RANS simulation of neutral atmospheric boundary layer flows over complex terrain by proper imposition of boundary conditions and modification on the k-ε model

In this study, a modelling methodology is proposed for RANS simulations of neutral Atmospheric Boundary Layer (ABL) flows on the basis of the standard k-ε model, which allows the adoption of an arbitrary shear stress model. This modelling methodology is first examined in the context of an open flat terrain in an empty domain to ascertain there are no substantial changes in the prescribed profiles. The results show that relatively good homogeneity can be achieved with this modelling methodology for various sets of inflow boundary profiles. In addition, to extend the solutions derived from the standard k-ε model to RNG k-ε model, the RNG k-ε model is in detail assembly and tuned. Finally, the topographic effects on surface wind speeds over a complex terrain are assessed with the combined use of the proposed methodology and the modified RNG model. The numerical results are in good agreement with wind tunnel testing results and long-term field observations. A discussion of the effects of horizontal homogeneity and turbulence models on the simulated wind flows over a complex terrain is also given.     

营养液钙源对微生物固化砂土效果影响的试验研究

微生物诱导碳酸钙沉淀(MICP)作为一种环保型地基处理技术,其机理是通过微生物诱导碳酸钙沉淀有效改善土体工程性能,参与固化反应的营养液成份不同对固化效果有显著影响。分别选用氯化钙和硝酸钙作为营养液中的钙源,通过渗透实验、干密度实验、吸水率实验、无侧限抗压强度实验从宏观角度分析钙源对微生物固化砂土物理力学指标的影响。同时,结合电镜扫描测试,从微观角度对比了不同钙源作用下碳酸钙沉淀晶体形态及空间分布的差异。研究结果表明:利用硝酸钙固化后的砂柱整体密实度更高,其破坏裂缝在饱水和干燥状态下比氯化钙固化后的砂柱更小;硝酸钙作为钙源固化后的砂柱渗透系数和吸水率更低,干密度和无侧限抗压强度也更高。电镜扫描结果显示,氯化钙为钙源形成的碳酸钙沉淀量较少,形态为球状,散落分布在砂粒表面;硝酸钙形成碳酸钙沉淀量较多,形态以球状或者立方体为主,包裹住砂颗粒,团聚效果更为明显。因此,就钙源而言,硝酸钙的微生物固化效果较氯化钙更好。     

垃圾渗滤液处理工程实例

利用厌氧UASB+膜生物反应器MBR+纳滤工艺处理垃圾填埋场产生的垃圾渗滤液,介绍了各处理阶段的设计、运行参数和经济技术指标,设计处理规模为100 m3/d。在进水ρ(COD)为10 000 mg/L,ρ(BOD5)为5 000 mg/L,经处理后,出水ρ(COD)达到60 mg/L,ρ(BOD5)约为20 mg/L,去除率分别达到99.4%、99.6%,且出水稳定,达到地方标准DB 11/307-2005《北京市水污染排放标准》中二级排放标准。     

如何实现小城镇生活垃圾资源化

小城镇生活垃圾处理应重视资源化,但小城镇生活垃圾资源化面I临城镇规模、垃圾组分、经济、技术和市场等众多因素的制约。逐一分析这些制约因素并结合实例提出了小城镇生活垃圾资源化的三种实现模式,即纳管模式、组团模式和单建模式,探讨了三种模式的适用范围。     

Assessing the organic composition of urban surface films using nuclear magnetic resonance spectroscopy

Recently it has been shown that urban surfaces are covered with a thin film which mediates the fate, distribution and accumulation of semi-volatile organic compounds in the environment. In this study we apply a combination of solution, semi-solids, and solid state nuclear magnetic resonance (NMR) methods to provide a general overview of the organic constituents. In surface film collected from 30 m2 of outside windows over an area of 12 km2 in downtown Toronto, we roughly estimate that the organic carbon is approximately 35% carbohydrate, approximately 35% aliphatics, approximately 20% aromatics, and approximately 10% carbonyl groups. Various aliphatic groups can be identified including a number of acids, alcohols, alkanes, and alkenes. Also, numerous intact aliphatic esters are apparent that have not been observed before, as well as carbohydrates. The aromatic species include a small portion that appears to be derived from a polymer of styrene, in addition a larger fraction is consistent with polyhydroxylated PAH derived material, although this assignment is tentative and based solely on 1-D NMR data only. In addition, signals from polybutadiene are present and while accurate quantification is not possible, it appears that this polymer may be up to a few percents by weight of the total organic material.     

