Optimization Study of Leucaena Leucocephala Seed Extract as Natural Coagulant on Decolorization of Aqueous Congo Red Solutions

Abstract

Coagulation is a water and wastewater treatment technology that has been widely used due to its high efficiency and effectiveness. Various inorganic salts are commonly used as coagulant; however, there are some negative impacts of utilization of these chemical coagulants, such as high costs, large sludge volume, and also potential negative impact to human health. To overcome these problems, natural-based coagulants have been explored to reduce and substitute chemical coagulants. In this study we investigated utilization of Leucaena leucocephala seed protein, extracted using 0.5 M MgCl2 solution as natural coagulant to treat synthetic Congo red wastewater. From the protein solubility profile at various pH, it could be observed that leucaena protein’s isoelectric point was around pH 4. The optimization of coagulation condition was done by using Response Surface Method (RSM)—Central Composite Design (CCD) with variations of pH (2.93–4.12), coagulant dose (183.52–496.58 mg eq BSA/L), and dye concentration (44.1–56 mg/L). This experimental design was used to obtain the optimum condition that gave maximum dye removal percentage and minimum sludge volume. It was found that pH, coagulant dose, and dye concentration were significant for dye removal and sludge volume. Furthermore, it became evident that charge neutralization was the coagulation mechanism in this study. Based on the obtained model, 88.61% dye removal with 16.93 mL/L sludge volume was obtained at the optimum condition. The predicted optimum condition was in a good agreement with experimental data with relatively low error value. The obtained result implies good potency of leucaena as natural coagulant.