Pollution reduction by recirculated fill-and-drain mesocosm wetlands packed with woodchip/pumice treating impervious road stormwater.

Constructed wetlands (CWs) are natural-friendly method to eliminate the pollutants stormwater pollutants. For this study, a pilot-scale treatment system consisting of a sedimentation tank (ST) and five recirculated fill-and-drain wetlands (namely CW-1, CW-2, CW-3, CW-4 and CW-5) were constructed to treat the first-flush from the impervious road. From bottom to top, the main substrates of CWs were selected as 0 cm woodchip + 60 cm pumice for CW-1, 15 cm woodchip + 45 cm pumice for CW-2, 30 cm woodchip + 30 cm pumice CW-3, 45 cm woodchip + 15 cm pumice CW-4 and 60 cm woodchip + 0 cm pumice for CW-5. During the operational period, the reduction efficiencies of TSS, total COD, total nitrogen and total phosphorus were 89-100%, 52-100%, 31-87% and 72-100% by CW-1, 92-100%, -27% to 78%, 8-85%, 49-94% by CW-2, 89-100%, -97% to 77%, -29% to 86%, -46% to 94% by CW-3, 89-100%, -115 to 69%, -21% to 99%, 35-94% by CW-4 and 59-100%, -342%to 88%, -20% to 88%, -77% to 99% by CW-5, respectively. Overall, the reduction efficiency, except for nitrogen, declined as the amount of woodchip increased. As excepted, the employment of woodchip improved denitrification via providing with carbon sources, resulting in low NO3 -N but unfavourable COD concentrations in the effluent. And the combination use of woodchip and pumice as CW-3 or CW-4 is suggested, whereas the specific amount of woodchip and pumice should be determined based on the regional environmental goal.