Enhancing water–wastewater treatment efficiency: synergistic approach using polyaluminum chloride, sodium alginate, and magnetite for Congo red removal

Inorganic coagulants such as polyaluminum chloride (PAC) have been used for years to treat water and wastewater. However, PAC as a coagulant can harm the living environment as it is toxic to humans and aquatic ecosystems. The use of natural and biocompatible materials such as sodium alginate as coagulant-aid can reduce the use of PAC. Another challenge in coagulation is the long settling time that amounts to 60–120 min. The introduction of iron oxide nanoparticles such as magnetite (Fe₃O₄) to the coagulation system can significantly reduce the settling time under an external magnetic field. This study proposed the combination of PAC, sodium alginate, and magnetite to solve those problems. The effect of pH (3–8), magnetite dose (12.5–50 mg/L), and sodium alginate dose (0.25–1.5 mg/L) on the removal of Congo red dye wastewater was investigated. It was found at pH = 3 was the best coagulation pH, indicating the charge neutralization of Congo red by PAC. The settling time with the addition of 37.5 mg/L magnetite can achieve equilibrium in 20 min, compared to one without magnetite (60 min). Furthermore, the use of sodium alginate at dose of 0.5 mg/L gave 81.7% removal of Congo red compared to PAC only (48.3%). The results in this study indicate the high potential of sodium alginate as a coagulant-aid in conjunction with PAC and magnetite in water-wastewater treatment.