NOVELTY - Wastewater treatment process (P1) involves subjecting wastewater to activated sludge process using floc-like aerobic biomass, where wastewater is fed to granular biomass process operated in parallel to activated sludge process and using aerobic granular biomass, and part of the biomass issuing from granular biomass process is fed to the activated sludge process, where part of the biomass fed to activated sludge process has a lower settling velocity than the part of the biomass of granular biomass process which is not fed to activated sludge process.    USE - For biological treatment of wastewater using activated sludge reactor in hybrid process including aerobic granular biomass reactor.    ADVANTAGE - The system provides a cost-effective solution to improve the capacity of biological removal of phosphorus of an existing conventional activated sludge (CAS) system equipped with chemical phosphorus removal. The system allows additional biological phosphorus removal capacity to be introduced in the CAS system without the elaborate construction of separate anoxic and anaerobic compartments in the CAS system and with chemical phosphorus removal in the CAS system becoming less important or even superfluous. The wastewater was treated in the aerobic granular biomass (AGB) system operating in parallel to the CAS system, part of the low weight organics were biodegraded by the AGB in anaerobic zones of the granules, this results in lower energy consumption for aeration and the production of biogas, which could be captured and utilized.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for installation for carrying out the process (P1) comprising activated sludge reactor (3) with liquid inlet, liquid outlet, gas inlet, granular biomass reactor (4) with liquid inlet at bottom of the reactor and liquid outlets at one third of the height of reactor, a gas inlet at the bottom of the reactor, liquid line connecting an outlet of granular biomass reactor with inlet of activated sludge reactor, and separator (5) connected with liquid outlet of activated sludge reactor, having sludge outlet and clarified liquid outlet, and further comprising device for regulating relative liquid flows to liquid inlet of activated sludge reactor and liquid inlet of the granular biomass reactor.    DESCRIPTION OF DRAWING(S) - The figure shows schematic view of hybrid wastewater treatment process comprising waste sludge processing unit.    Sludge volume index (1)    Settling velocity (2)    Activated sludge reactor (3)    Granular biomass reactor (4)    Separator (5)