摘要
活性污泥处理工艺是最广泛应用的废水生物处理技术。研究活性污泥的絮凝动力学，分析絮凝形成絮体的粒径分布及其演化过程、影响因素，对于完善活性污泥流体动力学，理解反应池中的污泥分布和二沉池中的泥水分离情况，以及研究江河、湖泊、海岸中自然絮体的形成与聚集等，都具有重要意义。
基于群体平衡（Population Balance）的活性污泥絮凝动力学是在絮体质量和数量守恒的假设下研究絮凝过程中絮体的粒径分布及其变化，目前还存在一些需要解决的问题和改进的方面，如有效的絮体聚并效率模型和子颗粒粒径分布函数的构建，絮体粒径分布随时间演化过程的模拟，影响絮凝的关键因素（如EPS含量和Zeta电位）与絮凝动力学参数间的关系等。为此，本论文进行了以下的研究：
①应用激光粒度仪测量了好氧活性污泥絮体在絮凝过程的粒径分布，研究了速度梯度、VSS/SS、EPS含量及Zeta电位对絮体粒径分布的影响。结果表明：絮体平均粒径与速度梯度显著负相关，与Kolmogrov尺度数量级基本相当，其间差异性与污泥VSS/SS、絮体强度等有关；相同的速度梯度下，絮体平均粒径与VSS/SS或EPS含量显著正相关，与Zeta电位负相关；有机质和EPS会增强絮凝效果，EPS中蛋白质比多糖对絮凝的促进作用更明显。
②应用显微图像分析方法，计算得到活性污泥絮体的分形维数。结果表明：絮体二维分形维数与VSS/SS（或EPS含量）负相关，且与絮体的层次结构有关（大絮体与小絮体的分形维数有差异）；活性污泥絮体三维分形维数与絮体粒径负相关，符合幂函数关系式。
③改进了基于群体平衡的活性污泥絮凝动力学模型：提出了由絮体破碎形成的子颗粒的二项式分布函数，用二项式分布参数Cp表征絮体破碎的主要方式（破裂或侵蚀）；在模型参数校核中，提出“平衡因子”——即破碎系数A与聚并效率α的比，不仅减少了模型需要校核的参数数量，更有助于简捷地实现絮凝过程中絮体粒径分布随时间演化过程的模拟。模拟结果表明：1）模型能够较好地模拟絮凝过程中絮体的粒径分布及其演化过程；2）平衡因子与平均速度梯度呈幂函数关系，随着速度梯度的增加而增加；3）聚并效率与平均速度梯度呈幂函数关系，随着速度梯度的增加而减小；4）破碎系数仅与污泥类型有关，与速度梯度无关；5）絮体颗粒区间划分数量不影响参数校核结果，区间划分数量愈多，絮体粒径分布的模拟精度愈高；6）子颗粒二项式分布较二元分布对絮体粒径分布的模拟精度更高。
④对絮体聚并效率模型和破碎频率模型进行了研究和修正，结果表明：1）与聚并效率为常数相比，认为聚并效率与絮体粒径差有关的Friedlander模型和Pruppacher and Klett模型可提高絮体粒径分布的模拟精度；2）文中所构建的Pruppacher and Klett修正模型可以适用于不同速度梯度时絮体粒径分布演化过程的模拟；3）Kusters破碎频率模型较Pandaya and Spielman破碎频率模型可改善大粒径絮体的体积分数分布模拟，实现平均粒径的准确模拟；4）假设絮体的破碎频率与最大粒径成正比，且存在一个最大的破碎频率，文中所构建的Pandaya andSpielman修正模型，可实现絮体粒径分布和平均粒径的同时准确模拟。
⑤基于絮凝动力学模型，分析了影响活性污泥絮凝的关键因素（EPS含量和Zeta电位）与絮凝动力学参数间的关系，结果表明：1）平衡因子A/α与EPS含量或Zeta电位线性负相关；EPS含量愈大或Zeta电位愈小，A/α愈小，更有利于絮凝，絮体的平均粒径愈大；2）子颗粒二项式分布可以更好地描述不同EPS含量或Zeta电位的絮体粒径分布的宽度；二项式分布参数Cp与EPS含量或Zeta电位线性正相关，说明不同EPS含量或Zeta电位的活性污泥絮体的破碎方式可能存在差异——当EPS含量增加时，絮体的破碎方式可能由侵蚀为主逐渐演变为破裂为主；添加Al3+时絮体可能以侵蚀的破碎方式为主，絮体的稳定性较强；添加Ca2+时絮体可能以破裂的破碎方式为主，絮体的稳定性较弱；相对于Ca2+，Al3+对絮凝的促进作用更为显著。
Activated sludge process has been widely used in wastewater biological treatment.Study on the flocculation dynamics of activated sludge, which focuses on the evolutionand effect factors of Floc Size Distribution (FSD) during flocculation process, has greatsignificance to the development of activated sludge fluid dynamics, the understandingof the distribution and sedimentation behavior of activated sludge in reactor orsedimentation tank and the investigation of the aggregation and formation of flocs innatural rivers, lakes and coasts.
