In-situ microscopy investigation of floc development during coagulation-flocculation with chemical and natural coagulants

This study aimed to include in-situ microscopy in the analysis of floc development during coagulation-flocculation for drinking water treatment. To this end, jartest series were carried out for natural and synthetic waters using aluminum sulfate, sulfate chloride, ferric chloride, and Opuntia sp. as coagulants. Coagulation under optimized conditions was monitored by an in-situ microscope in conjunction with image analysis. Obtained results enabled some insights on the coagulation process. Images captured different stages of initial floc development, including flocs exhibiting heterogeneous, branched, and irregular surface structures. From image analysis, wide distributions of flocculated particle sizes were found for both natural (19-15834 mu m) and synthetic water (19-21607 mu m), suggesting the occurrence collisions by adhesion and transport between particles, thus influencing floc formation rates depending on the medium. Average size and number of flocs, as determined by the image analysis algorithm as a function of the time, showed inverse correlation of floc growth with water clarification. The microscopic images also illustrated how different coagulants in different water sources undergo breaking through fragmentation or erosion. Our findings also highlight the importance of investigating additional aspects that involve conditions of mixing, development, breaking, regrouping, and resistance of flocs.