This paper discusses dissolved-air flotation (DAF) for tertiary treatment and secondary effluent polishing. The process has the capcity to handle high concentrations of feed solids, particularly important during upset conditions during secondary treatment. Performance of DAFs applied to secondary effluents at five different plants are presented. Even during upset conditions with high feed TSS, removals through the DAF are expected to be approximately 90%. For well operated secondary treatment systems and feed TSS at 10 to 20 mg/L, DAF effluent turbidities can be expected to be below 1 to 2 NTU.