A laboratory divisional influent D-A2/O reactor was designed to treat sewage. All the trials lasted 8 months, and the results indicated that volume ratio of the optimal divisional influent of anaerobic and that of anoxia was 8:2; when the optimal hydraulic retention time(HRT) was 6 h, the optimal mixed-liquor return volume ratio was 200%, and the optimal sludge return volume ratio was 100%; and the optimal double anaerobic/anoxia alternative operating time(DAOT) was 1h. Under these conditions as above, the ...