Enhancing low-temperature nitrification biofilter with Acinetobacter harbinensis HITLi7T for efficient ammonia nitrogen removal in engineering applications

Low temperature has always been a significant limitation for the biological removal of ammonia nitrogen (NH3-N) from water. Acinetobacter harbinensis HITLi7(T) (HITLi7(T)) was used to enhance the low-temperature nitrification biofilter (LTNB) with a treatment capacity of 20,000 m(3)/d. At 2 degrees C, with an empty bed contact time of 3 h, the LTNB achieved NH3-N removal levels of 1.2 similar to 1.5 mg/L. The nitrifying bacteria (Nitrosomonas, Nitrosospira, Nitrospira and Candidatus_Nitrotoga) were significantly enriched. PICRUSt2 and FAPROTAX revealed the nitrification pathway of NH3-N conversion to hydroxylamine, then to nitrite, and finally to nitrate. The high co-occurrence of HITLi7(T) with the nitrifying bacteria suggested that HITLi7(T) might also promote the enrichment of nitrifying bacteria. Life cycle assessment showed that LTNB was an economical and environmentally friendly method for NH3-N removal. These results indicated that HITLi7(T) enhanced the nitrification performance of biofilters, improved the cold tolerance of nitrifying bacteria, and had potential for practical applications.