Hybrid constructed wetland for treatment of power plant effluent polluted with hydrocarbons

Constructed wetlands (CWs) have good potential for application in the treatment of various types of polluted water in Iraq, including industrial wastewater, due to their low cost relative to the current conventional treatment technologies. Hybrid CW with a continuous-flow system was tested for the treatment of highly polluted industrial wastewater from the Al-Najibiyia Power Plant in Basrah City for 72 days with 5 days of retention time. The system consisted of a horizontal subsurface flow system (HSSF) planted with Phragmites australis (Cav.) followed by a surface flow (SF) system planted with Hydrilla verticillata (L.f.) Royle. A second system without plants served as a contaminant control system. Total petroleum hydrocarbons (TPHs), petroleum aromatic hydrocarbons (PAHs) and water quality were measured for both raw and treated wastewaters and plant status parameters were monitored. The presence of both plants and substrate had a significant effect on the removal efficiency and mass removal rate of all pollutants at (p < 0.05). The planted system performance showed a percentage removal of pollutants reaching to: 65.9 % for BOD5, 91.0 % for COD and 88.8 % for total suspended solids (TSS) while removal efficiency of BOD5, COD and TSS for unplanted systems was only 44.7, 64.5 and 68.7 %, respectively. The removal efficiencies of TPHs, and PAHs by the hybrid system were 96.5, and 96.0 %, compared to only 71.0 % and 51.0 % for unplanted system, respectively, showing that hybrid CW could enhance pollutant removal efficiency better than single CW. It is revealed also that the high efficiency in removing pollutants is the result of the plant and substrate presence and the interaction between plants and the surrounding microbial community. Thus, constructed wetlands (CWs) are a good option for industrial wastewater treatment due to its simple construction and effectiveness to remove hydrocarbons.