Integrated valorization of waste cooking oil and spent <i>Coccus nucifera</i> biosorbent for biodiesel production

Abstract This study investigates the sustainable valorization of Coccus nucifera shell ash within a circular economy framework, addressing waste management and renewable energy production. Motivated by the need for eco‐friendly solutions to dye pollution and biodiesel production, this research hypothesizes that Coccus nucifera shell ash can function as both an efficient adsorbent for methylene blue (MB) dye and a green catalyst for biodiesel synthesis. MB adsorption was evaluated under varying conditions, achieving a 98.93% removal rate with an adsorption capacity of 19.787 mg/g at pH 8. Calcined ash was then utilized as a heterogeneous catalyst, attaining a 92.08% biodiesel yield with a relative standard deviation of 1.028% from waste cooking oil (W.C.O.) at optimized conditions (adsorbent dosage: 0.375 g, contact time: 150 min, temperature: 65°C, MTOR: 18.5 mL) using the Taguchi method. Gray relational analysis identified temperature as the most critical factor. This study demonstrates an innovative dual‐function approach, highlighting the potential of Coccus nucifera shell ash for integrated dye remediation and biodiesel production, aligning with sustainability goals.