Allura red in aquatic systems: Treatment technologies, process intensification strategies, and future perspectives...

Allura Red (E129) is a widely used synthetic azo dye in food, pharmaceutical, and beverage industries, whose increasing discharge into aquatic systems has raised environmental and public health concerns. Its recalcitrant nature, potential toxicity, and formation of aromatic amine intermediates during degradation necessitate effective wastewater treatment strategies. Although numerous laboratory-scale studies report high removal efficiencies, a consolidated critical assessment of treatment technologies with emphasis on mechanism, scalability, and sustainability remains limited. This review systematically evaluates major approaches for Allura Red removal, including adsorption, advanced oxidation processes (AOPs), electrochemical oxidation, membrane filtration, photocatalysis, and biological treatments. Adsorption is identified as the most extensively studied technique due to operational simplicity and low cost; however, limitations like adsorbent regeneration, pore blockage, and secondary waste generation hinder large-scale implementation. AOPs and electrochemical methods demonstrate rapid degradation and high mineralization efficiencies (>95%) but are constrained by energy demand and operational costs. Membrane systems provide high rejection rates yet suffer from fouling, while biological methods offer eco-friendly alternatives with longer treatment times. Key research gaps include insufficient pilot-scale validation, limited toxicity assessment of degradation by-products, and lack of life-cycle and techno-economic analyses. Future efforts should focus on hybrid systems, green materials, and scalable sustainable designs.