Study on negative pressure assisted hydrodynamic cavitation (NPA-HC) degradation of methylene blue in dye wastewater

Abstract

Hydrodynamic cavitation (HC), as a new AOP, has been tried to treat some organic dye wastewater. In traditional HC equipment only positive pressure from water pump was used, which results in a low degradation extent. In this paper, the negative pressure from water pump is used to intensify the whole HC effect for enhancing the decolorization and mineralization of methylene blue (MB) in wastewater. Some influence factors (orifice plate hole number, inlet pressure, initial concentration and solution temperature) on MB degradation efficiency are studied. The determined results of Total Organic Carbon (TOC) and Liquid Chromatograph-Mass Spectrometer (LC-MS) were used to identify MB mineralization extent and confirm the intermediate products during MB degradation, respectively. The results showed that, under the conditions of low temperature, high inlet pressure and moderate dye concentration, the negative pressure assisting hydrodynamic cavitation (NPA-HC) system displayed a significantly enhanced MB degradation effect. The most efficient combination of 25 hole negative pressure assisted 3 hole positive pressure is obtained. At 30 °C in 10 mg/L MB solution, the degradation ratios are 27.43% (in NPA-HC) and 97.48% (in NPA-HC+H2O2 (MB/H2O2 = 1.0:7.5 in molar ratio)), respectively. And that, in single positive pressure HC system the MB degradation ratio is only 16.23%. This study provides a feasible method for intensifying organic dye HC degradation and enlarging wastewater treatment scale.