【作者】 胡学斌；

【导师】 龙腾锐；

【作者基本信息】 重庆大学 ， 市政工程， 2009， 博士

【摘要】 随着城市污水产生量的增长和处理率的提高,污水厂污泥伴生的环境问题日渐突出。论文在全面综述国内外污泥处理技术的基础上,发现污泥处理过程繁琐、建设和运行成本高是造成污泥处理率低下的最主要原因,认为开发一种融合污泥浓缩、污泥消化于一体的简易多功能污泥处理技术不仅可以简化污泥处理流程,而且可以解决污泥处理成本高的技术难题。为了解决污泥浓缩消化一体化反应技术工程应用中存在的问题,论文在课题组前期小试研究成果的基础上,以重庆市鸡冠石污水厂为试验现场、对两相一体式污泥浓缩消化反应器(TISTD)进行了中试试验研究。研究内容包括:以TISTD小试反应器为基础,用计算流体动力学FLUENT软件对TISTD小试反应器进行流态分析和优化研究;根据流态相似原理进行TISTD中试反应器的设计和中试反应器流态特性研究;最后以重庆市鸡冠石污水厂二沉回流污泥为研究对象,按照中试规模对TISTD反应器的运行效能和动力学特征进行了系统研究。取得的主要成果有:①以计算流体动力学FLUENT软件为基础,建立了TISTD反应器的物理模型;建立了对反应器进泥管、出水管、排泥管、内循环管、沼气循环管等构件进行网格加密、对近壁面进行网格细化的TISTD反应器四面体非结构化网格划分模式;确定了TISTD反应器的计算流体力学数学模型,建立了与TISTD反应器匹配的计算流体力学边界条件和初始条件,为反应器的优化设计提供了理论基础。②采用计算流体动力学FLUENT软件对TISTD小试装置的流场进行了模拟和优化,发现TISTD反应器小试装置存在外反应室进泥短流及内反应室循环不均匀等流态问题。论文针对TISTD反应器流态问题,提出了如下改进建议:改变进泥管的位置、在内外反应室隔板上部开设连通孔、调整上下连通孔的尺寸、将内循环管调整成为一个整体、调整内循环管出口高度、调整内循环管尺寸等。基于实现较为理想流态需要对反应器多部位进行调整的具体情况,论文还采用5因素4水平的L1 6( 45)正交试验方法、以计算流体动力学参数即流速方差加权平均值、总动能和平均湍流强度作为考核指标探寻了反应器各构件的最佳组合方式,为反应器中试装置的设计提供了依据。③论文根据流态模拟及优化结果进行了TISTD反应器中试装置的设计;并根据中试试验基地的情况,建立了TISTD中试试验系统。针对中试装置采用沼气回流搅拌方式的特点,重点研究了气体回流量对TISTD反应器内、外反应室流态的影响,发现:沼气气体回流量从0 L·min-1增加到12 L·min-1的过程中,反应器的流态从偏向活塞流到偏向混合流发展;当气体回流为12 L·min-1时,完全混合流态势最强;研究进一步发现泵入进样方式赋予了进泥一个不可忽略的初始速度,将对外反应室流态产生冲击,不利于污泥的浓缩;但是,泵回流污泥却有利于提高内反应室污泥的混合流态。④采用逐渐培养法成功启动了TISTD中试反应器。启动试验结果表明,在35±2℃、投配率为10%的条件下,经过大约55天的启动运行,TISTD中试反应器内各项指标趋于稳定。启动运行期间未出现酸化现象。论文在分析厌氧体系中污泥基质降解进程时发现,在剩余污泥的两相厌氧消化中,污泥基质释放的NH3对维持反应器pH、碱度以及反应器的稳定运行具有重要意义。⑤论文进一步研究了TISTD中试反应器的处理效能。发现在污泥投配率为24%、温度33~35℃时,污泥的产气率最高,可以达到340L/KgVSS,产气中CH4含量大于60%。经过TISTD中试反应器处理的污泥VS/TS下降了22%左右,处理后污泥的有机质含量极低,约21%,含水率约90%,污泥体积仅为原污泥1/10,污泥的浓缩消化效果明显。⑥论文初步研究了反应器温度对污泥处理效能的影响。结果表明,当温度维持在33~35℃时,反应器运行良好,产气量约300L/d;当反应器温度下降到32℃,产气量开始有明显下降,降幅达1/3;当反应器内温度下降到30℃,产气量急剧下降,降幅超过2/3;一旦反应器温度低于28℃后,产气过程基本停止。论文还对反应器的运行能耗进行了分析,发现反应器耗能与生污泥温度直接相关,当生污泥温度高于25℃时,能耗约15 Kwh/m3左右;当生污泥温度低于18℃时,能耗将超过40 Kwh/m3。⑦论文最后对TISTD反应器有机物去除动力学进行了分析。基于米-门公式,采用试验数据求定了中试反应器有机物的降解动力学参数K s、νmax。通过对不同投配率下有机物降解速率与产甲烷速率关系的研究,得到TISTD反应器的甲烷产率系数y=0.3614mL/mg,该值与理论值0.35 mL/mg接近,说明该研究得到的中试装置设计合理,运行状态良好。研究成果为TISTD反应器的工程设计、启动和运行提供了较系统的理论和技术支撑,对推动污泥浓缩消化一体化反应技术工程化应用具有重要意义。更多还原

