during the test, and Cd was quickly removed from the soil while Pb was removed more slowly. The average removal efficiencies of Cd and Pb were 68.7 and 38.7%, respectively, after 60 h of remediation.