Slow-Release Carbon Dots Preparation and Their Accelerating Effects on the Anaerobic Denitrification

Abstract

Carbon dots (CDs) can improve microbial electron transfer rates and denitrification activities via entering the cells. To avoid the frequent addition of CDs in practical application, in this study, CDs were first covalently immobilized on bio-carrier polypropylene nonwoven fabric. The immobilized CDs significantly increased nitrate removal by 47.2% and reduced the accumulation of nitrite and N2O, because they could be slowly released to enter the cells and enhance the activities of the denitrifying-related enzymes and electron transfer system of Pseudomonas stutzeri ATCC 17588. During the tested 10 cycles of the slow-release CDs (SRCDs), they exhibited high accelerating performance with an average increase of 39.9% in nitrate removal. Proteomics analysis showed that the slow-release performance of SRCDs was mainly attributed to the catalytic effect of extracellular amidases and esterases. SRCDs addition also resulted in the increase of denitrification rate by the enriched denitrification community dominated in genera Pseudomonas, Thauera and Pannonibacter. Further metagenomics analysis showed that the three genera containing genes encoding amidases and denitrifying-related enzymes could perform denitrification process together via obtaining SRCDs. These results indicate that SRCDs are of potential application for the treatment of nitrate-containing wastewaters.

Keywords: Slow release, immobilized carbon dots, anaerobic denitrification, amidases and esterases, bacterial community