Constructed wetlands for petroleum refinery wastewater treatment: a state-of-the-art review.

Constructed wetland systems provide an economically viable and sustainable approach compared to the traditional technologies for the treatment of petroleum hydrocarbons contaminated wastewater, an important issue for the oil industry worldwide. This paper collects the last decade of research on the effectiveness of CWs for polycyclic aromatic hydrocarbons (PAHs), total petroleum hydrocarbons (TPHs), and other noxious pollutant removal through natural degradation bioprocess, phytoextraction, and phytoimmobilization. Through the investigation of different designs (horizontal and vertical flow systems), operational parameters (pH, hydraulic retention time and temperature), and plant-microbe interactions, research has led to the identification of the optimal conditions for hydrocarbon removal. Key findings reveal that more than 90% elimination of pollutants such as benzene, TPHs, and PAHs occurs via CWs when supported by hydrocarbon-degrading microbial consortia including Pseudomonas, Acinetobacter, Rhodococcus, and Mycobacterium acting in synergy with native macrophytes. However, several challenges remain, including the incomplete degradation of high molecular weight PAHs, the presence of co-contaminants, and the impacts of climate change on system performance.