<p>Biowaste utilization is a necessary step for environmental sustainability and pollution control. In this work, we have prepared a cost-effective, fluorine-free, robust superhydrophobic/superoleophilic polyurethane (PU) sponge coated with <i>functionalized</i>-calcium carbonate (<i>f</i>-CaCO₃) and reduced graphene oxide (rGO) derived from biowastes such as egg shells and mango seeds in order to use it as a potential adsorbent for oil/water separation. The coating of both <i>f</i>-CaCO₃ and rGO seems to enhance the hydrophobicity of the porous surface of the PU sponge with WCA (water contact angle) of 158 ± 2°. The <i>f</i>-CaCO₃/rGO/PU sponges are seen to be resistant towards various environmental conditions and show greater ability towards high adsorption efficiency and oil/water selectivity. The oil adsorption capacity and recyclability of fabricated sponges with different oils have been reported. The corresponding sponges are obtained as a proficient material for the recovery of adsorbed oil and oppose various mechanical deformations. The current research proposes a waste-derived, fluorine-free route to fabricate a cost-effective, reusable, and superhydrophobic/superoleophilic f-CaCO₃/rGO/PU sponge for oil-spill mitigation while advancing biowaste valorization through the integration of eggshell-derived calcium carbonate and mango-seed-derived graphenic carbon towards the remediation of oil spillage and providing a novel approach towards biowaste utilization.</p> Graphical Abstract <p></p>