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, UVevis 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. (C) 2020 Elsevier Ltd. All rights reserved.