Formation of aerobic granular sludge was examined in a novel continuous flow configuration, at 20 +/- 1 degrees C. Synthetic proteinaceous wastewater with municipal primary effluent characteristics was used (i.e., COD = 370 +/- 30 mg/L; TN = 43 +/- 7 mg/L; and TP = 10 +/- 2 mg/L). Various levels of selective pressure were applied after inoculation with flocculent sludge (i.e., estimated velocity gradients during settling between 1 and 9 1/s). Impeller rpm of 15 and below generated floccular-granular biomass, while 20 rpm and above generated large granules with a filamentous population. Effluent soluble COD, total inorganic nitrogen, and phosphate of 25 +/- 7 mg/L, 11 +/- 1 mg/L, and 0.1 +/- 0.1 mg/L, respectively, were obtained. Observed yields were as low as 0.08-0.19 g-VSS/g-COD and whole sludge solids retention time was 18 +/- 1 d. Famine conditions developed for 90% of the total aerobic volume and > 45 +/- 3% anaerobic substrate utilization was recorded. Aerobic granulation was demonstrated feasible under continuous flow providing adequate treatment with low biomass yields.