【作者】 冯国红；

【导师】 谭蔚；

【作者基本信息】 天津大学 ， 化工过程机械， 2014， 博士

【摘要】 污水污泥是城市和工业污水处理厂的主要副产物，随着城市化进程的加快，废水的排放量急剧增加，带来了日益严重的环境污染问题。我国关于污泥不同处置方式的标准均要求污泥脱水后滤饼固相质量含量大于40wt%，基于环保与经济并重的理念，如何最大程度提高污泥的处理能力、降低滤饼含水率以满足污泥后续的处置要求，是目前亟待解决的问题。机械脱水以其操作简单、成本低廉等特点一直备受各污水处理厂青睐。但由于污泥中含有大量菌胶团、微生物以及结合水，其特殊性质决定了污泥很难脱水，不经过任何预处理甚至无法脱水。因此，本文以降低城市污泥滤饼含水率和提高污泥处理能力为目标，针对化学絮凝调理及热水解预处理改善污泥脱水机理展开了理论和实验研究，并研究了热水解预处理对污泥流变行为的影响机理，主要完成的工作如下：（1）针对化学絮凝调理的城市污泥的过滤压榨脱水过程，提出了过滤速率、滤饼固含量、净固相产量等8个参数作为评价污泥过滤压榨脱水特性的指标。采用均匀设计法设计污泥过滤压榨脱水实验，建立了絮凝剂（PAC和CaO）剂量、过滤压力以及压榨压力与过滤速率、滤饼固含量以及净固相产量等评价指标之间的模型方程。结果表明：CaO对过滤速率、滤饼固含量、净固相产量等均有最显著的影响。随着CaO剂量的增大，污泥的脱水特性逐步改善，当CaO剂量达到50%左右时（CaO质量与污泥干固相的质量比），净固相产量最大。PAC对滤饼固含量的影响较小，过滤阶段、压榨阶段以及整个脱水过程的最佳PAC剂量一致，约为10%（PAC质量与污泥干固相的质量比）。过滤压力对过滤速率无显著影响，但是较高的过滤压力能够增加污泥总处理量；较高的压榨压力有利于滤饼内粒子的蠕变变形，有利于获得更干的滤饼和较高的压榨速率。在本研究范围内，当压榨压力增加到3.5MPa以上时，压榨速率的增加变缓。（2）复合化学絮凝调理城市污泥的过滤压榨脱水机理研究结果表明：复合化学絮凝调理提高了滤饼的渗透性，降低了滤饼的弹性和粘性，显著地提高了滤饼中粒子的蠕变能力。同时由于复合化学絮凝调理削弱了固相颗粒表面与结合水之间的结合强度，提高了毛细水和结合水的去除速率，有利于污泥的压榨脱水。（3）针对热水解预处理城市污泥的过滤压榨脱水过程，研究了热水解预处理对污泥物理性质的影响。基于流变理论，建立了描述污泥流变特性的方程。结果表明：热水解预处理后，污泥的结合水含量、颗粒粒径以及非牛顿流体特性均随热水解温度的升高而逐渐降低；污泥颗粒的密实程度增加，絮体分形维数升高。但当温度超过170℃后，污泥物理特性的变化趋势减缓。经170℃热水解的污泥，当固相浓度小于150g/L时，其剪切应力与剪切速率之间的关系可由牛顿流体模型表示；热水解污泥粘度与浓度之间、粘度与温度之间的关系分别满足指数方程和阿伦尼乌斯方程；粘弹特性参数与频率之间的关系可由对数方程描述；热水解污泥的触变性即粘度随时间的变化关系符合一阶触变动力学模型。（4）基于过滤压榨理论，研究了热水解温度对污泥特性的影响，提出并确定了热水解预处理的温度门槛值。针对本文研究的污泥，热水解污泥脱水特性转变温度下门槛值为120℃，上门槛值为170℃。热水解污泥过滤压榨脱水机理研究结果表明：热水解预处理能够降低污泥中结合水的含量和污泥固相中有机物的含量，进而影响污泥的脱水性能。污泥中有机固相在热水解过程中发生溶解和水解，导致颗粒软度下降，压缩系数减小（从1.1降至0.7），从而提高了污泥的过滤性能，过滤60min时，滤液量涨幅达7倍。另外，经热水解预处理后，污泥中的颗粒更加密实，过滤过程中形成的滤饼结构更加紧凑，因此主压榨阶段的贡献降低；热水解致使污泥粘弹性降低，有利于滤饼内颗粒的蠕变变形，蠕变参数增大近12倍，第二压榨阶段的作用增加；结合水含量的降低削弱了第三压榨阶段的作用。本文的研究结果为城市污泥的化学絮凝与热水解预处理提供了理论依据，为污泥的减量化工艺设计提供了参考，对解决污泥的脱水问题具有重要的理论意义和应用价值。更多还原

