A wastewater treatment facility incorporates a trivalent cation salt to
promote coagulation of flocculent material. The trivalent cation salt is
typically added between a primary and a secondary treatment stage in the
wastewater treatment facility. The trivalent cation is typically an
aluminum salt. The amount of trivalent cation can be optimized by
targeting a (M/D)/T ratio of less than about 1.0, where M is a monovalent
cation equivalent concentration and D is a divalent cation equivalent
concentration in the wastewater and T is a mass of the trivalent cation
in the sludge. The amount of trivalent cation can also be optimized by
targeting a M/T ratio of less than about 1.0, where M is a monovalent
cation equivalent concentration in the wastewater and T is a mass of the
trivalent cation in the sludge.