Diffusion Coefficient and Microbial Community Structure Dynamics During Acclimation of Encapsulated Immobilized Denitrifying Bacteria
To address nitrate nitrogen accumulation in aquaculture tailwater, a core-shell encapsulated immobilized denitrifying bacterial capsule containing lychee seed powder and denitrifying activated sludge was developed. The capsule's micro-morphology, bacterial activity recovery, growth, community structure changes, and diffusion coefficient dynamics during acclimation were investigated. The capsule shell exhibited a honeycomb porous structure with an average pore size of (0.25 ± 0.063) μm. Denitrifying bacterial activity recovered rapidly, with nitrate nitrogen removal efficiency stabilizing at 83.61% by day 21. Biomass within the capsules increased progressively, reaching (21.96 ± 0.28) mg·(g-pellet)−1 on day 30. The effective diffusion coefficient decreased with biomass growth, dropping to 0.232 × 10−9 m²·s−1 by day 30. Organic carbon source and encapsulation acclimation environment altered the microbial community structure; after acclimation, dominant genera were Methylobacterium (22.8%), Brevibacillus (18.1%), and Azospirillum (17.3%). Denitrifying bacteria containing nirS- and nirK- genes predominantly belonged to Proteobacteria (>99%). Genera involved in organic carbon metabolism and denitrification, including Bosea, Bradyrhizobium, Rhizobacter, and Alicycliphilus, increased in abundance. The encapsulated denitrifying bacteria exhibited short activity recovery time and excellent denitrification performance, making them suitable for denitrification of aquaculture tailwater or other low C/N ratio wastewater.