The invention discloses a 
sewage treatment device, 
system and method. The 
sewage treatment device comprises a reaction column, an aerator, a water feeder and a water drainage device, wherein the reaction column is vertically arranged, the water feeder is arranged below the reaction column, the aerator is arranged at the bottom of the reaction column, the water drainage device is arranged above the reaction column, an 
activated sludge water purification region, a 
biofilm water purification region and a clear water region are arranged in the reaction column from bottom to top according to a 
water flow direction sequentially; and a bearing layer with the capabilities of water permeability and 
sludge isolation is arranged between the 
activated sludge water purification region and the 
biofilm water purification region. The 
sewage treatment system comprises a plurality of 
sewage treatment devices which are connected in series with one another. The 
sewage treatment method comprises the following steps: (1) a starting phase, namely, injecting 
activated sludge into the activated 
sludge water purification regions of the reaction columns in each 
sewage treatment device in the sewage 
treatment system, and carrying out smothering 
aeration; and (2) a continuous running phase, namely, regulating according to the following principles: the longer the 
running time is, the larger the water inlet quantity is, and the larger the 
aeration quantity is. The sewage treatment device, 
system and method are strong in loading ability, long in 
backwashing period and low in 
energy consumption and 
sludge discharge.