Plasma electrolysis as a sustainable strategy for Remazol Red RB-133 degradation in azo dye wastewater

Abstract

This study investigates the degradation of Remazol Red RB-133 in batik wastewater using plasma electrolysis, an advanced oxidation process (AOP) that generates highly reactive hydroxyl radicals (OH). The plasma system, operated at 60°C with air injection, achieved rapid degradation 86.4% within 5 minutes and up to 99% after 60 minutes exceeding the performance of non-plasma techniques such as electrocoagulation. Degradation kinetics were characterized through UV-Vis spectroscopy and LC-MS/MS, revealing the progressive breakdown of azo chromophores and aromatic rings into low-molecular-weight, less toxic intermediates, which were subsequently mineralized into CO2 and H2O, as indicated by significant degradation in Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC). Mass spectral analysis confirmed the formation and subsequent transformation of intermediate compounds, including carboxylic acids and inorganic ions such as SO42-, NO3-, and NH4+. The degradation mechanism followed a radical-based pathway comprising initiation, propagation, and termination stages. These findings demonstrate the high efficiency and environmental sustainability of plasma electrolysis for treating dye-laden wastewater and provide insights into the mechanistic pathway of azo dye mineralization, contributing to the advancement of water treatment technologies aligned with SDG 6.