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•Cu(II) was used to improve Cr(VI) reduction performance.•Cu(II) was used as electron-shuttle mediator in MFCs.•The MFC showed high power density and reduction rate.•The reduced ...chromium was deposited on the surface of cathode electrodes.
Cu(II) ion was employed as an electron-shuttle mediator to enhance bioelectricity output and accelerate reduction rate of Cr(VI) in a dual-chamber microbial fuel cell (MFC). In the presence of Cu(II), power density and the Cr(VI) reduction rate were 1235.53 mW m−2 and 1.191 g m−3 h−1, respectively, which were 1.44 times and 1.17 times than that of MFC in the absence of Cu(II). A series of electrochemical analysis confirmed the presence of Cu(II) can diminish overpotential and diffusional resistance of MFC, further accelerating electrochemical reduction process of Cr(VI) via an indirect mechanism. After reduction, Cr(VI) and Cu(II) in this work were mainly deposited on cathode electrodes in the form of Cr(OH)3 and little Cu, thus wastewater containing Cr(VI) was successfully treated by bio-electrochemical technology. The aim of this work was to study the efficacy of Cu(II) as an electron-shuttle mediator for improved bioelectricity generation and Cr(VI) reduction in MFCs.
In this paper, the enhanced adsorption of methylene blue (MB) dye ion on the activated carbon (AC) modified by three surfactants in aqueous solution was researched. Anionic surfactants—sodium lauryl ...sulfate (SLS) and sodium dodecyl sulfonate (SDS)—and cationic surfactant—hexadecyl trimethyl ammonium bromide (CTAB)—were used for the modification of AC. This work showed that the adsorption performance of cationic dye by activated carbon modified by anionic surfactants (SLS) was significantly improved, whereas the adsorption performance of cationic dye by activated carbon modified by cationic surfactant (CTAB) was reduced. In addition, the effects of initial MB concentration, AC dosage, pH, reaction time, temperature, real water samples, and additive salts on the adsorption were studied. When Na+, K+, Ca2+, NH4+, and Mg2+ were present in the MB dye solution, the effect of these cations was negligible on the adsorption (<5%). The presence of NO2- improved the adsorption performance significantly, whereas the removal rate of MB was reduced in the presence of competitive cation (Fe2+). It was found that the isotherm data had a good correlation with the Langmuir isotherm through analyzing the experimental data by various models. The dynamics of adsorption were better described by the pseudo-second-order model and the adsorption process was endothermic and spontaneous. The results showed that AC modified by anionic surfactant was effective for the adsorption of MB dye in both modeling water and real water.
A novel nanoscale photocatalyst CNTs/P-TiO₂ was successfully prepared by hydrothermal method. The morphology and the physicochemical properties of the prepared samples were investigated using TEM, ...XPS, XRD, BET, FTIR, TG-DSC and UV–vis DRS spectroscopy. The photocatalytic activity was evaluated by degradation of methyl orange (MO) dye. The results demonstrated that CNTs/P-TiO₂ nanoparticles could effectively photodegrade MO not only under UV irradiation but also under visible-light (VL) irradiation. The MO degradation performance on CNTs/P-TiO₂ was superior to that of the commercial P25. The optimal mass ratio of CNTs to P-TiO₂ in the nanocomposite catalyst was 5:100. The synergetic effect was discussed in terms of different roles played by phosphorus doping and introducing CNTs into the composite catalysts.
In this study, selected heavy metals (Hg, As, Cd, Pb, Cr, Cu and Zn) in the lake water and sediments from the Caohai wetland, which is a valuable state reserve for migrant birds in China, were ...investigated to assess the spatial distribution, sources, bioavailability and ecological risks. The results suggested that most of the higher concentrations were found in the eastern region of the lakeshore. The concentration factor (CF) revealed that Hg, Cd and Zn were present from moderate risk levels to considerable risk levels in this study; thus, based on the high pollution load index (PLI) values, the Caohai wetland can be considered polluted. According to the associated effects-range classification, Cd may present substantial environmental hazards. An investigation of the chemical speciation suggested that Cd and Zn were unstable across most of the sites, which implied a higher risk of quick desorption and release. Principal component analysis (PCA) indicated that the heavy metal contamination originated from both natural and anthropogenic sources.
