Site-specific risk assessment and integrated management decision-making: A case study of a typical heavy metal contaminated site, Middle China

<p>A typical contaminated land was spatially investigated and assessed based on Chinese guidelines to establish remediation strategy for exploring the shortcomings of the current guidelines to suggest improvements. Results showed that Cr, As, Pb, and Cd should be regarded as the priority pollutants under sensitive land use, while Cr and As should be regarded as the priority pollutants under insensitive land use. Ingestion of soil for each studied metal appeared to be the main exposure pathway under both the land uses. The calculated screening values of the priority metals were conservative to certain extent—even some were lower than their background values. Therefore, an integrated risk management strategy was suggested and the hierarchic clean-up values were proposed considering the health risk, local background value, land remediation cases, current remediation technology, and financial cost. Consequently, it was suggested the clean-up values of Cr(VI), Cr, As, Pb, and Cd, under future sensitive land use, should be 7.5, 1000, 30, 250, and 1.4 mg/kg in the first class control layer, respectively. For future insensitive land use, the clean-up values of Cr(VI), Cr, As, Pb, and Cd should be 20.4, 8000, 60, 580, and 4.3 mg/kg in the first class control layer, respectively.</p

Highly Sensitive Strategy for Hg²⁺ Detection in Environmental Water Samples Using Long Lifetime Fluorescence Quantum Dots and Gold Nanoparticles

The authors herein described a time-gated fluorescence resonance energy transfer (TGFRET) sensing strategy employing water-soluble long lifetime fluorescence quantum dots and gold nanoparticles to detect trace Hg²⁺ ions in aqueous solution. The water-soluble long lifetime fluorescence quantum dots and gold nanoparticles were functionalized by two complementary ssDNA, except for four deliberately designed T–T mismatches. The quantum dot acted as the energy-transfer donor, and the gold nanoparticle acted as the energy-transfer acceptor. When Hg²⁺ ions were present in the aqueous solution, DNA hybridization will occur because of the formation of T–Hg²⁺–T complexes. As a result, the quantum dots and gold nanoparticles are brought into close proximity, which made the energy transfer occur from quantum dots to gold nanoparticles, leading to the fluorescence intensity of quantum dots to decrease obviously. The decrement fluorescence intensity is proportional to the concentration of Hg²⁺ ions. Under the optimum conditions, the sensing system exhibits the same liner range from 1 × 10^–9 to 1 × 10^–8 M for Hg²⁺ ions, with the detection limits of 0.49 nM in buffer and 0.87 nM in tap water samples. This sensor was also used to detect Hg²⁺ ions from samples of tap water, river water, and lake water spiked with Hg²⁺ ions, and the results showed good agreement with the found values determined by an atomic fluorescence spectrometer. In comparison to some reported colorimetric and fluorescent sensors, the proposed method displays the advantage of higher sensitivity. The TGFRET sensor also exhibits excellent selectivity and can provide promising potential for Hg²⁺ ion detection

Optimization of Copper(II) Adsorption onto Novel Magnetic Calcium Alginate/Maghemite Hydrogel Beads Using Response Surface Methodology

Magnetic calcium alginate hydrogel beads (m-CAHBs, 3.4 mm average diameter) composed of maghemite nanoparticles and calcium alginate were prepared and characterized by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX). The response surface methodology was used to model and optimize the adsorption removal of Cu­(II) from aqueous solution by m-CAHBs. Adsorption experiments were also carried out to examine the effect of three parameters, such as pH (2.0–6.0), adsorbent dosage (2.0–6.0 g L^–1) and initial Cu­(II) ion concentration (250–750 mg L^–1). Maximum percent removal was attained under the optimum conditions with pH 2.0, 2.0 g L^–1 adsorbent dosage for 250 mg L^–1 initial Cu­(II) ion concentration. The amount of Cu­(II) adsorption after 6 h was recorded as high as 159.24 mg g^–1 for 500 mg L^–1 initial Cu­(II) ion concentration. The adsorption kinetics indicated that the adsorption process was better described by the pseudo-second-order kinetic model. Desorption experiments indicated that the adsorption mechanism of Cu­(II) occurred preferentially more by chelation than by electrostatic interaction. The percent removal of Cu­(II) on m-CAHBs could still be maintained at 73% level at the fifth cycle

How Does Poly(hydroxyalkanoate) Affect Methane Production from the Anaerobic Digestion of Waste-Activated Sludge?

