高浓度悬浊液架桥絮凝分形体的形态学研究

对85kg／m^3的黄河泥沙水进行了高浓度悬浊液架桥絮凝沉降试验，考察了架桥絮凝分形体的形态学特性，并用电镜观察了絮体构造。结果表明，絮体结构及其形成过程具有分形特征；参数“分维D”可用于定量表征分形絮凝体的形态学特性：①絮体生长机制以DLCA与RLCA模式为主，其生长模式从快速混合阶段的分枝状DLCA结构逐步向慢速絮凝阶段的密实RLCA构型演变；②粒径分布在3个区域，其曲线形状类似广义的正态分布，“分维”能定量确定絮体密实性与沉降特性达最佳时的粒径范围；③分形结构的不断演变引起絮体内部渗透性显著不同，分形絮体自由沉降规律不能用Stokes定律进行合理解释；④在一定粒径范围内，絮体有效质量密度与Stokes粒径存在双对数线性关系，絮体的孔隙率是影响其密实性的主要原因；⑤对相同含沙量的泥沙水絮凝时，Al2（SO4）3形成的无机混凝剂絮体结构与高分子架桥絮体分形结构相比，具有絮体粒径小、结构脆弱，能承受的剪切强度G值低等特点。     

阳离子聚合物用于低温、低浊水处理及其絮凝形学特性

西安市曲江水厂低温、低浊水(T＜10℃、C0＜10 NTU)模拟试验中,投加阳离子型高分子聚合物,采用微絮凝-深床直接过滤技术、分形数学理论与图像分析技术,研究滤料粒径、原水浊度、原水温度、药剂种类、聚合物分子质量及投加量、混合强度等对处理效果的影响,对不同药剂低温、低浊水的絮凝形态学特性,絮体结构的分形特性及其作用机理进行分析,得出①当T＜4℃、C0＜4 NTU时,不宜单独采用Al2(SO4)3或PAC;当4.5℃＜T＜10℃、C0＜10 NTU时,只投加Al2(SO4)3或PAC时,宜用细砂过滤;②聚合物作絮凝剂宜用粗砂过滤;③单独用聚合物作絮凝剂宜投加分子质量较低的弱阳性或低剂量较高分子质量的强阳性聚合物;用作助凝剂宜投加强阳性或增加弱阳性聚合物剂量,且能显著减少主混凝剂用量;④阳离子聚合物兼备电性中和与吸附架桥絮凝机理,能形成粒径较大、吸附性能与过滤性能良好的网状絮体结构,且能显著减少污泥体积,污泥沉降与脱水效果好,但分维值低.     

水力紊动条件对含沙高浊水絮体分形结构的影响

在含沙量为85 kg/m3的悬浊液中投加阳离子高分子聚合物,改变水力紊动条件速度梯度G与剪切絮凝时间t,借助沉降技术、图像分析技术及分形特性定量表征参数"分维"探讨了架桥絮体结构的动态演变特性,得出①絮体分形结构从快速混合阶段疏松多孔、开放的分枝状DLCA模式逐步向慢速絮凝阶段密实的RLCA模式演变,在絮凝时间为180 s时出现最佳构型,随后结构密实性有微小降低的趋势;②絮体的最佳分形结构只能维持一段时间;③分形结构达最佳状态时的水力紊动强度Gt值存在两个临界值快速混合阶段G1t1=2 350±100,慢速絮凝阶段G2t2=12 420±100;④不同含沙量架桥絮体分形结构致密度最高时所需的最佳Gt值相近.但含沙量越低,搅拌速率r或速度梯度G值应降低,絮凝时间t值需增加,絮团内部孔隙率增加,分维值下降.     