Flocculation dynamics of activated sludge based on population balance frameworkaims at the evolution of FSD during flocculation process under the assumption of theconservation of mass and quantity of flocs. However, some problems in this fieldremain unresolved and further research is needed, including the effective model forcollision efficiency and daughter particle distribution function, the modelling of theevolution of FSD during flocculation process, and the relationship between kineticparameters of kernel structures for aggregation and breakage and the key factors (EPScontent and Zeta potential) that affect the flocculation. In this thesis, the followingwork was conducted and conclusions were drawn:
①FSD of aerobic activated sludge during flocculation process was measured bylaser particle size analyzer, and the influence of velocity gradient, VSS/SS, EPScontent and Zeta potential on FSD was investigated. The results showed that the flocvolume-average size was negatively correlated to velocity gradient, and theorder-of-magnitude of the floc volume-average size was equivalent to that ofKolmogorov scale (their differences were depended on sludge VSS/SS, floc strengthand etc). As fixing velocity gradient, the floc volume-average size was positivelycorrelated to VSS/SS and EPS, whereas negatively to Zeta potential. Organic matterand EPS play important roles on the flocculation of activated sludge by enhancing thefloc strength and improving the flocculation effect. Compared with polysaccharide,protein in EPS seems to be more beneficial to the flocculation of activated sludge.
②The equivalent and maximium diameter of aerobic activated sludge floc weredetermined using microscopy and image analysis and thus the2D fractal dimension D2were obtained by fitting the maximum diameter and equivalent diameter. It was foundthat2D fractal dimension was negatively related to VSS/SS (or EPS content), and seemed to be related to the level of floc structure (there are non-ignorable differencesbetween the fractal dimension of large floc and that of small ones). The3D fractaldimension of aerobic activated sludge was also negatively related to floc size,displaying a power function form.
③Different from the previous studies, the population balance framework-basedmodel of flocculation dynamics were modified as follows:(i) according to theknowledge that the floc were form through the aggregation of basic particles, abinomial distribution function was proposed for daughter particle distribution due tobreakage and the parameter Cpof binomial distribution was used to characterise themain mechanism of breakage, erosion or splitting;(ii)“balance factor”, defined as theratio of breakage coefficient (A) to collision efficiency (α), was proposed for thecalibration of the model, which contributes to the reduce of the parameters needed tobe calibrated and the efficient simulationof the evolution of FSD. The simulationresults show that:(i) not only the FSD of activated sludge at stable states, but also theevolution of FSD during flocculation process could be simulated well;(ii) the balancedfactor displays power function relation to the average velocity gradient, increasing withthe increasing average velocity gradient,(iii) collision efficiency determines the speedof the flocculation process, and diaplays power function relation to average velocitygradient, decreasing with the increasing average velocity gradient;(vi) breakagecoefficient seems only related to the character of activated sludge not velocity gradient;(v) geometric grid factor (or number of classes) used in discretization equation of PBMhas not affect the calibrated value of balanced factor, and more accurate results isobtained with more geometric grids;(iv) compared with binary distribution, moreaccurate results was obtained with binomial distribution.
④The models for collision efficiency and breakage frequency were investigatedand modified. It was concluded that:(i) compared with the rectilinear model, whichsupposed collision efficiency is constant, the curvilinear models treating collisionefficiency as the function of particle size ratio, proposed by Friedlander (1965) andPruppacher and Klett (1978), could improve simulation accuracy of FSD;(ii) themodified Pruppacher and Klett (1978) model could be used to simulate the evolution offloc average size during flocculation process;(iii) Kusters (1991) model for breakagefrequency could improve simulation accuracy of large-size floc distribution, andsimulate the evolution of floc average size well;(vi) By supposing that breakagefrequency has positive correlation with the maximum size of floc and increases with floc size until arriving at a maximum value, the modified Pandaya and Spielman (1983)model for breakage frequency was proposed and not only the evolution of FSD but alsothat of floc average size during flocculation process at different velocity gradient couldbe simulated well by this model.
