Quantitative Comparative Evaluation of Aluminum- and Iron-Based Coagulants for Domestic Greywater Treatment

Greywater treatment is an essential component of sustainable water management strategies, particularly in regions experiencing water scarcity. This study presents a quantitative comparative evaluation of three conventional inorganic coagulants—aluminum sulfate (Al2(SO4)3), ferric sulfate (Fe2(SO4)3), and ferric chloride (FeCl3)—for domestic greywater treatment using standardized jar test procedures. The initial turbidity of the greywater was 186 ± 5 NTU. Coagulant performance was assessed based on final turbidity, removal efficiency, and pH variation, with dosages expressed as mg of active metal per liter to ensure comparability. Ferric chloride exhibited the highest turbidity removal efficiency, achieving a maximum removal efficiency of 96.2 ± 0.8% at 68.8 mg Fe/L and reducing turbidity to 7 ± 1 NTU. Ferric sulfate achieved a maximum removal efficiency of 92.5 ± 1.2%, while aluminum sulfate reached 84.9 ± 1.4% under the evaluated conditions. Statistical analysis confirmed significant differences among coagulants at intermediate and high dose ranges (p < 0.05). The results indicate that ferric chloride provides the most effective clarification performance for the tested greywater matrix, while maintaining final pH values within a suitable range for non-potable reuse. This study contributes to coagulant selection for decentralized greywater treatment systems through standardized, quantitative comparison under identical operational conditions.