Advancing nitrogen removal in low-temperature sewage treatment: Role of the adaptive activated sludge process

Low temperatures present significant challenges to sewage treatment, particularly in rural areas with underdeveloped economies. This study investigates the efficiency of wastewater treatment using the adaptive activated sludge (AAS) process under varying temperatures and fluctuating water flow conditions. Metagenomics sequencing is employed to elucidate the nitrogen removal pathway and functional microbial enrichment at low temperatures (12 degrees C). The findings reveal that the AAS process consistently achieves high removal efficiencies, with 84 % for COD and 64 % for TN over a 139-day operational period at low temperatures (12 degrees C). Notably, despite reduced microbial activity, nitrogen removal performance remains robust, compared to systems operating at room temperature (24 degrees C). Metagenomics sequencing reveals a significant reduction in the nxr gene abundance, from 10.5 % to 8.3 %, indicating the effective suppression of nitrite-oxidizing bacteria, facilitating partial nitrification. Furthermore, the high abundance of heterotrophic ammonia-oxidizing bacteria suggests that nitrification is accomplished through an organic metabolic pathway, characteristic of heterotrophic nitrification. Overall, the AAS system effectively mitigates temperature shocks while operating with low carbon input. Thus, AAS presents a novel approach to achieving partial nitrification in low-temperature rural sewage treatment.