Conditions and Mechanisms Affecting Nutrient Removal in a Carrousel Oxidation Ditch with low Dissolved Oxygen Concentration

The approach for Nutrient removal called SND (in time and in space with constant conditions) was applied in OD(Oxidation ditch)which is a situation where SND often has a significant impact. Usually in the OD, the spatial anoxic zones along the ditch are created by adjusting the aeration at different points; and as high internal recycle flow subjects mixed liquor to alternating aerobic and anoxic conditions, there exist obvious advantages in performing SND in the ditch. Carrousel Oxidation Ditch with low dissolved oxygen was used to deal with domestic wastewater in the A Plant. The stable system demonstrated that the data revealed that removal rates of COD, NH4-N, TN, and TP were 87%, 86%, 80% and 60%, respectively. Although hydraulic retention time (HRT) was only 5-6 hours less than that of design (15 hours), the removal of nitrogen because of SND and phosphorus met the second-class standard GB18918-2002 of China. As well as the analyses demonstrated that there was a good phenomena of SND in the oxidation ditch (OD) because of low DO and then got a good removal phosphorus for low nitrate concentration in RAS. However, the increasing of nitrogen and phosphorus from oxidation ditch end to secondary sedimentation effluent were negative to removal nitrogen and phosphorus.