A Comparison of the Mechanism of TOC and COD Degradation in Rhodamine B Wastewater by a Recycling-Flow Two- and Three-dimensional Electro-Reactor System

Abstract

Dye wastewater, as a kind of refractory wastewater (with a ratio of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of less than 0.3), still needs advanced treatments in order to reach the discharge standard. In this work, the recycling-flow three-dimensional (3D) electro-reactor system was designed for degrading synthetic rhodamine B (RhB) wastewater as dye wastewater (100 mg/L). After 180 min of degradation, the removal of total organic carbon (TOC) and chemical oxygen demand (COD) of RhB wastewater were both approximately double the corresponding values in the recycling-flow two-dimensional (2D) electro-reactor system. Columnar granular activated carbon (CGAC), as micro-electrodes packed between anodic and cathodic electrodes in the recycling-flow 3D electro-reactor system, generated an obviously characteristic peak of anodic catalytic oxidation, increased the mass transfer rate and electrochemically active surface area (EASA) by 40%, and rapidly produced 1.52 times more hydroxyl radicals (·OH) on the surface of CGAC electrodes, in comparison to the recycling-flow 2D electro-reactor system. Additionally, the recycling-flow 3D electro-reactor system can maintain higher current efficiency (CE) and lower energy consumption (Es).