Nitrogen Removal Performance and Microbial Community Analysis of Activated Sludge Immobilization

Abstract

Immobilization of activated sludge was used to further remove nitrogen from secondary effluent. Intermittent sequencing batch reactor experiments were conducted to measure nitrogen removal in synthetic wastewater with initial total nitrogen concentrations (TN) of 10-45 mg·L-1 and C/N ratio of 1.78-10, and microbial community characteristic of embedding beads was investigated. When the packing ratio of embedding beads was 10%, and the temperature of wastewater, dissolved oxygen (DO), initial concentration of chemical oxygen demand (COD) were maintained at 10-15℃, 2-4 mg·L-1, and 80-100 mg·L-1, respectively, the results showed that the maximum total nitrogen removal loads ranged from 7.78 to 23.18 mg·(L·h)-1during the stable phase. SEM observations showed that the embedding beads were highly porous and microorganisms adhered to the interior and external surface of embedding beads, demonstrating that embedding beads acted as an ideal support material. Based on high-throughput sequencing analysis, the structure of microbial communities in the beads'interior and exterior changed significantly compared with embedding activated sludge. The advantage of denitrifying bacteria in embedding beads was obvious and the microbial diversity was good. Some microorganisms which can conduct both heterotrophic nitrification and aerobic denitrification, were identified. These processes may facilitate pathways for untraditional biological denitrification in the beads'interior.