Abstract
Many researchers consider bio-promoters with high efficiency that are reusable and produce no secondary pollution to be a promising method for enhancing biodegradation efficiency. Here, we first report that modified micro-graphite (MMG) is: a more efficient bio-promoter with denitrifying bacteria than the control group, and the nitrate degradation efficiency is 118.6% higher than that of the control group (without MMG). In an up-flow anaerobic sludge bed (UASB) reactor, the coupling system works even better than batch experiments and the efficiency is up to four times higher. The interactive mechanism of the heterogeneous catalytic process was also studied. The stress effect produced by MMG results in: an increase in the abundance of the crp gene (40.6%), and an increase in the transcript levels of the denitrifying genes narL, narG and nirS (1035.1%, 48.2% and 97.7%, respectively). This increases the ability of denitrifying enzymes to accelerate denitrification.
Simultaneously, our investigation into micro-MoS2 reveals its potent catalytic role in accelerating the complete bio-denitrification process in a highly heterogeneous system. The research demonstrates that micro-MoS2 increases the degradation rate by 116.3% under 125 mg/L nitrate. The catalytic effect of micro-MoS2 on denitrification could be achieved through its interaction with the pili or flagellum of denitrifying bacteria, specifically Paracoccus versutus and Paracoccus denitrificans. This interaction stimulates an increase in the abundance of denitrification genes and the transcript levels of narL (93.82 times), narG (16.34 times) and nirK genes (12.27 times) within the bacterial cells, which leads to an increase in the expression levels of denitrifying enzymes.
This study is the first to reveal the physical-biological-chemical degradation process of nitrate in a highly heterogeneous system. These findings have significant implications for the design and optimization of biodegradation processes and bio-denitrification systems, particularly for addressing the treatment of high-concentration nitrate wastewater.