Intracellularly-photosensitized bio-hybrid with biogenic quantum dots for enhanced wastewater denitrification

Synergizing photocatalytic and biological processes in bio-hybrids offers opportunities to address the carbon deficiency challenge of wastewater denitrification, but is currently limited by the sluggish reaction kinetics due to inefficient transmembrane electron transfer. Herein, we report a self-assembled, intracellularly-photosensitized bio-hybrid, consisting of heterotrophic denitrifiers Pseudomonas aeruginosa and biogenic selenide/ sulfide quantum dots (CdSe_xS_1-x QDs), to allow significantly improved photo-electrons utilization. It achieved 97.1 % nitrate removal within 36 h for treating low-carbon wastewater, which is 3.5-fold and 3-fold faster than those of the bare cells and the physically-mixed cells and bio-QDs. The selectivity for nitrogen gas production reached 72.1 %, against only 59.9 % in the bare cells control. Accordingly, the expression of several key denitrifying enzymes was stimulated by the photo-excited electrons. The bio-hybrid exhibited good denitrification performance during 5 cyclic operations. Its good performance for treating several real wastewaters was also demonstrated. This work broadens the application niches of photocatalytic bio-hybrid and may inspire the development of more sustainable biotechnologies for low-carbon wastewater denitrification application.