Hierarchical dissolved oxygen bioreactor

The invention relates to the technical field of biological denitrification equipment, and provides a graded dissolved oxygen bioreactor which comprises a reaction tank, a driving part, a rotating shaft and a plurality of stirring discs, the stirring disc comprises a disc body, a first disc cover, a second disc cover and a fastener; a plurality of mounting blocks are arranged on the side, close to the second disc cover, of the first disc cover at intervals, a plurality of first mounting grooves are formed in the side, close to the first disc cover, of the second disc cover at intervals, and the mounting blocks are inserted into the first mounting grooves; one end of the fastener sequentially penetrates through the second disc cover and the mounting block and is in threaded connection with the second disc cover, and the other end of the fastener abuts against the second disc cover. The first disc cover and the second disc cover are both in threaded connection with the disc body, and a receding hole allowing the