Performance of a half-saturated vertical flow wetland packed with volcanic gravel in stormwater treatment. 
A half-saturated pilot-scale wetland planted with Acorus calamus was built to treat urban stormwater.  The design comprises a sedimentation tank for pretreatment, and a vertical flow volcanic gravel wetland bed equipped with a recirculation device.  Eighteen rainfall events were monitored in 2012.  The treatment system achieved total removal efficiencies of 99.4, 81, 50, and 86% for suspended solids, organic matter, nitrogen and phosphorus, respectively, and 29, 68, and 25% for copper, zinc, and lead, respectively, at a 3-day hydraulic residence time.  In the wetland bed, the removal of ammonia, total nitrogen, and zinc were improved by recirculation.  Plant uptake provided 18% of nitrogen removal and 39% of phosphorus removal.  During the experimental stage, only 1.4% of the pore volume in substrate was reduced due to clogging, implying that the wetland can operate without clogging for a relatively long period.