Hydrodynamic cavitation as a pretreatment to enhance organic matter solubilization in orange waste prior to anaerobic digestion

Abstract

This study evaluated the effectiveness of using hydrodynamic cavitation (HC) as a pre-treatment strategy for orange wastes. Two pressures, 3 and 5 bar, were tested, and time intervals of 0, 5, 10, 20, 30, and 45 min were investigated. An orifice plate with one concentric conical hole (3/10 mm) was used as the cavitation inducer. Among all the examined cases, the results of the multi-stage author's Multi-Criteria Determination of Recommended Variants (MCDRV) analysis showed that the most advantageous variant, in terms of enhancing the solubilization of organic matter and energy consumption, was a pressure of 3 bar and a cavitation time 20 min. under these conditions, the DOC/TOC (dissolved to total organic carbon) ratio was enhanced 2.45-fold. Additionally, a two-fold increase in the sCOD/COD (soluble to total chemical oxygen demand) ratio was achieved with an energy consumption of 0.164 kWh. In turn, in the second step of the MCDRV method, the determined optimal sub-set contained variants with a  pressure of 3 bar and cavitation times of 10 and 30 min, respectively. Importantly, in all analyzed cases, the releases of both d-limonene and phenols was observed, which might potentially inhibit subsequent anaerobic digestion.