Removal of fluoride from aqueous solution by TiO2 and TiO2–SiO2 nanocomposite

Adsorption plays an important role in the removal of pollutants such as fluoride from aqueous solutions. With the rapid development of environmental technology, TiO2 particle has become promising material to adsorb fluoride ion because of its low cost, non-toxic, good chemical stability, and good sorption ability. This work used sol-gel and hydrothermal synthesis methods to prepare TiO2 particles and load them onto SiO2 particles. The physicochemical properties such as heat stability, particle size, and surface area of the resulting TiO2 adsorbents were characterized with various analytical methods. In addition, their adsorption abilities to fluoride were determined under various conditions including different initial fluoride concentration, pH and coexisting ions. The maximum adsorption capacity of the TiO2 adsorbents can reach up to 94.3 mg/g. The adsorption isotherms of fluoride onto the TiO2 adsorbents can be closely described by the Langmuir model, suggesting the monolayer adsorption process

An Edge Caching Strategy Based on User Speed and Content Popularity for Mobile Video Streaming

Mobile users’ demands to delay-sensitive video streaming media put forward new requirements for mobile networks, such as architecture optimization. Edge caching as a new paradigm is proposed to enhance the quality of service (QoS) for mobile users at the network edge. Due to the limited coverage of edge cache nodes, the frequent handoffs between base stations would aggravate network traffic overhead, resulting in a bad experience of high latency and service interruption when mobile users browse videos. This paper first proposes a three-layer mobile edge network architecture and applied edge caching to video streams to build an efficient caching system. Given the user’s mobility and low latency of mobile video streaming, we propose an edge caching strategy based on user speed and content popularity. Horizontally, the user’s speed affects the spanning area and the buffer size of the cache on edge; vertically, content popularity determines the priority of cached videos. Experimental results demonstrate that our caching strategy outperforms other schemes in terms of the average delay and the cache hit ratio in mobile video streaming scenes compared with the other three classic caching methods

Removal of ammonium from aqueous solutions using alkali-modified biochars

Biochars converted from agricultural residuals can effectively remove ammonium from water. This work further improved the sorption ability of biochars to aqueous ammonium through alkali modification. Three modified biochars were prepared from agricultural residuals pre-treated with NaOH solution through low-temperature (300 °C) slow pyrolysis. The modified biochars effectively removed ammonium ions from water under various conditions with relatively fast adsorption kinetics (reached equilibrium within 10 h) and extremely high adsorption capacity (>200 mg/g). The Langmuir maximum capacity of the three modified biochars were between 313.9 and 518.9 mg/g, higher than many other ammonium adsorbents. Although the sorption of ammonium onto the modified biochar was affected by pH and temperature, it was high under all of the tested conditions. Findings from this work indicated that alkali-modified biochars can be used as an alternative adsorbent for the removal of ammonium from wastewater

Is grain zinc concentration in wheat limited by source?

Abstract Increasing zinc (Zn) concentration in wheat grain is important to human health. In order to clarify the source limitations of grain Zn concentration, ears of winter wheat were grown in detached ear culture under different Zn supply levels (0, 30, 60, 90 and 120 μmol l -1 ) and sucrose supply levels (2%, 4% and 6%). To investigate sink limitations, some ears were subjected to partial spikelet removal. The result showed that wheat grain yield did not change; however, the concentration of Zn, iron (Fe), manganese (Mn), and protein in grain was significantly (p<0.05) increased by Zn application. At 90 μ mol l -1 Zn supply, grain Zn concentration reached a maximum of 100 mg kg -1 ; compared to the no Zn treatment, this represented 5.5 to 9.8-fold and 5.7 to 8.4-fold increase, for superior grain and inferior grain, respectively. With the increase in sucrose supply, grain weight, as well as the content of micronutrients and protein significantly (p<0.05) increased, while the concentrations of these significantly (p<0.05) decreased. The partial spikelet removal treatment, along with increasing single grain weight, also increased grain Zn concentration and grain Zn content by 24.0 to 33.4%, 4.1 to 30.8%, and 34.7 to 75.0%, respectively. The concentration and content of Fe, Mn, and protein in wheat grain also increased. These results indicated that Zn concentration in wheat grain was mainly restricted by the source, and the concentration of Zn, Fe, and protein may be increased simultaneously in wheat grain in certain source supply ranges

Delayed wet season increases soil net N mineralization in a seasonally tropical forest

Seasonal precipitation regime plays a vital role in regulating nutrient dynamics in seasonally dry tropical forests. Present evidence suggests that not only wet season precipitation is increasing in the tropics of South China, but also that the wet season is occurring later. However, it is unclear how nutrient dynamics will respond to the projected precipitation regime changes. We assessed the impacts of altered seasonal precipitation on soil net N mineralization in a secondary tropical forest. Since 2013, by reducing throughfall and/or irrigating experimental plots, we delayed the wet season by two months from April–September to June–November (DW treatment) or increased mean annual precipitation by 25% in July and August (WW treatment). We measured soil net N mineralization rates and assessed soil microbial communities in January, April, August and November in 2015 and 2017. We found that a wetter wet season did not significantly affect soil microbes or net N mineralization rates, even in the mid-wet season (August) when soil water content in the WW treatment increased significantly. By contrast, a delayed wet season enhanced soil microbial biomass and altered microbial community structure, resulting in a two-fold increase in net N mineralization rates relative to controls in the early dry season (November). Structural equation modeling showed that the changes in net N mineralization during the early dry season were associated with altered soil microbial communities, dissolved organic N, and litterfall, which were all affected by enhanced soil water content. Our findings suggest that a delayed wet season could have a greater impact on N dynamics than increased precipitation during the wet season. Changes in the seasonal timing of rainfall might therefore influence the functioning of seasonally dry tropical forests