NOVELTY - A sewage treatment apparatus comprises outer ring as biotreatment zone (4) filed with filler (9) having surface grown with cultured and acclimated biomembrane and equipped with aeration pipeline system (7) and water outlet (6), inner ring as complete active sludge biotreatment zone (3) provided with sewage inlet pipe (1), sludge reflux pipe (2) and water outlet (5) connecting with outer ring, baffle wall, gate (8) equipped on baffle wall to control flow of anaerobically treated sewage from inner ring to outer ring, and controllable reflux gate designed on bottom of outer ring.    USE - A sewage treatment apparatus.    ADVANTAGE - The apparatus has synergy of active sludge and biomembrane, flexible operation, performs anaerobic, anoxic and/or aerobic treatment, saves investment of project, reduces land area of occupancy, and reduces sludge reflux amount by 40-80% and operation cost by 18-31%.    DETAILED DESCRIPTION - A sewage treatment apparatus comprises outer ring as biotreatment zone (4) filed with filler (9) having surface grown with cultured and acclimated biomembrane and equipped with aeration pipeline system (7) at lower or middle part and water outlet (6) at upper part, inner ring as complete active sludge biotreatment zone (3) provided with sewage inlet pipe (1) and sludge reflux pipe (2) extending to bottom part and water outlet (5) at upper part to connect with outer ring, baffle wall separating inner and outer rings, gate (8) equipped on baffle wall to control flow of anaerobically treated sewage from inner ring to outer ring, and controllable reflux gate designed on bottom of outer ring. The outer ring and baffle wall comprises stainless steel, carbon steel, glass steel, or reinforced concrete. An INDEPENDENT CLAIM is included for a method of treating sewage comprising:    (A) culturing active sludge in inner ring and culturing and acclimatizing surface biomembrane of filler in outer ring;    (B) feeding sewage into inner ring through sewage inlet pipe, controlling amount of refluxed sludge entering inner ring at 20-60% and mixing quickly fed sewage with refluxed sludge in active sludge treatment zone of inner ring;    (C) mixing with biological active sludge mixed solution in anaerobic condition in tank, flowing mixed solution from lower to upper part of inner ring and forming suspension of active sludge layer with high concentration;    (D) passing sewage through sludge suspension layer to reach inner ring water outlet pipe at sewage retention time of 1.5-3 hours in inner ring and flowing into cooperative treatment zone of outer ring;    (E) flowing anaerobically treated sewage spirally forward along clearance of fillers;    (F) allowing air in aeration pipeline system to move from lower to upper part;    (G) contacting sewage with active sludge on fillers and biomembrane at retention time of 4-8 hours in outer ring; and    (H) discharging sewage through water outlet of outer ring.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic side view of sewage treatment apparatus.    Sewage inlet pipe (1)    Sludge reflux pipe (2)    Active sludge biotreatment zone (3)    Biotreatment zone (4)    Water outlet (5, 6)    Aeration pipeline system (7)    Gate (8)    Filler (9)