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Algal-Bacterial Symbiosis System Treating 
High-Load Printing and Dyeing Wastewater in 
Continuous-Flow Reactors under Natural Light

This study investigated the symbiotic structure relationship between mixed algae andactivated sludge while treating high-load printing and dyeing wastewater under natural light. Theeffects of hydraulic retention time (HRT) (12 h, 16 h and 20 h) and aeration rate (0.1–0.15, 0.4–0.5and 0.7–0.8 L/min) on algal–bacterial symbiosis (ABS) and conventional activated sludge (CAS)systems. Experimental results showed that the ABS system exhibited the best removal performancefor chemical oxygen demand (COD), ammonia nitrogen (NH4+-N) and total phosphorus (TP),which was increased by 12.5%, 23.1% and 10.5%, respectively, and reduced colour 80 timescompared with the printing and dyeing wastewater treatment plant. Algae growth could bepromoted under lower dissolved oxygen (DO), and the addition of algae could provide more DO tothe ABS system. The particle size distribution of sludge in the ABS system was stable, whichguaranteed a stable treatment effect. In addition, the COD and colour could be further degradedunder the conditions of no external carbon source and longer HRT. It is expected that the presentstudy will provide a foundation for the practical application of the ABS system, and new insightsfor the treatment of printing and dyeing wastewater.