Resistance of CANON systems with different granules/flocs sludge ratios to alternating low-temperature operation

The particle-floc coupled completely autotrophic nitrogen removal over nitrite (CANON) system has been shown to have a strong low-temperature endurance. However, more research is needed to clarify the effects of temperature fluctuations during alternating ambient-cold seasons on reaction systems with different granular sludge/flocculated sludge ratios. In this study, low-ammonia-nitrogen wastewater was treated to explore the resistance of different proportion coupling systems to alternating low temperatures of 25-10 degrees C. The nitrogen removal performance of the high-granular system fluctuated less before and after cooling with higher stability, and the nitrogen removal rate remained at approximately 0.100 kgN/m(3)/d. Granular sludge disintegrated after being subjected to a brief temperature reduction, resulting in the formation of flocculated sludge. When subjected to a low-temperature shock, the activity of functional bacterial in the system significantly declined by >50 %. After a period of low-temperature operation, the temperature at which the microorganisms exhibited optimal activity reduced. At low temperatures, the main genus in the system was Candidatus Kuenenia, and after rewarming, the dominant genus changed to Candidatus Brocadia. The expression of hzs during alternating low temperatures was strongly affected by temperature and was the rate-limiting gene in this system.