Landfill leachate wastewater (LLW) is a highly polluted effluent rich in organic matter and nutrients but difficult to treat due to high turbidity, salinity, and recalcitrant compounds. This study investigated an integrated strategy combining chemical pretreatment and nutrient stoichiometry optimization to enhance simultaneous wastewater remediation and lipid production by Scenedesmus sp. Raw LLW was subjected to different pretreatment methods, including polyaluminum chloride, Ca(OH)2 coagulation, and Fenton oxidation followed by Ca(OH)2 neutralization. Among them, Ca(OH)2 pretreatment provided the most favorable growth conditions, supporting a maximum biomass concentration of 0.85 g/L and a specific growth rate of 0.60 day−1, while effectively reducing turbidity, chloride, and organic load. Fenton–Ca(OH)2 pretreatment further enhanced lipid accumulation (up to 23% dry weight) but slightly inhibited biomass growth due to residual H2O2. Subsequent optimization of the molar nitrogen-to-phosphorus (N:P) ratio in Ca(OH)2-pretreated LLW revealed that an N:P ratio of 35:1 maximized algal performance, yielding 2.15 g/L dry weight and 26.7% lipid content, along with high pollutant removal efficiencies (74% chemical oxygen demand, 78% biochemical oxygen demand, 85% total nitrogen, and 92% total phosphorus). Fatty acid methyl ester analysis showed dominance of palmitic (C16:0) and stearic (C18:0) acids (≈80–90% of total fatty acids), indicating a lipid profile highly suitable for hydroprocessed esters and fatty acid-based sustainable aviation fuel production. Overall, this study demonstrates that coupling LLW pretreatment by Ca(OH)2 with nutrient ratio optimization enables efficient phycoremediation and the generation of high-quality lipid feedstock, supporting a circular and sustainable bioenergy pathway.
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