以氯化和时间控制实现亚硝化型硝化反硝化

研究了以氯化方法在生物脱氮工艺中实现亚硝化型硝化反硝化的可行性。试验表明，借助氯的作用和硝化反应中的延迟时间的影响，可以在常温下保持很稳定的完全的亚硝化型硝化反硝化反应。在投加氯形成短程硝化反应后，不加氯，仅采取控制曝气时间的手段时，这种完全的亚硝化型硝化反硝化反应也可以保持至少20天。试验结果表明，硝化菌应是被杀死而不是仅仅被抑制。在实际工艺应用中，亚硝化型硝化反硝化所带来的益处可以弥补在反应过程中投加氯的费用，因此，在SBR中以氯化的方法结合时间控制以达到亚硝化型硝化反硝化是可行的。     

用实时控制SBR实现生活污水的短程硝化

采用间歇式活性污泥法 (SBR)处理生活污水 ,根据反应过程中DO、pH值和氨氮、亚硝酸氮、硝酸氮浓度变化的相应关系 ,控制曝气终点 ,实现了短程硝化。研究表明 ,短程硝化与全程硝化是相对的 ,没有绝对的短程硝化。对亚硝酸菌占绝对优势的混合液 ,进行长时间延时曝气 ,短程硝化可向全程硝化转化。实时控制是实现短程硝化的关键。采用实时控制方法 ,在 32± 1℃ ,亚硝酸氮积累率长期稳定地维持在 99%以上。在 2 1±1℃ ,通过控制低溶解氧浓度和曝气时间可实现短程硝化。     

异养硝化-好氧反硝化菌株DN1.2的脱氮特性研究

对一株具有异养硝化-好氧反硝化能力的恶臭假单胞菌Pseudomonas putida DN1.2进行了研究,初步探讨了不同碳源种类、碳氮比、pH值、温度、氨氮质量浓度对DN1.2菌株脱氮作用的影响.结果表明,该菌在异养硝化过程中能同时去除化学需氧量(COD)和氨氮,并且不积累硝酸盐和亚硝酸盐.碳氮比是影响其脱氮效果的重要因素.不同碳源种类下菌株的脱氮能力按大小排序为:乙酸盐＞葡萄糖＞柠檬酸盐＞甘油.脱除氨氮和COD的最适初始pH为7 0～7 5,最适温度为30～34℃.在菌株DN1 2转化的氨氮中有超过50%的部分被完全从水体中去除,细胞对氨氮的同化率为38 5%.     

处理城市污水的反硝化脱氮除磷新工艺研究进展

反硝化脱氮除磷可以实现同步反硝化脱氮和除磷,代表了当前污水处理可持续发展战略的发展趋势。本文对反硝化脱氮除磷的新工艺进行了重点介绍,这些工艺充分发挥了反硝化聚磷菌的优势,可提高处理效率、简化操作、降低处理费用,成为目前脱氮除磷工艺技术研究的热点和重点。     

低溶解氧短程硝化及同步脱氮研究

采用SBR反应器,以实际生活污水为研究对象,通过实验研究了在常温条件下通过控制低溶解氧(DO)实现短程硝化的可行性及控制条件.在曝气量由60 L·h-1逐渐降低到28 L·h-1的过程中,实现了由全程硝化到短程硝化的转变,亚硝酸盐积累率达到95%以上,出水硝态氮稳定在2.0mg·L-1以下.在低溶解氧短程硝化过程中,伴随着显著的同步脱氮:曝气量为32 L·h-1条件下实现了平均总氮去除率达54.6%.在实现短程硝化后,再次提高曝气量为40L·h-1时,短程硝化可以稳定保持.实验结果表明,通过控制低溶解氧可以实现常温条件下生活污水的短程硝化,过程中同步脱氮效果明显;系统可以在相对较高的溶解氧浓度下稳定运行.     

