This paper describes how bench-scale flocculation tests were scaled up to design plant scale flocculators in secondary clarifiers to yield markedly improved plant performance. Bench-scale tests were conducted to test the merits of the addition of a flocculation step to secondary sedimentation tanks in activated sludge plants. These bench-scale tests proved promising enough to justify incorporation of flocculators into secondary clarifiers at Eugene, Oregon, and Santa Rosa, California. Tests at these plants proved the original concept that secondary effluent quality could be dramatically improved. The technology has since been used to save millions of dollars in capital costs by avoiding effluent filtration.