Enhancement of Microbial and Metabolic Mechanisms in an Aerobic Bioreactor with Immobilized Microflora by Simple and Complex Electron Donors

Abstract

Microflora immobilization is promising for nutrient removal applications in sewage; however, the metabolic and microbial mechanism needs to be further explored. Heterotrophic nitrification-aerobic denitrification (HN-AD) bacterium and efficient nitrogen (N) removal bacteria were selected and immobilized on corncob particles using alginate polymer to prepare microbe–organic complex beads. The complex beads were then added into activated sludge under a continuous-flow aerobic bioreactor with sufficient sodium acetate also applied as a simple electron donor. The role of polymer electron donors under carbon-rich conditions was then studied. Results showed that the total nitrogen removal rate improved by 8.3% (reaching 91.2%) and ammonium nitrogen removal rates were approximately 98%. Only 0.59 mg/L of nitrate nitrogen was detected in the treatment group. 16S rRNA gene sequencing results showed that bacterial richness in activated sludge within the treatment group was significantly higher than within the control group (p < 0.05), and KEGG pathways analysis indicated that carbon (C) metabolism gene and N-cycle-related genes were also improved. This suggested that polymer electron donors generated complex C sources that nourished diverse bacterial species related to N cycles so that the N removal rate could be strengthened and further improved by simple electron donors and the microflora.