深街道峡谷内高架桥对污染物传播特性影响的模拟研究

城市化进程导致在城市中出现通风条件较差的深街谷,建设于深街谷内的高架桥会加重周边街谷内空气污染.用计算流体力学模拟方法（CFD）探索在不同环境风速下的深街谷中,高架桥的高度和宽度对街谷内气流组织与污染物扩散的影响.结果表明:高架宽度小于0.8倍街谷宽度时的高架桥不会抑制桥下空间的流动;桥宽增加会改变桥下空间的涡旋结构和涡旋方向,近地面流动方向由之前的从右至左流动变为从左至右流动,因而桥下空间污染分布也发生明显改变;高架桥宽度的增加导致两侧低层住户受到较大影响,对背风面住户的影响更为明显;但高架宽度为0.5倍街谷宽度的高架桥能对迎风面中层住户造成影响;增加高架桥的高度,其下方污染物浓度增加;当高架桥位于街谷冠层时,下部空间的污染物浓度急剧增加;冠层处及涡旋交界面高架桥对两侧住户产生较大影响,而其他高度高架桥对两侧住户影响不大;随着环境风速的增加,高架桥对近地面源污染物扩散的阻碍作用逐渐减弱.研究显示,深街谷中增加高架桥的宽度、高度都会导致街谷内空气质量的恶化,而高架桥会阻碍因环境风速增加对街谷内空气质量的改善.      

隔声屏障对街道峡谷污染物扩散的影响

对带有隔声屏障的街道峡谷内流场和污染物浓度场进行了数值模拟,探讨了风速、隔声屏障高度及与建筑物间的距离对流场及污染物扩散的影响。模拟结果显示:街谷内由1个稳定的主涡及街角两侧隔声屏障所在区域的3个附属涡组成。隔声屏障改变了街谷底部的流型,提高了街谷内的x、y方向速度峰值,但在隔声屏障附近区域x方向速度场明显减弱,这也是污染物聚集原因之一。与无隔声屏障相比,隔声屏障的存在物理性阻隔了污染物扩散路径,提高了街道峡谷内污染物浓度峰值,其中行人高度处背风面污染物浓度升高27.51%~28.72%,迎风面污染物浓度升高11.64%~19.99%。街谷内污染物浓度的分布和峰值由风场、隔声屏障高度及与建筑物之间的距离共同决定。     

不同气温层结条件下地面加热对街谷扩散能力的影响

利用CFD数值模拟方法研究了气温层结与地面加热作用对街谷环流和污染物扩散的影响.针对高宽比为0.5和1.0的两种街谷,总共进行了18组敏感性数值试验,结果表明相对于气温层结,地表加热是决定街谷附近污染物扩散能力的更为重要的因素,地表加热作用可显著提高街谷的扩散能力.在地表存在加热的情况下,流场结构、空气交换系数、湍流强度总体上均朝着有利于清除街谷内污染物的方向发展,即使是在稳定层结下,地表加热作用所产生的热力环流也会使得污染物能够被有效地输送和扩散到街谷之外,从而使得近地面的污染物浓度下降.     

动态风场及交通流量下街道峡谷内污染物扩散模拟

根据现场实测数据,应用标准k-ε模型研究了动态风场及交通流量下三维街道峡谷内的污染物扩散规律,数值模拟利用CFD软件FLUENT,其中动态风场和车流量变化信息通过用户自定义编程实现.结果发现,动态风场下空气在街道内部不断经历膨胀和压缩的过程,街道峡谷内部流场形态时刻都在变化;当风速由大变小时,空气膨胀出街谷,流型呈近似椭圆形分布;当风速由小变大时,空气压缩在街谷内部,流型呈近似圆形分布.风速的不断变化引起街谷内、外大气的压缩和膨胀过程,这种过程能够改善街谷内污染物的扩散情况.背风面行人高度处,动态来流下的平均污染物浓度要比定常来流下低17.7%;迎风面行人高度处,动态来流下的平均污染物浓度要比定常来流下低27.1%.动态环境下污染物浓度的分布和峰值由风场和车流量变化共同决定.     

