Integrated modified septic tank and constructed wetland: an alternative green technology for phytoremediation of highly polluted leachate

The study aimed to treatment of high organic matter concentration in leachate produced by municipal waste in developing countries. The average properties of the raw leachate were investigated, including chemical oxygen demand (COD), biochemical oxygen demand (BOD5), and total suspended solids (TSS), which were found to be 55,058.7, 34,500, and 8080 mg/L, respectively. The study evaluated the performance of integrated systems consisting of modified septic tanks (MST) and horizontal flow subsurface flow constructed wetland (HF-SFCW) to treat this type of leachate. The maximum removal efficiencies for COD, BOD5, and TSS were 61.18%, 55.07%, and 64.6% for MST, and 67.93%, 61.90%, and 71.11% for HF-SFCW. Also, the percentage phosphorus removal was 35.41% for MST and 54.16% for HF-SFCW, while the efficiency of nitrogen compound removal was reported differently for the two methods. MST showed an increase in ammonium concentration due to anaerobic conditions and denitrification, while HF-SFCW showed a significant decrease in ammonium concentration and a slight increase in nitrate and nitrite concentrations. The study concluded that MST and HF-SFCW planted with Phragmites australis exhibited good phytoremediation performance in heavily polluted leachate.