Recent studies demonstrate that, besides being used for production of biodegradable plastics, poly­(hydroxyalkanoate) (PHA) that is accumulated in heterotrophic microorganisms during wastewater treatment has another novel application direction, i.e., being utilized for enhancing methane yield during the anaerobic digestion of waste-activated sludge (WAS). To date, however, the underlying mechanism of how PHA affects methane production remains largely unknown, and this limits optimization and application of the strategy. This study therefore aims to fill this knowledge gap. Experimental results showed that with the increase of sludge PHA levels from 21 to 184 mg/g of volatile suspended solids (VSS) the methane yield linearly increased from 168.0 to 246.1 mL/g of VSS (<i>R</i>² = 0.9834). Compared with protein and carbohydrate (the main components of a cell), PHA exhibited a higher biochemical methane potential on a unit VSS basis. It was also found that the increased PHA not only enhanced cell disruption of PHA cells but also benefited the soluble protein conversion of both PHA- and non-PHA cells. Moreover, the reactor fed with higher PHA sludge showed greater sludge hydrolysis and acidification than those fed with the lower PHA sludges. Further investigations using fluorescence in situ hybridization and enzyme analysis revealed that the increased PHA enhanced the abundance of methanogenic Archaea and increased the activities of protease, acetate kinase, and coenzyme F420, which were consistent with the observed methane yield. This work provides insights into PHA-involved WAS digestion systems and may have important implications for future operation of wastewater treatment plants

Iron-Based Bimetallic Nanocatalysts for Highly Selective Hydrogenation of Acetylene in <i>N</i>,<i>N</i>‑Dimethylformamide at Room Temperature

Selective hydrogenations of alkynes are a class of essential reactions in organic synthesis chemistry. Particularly, the selective hydrogenation of acetylene to ethylene is a key step in the production of polymers. Here we have successfully performed selective hydrogenation of acetylene to ethylene in <i>N</i>,<i>N</i>-dimethylformamide by iron-based nanoparticles, especially by Pd–Fe bimetallic NPs. NaBH₄ as a hydrogen source can significantly increase the catalytic performances of nanocatalysts for acetylene hydrogenation. More importantly, the reaction is carried out at exceptionally mild temperature and under additive-free conditions with high ethylene selectivity (>90%) as well as excellent catalyst reactivity and stability. By this strategy, we could attain a catalytic activity higher by a factor of 2.2 orders of magnitude than that of the currently used industrial method. This approach may open a new way to perform selective acetylene and other alkynes hydrogenation under mild conditions, and offer another promising application for zerovalent iron reduction method

Enhancing Sewage Sludge Dewaterability by a Skeleton Builder: Biochar Produced from Sludge Cake Conditioned with Rice Husk Flour and FeCl₃

Biochar produced from sludge cake conditioned with rice husk flour and FeCl₃ (biochar-conditioned) was used to enhance sewage sludge dewaterability. The pyrolysis temperature and dosage of biochar-conditioned were optimized, and the effect of biochar produced from raw sludge cake (biochar-raw) and biochar-conditioned on the sewage sludge dewaterability was compared. Moreover, the mechanisms of biochar-conditioned improving sludge dewaterability as a skeleton builder were analyzed. The optimal pyrolysis temperature of biochar-conditioned was 400 °C. The biochar-conditioned contained the sludge-based biochar with a high content of iron and rice husk-based biochar. Compared with biochar-raw, biochar-conditioned prepared at 400 °C was more effective at enhancing the sludge dewaterability, and the optimal biochar-conditioned dosage was 70% dry sludge (DS). Compared with adding FeCl₃ alone, the sludge specific resistance to filtration decreased by 63.9%, the net sludge solids yield increased by 39.2%, and the net percentage sludge water removal increased to 98.36%. Large cracks made the sludge cakes permeable, so that more sludge moisture was filtered from the sludge cake. In addition, adding biochar-conditioned reduced the turbidity and SCOD of sludge filtrate and adjusted the sludge pH to neutral. Using biochar-conditioned to condition the sewage sludge as a skeleton builder is promising

