浅谈某城镇污水处理厂二沉池翻泥问题及措施

本文论述了造成二沉池翻泥的原因,并以某污水处理厂为例,探讨了该厂二沉池翻泥问题的思路和方法。结合该厂实际情况,通过采取降低污泥浓度、辅助投加絮凝剂、改变曝气模式等措施,解决了活性污泥沉降性差的问题,对防止二沉池翻泥具有积极意义。     

活性污泥法污水处理厂的运行模拟

结合ASM1和二沉池模型组成活性污泥模拟系统,将某污水处理厂的常规检测数据转化为活性污泥系统模型所需的组分数据,然后调整模型参数,使污水处理厂出水指标最接近于污水处理厂实际数据,从而确定适合该污水处理厂的模型参数,最后对该污水处理厂的工艺参数进行了模拟改造。     

二沉池表面负荷取值的探讨

就活性污泥法在不同系统中二沉池的设计参数如何取值进行了探讨，认为在延时曝气系统的二沉池设计中除了根据表面负荷计算之外，还应考虑固体负荷这一因素。     

混凝超滤组合工艺深度处理市政污水试验

以氧化沟工艺二沉池出水和序批式活性污泥工艺二沉池出水为原水,分别采用絮凝-砂滤-超滤和直流混凝-超滤的预处理工艺。结果表明,2种工艺处理出水的污泥密度指数小于2,浊度达到0.04￣0.1NTU,对CODCr去除率在20%￣60%,并在一定程度上降低了氨氮、总磷等污染物的质量浓度。污泥密度指数,浊度与产水量均达到了反渗透进水水质的要求。     

利用中水系统解决二沉池冬季稳定运行的运营实践

西北L市Y污水处理厂设计规模为26万m3/d,采用AAO工艺.Y污水处理厂运行过程中,发现日进水量波动较大,某典型日时变化系数按照最大时进水量/平均时进水量核算,已超过原设计总变化系数1.3.自2011年运行以来,每年冬季均发生污泥膨胀,对二沉池的稳定运行造成很大风险.通过采取超越初沉池和投加硅藻土药剂的方式,提高活性污泥无机物成分来增加其沉降性.随着进水量接近设计值,利用厂内中水系统作为冬季应急期间的二沉池,以降低现有二沉池的表面负荷,同时调整中水系统运行参数确保其出水达标,保障了Y污水处理厂的稳定运行.     

基于CFD的竖流式二沉池实际工况的模拟

为了探究实际工况下竖流式二沉池的流场变化及污泥质量浓度分布情况,利用RNG k-epsilon湍流模型和mixture模型,对其进行二维瞬态数值模拟,比较不同负荷、不同回流比对二沉池内部的流场变化和污泥质量浓度分布的影响。结果表明:q=0.5 m~3/(m~2·h)是竖流式二沉池比较理想的设计表面负荷;回流比对二沉池的稳定运行具有一定的影响,竖流二沉池的进口部分设计参数应当结合回流比进行适当的调整。     

用HYDRONET高效气浮技术替代市政污水厂二沉池的试验研究

在活性污泥法中,二沉池占地面积可观。利用悬浮一附着型纤毛填料技术加瑞士高效气浮技术HYDRONET和某市政污水处理厂卡鲁赛尔氧化沟后的辐流式二沉池的沉淀效果的对比试验,可知出水SS小于2mg／L,优于同期该污水处理厂二沉池出水,得出该高效工艺组台可以替代市政污水处理厂二沉池的结论,并可节省土地。     

污水厂二沉池运行控制中的计算方法

二沉池运行中,池体尺寸是固定的,需要根据污泥沉降情况,确定出运行需要的回流比,表面负荷等工艺参数。常用的二沉池设计计算公式是先假定污泥浓度,SVI,回流比,表面负荷等因素,计算得出池体尺寸。对设计公式进行反向推导,则可在池体尺寸已经确定的条件下,根据曝气池污泥沉降情况,确定出合理的污泥回流比和表面负荷,从而便于污水厂运行人员对二沉池进行调控。     

污水处理A/O工艺低负荷运行污泥性状改善调整实例

含油污水生化系统(A/O工艺)长期在低污泥负荷状态下运行,活性污泥的性状差,二沉池出水水质不稳定,影响污水回用,以改善活性污泥的性状为切入点,通过科学分析研究,采取实施针对性措施,使污泥性状得以改善、二沉池出水稳定达标,同时摸索出适合本装置工艺特点的调整操作手段。     

