• Chemically-generated solids associated with the use of chemical coagulants, flocculants, and lime
• The incorporated water that comprises most of a residue’s weight and bulk
• The solids removed from the untreated water source.

From a direct treatment perspective, for a given raw water quality and degree of clarification, only the amount of chemically- generated solids can be controlled and reduced.

Coagulant-generated solids exist primarily as the metal hydroxides of the corresponding inorganic coagulants. Due to the molecular weight difference between Al(OH)₃ and Fe(OH)₃, the use of Al-based coagulants will typically generate, on a weight basis, 20 – 50% less chemical sludge than Fe-based coagulants. In specific applications, aluminum chlorohydrate and polyaluminum chorides are, on an equal metals basis, 25 – 30% more efficient than alum, and thus will reduce coagulant-generated solids formation by similar amounts.

Significant residue minimization can be accomplished by onsite dewatering prior to disposal. In such cases, careful coagulant selection can significantly increase the effectiveness of the dewatering process, thus significantly reducing the total residue weight and thus the corresponding disposal cost.