【Abstract】 Sewage sludge from wastewater treatment plants (WWTPs) has been an increasingly serious environmental problem in China as municipal wastewater discharge and treatment rate grow rapidly in recent years. With comprehensively reviewing the state of the arts of international and national sludge treatment technologies, it is found that complicated treatment process and high construction & operation cost are the most important influencing factors for too low sludge treatment rate at present. So it is necessary to develop new-typed simple and efficient sludge treatment technology with thickening and digestion integrated, which can not only simplify the treatment process, but also lower the sludge treatment cost. To solve the practical problems, a pilot-scale experimental study of a two-phase integrated sludge thickening and digestion reactor (TISTDR) was built in Chongqing Jiguanshi (WWTP) based on the bench-scale experimental study having been carried out previously. The study aspects include: fluidal condition analysis and optimization of bench-scale TISTDR with application of computational mechanics software FLUENT based on the previously developed bench-scale TISTDR; Design of pilot-scale TISTDR and its fluidal in accordance with fluidal similarity principle; and systematic study of operational performance and kinetics characteristics of TISTDR with pilot scale using the returned sludge from the secondary sedimentation tank of Chongqing Jiguanshi WWTP as subject. The main results are as follows:①Physical model of the TISTDR was established based on FLUENT software. A tetrahedral non-structural mesh method for mesh densification of the structural parts such as inlet sludge pipe, water drainage pipe, outlet sludge pipe, internal recycle pipe and methane recycle pipe and mesh refinement of the near wall was established. A computational mechanics mathematical model of the TISTDR was defined and the boundary condition and initial condition accordant to the TISTDR was established, which provided theoretical basis for optimization design of the pilot-scale TISTDR.②The fluidal field was simulated and optimized by applying FLUENT. It has found that the bench-scale TISTDR had some problems such as inlet sludge short flow in the outer reaction chamber and uneven recycle in the inner reaction chamber. Improvement measures to the these problems were proposed as: change the place of sludge feeding pipe, set the connecting hole at top of the divider between the outer chamber and the inner chamber, adjust the size of connecting hole, adjust the internal recycle pipe to become a unity, and adjust the height of the internal recycle pipe outlet and the size of the internal recycle pipe. With regard of the need of adjusting multiple structural parts to create ideal fluidal status, the optimization combination pattern of various structural parts was investigated by using L1 6( 45) orthogonal experimental method and computational mechanics indexes as performance indicators such as weighted average of velocity variance, total kinetic energy and average intensity of turbulence, which provided basis for the optimization design of the pilot-scale experiment facility.③A pilot-scale TISTDR experiment facility was designed based on the simulation and optimization results of fluidal status and a pilot-scale TISTDR experimental system was built with consideration of the real setting of the experimental base. By using methane backflow as stirring method, the effects of gas backflow rate on the fluidal status in the inner and outer reaction chamber were investigated emphatically. It has been found that when the backflow rate increased from 0 L·min-1 to 12 L·min-1 gradually, the fluidal status of the reactor developed from piston flow alike to mixed flow alike, and when the backflow rate of methane was 12 L·min-1, the tendency of completely mixed flow was the strongest. The study further found that pumped-in feeding pattern have created a non-negligible initial velocity, which would produce shock on the fluidal status of outer reaction chamber and would be adverse to the sludge thickening. However, pumping-in returned sludge would be helpful to improve the formation of completely mixed flow in the inner reaction chamber.④The pilot-scale TISTDR was started successfully with a step-by-step culture. The results indicated that under the condition of 35±2°C and dosing rate of 10%, the pilot-scale TISTDR was stable for various parameters after operated for 55 days. Acidification phenomena were not observed in startup period, indicating that selecting surplus sludge of the secondary sedimentation tank with relatively low organic content was safer for the TISTDR startup. In analyzing the degradation process of sludge substrate in the anaerobic system, NH3, released from the sludge substrate in the diphase anaerobic digestion of surplus sludge, played an important role in maintaining the level of pH and alkalinity as well as the stability of the reactor operation.⑤The treatment performance of the pilot-scale TISTDR was further studied. The results indicated that when the sludge dosing rate was 24% and the temperature inside of the reactor was kept at 33°C~35°C, the gas yield of sludge would be the highest, reaching about 340L/kgVSS and with CH4 content over 60%. After treatment, the sludge VS/TS reduced for about 22% and the treated sludge have lower organics content, 21%. With a water content of 90%, the treated sludge had a volume of only 1/10 of that of raw sewage sludge, proving a significant digestion effect.⑥The influencing effect of temperature on sludge treatment performance was preliminarily studied. The results indicated that when the temperature inside of the reactor was kept at 33°C~35°C, the reactor was operated well and the gas yield was about 300 L/d; while when the temperature decreased to 32°C, the gas yield began to decrease quite significantly with a range of 1/3; and when the temperature decreased to 30°C, the gas yield decreased sharply with a range over 2/3; if the temperature further decreased to 28°C, gas generation stopped. The operational energy consumption was analyzed also. The results indicated that energy consumption was directly correlated to the temperature of raw sewage sludge. When above 25°C, the energy consumption was 15kwh/m3, and when below 18°C, the energy consumption exceeded 40 kW·h/m3.⑦The kinetics of organics treatment of TISTDR was analyzed finally. The kinetics parameters such as K s andνmax were identified based on Michaelis–Menten equation and experimental data. By investigating the relationship between organic degradation rate and methane generation rate under different sludge dosing rate conditions, the coefficient of methane generation was obtained as y=0.3614mL/mg, which was close to the theoretical value of 0.35 mL/mg, proving that the design of the developed pilot-scale facility was reasonably and it had a good operational condition.The above results of study provided systematical support both theoretically and technically and are of great importance for advancing the engineering of TISTDR technology.更多还原