Investigation on the by-pass line orifice plate assisted hydrodynamic cavitation (B-PLOPA HC) degradation of basic fuchsin (BF) in wastewater

HC technology has been widely used in the field of wastewater treatment due to its advantages of simple operation, low operating cost and large treatment capacity. However, the conventional HC devices that rely solely on the main line cavitator to treat organic pollutants show unsatisfactory degradation effect. Therefore, it is difficult to enhance the degradation effect of organic pollutants only by optimizing the cavitator geometry and experimental operation parameters. In fact, for traditional HC device the pressure in front of the throttle valve in the by-pass line is same as the inlet pressure of the main line cavitator. In this study, the orifice plate cavitator is firstly used to replace the throttle valve in the by-pass line of the traditional HC device to form a by-pass line orifice plate assisted hydrodynamic cavitation (B-PLOPA HC) device after optimizing the cavitator geometry and experimental operation parameters, realizing the synchronous occurrence of HC effects in the main and by-pass line cavitator and greatly enhancing the degradation effect of organic pollutants. A triphenylmethane dye, basic fuchsin, is used as the simulated pollutant to carry the degradation experiment by using an improved HC device. It was found that, under inlet pressures of 3.0, 4.0 and 5.0 bar within 90 min, the degradation ratios of basic fuchsin were increased from 59.72 %, 73.60 % and 65.23 % by using conventional HC device to 80.93 %, 81.15 % and 81.38 % by using B-PLOPA HC device, respectively. Correspondingly, the wastewater treatment costs were reduced by 41.82 %, 26.16 % and 29.87 %, respectively, compared with those before modification. Obviously, such modification not only enhances the degradation effect of organic pollutants, but also reduces the cost of wastewater treatment. Besides, the active substances generated in B-PLOPA HC system were explored by adding free radical trapping agent. According to the determined results from Liquid Chromatograph Mass Spectrometer (LC-MS) and Total Organic Carbon (TOC), the possible degradation path of basic fuchsin is proposed. In a word, the overall HC effect of system is effectively strengthened through the use of the by-pass line orifice plate. This study provides a solid theoretical basis for large-scale application of HC technology in the field of wastewater treatment. © 2021 Elsevier Ltd. All rights reserved.