Characteristic analysis on temporal evolution of floc size and structure in low-shear flow

A series of flocculation tests were performed to investigate the effect of low-shear rates (G = 3-16 s⁻¹) on flocculation of kaolin suspension by polyaluminum chloride (PACl), with the goal of understanding floc growth mechanisms. Results were reported in terms of floc average size (d_p) and boundary fractal dimension (D_pf), derived from a non-intrusive optical sampling and digital image analysis technique. As expected, the rate of floc aggregation increased with increasing G, resulting in faster changes in aggregate size and structure in the initial stage of flocculation. Nevertheless, steady state was attained faster for D_pf than for d_p at the same shear rates, possibly due to the self-similarity of fractal aggregates. An interesting finding was that at G = 3 s⁻¹, an obvious plateau was observed for the average-size evolution at steady state; for shear rates of 6 and 7 s⁻¹, the flocs exhibited some decrease after reaching the peak of size, mainly as a result of floc settling at steady state; and for G = 11-16 s⁻¹, a decrease in floc size was possibly attributed to the irreversibility of PACl-floc breakage. The process of floc growth was described using a fractal growth model, which defined flocculation as the result of the combined processes of aggregation and restructuring. The conceptual model could effectively characterize temporal changes in floc size and structure, and found that fragmentation followed by reformation seemed to be more effective in forming larger and more compact aggregates than the restructuring process due to erosion and reformation, which may provide useful insights for the design of flocculation reactors.     

The impact of pH on floc structure characteristic of polyferric chloride in a low DOC and high alkalinity surface water treatment

The adjustment of pH is an important way to enhance removal efficiency in coagulation units, and in this process, the floc size, strength and structure can be changed, influencing the subsequent solid/liquid separation effect. In this study, an inorganic polymer coagulant, polyferric chloride (PFC) was used in a low dissolved organic carbon (DOC) and high alkalinity surface water treatment. The influence of coagulation pH on removal efficiency, floc growth, strength, re-growth capability and fractal dimension was examined. The optimum dosage was predetermined as 0.150 mmol/L, and excellent particle and organic matter removal appeared in the pH range of 5.50-5.75. The structure characteristics of flocs formed under four pH conditions were investigated through the analysis of floc size, effect of shear and particle scattering properties by a laser scattering instrument. The results indicated that flocs formed at neutral pH condition gave the largest floc size and the highest growth rate. During the coagulation period, the fractal dimension of floc aggregates increased in the first minutes and then decreased and larger flocs generally had smaller fractal dimensions. The floc strength, which was assessed by the relationship of floc diameter and velocity gradient, decreased with the increase of coagulation pH. Flocs formed at pH 4.00 had better recovery capability when exposed to lower shear forces, while flocs formed at neutral and alkaline conditions had better performance under higher shear forces.     

Side-stream membrane bioreactors: Influence of stress generated by hydrodynamics on floc structure, supernatant quality and fouling propensity

This work aims to characterise the impact of hydrodynamics on sludge properties and consequently on fouling mechanisms in side-stream membrane bioreactors (MBRs). Two side-stream processes which generate very different shear stresses are compared, without filtration. This operating mode permits specific quantification of the impact of the external loop (and of induced shear stress) on floc structure/morphology, supernatant quality and fouling propensity. The study shows that low constraints (7 × 10⁻³ Pa) generated on submerged side-stream hollow fibre modules have no significant impact on sludge properties. In contrast, high shear stresses (72 Pa) associated with a crossflow configuration induce very significant modifications of the mixed liquor which increases its fouling propensity (measured in a standard filtration cell). A theoretical explanation of the role of turbulence on the floc size distribution is given. Based on a Kolmogorov microscale calculation, it seems possible to predict the mean floc size reached in both filtration systems, for a given shear stress intensity. Disaggregation is characterised by a two-step kinetic: first a short-term breakage attributed to fragmentation and loss of weak strength bonds, and secondly a longer-term breakage probably due to erosion phenomena and removal of high strength bonds. Only the second step induces a significant release and an accumulation of soluble protein-like substances. Soluble organic matter strongly enhances the fouling propensity of the mixed liquor. This seems to be amplified by the concentration of protein-like substances. The importance of considering the protein and carbohydrate content as well as floc size is also pointed out in the paper.     

