Purification capacity of a highly loaded laboratory scale tidal flow reed bed system with effluent recirculation

The purification capacity of a laboratory scale tidal flow reed bed system with final effluent recirculation at a ratio of 1:1 was investigated in this study. In particular, the four-stage reed bed system was heavily loaded with strong agricultural wastewater. Under the hydraulic and organic loading rates of 0.43 m3/m2·d and 1055 gCOD/m2·d, respectively, the average removal efficiencies obtained for COD, BOD5, SS, NH4–N and P were 77%, 78%, 66%, 62% and 38%, respectively. Even with the high loading rates, approximately 30% of NH4–N was converted into NO2–N and NO3–N from the mid-stage of the system where nitrification took place. The results suggest that the multi-stage reed bed system could be employed to treat strong wastewater under high loading, especially for the substantive mass removal of solids, organic matter and ammoniacal-nitrogen. Tidal flow combined with effluent recirculation is a favourable operation strategy to achieve this objective.