⑤The relationship between the parameters of flocculation dynamics and somekey factors (EPS content and Zeta potential) affecting the flocculation was investigatedusing the model of flocculation dynamics. It was found that:(i) The balanced factor(A/α) is positively correlated to EPS content or Zeta potential, decreasing with theincreasing EPS content or the decreasing Zeta potential (in absolute value); averagevelocity gradient with the later and EPS present significant linear inverse proportionrelationship; the smaller value of balanced factor, the more beneficial to flocculationand the lager floc average size obtained;(ii) the wide or narrower shape of FSD withdifferent EPS content or Zeta potential could be simulated very well using the binomialdistribution for daughter particle, and the parameter Cpof binomial distribution ispositively related to EPS content or Zeta potential, which indicates that breakagemechanism of different activated sludge may be not the same (activated sludge floccontaining high EPS content seems to represent splitting mechanism, whereas thatcontaining low EPS content seems to represent erosion mechanism; activated sludgefloc adding Al3+has strong stability and seems to represent erosion mechanism,whereas that adding Ca2+has weakly stability and seems to represent splittingmechanism).
引文
董峰,张捍民,杨凤林.数学模拟好氧颗粒污泥的形成及水力剪切强度对颗粒粒径的影响[J].环境科学,2012,33(01):181-190.
冯骞,薛朝霞,汪翔.水流剪切力对活性污泥特性影响的试验研究[J].河海大学学报:自然科学版,2006,34(4):374-377.
金鹏康,王晓昌.腐殖酸絮凝体的形态学特征和混凝化学条件[J].环境科学学报,2001,21(增刊):23-29.
李冬梅,施周,梅胜等.2006.絮凝条件对絮体分形结构的影响[J].环境科学,27(3):488-492.
李振亮.基于VOF法的絮凝搅拌器流场数值模拟[J].科学技术与工程,2013,13(20):6007-6010.
刘翔,黄映恩,刘燕等.活性污泥和生物膜的胞外聚合物提取方法比较[J].复旦学报:自然科学版,2011,50(5):556-562.
龙腾锐,龙向宇,唐然等.胞外聚合物对生物絮凝影响的研究[J].中国给水排水,2009,25(243):30-34.
南军,贺维鹏,李圭白.絮凝过程絮体粒度分布特征及流场仿真[J].北京工业大学学报,2010,36(03):353-358.
苏军伟,顾兆林, Xu X Yun.离散相系统群体平衡模型的求解算法[J].中国科学:化学,2010,40(02):144-160.
王浩宇,苏本生,黄丹等.好氧污泥颗粒化过程中Zeta电位与EPS的变化特性[J].环境科学,2012,33(5):1614-1620.
王铁峰.气液-浆-反应器流体力学行为的实验研究和数值模拟[D].北京:清华大学,2004.
王毅力,黄承贵.好氧污泥絮体与厌氧颗粒污泥的剪切稳定性分析[J].中国环境科学,2009,29(04):380-385.
张兰河,李军,郭静波. EPS对活性污泥絮凝沉降性能与表面性质的影响[J].化工学报,2012,63(6):1865-1871.
钟润生,张锡辉,肖峰等.絮体分形结构对沉淀速度影响研究[J].环境科学,2009,30(08):2353-2357.
周琪,林涛,谢丽等.污水处理生物絮体絮凝沉淀机理分析的综述[J].同济大学学报(自然科学版),2009,37(1):78-93.
Adler P. Heterocoagulation in shear flow[J]. Journal of Colloid and Interface Science,1981,83(1):106-115.
Andreadakis A D. Physical and chemical-properties of activated-sludge floc[J]. Water Research,1993,27(12):1707-1714.
Antunes E, Garcia F, Ferreira P, et al. Modelling PCC flocculation by bridging mechanism usingpopulation balances: Effect of polymer characteristics on flocculation[J]. Chemical EngineeringScience,2010,65(12):3798-3807.
Badireddy A R, Chellam S, Gassman P L, et al. Role of extracellular polymeric substances inbioflocculation of activated sludge microorganisms under glucose-controlled conditions[J].Water Research,2010,44(15):4505-16.
Biggs C and Lant P. Activated sludge flocculation: on-line determination of floc size and the effectof shear[J]. Water Research,2000,34(9),2542–2550.
Biggs C and Lant P. Modelling activated sludge flocculation using population balances[J]. PowderTechnology,2002,124(3):201-211.
