How β-Cyclodextrin-Functionalized Biochar Enhanced Biodenitrification in Low C/N Conditions via Regulating Substrate Metabolism and Electron Utilization

Biodenitrification plays a vital role in the remediation of nitrogen-contaminated water. However, influent with a low C/N ratio limits the efficiency of denitrification and causes the accumulation/ emission of noxious intermediates. In this study, beta-cyclodextrin-functionalized biochar (BC@beta-CD) was synthesized and applied to promote the denitrification performance of Paracoccus denitrificans when the C/N was only 4, accompanied by increased nitrate reduction efficiency and lower nitrite accumulation and nitrous oxide emission. Transcriptomic and enzymatic activity analyses showed BC@beta-CD enhanced glucose degradation by promoting the activities of glycolysis (EMP), the pentose phosphate pathway (PPP), and the tricarboxylic acid (TCA) cycle. Notably, BC@beta-CD drove a great generation of electron donors by stimulating the TCA cycle, causing a greater supply of substrate metabolism to denitrification. Meanwhile, the promotional effect of BC@beta-CD on oxidative phosphorylation accelerates electron transfer and ATP synthesis. Moreover, the presence of BC@beta-CD increased the intracellular iron level, causing further improved electron utilization in denitrification. BC@beta-CD helped to remove metabolites and induced positive feedback on the metabolism of P. denitrificans. Collectively, these effects elevated the glucose utilization for supporting denitrification from 36.37% to 51.19%. This study reveals the great potential of BC@beta-CD for enhancing denitrification under low C/N conditions and illustrates a potential application approach for beta-CD in wastewater bioremediation.

Automated summary

In this study, beta-cyclodextrin-functionalized biochar (BC@beta-CD) was used to enhance the denitrification performance of Paracoccus denitrificans under low C/N conditions. BC@beta-CD promoted metabolic pathways, activated enzyme activity, increased electron donor generation, accelerated electron transfer and ATP synthesis, raised intracellular iron level, and induced positive feedback, resulting in a 15.82% increase in denitrifying microbial utilization. This study reveals the great potential of BC@beta-CD for enhancing denitrification under low C/N conditions and illustrates a potential application approach for beta-CD in wastewater bioremediation.