Recycling EDTA solutions used to remediate metal-polluted soils

The objective of this research was to investigate the recycling of ethylenediamine-tetraacetic acid (EDTA) used for the removal of trace metals from contaminated soils. We successfully used Na2S combined with Ca(OH)2 to precipitate the trace metals allowing us to recycle the EDTA. The results of batch and column leaching experiments show that both Ca-EDTA and Na-EDTA are powerful chelating agents with a similar soil remediation potential. The major advantage of Ca-EDTA is the preservation of soil organic matter. We found that Na2S was capable of separating the metals Cd, Cu and Pb from EDTA; however, the precipitation of Zn required the addition of Ca(OH)2. After reusing the reclaimed EDTA seven times, over a 14-day period, EDTA reagent losses ranged from 19.5% to 23.5%. Successive washing cycles enhanced the removal of trace metals from contaminated soils. The metal sulfide precipitates contain high concentrations of metals and could potentially be recycled.     

三峡库区水华优势藻类生长动力学的普适性研究

从蓝绿藻中选取绿藻门的普通小球藻(Chlorella vulgaris,CV藻)为研究对象,应用Monod方程考察氮、磷营养盐对CV藻生长的影响,分别计算出CV藻对TP、TN的半饱和常数KSP和KSN结果表明KSN>>KSP,说明TP对CV藻生长的影响明显大于TN.CV藻生长速率对磷质量浓度反应很灵敏:与空白值相比,在0.002 mg·L-1的低浓度下u就有提高,而浓度到0.2 mg.L-1时,u明显增大;但在0.000-0.050 mg·L-1氮浓度范围内u几乎没有变化.通过系统比较CV藻与优势蓝绿藻,甚至海水藻的生长动力学特征,探讨了CV藻与其它蓝绿藻的动力学普适性和共同性,证实这些藻类都具有非常类似的生长动力学和生态学特征.因此,推测CV藻生长动力学模型可以从整体上反映和代表库区优势蓝绿藻的生长行为.同时分析和归纳了蓝绿藻生长模型的相似性和规律性,得出三峡库区优势藻类生长行为存在普遍一致性的初步结论.     

Preparation and catalytic properties of ZrO2-Al2O3 composite oxide supported nickel catalysts for methane reforming with carbon dioxide

ZrO2-Al2O3 composite oxides and supported Ni catalysts were prepared, and characterized by N2 adsorption/desorption, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The catalytic performance and carbon deposition was also investigated. This mesoporous composite oxide is shown to be a promising catalyst support. An increase in the catalytic activity and stability of methane and carbon dioxide reforming reaction was resulted from the zirconia addition, especially at 5wt% ZrO2 content. The Ni catalyst supported ZrO2-Al2O3 has a strong resistance to sintering and the carbon deposition in a relatively long-term reaction.     

Tolerance of the black soldier fly,Hermetia illucens (Diptera: Stratiomyidae) to pH value,pungency, and NaCl in foodstuffs北大核心CSCD

The black soldier fly (BSF), Hermetia illucens, has been considered impressive as a saprophagous insect, for its high ability to convert organic waste to insect protein and oil. Hence, it has been regarded by the municipal administration that BSF might be used as a medium to deal with food waste. However, food waste in China has been characterized as having a high salt content, oily, and very spicy, which usually renders them unsuitable for animal feeding. In order to assess the technological reliability for BSF conversion of food waste, the tolerance of BSF for pH values, pungency, and NaCl in food were investigated in this case. Results indicated that strong acidity (pH = 3) was not good for the development of BSF, demonstrating less body weight and eclosion failure. In contrast, strong basicity (pH = 11) seemed to be beneficial for larval development with high biomass, and there is no difference in pupation, eclosion, larval biomass, and livability for BSF for pH values between 5 and 11. With regards to salinity, liner correlations were observed; the salinity strength increased along with the extension of the larval phase, but body weight, pupation rate, emerging rate, and livability were still consistent under 6% density of salinity. Influence of pungency on BSF larvae has not yet been found. In conclusion, BSF showed a high tolerance to pH value, pungency, and salinity in foodstuffs. Hence, it is expected that food waste from common environments might have a lesser possibility to cause negative effects on BSF development, which could be good news for BSF conversion technology. As for the process design, the conclusion suggested that food waste optimum for BSF is expected to be alkaline and low-salt, which would be helpful to improve the efficiency and harvest. © 2018 Science Press. All rights reserved.     

