An Investigation into the Factors Influencing the Effectiveness of a Biodegradable Natural Coagulant Derived from Phaseolus vulgaris Seeds and Coagulation Mechanism

One of the major criteria for monitoring water and wastewater quality is turbidity, which is most often reduced using chemical coagulants and flocculants, such as alum and iron salts and acrylamide. However, due to their detrimental effects, intensive investigations into natural coagulants and flocculants have recently been conducted. These coagulants are biodegradable, derived from renewable sources, and do not pose health risks, making them a sustainable solution for water and wastewater treatment. Coagulation and flocculation using natural coagulants is a complex phenomenon influenced by multiple factors. In this study, the impact of the solvent used to extract the natural coagulant from Phaseolus vulgaris seeds on its coagulation effectiveness was examined, along with the effects of pH, the initial turbidity of the treated water, and the applied coagulant dose. The extract obtained using 0.5 mol/L NaCl demonstrated higher coagulation activity compared to the extract obtained with distilled water. Both extracts exhibited improved performance in water with higher initial turbidity (200 NTU) and at the lowest pH tested (pH 6). Under these conditions, the water extract achieved a maximum coagulation activity of 58.4% at a dose of 0.1 mL/L, while the NaCl extract reached an 83.5% turbidity reduction at a dose of 0.4 mL/L. The dominant coagulants in the NaCl extract of Phaseolus vulgaris seeds are anionic polyelectrolytes. In the presence of divalent cations, these coagulants destabilize negatively charged particles through either the bridging mechanism or the sweep coagulation mechanism.