短程硝化反硝化技术研究

目前,高效、低耗去除水中氦污染物是国内外广泛关注的环境问题,短程硝化反硝化脱氮技术则是当前的研究热点。本论文针对短程硝化反硝化脱氨的机理和影响因素进行了研究,以深入理解短程硝化反硝化现象,对发展可持续污水生物处理工艺具有重大推动意义。     

A2N反硝化除磷脱氮系统处理生活污水研究

研究了生活污水COD／TN比值变化对A2N反硝化除磷脱氮新工艺去除氮、磷的影响情况。同时利用间歇试验着重探讨了DNPAOs污泥在不同硝态氮浓度、不同电子受体时的摄磷和放磷状况。A2N连续流工艺长期的运行结果表明：双泥系统的建立(生物膜硝化池独立于除磷污泥)可以降低碳源的好氧消耗,较大程度地减少聚磷菌和反硝化菌之间对碳源的竞争,同时保证了生长速率较小的硝化菌可以在稳定状态中生长,利于增强系统脱氮除磷的稳定性。     

乙酸钠与甲醇为外加碳源在反硝化过程中的比较

现有污水厂常存在碳源不足的现象,比反硝化速率较低,反硝化过程得不到彻底进行。本研究利用倒置A2／O系统的活性污泥,以某污水厂初沉池出水与不同量的甲醇及乙酸钠配制为一系列原水,进行反硝化反应效能的研究,以对比甲醇及乙酸钠对反硝化作用的强化效果差异。研究结果表明污水厂初沉池出水碳源中不容或复杂的可溶性有机物占较大比例。以乙酸钠为外加碳源时,可得较高的比反硝化速率。而以甲醇为外加碳源时,反硝化效率较乙酸钠高。通过不同的碳源补偿均能在一定程度上改善脱氮效果。     

城市污水短程硝化的控制策略及对污泥种群的影响

采用有效容积为54m3的大型中试序批式活性污泥处理(SBR)反应器,研究了在常温下处理碳氮比(C/N)平均值为2.16的以生活污水为主的实际城市污水时短程硝化的实现和稳定问题.试验结果表明,采用分段进水的运行模式,使出水总氮(TN)达到了小于3mg/L的深度脱氮效果.同时通过对SBR反应阶段的实时控制,优化了污泥种群结构,从而实现了温度为12～26℃、平均溶解氧(DO)浓度在2.5mg/L以上的环境条件下长期稳定的短程硝化反硝化,系统维持95%以上的亚硝化率稳定运行180天以上.应用荧光原位杂交(FISH)技术对系统中的氨氧化菌(AOB)和亚硝酸盐氧化菌(NOB)的数量进行了分析,结果也证明了系统中氨氧化菌在硝化菌中占绝对优势,亚硝酸盐氧化菌已逐步被淘汰.     

不同硝态氮组成下反硝化过程控制参数pH变化规律

采用序批式反应器(Sequencing Batch Reactor,SBR)反应器,在(21±1)℃下,以NO3--N和NO2--N为电子受体,在碳源充足的条件下对反硝化过程中的pH变化规律进行了研究。结果表明,反硝化过程中pH曲线上不仅出现了指示反硝化结束的特征点,还出现了表示硝酸盐完全还原为亚硝酸盐的特征点。此外,在起始NOx--N(NO2--N+NO3--N)浓度与pH值相同的条件下,起始NO2--N浓度所占的比例越高,反硝化结束时pH曲线上峰点的值越高,在反硝化过程中产生的总碱度却相等。研究分析发现NO2--N所占比例不同,反硝化过程中产生的碱度类型就不同,这是造成pH增量不同的根本原因。这些研究结果为更好地控制污水处理工艺提供了参考数据。     

Real gas choked flow conditions at low reduced-temperatures

Real gas choked mass flux is calculated for a frictionless stream expanding isentropically until it reaches the speed of sound and without phase changes. The other parameters associated with the choked state are the pressure, density, temperature ratios, and the speed of sound. Departure of the choked mass flux from the ideal gas model is discussed first in absolute terms and then in relative terms, using the Principle of Corresponding States, for gases with boiling points in the low temperature range. Reduced-stagnation pressures are examined up to values of 30 for hydrogen, neon, nitrogen, argon, methane, krypton, xenon, and R-14 and up to 100 for ⁴He. The corresponding reduced-stagnation temperatures go down to 1.4 and in some cases down to 1.2 for nitrogen and argon. Also discussed are the limiting values of stagnation parameters for which no phase change occurs in the choked state. Compared to the ideal gas, the mass flux may almost double and the critical pressure ratio may decrease by an order of magnitude. The relevance of results is discussed qualitatively and quantitatively for Joule-Thomson cryocooling.     