二沉池两相流数值模拟及混合液流变性质的影响

基于实际二沉池尺寸、流变性质、回流等工况,采用数值模拟方法对二沉池固液两相动力学行为进行模拟研究。结果表明,二沉池内存在多个漩涡,且分布于二沉池上部、中部和下部;混合液的流动速度在二沉池上部和污泥斗区域较低,在二沉池中下部较高;污泥高含量区分布于污泥斗及二沉池底部区域,且越靠近二沉池右侧壁面污泥层厚度不断降低。混合液流变性质模型为拟合污泥含量的赫谢尔-巴尔克莱模型时,模拟得到的速度及污泥层厚度与牛顿流体(水)模拟得到的结果较为相近且与实验结果误差不显著,但牛顿流体对二沉池底部的污泥含量预估较低,当混合液流变性质为赫谢尔-巴尔克莱模型时(与污泥含量无关)速度及污泥含量的模拟结果均较差。     

Flotation efficiency of activated sludge flocs using population balance model in dissolved air flotation

The activated sludge process is one of the most frequently used processes for biological wastewater treatment. Conventional gravity sedimentation (CGS), which is widely used as a secondary clarifier in activated sludge processes, has a routine problem due to floating tendency, called bulking, caused by filamentous microorganisms. Dissolved air flotation (DAF) has been applied as potential alternative to CGS as a secondary clarifier. A series of experiments were performed to measure physico-chemical characteristics and removal efficiency of activated sludge flocs. The removal efficiency of flocs corresponding in lag and exponential growth phases was lower, while that of flocs both in stationary and endogenous phases considerably increased. The rise velocity of floc/bubble agglomerates was calculated by using a population balance (PB) model explaining the distribution of floc/bubble agglomerates. The experimental results of flotation efficiency showed a similar tendency with the results predicted by PB model for the rise velocity and distribution of floc/bubble agglomerates. It was found from our study that the DAF process was very effective as a secondary clarifier in the activated sludge process.     

Analysis and simulation of the sludge profile dynamics in a full‐scale clarifier

A one‐dimensional clarifier model was assessed for its capability to describe dynamic full‐scale sludge concentration profiles by using the settling properties calibrated with batch settling curve data collected by a SettloMeter^®. These sludge concentration profiles and batch settling tests formed part of a detailed one‐month measuring campaign on a full‐scale wastewater treatment plant; the measurements showed a daily variation in settling properties. Using the settling properties obtained from batch settling tests and a one‐dimensional model without dispersion, the dynamics of the full‐scale clarifier were analysed and the need for dispersion clearly shown. The parameters of the dispersion model were estimated from the full‐scale sludge concentration profiles. The settling properties of activated sludge can be automatically determined by fitting the model to the on‐line batch settling curve measurements and are needed as input to the one‐dimensional model. This model can therefore be used for operation and control. The dispersion model parameters have to be determined from dynamic sludge concentration profiles but are assumed to be constant for a specific clarifier. Copyright © 2005 Society of Chemical Industry     

Numerical simulation of secondary clarifier with activated sludge and suction lift removal system: Modified Casson model and sludge withdrawing sensitivity analysis

A computational fluid dynamics model that predicts the sedimentation of activated sludge in a circular secondary clarifier with activated sludge is developed. The axisymmetric single-phase flow is simulated by using a CFD code that has been written with Intel Visual Fortran. First, sludge withdrawing by suction-lift in the near-bottom region of the clarifier is simulated using suction at the bottom of clarifier. The flow and settling processes are simulated using k-e turbulence model on a two-dimensional and orthogonal grid. A convection-dispersion equation that is extended to incorporate the sedimentation of activated sludge in the field of gravity is used. The computational domain includes the sludge blanket where the viscosity is affected by the rheological behavior of the sludge. Experimental data provided by Weiss et al. show that the relationship between shear stress and shear rate follows the Casson law for the shear rates lower than 50 s-1. Plastic viscosity of activated sludge is not removed from the concentration diffusion, so using regular non-Newtonian models leads to overestimation of blanket height. Modified Casson model is introduced to overcome the blanket height overestimation problem. Results show that the local sludge distribution in the clarifier has excellent agreement with concentration profile measurements of Weiss et al., for different treatment plant loadings. Alternative sludge withdrawing methods include withdrawing from pipes position at the bottom of clarifier and withdrawing by using sink terms in governing equations are used. Results show that the first withdrawing method gives less error comparing to these withdrawing methods.     