Changes in CO2 flux for different recovery processes of desertification in the alpine meadows of Northwest Sichuan北大核心CSCD

Desertification has emerged as a serious threat to the alpine meadows of Northwest Sichuan in recent decades. Artificial vegetation had certain effects on desertification recovery, while how the CO2 flux changed and its reasons are still unclear. During the growing season in 2016 (i.e., from July to September), we selected the desertified alpine meadows with different recovery degrees, including the early stage of restoration, the middle stage of restoration, the late stage of restoration, and control (the unrecovered desertification meadow) as four transects. CO2 flux was measured by the instrument LI-8100, and the microenvironment factors that affected CO2 flux changes were analyzed. The results showed that the carbon sequestration function of desertified alpine meadows gradually increased with the degree of recovery. Net ecosystem exchange (NEE) were -1.61, -3.55, and -4.38 μmol m-2 s-1 in the early, mid-term, and late transects, respectively, and the most dramatic changes occurred from the early stage to mid-term stage, increasing by 120.50%. Both ecosystem respiration (ER) and soil respiration (SR) were enhanced significantly with restoration (P < 0.05). In mid or late July, NEE, ER, and SR reached their maximum values, and thereafter, the indicators varied to near zero (P < 0.05). During the whole growing season, the daily dynamic in CO2 flux for the control alpine meadow was mild and retained the trend of continuous release all day, but that in the desertified alpine meadow was a single peak pattern. Moreover, with restoration process, the peak of CO2 flux increased and reached a peak in the late stage of the recovery process. The regression analysis showed that there was a significant positive correlation between CO2 flux and vegetation coverage, aboveground biomass, and soil moisture (0-5 cm) (P < 0.01), and a weak correlation with 0-5-cm soil temperature (P < 0.01). This indicates that topsoil moisture (5 cm) is a more significant factor for CO2 flux than topsoil temperature during the growing season in the restoration of desertified alpine meadows in Northwest Sichuan. In general, the vegetation recovery significantly improved the carbon-sequestration ability of the desertified alpine meadows during the growing season in Northwest Sichuan, and at the middle stage of restoration, the carbon-sequestration ability improved significantly due to vegetation restoration and increase in topsoil (0-5 cm) moisture. © 2018 Science Press. All rights reserved.     

Interspecific association among main plant species in the unstable slope with high-frequency debris flow北大核心CSCD

To determine the characteristics of vegetation community structure and the relationship between species in the frequent watersheds of debris flow in fragile ecological environments, based on sample survey and 2 × 2 joint table techniques, we used analysis of variance test, χ2 test, Jaccard index, Pearson correlation coefficient, and Spearman's rank correlation coefficient test to study the main plant species correlations in the stable zone, instable zone, and deposit zone of the unstable slope. The analysis of variance test showed that all 45 species pairs had a significant negative correlation in the stable zone and instable zone, whereas there was no significant negative correlation in the deposit zone, which showed that the species had an independent distribution trend. The results from the different tests showed that there were 1 pair, 4 pairs, and 4 pairs from the stable zone, instable zone, and deposit zone, respectively, which had significant interspecific association under the χ2 test and the ratios of positive correlation pairs to negative correlation pairs were 0.55, 0.67, and 0.67 in the stable zone, instable zone, and deposit zone, respectively. There were 8 pairs, 5 pairs, and 5 pairs from the stable zone, instable zone, and deposit zone, respectively, which had significant interspecific association from the Pearson correlation analysis test, and the ratios of positive correlation pairs to negative correlation pairs were 0.36, 0.45, and 0.45 in the stable zone, instable zone, and deposit zone, respectively. There were 10 pairs, 6 pairs, and 9 pairs from the stable zone, instable zone, and deposit zone, respectively, which had significant interspecific association from the Spearman's rank correlation analysis test and the ratios of positive correlation pairs to negative correlation pairs were 0.5, 0.55, and 0.6 in the stable zone, instable zone, and deposit zone, respectively. The three test results showed general similarities but there were some differences. Most species pairs did not reach a significant level in the three zones and the number of negatively related species was more than the number of positively related species. In brief, this loose interspecific relationship indicates that the entire plant community was not stable, and the interspecific relationships among species are susceptible to environmental interference in the ecologically fragile areas of the debris flow basin. Therefore, rational selection and configuration of species should be applied to promote community structure development and ecological environmental improvement in vegetation restoration process areas with high-frequency debris flow. © 2018 Science Press. All rights reserved.     

