The nitrogen removal efficiency of the algae-bacteria symbiotic system (ABSS) remains challenging due to competition for light capture and insufficient electron donors in aquaculture wastewater. To overcome this bottleneck issue, we first identified and reported the introduction of photogenerated electrons into ABSS by coupling them with carbon dots (CDs). The energy metabolism (21.52 %-56.25 %) and pollutant degradation efficiency (89.36 %-96.42 %) of ABSS/CDs surpassed the biochemical limit observed in traditional ABSS. Notably, the addtion of CDs facilitated an opening of the plastoquinone-pool (PQ-pool) valve and accelerated electron transfer rates, enabling photogenerated electrons to selectively target light-harvesting complexs as activation sites, thereby mobilizing photosynthesis and respiratory system activity to enhance nicotinamide adenine dinucleotide reduced (NADH) and adenosine triphosphate (ATP) production while promoting tricarboxylic acid (TCA) and Calvin cycle processes. In simulated swine wastewater treatment, ABSS/CDs achieved higher removal rates for the chemical oxygen demand (COD), total nitrogen (TN) and ammonium-nitrogen (NH4+-N) (100 %, 99.23 % and 98.62 % respectively) compared to pure culture systems alone. Network-based analysis revealed that ABSS/CDs improved microbial community structure stability within the photobioreactor while demonstrating efficient coupling between fungi, nitrifying bacteria, and denitrifying bacteria for enhanced performance in nitrogen removal processes. The upregulation of nitrogen metabolism and PQ-pool genes maintains efficient electron transport rates and contributes to nitrogen removal. This study expands our understanding of the physiological aptitudes of ABSS and provides valuable insights into applying CDs photoelectrons for enhanced wastewater treatment.
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