二次沉淀池污泥沉降过程及其优化研究

The performance of secondary sedimentation tank determines the effluent quality of activated sludge system. With the increasing demand of discharge standard, it need further improve the sedimentation efficiency to improve effluent quality. Conventional sedimentation technologies used solid flux to adjust the sedimentation efficiency. These technologies have been developed to the extreme, and are difficult to further improve. Solids flux theory empirically describes the sludge settling velocity using sludge concentration, and complex settlement process is unclear. In fact, sludge settling process is a slow movement process under the joint action of gravity and other forces. Therefore, it is difficult to further improve sedimentation efficiency using flux theory. The mathematical equations of drag force, solid force and shear stress force are developed according to particle image velocity, radio isotope tracer technique, photoelastic and rheological experiments. Optical coherence tomography will be used to obtain sludge floc structure. Then, a new force-based mechanical model of sludge settling process will be developed. Sludge floc settling, batch settling and continuous settling will be used to verify this model. Finally, the model will apply to optimize the structure and operation of secondary sedimentation tank. This model can better reflect complex sludge settling process than solid flux model, and can accurately predict the suspended solids in effluent. This model make it possible to further optimize and improve the performance of sedimentation.

二沉池沉淀效果决定着整个活性污泥系统的出水水质。随着排放标准的提高，需要进一步提升沉淀效果以提高出水水质。传统的沉淀工艺大多利用固体通量来调控整个沉淀效果，目前已发展到极致，很难进一步提高。固体通量理论利用污泥浓度经验的描述沉降速度，对复杂的沉降过程认识尚不清楚，实际上污泥沉降是在重力等作用力作用下的缓慢运动过程，因此通量理论很难进一步提高沉淀效果。针对以上问题，本项目利用摄像测速、同位素示踪、光弹性和流变实验等，建立适合描述污泥运动的曳力、固体压力和固体剪应力方程；同时利用光学相干断层扫描获得实际污泥絮体结构，在此基础上建立基于作用力的污泥沉降力学模型。同时利用单个絮体沉降、间歇沉降和二沉池连续沉降验证模型，最后利用该模型对二沉池结构和运行条件行优化。相比固体通量模型，该模型可更好的反映复杂的污泥沉降过程，预测出水中悬浮固体含量，使进一步优化和提高污泥沉淀效果成为可能。

二沉池作为生物处理最末端的单元决定着整个系统的处理效果。随着排放要求的逐步提高，需要进一步提高污泥沉淀效果，从而提高生物处理工艺的效果。而污泥沉降过程非常复杂，现有的固体通量模型对污泥沉降运动特性和机制认识还不清楚，无法准确的模拟预测污泥层高度以及污泥浓度分布，极大地限制了沉淀效果的进一步提高。相比固体通量模型，本项目按照任务书的研究内容，建立了利用PET/CT测量污泥浓度分布的方法，通过对固体力、曳力方程的修正，建立了基于作用力的污泥沉降模型。同时利用污泥沉降间歇实验确定沉降模型的参数。之后将该基于作用力的污泥沉降模型用于模拟污泥间歇沉降过程，其结果表明该模型可很好的模拟污泥间歇沉降过程中污泥浓度和沉降速度的变化，其次利用该沉降模型模拟了自养、异养和混合营养3种污泥的沉降过程，通过模型阐释了三种不同污泥沉降性差异的原因。最后利用该作用力沉降模型模拟验证了实际污水厂污泥固液分离过程，模拟沉淀池运行条件（回流比和表面负荷）对沉淀效果的影响，并基于建立的作用力模型模拟比较了三种沉淀池类型（平流、竖流和辐流），最后对二沉池结构进行优化，该项目的研究结果可为现有二沉池进一步提高沉淀效果提供理论依据和技术支撑，已完成任务书规定的研究内容。