Chemical and Bio-Based Coagulation Coupled with Adsorption: Advancing Leachate Treatment Chemistry

Leachate from the Magtaa Kheira landfill exhibits complex physicochemical characteristics that restrict the efficacy of single-treatment processes. This study assessed a sustainable two-stage treatment strategy combining coagulation–flocculation and adsorption. During the initial stage of the study, both aluminum sulfate (AS) and a bio-based coagulant derived from Moringa oleifera seeds (MOS) were evaluated for their effectiveness in the pretreatment of leachate. Box–Behnken Design combined with Response Surface Methodology was used to optimize the coagulation process using aluminum sulfate (AS). The highest removal efficiencies were 91% for turbidity and 85% for chemical oxygen demand (COD) removal, achieved at an AS concentration of 1.44 g·L−1 and an initial pH of 8. In parallel, the performance of MOS extract was investigated as an eco-friendly alternative to AS. An FTIR analysis revealed the presence of protein-associated hydroxyl (3288 cm−1) and carboxyl and amine groups (1647 cm−1), which are integral to destabilization via hydrogen bonding, while SEM confirmed a surface morphology conducive to effective floc formation. MOS demonstrated comparable turbidity removal to AS, significantly reducing both sludge generation and chemical consumption. Following the coagulation stage, treated leachates were passed through a granular activated carbon (GAC) column, enhancing overall COD removal to over 94% to reach acceptable discharge and reuse levels. The coagulation–adsorption sequence, incorporating both chemical and bio-based coagulants, provides an efficient and sustainable approach for the treatment of complex leachate, addressing both performance and environmental considerations.