Simultaneous extraction of caffeic acid and production of cellulose microfibrils from coffee grounds using hydrodynamic cavitation in a Venturi tube

Large quantities of spent coffee grounds (SCGs) are produced daily across the globe, accumulating as industrial waste in factories. Developing a process that both extracts high-value components and utilizes the bulk material would offer significant academic and industrial advantages. This study explores the use of hydrodynamic cavitation, which utilizes the chemical and physical effects produced by bubble collapse, for high-efficiency, continuous processing. The optimization of cavitation conditions was conducted by measuring the aggressive intensity of hydrodynamic cavitation within a Venturi tube. Then, unbrewed coffee grounds was processed by hydrodynamic cavitation to obtain stable results, as caffeic acid in SCGs varied depending on how the coffee was brewed. It was revealed that the hydrodynamic cavitation in the Venturi tube increased extraction rate of coffeic acid and simultaneously generates cellulose microfibrils. Note that the upstream pressure of the Venturi tube was 3.4 MPa, which was generated by a screw pump, and the aggressive intensity of the hydrodynamic cavitation was enhanced by optimizing the downstream pressure of the Venturi tube. The type of cavitation, closely linked to the aggressive intensity, was also analyzed through high-speed photography.