Efficient removal of Fe and Cu from industrial wastewater using calcium oxide and polymeric flocculants: performance and economic assessment

Industrial wastewater containing heavy metals such as iron (Fe) and copper (Cu) remains a major environmental concern in Malaysia, since industrial effluents significantly contribute to national water pollution loads. Without proper treatment, these contaminants can accumulate in the ecosystem and pose long term risks to human health and aquatic life. This study evaluates the performance, sludge characteristics, and cost implications of alkaline precipitation using sodium hydroxide (NaOH) and calcium oxide (CaO) in the presence and absence of a polymeric flocculant (SW204) for heavy metal removal. Experimental findings reveal that both NaOH and CaO effectively removed heavy metals, where NaOH achieved removal efficiencies of 91.6% for Fe and 93.5% for Cu, while CaO removed 98.9% of Fe and 99.17% of Cu. The addition of polymer improved the treatment efficiency where removal up to 99.73% Fe and 99.80% Cu was achieved with the CaO and polymer system. Settling time improved drastically from 30 min when using NaOH to 2 min when using CaO and the polymer system, indicating the formation of denser and more compact flocs. The specific gravity and sludge weight also increased by approximately 4% with polymer addition, which may influence the disposal costs. Economic analysis revealed that CaO treatment is substantially more cost-effective than NaOH, yielding savings of approximately RM 15.77 per m−3 of effluent treated. Therefore, the combination of CaO and polymers provided the best balance of removal efficiency, settling performance, and cost reduction. The findings support the use of CaO-based systems as sustainable, high-efficiency alternatives for industrial wastewater treatment, all of which aligns with UN Sustainable Development Goals 6 (Clean Water and Sanitation) and 12 (Responsible Consumption and Production).

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