Removal of arsenic by pilot-scale vertical flow constructed wetland

Four pilot-scale Vertical Flow Constructed Wetlands(VFCWs) filled with gravel and planted with Phragmites australis were operated for seven months in the field to study the efficiency of arsenic removal in contaminated wastewater. The average arsenic removal efficiency by the VFCWs was 52.0%±20.2%, 52.9%±21.3%, and 40.3%±19.4% at the theoretical concentrations of 50 μg/L(CW50), 100 μg/L(CW100), and 500 μg/L(CW500) arsenic in the wastewater, respectively. The results also showed no significant differences in the removal efficiency for conventional contaminants(nitrogen, phosphorus, or chemical oxygen demand) between wastewater treatments that did or did not contain arsenic(P>0.05), except for phosphorus in CW500. The highest average monthly removal rate of arsenic occurred in August(55.9%–74.5%) and the lowest in November(7.8%–15.5%). The arsenic removal efficiency of each VFCW was positively correlated with temperature(P < 0.05). Arsenic accumulated in both substrates and plants, with greater accumulation associated with increased arsenic concentrations in the influent. The maximum accumulated arsenic concentrations in the substrates and plants at the end of the experiment were 4.47 mg/kg and 281.9 mg/kg, respectively, both present in CW500. The translocation factor(TF) of arsenic in the reeds was less than 1, with most of the arsenic accumulating in the roots. The arsenic mass balance indicated that substrate accumulation contributed most to arsenic removal(19.9%–30.4%), with lower levels in plants(3.8%–9.5%). In summary,VFCWs are effective for the treatment of arsenic-containing wastewater.