A constructed wetland may consume different levels of pollution in different types of wastewater. The focus of this study was the removal of heavy metals (Pb, Cr, and Cd) by plants and their fate in constructed wetland mesocosms. With hydraulic regime manipulation, heavy metals were retained in the ferric dewatered sludge either by adsorption to the carboxylate groups and iron oxy-hydroxide under anaerobic conditions or by co-precipitation with iron oxy-hydroxide under aerobic conditions. Under anaerobic conditions, most heavy metals accumulate in the bottom layer and decrease when moving to the top one. In turn, under aerobic conditions, most of the heavy metals accumulate in the bottom and top layers. Plants play a minor role in heavy metal removal. About 16% of total heavy metals added to the ferric dewatered treatment sludge were taken up by plants. Roots accumulated roughly 64% of the total lead take up by plants, 66% of the chromium, and 63% of the cadmium, respectively, and passed 36%, 34%, and 37% of the aboveground tissues for harvesting. As a conclusion of this study, when constructed wetland is used, the role of hydraulic regime, substance used, and vegetation should not be ignored in the process of wastewater purification in constructed wetland.