What is the mechanism behind pin floc formation during the coagulation-flocculation process and how can it be rectified?

Pin floc formation during coagulation-flocculation is characterized by the formation of very small, weak, and poorly settling flocs, often described as being about the size of a pinhead. This is usually due to either under-coagulation or over-coagulation, leading to unstable particles that don't aggregate effectively. The mechanism behind pin floc formation typically involves one or more of the following issues: 1) Insufficient Coagulant Dosage: When the coagulant dosage is too low, the charge neutralization of the colloidal particles is incomplete. This means the particles still retain some of their negative charge, causing them to repel each other and hindering the formation of larger flocs. 2) Over-Coagulation and Restabilization: Conversely, an excessive coagulant dosage can also cause pin floc. Adding too much coagulant can reverse the charge of the particles, making them positively charged and causi....