Transfers and transformations of zinc in constructed wetlands: Mitigation of a refinery effluent

Two pilot-scale wetlands were constructed to facilitate transfers and trans formations of Zn in a secondary refinery wastewater effluent. The wetlands (6.1 x 30.5 m, width x length) were planted with Scirpus californicus and w ere operated with 24-h nominal hydraulic retention times (HRT). To evaluate wetland performance in terms of Zn removal at two water depths, one wetlan d was amended with a nominal concentration of 4.0 mg Zn/l as ZnCl2 for 144 days at an operational water depth of 0.3 m, and for an additional 22 days at a water depth of 1 m. The second wetland served as an unamended control. From wetland inflow to outflow, approximately 38% of total recoverable and 65% of soluble Zn was removed during the experiment at the 0.3-m water dep th. During the flooded period (1.0-m water depth), approximately 18% of tot al recoverable and 66% of soluble Zn was removed from the effluent; Toxicit y of effluent to Ceriodaphnia dubia Richard and Pimephales promelas Rafines que decreased from inflow to outflow by similar to 54 and 73%, respectively , at the 0.3-m water depth, and by at least 100% at the 1.0-m water depth. These data illustrate successful construction of wetlands for transfers and transformations of Zn from the water column and for decreases in associate d toxicity. (C) 2000 Elsevier Science B.V. All rights reserved.