Comparison of the Treatment Performances of High-strength Wastewater in Vertical Subsurface Flow Constructed Wetlands Planted with Acorus calamus and Lythrum salicaria

Abstract

The ability of pilot-scale vertical subsurface flow constructed wetlands (VSCWs) to treat two types of high-strength [400 mg/l of COD or 80 mg/l total nitrogen (TN)] simulated wastewater under greenhouse conditions was studied during an 8-month period. Eighteen CWs units were used: six units were planted with Acorus calamus (A. calamus), another six units were planted with Lythrum salicaria (L. salicaria) and six units were unplanted. Each set of units was operated at hydraulic loading rates of 40 l/d. The treatment performance displayed that average removal rates of chemical oxygen demand (COD), TN, total phosphorous (TP) and total organic carbon (TOC) were 44-66%, 35-63%, 47-76% and 22-40%, respectively. Both species grew well under any high loading treatment. We noted that plant uptake and storage were both important factors responsible for nitrogen removal during the study period. Both planted wetlands improved pollutants removal compared with the unplanted control wetland. L. salicaria produced more shoots and biomass than the A. calamus, which can remove more P nutrients than A. calamus especially for high nitrogen (N) loading treatment. However, A. calamus was always more efficient species that improved nitrogen nutrients plant uptake because of their longer growth period. Our findings suggested that the vertical subsurface flow constructed wetlands could well treat the high-strength wastewater in greenhouse condition. If good capacity of all nutrients removal is considered, A. calamus is more appropriate than L. salicaria particularly under high N loading in the influent.