Enhanced nitrogen removal at psychrophilic conditions through bioaugmentation with immobilized bacterial cells capable of heterotrophic nitrification‐aerobic denitrification

Abstract

Low temperature severely restricts the nitrogen removal efficiency of biological wastewater treatment processes. To address this challenge, this study applied an immobilization technique using the cold‐adapted strain Pseudomonas sp. f6 to enhance nitrogen removal under low‐temperature conditions. Among three carrier materials evaluated (bio‐cord, MBBR, and ceramic filler), bio‐cord exhibited the best immobilization performance, achieving 1.6‐ and 1.3‐fold higher COD Cr removal efficiency than MBBR and ceramic filler, respectively. Notably, the highest nitrogen removal efficiency was observed at 10 °C, with the addition of nitrate‐N, where the COD Cr and NH 4 + ‐N removal efficiencies were 1.10 and 1.15 times those at 15 °C, respectively. This counterintuitive result demonstrates that Pseudomonas sp. f6 maintains high metabolic activity despite decreasing temperatures. Microbial community analysis further revealed a key ecological mechanism: as the temperature declined, the relative abundance of Pseudomonas sp. f6 gradually increased, and it shifted from the second to the first dominant genus, indicating superior cold tolerance of Pseudomonas over Thauera . This study provides an effective low‐temperature‐resistant immobilized bio‐cord system for enhanced nitrogen removal and identifies a temperature‐driven succession pattern of functional bacteria. These findings offer both theoretical insights and practical engineering support for biological nitrogen removal in cold‐region wastewater treatment. © 2026 Society of Chemical Industry (SCI).