Slow release performance of the immobilized carbon dots and their enhancing effect on 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 fabrics. The immobilized CDs (iCDs) could be slowly released and enter the cells, thus enhancing the activities of the denitrifying-related enzymes and electron transfer system of Stutzerimonas stutzeri ATCC 17588, during which the nitrate removal rate was significantly increased by 47.2 % with the reduced accumulation of nitrite and N2O. During the tested 10 cycles, the iCDs exhibited stable accelerating performances on nitrate removal (an average increase of 39.9 %). Proteomics analysis showed that the slow-release performance of iCDs was mainly attributed to the catalytic effect of extracellular amidases and esterases. At the community level, the iCDs addition also resulted in the increase of denitrification rate mediated by the enriched denitrification community containing main genera Stutzerimonas, 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 iCDs. These results indicate that iCDs are of potential application for the treatment of nitrate-containing wastewaters.