【Abstract】 Sewage sludge is the main by-product of urban and industrial wastewatertreatment plant. With the speeding up of urbanization, discharge amount ofwastewater increases dramatically, and then serious environmental problems areappeared. Standards about disposal ways for sludge in China require that solidscontent of filter cake is larger than40wt%. Based on the idea of equal attention toenvironmental protection and economy, it is the problem to be solved that how toimprove processing capacity of sludge, and how to reduce moisture content of filtercake in order to satisfy subsequent processing requirements, such as landfill,incineration.Mechanical dewatering methods with simpler operation and lower cost, havebeen praised by most of sewage treatment plants. However, nature of the sludge(composed by lots of zoogloea, microorganisms and bound water), determined that itis difficult to dewater without any pretreatment.In this paper, the aims were to reducemoisture content of filter cake and improve processing capacity of sludge. Themechanisms that flocculation conditioning and thermal hydrolysis pretreatmentimprove sludge dewaterability were studied, and the effect of thermal hydrolysis onsludge rheology was analyzed.The main work is as follows:（1）Eight parameters (such as filtration rate, cake solids content and net solidsyield) as evaluation indexes of sludge dewaterability were come forward. Uniformdesign was employed to design filtration and expression dewatering experiments,and equations on independent variables (PAC dose, lime dose, filtration pressure andexpression pressure) and dependent variables (such as solids content of filter cake,net solids yield.) were established. Results show that lime had the most significantimpact on each dependent variable, such as filtration rate, cake solids content and netsolids yield.Sludge dewaterability could improve with the increase of lime dosage.As the lime doseage reaches50%(lime mass ratio to dry solids mass in sludge),maximum net solids yield was obtained. Effect of PAC on cake dry solids content wasnegligible. The optimum dose of PAC for the filtration stage was10%(PAC massratio to dry solids mass in sludge), which was in accordance with that for the expression stage and for the whole dewatering process. In addition, filtration pressurehad little effect on filtration rate, while handling capacity of sludge increased athigher filtration pressure. Furthermore, higher expression pressure could contributeto the mobility of particles in filter cake, and then drier cake and higher expressionrate were obtained. However, when the expression pressure exceeded3.5MPa, theexpression rate increased slowly in this study.（2）Mechanism of filtration and expression dewatering on municipal sludgeconditioned by composite flocculation was studied. Results showed compositeflocculation conditioning increased permeability of filter cake, improving creepability of particles in filter cake, and reduced elasticity and viscosity of filter cake.Meanwhile, bonding strength between water and particle surface was weakend, andthen removal rate of bound water and capillary water increased, which is beneficialto expression dewatering.（3）Effect of thermal hydrolysis on sludge physical characteristics was studied.Based on rheological theory, equations describing rheological properties of sludgewere established. Bound water content, particle size and non-Newtonian fluidcharacteristics of sludge, decreased with the thermal hydrolysis temperature.Sludgefloc became more compact, and the fractal dimension of floc increased. However,when the thermal hydrolysis temperature reaches170℃, the decreased trend isgradually. For sludge with hydrolysis at170℃, as the solids content is lower than150g/l, the relationship between shear stress and shear rate could be expressed byNewtonian fluid model, while relationships (between sludge viscosity and sludgeconcentration, between sludge viscosity and temperature) were satisfiedexponential equation and Arrhenius equation, respectively. Correlation betweenviscoelasticity parameters and frequency were described by logarithmic equations,and evolution of viscosity over time can be simulated by one order thixotropickinetic equation.（4）Based on expression theory, impact of thermal hydrolysis temperature onsludge characteristics was carried out, and proposed threshold value of thermalhydrolysis temperature. The lower threshold value was120℃, and the higher was170℃. After thermal hydrolysis, reduction of bound water content andorganic matter content in sludge solids improved sludge dewaterability. Dissolutionof suspended organic solids and hydrolysis of macromolecular components, led todecreased particle softness and lower compression coefficient (from1.1to0.7), which improved sludge filterability. Filtrate amount significantly increased by nearly7times during60min, and a much compacter and less elastic filter cake was built up.Consequently, for expression stage, contribution of primary consolidation stagedecreased. Creep factor increased by nearly12times, suggesting that the mobility ofparticles in filter cake became easier, and the contribution of secondary consolidationstage also increased. Due to the reduced bound water content, the contribution oftertiary consolidation stage decreased.The results of this study provide theoretical basis for pretreatments of chemicalflocculation and thermal hydrolysis, and provide reference for design of sludgereduction process. It has important theoretical significance and application value forsolving problem of sludge dewatering.更多还原