Purified Moringa oleifera Protein as a Terminal Disinfectant for Coagulated Domestic Wastewater: Benchmarking Against Sodium Hypochlorite, Cost, and

ABSTRACT

Purified plant proteins are proposed as chlorine‐free disinfectants, but their performance in real wastewater is rarely benchmarked against hypochlorite in the same matrix or translated into cost and environmental impact. We prepared a papain‐assisted purified Moringa oleifera protein (PMOC; 86.0% protein) and tested it first as a coagulant, then as a terminal disinfectant, in domestic wastewater. Coagulation‐stage conditions were evaluated with a 30‐run face‐centered central composite design (pH 3–11, 30–60 min, 0.50–2.00 g L ⁻¹ ). The selected condition (pH 7, 45 min, 2.00 g L ⁻¹ ) removed 86.1% ± 0.1% of total coliforms in three independent runs. The clarified supernatant was then split into supplementary‐PMOC (25–200 mg L ⁻¹ ) and NaOCl (1.0–2.0 mg L ⁻¹ as Cl ₂ ) branches without further settling. After 30 min, 50 mg L ⁻¹ PMOC reduced Escherichia coli by 1.87 ± 0.04 log and total coliforms by 1.77 ± 0.005 log. In paired tests, these reductions were equivalent within ±0.3 log to those from 1.0 mg L ⁻¹ NaOCl (1.79 ± 0.01 and 1.72 ± 0.02 log), while 1.5–2.0 mg L ⁻¹ NaOCl produced greater E. coli inactivation. All PMOC doses met the national total‐coliform limit without chlorine addition. A stage‐specific life‐cycle assessment (ecoinvent 3.12, EF 3.1) and a cost model showed that the current purification route has 83‐ to 133‐fold higher climate burdens than NaOCl and alum–lime, driven mainly by hexane, grid electricity and NaOH. PMOC can therefore serve as a nonoxidant polishing agent, but its practical use depends on less solvent‐ and energy‐intensive purification.