Simultaneous adsorption and degradation of Zn2+ and Cu2+ from wastewaters using nanoscale zero-valent iron impregnated with clays

Clays such as kaolin, bentonite and zeolite were evaluated as support material for nanoscale zero-valent iron (nZVI) to simultaneously remove Cu²⁺ and Zn²⁺ from aqueous solution. Of the three supported nZVIs, bentonite-supported nZVI (B-nZVI) was most effective in the simultaneous removal of Cu²⁺ and Zn²⁺ from a aqueous solution containing a 100 mg/l of Cu²⁺ and Zn²⁺, where 92.9 % Cu²⁺ and 58.3 % Zn²⁺ were removed. Scanning electronic microscope (SEM) revealed that the aggregation of nZVI decreased as the proportion of bentonite increased due to the good dispersion of nZVI, while energy dispersive spectroscopy (EDS) demonstrated the deposition of copper and zinc on B-nZVI after B-nZVI reacted with Cu²⁺ and Zn²⁺. A kinetics study indicated that removing Cu²⁺ and Zn²⁺ with B-nZVI accorded with the pseudo first-order model. These suggest that simultaneous adsorption of Cu²⁺and Zn²⁺ on bentonite and the degradation of Cu²⁺and Zn²⁺ by nZVI on the bentonite. However, Cu²⁺ removal by B-nZVI was reduced rather than adsorption, while Zn²⁺ removal was main adsorption. Finally, Cu²⁺, Zn²⁺, Ni²⁺, Pb²⁺ and total Cr from various wastewaters were removed by B-nZVI, and reusability of B-nZVI with different treatment was tested, which demonstrates that B-nZVI is a potential material for the removal of heavy metals from wastewaters.     

Presence of bacteria in aqueous solution influences virus adsorption on nanoparticles

Virus contamination in wastewater is usually accompanied by the existence of various bacteria. Nanoparticles (NPs) have been shown to efficiently remove virus. In this study, bacterial cells, supernatants, and cultures were harvested separately from three strains at the culture ages of 6 and 24 h, corresponding to the log and stationary phases, respectively. The aim is to investigate how their presence affects virus adsorption on the three Fe and Al oxide NPs (α-Fe₂O₃, γ-Fe₂O₃-B, and Al₂O₃) and how these effects change with bacterial growth phase. Bacteriophage phiX174 was used as a virus model. Results showed that bacterial cells, supernatants, and cultures harvested at 6 h generally reduced virus adsorption by an average of 0.75?±?0.84, 7.7?±?9.0, and 10.3?±?8.6 %, respectively, while those harvested at 24 h reduced virus adsorption by an average of 2.1?±?0.93, 21.5?±?6.6, and 24.6?±?6.9 %, respectively. Among the NPs, α-Fe₂O₃ showed more sensitivity to bacteria than the other two, probably because of its relatively higher value of point of zero charge. It was found that cell-induced and supernatant-induced reductions were combined to achieve added results, in which the supernatants contributed much more than the cells, implying that the bacterial exudates might be more crucial in the reduced virus adsorption than the bacterial cells. These results strongly demonstrated that the bacteria-induced reduction in virus adsorption became more significant with culture age. It is suggested that studies conducted in the absence of bacteria may not accurately evaluate the potential of virus removal efficiency of the NPs in bacteria-containing environments.     

Using biochar for remediation of soils contaminated with heavy metals and organic pollutants

Soil contamination with heavy metals and organic pollutants has increasingly become a serious global environmental issue in recent years. Considerable efforts have been made to remediate contaminated soils. Biochar has a large surface area, and high capacity to adsorb heavy metals and organic pollutants. Biochar can potentially be used to reduce the bioavailability and leachability of heavy metals and organic pollutants in soils through adsorption and other physicochemical reactions. Biochar is typically an alkaline material which can increase soil pH and contribute to stabilization of heavy metals. Application of biochar for remediation of contaminated soils may provide a new solution to the soil pollution problem. This paper provides an overview on the impact of biochar on the environmental fate and mobility of heavy metals and organic pollutants in contaminated soils and its implication for remediation of contaminated soils. Further research directions are identified to ensure a safe and sustainable use of biochar as a soil amendment for remediation of contaminated soils.     

