Removal of Total Phosphorus From Septic Tank Effluent by theHybrid Constructed Wetland System

The main objectives of this study were to: (1) investigate the performance of TP removal from septic tank effluent by the hybrid constructed wetland consisting of a horizontal flow, and a vertical flow unit in series, (2) compare the discrepancy in TP removal efficiencies by different plant species, and (3) investigate the effects of HRT, plant and season on the removal of TP in the hybrid constructed wetlands. The results show that the average removal rates of total phosphorus (TP) for the hybrid system consisting of HF1+VF1(planted Cyperus alternifolius, Hedychium coronarium Koen) in summer, autumn, winter and spring were, respectively, 96.8%, 97.4%, 94.5%, and 93.4% and were, respectively, 97.6%, 97.7%, 97.2%, and 98.3% for the hybrid system consisting of HF2+VF2(planted Schoenoplectus lacustrwas, canna indica), while were, respectively, 93.1%, 96.6%, 91.6%, and 90.7% for the hybrid system consisting of HF0+VF0 (unplanted). It is apparent that planted wetlands could improve their effluent quality. The removal capacities of phosphorus by four plant species (Cyperus alternifolius, Hedychium coronarium Koen, Schoenoplectus lacustrwas, and canna indica) were compared in these hybrid systems for the treatment of septic tank effluent. The removal capacity of phosphorus by these plants ranged from 2.0 g/m2 to 13.33 g/m2; Cyperus alternifoliu showed the highest uptake on TP, while Hedychium coronarium Koen showed the least uptake. Different plants had different phosphorus capacities by plant uptake. Based on nutrient balance in one year's operation, 2.3% to 15.5% of TP were exhibited by aboveground biomass, indicating that macrophytes are essential to efficient phosphorus removal in the hybrid constructed wetland.