ABSTRACT
This chapter uses both the mechanistic and operational definitions of the term coagulation. Sodium silicate modified by acidification was utilized as a coagulation aid to improve the treatability of water from Lake Michigan. Aluminum and iron salts are equally capable of reducing inorganic turbidity to an acceptable level. However, they vary significantly in their ability to remove soluble Natural Organic Matter. Several laboratory studies have been conducted to investigate variables affecting sludge thickening and dewatering characteristics. These must be viewed within the framework of overall treatment efficiency within such other issues as concurrent organics removal, solids separation characteristics, and minimization of residual alum concentrations. Destabilization of colloids by charge neutralization requires collisions between the colloids and the incipiently forming products of the hydrolysis reactions. The mechanisms of coagulation with organic polymers are charge neutralization and interparticle bridging. The high intensities of mixing may not be necessary for organic polymers because these mechanisms are slightly different than those for inorganic coagulants.