Quantitative evaluation of environmental risks of flotation tailings from hydrothermal sulfidation–flotation process

Floatation tailings (FT) are the main by-products of the hydrothermal sulfidation–flotation process. FT (FT₁ and FT₂) were obtained by treating two different neutralization sludges (NS) (NS₁ and NS₂). This paper quantitatively evaluated the environmental risks of heavy metals (Zn, Cd, Cu, Pb, and As) in FT versus NS. The total concentration and leaching rates (R ₂) of heavy metals in FT were much lower than those in NS, demonstrating that the hydrothermal sulfidation–flotation process was able to effectively suppress the mobility and leachability of heavy metals. The BCR-three sequence leaching procedure of FT confirmed that all metals were transformed into more stable forms (residue and oxidizable forms) than were found that in NS. The potential ecological risk index indicated that the overall risks caused by heavy metals decreased significantly from 6627.59 and 7229.67 (very serious risk) in NS₁ and NS₂, respectively, to 80.26 and 76.27 (low risk) in FT₁ and FT₂, respectively. According to the risk assessment code, none of the heavy metals in FT posed significant risk to the natural environment except Zn (with low risk). In general, the risk of heavy metals in FT had been well controlled.     

Application of 15N–18O double stable isotope tracer technique in an agricultural nonpoint polluted river of the Yangtze Delta Region

One strategy to combat nitrate (NO₃-N) contamination in rivers is to understand its sources. NO₃-N sources in the East Tiaoxi River of the Yangtze Delta Region were investigated by applying a ¹⁵N–¹⁸O dual isotope approach. Water samples were collected from the main channel and from the tributaries. Results show that high total N and NO₃-N are present in both the main channel and the major tributaries, and NO₃-N was one of the most important N forms in water. Analysis of isotopic compositions (δ ¹⁸O, δD) of water suggests that the river water mainly originated from three tributaries during the sampling period. There was a wide range of δ ¹⁵N-NO₃ (?1.4 to 12.4 ‰) and a narrow range of δ ¹⁸O-NO₃ (3.7 to 9.0 ‰) in the main channel waters. The δ ¹⁵N and δ ¹⁸O-NO₃ values in the upper, middle, and lower channels along the river were shifted as 8.2, 3.5, and 9.5 ‰, and 9.0, 4.2, and 6.0 ‰, respectively. In the tributary South Tiao, the δ ¹⁵N and δ ¹⁸O-NO₃ values were as high as 9.5 and 7.0 ‰, while in the tributaries Mid Tiao and North Tiao, NO₃-N in most of the samples had relatively low δ ¹⁵N and δ ¹⁸O-NO₃ values from 2.3 to 7.5 ‰ and 4.7 to 7.0 ‰, separately. Our results also suggest that the dual isotope approach can help us develop the best management practice for relieving NO₃-N pollution in the rivers at the tributary scale.     

Fourier transform infrared and fluorescence spectral features of organic matter in conventional and organic dairy manure

Organic dairy production has exhibited potential for growth in the United States dairy sector. However, little information is available on whether there is any difference in manure composition and quality between organic (OD) and conventional (CD) dairy manure even though the composition and quality are important parameters with respect to availability, utilization, and cycling of manure nutrients and environmental impact evaluation. We comparatively characterized whole and water-extracted materials of 15 OD and seven CD dairy manure samples by Fourier transform infrared (FT-IR) and fluorescence spectroscopies. Fourier transform infrared features of manure organic matter varied mainly in the 1650 to 1550 cm range, reflecting the presence of different N compounds in these manure samples. Fluorescence data revealed five fluorophore components present in the water-extracted organic matter from the manures. We found no clearly distinct value ranges in whole and water-extractable organic matter between the two types of dairy manure with respect to C and N contents and FT-IR and fluorescence spectral features. However, based on the average values, we observed general pattern differences on the effect of organic farming on the manure composition: OD contained less soluble C and N compounds on dry weight basis but more hydrophobic aliphatic groups in whole manure. The soluble organic matter in OD samples contained more stable humic- and lignin-related components and less amino/protein N-related components based on their spectroscopic features. These differences might be attributed to more forage feedstuffs in organic dairy farming management and more protein additives in conventional dairy feedstuffs. Information from this work may be useful in aiding organic dairy farmers in making manure management decisions.     

