Simplified MBAS and Modified BiAS-thio Methods for Monitoring Anionic and Nonionic Surfactants in Municipal Wastewater Treatment Plants Using Spectrophotometric Methods

The increasing production and use of surfactants have resulted in their widespread occurrence in municipal wastewater and aquatic environments. Routine monitoring remains challenging because conventional analytical methods are time-consuming, require large volumes of hazardous organic solvents, and are poorly suited to complex environmental matrices. This study evaluated the applicability of a simplified methylene blue active substances (MBAS) method for anionic surfactants and a modified spectrophotometric iodobismuthate (BiAS-thio) method for nonionic surfactants for routine monitoring in a full-scale municipal wastewater treatment plant serving approximately 67,500 population equivalent (PE). The proposed methods enabled reliable determination of both surfactant groups while substantially reducing analytical time and solvent consumption compared with conventional procedures. Statistical evaluation demonstrated excellent agreement between the simplified and reference MBAS methods. The treatment plant achieved removal efficiencies of 96.8% for anionic surfactants and 98.3% for nonionic surfactants. The scientific novelty of this work lies in the practical validation of simplified spectrophotometric methods that provide reliable, rapid, and less solvent-intensive determination of anionic and nonionic surfactants in complex municipal wastewater, making them suitable for routine environmental monitoring.