| ABSTRACT |
The invention relates to a limestone-derived calcium hydroxide [Ca(OH)2] paste coagulant for wastewater treatment. The coagulant is prepared from natural limestone composed primarily of calcium carbonate (CaCO3), which is calcined to calcium oxide (CaO) and subsequently hydrated to form Ca(OH)2 paste. The resulting formulation is a stable, ready-to-use semi-solid coagulant with improved handling, reduced dust formation, and enhanced dosing consistency compared to conventional powdered lime. The Ca(OH)2 paste is applied for treatment of industrial wastewater such as Palm Oil Mill Effluent, achieving simultaneous removal of sulphate and chemical oxygen demand (COD) through coagulation, precipitation, and flocculation. Calcium ions released from the coagulant promote sulphate precipitation as calcium sulfate, while alkalinity enhances contaminant destabilization. The invention further enables partial regeneration of spent slurry, reducing fresh chemical demand, sludge production, and operational cost, thereby providing a sustainable and environmentally friendly alternative for industrial wastewater treatment.
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