Characteristics of flow regime adjustment enhancing carbon source recovery in activated primary sedimentation tank

In this study, different numbers of baffles were arranged in settling zone of an activated primary sedimentation tank (APST) to adjust the flow regime of sewage, and the characteristics of flow regime adjustment enhancing carbon source recovery in the APST were explored. The results showed that, compared with the APST without baffles, setting one baffle at the front end of settling zone led to the lowest sedimentation loss of soluble chemical oxygen in the settling zone, and the SCOD and volatile fatty acid concentrations in the effluent increased by 52 mg/L and 4.49 mg/L, respectively, furthermore, the SCOD/total nitrogen (TN), and SCOD/total phosphorus (TP) in the effluent also increased by 22.47%, and 11.95%, respectively. To evaluate the mechanism of setting baffles for carbon source recovery, the numerical simulation of flow regime adjustment was utilized. The results showed that, under the condition of setting one baffle, three large recirculation zones were formed which increased the probability of collision and friction between particulates to avoid the dissolved carbon that had been desorbed in the mechanical agitation zone from being re-adsorbed and settling in the settling zone. Moreover, the baffle changed the streamlines of sewage, thereby resuspending more small carbon sources that had already settled and increasing the carbon source content of effluent. Thus, this study provided a new method of adjusting sewage flow regime in APST for enhancing the efficiency of carbon source recovery which could help improving biological nitrogen and phosphorus removal in wastewater treatment plants.