Effect of solids retention time on structure and characteristics of sludge flocs in sequencing batch reactors

The effect of solids retention time (SRT) (4-20 d) on sludge floc structure, size distribution and morphology in laboratory-scale sequencing batch reactors receiving a glucose-based synthetic wastewater was studied using image analysis in a long-term experiment over one year. Floc size distribution (>10 microm) could be characterized by a log-normal model for no bulking situations, but a bi-modal distribution of floc size was observed for modest bulking situations. In each operating cycle of the SBRs, the variation in food /microorganisms ratio (0.03-1.0) had no significant influence on floc size distribution and morphology. The results from a long-term study over one year showed that no clear relationship existed between SRT and median floc size based on frequency. However, sludge flocs at the lower SRTs (4-9 d) were much more irregular and more variable in size with time than those at higher SRTs (16 and 20 d). The level of effluent-suspended solids at lower SRTs was higher than that at higher SRTs.     

垫江盐盆岩盐矿地质特征及资源潜力

垫江盐盆位于四川盆地东部,早中三叠世嘉陵江、雷口坡时期广泛接受蒸发型盐类沉积,在长寿—垫江—带形成了多期次岩盐沉积。通过对区内岩盐、油气钻井含盐系对比分析发现,垫江盐盆具有3个成盐期:下三叠统嘉陵江组四段二亚段(T_1J~(4-2))、四段四亚段(T_1J~(4-4))和中三叠统雷口坡组一段一亚段(T_2l~(1-1)),岩盐直接顶底板为硬石膏岩或杂卤石,从T_1J~(4-2)至T_2l~(1-1),岩盐沉积具有层数变多、厚度变薄、向北东方向缩小的趋势。另外,通过DTM分析编制的岩盐沉积等厚线图,为垫江盐盆岩盐资源潜力估算提供了可靠的依据,据估算垫江盐盆岩盐远景资源量约300亿t,其中未受构造影响区块资源量约230亿t。     

The characteristics of the bacterial community structure and population dynamics for phosphorus removal in SBR activated sludge processes

The characteristics of the bacterial community structure and population dynamics for phosphorus removal in activated sludge were investigated using laboratory-scale sequencing batch reactor (SBR) activated sludge processes fed with four different carbon sources. Phosphorus removal activity, quinone profile of the activated sludge and isolated bacterial strains were monitored. An enhanced phosphorus removal activity was accompanied by the increase in ubiquinone-9 (Q-9). The relationships between phosphorus removal activity and Q-9 contents of the isolated bacterial strains were dependent neither on the organic substrates nor on the species of isolated bacterial strains. The enhanced phosphorus removal capability of activated sludge seemed to be due to the increase in the populations of bacteria with activity of phosphorus removal, i.e. species succession of bacteria in activated sludge ecosystems, rather than the increase in the phosphorus removal capability of phosphorus removal bacteria. Not only Acinetobacter but also Pseudomonas identified from isolated strains were regarded as representative polyphosphates-accumulating organisms and predominant species to the whole of bacterial population in activated sludge for phosphorus removal.     

