In high rate solids contact type clarifier, coagulants and large quantities of recirculating sludge’s are thoroughly mixed and are retained in intimate contact for a prolonged period of time in the draft tube and cone sections of the solid clarifier.
If using microbial purification there will be zero sludge to worry about. If not most WWTP add to the existing problems by using chlorine to kill everything in its path. This does include the end user. Just slower.