Effects of hardness and alkalinity on the removal of arsenic(V) from humic acid-deficient and humic acid-rich groundwater by zero-valent iron

The effects of hardness (Ca2+) and alkalinity (HCO3-) on arsenic(V) removal from humic acid (HA)-deficient and HA-rich groundwater by zero-valent iron (Fe-0) were investigated using batch experiments. Arsenic, in general, is removed from groundwater possibly by adsorption and co-precipitation with the iron corrosion products. However, in the co-presence of HCO3- and Ca2+, the removal rate of arsenic increased with increasing concentrations of either Ca2+ or HCO3-. It was observed that the removal of arsenic was significantly enhanced by the formation of CaCO3 as a nucleation seed for the growth of large iron (hydr)oxide particles. In the co-existence of Ca2+, HCO3- and HA, the presence of HA diminished the positive role of Ca2+ due to the formation of Fe-humate complexes in solution and delaying of the formation of CaCO3. As a result, the formation of the large iron (hydr)oxide particles was inhibited in the earlier stage which, in turn, affected the removal of arsenic. However, after the formation of CaCO3 and the subsequent growth of such particles, the presence of large iron (hydr)oxide particles resulted in the rapid removing of arsenic and Fe-humate by adsorption and/or co-precipitation. (C) 2009 Elsevier Ltd. All rights reserved

Effects of Humic Acid, Calcium and Bicarbonate on Arsenic(V) Removal from Groundwater by Zero-Valent Iron

The effects of humic acid (HA), Ca(2+) and HCO(3)(-) on the arsenic(V) removal from groundwater by zero-valent iron (Fe(0)) were investigated using batch experiments. Arsenic was removed from groundwater, possibly by adsorption and co-precipitation, with the iron corrosion products. Ca(2+) was observed to enhance significantly. the removal of arsenic due to its aggregation with iron corrosion products. Higher Ca(2+) concentration resulted in a faster removal rate of arsenic in the absence of HA. However, the presence of HA diminished the positive role of C(2+) because of the formation of soluble Fe-humate complexes and the dispersion of colloidal iron corrosion products by HA in the groundwater. In the co-presence of Ca(2+) and HCO(3)(-), the removal rate of arsenic increased with the higher concentrations of HCO(3)(-), which could result from the formation of CaCO(3)(-) and subsequently contribute to the aggregation of iron corrosion products. In the co-existence of HA, Ca(2+) and HCO(3)(-), HA delayed the aggregation of iron corrosion products and thus inhibited the removal of arsenic, However, after the binding capacity of HA with dissolved iron was saturated, the presence of Ca(2+) and HCO(3)(-) resulted in rapid aggregation of Fe-humate complexes and colloidal iron corrosion products and thus the removal of arsenic was significantly enhanced

Numerical Simulations of Air Flow and Traffic–Related Air Pollution Distribution in a Real Urban Area

With increasing urbanization, urban air pollutants are becoming more and more relevant to human health. Here, combined with meteorological observation data, a numerical simulation of typical urban blocks in Shanghai was carried out to understand the spread of air pollutants caused by road traffic sources (ground–level and viaduct–level). Firstly, we analyzed the wind environment characteristics. Then, we quantitatively analyzed the pollutant distribution profiles and the contributions of two pollutant sources (PSV). Finally, we analyzed seven urban morphological parameters based on ventilation efficiency indices. Results revealed the following. (1) Ventilation patterns within the architectural complex are determined by local geometry; (2) Pollutants released at ground level were dominant when the Z–plane Z–plane ≥ 8 m high; (3) From ground level to a height of 60 m, the spatially–averaged normalized concentration (C*) tended to decrease gradually with distance from the source. C* increased irregularly with an increase in distance between 60 m and 86 m. Above 86 m, C* tended to increase linearly; (4) Vertical profiles of C* around buildings were building–specific, and their rate of change was inconsistent with height increases. In general, the correlations between C* and VRw, and between C* and KEturb were larger on the windward side of PSV upstream buildings than on the leeward side. Buildings downstream of the PSV showed the opposite situation; (5) At pedestrian level, the seven urban morphological parameters had no significant correlation with VRw, Cir*, and Czs*

Numerical Simulations of Air Flow and Traffic–Related Air Pollution Distribution in a Real Urban Area

