The invention discloses a biological 
sewage treatment device and a biological 
sewage treatment method for synchronous 
nitrogen and 
phosphorus removal and 
sludge reduction. The device comprises a water inlet 
pipe 1, an anaerobic pond 2, a mid-
sedimentation tank 3, an intermediate 
pool 4, a BAF 5, an anoxic pond 6, a post-
aeration tank 7, a secondary 
sedimentation tank 8, and a water outlet 
pipe 9 in series connection in order; the treatment process comprises the following steps: mixing 
raw water and P-rich returned 
sludge in the anaerobic pond, wherein denitrifying 
phosphorus accumulating 
bacteria (DPBs) absorb and store VFA in a body in a form of PHB (poly-beta-hydroxybutyrate) and release a large amount of 
phosphorus; removing VOD remained in the BAF and nitrating the 
nitrogen; introducing BAF 
nitrification liquid and the 
sludge in the mid-
sedimentation tank into the anoxic pond together, wherein the DPBs performs 
denitrification for absorbing the phosphorous by using the PHB in the body as an 
energy source and a 
carbon source and using NO3<-> as an 
electron acceptor; removing the unnecessary phosphorus contained in the post-
aeration tank and blowing off the 
nitrogen to prevent the sludge from floating upwards; discharging the supernatant in the secondary sedimentation tank, wherein part of the sludge containing a large amount of DPBs is refluxed and the remaining sludge is discharged. The biological 
sewage treatment device and the biological 
sewage treatment method for the synchronous nitrogen and the phosphorus removal and the sludge reduction resolves the conflict between the 
denitrification and the phosphorous removal, and ensures the stable 
water quality of 
effluent and low yield of the sludge.