Ultrasound-assisted nanofiltration for remazol brilliant blue reactive removal: elucidating the role of ph in efficacy and by-product formation

The effective treatment of dye-laden industrial effluents remains a critical challenge in environmental engineering. This study introduces a novel hybrid system integrating ultrasound (US) and nanofiltration (NF) technologies for the removal of Remazol Brilliant Blue Reactive (RBBR) dye from aqueous solutions. RBBR, a widely used textile dye, poses significant environmental and health risks due to its persistence and toxicity. For the first time, the influence of pH on the performance of a hybrid US-NF system for RBBR removal, including by-product formation and membrane fouling was systematically investigated. Initially, the US and NF processes were optimized independently by systematically varying key parameters such as US frequency, exposure time, membrane pressure, and solution pH. Ultrasonic treatment at 575 kHz resulted in 79 % reduction in absorbance and 58 % total organic carbon (TOC) removal at pH 3 after 90 min, indicating partial oxidation of the dye. NF alone consistently removed over 99 % of the dye across all tested pH values, though a flux decline of 16 % was observed at pH 3 due to fouling. The hybrid US-NF system maintained over 99 % dye rejection while completely eliminating flux decline at an optimal pH of 3, significantly outperforming the standalone NF process. Degradation by-products were confirmed via mass spectrometry and Fourier-transform infrared spectroscopy, highlighting the complementary role of NF in removing potential intermediates. These results demonstrate the potential of US–NF coupling as a robust and sustainable approach for advanced treatment of dye-contaminated wastewater, contributing to the development of cleaner industrial processes and improved water reuse practices.