A self-driven electrochemical system contains microbial fuel cell and microbial electrolysis cell is developed to reduce Cr(VI) and Pb(II) without external energy input, and the performance of ...coupling system is in connection with cathode materials, initial concentration of metal ions, and anions. Pb(II) reduction is similar to all materials, while nickel foam electrode shows the optimal Cr(VI) reduction rate (1.72 g m−3 h−1) and achieves the maximum output power (702.86 mW m−2), following by stainless steel mesh electrode (1.47 g m−3 h−1 and 477.84 mW m−2) and carbon cloth electrode (1.32 g m−3 h−1 and 420.65 mW m−2). Besides, Cr(VI) (from 1.69 g m−3 h−1 to 1.73 g m−3 h−1) and Pb(II) (from 4.09 g m−3 h−1 to 4.16 g m−3 h−1) reduction rates for nickel foam electrodes are increased with initial Pb(II) concentration (except 300 mg L−1). The self-driven system using nickel foam electrode and PbCl2 catholyte achieves a 0.402 g m−3 h−1 increase in Cr(VI) reduction rate, a 0.447 g m−3 h−1 increase in Pb(II) reduction rate, a 3.33% increase in Pb-yield, and a 15.85% increase in system efficiency comparing to catholyte with (CH3COO)2Pb. These results confirm that a self-driven system can be used to reduce Cr(VI) and Pb(II) simultaneously, providing a promising approach for exploiting the power generation from microbial fuel cells in-situ.
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•Pb(II) reduction were driven by Cr(VI)-reduced MFC.•Pb(II) reduction mainly depended on the electrode materials.•Nickel foam was high-effective for Cr(VI) and Pb(II) reduction.•Pb(II) was deposited on the electrode in the form of pure lead.
Due to the nonsystematic nature of previous studies on mercury (Hg) mobility with humic substances (HS) in terrestrial ecosystems and the uncertainty of Hg accumulation in plants, oxygen-rich humic ...acid (HA), which is the main component of HS, was used as the target in this study. Batch sorption tests and a series of pot experiments were designed to investigate the effect of HS on Hg binding and therefore Hg uptake in rice plants under extreme conditions, i.e., a high Hg/HS concentration ratio. The results showed that HA was eligible for Hg binding, though it has a tiny proportion of sulfur according to its characteristics analysis. The binding of HA and Hg was a chemisorption process in a single layer that followed the pseudo-second order and Langmuir models, and it was also verified that the pH was dependent on the ion strength associated with high Hg/HA concentration ratios. Based on the pot experiments, the performance of HA with Hg was investigated. The Hg in the toxicity characteristic leaching procedure (TCLP) leachate under high Hg/HA concentration ratios declined significantly, and accordingly, all treatments met the concentration criteria of 0.1 mg/l (GB 5085.3–2007) for wastes after 30 days of exposure. At concentration ratios of 50, 25, and 10 μg Hg/mg HA, we observed that HA application promoted rice plant growth, as reflected in the increase of fresh weight of different organs. Regarding accumulation in the soil-plant system, the degradation of HA to smaller molecules by rhizosphere microorganisms and organic acids in roots made HA available for plant uptake through the vascular bundle in roots, thus promoting Hg transformation in plants to a certain extent. However, considering the decline in available Hg in the soil, the Hg concentrations of roots, straw, and grains in the ripening stage were found to be lower than those in the standalone Hg treatments. HA clearly has a direct effect on Hg and an indirect influence on plants exposed to Hg under extreme conditions (very high Hg/HA concentration ratios); thus, the biogeochemical behavior of Hg at high Hg/HA concentration ratios should be considered and further investigated.
Graphene oxide@sodium alginate (GO@SA) composites were prepared by combining graphene oxide (GO) with sodium alginate (SA) for adsorption of Pb(II). Fourier-transform infrared spectra (FT-IR) and ...field emission scanning electron microscopy (FESEM) were used to characterize the structure and morphology of the composites. And the adsorption performance of Pb(II) by GO@SA was studied. The adsorption capacity of Pb(II) by GO@SA increased with the increase of pH and temperature. The adsorption process was consistent with the Langmuir isothermal adsorption model and quasi-second-order kinetic model, and the adsorption process was spontaneous and endothermic. At 303.15 K, the maximum adsorption capacity fitted by the Langmuir isothermal model was 241.5 mg/g.