街道峡谷对称性对污染物扩散的影响

采用数值模拟的方法,研究了行列式和错列式街谷两侧建筑物的对称性对街谷内和下游建筑尾流区污染物浓度的影响,并引入3个用于评价室内空气环境的指标来描述街谷中人员区域内的空气质量.结果表明,平均残留时间(ART)和有效通风率(PFR)可用于评价不对称街谷内的空气质量.街谷的不对称性对街谷内部和下游建筑尾流区污染物浓度分布均有明显影响.下游建筑越低,则尾流区的浓度越高.行列式和错列式街谷中人员活动空间的无量纲平均浓度分别在建筑高度比例为7/3和7/2时最大.为在城市规划中尽可能避免出现最不利比例的街谷,根据平均残留时间和有效通风率等指标,给出了上下游建筑高度比与最不利街谷改善率的关系.     

上游建筑对街道峡谷内流场和污染物分布特征的影响

利用数值模拟方法研究了不同的上游阻挡建筑布局下,行列式和错列式街谷内气流速度和污染物浓度场特征.结果指出,阻挡建筑的存在改变了街谷内的二次流,从而对流场和浓度场均有明显影响.在行列式街谷中,无论上游建筑以何种布局存在,都会减小街谷内污染物浓度.若不考虑上游建筑的存在,将会过高估计行列式街谷内污染程度;在错列式街谷中,与街谷建筑并列的上游阻挡建筑会减小街谷内污染物浓度,而与街谷建筑错列布置的阻挡建筑会增大街谷内污染物浓度;数值模拟结果还表明,街谷内污染物的扩散和清除效果受气流速度和涡流特性的共同作用.     

城市建筑布局对街区交通污染物扩散特征的影响

该文采用CFD数值模拟技术对3种典型城市布局下街谷风环境与污染物扩散特性进行研究。结果表明,在3种城市建筑布局中,对称式布局中流经建筑群周围的气流比较均匀,交错式布局中气流受建筑阻碍作用明显,在街谷内绕流现象显著;街谷对应的背风建筑长度沿y轴方向大于迎风建筑时,建筑两侧气流反向向外流动,增加污染物向外扩散的通道;在街谷一气流速度大小满足布局Ⅰ布局Ⅱ布局Ⅲ趋势,而街谷二满足布局Ⅱ布局Ⅲ布局Ⅰ趋势,街谷一污染物浓度大小满足布局Ⅲ布局Ⅰ布局Ⅱ趋势,而街谷二满足布局Ⅱ布局Ⅲ布局Ⅰ趋势;街谷内污染物浓度分布受气流速度和涡流结构双重因素的影响,每种布局下街谷二污染物平均浓度均大于街谷一,同一布局下不同街谷内污染物浓度存在差异。因此,合理规划城市建筑布局是有效缓解交通污染的有效途径。     

南北向街谷内热不稳定流场日变化规律的模拟研究

城市街谷内热不稳定流动是促进污染物扩散的重要影响因素之一.本文基于街谷内热平衡分析,结合大涡模拟方法,研究了一个南北走向的城市街谷内温度、风场的日变化特征,并分析了壁面对流换热及长波辐射对街谷内环境的影响.结果显示:壁面对流换热是影响街谷内温度、风场的主要因素,而长波辐射的影响非常小,长波辐射引起街谷内空气温度升高不足对流换热影响的10％,而其对平均风速和脉动量的影响更是在2％和1％以内;街谷内空气温度从早上开始逐渐增加,到15:00的时候达到最大,可达311 K(38℃);上午时段,迎风面壁面热浮力减弱街谷内风速,街谷底部和迎风墙侧的脉动量根均方值较大,而下午时段街谷顶部的脉动量根均方值达到最大.街谷内不同位置和不同时段内,通过建筑材料选择和表面结构设计,适当调控建筑壁面的温度,可以促进街谷内温度分布和空气流通改善.     

风向对街道峡谷内污染物扩散的影响

采用Fluent软件,选用RNG k-ε湍流模型,对长高比为5的街道峡谷(简称街谷)在0°～90°风向下流场和污染物浓度场进行了数值模拟. 结果表明: 0°～75°风向时,街谷内流场呈明显的三维特性,90°风向时,流动表现出中长街谷的二维特点;风向对街谷内壁面污染物浓度的分布有显著影响,90°风向下的街谷壁面浓度最大,其次是45°风向,其余风向下的相对较小,污染物浓度的计算值与风洞试验值在趋势上吻合较好;壁面污染物浓度的分布由街谷内长度方向漩涡、来流冲角产生的进口回流及沿长度方向的流动所决定,壁面浓度的分布差异均可从附近的流场获得解释. 街道峡谷内长度方向的漩涡模拟过强会导致地面附近污染物浓度的计算值偏离试验值.      

