Abstract
Aerobic granular sludge technology offers a possibility to design compact wastewater treatment plants based on simultaneous chemical oxygen demand (COD), nitrogen and phosphate removal in one sequencing batch reactor. In earlier studies, it was shown that aerobic granules, cultivated with an aerobic pulseโfeeding pattern, were not stable at low dissolved oxygen concentrations. Selection for slowโgrowing organisms such as phosphateโaccumulating organisms (PAO) was shown to be a measure for improved granule stability, particularly at low oxygen concentrations. Moreover, this allows long feeding periods needed for economically feasible fullโscale applications. Simultaneous nutrient removal was possible, because of heterotrophic growth inside the granules (denitrifying PAO). At low oxygen saturation (20%) high removal efficiencies were obtained; 100% COD removal, 94% phosphate (Pโ) removal and 94% total nitrogen (Nโ) removal (with 100% ammonium removal). Experimental results strongly suggest that Pโremoval occurs partly by (biologically induced) precipitation. Monitoring the laboratory scale reactors for a long period showed that Nโremoval efficiency highly depends on the diameter of the granules. ยฉ 2005 Wiley Periodicals, Inc.