Bonanomi E, Sefcik J, Morari M, and Morbidelli M. Analysis and control of a turbulentcoagulator[J]. Industrial&Engineering Chemistry Research,2004,43(19):6112-6124.
Bridgeman J, Jefferson B, and Parsons S. Assessing floc strength using CFD to improve organicsremoval[J]. Chemical Engineering Research&Design,2008,86(8A):941-950.
Bridgeman J, Jefferson B, and Parsons S. Computational fluid dynamics modelling of flocculation inwater treatment: A review[J]. Engineering Applications of Computational Fluid Mechanics,2009,3(2):220-241.
Bruus J H, Nielsen P H, and Keiding K. On the stability of activated-sludge flocs with implicationsto dewatering[J]. Water Research,1992,26(12):1597-1604.
Bushell G C, Yan Y D, Woodfield D, et al. On techniques for the measurement of the mass fractaldimension of aggregates[J]. Advances in Colloid and Interface Science,2002,95(1):1-50.
Calabrese R, Wang M, Zhang N, and Gentry J. Simulation and analysis of particle breakagephenomena[J]. Chemical Engineering Research&Design,1992,70(A2):189-191.
Camp T and Stein P. Velocity gradients and internal work in fluid motion. Journal of the BostonSociety of Civil Engineers,1943,30(4),219–237.
Clark M and Flora J. Floc restructuring in varied turbulent mixing[J]. Journal of Colloid andInterface Science,1991,147(2):407-421.
Coufort C, Bouyer D, and Line A. Flocculation related to local hydrodynamics in a taylor-couettereactor and in a jar[J]. Chemical Engineering Science,2005,60(8-9):2179-2192.
Coufort C, Bouyer D, Liné A, et al. Modelling of flocculation using a population balance equation[J].Chemical Engineering and Processing,2007,46(12):1264-1273.
Coufort C, Dumas C, Bouyer D, et al. Analysis of floc size distributions in a mixing tank. ChemicalEngineering and Processing,2008,47:287-294.
De Clercq J, Nopens I, Defrancq J, et al. Extending and calibrating a mechanistic hindered andcompression settling model for activated sludge using in-depth batch experiments[J]. WaterResearch,2008,42(3):781-791.
Ding A, Hounslow M, and Biggs C. Population balance modelling of activated sludge flocculation:Investigating the size dependence of aggregation, breakage and collision efficiency[J].Chemical Engineering Science,2006,61(1):63-74.
Ducoster J. A two-scale PBM for modeling turbulent focculationin water treatment processes.Chemical Engineering Science,2002,57(1):2157-2168.
Dupont R and Dahl C. A one-dimensional model for a secondary settling-tank includingdensity-current and short-circuiting[J]. Water Science and Technology,1995,31(2):215-224.
Eriksson L and Alm B. Study of flocculation mechanisms by observing effects of a complexingagent on activated-sludge properties[J]. Water Science and Technology,1991,24(7):21-28.
Fenu A, Guglielmi G, Jimenez J, et al. Activated sludge model (ASM) based modelling ofmembrane bioreactor (MBR) processes: A critical review with special regard to mbrspecificities[J]. Water Research,2010,44(15):4272-4294.
Flesch J, Spicer P, and Pratsinis S. Laminar and turbulent shear-induced flocculation of fractalaggregates[J]. AIChE Journal,1999,45(5):1114-1124.
Fluent Incorporated. FLUENT6.1User’s Guide[M]. Fluent Incorporated,2006.
Francois R, Van Haute A. Structure of hydroxide flocs [J]. Water Research,1985,19(10):1249-1254.
Friedlander S K. Mass and heat transfer to single spheres and cylinders at low Reynolds number[J].Americal Institute of Chemical Engineers,1957,3(1):43-48.
Govoreanu R. Modelling the activated sludge flocculation process: on-line measurementmethodology and modelling [D]. Gent: Universiteit Gent,2004.
Grasso D, Subramaniam K, Butkus M, et al. A review of non-dlvo interactions in environmentalcolloidal systems[J]. Reviews in Environmental Science and Biotechnology,2002,1(1):17-38.
Grau P, Vanrolleghem P, and Ayesa E. BSM2plant-wide model construction and comparativeanalysis with other methodologies for integrated modelling[J]. Water Science and Technology,2007,56(8):57-65.
Gregory J. The density of particle aggregates[J]. Water Science and Technology,1997,36(4):1-13.
Grijspeerdt K and Verstraete W. Image analysis to estimate the settleability and concentration ofactivated sludge[J]. Water Research,1997,31(5):1126-1134.
