Stability of algal-bacterial granules in continuous-flow reactors to treat varying strength domestic wastewater

Abstract Stability of algal-bacterial granules was investigated in two continuous-flow systems to treat synthetic domestic wastewater using single (R 1 ) and series (R 2  = R 2-1  + R 2-2 with automatically internal recirculation) reactors by seeding 50% (w/w) algal-bacterial granules. Almost similar organics and phosphorus removal efficiencies were obtained from the two systems, with no significant difference found for each between the designed two operation stages. However, R 2 exhibited superior performance on total nitrogen (TN) removal (76%). When double increased strength influent fed to R 1 , R 1 achieved better denitrification with TN removal increased from 29% to 80%, possibly due to the increased influent organics concentration favored the denitrification process. Most importantly, the two systems well maintained their granular stability, and all granules became algal-bacterial ones with very little change detected in algae content in granules after 120 days’ operation. At last, the mechanisms were proposed regarding the formation and enhanced stability of new algal-bacterial granules in continuous-flow reactors.