关于机动车几何嵌入对城市街谷影响的研究

文章基于机动车几何体嵌入建立了城市街谷内空气流动和污染物分布模型,应用FLUENT 6.3进行了数值模拟,将尾气排放模化为速度输入边界条件,探究了不同来流风速下,街谷内流场和污染物分布。结果表明:机动车空间几何模型的构建更为细致地模拟了街谷近地层的空气流动及污染物分布。由于车辆模型的嵌入,街谷近地面污染物浓度不再呈现单调一致的变化规律;当来流风速为0.3 m/s时,在横向车辆之间局部子涡的影响下,污染物浓度呈增大-减小-增大的趋势;当来流风速增至1 m/s时,近地层污染物浓度先增大后减小,道路中部污染物浓度达到最大;随着来流风速的进一步增大,即3 m/s和5 m/s工况下,街谷内的风场环境由来流风占主导,污染物浓度自迎风面至背风面呈宏观上增大,在背风面有小幅衰减,污染物浓度最大值出现在背风侧机动车道。研究可为预测城市街谷近地层内污染物分布提供依据。     

Toxic effects of acetochlor, methamidophos and their combination on nifH gene in soil

Toxic effects of two agrochemicals on nifH gene in agricultural black soil were investigated using denaturing gradient gel electrophoresis （DGGE） and sequencing approaches in a microcosm experiment. Changes of soil nifH gene diversity and composition were examined following the application of acetochlor, methamidophos and their combination. Acetochlor reduced the nifH gene diversity （both in gene richness and diversity index values） and caused changes in the nifH gene composition. The effects of acetochlor on nifH gene were strengthened as the concentration of acetochlor increased. Cluster analysis of DGGE banding patterns showed that nifH gene composition which had been affected by low concentration of acetochlor （50 mg/kg） recovered firstly. Methamidophos reduced nifH gene richness that except at 4 weeks. The medium concentration of methamidophos （150 mg/kg） caused the most apparent changes in nifH gene diversity at the first week while the high concentration of methamidophos （250 mg/kg） produced prominent effects on nifH gene diversity in the following weeks. Cluster analysis showed that minimal changes of nifH gene composition were found at 1 week and maximal changes at 4 weeks. Toxic effects of acetochlor and methamidophos combination on nifH gene were also apparent. Different nifH genes （bands） responded differently to the impact of agrochemicals： four individual bands were eliminated by the application of the agrochemicals, five bands became predominant by the stimulation of the agrochemicals, and four bands showed strong resistance to the influence of the agrochemicals. Fifteen prominent bands were partially sequenced, yielding 15 different nifH sequences, which were used for phylogenetic reconstructions. All sequences were affiliated with the alpha- and beta-proteobacteria, showing higher similarity to eight different diazotrophic genera.     

Arsenic uptake by arbuscular mycorrhizal maize （Zea mays L.） grown in an arsenic-contaminated soil with added phosphorus

The effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and phosphorus (P) addition (100 mg/kg soil) on arsenic (As) uptake by maize plants (Zea mays L.) from an As-contaminated soil were examined in a glasshouse experiment.Non-mycorrhizal and zero-P addition controls were included.Plant biomass and concentrations and uptake of As,P,and other nutrients,AM colonization,root lengths,and hyphal length densities were determined.The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium.Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments,but shoot and root biomass of AM plants was depressed by P application.AM fungal inoculation decreased shoot As concentrations when no P was added,and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition,respectively.Shoot and root uptake of P,Mn,Cu,and Zn increased,but shoot Fe uptake decreased by 44.6%,with inoculation, when P was added.P addition reduced shoot P,Fe,Mn,Cu,and Zn uptake of AM plants,but increased root Fe and Mn uptake of the nonmycorrhizal ones.AM colonization therefore appeared to enhance plant tolerance to As in low P soil,and have some potential for the phytostabilization of As-contaminated soil,however,P application may introduce additional environmental risk by increasing soil As mobility.     

