Use of a plant-based coagulant in coagulation-ozonation combined treatment of leachate from a waste dumping site

In this study, Ocimum basilicum L. has been evaluated as an active natural coagulant to be used in combination with alum for leachate pre-treatment. Leachate samples were collected from a municipal solid waste open dumping site with COD of 4000 mg l−1 and color of 4500 PCU. Response surface methodology (RSM) based on a three-variable-five-level central composite rotatable design (CCRD) was employed to study and optimize the coagulation-flocculation (CF) process. A quadratic polynomial model was fitted to the data with an R2 of 0.92. The effect of three parameters including contact time, pH, and alum-O. basilicum ratio on the color and COD reduction were analyzed. At the optimal conditions of 15 min, pH 7 and alum:O. basilicum ratio of 1:1, 64.4% COD and 77.8% color removal were obtained in the pretreatment stage. Ozonation process was applied to leachate after coagulation. The optimal reaction time for the post-ozonation by 0.2 g O3 l−1 h−1 was 30 min. The integrated technique consisted of CF and ozonation was proved to be an efficient process for the treatment of leachate with 92% color removal and 87% COD reduction.