TITLE:
Performance Enhancement Mechanisms and Community Ecology of an Immobilised Carrier System for Low-Temperature Partial Nitrification-Denitrification
AUTHORS:
Yahang Chen, Hong Yang
KEYWORDS:
Immobilised Carriers, Partial Nitrification-Denitrification, Low Temperature, Microbial Community, Process Resilience
JOURNAL NAME:
Open Access Library Journal,
Vol.13 No.5,
May
29,
2026
ABSTRACT: Low temperature has long been recognized as a critical constraint limiting the engineering application of mainstream partial nitrification-denitrification processes in cold regions. Compared with conventional activated sludge systems, immobilised carrier technology exhibits outstanding advantages in biomass retention, microenvironmental stability, and anti-shock capacity, making it a promising alternative for low-temperature wastewater treatment. However, its long-term operational performance and microbial adaptation mechanisms under continuous and gradually decreasing low-temperature stress (down to 6?C) remain insufficiently understood. In this study, an A/O-type immobilised carrier partial nitrification-denitrification system was developed, and its performance was evaluated through a 175-day stepwise cooling experiment (from 22?C to 6?C). The results indicated that the stable operating temperature range of the system was extended to 8?C. When the temperature was above 8?C, the Total Nitrogen Removal Efficiency (TNRE) could be restored to nearly 60% (the theoretical maximum) by adjusting Hydraulic Retention Time (HRT) and Dissolved Oxygen (DO), and the system recovered rapidly from temperature shocks within 1 - 2 days. Batch tests and microbial community analysis confirmed that the unique microenvironment inside the carriers effectively maintained stable partial nitrification (nitrite accumulation rate, NAR > 90%) at temperatures ≥ 8?C by continuously inhibiting the dominant nitrite-oxidising bacteria Nitrospira. Although denitrification was the rate-limiting step, the immobilised carriers acted as microbial refuges, driving community succession toward functional redundancy and enriching psychrotolerant genera such as Flavobacterium to prevent functional deterioration. This study reveals the structural advantages and ecological resilience of immobilised carriers against low-temperature stress, providing a solid theoretical foundation and technical support for the practical application of partial nitrification-denitrification processes in wastewater treatment plants in cold regions.