Effectiveness of using water-extracted Leucaena leucocephala seeds as a coagulant for turbid water treatment: effects of dosage, pH, mixing speed, mixing time, and settling time

Natural materials have a high potential to be used as coagulant/flocculant owing to the problems of inorganic materials. Petai belalang (Leucaena leucocephala) is a widely abundant plant in Malaysia and very efficient as a plant-based coagulant in previous research. This research investigated the effectiveness of seeds of L. leucocephala in removing turbidity from synthetic wastewater and the effect of operation parameters of jar test on treatment performance through optimization of dosage, pH, rapid mixing speed and time, slow mixing speed and time, and settling time. The water extraction method was used to extract the active ingredients from the seeds by drying and pulverizing the seeds and then dissolving them in distilled water at a concentration of 20 g/L. The extraction solution of the seeds gives removal efficiency of turbidity of 93.05% at the optimum operation parameters dosage, pH, rapid mixing speed and time, slow mixing speed and time, and settling time of 120 mg/L, 6.5, 260 rpm for 11 min, 30 rpm for 15 min, and 30 min, respectively. It is expected that bridging was the possible mechanism given that the flocs are formed under the same negative zeta potential condition. With this high performance of L. leucocephala, it has high potential to be used as a coagulant in wastewater treatment at specific operation parameters with further exploration to determine the optimum extraction method of the active ingredients.