Fe3O4@Polyaniline enhanced algal-bacterial symbiotic granular sludge for efficient pollutant removal under low aeration conditions.

Aerobic granular sludge is a promising wastewater treatment technology, but its practical application is still constrained by high aeration demand and limited operational stability. In this study, an algal-bacterial symbiotic granular sludge system was developed under Fe3O4@polyaniline-assisted cultivation and evaluated under reduced aeration conditions. Under illumination, algal-bacterial symbiosis was established in the system, and the dissolved oxygen concentration remained at 6.8-7.1 mg/L when the aeration intensity was reduced from 2.5 to 1.7 L/min. Fe3O4@polyaniline-assisted cultivation was beneficial for granulation and biomass retention during start-up, while the algal-bacterial system maintained stable carbon, nitrogen, and phosphorus removal under reduced aeration. Stoichiometric mass balance analysis indicated that bacterial metabolism remained the dominant estimated removal pathway, whereas the relative contribution of algae increased under reduced aeration. Microbial community analysis further showed that bacterial diversity was maintained, while algal proliferation increased at lower aeration intensity. This study offers an energy efficient algal-bacterial symbiotic granular sludge cultivation strategy, presenting a viable solution for sustainable wastewater treatment.