Continuous‐Flow Surface Aeration Systems

An aeration process in an activated sludge plant is a continuous‐flow system. In this system, there is a steady input flow (flow from the primary clarifier or settling tank with some part from the secondary clarifier or secondary settling tank) and output flow connection to the secondary clarifier or settling tank. The experimental and numerical results obtained through batch systems can not be relied on and applied for the designing of a continuous aeration tank. In order to scale up laboratory results for field application, it is imperative to know the geometric parameters of a continuous system. Geometric parameters have a greater influence on the mass transfer process of surface aeration systems. The present work establishes the optimal geometric configuration of a continuous‐flow surface aeration system. It is found that the maintenance of these optimal geometric parameters systems result in maximum aeration efficiency. By maintaining the obtained optimal geometric parameters, further experiments are conducted in continuous‐flow surface aerators with three different sizes in order to develop design curves correlating the oxygen transfer coefficient and power number with the rotor speed. The design methodology to implement the presently developed optimal geometric parameters and correlation equations for field application is discussed.     

微旋流沉降器分离效率的准数模型

通过因次分析和实验数据回归建立了新型微旋流沉降器的无因次准数模型。用模拟悬浮液通过改变流体流量?原水浊度?絮凝剂量?沉降器波纹板斜槽的直径进行沉降实验,测定进水流量、絮凝体沉速、进出水及澄清器内各点溢流水的浊度。结果表明:絮凝体沉速对出水浊度的影响最大;流体流速较小时,增大流速出水浊度减小,流速较大时,增大流速出水浊度增大;波纹斜槽直径越小分离效率越高。实验数据回归的分离效率准数模型与实验及工业数据吻合良好。     

Comparison of various settling velocity functions and non-Newtonian fluid models in circular secondary clarifiers

An axisymmetric single-phase model that predicts the sedimentation of activated sludge in a circular secondaryclarifier is developed. The k-ɛ turbulence model is used on a two-dimensional, orthogonal and stepwise grid. The concentration equation, which is extended to incorporate the sedimentation of activated sludge in the field of gravity, governs the mass transfer in the clarifier. The computational domain includes the sludge blanket where the viscosity is affected by the rheological behavior of the sludge. Results in case of non-Newtonian fluid model are compared with another numerical approach provided by Lakehal et al. Non-Newtonian fluid models—Bingham, Casson, and Herschel-Bulkley—are used. The influence of settling velocity functions and non-Newtonian models on the flow behavior isinvestigated. Finally, the best models are introduced and the ways that the non-Newtonian model introduces the plastic viscosity are discussed.     

Theory of Clarifier Operation. V. A Simplified Model,Design Aspects,and Time-Dependent Feeds

Abstract

Simplified mathematical models for slurry settling under quiescent conditions and in two types of upflow clarifier are presented. Effective floe radius and a coefficient in the expression for the viscosity, the only adjustable parameters, are determined by fitting to published data on settling velocities of stirred ferric hydroxide floes. These parameters are then used to calculate rates of sludge blanket rise in a reactor-clarifier operated at various flow rates. Agreement with data on ferric hydroxide floes is satisfactory. The responses of clarifiers of two different designs to transient hydraulic overloads are then calculated. The models indicate that the reactor-clarifier (fed in the middle, sludge wasted at the bottom) performs better than a clarifier which is fed at the bottom and from the middle of which sludge is wasted.     

The theoretical densimetric Froude number values with favourable effect on the clarifier performance

The performance of secondary clarifiers is strongly related to density effects in the sedimentation vessel. The upper level of the clarifier's chamber – once considered to be inactive at the sedimentation process – now appears to play an important role in solids removal. A fully developed three-layer flow phenomenon that develops in some cases is proved to promote settling. Therefore, investigation of flow patterns at different operative conditions was carried out. Experiments were conducted in a model of a circular, centre-feed settling tank with continuous operation. Ground hazelnut shells served as the settling matter; in one set of experiments only dye was used. All laboratory runs were filmed and analysed, qualitatively and quantitatively, by means of computer-aided visualisation. The results of the study showed that a determining factor of the conditions favourable for formation of a fully developed three-layer flow is the theoretical densimetric Froude number. If the hydraulic and solid loadings are soundly chosen in accordance with these findings, the clarifier performance can be evidently improved.     

周进周出式二沉池流态数值模拟

为了研究湘潭市河东污水处理厂周进周出式二沉池的流态,利用改进的RNGk-ε双方程模型,借助FLUENT6.3软件,对不同回流比情况下的周进周出式二沉池流态进行了数值模拟.结果表明:湘潭市河东污水处理厂周进周出式二沉池并不存在短流现象;随着回流比的增大,容积利用率逐渐增大,周进周出式二沉池实际流态基本上能达到设计目的,容...     

计算流体力学在二沉池改造中的应用

利用计算流体力学对污水处理厂二沉池内流场进行了数值模拟,得到二沉池内流场速率分布规律,进而确定流态临界位置水流速率,并将其作为标准速率。基于此,在二沉池内对挡板结构进行改造。改造后二沉池的模拟计算结果表明,二沉池在保证出水水质的情况下很好地满足了增大处理量的要求。