Potential of plant polyphenol oxidases in the decolorization and removal of textile and non-textile dyes

In this study an effort has been made to use plant polyphenol oxidases; potato （Solanum tuberosum） and brinjal （Solanum melongena）, for the treatment of various important dyes used in textile and other industries. The ammonium sulphate fractionated enzyme preparations were used to treat a number of dyes under various experimental conditions. Majority of the treated dyes were maximally decolorized at pH 3.0. Some of the dyes were quickly decolorized whereas others were marginally decolorized. The initial first hour was sufficient for the maximum decolorization of dyes. The rate of decolorization was quite slow on long treatment of dyes. Enhancement in the dye decolorization was noticed on increasing the concentration of enzymes. The complex mixtures of dyes were treated with both preparations of polyphenol oxidases in the buffers of varying pH values. Potato polyphenol oxidase was significantly more effective in decolorizing the dyes to higher extent as compared to the enzyme obtained from brinjal polyphenol oxidase. Decolorization of dyes and their mixtures, followed by the formation of an insoluble precipitate, which could be easily removed simply by centrifugation.     

Removal of heavy metals from sewage sludge by low costing chemical method and recycling in agriculture

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Single and joint effects of pesticides and mercury on soil urease

The influence of two pesticides including chlorimuron-ethyl and furadan and mercury （Hg） on urease activity in 4 soils （meadow burozem and phaeozem） was investigated. The soils were exposed to various concentrations of the two pesticides and Hg individually and simultaneously. Results showed that there was a close relationship between urease activity and organic matter content in soil. Chlorimuron-ethyl and furadan could both activate urease in the 4 soils. The maximum increment of urease activity by chlorimuronethyl was up to 14%-18%. There was almost an equal increase （up to 13%-21%） in the urease activity by furadan. On the contrary, Hg markedly inhibited soil urease activity. A logarithmic equation was used to describe the relationship （P〈0.05） between the concentration of Hg and the activity of soil urease in the 4 tested soils. Semi-effect dose （ED50） values by the stress of Hg based on the inhibition of soil urease in the 4 soils were 88, 5.5, 24 and 20 mg/kg, respectively, according to the calculation of the corresponding equations. The interactive effect of chlorimuron-ethyl or furadan with metal Hg on soil urease was mainly synergic at the highest tested concentrations.     

Isolation and preliminary characterization of a 3-chlorobenzoate degrading bacteria

A study was conducted to compare the diversity of 2-, 3-, and 4-chlorobenzoate degraders in two pristine soils and one contaminated sewage sludge. These samples contained strikingly different populations of mono-chlorobenzoate degraders. Although fewer cultures were isolated in the uncontaminated soils than contaminated one, the ability of microbial populations to mineralize chlorobenzoate was widespread. The 3- and 4-chlorobenzoate degraders were more diverse than the 2-chlorobenzoate degraders. One of the strains isolated from the sewage sludge was obtained. Based on its phenotype, chemotaxonomic properties and 16S rRNA gene, the organism S-7 was classified as Rhodococcus erythropolis. The strain can grow at temperature from 4 to 37℃. It can utilize several （halo）aromatic compounds. Moreover, strain S-7 can grow and use 3-chlorobenzoate as sole carbon source in a temperatures range of 10-30℃ with stoichiometric release of chloride ions. The psychrotolerant ability was significant for bioremediation in low temperature regions. Catechol and chlorocatechol 1,2-dioxygenase activities were present in cell free extracts of the strain, but no （chloro）catechol 2,3- dioxygenase activities was detected. Spectral conversion assays with extracts from R. erythropolis S-7 showed accumulation of a compound with a similar UV spectrum as chloro-cis,cis-muconate from 3-chlorobenzoate. On the basis of these results, we proposed that S-7 degraded 3-chlorobenzoate through the modified ortho-cleave pathway.     

Organochlorine pesticides in soils under different land usage in the Taihu Lake region, China

