Multidye biosorption of Sunset yellow (SY), Eosin yellow (EY) and Indigo carmine (IC) dyes onto chemicallymodifiedbiomassofbrownalgaSargassumglaucescenswasstudied.Principalcomponentwavelet neural network (PC-WNN) was applied for the simultaneous determination of anionic dye concentrations in ternary solutions. Experimental parameters were optimized using response surface methodology (RSM) with a Doehlert design. The optimal biosorption conditions were identified as biosorbent dosage 0.2 g L−1, pH 3, and time 25 min. The maximum total biosorption capacity was 0.102 mmol g−1. The Hill isotherm was the most suitable adsorption models in single and ternary systems. Scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) analysis confirmed possible interactions between biosorbent surface and dye molecules.