微生物和化学絮凝剂复配形成絮体的分形特征

将微生物絮凝剂分别与无机絮凝剂AlCl3和FeCl3复配,考察了在不同配比条件下处理高浊度和低浊度水时所形成絮体的分形特征。结果表明,对于高浊水,当微生物絮凝剂与AlCl3的投量分别为10mL／L和2mL／L,或微生物絮凝剂与FeCl3的投量分别为10mL／L和0．5mL／L时,出水水质稳定且处理效果最优;处理低浊水时,若微生物絮凝剂与AlCl3复配则其最佳投量分别为5mL／L和1mL／L,若与FeCl3复配则其最佳投量分别为5mL／L和0．25mL／L。无论处理高浊水还是低浊水,处理效果及稳定性达最优时絮体的分形维数均在1．4-1．6之间。     

聚丙烯酰胺对水厂污泥脱水性能影响的研究

通过观察不同絮凝剂形成絮体的情况、絮体沉淀效果、对沉降速度的测定,研究了阴阳离子不同相对分子质量聚丙烯酰胺（PAM）对水厂污泥脱水性能的影响。结果表明,阴、阳聚丙烯酰胺因其具有吸附架桥的作用,能够改变污泥絮体结构,能够提高污泥的脱水和沉降性能,其脱水和沉降性能与阴阳离子和相对分子量有密切的关系。     

微涡旋絮凝在宁夏某水厂改造中的应用评价

采用传统折板絮凝池处理低浊水时面临絮体沉降性差、“跑矾”等现象.为解决上述问题,宁夏某水厂采用微涡旋絮凝工艺对折板絮凝池进行升级改造,但改造完成后的运行效果仍不理想.通过分析对比微涡旋絮凝池和折板絮凝池中的颗粒数、浊度、絮体沉降体积、分形维数、分子荧光光谱等,讨论现有微涡旋改造的不足,并建立一套评价体系,以指导水厂的升级改造.试验结果表明:经过微涡旋改造后除第二絮凝段外,其他各段对浊度的去除率分别提高了8.7％、6.7％、6.5％、56.1％,絮体颗粒数分别降低了20.8％、14.7％、25.2％、48.4％;第二絮凝段由于布水方式和填加微涡旋球过多(水力扰动过大、短流)等问题,使得絮体的形成受到影响,对浊度和颗粒数的去除率相比折板絮凝池无明显提高.所采用的评价指标能够评价水厂微涡旋改造,具有广泛的应用性,为今后水厂的升级改造提供了良好的评价体系.     

纳米SiO_2用于含表面活性剂原水的处理

在含表面活性剂十二烷基硫酸钠(SDS)的低浊(6 NTU)高岭土原水中,投加纳米SiO_2进行动态混凝与静沉试验,借助图像分析技术与定量控制参数,探讨了纳米SiO_2的作用效果与形态学特性.结果表明:絮体的形成与生长具有分形特征,分形结构是影响颗粒混凝、絮团密实度与沉降特性的主要因素;SDS的存在对絮凝初期絮体的形成起阻碍作用,随后SDS与混凝剂的混合体共同对粒子作用,促进絮凝,絮体变大且密实,沉降性能改善;SDS和SiO_2对高岭土粒子存在竞争吸附;单独投加纳米SiO_2时形成的絮体小而脆弱,而以纳米SiO_2为助凝剂能促使PAC絮体结构向更密实的构型转变,对浊度和SDS的去除率提高.     

水泥-石灰石粉浆体絮体生长多重分形特征

采用多重分形理论描述了水泥-石灰石粉浆体絮体生长的分布特征,探讨了浆体絮体生长特征与多重分形谱特征参数的关系.结果 表明:随着颗粒总比表面积(SSA)的增加,絮体间的小空隙与大空隙数目增加,絮体分布变分散,小粒径絮体数目减小,大粒径絮体数目稳定,絮体尺寸减小,整体上延缓了絮体生长,而随着SSA的继续增加,絮体生长呈现相反的结果;水泥-石灰石粉浆体絮体生长具有多重分形特征,谱宽、左谱宽和右谱宽可表征絮体生长的空间分布,且谱宽的准确性更高;谱差与左谱值可描述絮体生长的尺寸分布,且谱差的准确性更高.     