安徽省旅游业转型升级对策研究

随着我国经济增长结构和产业增长方式调整转变,旅游业转型升级成为提高旅游业经济效益,实现旅游业可持续发展的必然要求。在全面分析安徽省旅游业转型升级背景的基础上,结合安徽省旅游业转型升级的优势条件与制约因素,提出安徽省旅游业在旅游产业结构、旅游产品、旅游企业、旅游市场、旅游人才等方面转型升级的路径与对策。     

Arsenic stabilization by zero-valent iron,bauxite residue,and zeolite at a contaminated site planting Panax notoginseng

Panax notoginseng (Burk.) F.H. Chen, a rare traditional Chinese medicinal herb, is a widely used phytomedicine used all over the world. In recent years, the arsenic contamination of the herb and its relative products becomes a serious problem due to elevated soil As concentration. This study aimed to evaluate the effects of different types and dosages of amendments on As stabilization in soil and its uptake by P. notoginseng. Results showed that comparing to control treatment, the As concentrations of P. notoginseng declined by 49–63%, 43–61% and 52–66% in 0.25% zero-valent iron (Fe(0)), 0.5% bauxite residue, and 1% zeolite treatment, respectively; whereas the biomasses were elevated by 62–116%, 45–152% and 114–265%, respectively. The As(III) proportions of P. notoginseng increased by 8%, 9%, and 8%, and the transfer factors of As from root to shoot increased by 37%, 42% and 84% in the optimal treatments of Fe(0), bauxite residue, and zeolite. For soil As, all the three amendments could transform the non-specifically adsorbed As fraction to hydrous oxides Fe/Al fractions (by Fe(0) and red mud) or specifically adsorbed As fraction (by zeolite), therefore reduced the bioavailability of soil As. With a comprehensive consideration of stabilization efficiency, plant growth, environmental influence, and cost, Fe(0) appeared to be the best amendment, and zeolite could also be a good choice. In conclusion, this study was of significance in developing As contamination control in P. notoginseng planting areas, and even other areas for medicinal herb growing.     

Effects of nitrogen application rate and a nitrification inhibitor dicyandiamide on methanotroph abundance and methane uptake in a grazed pasture soil

Methane-oxidizing bacteria (methanotrophs) in the soil are a unique group of methylotrophic bacteria that utilize methane (CH₄) as their sole source of carbon and energy which limit the flux of methane to the atmosphere from soils and consume atmospheric methane. A field experiment was conducted to determine the effect of nitrogen application rates and the nitrification inhibitor dicyandiamide (DCD) on the abundance of methanotrophs and on methane flux in a grazed pasture soil. Nitrogen (N) was applied at four different rates, with urea applied at 50 and 100 kg N ha^?1 and animal urine at 300 and 600 kg N ha^?1. DCD was applied at 10 kg ha^?1. The results showed that both the DNA and selected mRNA copy numbers of the methanotroph pmoA gene were not affected by the application of urea, urine or DCD. The methanotroph DNA and mRNA pmoA gene copy numbers were low in this soil, below 7.13?×?10³ g^?1 soil and 3.75?×?10³ μg^?1 RNA, respectively. Daily CH₄ flux varied slightly among different treatments during the experimental period, ranging from ?12.89 g CH₄ ha^?1 day^?1 to ?0.83 g CH₄ ha^?1 day^?1, but no significant treatment effect was found. This study suggests that the application of urea fertilizer, animal urine returns and the use of the nitrification inhibitor DCD do not significantly affect soil methanotroph abundance or daily CH₄ fluxes in grazed grassland soils.     

诱导结晶工艺中诱品载体的选择与改性

以含铜废水为处理对象,重点考察了诱晶载体的表面性质及表面负荷对诱导结晶过程的影响。结果表明,在工艺启动初期,白云石以及碱式碳酸铜为诱晶载体时,铜的去除率在90％以上,石英砂对铜的去除率较低,但石英砂经表面改性后对铜的去除效率亦可达90％以上。在运行稳定后,几类诱导载体对铜的去除率皆能稳定在95％,说明诱晶载体的表面性质对诱导结晶工艺的影响主要在于反应启动初期,选择与目标结晶产物结构、成分相同或相似的诱晶载体有利于诱导结晶过程的进行。此外,研究结果还表明,诱晶载体表面负荷对结晶过程影响较大,诱导结晶除铜工艺中载体表面负荷不宜高于0．054gCu／（m2·d）。