Guan J, Waite T, Amal R. Rapid structure characterization of bacterial aggregates[J]. EnvironmentalScience&Technology,1998,32(23):3735–3742.
Guo L, Zhang D, Xu D, et al. An experimental study of low concentration sludge settling velocityunder turbulent condition[J]. Water Research,2009,43(9):2383-2390.
Han M and Lawler D F. The (relative) insignificance of G in flocculation[J]. Journal AmericanWater Works Association,1992,84(10):79-91.
Henze M. Biological wastewater treatment: Principles, modelling and design[M]. London: IWAPublishing,2008.
Hounslow M, Ryall R, and Marshall V. A discretized population balance for nucleation, growth, andaggregation[J]. AIChE Journal,1988,34(11):1821-1832.
Hulburt H and Katz S. Some problems in particle technology. a statistical mechanical formulation[J].Chemical Engineering Science,1964,19(8),555–574.
Jorand F, Zartarian F, Thomas F, et al. Chemical and structural (2D) linkage between bacteria withinactivated-sludge flocs[J]. Water Research,1995,29(7):1639-1647.
Khelifa A and Hill P S. Models for effective density and settling velocity of flocs[J]. Journal ofHydraulic Research,2006,44(3):390-401.
Kramer T and Clark M. Influence of strain rate on coagulation kinetics[J]. Journal of EnvironmentalEngineering,1997,123(5),444-452.
Kumar J, Peglow M, Warnecke G, et al. Improved accuracy and convergence of discretizedpopulation balance for aggregation: The cell average technique[J]. Chemical EngineeringScience,2006,61(10):3327-3342.
Kumar S and Ramkrishna D. On the solution of population balance equations by discretization—I. Afixed pivot technique[J]. Chemical Engineering Science,1996a,51(8):1311-1332.
Kumar S and Ramkrishna D. On the solution of population balance equations by discretization—II.A moving pivot technique[J]. Chemical Engineering Science,1996b,51(8):1333-1342.
Kumar J and Warnecke G. Convergence analysis of sectional methods for solving breakagepopulation balance equations-i: The fixed pivot technique[J]. Numerische Mathematik,2008a,111(1):81-108.
Kumar J and Warnecke G. Convergence analysis of sectional methods for solving breakagepopulation balance equations-ii: The cell average technique[J]. Numerische Mathematik,2008b,110(4):539-559.
Kusters K. The influence of turbulence on aggregation of small particles in agitated vessels[D].Netherlands: Technische Universiteit Eindhoven,1991.
Kusters K, Wijers J, and Thoenes D. Aggregation kinetics of small particles in agitated vessels[J].Chemical Engineering Science,1997,52(1):107-121.
Le Moullec Y, Gentric C, Potier O, et al. Comparison of systemic, compartmental and cfd modellingapproaches: Application to the simulation of a biological reactor of wastewater treatment[J].Chemical Engineering Science,2010,65(1):343-350.
Lee G, Yoon E S, Lim Y I, et al. Adaptive mesh method for the simulation of crystallizationprocesses including agglomeration and breakage: The potassium sulfate system[J]. Industrial&Engineering Chemistry Research,2001,40(26):6228-6235.
Li D H and Ganczarczyk J. Fractal geometry of particle aggregates generated in water andwaste-water treatment processes[J]. Environmental Science&Technology,1989,23(11):1385-1389.
Li D H and Ganczarczyk J. Structure of activated sludge flocs[J]. Biotechnology and bioengineering,1990,35(1):57-65.
Li D H and Ganczarczyk J. Factors affecting dispersion of activated sludge flocs[J]. WaterEnvironment Research,1993,65(3):258-263.
Li H, Wen Y, Cao A, et al. The influence of additives (Ca(2+), Al(3+), and Fe(3+)) on theinteraction energy and loosely bound extracellular polymeric substances (EPS) of activatedsludge and their flocculation mechanisms[J]. Bioresource Technology,2012,114:188-194.
Li X Y and Logan B. Collision frequencies between fractal aggregates and small particles in aturbulently sheared fluid[J]. Environmental Science&Technology,1997a,31(4):1237-1242.
Li X Y and Logan B. Collision frequencies of fractal aggregates with small particles by differentialsedimentation[J]. Environmental Science&Technology,1997b,31(4):1229-1236
Li X Y and Yang S F. Influence of loosely bound extracellular polymeric substances (EPS) on theflocculation, sedimentation and dewaterability of activated sludge[J]. Water Research,2007,41(5):1022-30.