A spatial scan statistic for zero-inflated Poisson process

The scan statistic is widely used in spatial cluster detection applications of inhomogeneous Poisson processes. However, real data may present substantial departure from the underlying Poisson process. One of the possible departures has to do with zero excess. Some studies point out that when applied to data with excess zeros, the spatial scan statistic may produce biased inferences. In this work, we develop a closed-form scan statistic for cluster detection of spatial zero-inflated count data. We apply our methodology to simulated and real data. Our simulations revealed that the Scan-Poisson statistic steadily deteriorates as the number of zeros increases, producing biased inferences. On the other hand, our proposed Scan-ZIP and Scan-ZIP+EM statistics are, most of the time, either superior or comparable to the Scan-Poisson statistic.     

一株氯苯优势降解菌的降解条件优化

以氯苯降解率为降解效果指标,以降解温度、初始pH、降解时间、接种量和氯苯初始浓度为影响因素,对实验室保藏的一株氯苯优势降解菌株Lysinibacillus fusiformis LW13降解氯苯的降解条件进行优化。单因素试验结果表明,该降解菌株对氯苯的适宜降解条件分别为:温度20～40℃,pH为8.0,降解时间4 d,接种量2%～4%,氯苯初始浓度60～140 mg/L。以降解温度、氯苯初始浓度和接种量这三个显著影响因素进行正交试验,结果表明各影响因素的主次顺序为降解温度>氯苯初始浓度>接种量,最佳降解条件为降解温度35℃、氯苯初始浓度100 mg/L和接种量4%,最佳降解条件下氯苯降解率可高达93.8%。     

植被在大气汞收支中作用的研究进展与展望

在汞的生物地球化学循环中,对于"源"和"汇"的认识还存在许多不确定性。大气汞收支不平衡的问题使得植被在汞循环中的作用日益凸现;开展植被在大气汞收支中作用的研究有助于为全球汞减排政策的制定提供参考。本文首先概述了植被中汞的来源和影响因素及其与大气汞的源汇关系;进而重点论述了植被参与大气汞收支的主要方式:凋落物沉降、生物质燃烧和植被表面与大气汞的动态交换,并阐述了植被在大气汞污染监测中的应用;最后在总结我国相关研究的基础上展望了未来的发展方向。     

Enhanced dewatering characteristics of waste activated sludge with Fenton pretreatment: effectiveness and statistical optimization

In this work, the enhanced dewaterabing characteristics of waste activated sludge using Fenton pretreatment was investigated in terms of effectiveness and statistical optimization. Response surface method （RSM） and central composite design （CCD） were applied to evaluate and optimize the effectiveness of important operational parameters, i.e., H202 concentrations, Fe2＋ concentrations and initial pH values. A significant quadratic polynomial model was obtained （R2= 0.9189） with capillary suction time （CST） reduction efficiency as the response. Numerical optimization based on desirability function was carried out. The optimum values for H202, Fe2, and initial pH were found to be 178 mg-g-1 VSS （volatile suspended solids）, 211mg.gI VSS and 3.8, respectively, at which CST reduction efficiency of 98.25% could be achieved. This complied well with those predicted by the established polynomial model. The results indicate that Fenton pretreatment is an effective technique for advanced waste activated sludge dewatering. The enhancement of sludge dewaterability by Fenton＇s reagent lies in the migration of sludge bound water due to the disintegration of sludge flocs and microbial cells lysis.