Immobilization of ammonia oxidizing bacteria using mycelial pellets: Preparation, characteristics, and application for nitritation

Ammonia-oxidizing bacteria (AOB) sourced from an aerobic granular sludge (AGS) process were rapidly enriched by progressively increasing ammonia nitrogen (NH₄⁺-N) loads, achieving a Nitrosomonas abundance of 20.7 % and a nitrite accumulation rate exceeding 80 %. Mycelial pellets formed by Cladosporium, isolated from the same AGS system, provided a porous surface structure for the immobilization of the enriched AOB, creating mycelial pellet/AOB composites. Robust microbial colonization and aggregation in mycelial pellet porous matrix were facilitated by a higher level of extracellular polymeric substances (EPS) compared to conventional AGS. Static tests showed a maximum NH₄⁺-N oxidation rate of 17.7 mg/(gMLVSS·h), higher than free AOB (8.5 mg/(gMLVSS·h)). In multi-recycling tests, the composites maintained 96.6 % NH₄⁺-N oxidation, demonstrating superior repeatability and stability. The results highlight advantages of mycelial pellets as biocompatible carriers in immobilizing AOB sourced from the same system, offering insights into improved nitritation performance and durability, making them promising for practical wastewater treatment.