Li X Y and Yuan Y. Collision frequencies of microbial aggregates with small particles bydifferential sedimentation[J]. Environmental Science&Technology,2002,36(3):387-93.
Li Z L, GUO L S, ZHANG D J, et al. Simulation of liquid-gas flow in full-scale Caroussel oxidationditch with surface aeration. Journal of Central South University,2012,19:16151621.
Liao B Q, Allen D G, Droppo I G, et al. Bound water content of activated sludge and its relationshipto solids retention time, floc structure, and surface properties[J]. Water Environment Research,2000,72(6):722-730.
Liao B Q, Allen D G, Droppo I G, et al. Surface properties of sludge and their role in bioflocculationand settleability[J]. Water Research,2001,35(2):339-50.
Liao B Q, Droppo I G, Leppard G G, et al. Effect of solids retention time on structure andcharacteristics of sludge flocs in sequencing batch reactors[J]. Water Research,2006,40(13):2583-2591.
Liao B Q, Lin H J, Langevin S P, et al. Effects of temperature and dissolved oxygen on sludgeproperties and their role in bioflocculation and settling[J]. Water Research,2011,45(2):509-20.
Litster J, Smit D, and Hounslow M. Adjustable discretized population balance for growth andaggregation[J]. AIChE Journal,1995,41(3):591-603.
Liu X M, Sheng G P, Luo H W, et al. Contribution of extracellular polymeric substances (EPS) tothe sludge aggregation[J]. Environmental Science&Technology,2010,44(11):4355-4360.
Maerz J, Verney R, Wirtz K, et al. Modeling flocculation processes: Intercomparison of a sizeclass-based model and a distribution-based model[J]. Continental Shelf Research,2011,31(10):S84-S93.
Maggi F. Flocculation dynamics of cohesive sediment[D]. Delft: Delft University of Technology,2005.
Maggi F, Mietta F, and Winterwerp J. Effect of variable fractal dimension on the floc sizedistribution of suspended cohesive sediment[J]. Journal of Hydrology,2007,343(1-2):43-55.
Maggi F, Winterwerp J. Method for computing the three-dimensional capacity dimension fromtwo-dimensional projections of fractal aggregates[J]. Physical Review E,2004,69:011405.
Maggioris D, Goulas A, Alexopoulos A et al. Prediction of particle size distribution in suspensionpolymerization reactors: Effect of turbulence nonhomogeneity[J]. Chemical EngineeringScience,2000,55(20):4611-4627.
Mahmud T, Haque J N, Roberts K J, et al. Measurements and modeling of free-surface turbulentflows induced by a magnetic stirrer in an unbaffled stirred tank reactor[J]. ChemicalEngineering Science,2009,64:4197-4209.
McAnally W and Mehta A. Collisional aggregation of fine estuarial sediment[C]. Coastal andEstuarine Fine Sediment Processes,2000,3:19-39.
Mietta F, Chassagne C, Verney R, et al. On the behavior of mud floc size distribution: Modelcalibration and model behavior[J]. Ocean Dynamics,2011,61(2-3):257-271.
Mikkelsen L H and Kelding K. The shear sensitivity of activated sludge: An evaluation of thepossibility for a standardised floc strength test[J]. Water Research,2002a,36(12):2931-2940.
Mikkelsen L H and Keiding K. Physico-chemical characteristics of full scale sewage sludges withimplications to dewatering[J]. Water Research,2002b,36(10):2451-2462.
Nguyen T P, Hilal N, Hankins N P, et al. Determination of the effect of cations and cationicpolyelectrolytes on the characteristics and final properties of synthetic and activated sludge[J].Desalination,2008,222(1-3):307-317.
Ni B J, Fang F, Xie W M, et al. Characterization of extracellular polymeric substances produced bymixed microorganisms in activated sludge with gel-permeating chromatography,excitation-emission matrix fluorescence spectroscopy measurement and kinetic modeling[J].Water Research,2009,43(5):1350-8.
Nielsen P H and Jahn A. Extraction of EPS. In: Microbial extracellular polymeric substances:Characterization, structure, and function[M] ed. Wingender J, Neu T, and Flemming H.Springer Verlag.1999, Chapter3:49-72.
Nopens I. Modelling the activated sludge flocculation process: A population balance approach[D].Gent: Gent universiteit,2005.
Nopens I, Beheydt D, and Vanrolleghem P A. Comparison and pitfalls of different discretisedsolution methods for population balance models: A simulation study[J]. Computers&ChemicalEngineering,2005b,29(2):367-377.