南方低浊高藻水的网格絮凝工艺优化

南方水库水多呈低浊高藻特征，根据速度梯度理论设计的传统网格絮凝池对其处理时存在一定的局限性。依据微涡漩理论对传统网格絮凝池进行了改造，结果表明它能降低沉后水浊度，提高对CODMn和藻类的去除效率。等效粒径和分形维数的研究结果表明，改型池内形成的絮体粒径大且密实、沉降性好，此外改型池的水头损失和药耗也较低。     

有机羧酸对硫酸铝混凝絮体特性的影响分析

原水中有机物的成分对混凝絮体特性的影响直接关系到混凝工艺的处理效果。以草酸和柠檬酸为研究对象,分析了混凝过程中有机羧酸的存在对混凝过程形成的絮体颗粒大小、分形维数、Zeta电位的影响。结果表明:当有机羧酸浓度在一定范围内时,随着其浓度的增加,絮体颗粒的Zeta电位及分形维数降低,同时絮体颗粒的成长速率及其稳定成长后的大小均呈下降趋势,并且柠檬酸带来的这种抑制作用更加显著,这是因为有机羧酸占据了微絮体表面而导致絮体活性及致密性降低。     

水泥净浆絮凝结构研究

通过试验研究了掺加超塑化剂前后水泥净浆流动度的变化,并结合光学显微镜观察相应的水泥絮凝结构,讨论了微观絮凝结构与宏观流动度的联系.得出结论,水泥的絮凝结构中确实包裹了大量的自由水,严重影响了水泥的流动性.同时还应用分形理论得出水泥絮团属于典型的分形结构,其分形维数为1.846 8.     

Settling velocities and permeabilities of microbial aggregates

The hydrodynamics of microbial aggregates, including settling velocity and permeability features, were investigated through detailed settling experiments. Microbial aggregates ranging from 1.0 to 2.5 mm were generated in a lab-scale sequencing batch reactor (SBR) and also collected from a full-scale activated sludge (AS) treatment process. An apparatus of vertically connected double settling columns, filled with solutions of different densities, was used to measure the settling velocities and thus to characterise the internal permeation of individual microbial aggregates. It was demonstrated that the microbial aggregates were highly porous and fractal. However, their settling velocities observed in deionised water, EDTA and NaCl solutions were only slightly faster than predicted by Stokes' law for identical but impermeable particles. The fluid collection efficiencies calculated from measured settling velocities were less than 0.10 for most microbial aggregates, which was much lower than those previously determined for non-biological aggregates of latex microspheres. It is suggested that microbial aggregates could have a largely reduced permeability, as the pores between the microorganisms in the aggregates may be clogged by the cell's exopolymeric material with the water retained.     

Settling Behaviour and Clay Mineralogy

Sedimentary soils are formed due to the process of settling of soil particles in suspension. The settling process is physico-chemical in nature as the soil contains chemically active clay minerals. The extent to which the clay mineralogy affects the settling process depends upon the initial water content of the soil-water suspension. For montmorillonitic soils, the limiting water content at which the nature of settling changes from a discrete free type to a flocculated free type increases with an increase in the soil plasticity and decreases with an increase in the soil plasticity for kaolinitic soils. While the diffuse double layer repulsion controls this kind of behaviour of montmorillonitic soils, the behaviour of kaolinitic soils can be attributed to the fabric effect.     

基于数字图像处理技术的沥青混合料分形特性

基于数字图像处理技术,以直观的沥青混合料体积组成为研究对象开展了沥青混合料的分形特性研究.分析说明了沥青混合料中的集料颗粒、空隙和矿料间隙都具有典型的分形特性,并给出了相应的分形维数计算方法.试验结果表明,采用小岛法可以定量描述集料颗粒和空隙的分形特性,利用计盒维数法能够描述荷载作用下沥青混合料中矿料间隙的分形特性.     

