Treatment of wastewater with aerobic granular sludge (AGS) has major advantages compared to activated sludge. The only commercial system that uses AGS is the Nereda® batch process. The disadvantage of this system is the lack of existing infrastructure. AGS in continuous systems could be a solution to this disadvantage. That’s why the HARKOS pilot is built. This pilot is based on the enhanced biological phosphorus removal (EBPR) process. The aim of this study is to make sure this pilot runs according to the EBPR process (reactor characterization) and to apply biological selective pressure for granulation. This biological selective pressure consists out of four pillars. Prevention of COD overshoot into the aerobic zone, as much COD in the anaerobic zone to storage polymers, enrichment for bio-p organisms and compartmentalization of the reactor. It’s concluded that the pilot is characterized, that no COD overshoot is present, that more COD is stored as storage polymers, that the sludge is enriched for bio-p organisms and that the reactor is well enough compartmentalized. The biological selective pressure is applied. If enough physical selective pressure is applied granulation will start in the HARKOS pilot.