Nopens I, Nere N, Vanrolleghem P A, et al. Solving the inverse problem for aggregation in activatedsludge flocculation using a population balance framework[J]. Water Science and Technology,2007,56(6):95-103.
Oda T, Yano T, and Niboshi Y. Development and exploitation of a multipurpose CFD tool foroptimisation of microbial reaction and sludge flow[J]. Water Science and Technology,2006,53(3):101-10.
Pandya J and Spielman L. Floc breakage in agitated suspensions-effect of agitation rate[J].Chemical Engineering Science,1983,38(12):1983-1992.
Parker D, Asce A, Kaufman W, et al. Floc breakup in turbulent flocculation processes[J]. Journal ofthe Sanitary Engineering Division,1972,98(1):77-79.
Parker D, Kaufman W, and Jenkins D. Characteristics of biological flocs in turbulent regimes[M].Califormia: University of California,1970.
Pruppacher H and Klett J. The microphysics of clouds and precipitation[M]. Dordrecht: SpringerNetherlands,1978.
Ramalingam K, Xanthos S, Gong M, et al. Critical modeling parameters identified for3D CFDmodeling of rectangular final settling tanks for new york city wastewater treatment plants[J].Water Science and Technology,2012,65(6):1087-1094.
Ramkrishna D. Population balances: Theory and applications to particulate systems inengineering[M]. London: Academic Press,2000.
Saffman P and Turner J. On the collision of drops in turbulent clouds[J]. Journal of Fluid Mechanics,1956,1(1):16–30.
Samaras K, Zouboulis A, Karapantsios T, et al. A CFD-based simulation study of a large scaleflocculation tank for potable water treatment[J]. Chemical Engineering Journal,2010,162(1):208-216.
Schuetz S and Piesche M. A model of the coagulation process with solid particles and flocs in aturbulent flow[J]. Chemical Engineering Science,2002,57(20):4357-4368.
Schuler A and Jang H. Causes of variable biomass density and its effects on settleability in full-scalebiological wastewater treatment systems[J]. Environmental Science&Technology,2007,41(5):1675-1681.
Selomulya C, Bushell G, Amal R, et al. Understanding the role of restructuring in flocculation: Theapplication of a population balance model[J]. Chemical Engineering Science,2003,58(2):327-338.
Serra T and Casamitjana X. Modelling the aggregation and break-up of fractal aggregates in a shearflow[J]. Applied Scientific Research,1998,59(2-3):255-268.
Serra T and Logan B E. Collision frequencies of fractal bacterial aggregates with small particles in asheared fluid[J]. Environmental Science&Technology,1999,33(13):2247-2251.
Sheng G P, Yu H Q, and Li X Y. Stability of sludge flocs under shear conditions[J]. BiochemicalEngineering Journal,2008,38(3):302-308.
Sheng G P, Yu H Q, and Li X Y. Stability of sludge flocs under shear conditions: Roles ofextracellular polymeric substances (EPS)[J]. Biotechnology and Bioengineering,2006,93(6):1095-102.
Sheng G P, Yu H Q, and Li X Y. Extracellular polymeric substances (EPS) of microbial aggregatesin biological wastewater treatment systems: A review[J]. Biotechnology Advances,2010,28(6):882-94.
Sobeck D and Higgins M. Examination of three theories for mechanisms of cation-inducedbioflocculation[J]. Water Research,2002,36(3):527-538.
Soos M, Sefcik J, and Morbidelli M. Investigation of aggregation, breakage and restructuringkinetics of colloidal dispersions in turbulent flows by population balance modeling and staticlight scattering[J]. Chemical Engineering Science,2006,61(8):2349-2363
Spicer P and Pratsinis S. Coagulation and fragmentation: Universal steady-state particle-sizedistribution[J]. AIChE Journal,1996,42(6):1612-1620.
Takács I, Patry G G, and Nolasco D. A dynamic-model of the clarification thickening process[J].Water Research,1991,25(10):1263-1271.
Tang P, Greenwood J, and Raper J A. A model to describe the settling behavior of fractalaggregates[J]. Journal of Colloid and Interface Science,2002,247(1):210-219.
Tang P and Raper J A. Modelling the settling behaviour of fractal aggregates-a review[J]. PowderTechnology,2002,123(2-3):114-125.
Thomas D, Judd S, and Fawcett N. Flocculation modelling: A review[J]. Water Research,1999,33(7):1579-1592.
Torfs E, Bellandi G, Nopens I. Towards mechanistic models for activated sludge flocculation underdifferent conditions based on inverse problems. Water Science&Technology,2012a,65(11):1946-1953.
