N-doped carbon dots/g-C3N4 photoexcitation simultaneously enhanced the microbial degradation of nitrate and oxytetracycline in a low C/N ratio aquaculture wastewater

The low carbon-to-nitrogen (C/N) ratio in aquaculture wastewater presents challenges for biological treatments, particularly regarding combined pollution, such as nitrate and oxytetracycline. Herein, this study introduces a synergistic system that integrates photocatalysts (N-doped carbon dots/g-C3N4) with a domesticated microbial community. In artificial wastewater at a C/N ratio of 2, the synergistic system removed completely nitrate and degraded 91.2 % of oxytetracycline simultaneously at 24 h. Moreover, within this system, the accumulation of nitrite was effectively eliminated and the nitrogen production ratio was increased to 82.6 %. Noticeably, oxytetracycline was transformed efficiently into low molecular weight products. In the synergistic treatment process, photocatalysis serves a role in enhancing biodegradation. The generated photoelectrons are efficiently transported through the biofilms, boosting microbial metabolic activity. This increase in microbial activity leads to improved removal of both nitrate and oxytetracycline. The synergistic system was also operated in actual aquaculture wastewater environment to evaluate its practical application potential. The Synergistic system exhibited removal efficiencies for nitrate and oxytetracycline that were 2.1 and 1.8 times higher, respectively, compared to biodegradation treatments. The proposed synergistic system offers a promising strategy to simultaneously tackle nitrate-oxytetracycline pollution, particularly in wastewater characterized by a low C/N ratio, without limiting its applicability to aquaculture wastewater.