Effectiveness Analysis of Natural and Synthetic Coagulants in Domestic Wastewater Treatment: Coagulation–Flocculation Mechanism and Water Chemical Characterization Study

Abstract

Domestic wastewater treatment using natural coagulants is gaining attention as a sustainable alternative to synthetic chemicals. This study compared the effectiveness of three natural coagulants (Moringa oleifera seed extract, Phaseolus vulgaris saline extract, and chitosan) against two synthetic coagulants (polyaluminum chloride, PAC, and alum) for treating real, moderately high-strength domestic wastewater from Yogyakarta, Indonesia. Jar tests were performed in triplicate, measuring turbidity, total suspended solids (TSS), chemical oxygen demand (COD), and pH. Results showed that PAC at 14 mg/L achieved the highest turbidity removal (94.2 ± 2.1%), followed by alum (89.5 ± 3.4%) and M. oleifera at a much higher dosage of 4000 mg/L (86.3 ± 4.2%). P. vulgaris extract (0.4 mL/L) removed 79.1 ± 5.0% of turbidity, while chitosan (50 mg/L) removed 64.2 ± 6.1%. For COD removal, PAC reached 63.5 ± 3.2%, chitosan 58.3 ± 4.7%, and M. oleifera 55.7 ± 4.5%. A hybrid formulation combining 3.5 mg/L PAC and 0.3 mL/L P. vulgaris extract achieved 91.8% turbidity removal, nearly matching PAC alone while using 75% less synthetic chemical. We conclude that although PAC remains the most reliable coagulant for high-strength wastewater, natural coagulants especially in hybrid forms offer a viable, low-toxicity option for decentralized treatment applications.