Flotation-based dye removal system: Sweet potato protein fabricated from agro-industrial waste as a collector and frother

Hazardous synthetic dyes have emerged as an imperative issue of water contamination . This investigation focused on the development of a green flotation-based dye removal (FBDR) system to remove trace crystal violet (CV). A natural protein derived from sweet potato waste which was a readily available and low-cost agro-industrial residual was utilized as the collector and frother , due to its biodegradability and nontoxicity. In the first-stage of FBDR, an inclined foam channel with hydrophobic surface was employed to continuously recover sweet potato protein (SPP). Its recovery percentage and volume ratio reached 84.7 ± 4.2% and 7.2 ± 0.4, respectively. Enriched SPP (10.4 ± 0.5 g/L) was then collected by isoelectric precipitation and freeze drying. Encouragingly, SPP induced the desirable foaming and stable bubbles of the solution. Analytical tests, including SEM , FTIR, UV–vis spectra, and fluorescence measurements, confirmed that the SPP-CV complex was formed mainly through the hydrophobic force . In the second-stage, an excellent CV removal was generated with the collection of SPP. The removal efficiency and enrichment ratio of CV were 95.8 ± 4.5% and 9.2 ± 0.4, respectively. The kinetic study indicated that the removal rate markedly increased with increasing air flowrate . In conclusion, this investigation demonstrated the waste protein could be an effective, inexpensive and eco-friendly alternative for classical collector and/or frother, and provided new insights into the disposal of dye wastewaters.