Recent advances in three typical configurations and applications of bioelectrochemical systems北大核心CSCD

As the world's freshwater resources and available energy are alarmingly decreasing, the bioelectrochemical system (BES) is a cutting-edge technology for the resolution of the resource and energy issue. Researchers have paid much attention to t he application of t he BES configuration. Based on t he brief i ntroduction of m icrobial f uel cell a nd m icrobial electrolytic cell structure, principles, and domestic and foreign research, the BES and its influencing factors are introduced, specifically including: microbial activity, electrode materials, and configuration. Three important aspects (i.e., the electrode chamber, the reaction chamber, and micro-sensor) are summarized, and the advantages and disadvantages of single-electrode and multi-electrode chambers are compared, based on the microbial desalination cell. Microbial electrolysis desalination cell: Microbial electrolysis desalination and chemical-production cell have been discussed to introduce increasing reaction chamber configuration; this review focuses on the research of BES monitoring with regards to biochemical oxygen demand. The potential applications of the research progress are explored. The results show that the configuration of multi-chamber microbial fuel cell is complex and its efficiency is low, while the single chamber configuration is advantageous. The reaction chamber added is mainly aimed at desalination, and the study of the desalination pool still needs to be focused on optimizing the cation exchange membrane to maintain the anode pH balance and reduce the air cathode dissolved oxygen. Microbial electrode sensor can be applied in more areas, and its sensitivity and long-term stability need to be further improved. However, there is relatively less research on the abundance and activity of electricigen communities; the configurations and scopes of application of BES are still the research priority. © 2018 Science Press. All rights reserved.     

Effects of two different intercropping systems on arbuscular mycorrhizal fungal colonization and polychlorinated biphenyl (PCB) dissipation北大核心CSCD

Polychlorinated biphenyls (PCBs) are typical organic contaminants in the environment. It is indicated that plants and soil microorganisms have a positive synergistic effect on the remediation of PCB-contaminated soil. To investigate the effect of intercropping on arbuscular mycorrhizal (AM) fungal colonization and PCB remediation, a pot-cultivation experiment with two intercropping treatments, corn (Zea mays L.) / ryegrass (Lolium perenne L.) and corn/alfalfa (Medicago sativa L.), and a corn monoculture was conducted in a greenhouse. All treatments were inoculated with Funneliformis mosseae M47V. Plant biomass, root mycorrhizal colonization rate, concentration of PCBs and their homologs in soil, 16S rDNA gene abundance, and community composition measured by Terminal Restriction Fragment Length Polymorphism (T-RFLP) were determined after harvesting the plants. Intercropping significantly increased the root mycorrhizal colonization rate and plant biomass of corn (P < 0.05), as well as the available N content of the soil. A significant difference of the bacterial community composition was found among different treatments (P < 0.05). Compared with corn monoculture, corn/alfalfa intercropping significantly increased soil bacteria abundance (P < 0.05). The dissipation rates of total PCBs, as well as that of penta-chloro biphenyls were significantly increased in the intercropping treatments, when compared to the corn monoculture treatment. Moreover, corn/ryegrass intercropping has a significantly positive effect on the dissipation of tri-chloro biphenyls. Non-metric multidimensional scaling (NMDS) analysis indicated that the PCBs homologues composition were significantly correlated with the relative abundance of 128 bp and 148 bp T-RFs. Corn intercropping with ryegrass or alfalfa has a positive effect on root mycorrhizal colonization rate and plant biomass of corn. Inoculation of AM fungi in intercropping treatments significantly improved the efficiency of PCB remediation by promoting bacterial abundance and shifting the bacterial community composition. In conclusion, intercropping combined with AM fungi have positive synergistic effects on the remediation of PCB-contaminated soils. © 2018 Science Press. All rights reserved.     

Spatial variability in soil water and salinity in Tamarix community in a semiarid saline region of the upper Yellow River北大核心CSCD

Tamarix is widely distributed in semiarid saline regions of the upper Yellow River. The community of Tamarix affects the spatial distribution of soil water and salinity. It is important to explore the dynamic response relationship of Tamarix community and spatial distribution of soil water and salinity in order to evaluate the effects of vegetation community construction and ecological restoration in this region. The natural Tamarix community in the secondary saline-alkali land of the Ningxia Yellow River Irrigation Area was investigated in July 2016. Classical statistics and geostatistics were used to analyze the spatial distribution characteristics of soil water and salinity. The results showed that the soil water content was relatively low (1.98%-7.55%), whereas the soil salinity was high (average conductivity 10.28-25.38 mS/cm) in the study area. The variability coefficient range of soil water and salinity was 36.1%-83.7%, both with moderate variations. Furthermore, the variation degree of soil salinity decreased with the increase in soil depth. The soil water and salinity had obvious spatial structure characteristics, which was mainly affected by structural factors or structural factors associated with stochastic factors. The coefficients of nugget were 0.04%-49.88%, indicating the strong spatial correlation. The spatial distribution of soil water and salinity in Tamarix community showed a patchy pattern; the soil water and salinity distribution in the areas with high Tamarix growing density were considerably high. The correlation analysis showed that there was a positive correlation between soil water and salinity in the study area. In conclusion, soil water and salinity restrict the distribution and growth of Tamarix. Furthermore, the distribution and growth of Tamarix enhanced the spatial variability of soil water and salinity. Keywords. © 2018 Science Press. All rights reserved.