粤港澳大湾区惠州断裂特征及活动性研究

惠州断裂是惠州盆地的西边界断裂,横穿惠州市城区,前人对惠州断裂活动性的调查研究较薄弱。因此,厘定惠州断裂的构造特征和活动性,对惠州市的城市规划、基础设施建设及开发有着至关重要的意义。本文在野外地质构造调查解析、物探和钻探等工作基础上,结合第四纪地层年代学测试分析对惠州断裂展开研究工作。构造解析及钻孔揭露表明,惠州断裂为正断层,表现出了右行走滑的特征,具有明显的分带性,力学性质具张性、压扭性、张扭性多期次交替转换特征,对第四纪地貌具有控制作用。结合物探和第四纪地层年代学研究表明,惠州断裂错断了第四纪地层,其在晚更新世末期仍有活动,最新一次活动的时间应在距今10～(24±2)ka,可将惠州断裂定为活动断层。研究成果可为惠州市今后的城市工程选址、规划和建设提供重要的基础地质资料。     

河南申家沟铝土矿化学元素分布及特征研究

申家沟铝土矿位于河南省嵩箕铝(粘)土矿成矿区内。通过对申家沟铝土矿层典型剖面样品进行全岩测试分析,对各个单元层样品的常量、微量、稀土元素的地球化学特征进行研究,认为申家沟铝土矿具有低铝、高硅、含铁的特点,含铝岩层中轻稀土元素相对富集,申家沟铝土矿成矿物质来源为本溪组底板碳酸盐岩。     

Long-term storage conditions for carriers with denitrifying biomass of the fluidized, methanol-fed denitrification reactor of the Montreal Biodome, and the impact on denitrifying activity and bacterial population

The Montreal Biodome has a denitrification system to stabilize the nitrate concentration in its 3 million liter seawater aquarium. However, this microbial process has failed periodically due to various technical problems. The system can take several weeks to recover its full denitrification capacity. In order to provide the denitrification system with a backup of active biomass, different freezing conditions for the denitrifying biomass were tested. The biomass was conserved for 1 week-17 months at -20 degrees C with and without glycerol or at -80 degrees C with and without glycerol, and the denitrifying activity was tested in batch culture for 140 h periods at various intervals. Our results showed that glycerol was required for fast recovery of the microbial community's denitrifying activity. The -20 degrees C and -80 degrees C conservation temperatures with glycerol gave similar results although there was a short period of nitrite accumulation in the -20 degrees C sample. There were no substantial changes in the microbial community of any of the frozen samples after 17 months of conservation as monitored by denaturing gradient gel electrophoresis. This is the first report on the long-term conservation of a complex denitrifying population by freezing.     

河北坝上小滦河流域不同沉积单元粒度特征及其荒漠化的影响

河北坝上承德市小滦河流域位于浑善达克沙地东南缘,是我国主要的土地荒漠化区之一。本文通过对不同沉积单元的物质结构、粒度特征分析,探讨土地荒漠化的地质作用。研究发现,在河流侵蚀和沉积作用、风搬运和沉积作用地质营力作用下,形成砾、砂、粉砂、粘土河流相沉积物,砂质风成相沉积物及混合结构沉积物;划分出河流谷地就地起沙型、沙地内部就地起沙型、风沙侵入型3种荒漠化类型。建议在河道相砂砾石草-湿地单元可适当发展马铃薯和中药材等产业,风积相垄状裸露沙地单元需采取灌、草为主的生态修复和封育管控,河湖-风力混合草地单元要采取合理的放牧政策,避免沙漠化和草场的退化。     

青海洪水河锰矿床地质特征及成因探讨

洪水河锰矿位于东昆仑东端,大地构造位置上属秦祁昆造山系东昆仑弧盆系—北昆仑岩浆弧,北接柴达木地块,在成矿带的划分上属伯喀里克—香日德金-铅-锌-钼—石墨—萤石(Cu、稀有、稀土)成矿带。作者通过3年工作发现2条锰矿带,圈出锰矿体7条。在对洪水河锰矿床地质特征研究基础上,查明了锰矿成矿地质条件、控矿因素,成因属于沉积变质型,并建立了东昆仑成矿带沉积变质型锰矿床地质—地球物理找矿模型,确定中元古界狼牙山组为东昆仑锰矿重要含矿层位。     