Removal of Elemental Mercury from Simulated Flue Gas over Peanut Shells Carbon Loaded with Iodine Ions, Manganese Oxides, and Zirconium Dioxide

A low-cost material with high adsorption and oxidation ability for Hg⁰ capture is needed, whereas it is hard to prepare by present methods. Here, halide ions (I^–) and metal oxides (MnO_<i>x</i> and ZrO₂) were both loaded on peanut shells carbon to synthesize 6Mn-6Zr/PSC-I3. Various characterizations and experiments were used to investigate the physiochemical properties and Hg⁰ removal performances. The sample exhibited an abundant pore structure and the active components dispersed well on its surface. The excellent total Hg⁰ removal efficiency (more than 90%) was obtained in a wide reaction temperature range (150–300 °C) under a N₂ + 6% O₂ atmosphere. Moreover, the Hg⁰ adsorption capacity in 1440 min was 5587.0 μg·g^–1 and the Hg⁰ oxidation efficiency after reaching adsorption equilibrium was more than 30%. Further, the reaction mechanism at 150 °C was proposed. The main chemical adsorption sites of carbon-iodine groups dominate Hg⁰ removal at the initial reaction stage. As reaction progresses, chemical adsorption is weakened due to the gradual saturation of adsorption sites, whereas catalytic oxidation caused by lattice oxygen and hydroxyl oxygen substitutes chemical adsorption and dominates Hg⁰ removal at the final reaction stage. Thus, the 6Mn-6Zr/PSC-I3 with economic and environmental benefits has a promising prospect in industrial applications

Plasmonic Bi Metal Deposition and g‑C₃N₄ Coating on Bi₂WO₆ Microspheres for Efficient Visible-Light Photocatalysis

A low-cost semiconductor-based photocatalyst using visible light energy has attracted increasing interest for energy generation and environmental remediation. Herein, plasmonic Bi metal was deposited in situ in g-C₃N₄@Bi₂WO₆ microspheres via a hydrothermal method. As an electron-conduction bridge, metallic Bi was inserted as the interlayer between g-C₃N₄ and the surface of Bi₂WO₆ microspheres to enhance visible light absorption due to the surface plasmon resonance (SPR) effect and facilitate efficient electron-carrier separation. Different characterization techniques, including XRD, SEM, TEM, UV–vis, XPS, photoluminescence, and photocurrent generation, were employed to investigate the morphology and optical properties of the as-prepared samples. The results indicated that the g-C₃N₄(20%)@Bi@Bi₂WO₆ microsphere sample exhibited an extraordinary enhanced photocatalytic activity, higher than those of the g-C₃N₄, Bi₂WO₆, and g-C₃N₄(20%)@Bi₂WO₆ samples. It implies that the heterostructured combination of g-C₃N₄, metallic Bi, and Bi₂WO₆ microspheres provided synergistic photocatalytic activity via an efficient electron transfer process. On the basis of the results, a possible photocatalytic mechanism of the as-prepared samples was proposed. The present study demonstrated the feasibility of utilizing low-cost metallic Bi as a substitute for noble metals to design a doped photocatalysis composite with enhanced photocatalytic performance

Redundancy analysis of soil productivity data in (a) different erosion intensities with no-tillage operation and (b) same erosion intensity but different farming method systems.

<p>Significant soil variables and supplementary parameters are indicated by solid lines with filled arrows and dotted lines with filled arrows, respectively. Soil productivity variables are indicated by solid lines with unfilled arrows. Samples from subplots A, B, C, D, and E are represented by circle, inverted triangle, left triangle, right triangle, and box, respectively. Black-filled symbols in Figure 3a refer to the samples from high rainfall intensity treatment, and unfilled symbols refer to the samples from low rainfall intensity treatment. Gray-filled symbols in Figure 3b refer to the samples from no-tillage treatment, and unfilled symbols refer to the samples from tillage treatment.</p

Design of blocks and sampling strategy of the simulated rainfall and grass planting experiments.

<p>Design of blocks and sampling strategy of the simulated rainfall and grass planting experiments.</p