With increasing urbanization, urban air pollutants are becoming more and more relevant to human health. Here, combined with meteorological observation data, a numerical simulation of typical urban blocks in Shanghai was carried out to understand the spread of air pollutants caused by road traffic sources (ground–level and viaduct–level). Firstly, we analyzed the wind environment characteristics. Then, we quantitatively analyzed the pollutant distribution profiles and the contributions of two pollutant sources (PSV). Finally, we analyzed seven urban morphological parameters based on ventilation efficiency indices. Results revealed the following. (1) Ventilation patterns within the architectural complex are determined by local geometry; (2) Pollutants released at ground level were dominant when the Z–plane < 8 m high, and pollutants released from the viaduct source were 0.8–6.1% higher when the Z–plane ≥ 8 m high; (3) From ground level to a height of 60 m, the spatially–averaged normalized concentration (C*) tended to decrease gradually with distance from the source. C* increased irregularly with an increase in distance between 60 m and 86 m. Above 86 m, C* tended to increase linearly; (4) Vertical profiles of C* around buildings were building–specific, and their rate of change was inconsistent with height increases. In general, the correlations between C* and VRw, and between C* and KEturb were larger on the windward side of PSV upstream buildings than on the leeward side. Buildings downstream of the PSV showed the opposite situation; (5) At pedestrian level, the seven urban morphological parameters had no significant correlation with VRw, Cir*, and Czs*

SiO₂ Modification of Silicon Carbide Membrane via an Interfacial In Situ Sol–Gel Process for Improved Filtration Performance

Silicon carbide (SiC) membrane has emerged as a promising class of inorganic ceramic membranes with many advantageous attributes and has been used for a variety of industrial microfiltration (MF) processes. The state-of-the-art industrial manufacturing of SiC membranes based on the particle sintering method can only achieve an average pore size that ranges from 40 nm to a few micrometers, which is still unsatisfactory for ultrafiltration (UF) applications. Thus, the pore size control of SiC membranes remains a focus of continuing study. Herein, we provide an in situ sol–gel modification strategy to tailor the pore size of SiC membranes by a superficial deposition of SiO2 onto the membrane surface and membrane pore channels. Our in situ sol–gel modification method is simple and effective. Furthermore, the physical characteristics and the filtration performance of the membrane can easily be controlled by the in situ reaction time. With an optimal in situ reaction time of 30 min, the average pore size of the membrane can be reduced from macropores (400 nm) to mesopores (below 20 nm), and the retention ability for 20 nm fluorescent PS microspheres can be improved from 5% to 93%; the resultant SiC/SiO2 composite membranes are imparted with water permeance of 77 L·m−2·h−1·bar−1, improved anti-protein-fouling properties, excellent performance, and anti-acid stabilities. Therefore, modified SiC/SiO2 membranes based on the in situ sol–gel process have great potential as UF membranes for a variety of industrial processes

Formulating and Optimizing a Novel Biochar-Based Fertilizer for Simultaneous Slow-Release of Nitrogen and Immobilization of Cadmium

This study aimed to develop and optimize a novel biochar-based fertilizer composed of rice husk biochar and urea–hydrogen peroxide (UHP), which can simultaneously slowly release nitrogen and immobilize cadmium (Cd). Response surface methodology (RSM) was adopted to optimize the fertilizer formulation with the lowest nitrogen release rate. Under the optimized conditions, the cumulative nitrogen release rate of the biochar-based fertilizer was 17.63%, which was significantly lower than that of ordinary fertilizer. Elementary analysis, scanning electron microscopy (SEM) images, and Fourier transform infrared (FTIR) spectroscopy proved that UHP attached to the porous structures of the biochar. The adsorption test showed that the adsorption of Cd onto biochar-based fertilizer quickly reached equilibrium with an equilibrium adsorbing quantity (Qe) of 6.3279 mg·g−1 with an initial concentration of 10 mg·L−1. Compared to original biochar, the Cd immobilization ability of biochar-based fertilizer was significantly better. The adsorption of Cd on biochar-based fertilizer is mainly based on a monolayer adsorption behavior. Finally, improved crop growth was demonstrated by pot experiments, which showed a significant increase in the biomass of cabbage. The concept and findings presented in this study may be used as references in developing a novel biochar-based fertilizer for simultaneously enhancing crop yield and reducing environmental risk

Spatiotemporal analysis of the future carbon footprint of solar electricity in the United States by a dynamic life cycle assessment

Summary: Solar photovoltaics (PVs) installation would increase 20-fold by 2050; however, considerable greenhouse gas (GHG) emissions are generated during the cradle-to-gate production, with spatiotemporal variances depending on the grid emission. Thus, a dynamic life cycle assessment (LCA) model was developed to assess the accumulated PV panels with a heterogeneous carbon footprint if manufactured and installed in the United States. The state-level carbon footprint of solar electricity (CFEPV-avg) from 2022 to 2050 was estimated using several cradle-to-gate production scenarios to account for emissions stemming from electricity generated from solar PVs. The CFEPV-avg (min 0.032, max 0.051, weighted avg. 0.040 kg CO2-eq/kWh) in 2050 will be significantly lower than that of the comparison benchmark (min 0.047, max 0.068, weighted avg. 0.056 kg CO2-eq/kWh). The proposed dynamic LCA framework is promising for planning solar PV supply chains and, ultimately, the supply chain of an entire carbon-neutral energy system to maximize the environmental benefits