<![CDATA[To address feedstock costs and environmental sustainability, this study employed a dual-waste valorization strategy by converting high-free fatty acid (FFA) sludge palm oil (SPO) into biodiesel using silica-rich water treatment sludge from PDAM as a low-cost support for a heterogeneous K2O/SiO2 catalyst. Due to the high initial acidity of SPO, a two-step process was used: acid esterification to reduce FFA levels below 2%, followed by alkaline transesterification. Optimization of the reaction parameters identified the ideal conditions as 6% catalyst loading, a 15:1 methanol-to-oil molar ratio, and a 2-hour reaction time at 63°C. Under these conditions, the process achieved a biodiesel yield of 70.43% with a high methyl ester purity of 98.01%. The produced biodiesel met the SNI 7182:2015 quality standards for density and acid number. Although the catalyst demonstrated stability over two consecutive cycles, its activity declined in the third cycle due to active-site leaching. This work confirms the viability of integrating industrial and municipal waste streams for sustainable and cost-effective bioenergy production.]]>
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