Beyond removal: integrating treatment performance and environmental burden in ferric and aluminium-based wastewater coagulation

Coagulation–flocculation remains a key step in industrial wastewater treatment; however, its optimisation is often based solely on removal efficiency, with limited consideration of environmental burden. This study aims to comparatively evaluate ferric chloride (FeCl3) and aluminium sulphate (Al2(SO4)3) by integrating treatment performance with a screening-level environmental assessment. Jar-test experiments were conducted using a high-strength industrial wastewater (COD: 2136 mg/L, BOD5: 1085 mg/L, TSS: 798 mg/L) to investigate dose–response behaviour. Changes in COD, BOD5, TSS, and TP were monitored across different coagulant doses, supported by exploratory statistical analysis to interpret system-level behaviour. Both coagulants exhibited narrow optimum dose ranges. FeCl3 achieved higher removal efficiencies, particularly for organic parameters, whereas performance declined at elevated doses due to floc instability. Statistical evaluation indicated that COD and BOD5 followed similar trends, while TSS and TP exhibited partially distinct behaviour. The environmental analysis, based on Global Warming Potential (GWP) and Cumulative Energy Demand (CED), showed consistently lower impacts for FeCl3 compared with alum across all tested conditions. Overall, the results suggest that FeCl3 provides a more favourable balance between treatment efficiency and environmental burden for this type of high-strength wastewater. The findings emphasise that effective coagulation requires careful dose optimisation and highlight the importance of integrating performance and environmental considerations in coagulant selection.