Azo Dye-Rich Wastewater Treatment by Combined Biodegradation–Adsorption Approach: Optimization, Modeling and Toxicity Analysis

Abstract

Of various aquatic pollutants, azo dyes are inevitable toxicants appearing in almost all major streams of effluents. Besides being potent mutagens and carcinogens, azo dyes are also often of biorecalcitrant nature. In this study, coimplementation of adsorption and biodegradation has been carried out to achieve complete removal of Direct Red 21 from effluents. This study investigated the potential of graphene oxide as support material for azo dye-degrading bacterial strain (Pseudomonas mendocina). Application of immobilized microorganism offered a number of advantages like higher percentage of dye removal (~99.78%), rise in metabolic activity, and stronger resistance to toxicants. Moreover, this combined approach was cost-effective and re-utilizable without significant loss of activity. The experimental parameters were optimized and modeled using Central Composite Design of Response Surface Methodology. The immobilized GO sheets were characterized using SEM. Toxicity effects of effluents were determined using chickpea seeds (Cicer arietinum). Results proved that the treated water is biologically safe and fit for discharge or reuse in agricultural processes.