Refractory organic pollutants in tail water of dyeing wastewater treatment have aroused wide concern. Their efficient and cost-effective removal reduced their threat to public health and ecosystem. Herein, a novel short-cut photocatalysis/algal degradation-based hybrid technology was implemented in efficient removal of methylene blue (MB) in simulated tail water using reliable titanium dioxide and common Chlorella pyrenoidosa, and the mechanisms in processes were emphasized. The treatment efficiency was significantly improved via pretreatment before chemical and biological degradation. MB of 79.71% was concentrated as the adsorption of the modified titanium dioxide and the collection of titanium dioxide by inorganic coagulant. The supernatant with low concentration of MB after coagulation was able to be directly treated by Chlorella pyrenoidosa. MB of 93.7% was degraded and transformed to intermediates in short-cut photocatalysis under visible light in 1 h. The intermediates owning the low biological inhibition were easily further degraded by Chlorella pyrenoidosa in 6 days. Mechanism analysis implied that the modified titanium dioxide was not simple monolayer adsorption, and physical adsorption was dominant. The coagulant played an essential role of charge neutralization in collection of the modified titanium dioxide. The removal of photocatalytic intermediates was divided to fast adsorption of Chlorella pyrenoidosa, low desorption in lag period of algae, and gradual biodegradation that accompanied with the increase of algal cell quantity.
Keywords: Algae; Biodegradation; Dyeing wastewater; Photocatalysis; Tail water; Titanium dioxide.