NOVELTY - The apparatus comprises an advanced sewage treatment apparatus (100), a sludge treatment apparatus (200), and a microalgae cultivation apparatus (300). The sludge treatment apparatus includes: a first aerobic reactor, which is operated under aerobic conditions and serves to reduce activity of microorganisms in sludge and to ferment the sludge by fermentation of the microorganisms; and a second aerobic reactor, which is operated in a state in which air is injected in an amount larger than that in the first aerobic reactor and serves to increase the fermentation activity of the microorganisms.    USE - The apparatus is useful for cultivating microalgae using effluent from sludge treatment (claimed) or livestock excretions, where the microalgae are useful as animal feed and a raw material for bioenergy.    ADVANTAGE - The apparatus cultivates the microalgae with improved efficiency and less discharge amount of sludge and without the need of additional apparatuses.    DETAILED DESCRIPTION - The apparatus comprises an advanced sewage treatment apparatus (100), a sludge treatment apparatus (200), and a microalgae cultivation apparatus (300). The sludge treatment apparatus comprises: a first aerobic reactor, which is operated under aerobic conditions and serves to reduce the activity of microorganisms in sludge and to ferment the sludge by fermentation of the microorganisms; a second aerobic reactor, which is operated in a state in which air is injected in an amount larger than that in the first aerobic reactor and serves to increase the fermentation activity of the microorganisms and to degrade the sludge; and a membrane bio-reactor (MBR) (230), which serves to receive effluent from the second aerobic reactor and to biologically remove high-concentration organic matter from the effluent by the action of aerobic microorganisms while removing total suspended solids using the membrane. The effluent from the second aerobic reactor is separated into concentrated sludge. The effluent from the MBR is supplied to the microalgae cultivation apparatus. The concentrated sludge is returned to the second aerobic reactor. The concentration of nitrate nitrogen increases in the order of the first aerobic reactor, the second aerobic reactor and the MBR reactor. The microalgae cultivation apparatus comprises a microalgae cultivation reactor (310) and a microalgae membrane, in which the microalgae cultivation reactor serves to cultivate microalgae using, as nutrient, the effluent from the MBR reactor of the sludge treatment apparatus. The microalgae membrane serves to water in the microalgae cultivation reactor into microalgae and treated water. The advanced sewage treatment apparatus comprises: an anaerobic reactor serving to remove phosphorus from influent water while denitrifying nitrite nitrogen and nitrate nitrogen; a first intermittent aeration reactor and a second intermittent aeration reactor, which are operated under different conditions such as aerobic conditions and oxygen-free conditions, serve to convert organic nitrogen and ammonia nitrogen to nitrite nitrogen and nitrate nitrogen under aerobic conditions while allowing phosphorus in influent water to be taken by phosphorus-storing microorganisms, and serve to reduce nitrite nitrogen and nitrate nitrogen into nitrogen gas under oxygen-free conditions; and a first ceramic membrane and a second ceramic membrane, which are provided in the lower portions of the first intermittent aeration reactor and the second intermittent reactor, respectively, and serve to produce treated water, where the first intermittent aeration reactor and the second intermittent aeration reactor are operated under different conditions. The influent water discharged from the anaerobic reactor is supplied to one of the first intermittent aeration reactor and the second intermittent aeration reactor operated under aerobic conditions. The air is injected into the first intermittent aeration reactor through the first ceramic membrane to maintain the first intermittent aeration reactor in aerobic conditions while treated water is discharged to the outside through the second ceramic membrane, and the sludge in the second intermittent aeration reactor is supplied to the aeration reactor of the sludge treatment apparatus, when the first intermittent aeration reactor is under aerobic conditions and the second intermittent aeration reactor is under oxygen-free conditions. Each of the first ceramic membrane and the second ceramic membrane are provided with an air injection line and a treated-water discharge line, in which the air injection line serves to inject air into the first ceramic membrane or the second ceramic membrane. The treated-water discharge line serves to discharge treated water produced by the first ceramic membrane or the second ceramic membrane to the outside. The air is injected into the first ceramic membrane or the second ceramic membrane through the air injection line while the treated-water discharge line is blocked when the first intermittent aeration reactor or the second intermittent aeration reactor is under aerobic conditions. The injection of air through the air injection line is blocked while treated water produced by the first ceramic membrane or the second ceramic membrane is discharged to the outside when the first intermittent aeration reactor or the second intermittent aeration reactor is under oxygen-free conditions. An INDEPENDENT CLAIM is included for a method for cultivating microalgae using effluent from sludge treatment.    DESCRIPTION OF DRAWING(S) - The diagram shows a block diagram of an apparatus for cultivating microalgae.    Advanced sewage treatment apparatus (100)    Sludge treatment apparatus (200)    Membrane bio-reactor (230)    Microalgae cultivation apparatus (300)    Microalgae cultivation reactor. (310)