Polishing of synthetic electroplating wastewater in microcosm upflow constructed wetlands: Effect of operating conditions

This paper addresses the issue of polishing electroplating wastewater in subsurface vertical flow constructed wetland. Electroplating wastewater treatment or polishing in constructed wetlands (CWs) was studied to a very limited degree. Four types of microcosm upflow constructed wetlands were selected for the experiment based on type of bed media and the presence or absence of vegetation (Phragmites australis). The main objective of the system design was to promote metals removal by precipitation as sulfides mediated by sulfate reducing bacteria. The experimental system consisted of eight PVC columns (diameter 20 cm) filled up to. 63.5 cm with either gravel or gravel-peat mixture and was operated for one year, polishing synthetic electroplating wastewater. The wastewater used in this study contained metals (Cu, Ni, Pb and Zn), cyanides and sulfates, which typically occur in electroplating wastewater. During the experiment the effect of the following factors was studied: presence of vegetation, hydraulic loading, wastewater strength, type of bed media, and addition of lactates as external carbon source for the columns with gravel. The results showed that the uplow columns can efficiently remove metals (with the exception of Pb) and cyanides. It was observed that the removal efficiency of Cu, Ni and Zn increases with increasing influent concentration of metals and increasing hydraulic loading rate. The role of plants and bed media was minor. The addition of lactates to the feed of the columns with gravel was found to improve the reduction of metals concentration in the passing wastewater.