Cultivation of aerobic granular sludge in continuous flow under various selective pressure.

ABSTRACT

Formation of aerobic granular sludge was examined in a novel continuous flow configuration, at 20 ±â€¯1 °C. Synthetic proteinaceous wastewater with municipal primary effluent characteristics was used (i.e., COD = 370 ±â€¯30 mg/L; TN = 43 ±â€¯7 mg/L; and TP = 10 ±â€¯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 ±â€¯7 mg/L, 11 ±â€¯1 mg/L, and 0.1 ±â€¯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 ±â€¯1 d. Famine conditions developed for 90% of the total aerobic volume and >45 ±â€¯3% anaerobic substrate utilization was recorded. Aerobic granulation was demonstrated feasible under continuous flow providing adequate treatment with low biomass yields.