As-cast microstructures and behavior at high temperature of chromium-rich cobalt-based alloys containing hafnium carbides

Hafnium is often used to improve the high temperature oxidation resistance of superalloys but not to form carbides for strengthen them against creep. In this work hafnium was added in cobalt-based alloys for verifying that HfC can be obtained in cobalt-based alloys and for characterizing their behavior at a very temperature. Three Co–25Cr–0.25 and 0.50C alloys containing 3.7 and 7.4 Hf to promote HfC carbides, and four Co–25Cr– 0 to 1C alloys for comparison (all contents in wt.%), were cast and exposed at 1200 °C for 50 h in synthetic air. The HfC carbides formed instead chromium carbides during solidification, in eutectic with matrix and as dispersed compact particles. During the stage at 1200 °C the HfC carbides did not significantly evolve, even near the oxidation front despite oxidation early become very fast and generalized. At the same time the chromium carbides present in the Co–Cr–C alloys totally disappeared in the same conditions. Such HfC-alloys potentially bring efficient and sustainable mechanical strengthening at high temperature, but their hot oxidation resistance must be significantly improved.     

Chitosan-collagen/organomontmorillonite scaffold for bone tissue engineering

A novel composite scaffold based on chitosan-collagen/organomontmo-rillonite (CS-COL/OMMT) was prepared to improve swelling ratio, biodegradation ratio, biomineralization and mechanical properties for use in tissue engineering applications. In order to expend the basal spacing, montmorillonite (MMT) was modified with sodium dodecyl sulfate (SDS) and was characterized by XRD, TGA and FTIR. The results indicated that the anionic surfactants entered into interlayer of MMT and the basal spacing of MMT was expanded to 3.85 nm. The prepared composite scaffolds were characterized by FTIR, XRD and SEM. The swelling ratio, biodegradation ratio and mechanical properties of composite scaffolds were also studied. The results demonstrated that the scaffold decreased swelling ratio, degradation ratio and improved mechanical and biomineralization properties because of OMMT.     

Capacitance based mass metering for cryogenic fluids

This paper describes a method for measuring the mass of cryogenic fluids in on-board rocket propellant tanks or ground storage tanks. Linear approximations to the Clausius-Mossotti relationship serve as the foundation for a capacitance based mass sensor, regardless of fluid density stratification or tank shape. Sensor design considerations are presented along with the experimental results for a capacitance based mass gage tested in liquid nitrogen. This test data is shown to be consistent with theory resulting in a demonstrated mass measurement accuracy of ±0.75% and a deviation from linearity of less than ±0.30% of full scale mass. Theoretical accuracies are also shown to be ±0.73% for hydrogen and ±1.39% for oxygen for a select range of pressures and temperatures.     

Equipment using a “static-analytic” method for solubility measurements in potentially hazardous binary mixtures under cryogenic temperatures

A new apparatus designed to study, at cryogenic temperatures, thermodynamic equilibria of potentially explosive binary systems such as hydrocarbon-oxygen mixtures is described herein. This equipment has an equilibrium cell which was especially designed to minimize hazards while allowing accurate phase equilibrium measurements. Reliability of results, obtained with this equipment has been verified by working on the nitrogen-propane system, for which data are already available in literature, over a large range of compositions and at various temperatures. Four isothermal curves describing liquid phase compositions at 109.98, 113.77, 119.75 and 125.63 K have been determined. Our experimental data are represented within 2% in compositions and in pressures through the Peng-Robinson equation of state implying Mathias-Copeman alpha function and Huron-Vidal mixing rule. Comparisons to literature allow pointing out: good agreement is observed with Kremer and Knapp data (1983) while the three sets of Poon and Lu data (1974) presenting systematic positive deviation are consequently judged as suspicious.     

