钛盐混凝除藻过程中藻细胞破损机理、藻类有机物释放规律及含藻污泥回用研究

Algae pollution has become the key problem to be resolved by water treatment plants. Coagulation-Precipitation is the effective way for algae removal. Utilizing novel titanium based coagulants for algae removal are not only expected to achieve efficient algae removal without cell damage, but also the coagulated algae-containing sludge can be recycled to obtain valuable by-product named TiO2. Fundamental research will be carried out in terms of coagulation process using titanium coagulants, algae damage mechanism, release characteristics of algae derived organic matter (AOM) and coagulated sludge recovery. The detailed contents are as follows. The removal efficiency of algae and AOM by titanium based coagulants and the conventional coagulants is comparatively investigated. The influencing factors on algae and AOM removal are studied and the coagulation removal mechanisms will be deduced in combination with coagulation efficiency. The effect of coagulant type and coagulation conditions on algal cell integrity and metabolite release characteristics is evaluated, obtaining the optimized experienced parameters for algae removal without algal cell damage. Characteristics of flocs formed by titanium based coagulants are investigated through on-line monitoring of dynamic coagulation process. The influence of floc characteristics on algae removal efficiency and cell integrity is studied, suggesting the relationship between floc characteristics and complete removal of algal cells. After coagulation and sedimentation process, the algal cell stability and the release of microcystins during algae-containing sludge reduction and sludge-containing water reuse processes are investigated, optimizing the operating conditions for both sludge reduction and harmless water recycling. The sludge recovery technology is investigated and optimized through calcination of algae-containing sludge after dehydration. The morphological transformation model of titanium during algae removal and sludge recovery processes is established. This research aims to evaluate the removal of algae using titanium coagulants and reveal the algae cell damage mechanism, release characteristics of AOM and algae-containing sludge reuse. This project is of great theoretical significance to the popularization and application of titanium based coagulants for algae removal and has important guiding value to chemical sludge reuse.

水源地藻类污染已成为饮用水厂亟需解决的关键问题，混凝沉淀是去除藻类的有效途径。采用新型钛盐混凝沉淀除藻，有望取得高效无破损除藻与含藻污泥回用的双重功效。本项目对钛盐混凝沉淀除藻过程、混凝过程中藻细胞破损机理、藻类有机物释放规律及含藻污泥回用展开基础研究。具体内容包括：钛盐对藻细胞及藻类有机物的去除特性、影响因素及混凝除藻机理；混凝过程中藻细胞的破损作用、破损机理及藻类有机物释放规律和钛盐无破损除藻条件；钛盐所生成的絮体特性及其对藻类去除效果、藻细胞完整性和藻类有机物释放特性的影响；混凝沉淀后，污泥减量化过程中藻细胞完整性及藻类有机物释放特性，优化污泥脱水条件，研究污泥回用二氧化钛过程，建立钛在混凝和污泥回用过程中的形态转化模型。本项目旨在评价钛盐混凝除藻效能，揭示钛盐除藻过程中藻细胞的破损机理、藻类有机物的释放规律和含藻污泥回用，为钛盐在混凝除藻方面的应用及含藻污泥回用奠定理论基础。

本项目系统研究了钛盐混凝剂对含藻地表水的混凝效果和混凝行为，并结合钛盐混凝前后絮体电荷特性的变化，研究钛盐混凝除藻机理。实验结果表明，钛盐混凝剂可实现含藻水中藻细胞的高效无破损去除，并可协同去除地表水中的有机物，与传统的铝盐和铁盐混凝剂相比，钛盐在最佳混凝条件下，对有机物的去除具有明显优势，尤其是对荧光类有机物和低分子量有机物具有较强的混凝能力，去除率远远高于传统混凝剂。通过监测混凝过程中及混凝后藻细胞的存在状态和出水水质，研究了混凝过程中藻细胞的破损及藻类有机物的释放情况，明确了其影响因素和钛盐无破损除藻条件。实验结果表明，钛盐混凝剂可有效脱除藻细胞且混凝条件不会造成藻细胞的破损及藻类有机物的释放。采用粒径检测仪监测混凝动态过程中絮体特性的变化，研究了钛盐絮体特性与藻细胞去除效果和藻类有机物释放之间的关系。实验结果表明，和传统混凝剂相比，钛盐混凝过程产生的絮体生长速度快，絮体粒径大，絮体沉降速度快，这将有效缩短混凝过程，减少藻类有机物在混凝过程中释放的可能性。在不同pH条件下，钛盐混凝所得絮体恢复因子相比于传统混凝剂总体较高，这主要与混凝过程发生的混凝机理有关。除电中和作用外，吸附卷扫等混凝机理也是TiCl4混凝过程中的重要作用机理。混凝过程结束后，监测含藻污泥储存过程中藻细胞的破损与藻类有机物释放情况，并研究温度条件的影响，探索钛盐除藻污泥最佳储存时间。实验结果表明，钛盐混凝抑制了藻细胞的裂解和细胞损伤，与常规混凝剂所得絮体相比，钛盐混凝所得絮体在常温下贮存时间更长，从藻裂解和藻毒素释放的角度，钛盐所得含藻污泥在20℃和35℃下应分别在12 d和8 d内处理，以避免藻毒素释放，防止二次水污染。这为实际水处理过程污泥处置时间提供了参考价值。另外，混凝所得富藻含钛污泥经高温煅烧可得二氧化钛纳米颗粒，实验结果表明，所得产品对染料、重金属和有机物均具有与市售二氧化钛相当甚至更好的光催化降解效果。