Effect of air-assisted backwashing on the performance of an anaerobic fixed-bed bioreactor that simultaneously removes nitrate and arsenic from drinking water sources

Contaminant removal from drinking water sources under reducing conditions conducive for the growth of denitrifying, arsenate reducing, and sulfate reducing microbes using a fixed-bed bioreactor may require oxygen-free gas (e.g., N₂ gas) during backwashing. However, the use of air-assisted backwashing has practical advantages, including simpler operation, improved safety, and lower cost. A study was conducted to evaluate whether replacing N₂ gas with air during backwashing would impact performance in a nitrate and arsenic removing anaerobic bioreactor system that consisted of two biologically active carbon reactors in series. Gas-assisted backwashing, comprised of 2 min of gas injection to fluidize the bed and dislodge biomass and solid phase products, was performed in the first reactor (reactor A) every two days. The second reactor (reactor B) was subjected to N₂ gas-assisted backwashing every 3-4 months. Complete removal of 50 mg/L NO₃⁻ was achieved in reactor A before and after the switch from N₂-assisted backwashing (NAB) to air-assisted backwashing (AAB). Substantial sulfate removal was achieved with both backwashing strategies. Prolonged practice of AAB (more than two months), however, diminished sulfate reduction in reactor B somewhat. Arsenic removal in reactor A was impacted slightly by long-term use of AAB, but arsenic removals achieved by the entire system during NAB and AAB periods were not significantly different (p > 0.05) and arsenic concentrations were reduced from approximately 200 μg/L to below 20 μg/L. These results indicate that AAB can be implemented in anaerobic nitrate and arsenic removal systems.     

Continuous Gas Dehydration Using the Hygroscopic Ionic Liquid [EMIM][MeSO3] as a Promising Alternative Absorbent

Continuous gas drying experiments with the hygroscopic ionic liquid [EMIM][MeSO₃] show that it can be a very promising alternative drying agent to the absorbent triethylene glycol (TEG) commonly used in industrial gas drying processes. The HTU/NTU model in combination with the correlations of Onda et al. for mass transfer coefficients can be applied for the design of an absorption process with [EMIM][MeSO₃]. The major advantage of this ionic liquid (IL) is that well‐known problems associated with the regeneration of the absorbent TEG can be avoided using [EMIM][MeSO₃] due to extremely low vapor pressure and possible regeneration with air. The drying capacity of the IL system is about two times higher compared to TEG. Hence, a simple plant design comparable to that of industrial adsorption plants might be applied.     

功率和音频:不折不扣地集成在一起

本文主要讲述如何实现便携消费电子产品中电源管理和音频解决方案的集成。支持市面上大多数应用处理器的这些集成器件,实现了将电源管理与音频功能的完美结合,为制造商提供了性价比高、占位空间小的解决方案,满足了消费者对更小尺寸和更高性能的需求。     

Syngas Production via Reverse Water‐Gas Shift Reaction over a Ni‐Al2O3 Catalyst: Catalyst Stability,Reaction Kinetics,and Modeling

The synthesis of liquid fuels from CO₂, e.g., separated from flue gases of power plants, and H₂ from renewables, i.e., water electrolysis, is a concept for substituting fossil fuels in the transport sector. It consists of two steps, syngas production via reverse water‐gas shift (RWGS) and synfuel production by Fischer‐Tropsch synthesis. Research is concentrated on the RWGS using a Ni‐catalyst. The catalyst shows an appropriate performance in catalyzing the RWGS. The catalyst is stable at technically relevant temperatures. The intrinsic and effective kinetics were determined and considerations on a technical application of the process are proposed.     