This study developed a facile and environmentally-friendly method to prepare SiO
2
/silk fibroin (SF) composite melamine sponges modified using SF and hydrophobic SiO
2
nanoparticles (NPs). During ...the preparation procedure, the SiO
2
NPs were bonded to skeletons of porous sponges with the SF binding agent using a dip-coating method. The SiO
2
NPs and SF with hydrophobicity constructed a rough surface. The obtained sponges possess a high absorption capacity of 70.9–160.8 times of its weight for various oils and organic solvents and a high water-contact angle greater than 151°. More importantly, the modified sponges showed good recyclability, and could return to its original shape even after 100 cyclic compression. The as-prepared sponge also showed high buoyancy outstanding elasticity, and maintained high absorption capacity even after 10 cycles of repetitive absorption-desorption. The prepared sponges could efficiently separate oil or organic solvents from oil–water mixtures, indicating that the SiO
2
/SF/MS sponges are promising candidates for remediating oil spills and oily wastewater.
Two pyrene-degrading strains,
Pseudomonas aeruginosa
PA06 and
Achromobacter
sp. AC15 were co-incubated in equal proportions as a microbiological consortium and could enhance the degradation of ...pyrene. The enzymatic activities of the catechol 1,2-dioxygenase (C12O) and 2,3-dioxygenase activities (C23O) were produced complementary expression by
P. aeruginosa
PA06 and
Achromobacter
sp. AC15, respectively. Meanwhile, results showed that pyrene degradation was sufficiently promoted in the presence of sodium citrate as a co-metabolic carbon source, likely a result of enhanced biomass and biosurfactant production. The optimized dosage and ideal initial pHs were 1.4 g L
−1
and 5.5, respectively. We also analyzed the rate constant of pyrene degradation, cell growth, and enzyme activity. Results show that
P. aeruginosa
PA06 had a better effect than
Achromobacter
sp. AC15 in bacterial growth. However, the C23O or C12O activity produced by
Achromobacter
sp. AC15 continued at a similar or even faster than that of
P. aeruginosa
PA06. The mixed bacteria had a better effect than any single bacteria, suggesting the strains worked synergistically to enhance the degradation efficiency. In the co-metabolism system of 600 mg/L pyrene and 1.4 g/L sodium citrate, pyrene degradation reached 74.6%, was 1.57 times, 2.06 times, and 3.89 times that of the mix-culture strains, single PA06 and single AC15 without sodium citrate, respectively. Overall, these findings are valuable as a potential tool for the bioremediation of high-molecular-weight PAHs.
•The sources of sulfate in a karst-dominated wetland catchment has been disscussed.•Groundwater and rain water have contributed to sulfate in karst wetland water.•Local sulfur cycles processes were ...discussed in karst wetland ecosystem.
Sulphur plays a critical role in the biogeochemistry of wetlands. SO42− is the sulphur form that is most commonly assimilated by plants, and it is the medium of sulphur transformation in wetland ecosystems. The Caohai wetland is an important ecosystem on the Yunnan–Guizhou Plateau, SW China, and karst water is the most important water source in this wetland. In this study, the compositions of multiple isotopes (δ34SSO4 and δ18OSO4) were measured in groundwater, river water and wetland water in the Caohai catchment to elucidate the solute sources and behaviours of sulphate. The results suggest that SO42− in groundwater is mainly derived from sulphide oxidation. Groundwater contributes a significant amount of sulphate to river water, and it is the main sulphate source of wetland water during the high-flow season. In contrast, rain water is the main sulphate source of wetland water during the low-flow season due to the reduction in groundwater recharge. These data indicate that groundwater is not only an important water source in the karst-dominated wetland catchment but also provides pathways by which sulphate is transported to the wetland. In addition, due to the effects of dissimilatory sulphate reduction in the wetland, the sulphate isotope composition in wetland water was higher than those in the groundwater and inflowing rivers, which indicates that biogeochemical processes in wetland ecosystems influence the sulphate content and composition in karst water.
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