Constructd wetland system is one of the ecological engineering technologies used on wastewater treatments. In this study, we discussed the treatment efficiencies of oil refining and steel-milling wastewater by four lab-scale constructed wetland systems (0.8-m long by 0.4-m wide by 0.7-m deep), which were all filled with gravel media, and planted with Phragmites communis. The constructed wetland systems were designed into two types: free water surface (FWS) and subsurface flow (SSF) wetland systems, which were discharged with two different types of wastewater (oil refining and steel-milling). The experiments of this study were run by five stages. The experimental results showed that almost all of the contaminants could be reliably removed from wastewater by the constructed wetland systems, especially in the SSF systems. During the experiments, the second stage of the experiments had the best treatment efficiencies, in which the flowrate was controlled at 5mL/min. The hydraulic retention time (HRT) in FWS and in SSF werecalculated equal to 7.5days, and 5.36days, respectively.

In recent years, interest in wastewater treatment through constructed wetlands has been significantly increased because of their low cost and energy requirement. In this study, pilot-scale constructed wetland systems were developed to evaluate the efficacy and effectiveness on the treatment of oil-refining and steel-milling wastewater. The constructed wetland used to treat the oil-refining wastewater included one free water surface system (FWS) filled with sandy media and one subsurface flow system filled with gravel media. The plants grown on the wetland were Phragmites communis. The hydraulic retention time for the two systems was approximately 7 and 5 days, respectively. A two-stage subsurface flow constructed wetland system was used to treat steel-milling wastewater. This system, which filled with gravel media were planted with Phragmites communis (the first stage) and Typha orientalis (the second stage). The hydraulic retention time for this system was approximately 7 days. Experimental results showed that the two constructed wetland systems for the oil-refining wastewater treatment could remove most of the wastewater pollutants. Moreover, the first system (FWS) played a more important role on the wastewater treatment. The efficiency of the first stage of the wetland system, which was used for steel-milling wastewater treatment was not significant due to the inhibition of the plant growth by the wastewater. However, the treatment efficiency was increased at the second stage after planting new plants. Results from the two-stage treatment system indicate that higher treatment efficiencies were observed except for ammonium. Results from this study would be very useful in the design of constructed wetlands for practical application to treat oil-refining and steel-milling wastewaters.