Occurrence of Denitrifying Dephosphatation in a Hybrid Constructed Wetland System and Its Stability

Abstract

This study was conducted to explore the startup characteristics and stability of a hybrid constructed wetland (HCW) system with a denitrifying dephosphatation process, which was composed of two tidal flow-constructed wetlands (termed T-A and T-B). As the system was operated according to the two-time feeding tidal flow operation mode, denitrifying dephosphatation and nitrification could be respectively enhanced in T-A and T-B, and the HCW achieved ideal simultaneous denitrification and phosphorus removal effects when treating domestic sewage. The introduction of periodical carbon source supplements for phosphorus harvesting alleviated excessive phosphorus accumulation in T-A and increased the storage of PHB within denitrifying phosphate-accumulating organisms (DPAOs). Subsequently, a stable and efficient denitrifying phosphorus removal effect could be guaranteed to some extent as the HCW system was operated during the test. As the phosphorus harvesting cycle length was 30 d, the mean phosphorus recovery efficiency of the HCW system was 63.97% throughout the experiment. Regarding the typical cycle, the mean TP and NOx--N removal efficiencies of T-A could respectively achieve (97.86±0.70)% and (98.29±2.62)% during the denitrifying dephosphatation process, and the amounts of phosphorus release and PHB synthesis in T-A could also reach up to (1486.29±123.25) mg and (4.43±0.57) mmol·g-1, respectively, during the phosphorus harvesting process. Meanwhile, the utilization rate of the supplementary carbon in the system was (94.65±2.66)%. To summarize, this study offers a new method for simultaneous denitrification and phosphorus removal in constructed wetlands, and expands the development and application range of phosphorus recovery processes.