【作者】 杨寅；

【导师】 杨家宽；

【作者基本信息】 华中科技大学 ， 环境工程， 2011， 硕士

【摘要】 氧化沟工艺由于出水水质较好和抗冲击负荷能力较强等优势,在我国污水处理系统中得到了广泛的应用。然而,氧化沟运行过程中存在能耗过大所造成高处理成本等问题,导致一些污水处理厂面临“建得起、用不起”的窘境。氧化沟内的流场和溶解氧分布不仅对处理效果影响显著,而且与能量消耗密切相关。本论文以小试氧化沟的模拟实验装置以及平顶山污水处理厂实际氧化沟工艺为对象,进行基于流场和溶解氧分布的计算流体力学(Computational Fluid Dynamics,简称CFD)的数值模拟技术研究,同时开展了流场分布及溶解氧分布的监测校验研究,提出保证出水水质前提下的氧化沟优化运行模式,对污水处理工艺的节能降耗具有一定参考价值。主要开展了以下工作:1.以华中科技大学实验室0.73 m~3的小试氧化沟装置为研究对象,采用滑移壁面模型与风扇模型分别对曝气转碟与水下推进器进行建模,对网格划分与参数定义进行优化,模拟并实测校验了小试氧化沟的流场分布,结果表明滑移壁面模型与风扇模型可以较好地模拟曝气转碟和水下推进器开启时的流场分布。2.以平顶山污水处理厂50000 m~3的实际氧化沟工艺为研究对象,对实际氧化沟现有运行模式与优化运行模式下的流场分布进行模拟与实测,基于两种运行模式下流场分布的对比分析,对氧化沟运行模式提出能量优化配置建议:弯道入口处的曝气转碟一般情况下不必开启,可用弯道处的水下推进器进行替代;一般情况下,相邻的两个推流装置不必同时开启。3.利用单元分析法、氧传输模型及修正BOD-DO水质模型对实际氧化沟典型单沟直沟段的溶解氧分布特性进行了模拟,在典型单沟直沟段的好氧区与缺氧区分别设置测量断面进行了溶解氧浓度实际测量工作,并基于两种运行模式下溶解氧分布特性的对比分析,对氧化沟运行模式提出建议:曝气转碟开启过多不利于形成良好的溶解氧浓度梯度,氧化沟脱氮效应得不到正常发挥;同一沟段的相邻两组曝气转碟不必同时开启,否则造成能量浪费,且导致溶解氧浓度过高,不利于同步硝化反硝化作用。4.将现有运行模式与优化运行模式分别在东西两座氧化沟同时连续运行一个月,对比分析两种运行模式下氧化沟出水水质与能耗,优化运行模式下改良型氧化沟的脱氮效应得以正常发挥,并且比现有运行模式每小时节省电能98.43 kWh,约节省28.5%的电能,节能效果较为显著。氧化沟内的曝气转碟和水下推进器根据进水水量和水质的变化情况进行合理调节配置,可以使氧化沟内的流场分布均匀且形成良好的溶解氧浓度环境,从而达到节能减排的目的。氧化沟优化运行的动态模拟研究工作有待进一步深入。更多还原

【Abstract】 Oxidation ditch (OD) has been widely used as a modified activated sludge biological treatment process in China due to its reliability and good effluent quality. However, successful operation of an OD system may still be challenging for many wastewater treatment plants (WWTPs) in China for economical reason mainly caused by large energy consumption. Since the process efficiency depends heavily on the flow field and dissolved oxygen (DO) concentration profiles in an OD, which also have close relationship with energy consumption, it is necessary to study on flow pattern and oxygen mass transfer characteristics in OD systems. In this study, an experimentally-validated model based on computational fluid dynamics (CFD) simulation technology was proposed to predict flow patterns and oxygen mass transfer characteristics in a lab-scale OD and a full-scale OD in Ping Dingshan WWTP. Full-scale demonstration of system performance under two operating conditions (existing and improved) of the full-scale OD in Ping Dingshan WWTP was carried out and effects of these two operating conditions on effluent quality and energy consumption were compared. Based on the results of the research, an improving operating condition of the full-scale OD, which could not only reduce energy consumption but also satisfy effluent standards, was proposed.The following research work was carried out in this thesis:1. The flow field of the lab-scale OD (0.73 m~3) was simulated and validated for verification and optimization of simulation methods of disc aerators and submerged impellers. The result demonstrated that the flow field of the lab-scale OD with disc aerators and submerged impellers operationg could be simulated well by moving wall model and fan model.2. The flow fields of the full-scale OD (50000 m~3) under two operating conditions (existing and improved) were compared and analyzed. Several suggestions for energy saving were proposed as follows: an operating disc aerator in the entrance of the curve bend could be instead by an operating submerged impeller in the curve bend; the adjacent disc aerators could not be in operation simultaneously.3. Oxygen mass transfer in the typical straight channel of the full-scale OD was predicted by using a unit analysis method and the oxygen consumption was modeled by using modified BOD-DO Model. DO concentrations were measured at two test locations (in the aerobic zone and the anoxic zone) under the existing and improved operating conditions, respectively. Based on the simulation results and field measurements, the operating condition of surface aerators had a significant impact on the DO concentration profiles in the ditch. Under the existing operating condition, the DO concentrations were relatively high that caused waste of energy and the DO concentration gradients were not obvious; while under the improved operating condition, the DO concentrations showed apparent variations along the ditch and provided a more suitable environment for simultaneous nitrification and denitrification (SND).4. A comparison on the performance of two operating conditions was carried out in these two full-scale ODs concurrently for a month. The influent quality and effluent quality were monitored daily and energy consumptions for two operating conditions were calculated. The total energy consumption per hour under the improved operating condition is 98.43 kWh (28.5%) less than that under the existing operating condition.Since the influent flow rate, concentration and composition are likely to fluctuate day to day, an optimal operating condition should be derived from a dynamic model updated to accommodate actual process state and perturbations. The development of such a model is currently under investigation.更多还原