Phenolics and in-vitro degradability of protein and fibre in West African Browse

Relationships among soluble phenolics, soluble and insoluble proanthocyanidins (PAC), lignin, N, neutral-detergent fibre (NDF), and in-vitro degradability of protein and NDF were determined in 72 West African fodder trees and shrubs. Species were collected in the semi-arid (Niger), sub-humid (Nigeria) and humid/sub-humid (Benin) zones. Variation among species in chemical composition and in-vitro degradability of protein and NDF was large. Zones did not differ in mean content of phenolic compounds. Protein degradability was negatively correlated with soluble phenolics (r = ?0.34, P < 0.01) and soluble PAC (r = ?0.47, P < 0.001). NDF was positively correlated with soluble PAC (r = 0.44, P < 0.001), insoluble PAC (r = 0.28, P < 0.05) and lignin (r = 0.76, P < 0.001). NDF degradability was negatively correlated with soluble PAC (r = ?0.40, P < 0.001) and lignin (r = ?0.59, P < 0.001). Chemical composition and in-vitro degradability along with field observations can provide useful criteria for determining the nutritive value of browse species.     

Axial Dispersion and Wall Effects in Narrow Fixed Bed Reactors: A Comparative Study Based on RTD and NMR Measurements

Axial dispersion and wall effects in narrow fixed beds with aspect ratios < 10 were investigated, both by classical methods and by NMR imaging. The residence time distribution (RTD) in the center and at the wall was measured, system water/NaCl‐solution as tracer, and subsequently compared with radial velocity profiles based on NMR imaging. The influence of the aspect ratio and Re_p on dispersion and on the degree of non‐uniformity of the velocity profile was studied. The NMR results are consistent with the RTD and also with literature data of numerical simulations. For low aspect ratios, dispersion/wall effects have a strong influence on the reactor behavior, above all, in cases where a low effluent concentration is essential, as proven by breakthrough experiments with the reaction of H₂S with ZnO.     

滇池——生态水系、人文水际、效益水体

景观设计是对基地不同层面进行探讨,从而得出一个跟基地肌理融合的提案--这是很多设计先驱者(如麦克哈格和佐佐木英夫)的理念.首次踏足滇池,感到它正是这个理念的优良实验场.当中涉猎的生态、文化、经济、民生等课题,各层次的丰富多变,为设计提供了一个可发现的、自然萌生的答案.项目位于昆明滇池北部官渡区六甲乡的3个半岛,其中EDAW(Ltd)为宽200m、长12km的沿岸湿地区和连带绿网提供概念设计,旨在打造一片可涵养水源、提高生态多样性的多用途绿地景观.     

用于高效DC/DC变换器的沟槽MOSFET

面对市场对高效率电源的需求,工程师们无不急切期盼快速开关、低rDS(on)的功率MOSFET能有新进展。如今,一种新颖的厚底层氧化物工艺可以让Crss减小为栅极结构器件相应参数的一半,从而大大减少了器件导通所需的栅电荷,缩短了功率MOSFET的开关瞬态过程,同时让导通电阻保持在一个极低的水平上。这一技术对DC/DC变换器来说,意味着电路工作效率将得以提高。     

CT in the diagnosis of abdominal wall hernias: a preliminary study

The aim of the study was to estimate the value of CT in the diagnosis of abdominal wall hernias and at the same time to create a standard for this CT investigation. Twenty-four patients with suspected hernia of the abdominal wall were examined. All were operated on. The CT scans were assessed by two radiologists to estimate the interobserver variation. The CT diagnoses made by the two radiologists were correct in 83 % and 79 % of cases, respectively. The sensitivity was 0.83 in both CT evaluations and the specificity was 0.83 and 0.67, respectively. The predictive value of a positive CT finding was 0.94 and 0.88, while the predictive value of a negative CT finding was 0.63 and 0.57, respectively. The interobserver variation (kappa) was 0.87. The study therefore indicates that a positive CT finding of abdominal wall hernia is reliable, while a negative finding does not exclude the diagnosis. The interobserver variation of the CT diagnoses is acceptable. To achieve the highest diagnostic accuracy, it is recommended to always use the Valsalva manoeuvre, oral intake of contrast and 10/10 mm CT slices.