Investigation on intensified degradation of Rhodamine B and heat generation using a novel thermally assisted hydrodynamic cavitation device

Abstract

In this study, a thermally assisted hydrodynamic cavitation (HC) system was established by adding a water pre-heater in front of the cavitation device (orifice plate), which realizes the local heating of the flowing liquid, intensifies the HC effect and enhances Rhodamine B (RhB) degradation ratio and heat generation efficiency. The effects of preheating temperature, RhB initial concentration, orifice hole number, inlet pressure and solution volume on RhB HC degradation and heat generation were investigated. Free radical trapping experiments were performed to explore the active substances produced by the HC effect. Based on LC-MS and TOC data, the possible RhB degradation pathway and mechanism were proposed. When the preheating temperature rose from 10 °C to 50 °C, the RhB degradation ratio increased from 23.42% to 34.49% within 90 min cycle time, and the treatment cost decreased from 130.699 USD/m3 to 91.701 USD/m3. At 30 min cycle time, the solution temperature rose from 45.6 °C to 56.4 °C, the heat production increased from 149.46 KJ/L to 194.81 KJ/L and the corresponding thermal efficiency increased from 47.45% to 61.84%. Further, at 60 min cycle time, under the conditions of 30 °C preheating temperature, 30 mg/L RhB initial concentration, 3-hole orifice plate, 3 bar inlet pressure and 5.0 L RhB solution volume, the RhB degradation ratio was the highest (40.38%). After Fenton reagent was used, the RhB degradation ratio and heat production both were further enhanced. At 60 min cycle time, the RhB degradation ratio was 65.52%, solution temperature rose to 72.8 °C, the heat production reached 131.83 KJ/L and the treatment cost was only 45.447 USD/m3 at 30 °C preheating temperature. TOC test results show that the RhB mineralization ratio can reach 61.53% after 90 min cycle. All in all, this work proves that thermally assisted HC is an effective method to degrade organic dyes and generate heat, which can be used for large-scale treatment of organic dye wastewater.