Treatment performances of compost-based and gravel-based vertical flow wetlands operated identically for refinery wastewater treatment in Pakistan

This paper describes a constructed wetland treatment system designed to treat wastewater from oil refinery. In 2003, to promote the practical development of constructed wetlands (CWs) used for industrial wastewater treatment in Pakistan, a series of investigations was conducted to evaluate the feasibility of using constructed treatment wetlands to remove pollutants from refinery wastewater. The main objective of the research was to quantify the effect of different filter media on the treatment performance of vertical flow wetlands in the prevailing climate of Pakistan. Wastewater produced from the oil refinery contains high concentrations of organic and inorganic pollutants; therefore it cannot be discharged directly into river without any treatment. Phragmites karka were planted in both containers as a vertical flow wetland to evaluate their efficiencies in the purification of wastewater and their growth in wetlands fed with oil refinery wastewater. The results from a 1-year treatment showed that the purifying efficiency of constructed wetlands for oil-refined wastewater was low at the beginning but it improved gradually with the growth of plants and biofilm. Thus, a gravel-filled wetland and organic compost filled wetland were operated identically with primarily treated refinery wastewater at a hydraulic loading rate of 0.100 m d−1, intermittently. According to the results, the removal efficiencies for the compost and gravel wetland cells varied as follows during the experimental period of 1 year: total suspended solids (TSS) (51-73% and 39-56%), chemical oxygen demand (COD) (45-78% and 33-61%), biological oxygen demand (BOD) (35-83% and 35-69%) and significant removal of heavy metals, i.e. Fe2+, Cu2+ and Zn2+, was observed. The treatment performances of the compost-filled wetland were better than that of the gravel-filled wetland in terms of removal of COD and BOD. Since this study was a pioneer for implementation of vertical flow constructed wetlands in Pakistan using local sources, it has proved that this eco-technology could also be used effectively for water quality enhancement in Pakistan.