Fast removal of dyes from wastewater by combinatorial treatment by biosorption and visible light photodegradation

Purification of wastewater containing dyes just by photocatalytic degradation under visible light irradiation is usually a slow process, especially for the cases of high concentration dyes in the water. From the viewpoint of economy and efficiency, decreasing the dyes concentration of wastewater to an optimal level suitable for visible light photocatalytic degradation is one of the methods to adopt. Based on the above ideas, a novel treatment process was designed for dye removal from water, which consisted of biosorption and photocatalysis under the visible light irradiation. High concentration (~100mg/l) of dye waste water will be decreased rapidly after fast biosorption onto the biosorbents such as saponified apple juicing residue, sweet-stick bagasse, and then the obtained waste water with low concentration (~5mg/l) of dye will much easier be degraded thoroughly under visible light irradiation in short time. The basic experiments were conducted to evaluate the principal characteristics of these two unit operations, and their removal behaviour for dye molecules from water was clarified respectively. The process exhibits outstanding advantages, i.e., much faster, more thorough, and energy saving, showing the great perspective for the dye waste water cleaning in the industry.