黄河高浊度水沉淀池排泥管道阻力计算

由于设计规范中对黄河高浊度水的沉淀池排泥管道阻力计算未作出规定，故有必要在分析黄河高浊度水沉淀池排泥浆体特点的基础上进行试验。结果表明，杜兰德公式不适用于沉淀池排泥浆体的计算，分别给出了未经预处理及经过预处理的黄河高浊度水沉淀浆体管道阻力计算公式，并计算出工程设计中常用钢管管径的管道阻力。     

Errors in bound water measurements using centrifugal settling method

Centrifugal settling method (CSM) is commonly used to estimate the bound water content in sludges. The sludge sediment matrix should be purely plastic for accurate measurements to the bound water content. This communication, however, addressed for the first time that, owing to the inhibited elasticity of the sludge matrix, sediment height rebound was commonly observed for the flocculated sludge. Also, different sludges could have distinct elastic responses after centrifugation. There existed no simple correlation to incorporate the elastic rebound of sludge sediment in bound water measurement. The possible errors incorporated into CSM for measuring bound water contents were highlighted.     

Polymer flocculation mechanism in animal slurry established by charge neutralization

Flocculation and filtration of animal manure is practically and environmentally beneficial. However, the flocculation mechanism in manure need to be clarified to use the technique efficiently rather than relying on trial-and-error. Manures were flocculated with polyacrylamides. Floc size, dewaterability, dry matter and turbidity were measured. At optimal polymer volume, the charge neutralization was determined, i.e. amount of negative manure particle charge neutralized by positive polymer charge. The optimal cationic polymer properties were linear and very high molecular weight, which caused efficient particle catching. And it had medium charge density, which caused efficient particle attachment. The required charge neutralization was 5-23% (15% for the optimal polymer). Polymer bridging proved the dominant flocculation mechanism; patch flocculation may be slightly significant for some polymers, while coagulation proved insignificant. Manure’s high ionic strength, high dry matter content and highly charged small molecules caused bridging to be more dominant in manure than in other typically flocculated media.     

Permeability of fractal aggregates

It is well known that the permeability and density of an aggregate decreases with its size, affecting its settling velocity and coagulation rate (rate of particle capture) with other particles. This change in aggregate density with size can be described by fractal scaling relationships. Two distinctly different fractal scaling approaches, however, have been used to describe aggregate permeability. In one approach (single-particle-fractal model), the permeability is calculated by assuming primary particles are uniformly distributed in the aggregate. In the other approach (cluster-fractal model), it is assumed that aggregates are composed of primary particles separated into individual clusters that are less permeable than the aggregate. The overall permeability of the aggregate is dependent on the number and sizes of these clusters. Using three different permeability correlations (Brinkman, Happel and Carmen-Kozeny), it is demonstrated through comparison with aggregate settling velocity data that the single-particle-fractal model does not provide realistic predictions of settling velocity as a function of aggregate size. In addition, it is shown that the Carmen-Kozeny permeability equation does not produce realistic settling velocity relationships. The transport settling velocity and capture rate of sinking aggregates in natural and engineered environments should therefore only be calculated using the Happel or Brinkman equations and a cluster-fractal model.     

Colour and turbidity removal with reusable magnetic particles—II. coagulation with magnetic polymer composites

Composite particles containing magnetic iron oxides in an insoluble polymeric matrix were used to enhance the coagulation of a turbid, coloured river water. Uncharged magnetic particles increased the turbidity removal at a given alum dose, or alternatively achieved a desired level of turbidity removal at a lower alum dose. Rates of floc formation and settling were approximately double those obtained with alum alone. Grafting linear polymers to the magnetic particles increased their effectiveness. The uncharged particles could be reused after simply washing with water. Magnetic particles with grafted chains of cationic polymers, when used in conjunction with alum, gave excellent removal of colour and turbidity and rapid settling, but required brine for regeneration. These materials were also effective in coagulating algae. When used in high doses without alum, the cationic magnetic particles initially gave good turbidity and colour removal from river water, but could not be completely regenerated