Performance analysis of a half-batch multi-cell three-dimensional electrode reactor for drilling wastewater: COD removal, energy consumption and hydrodynamic characteristic

Although a three-dimensional electrode system (3DES) has made remarkable achievements in improving the property of electrodes and investigating pollutant degradation mechanism, the design of an electrochemical reactor for application in drilling wastewater has not been reported yet. In this study, a novel half-batch multi-cell 3DES reactor was constructed by us to degrade organic compounds from drilling wastewater. The separate effect of electrolysis time, current density, the configuration of granular activated carbon (GAC) electrodes, aeration rate and volumetric recirculation flow on chemical oxygen demand (COD) removal and energy consumption of the half-batch reactor were analyzed, and further optimization via response surface methodology (RSM). Results showed that the optimal operation conditions for the reactor included electrolysis time of 100 min, a current density of 9.2 mA/cm2, GAC electrode vertical configuration, an aeration rate of 2.67 L/min and a volumetric recirculation flow of 100 mL/min. Under these conditions, the maximum percentage COD removal was found to be 97.39% with an energy consumption of 77.89 kWh(kg COD)-1. The residence time distribution (RTD) method was carried out in continuous flow pattern to investigate the hydrodynamic characteristics of the reactor. Results showed that flow rate was the most dominant factor for the flow pattern of the reactor, followed by the aeration rate and current density. The low dispersion number and the percentage of dead volume are 0.214 and 3.87% when the flow rate of 100 mL/min, respectively, which indicates that there is an intermediate flow pattern existing in between plug-flow ideal and complete mixing flow, furthermore, it is close to the plug-flow ideal.