Torfs E, Dutta A, and Nopens I. Investigating kernel structures for Ca-induced activated sludgeaggregation using an inverse problem methodology[J]. Chemical Engineering Science,2012b,70(5):176-187.
Urbain V, Block J C, and Manem J. Bioflocculation in activated-sludge-an analytic approach[J].Water Research,1993,27(5):829-838.
Van Hulle S W and Vanrolleghem P. Modelling and optimisation of a chemical industry wastewatertreatment plant subjected to varying production schedules[J]. Journal of Chemical Technologyand Biotechnology,2004,79(10):1084-1091.
Vanderhasselt A and Vanrolleghem P. Estimation of sludge sedimentation parameters from singlebatch settling curves[J]. Water Research,2000,34(2):395-406.
Verney R, Lafite R, Brun-Cottan J C, et al. Behaviour of a floc population during a tidal cycle:Laboratory experiments and numerical modelling[J]. Continental Shelf Research,2011,31(10):S64-S83.
Wanner J. Activated sludge bulking and foaming control[M]. Frolida: Technomic Publishing,1994.
Wilén B M, Jin B, and Lant P. Impacts of structural characteristics on activated sludge flocstability[J]. Water Research,2003a,37(15):3632-3645.
Wilén B M, Jin B, and Lant P. The influence of key chemical constituents in activated sludge onsurface and flocculating properties[J]. Water Research,2003b,37(9):2127-2139.
Wilén B M, Jin B, and Lant P. Relationship between flocculation of activated sludge andcomposition of extracellular polymeric substances[J]. Water Science and Technology,2003c,47(12):95-103.
Wilén B M, Lumley D, Mattsson A, et al. Relationship between floc composition and flocculationand settling properties studied at a full scale activated sludge plant[J]. Water Research,2008,42(16):4404-18.
Wilén B M, Onuki M, Hermansson M, et al. Influence of flocculation and settling properties ofactivated sludge in relation to secondary settler performance[J]. Water Science and Technology,2006,54(1):147-55.
Winterwerp J C. A simple model for turbulence induced flocculation of cohesive sediment[J].Journal of Hydraulic Research,1998,36(3):309-326.
Winterwerp J C. On the flocculation and settling velocity of estuarine mud[J]. Continental ShelfResearch,2002,22(9):1339-1360.
Wynn E J. Improved accuracy and convergence of discretized population balance of lister et al[J].AIChE Journal,1996,42(7):2084-2086.
Xiao F, Li X, and Lam K. Investigation of the hydrodynamic behaviour of particles and aggregatesby particle image velocimetry (PIV)[J]. Water Science&Technology,2007,7:213-220
Xu F, Wang D P, and Riemer N. Modeling flocculation processes of fine-grained particles using asize-resolved method: Comparison with published laboratory experiments[J]. Continental ShelfResearch,2008,28(19):2668-2677.
Yang S F and Li X Y. Influences of extracellular polymeric substances (EPS) on the characteristicsof activated sludge under non-steady-state conditions[J]. Process Biochemistry,2009,44(1):91-96.
Yu G H, He P J, and Shao L M. Characteristics of extracellular polymeric substances (EPS) fractionsfrom excess sludges and their effects on bioflocculability[J]. Bioresource Technology,2009,100(13):3193-3198.
Yuan S J, Sun M, Sheng G P, et al. Identification of key constituents and structure of theextracellular polymeric substances excreted by bacillus megaterium TF10for their flocculationcapacity[J]. Environmental Science&Technology,2011,45(3):1152-7.
Yuan Y and Farnood R R. Strength and breakage of activated sludge flocs[J]. Powder Technology,2010,199(2):111-119.
Zhang D J, Guo L S, Xu D Y, et al. Simulation of component distributions in a full-scale carrouseloxidation ditch: A model coupling sludge-wastewater two-phase turbulent hydrodynamics withbioreaction kinetics[J]. Environmental Engineering Science,2010,27(2):159-168.
Zhang D J, Li Z L, Lu P L, et al. A method for characterizing the complete settling process ofactivated sludge[J]. Water Research,2006,40(14):2637-2644.
Zhang J J and Li X Y. Modeling particles size distribution dynamics in a flocculation system[J].AIChE Journal,2003,49(7):1870-1882.
Zita A and Hermansson M. Effects of ionic-strength on bacterial adhesion and stability of flocs in awaste-water activated-sludge system[J]. Applied and Environmental Microbiology,1994,60(9):3041-3048.