The behaviour of particles settling through water is according to Stoke's law which states that the drag resistance to settling is proportional to the diameter of the particle, however the gravitational settling force on the particle is proportional to the cube of the diameter. Therefore, increasing effective particle size by clumping particles together results in much higher settling velocity. Chemicals such as polymeric coagulants and flocculants work to enhance solid-liquid separation by clumping particles together. There are many chemistries available, whose function needs to be optimised through careful product selection based on your system's physical and chemical conditions and suitable application into your system.