Gas gap thermal switches using neon or hydrogen and sorption pump

The very low pressure obtained thanks to adsorption phenomenon at low temperature can be used to build cryogenic heat switches, which offer the possibility to make or break thermal contact between two parts of a cryogenic system. The ON (conducting) and OFF (insulating) states of the switch are obtained by varying the gas pressure between two copper blocks separated by a gap of 100 μm. This pressure is controlled by acting upon the temperature of a small sorption pump (activated charcoal) connected to the gap space. For a “high” sorption pump temperature, the gas previously adsorbed in the sorption pump is released to the gap between the two blocks, allowing a good thermal conduction through the gas (ON state). On the opposite, cooling the sorption pump allows a very good vacuum between the copper blocks, which efficiently break the thermal contact (OFF state). Experimental thermal characteristics (Conductance in the ON and OFF state, ON-OFF switching temperature) of such a “Gas Gap Heat Switch” are described using hydrogen or neon as exchange gas and are compared with theoretical calculations.     

Development of No-Vent™ liquid hydrogen storage system for space applications

A number of technological advances required to store and maintain normal-boiling-point and densified cryogenic liquids, including liquid hydrogen, under zero boil-off conditions in-space, for long periods of time, have been developed. These technologies include (1) thermally optimized compact cryogen storage systems that reduce environmental heat leak to the lowest-temperature cryogen, which minimizes cryocooler size and input power, and (2) actively-cooled shields that surround the storage systems and intercept heat leak. The processes and tools used to develop these technologies are discussed. A zero boil-off liquid hydrogen storage system technology demonstrator for validating the actively-cooled shield technology is presented.     

Development of a miniature cryogenic fluid circuit and a cryogenic micropump

This article presents the development of a miniaturized cryogenic fluid circuit for distributed cooling of low-temperature tracking detectors in high-energy physics (HEP). The heart of the circuit is a prototype cryogenic micropump. This volumetric pump is compatible with cooling powers of about 10-100 W, and capable of producing pressure heads of up to around 0.3 MPa. Besides detector and electronics cooling in HEP, potential applications are found in the field of superconductor technology.     

Integrated Resonant Self-Pumped Loop and pulse tube cryocooler for cryogenic cooling distribution

Cooling distribution is a vital technology concerning cryogenic thermal management systems for many future space applications, such as in-space, zero boil-off, long-term propellant storage, cooling infrared sensors at multiple locations or at a distance from the cryocooler, and focal-plane arrays in telescopes. These applications require a cooling distribution technology that is able to efficiently and reliably deliver cooling power (generated by a cryocooler) to remote locations and uniformly distribute it over a large-surface area. On-going efforts by others under this technology development area have not shown any promising results.This paper introduces the concept of using a Resonant Self-Pumped Loop (RSPL) integrated with the proven, highly efficient pulse tube cryocooler. The RSPL and pulse tube cryocooler combination generates cooling power and provides a distributive cooling loop that can be extended long distances, has no moving parts, and is driven by a single linear compressor. The RSPL is fully coupled with the oscillating flow of the pulse tube working fluid and utilizes gas diodes to convert the oscillating flow to one-directional (DC) steady flow that circulates through the cooling loop. The proposed RSPL is extremely simple, lightweight, reliable, and flexible for packaging. There are several requirements for the RSPL to operate efficiently. These requirements will be presented in this paper. Compared to other distributive cooling technologies currently under development, the RSPL technology is unique.     

Helium liquefaction with a commercial 4 K Gifford-McMahon cryocooler

This paper describes helium liquefaction using a commercial cryocooler with 1.5 W cooling power at 4.2 K (Sumitomo model RDK415D with compressor CSW-71D, consuming 6.5 kW electrical power), equipped with heat exchangers for precooling the incoming gas. No additional cooling power of cryoliquids or additional Joule-Thomson stages were utilized. Measurements of the pressure dependence of the liquefaction rate were performed. A maximum value of 83.9 g/h was obtained for 2.25 bar stabilized input pressure. Including the time needed to cool the liquefied helium to 4.2 K at 1 bar after filling the bottle connected to the cold head, and correcting for heat screen influences, this results in a net liquefaction rate of 67.7 g/h. Maintaining a pressure close to 1 bar above the bath during liquefaction, a rate of 55.7 g/h was obtained. The simple design enables many applications of the apparatus.