分级混凝机制与混凝过程控制研究

Coagulation-flocculation process is the key unit within the drinking water treatment process which can determine the efficiency and operating condition of the followed units. According to the problems on overlapping of coagulation stage and flocculation stage, coexistence of floc formation and breakage process, incompatibility of the coagulation-flocculation process and the coagulant characteristics during traditional coagulation-flocculation process, the mechanism of grading coagulation-flocculation function is advanced in this study. The System of the grading coagulation-flocculation is established based on hydraulic condition and coagulant characteristics. The coagulation stage and the flocculation stage are divided relatively with separated stages by the hydraulic grading method of adjusting rapid mixing intensity and mixing period, and the grading dosing method of coagulant with different characteristics is applied to study the coagulation-flocculation characteristics during coagulation stage and flocculation stage to improve separately the coagulation performance and the flocculation function, and the floc formation, floc settling performance and efficiency of pollution removal. The coagulant suitability is developed based on the grading coagulation-flocculation mechanism. The efficiencies and influence factors of the coagulants with different characteristcs are compared during the grading coagulation-flocculation process. The synergism between the coagulation stage and the flocculation stage is examined to determine influence factors of the coagulation stage to the flocculation stage. The study of the grading coagulation-flocculation process control is promoted based on hydraulic condition, water quality condition and coagulant characteristics. The control methods and technical parameters of the grading coagulation-flocculation process are submitted. It is provided a basis for the application of the grading coagulation-flocculation technique.

混凝过程是给水处理工艺中的关键环节，决定了后续处理单元的效能和运行工况。本课题针对传统混凝过程中存在的凝聚阶段和絮凝阶段重叠、絮体形成与破碎过程共存、混凝过程与混凝剂特性不协调等问题，提出分级混凝作用机制，建立基于水力条件和混凝剂特性的分级混凝系统，通过调节快速混合强度和混合时间的水力分级方式将凝聚过程和絮凝过程分离为相对独立的阶段，采用混凝剂分级投加方式研究不同特性混凝剂在凝聚和絮凝阶段的混凝特性，分别强化凝聚作用和絮凝作用，改善絮体的形态和沉降分离性能、以及混凝过程的除污染效能；开展基于分级混凝机制的混凝剂适配性研究，对比不同特性混凝剂在分级混凝过程中的效能和影响因素；研究凝聚过程与絮凝过程的协同性，确定凝聚过程对絮凝过程的影响因素，从水力条件、水质条件、混凝剂特性方面进行分级混凝过程控制研究，提出分级混凝过程的调控方法与技术参数，为分级混凝技术的应用提供依据。

本项目优化了分级混凝系统的除污染效能，解析了分级混凝作用机制，确定了分级混凝的动力学控制参数，建立了基于水力条件、水质特性及混凝剂特性的分级混凝系统；研究了分级混凝过程中混凝剂与混凝过程、水力条件及投加方式的适配性，研究了不同混凝阶段的协同性；建立了分级混凝过程控制方式。.研究结果表明，分级混凝除浊效果更佳、絮体沉降速率更快、高效除浊范围更宽。混凝剂投量相同时，分级混凝效能更佳，絮体沉降性能更加、结构更密实、强度更高、抗剪切能力更强。延长混合时间可提高胶体颗粒去除率，较短混合时间和较低絮凝搅拌强度有利于有机物的去除。混凝剂特性、投药量及投药间隔是分级混凝效能的关键因素。分级混凝的凝聚和絮凝阶段具有相互补偿作用和协同性，凝聚过程欠佳时可通过絮凝阶段的优化得到改善。混凝剂和磁种投量分别是除浊和絮体强度的关键因素，磁种应先于混凝剂0.5 min投加；回流污泥可改善絮凝效果，降低沉后水中溶解性铝和胶体态铝含量。PAM宜投加于絮凝反应的7.5min；壳聚糖的选择应参照絮凝搅拌强度，在低搅拌强度下壳聚糖分子量对絮体特性无明显影响，高分子量壳聚糖适用于低絮凝搅拌强度。混凝剂特性是决定分级投加比的关键因素，不同混凝剂的最佳投加比有显著差异，具有明显的混凝剂适配特性；第一级混凝剂投加应使胶体充分脱稳，第二级混凝剂投加点宜在絮凝阶段初期（1 min内）；絮凝阶段宜采用逐级降速的搅拌方式。锆盐对小分子有机物（< 10 kDa）去除效果更佳，絮体大且密实，与铝盐复配或分级投加可优化锆盐投量适用范围。分级混凝的混合强度和混合时间调控范围较宽，胶体脱稳程度更高，絮体沉降性能更稳定；混凝剂分级投加比调控在4/8−2/10，絮体特性取决于分级投药间隔调控范围（30−60s）。絮凝反应阶段初期提高搅拌强度可改善絮体结构，最佳搅拌转速100~150rpm，第二级投药可显著提高混凝效果，分级混凝投药量减少了32.3%。本项目的研究成果可为混凝机制的发展以及混凝过程的优化提供理论和技术支持。