Treating waste with waste: the potential of synthesized alum from bauxite waste for treating car wash wastewater for reuse

This study assessed the contaminant removal potential of a low-cost alum synthesized from bauxite slime waste compared to industrial grade alum [Al₂(SO₄)₃.18H₂O] in treating car wash wastewater using standard jar tests. The synthesized alum was subsequently applied as a coagulant to test the short-term performance of a bench scale flocculation–flotation system for treating car wash wastewater. Coagulant dosages and mixing intensities were optimized for both coagulants and differences were analyzed with R using two-way ANOVA with Tukey's (HSD) post hoc testing. Per the jar tests, percentage removal of up to 99%, 34%, and 75% of turbidity, anionic surfactants (AS), and COD, respectively, was achieved with 90 mg/L of the synthesized alum compared to 100%, 37%, and 74% for industrial grade alum. Contaminant removal efficiencies of both coagulants were comparable (p > 0.05). However, coagulant dosage strongly influenced the removal of turbidity, AS, and COD (p < 0.05) while mixing intensity influenced all but COD. The bench-scale flocculation–flotation system completely removed turbidity (100%) and reduced AS and COD by up to 92% and 99% respectively. The results of this study demonstrate the potential of alum synthesized from bauxite slime waste as a cheaper alternative for industrial grade alum in wastewater recycling for the car wash industry.