Evaluation of Calpurnia aurea seed extract as natural coagulant for reducing turbidity, color and COD from water and wastewater

Abstract

Turbidity, color, and chemical oxygen demand (COD) indicate water quality. Natural coagulants offer eco-friendly alternatives for treatment. This study investigates the potential of Calpurnia aurea seed extract as a natural coagulant for water and wastewater treatment. The extract was prepared through a multi-step process involving drying, grinding the seeds, sieving the seed powder, cold macerating using n-hexane solvent to defatting, and dissolution in distilled water (5 g/L). Protein content was quantified using the Kjeldahl method. Treatment conditions were optimized using the jar test and one-variable-at-a-time (OVAT) approach, yielding optimal parameters of 100 mg/L dosage, pH 3, rapid mixing at 300 rpm for 9 min, slow mixing at 45 rpm for 35 min, and a settling time of 70 min. Under these conditions, turbidity removal efficiencies reached 91.93% (synthetic wastewater), 87.89% (municipal wastewater), 69.93% (textile effluent), and 45.79% (Akaki river water). In this context, the efficiency for the Calpurnia aurea seed extract approaches the turbidity removal efficiencies of up to 99.77% reported for alum in previous studies. Color removal was most effective in textile effluent (63.73%), followed by municipal wastewater (49.77%) and Akaki river water (24.12%). COD reductions were highest in Akaki river water (78.49%), with moderate effects in municipal wastewater (46.28%) and textile effluent (30.75%). The extract’s coagulation mechanism is attributed to charge neutralization and colloidal particle binding. These findings highlight Calpurnia aurea seeds as a promising natural coagulant for improving water quality across diverse wastewater sources.