Simultaneous removal of vanadium and nitrogen in two-stage vertical flow constructed wetlands: Performance and mechanisms

Vanadium (V(V)) and nitrate, as co-concomitant pollutants in water bodies, pose potential threats to the eco-environment and human health. This study was to reveal the feasibility of simultaneous removal of V(V) and nitrate in the series-wound vertical flow constructed wetlands (CWs) with iron ore (B-CWs)/manganese ore (C-CWs)-wood substrates. The results showed that B-CWs could achieve efficient V(V) and NO3−-N removal with the influent of 2 and 10 mg/L (V(V)/NO3−-N = 1:5), respectively. With the increase of V(V)/NO3−-N ratio (V(V)/NO3−-N = 1:1), B/C-CWs exhibited better combined pollution removal. Even when nitrate was removed (V(V)/NO3−-N = 1:0), the systems could maintain a good capacity for V(V) removal. High V(V) (20 mg/L) significantly inhibited V(V) removal, with a slight recovery of the performance as the decrease of V(V) influent. High NO3−-N concentration (10 mg/L) effectively enhanced V(V) removal and restored C-CWs to the better level. V(IV) precipitates/oxides were the main reducing end-products. High abundance of V(V)-reducing bacteria and iron/manganese cycling pumps ensured efficient V(V) removal. [Display omitted] •Simultaneous removal of V(V) and nitrogen were achieved at low V(V)/NO3−-N ratio.•High V(V) inhibited but high NO3−-N enhanced V(V) removal.•V(IV) precipitates/oxides were the main reducing end-products.•Abundant V(V)-reducing bacteria and Fe/Mn-cycling pumps ensured efficient V(V) removal.