A field study was conducted in the Taihu Lake region, China in 2004 to reveal the organochlorine pesticide concentrations in soils after the ban of these substances in the year 1983. Thirteen organochlorine pesticides (OCPs) were analyzed in soils from paddy field, tree land and fallow land. Total organochlorine pesticide residues were higher in agricultural soils than in uncultivated fallow land soils. Among all the pesticides, ΣDDX (DDD, DDE and DDT) had the highest concentration for all the soil samples, ranging from 3.10 ng/g to 166.55 ng/g with a mean value of 57.04 ng/g and followed by ΣHCH, ranging from 0.73 ng/g to 60.97 ng/g with a mean value of 24.06 ng/g. Dieldrin, endrin, HCB and α-endosulfan were also found in soils with less than 15 ng/g. Ratios of p,p'-(DDD DDE)/DDT in soils under three land usages were: paddy field ＞ tree land ＞ fallow land, indicating that land usage inlfuenced the degradation of DDT in soils. Ratios of p,p'-(DDD DDE)/DDT ＞1, showing aged residues of DDTs in soils of the Taihu Lake region. The results were discussed with data from a former study that showed very low actual concentrations of HCH and DDT in soils in the Taihu Lake region, but according to the chemical half-lives and their concentrations in soils in 1980s, the concentration of DDT in soils seemed to be underestimated. In any case our data show that the ban on the use of HCH and DDT resulted in a tremendous reduction of these pesticide residues in soils, but there are still high amounts of pesticide residues in soils, which need more remediation processes.     

Sorption of 1-naphthol by plant cuticular fractions

The contribution of aliphatic-rich plant biopolymer to sorption of hydrophobic organic compounds is significantly important because of their preservation and accumulation in the soil environment,but sorption mechanism is still not fully understood.In this study, sorption of 1-naphthol by plant cuticular fractions was examined to better understand the contributions of respective fraction.Toward this end,cuticular materials were isolated from the fruits of tomato by chemical method.The tomato cuticle sheet consisted of waxes (6.5 wt%),cuticular monomer (69.5 wt%),and polysaccharide (24.0 wt%).Isotherms of l-naphthol to the cuticular fractions were nonlinear (N value (0.82-0.90)) at the whole tested concentration ranges.The KodKow ratios for bulk cuticle (TC1),dewaxed cuticle (TC2),cutin (TC4),and desugared cuticle (TC5) were larger than unity,suggested that tomato bulk cuticle and cutin are much powerful solption medium.Sorption capability of cutin (TC4) was 2.4 times higher than the nonsaponifiable fraction (TC3).The 1-naphthol interactions with tomato cuticular materials were governed by both hydrophobic-type interactions and polar (H-bonding) interactions. Removal of the wax and polysaccharide materials from the bulk tomato cuticle caused a significant increase in the sorption ability of the cuticular material.There was a linear negative trend between K_(oc) values and the amount of polysaccharides or fraction's polarities ((N O)/C);while a linear positive relationship between K_(oc) values and the content of cutin monomer (linear R~2=0.993) was observed for present in the cuticular fractions.Predominant sorbent of the hydrophobic organic compounds (HOCs) in the plant cuticular fraction was the cutin monomer,contributing to 91.7% of the total sorption of tomato bulk cuticle.     

Alterations of organ histopathology and metallolhionein mRNA expression in silver barb, Puntius gonionotus during subchronic cadmium exposure

Common silver barb,Puntius gonionotus,exposed to the nominal concentration of 0.06 mg/L Cd for 60 d,were assessed for histopathological alterations(gills,liver and kidney),metal accumulation,and metallothionein(MT)mRNA expression.Fish exhibited pathological symptoms such as hypertrophy and hyperplasia of primary and secondary gill lamellae,vacuolization in hepatocytes,and prominent tubular and glomerular damage in the kidney.In addition,kidney accumulated the highest content of cadmium,more than gills and liver.Expression of MT mRNA was increased in both liver and kidney of treated fish.Hepatic MT levels remained high after fish were removed to Cd-free water.In contrast,MT expression in kidney was peaked after 28 d of treatment and drastically dropped when fish were removed to Cd-free water.The high concentrations of Cd in hepatic tissues indicated an accumulation site or permanent damage on this tissue.     

Seed selections for crystallization of calcium phosphate for phosphorus recovery

Seed induces and promotes the crystallization of calcium phosphate, and acts as carrier of the recovered phosphorus （P）. In order to select suitable seed for P recovery from wastewater, three seeds including Apatite （AP）, Juraperle （JP） and phosphate-modified Juraperle （M-JP） were tested and compared. Batch and fixed-bed column experiments of seeded crystallization of calcium phosphate were undertaken by using synthetic wastewater with 10 mg/L P phosphate. It shows that AP has bad enduring property in the crystallization process, while JP has better performance for multiple uses, and M-JP is a hopeful seed for P recovery by crystallization of calcium phosphate.