青海泽库县晚三叠世尼玛隆—甘千花岗岩体地球化学特征及构造环境探讨

研究区位于青藏高原东北缘,西秦岭、祁连、东昆仑3个造山带的交汇部位,大地构造位置属印支造山带,同德—泽库弧后前陆盆地。岩浆活动以印支期中酸性岩浆岩最为发育。对该区晚三叠世尼玛隆—甘千花岗岩体利用LA-ICP-MS方法进行了锆石U-Pb同位素测年获得(225.9±1)Ma年龄值,表明岩体侵位于晚三叠世。岩石主量元素特征反应出明显的富碱、富钾特征,属中酸性岩体。岩体富集轻稀土,L/HREE=7.56～13.02,平均10.17;δEu=0.47～0.84,平均0.69,表明岩浆过程主要受部分熔融作用控制。微量元素分析显示岩体富集大离子亲石元素,花岗岩形成与同碰撞构造环境密切相关。初始岩浆的原岩来自早期岛弧火山岩的部分熔融,并且继承了早期岛弧火山岩的部分地球化学特征。     

甘肃龙首山成矿带芨岭铀矿床地质特征及找矿潜力分析

芨岭矿床位于龙首山成矿带中段,区内以发育钠交代热液型铀矿床而备受瞩目.在研究前人资料的基础上,结合近几年的铀矿勘查工作,本文对矿床的地质特征进行了系统总结,查明铀矿化受马路沟断裂构造、钠交代岩和热液蚀变三者共同控制.本文通过对该区成矿条件和最新勘查成果的分析,认为在芨岭矿床深部和外围有较好的成矿潜力,值得开展进一步铀矿...     

The Riverside and Berwyn experience: Contrasts in landscape structure, perceptions of the urban landscape, and their effects on people

Humans not only structure the landscape through their activities, but their perceptions of nature are affected by the spatial and temporal arrangements (structure) in the landscape. Our understanding of these interactions, however, is limited. We explored the relationship between landscape structure and peoples’ perceptions of nature in the Chicago, IL, USA, suburbs of Riverside and Berwyn because they offer contrasting paradigms of an urban landscape. Designed in the 1800s by Frederick Law Olmsted, Riverside has several unique design elements (curvilinear streets, ample setbacks, parkways of variable width with mowed grass and naturalistic groupings of trees) that define the structure and composition of this landscape. The urban forest was the keystone of Olmsted's desire to create a harmonious community characterized by “refined sylvan beauty”. In contrast, the adjacent community of Berwyn has right-angled streets with small lots and narrow setbacks for houses. Differences in landscape structure between the two communities produced differences in the diversity, size, and composition of woody vegetation. As measured by patch-size distribution, Riverside had greater diversity in landscape structure than Berwyn, and in turn, Riverside had greater diversity in the composition and size of the woody vegetation compared to Berwyn. Riverside tended toward a “natural” appearance with vegetation, while yards in Berwyn tended to be trimmed and edged. Significant differences between the mean ratings of Riverside and Berwyn respondents were found for six of seven community attribute categories. Riverside participants reported receiving greater benefit from the visual and nature-related features of the urban forest than did Berwyn respondents. Berwyn residents ranked social atmosphere for the community and locomotion (wayfinding) highest among the seven community attribute categories. Despite differences between the two communities, residents valued the green residential environment provided by vegetation. However, the more diverse urban landscape as measured by built structures, woody vegetation, and lot size and shape proved to be more satisfying to the residents of these two communities. The design concepts developed and implemented by Olmsted more than century ago in Riverside are still relevant to city planners striving to develop living environments that are satisfying to urban and suburban residents.     

