Historically, secondary clarifiers have contributed to instability in plant performance. The flocculator-clarifier development has demonstrated in a variety of plant situations that stable secondary process operation is achievable. Consistently low effluent SS levels (average values of 10 mg/l) are realistically achievable. This performance enhancement has been obtained at lower costs than for conventional designs. The clarifier incorporates some special design features including a large flocculator centerwell to incorporate dispersed solids into settleable floc. Other features include rapid sludge removal, inboard weir placement and deeper sidewater depths than conventionally used (5.5 to 6m).