The generation of acidic effluent presents a significant challenge in the environmentally sustainable conversion of lignocellulosic waste to cellulose via acid extraction. This study investigated cellulose extraction from spent coffee grounds (SCG) using a novel system of five serially-connected recycle flow reactors employing nitric acid as the solvent. Interestingly, combining the acidic effluent with alkaline-treated spent drilling mud (SDM) enabled the synthesis of an adsorbent for textile wastewater COD reduction. This approach achieved simultaneous treatment and valorization of acidic effluent, textile wastewater, and SDM. The results revealed that pure amorphous cellulose extracted from SCG (37.25 % yield) exhibited a porous structure with mesopores (20–50 μm) and macroparticles (200–500 μm). The adsorbent with a specific surface area of 27.95 m2/g achieved 60 % COD removal with an equilibrium adsorption amount of 53.11 mg/g at an optimal dosage of 100 g/L. The adsorption was spontaneous and endothermic, with multilayer and heterogeneous behavior (as evidenced by the Freundlich isotherm), followed a pseudo-second-order kinetic model. The techno-economic analysis demonstrated a cost-effective textile wastewater treatment solution at $0.021/1000 COD removal, achieved through the adsorbent production costing $1.11/kg. This integrated approach combined wastewater treatment with cellulose production at $23.57/kg, presenting a sustainable circular economy model.

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