内蒙古吉峰林场东区铅锌多金属矿地质特征及矿床成因

吉峰林场东区铅锌多金属矿区位于大兴安岭主脊铜铅锌银多金属成矿带中北段,塔河—吉峰深断裂带西侧。该矿已圈定铅锌多金属、金多金属两大矿化带,6条铅锌矿体、3条锌矿体、7条金矿体;矿化类型为铅锌多金属、金银多金属组合矿化;矿床成因类型初步认为属浅成低温热液、火山—次火山岩浆热液型矿床。铅锌银多金属成矿作用及金银成矿作用均属燕山晚期。矿区内岩浆、构造活动频繁强烈,矿化及蚀变作用强且普遍,成矿条件优越。     

The relationship between building characteristics and the chemical composition of surface films found on glass windows in Brisbane,Australia

Films found on the windows of residential buildings have been studied. The main aim of the paper was to assess the roles of the films in the accumulation of potentially toxic chemicals in residential buildings. Thus the elemental and polycyclic aromatic hydrocarbon compositions of the surface films from the glass windows of eighteen residential buildings were examined. The presence of sample amounts of inorganic elements (4.0–1.2 × 10⁶ μg m⁻²) and polycyclic aromatic hydrocarbons in the films (BDL - 620.1 ng m⁻²) has implications for human exposure and the fate of pollutants in the urban environment. To facilitate the interpretation of the results, data matrices consisting of the chemical composition of the films and the building characteristics were subjected to multivariate data analysis methods, and these revealed that the accumulation of the chemicals was strongly dependent on building characteristics such as the type of glass used for the window, the distance from a major road, age of the building, distance from an industrial activity, number of smokers in the building and frequency of cooking in the buildings. Thus, building characteristics which minimize the accumulation of pollutants on the surface films need to be encouraged.     

The effects of a chlorinated discharge and a thermal outfall on the structure and composition of the aquatic macroinvertebrate communities in the sheep river, Alberta, Canada

Physico-chemical and biological samples were collected from 12 sampling stations over a 13-month period to assess the effects of a small town's chlorinated sewage discharge and a thermal discharge on the Sheep River's macroinvertebrate communities. During the study, the chlorinated effluent plume was restricted to the left third of the channel for approx. 0.5 km at which point the effluent was thoroughly mixed due to an abrupt change in channel direction. Within the concentrated 0.5 km chlorinated plume, total residual chlorine TRC concentrations periodically exceeded 5.0 mg l⁻¹. Stations were categorized into similar community assemblages on the basis of species abundance and composition using heirarchical cluster analysis. Stations immediately downstream of the thermal outfall and those within the chlorinated plume had distinctly different structure and were dominated by Oligochaeta. Multiple discriminant analysis indicated that temperature was the principle discriminating variable immediately below the thermal discharge while the chlorinated sewage (MCSE) variable was the most important discriminant function within the chlorinated effluent plume. Following complete mixing of the effluent plume within the stream channel (0.6 km downstream of outfall), macroinvertebrate structure and diversity improved, presumably due to nutrient enrichment and dilution of TRC below detectable levels.     

The effects of variation in climatic temperature (1980–2001) on breeding activity and tadpole stage duration in the common toad, Bufo bufo

The effects of variation in climatic temperature on breeding behaviour and tadpole growth were investigated using data collected during a 22-year study of a single population of common toads, Bufo bufo, in southern England. Although the start of the breeding season each year, taken as the day when adult toads first arrived at their breeding pond in large numbers, showed no trend over time (1980–2001) it was highly correlated with climatic temperature. Thus, toads started breeding approximately 50 days earlier in the year following very mild winters (1993: February 2nd) compared with very cold ones (1986: March 23rd). Regression analysis of the relationship between the mean temperature of the 40 days immediately preceding the main arrival of toads at the breeding pond revealed that for every 1° increase (or decrease) the toads arrived 12 days earlier (or later). Although the duration of the tadpole stage was longer when spawning was early, toadlets still emerged from the pond earlier than when spawning was late. The increased length of the tadpole stage, in years when spawning was early, was due to an increase in the proportion of cold days when the minimum ground temperature was at or below 0 °C. Thus, the tadpole stage was approximately 6 days longer (or shorter) for every 5% increase (or decrease) in the proportion of cold days the tadpoles were exposed to.